Chart 2 Method for the manufacture of seamless ad welded steel pipe plus associated product applications

10 Seamless pipe

55

The main seamless tube manufacturing processes came into being toward the end of the nineteenth century As patent and proprietary rights expired the various parallel developments initially pursued became less distinct and their individual forming stages were merged into new processes Today the state of the art has developed to the point where preference is given to the following modern high- performance processes

ndash The continuous mandrel rolling process and the push bench process in the size range from approx21 to 178 mm outside diameter

ndash The multi-stand plug mill (MPM) with controlled (constrained) floating mandrel bar and the plug mill process in the size range from approx 140 to 406 mm outside diameter

ndash The cross roll piercing and pilger rolling process in the size range from approx 250 to 660 mm outside diameter

Aside from these broadly defined size range limits many facilities also operate in other dimensional ranges as described in the following sections and shown in Fig 1

In spite of many earlier tests trials and technologies the invention of the cross roll piercing process by the Mannesmann brothers toward the end of the 1880s is widely regarded as signalling the commencement of industrial-scale tube and pipe production

This cross roll concept marked the first departure from the characteristic feature of all the rolling processes known until that time ie the fact that the roll axes all lay in the same plane the rolls rotated in opposite directions and the stock exit speed approximated to the roll circumferential speed (Fig 2) In the cross roll piercing process the roll axes were arranged parallel to the stock axis but at an angle to the stock plane With the rolls rotating in the same direction therefore this arrangement produced a helical passage for the stock through the roll gap Moreover the exit speed was slower by about the power of 10 than the circumferential speed of the rolls

By introducing a piercing mandrel arranged in the roll gap solid round material could be pierced to produce a hollow shell in the rolling heat by the action of the cross rolls However it was not yet possible to produce tubes of normal wall thicknesses in useable lengths by the cross roll piercing process alone It was only after development and introduction of a second forming stage ndash the pilger rolling process ndash again by the Mannesmann brothers that it became practicable and economically viable to manufacture seamless

56

steel tube The pilgering process also constituted an unusual and innovative technology in that the thick-walled hollow shell was elongated to the finished tube dimensions by the discontinuous forging action of the pilger rolls ndash or ldquodiesrdquo ndash on a mandrel located inside the hollow shell

Needless to say this pioneering development encouraged many inventors at the time to submit a number of patent applications ndash in some cases merely to circumvent the proprietary rights of the Mannesmann brothers but also to break completely new ground in the manufacture of seamless tube

A member of the first group RC Stiefel a former Mannesmann employee is worthy of particular mention By further developing the cross roll piercing technique he succeeded in the USA in producing thin-walled hollow shells which were subsequently rolled out to the finished tube on a two-high plug mill which had already become well known from the welding process for which it was used This plug mill process was initially particularly successful in the USA and is today employed throughout the world to roughly the same extent as the cross roll piercing and pilgering process

The so-called continuous mandrel rolling mill is associated with the names Charles Kellog and later Aloys Fassl This process initially involved several two-high stands arranged in tandem by means of which the thin-walled hollow bloom was rolled over a mandrel bar to produce the finished tube Owing to difficult mechanical engineering and drive problems however the process was soon assigned to history Fifty years later with the advent of modern technology to solve in particular the open-loop and closed-loop control problems it was reborn as one of the most efficient tube rolling mills ever invented

Another possibility for the production of seamless tube was invented by H Ehrhardt By piercing a solid square ingot in a round die he was able to produce a thick-walled hollow shell with a closed bottom This shell was subsequently stretched on a mandrel bar through tandem-arranged ring dies to produce the final tube dimensions This so-called push bench process in its modified form has remained viable to this very day Once the various patents expired the following decades saw the original manufacturing processes modified to some extent and the individual forming facilities combined in a wide range of different

57

Fig 5 Pipe forming station

58

59

Fig Comoarision between longitudinal and cross rolling

Constellations Depending on the tube size and production mix and also the availability of starting material rolling mill facilities of comparatively disparate design were developed and built in the course of time

Moreover as a result of the further development of individual forming facilities new processes were also invented such as the cross roll piercing mill derivatives in the form of the Assel and Diescher processes or the tube extrusion process derived from the Ehrhardt press

60

Chart 3 Schedule of production and test operations in a modern plant for the longitudinal welding of large diameter line pipe Circle=production stage square =test stage

11 Spiral pipe production

61

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

The main seamless tube manufacturing processes came into being toward the end of the nineteenth century As patent and proprietary rights expired the various parallel developments initially pursued became less distinct and their individual forming stages were merged into new processes Today the state of the art has developed to the point where preference is given to the following modern high- performance processes

ndash The continuous mandrel rolling process and the push bench process in the size range from approx21 to 178 mm outside diameter

ndash The multi-stand plug mill (MPM) with controlled (constrained) floating mandrel bar and the plug mill process in the size range from approx 140 to 406 mm outside diameter

ndash The cross roll piercing and pilger rolling process in the size range from approx 250 to 660 mm outside diameter

Aside from these broadly defined size range limits many facilities also operate in other dimensional ranges as described in the following sections and shown in Fig 1

In spite of many earlier tests trials and technologies the invention of the cross roll piercing process by the Mannesmann brothers toward the end of the 1880s is widely regarded as signalling the commencement of industrial-scale tube and pipe production

This cross roll concept marked the first departure from the characteristic feature of all the rolling processes known until that time ie the fact that the roll axes all lay in the same plane the rolls rotated in opposite directions and the stock exit speed approximated to the roll circumferential speed (Fig 2) In the cross roll piercing process the roll axes were arranged parallel to the stock axis but at an angle to the stock plane With the rolls rotating in the same direction therefore this arrangement produced a helical passage for the stock through the roll gap Moreover the exit speed was slower by about the power of 10 than the circumferential speed of the rolls

By introducing a piercing mandrel arranged in the roll gap solid round material could be pierced to produce a hollow shell in the rolling heat by the action of the cross rolls However it was not yet possible to produce tubes of normal wall thicknesses in useable lengths by the cross roll piercing process alone It was only after development and introduction of a second forming stage ndash the pilger rolling process ndash again by the Mannesmann brothers that it became practicable and economically viable to manufacture seamless

56

steel tube The pilgering process also constituted an unusual and innovative technology in that the thick-walled hollow shell was elongated to the finished tube dimensions by the discontinuous forging action of the pilger rolls ndash or ldquodiesrdquo ndash on a mandrel located inside the hollow shell

Needless to say this pioneering development encouraged many inventors at the time to submit a number of patent applications ndash in some cases merely to circumvent the proprietary rights of the Mannesmann brothers but also to break completely new ground in the manufacture of seamless tube

A member of the first group RC Stiefel a former Mannesmann employee is worthy of particular mention By further developing the cross roll piercing technique he succeeded in the USA in producing thin-walled hollow shells which were subsequently rolled out to the finished tube on a two-high plug mill which had already become well known from the welding process for which it was used This plug mill process was initially particularly successful in the USA and is today employed throughout the world to roughly the same extent as the cross roll piercing and pilgering process

The so-called continuous mandrel rolling mill is associated with the names Charles Kellog and later Aloys Fassl This process initially involved several two-high stands arranged in tandem by means of which the thin-walled hollow bloom was rolled over a mandrel bar to produce the finished tube Owing to difficult mechanical engineering and drive problems however the process was soon assigned to history Fifty years later with the advent of modern technology to solve in particular the open-loop and closed-loop control problems it was reborn as one of the most efficient tube rolling mills ever invented

Another possibility for the production of seamless tube was invented by H Ehrhardt By piercing a solid square ingot in a round die he was able to produce a thick-walled hollow shell with a closed bottom This shell was subsequently stretched on a mandrel bar through tandem-arranged ring dies to produce the final tube dimensions This so-called push bench process in its modified form has remained viable to this very day Once the various patents expired the following decades saw the original manufacturing processes modified to some extent and the individual forming facilities combined in a wide range of different

57

Fig 5 Pipe forming station

58

59

Fig Comoarision between longitudinal and cross rolling

Constellations Depending on the tube size and production mix and also the availability of starting material rolling mill facilities of comparatively disparate design were developed and built in the course of time

Moreover as a result of the further development of individual forming facilities new processes were also invented such as the cross roll piercing mill derivatives in the form of the Assel and Diescher processes or the tube extrusion process derived from the Ehrhardt press

60

Chart 3 Schedule of production and test operations in a modern plant for the longitudinal welding of large diameter line pipe Circle=production stage square =test stage

11 Spiral pipe production

61

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

steel tube The pilgering process also constituted an unusual and innovative technology in that the thick-walled hollow shell was elongated to the finished tube dimensions by the discontinuous forging action of the pilger rolls ndash or ldquodiesrdquo ndash on a mandrel located inside the hollow shell

Needless to say this pioneering development encouraged many inventors at the time to submit a number of patent applications ndash in some cases merely to circumvent the proprietary rights of the Mannesmann brothers but also to break completely new ground in the manufacture of seamless tube

A member of the first group RC Stiefel a former Mannesmann employee is worthy of particular mention By further developing the cross roll piercing technique he succeeded in the USA in producing thin-walled hollow shells which were subsequently rolled out to the finished tube on a two-high plug mill which had already become well known from the welding process for which it was used This plug mill process was initially particularly successful in the USA and is today employed throughout the world to roughly the same extent as the cross roll piercing and pilgering process

The so-called continuous mandrel rolling mill is associated with the names Charles Kellog and later Aloys Fassl This process initially involved several two-high stands arranged in tandem by means of which the thin-walled hollow bloom was rolled over a mandrel bar to produce the finished tube Owing to difficult mechanical engineering and drive problems however the process was soon assigned to history Fifty years later with the advent of modern technology to solve in particular the open-loop and closed-loop control problems it was reborn as one of the most efficient tube rolling mills ever invented

Another possibility for the production of seamless tube was invented by H Ehrhardt By piercing a solid square ingot in a round die he was able to produce a thick-walled hollow shell with a closed bottom This shell was subsequently stretched on a mandrel bar through tandem-arranged ring dies to produce the final tube dimensions This so-called push bench process in its modified form has remained viable to this very day Once the various patents expired the following decades saw the original manufacturing processes modified to some extent and the individual forming facilities combined in a wide range of different

57

Fig 5 Pipe forming station

58

59

Fig Comoarision between longitudinal and cross rolling

Constellations Depending on the tube size and production mix and also the availability of starting material rolling mill facilities of comparatively disparate design were developed and built in the course of time

Moreover as a result of the further development of individual forming facilities new processes were also invented such as the cross roll piercing mill derivatives in the form of the Assel and Diescher processes or the tube extrusion process derived from the Ehrhardt press

60

Chart 3 Schedule of production and test operations in a modern plant for the longitudinal welding of large diameter line pipe Circle=production stage square =test stage

11 Spiral pipe production

61

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Fig 5 Pipe forming station

58

59

Fig Comoarision between longitudinal and cross rolling

Constellations Depending on the tube size and production mix and also the availability of starting material rolling mill facilities of comparatively disparate design were developed and built in the course of time

Moreover as a result of the further development of individual forming facilities new processes were also invented such as the cross roll piercing mill derivatives in the form of the Assel and Diescher processes or the tube extrusion process derived from the Ehrhardt press

60

Chart 3 Schedule of production and test operations in a modern plant for the longitudinal welding of large diameter line pipe Circle=production stage square =test stage

11 Spiral pipe production

61

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

59

Fig Comoarision between longitudinal and cross rolling

Constellations Depending on the tube size and production mix and also the availability of starting material rolling mill facilities of comparatively disparate design were developed and built in the course of time

Moreover as a result of the further development of individual forming facilities new processes were also invented such as the cross roll piercing mill derivatives in the form of the Assel and Diescher processes or the tube extrusion process derived from the Ehrhardt press

60

Chart 3 Schedule of production and test operations in a modern plant for the longitudinal welding of large diameter line pipe Circle=production stage square =test stage

11 Spiral pipe production

61

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Fig Comoarision between longitudinal and cross rolling

Constellations Depending on the tube size and production mix and also the availability of starting material rolling mill facilities of comparatively disparate design were developed and built in the course of time

Moreover as a result of the further development of individual forming facilities new processes were also invented such as the cross roll piercing mill derivatives in the form of the Assel and Diescher processes or the tube extrusion process derived from the Ehrhardt press

60

Chart 3 Schedule of production and test operations in a modern plant for the longitudinal welding of large diameter line pipe Circle=production stage square =test stage

11 Spiral pipe production

61

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Chart 3 Schedule of production and test operations in a modern plant for the longitudinal welding of large diameter line pipe Circle=production stage square =test stage

11 Spiral pipe production

61

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

In the production of spiral pipe (also known as helical seam pipe) hot strip or sheet is continuously shaped into a tube by a spiral forming facility applying a constant bending radius with the abutting strip edges also being continuously welded inline

In contrast to longitudinally welded pipe production in which each pipe diameter requires a certain plate width spiral pipe production is characterized by the fact that various pipe diameters can be manufactured from a single strip (skelp) or plate width

This is because the approach angle of the strip as it is fed into the forming unit can be modified The smaller this inlet angle the larger the pipe diameter (for a given strip width)

The technical and economic optimum in spiral pipe fabrication lies at a ratio of pipe diameter to starting material width of between 12 and 122

Fig 65 shows the ratio of pipe diameter to starting material width in a comparison between longitudinally welded and spiral pipe production and also the mathematical dependences which apply in spiral pipe production between feed angle stripskelp width and pipe diameter

At the current state of large-diameter pipe production technology the range of pipe diameters covered by the spiral welding process lies between approx 500 and 2500 mm The starting material employed for pipe wall thicknesses up to approx 20 mm takes the form of wide hot-rolled strip Plate in individual lengths up to 30 m are usually required for pipe wall thicknesses in excess of 20 mm

Spiral pipe production methods fall into two main categories

ndash Facilities with integrated forming and SAW welding lines

ndash Facilities with separate forming and SAW welding lines

Spiral pipe production in integrated forming and SAW welding lines

The integrated forming and SAW welding line can be regarded as the more conventional spiral pipe manufacturing facility In this configuration the production process comprises

ndasha strip preparation stage and

62

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

ndash the pipe forming operation with simultaneous inside and outside pass submerged-arc welding

Aside from welding the strips or plates together (this forms the skelp) the strip preparation stage also serves to straighten the skelp and trim it to an exact width The skelp edges have to be accuratelymachined within close tolerances and a defined edge crimping operation also has to be performed inorder to prevent impermissible ridge formationpeaking if the pipe forming operation is to besuccessful

Fig 68 (see also section 4242) provides a diagrammatic representation of the strip preparation and pipe forming processes in the case of a two-stage spiral pipe manufacturing configuration

The strip being fed in from the uncoiled is joined to the trailing end of the previous coil by submerged-arc welding from above The weld is deposited along the face which later will form part of the inside surface of the pipe The outside SAW pass is deposited in a separate line on the finished pipe The stripskelp then runs through a straightening mill and is cut to a constant width by an edge trimmer Additional tools also bevel the edges in preparation for the main SAW welding operation Before entry into the forming section the strip edges are crimped in order to avoid ridgingpeaking at the join

In an integrated facility the strip preparation stage is immediately followed by the forming process with simultaneous inside and outside submerged-arc welding A pinch-roll unit feeds the skelp at predetermined entry angle into the forming section of the machine

The purpose of the forming section is to bend the exactly prepared skelp of width B at a certain feed angle into a tubular cylinder of diameter D in line with the mathematical relationships indicated in figure

Various forming techniques may be applied to produce the spiral pipes Aside from the direct forming shoe process ndash which has its limitations ndash there are two main methods which are generally employed (Fig 66)

ndash 3-roll bending with an inside diameter roller cage and

ndash 3-roll bending with an outside diameter roller cage

In a 3-roll bending system numerous individual shaping and guiding rollers are employed rather than a single forming roll

63

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Chart 4 Standard dimensions for seamless and welded steel tube and pipe

64

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

The roller cage serves to fix the pipe axis and maximize the roundness of the pipe in order toensureoffset-free convergence of the strip edges at the welding point This facilitates attainment of accurate pipe dimensions so that the pipe exiting from the machine is already manufactured to within the standardized diameter roundness and straightness tolerances

Expansionsizing of the pipes after welding is therefore not necessary

In the spiral pipe forming and SAW welding machine the converging strip edges are first inside- welded at approximately the 6 orsquoclock position and then half a pipe turn further outside-welded in the 12 orsquoclock position Welding head alignment to the weld centre and gap control are performed automatically

The manufactured pipe string is subsequently cut to length by a flying parting-off device

The individual pipes are then taken to the finishing department where the production process iscompleted by machining of the pipe ends and the performance of any necessary rework Prior to pipeedge machining the pipes undergo a hydrostatic test (Fig) The entire weld region is then ultrasonically inspected with the weld zones at the pipe ends also being X-rayed

Fig Spiral pipe forming process

In addition each pipe end is also ultrasonically inspected over its full circumference for lapslaminations If required the weld zone and also the parent metal may be ultrasonically inspected following the hydrostatic test

65

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

As part of the quality assurance regime both in-process nondestructive inspections and offline mechanical tests are performed as production proceeds After the pipes have successfully passed through all the test and inspection stages including the dimensions check they are presented for final inspection and acceptance

The productivity of this process is determined by the speed of the submerged-arc welding operation The pipe forming process is capable of substantially higher production speeds In order better to utilize the efficiency of the spiral pipe forming section newer plants are being designed on the basis of separate forming and SAW welding lines

In this case the spiral pipe forming machine features a tack-welding facility which is capable of production speeds commensurate with those of the forming section

The submerged-arc welding of the seams is then performed offline in a number of separate welding stands

Spiral pipe production with separate forming and SAW welding lines

The main feature of this new technology is that there are two separate manufacturing processes

Stage 1 ndash Pipe forming with integral tack welding

Stage 2 ndash Inside and outside submerged-arc welding on separate welding stands

Fig 68 shows a diagrammatic representation of the pipe forming and tack welding facility

66

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Fig 6 Hydrostatic testing line with downstream pipe end machining section

Aside from the higher cost-efficiency of this process (achieved owing to the faster forming and tacking operation) there are also technical benefits derived from separating the pipe forming stage from the main welding stage as both operations can be individually optimized

In the spiral pipe forming section the merging strip edges (one on the already formed pipe section and the other on the incoming skelp) are continuously joined by inside tack welding

The tack-welding process is performed by the MAG method (see section 422) at a speed of 12 mmin in the region of the 6 orsquoclock position The shield gas employed is carbon dioxide Theweld edges below the welding position run with virtually no gap over a rigidly fixed guide roller A flying parting-off device cuts the tack-welded pipe string into the required individual lengths This pipe cutting process constitutes the last operation performed in the spiral forming machine Because of the high tack-welding speeds achieved it has becometorches operating with water injection

67

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

68

Fig 7 Diagrammatic representation of spiral pipe manufacturing line(pipe forming and tack-welding facility)

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Fig 8 Diagrammatic illustration of the spiral pipe manufacturing process with separate forming and welding lines 1forming and tack welding2combined two pass submerged arc welding stands(inside and outside passes performed simultaneously)

69

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

70

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Fig 9 computer controlled combined two pass submerge arc pipe welding stand for simultaneous inside and outside weld deposition

12 Production and Specification of Steel Pipe

To understand the production of steel pipe we must start at the beginning of basic steel production Most steel products are downstream value added products made from these four basic or primary forms of raw steel ingots billets blooms and slabs These forms can be produced in great volumes

71

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

and are easily re-heated extruded squeezed or formed into many other configurations so as to make virtually every steel product used today

Steel pipe is produced from two of these basic forms of steel the round billet and the slab A billet is a solid round bar of steel used to produce many other downstream products such as seamless pipe The other types of steel pipe are produced from slabs which are solid rectangular blocks of steel The slabs are reheated and processed into plate and coils

There are four methods used to produce steel pipe Fusion Weld Electric Resistance Weld Seamless and Double Submerged Arc Weld

Fusion Weld

One process for producing pipe is Fusion Weld sometimes called ldquoContinuous Weldrdquo and is produced in sizes 18rdquo to 4-12rdquo Fusion Weld pipe begins as coiled steel of the required width and thickness for the size and weight of pipe to be made Successive coils of steel are welded end to end to form a continuous ribbon of steel The ribbon of steel is fed into a leveler and then into a gas furnace where it is heated to the required temperature for forming and fusing The forming rolls at the end of the furnace shape the heated skelp into an oval The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

Seamless Pipe (SMLS)

Seamless Pipe is made when steel in a solid round cylindrical shape called a ldquobilletrdquo or a ldquotube roundrdquo is heated and then either pushed or pulled (while being rapidly rotated) over a mandrel with a piercing point positioned in the center of the billet This activity produces a hollow tube or ldquoshellrdquo The tube is then further finished until it becomes the size and wall thickness desired (Because the pipe is formed in a heated manner the pipe is normalized and should have a consistent steel cellular pattern throughout its circumference) Seamless pipe is made in sizes from 18rdquo to 26rdquo and is widely used in construction oil refining chemical and petro-chemical industries It is available in heavy wall thicknesses and exotic chemistries and is suitable for coiling flanging and threading It is however expensive in short supply and unavailable in long lengths

Electric Resistance Weld

72

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

The processing of Electric Resistance Welded (ERW) pipe begins as a coiled plate of steel with appropriate thickness and specific width to form a pipe that conforms to its relevant specification ERW pipe is cold formed The ribbon is pulled through a series of rollers that gradually form it into a cylin- drical tube As the edges of the now cylindrical plate come together an electric charge is applied at the proper points to heat the edges so they can be welded together

Electric Resistance Welded pipe is a high speed produc- tion product that can be made in continuous lengths up to 115rsquo It produces uniform wall thicknesses and outside dimen- sions and is made in a wide range of specifications It does however require minimum tonnage to set up on a specific size and sometimes has long lead times

Double Submerged Arc Weld (DSAW)

Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures When both inside welds and outside welds are performed the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW)

There are three common types of pipe produced by the DSAW process

Rolled and Welded

This method of manufacturing is also called the ldquoPyramid Roll Methodrdquo because it uses three rolls arranged in a pyra- midal structure The plate ordered by grade and thickness is rolled back and forth between the pyramid rolls until the cylinder is formed The cylinder is then moved to the welding UampOstations Most pyramid rolls are 20 feet in length or shorter Greater lengths are achieved by girth welding the five-foot

10-foot or 20-foot sections (or cans) together Berg Steel is the only producer capable of rolling 40-foot plates without a mid- weld and it is the only producer capable of sizing its product Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times It can be produced in The edges of the skelp are then firmly pressed together by rolls to obtain a forged weld The heat of the skelp combined with the pressure exerted by the rolls form the weld No metal is added into the operation Final sizing rolls bring the pipe into its required dimensions

73

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

UampO Method

This UampO Method is so called because it first uses a ldquoUrdquo press then an ldquoOrdquo press to complete cylinder forming from 40rsquo long plates ordered to size and grade The cylinder is then welded inside and outside by the submerged arc process by us- ing as many as five welding wires Most UampO is cold expanded either mechanically or hydraulically When it is cold expanded DSAW pipe gains in yield strength This method of pipe pro- duction produces exceptional quality with exact dimensional tolerances The primary use of this type of pipe is gas and oil transmission It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths

Manufacturing Output Using24rdquo OD x 500 Wall Per Eight Hour Shift

ERW SMLSUampO Press Spiralweld

Rolled amp Welded

1000Tons or16000rsquo

350 Tons or 6000rsquo

250 Tons or 4000rsquo

50 Tons or 800rsquo

10 Tons or 160rsquo

There are hundreds of specifications governing the pro- duction and use of steel pipe The following chart will exam- ine just a few of the common specifications you will normally see in the piling industry

Methods of Manufacture-Pipe Specifications

Grade FW ERW SMLS UampO SPIRAL RampW

Domestic size range

18rdquo-4rdquo

2rdquo-24rdquo

18rdquo-26rdquo

20rdquo-48rdquo

4rdquo-144rdquo

20rdquo-144rdquo

ASTM A-53 Yes Yes Yes No No No

74

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

ASTM A-106 No No Yes No No No

ASTM A-139 No No No Yes Yes Yes

ASTM A-252 No Yes Yes Yes Yes Yes

ASTM A-500 No Yes Yes No No No

API 5 L Yes Yes Yes Yes Yes Yes

AWWA C200 No Yes Yes Yes Yes Yes

pipe Specification

Grade Domestic size range

Usage

ASTM A-53 18rdquo thru 26rdquo Domestic and plumbing piping

under normal pressure and

temperaturesASTM A-106 1 8rdquo thru 26rdquo seamless pipe for high

temperatures and pressures

API 5 L 18rdquo thru 48rdquo oil and natural gas transmission

Digest of Common SpecificationsA-53 A-500 A-252 API 5L

75

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Type

Grades

Chemistr y

Yield

Tensile

Hydro

WallTolerance

OD Tolerance

Type

E

Type

S A

B

Max C

MN P S

A=30000

B=35000

A=48000

Min PSI

B=60000

Min PSI

S

eamle

ss

W

elded

None

Max of C P S

36000

58000

None

Seamless

ERW DSAW

123

005 Max Phos

1=30000

2=35000

3=46000

1=50000

2=60000

3=66000

None

Minimum wall not more than125 under nom

Seamless

ERW DSAW

X-42 X-52 X-56 60 X-65

C MN S

CB V X-

42=42000

X-52=52000

X-60=60000

X-42=60000

X-52=66000

X-60=75000

Yes

+15 -125

Each specification will vary slightly from the other as the only specification designed specifically for piling is ASTM A-252 The other specifications though intended for different uses can be used in a structural application The differences though subtle may be great enough to cause problems in substitution and care must be taken to evaluate any change

Notice that there is a weight tolerance for the ASTM A-252 pipe specification and that this tolerance is one half that of A-53 This means that the same wall thickness ordered for one specification may be thinner than that of the other For instance if you ordered 24 x 500 ASTM

A-53 and same amount of 24 x 500 ASTM A-252 the mini- mum wall thickness as addressed in the allowable variations section of the specification would be the same However the weight tolerance for A-53 is double that of A-252 In other words the minimum weight allowable for 24 x 500

A-53 whose theoretical weight is 12561ft is 11305ft (12561ft - 126ft) But the minimum weight allowable for the 24 x 500 steel pipe under the A-252 specification

Is 11933ft (12561ft - 628ft) Put more simply the mill is allowed to ship as low a wall thickness as 450 under the A-53 specification but can

76

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

only ship as low as 475 under the A-252 specification But if you followed the wall thickness tolerance only the mill would be allowed to ship as low as 438 wall (500 less 125)

For quality control purposes all the pertinent information about each piece of pipe can be found on the stencil affixed to that pipe Some mills stencil on the exterior and some on the interior of the tube Some mills are using the more modern bar codes affixed to the interior of the pipe Most mills will stencil

13 PLASMA CUTTING

77

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch In this process an inert gas (in some units compressed air) is blown at high speed out of a nozzle at the same time an electrical arc is formed through that gas from the nozzle to the surface being cut turning some of that gas to plasma The plasma is sufficiently hot to melt the metal being cut and moves sufficiently fast to blow molten metal away from the cut

Process

The HF Contact type uses a high-frequency high-voltage spark to ionize the air through the torch head and initiate an arc These require the torch to be in contact with the job material when starting and so are not suitable for applications involving computer numerical controlled (CNC) cutting

The Pilot Arc type uses a two cycle approach to producing plasma avoiding the need for initial contact First a high-voltage low current circuit is used to initialize a very small high-intensity spark within the torch body thereby generating a small pocket of plasma gas This is referred to as the pilot arc The pilot arc has a return electrical path built into the torch head The pilot arc will maintain itself until it is brought into proximity of the workpiece where it ignites the main plasma cutting arc Plasma arcs are extremely hot and are in the range of 25000 degC (45000 degF)[1]

Plasma is an effective means of cutting thin and thick materials alike Hand-held torches can usually cut up to 2 inches (51 mm) thick steel plate and stronger computer-controlled torches can cut steel up to 6 inches (150 mm) thick Since plasma cutters produce a very hot and very localized cone to cut with they are extremely useful for cutting sheet metal in curved or angled shapes

History

Plasma cutting grew out of plasma welding in the 1960s and emerged as a very productive way to cut sheet metal and plate in the 1980s[2] It had the advantages over traditional metal against metal cutting of producing no metal chips and giving accurate cuts and produced a cleaner edge than oxy-

78

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

fuel cutting Early plasma cutters were large somewhat slow and expensive and therefore tended to be dedicated to repeating cutting patterns in a mass production mode

As with other machine tools CNC (computer numerical control) technology was applied to plasma cutting machines in the late 1980s into the 1990s giving plasma cutting machines greater flexibility to cut diverse shapes on demand based on a set of instructions that were programmed into the machines numerical control[3] These CNC plasma cutting machines were however generally limited to cutting patterns and parts in flat sheets of steel using only two axes of motion (referred to as X Y cutting)

Safety

Proper eye protection such as welding goggles and face shields are needed to prevent eye damage called arc eye as well as damage from debris It is recommended to use lens shade 6 or darker for cutting to prevent the retina of your eye being flashed or burned

Starting methods

Plasma cutters use a number of methods to start the arc In some units the arc is created by putting the torch in contact with the work piece Some cutters use a high voltage high frequency circuit to start the arc This method has a number of disadvantages including risk of electrocution difficulty of repair spark gap maintenance and the large amount of radio frequency emissions[1] Plasma cutters working near sensitive electronics such as CNC hardware or computers start the pilot arc by other means The nozzle and electrode are in contact The nozzle is the cathode and the electrode is the anode When the plasma gas begins to flow the nozzle is blown forward A third less common method is capacitive discharge into the primary circuit via a silicon controlled rectifier

Inverter plasma cutters

Analog plasma cutters typically requiring more than 2 kilowatts use a heavy mains-frequency transformer Inverter plasma cutters rectify the mains supply to DC which is fed into a high-frequency transistor inverter between

79

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

10 kHz to about 200 kHz Higher switching frequencies give greater efficiencies in the transformer allowing its size and weight to be reduced

The transistors used were initially MOSFETs but are now increasingly using IGBTs With paralleled MOSFETs if one of the transistors activates prematurely it can lead to a cascading failure of one quarter of the inverter A later invention IGBTs are not as subject to this failure mode IGBTs can be generally found in high current machines where it is not possible to parallel sufficient MOSFET transistors

The switch mode topology is referred to as a dual transistor off-line forward converter Although lighter and more powerful some inverter plasma cutters especially those without power factor correction cannot be run from a generator (that means manufacturer of the inverter unit forbids doing so it is only valid for small light portable generators) However newer models have internal circuitry that allow units without power factor correction to run on light power generators

Plasma gouging

Plasma gouging is a related process typically performed on the same equipment as plasma cutting Instead of cutting the material plasma gouging uses a different torch configuration (torch nozzles and gas diffusers are usually different) and a longer torch-to-workpiece distance to blow away metal Plasma gouging can be used in a variety of applications including removing a weld for rework The additional sparks generated by the process requires the operator to wear a leather shield protecting their hand and forearm Torch leads also can be protected by a leather sheath or heavy insulation

CNC cutting methods

Some plasma cutter manufacturers build CNC cutting tables and some have the cutter built in to the table CNC tables allow a computer to control the torch head producing clean sharp cuts Modern CNC plasma equipment is capable of multi-axis cutting of thick material allowing opportunities for complex welding seams that are not possible otherwise For thinner material plasma cutting is being progressively replaced by laser cutting due mainly to the laser cutters superior hole-cutting abilities

80

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

A specialized use of CNC Plasma Cutters has been in the HVAC industry Software processes information on ductwork and creates flat patterns to be cut on the cutting table by the plasma torch This technology has enormously increased productivity within the industry since its introduction in the early 1980s

In recent years there has been even more development Traditionally the machines cutting tables were horizontal but now vertical CNC plasma cutting machines are available providing for a smaller footprint increased flexibility optimum safety and faster operation

Fig 11 Plasma cutting with a CNC machine Plasma cutting with a tilting head

New technology

In the past decade plasma torch manufacturers have engineered new models with a smaller nozzle and a thinner plasma arc This allows near-laser precision on plasma cut edges Several manufacturers have combined precision CNC control with these torches to allow fabricators to produce parts that require little or no finishing

Costs

Plasma torches were once quite expensive For this reason they were usually only found in professional welding shops and very well-stocked private garages and shops However modern plasma torches are becoming cheaper and now are within the price range of many hobbyists Older units may be very heavy but still portable while some newer ones with inverter

81

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

technology weigh only a little yet equal or exceed the capacities of older ones

14 PIPE BEVELING MACHINE

GENERAL -

The Pipe Bevelling Machine is used for the purpose of beveling the Pipe End Pipe is Beveled from the Outer and Front is faced by two different tools The Pipe remains Stationery and the Beveling Head rotates and comes out of the Head Stock for cutting the Pipe End The Pipe Bevelling Machine mainly consists of the following- Bed - Head Stock - Clamping Vice - Beveling Head

BED -

The Bed of Pipe Bevelling Machine is made of Cast Iron It is Very Rigid and sturdy in construction so as to take maximum Load and absorb max Vibrations It is provided with four Nos Foundation Holes of Dia M20 at four corners of the bed It is also provided with Four Tapped holes of 58 BSW near the Foundation Holes The Head Stock and Clamping Vice is fitted on the Bed

HEAD STOCK -

The Head Stock body of Pipe Bevelling Machine is made of Cast Iron It is Very rigid and sturdy in design The Head Stock is designed for Four Nos Spindle speeds All the Gears are of helical type made out of Axle Forging The width of gears is 50 mm The Shifting Gears slide on Splined Shafts The Shafts are mounted on Heavy Duty Ball Bearings The Input Shaft will be provided with a pulley having three grooves for C-Section V-belts

The Main Spindle is mounted on two Taper Roller Bearings mounted in Hard Chrome Plated Ground Sleeve The Sleeve along with main spindle fitted with Beveling Head is mounted in the Head Stock body and is movable To and Fro along its axis A Hyd Cylinder actuated electrically makes the movement of the sleeve in the Head Stock The Movement of the Sleeve can also be made

82

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

manually The Head Stock is Oil Filled It is provided with Oil Filling hole Oil Drain hole and Oil Level Indicator

CLAMPING VICE -

The Box Type Clamping Vice is fitted on the Bed The Vice is provided with Round Clamping Jaws for each size (4 5 6 7 8) The Vice will be Self-centering type The movement of the Clamping Jaws is made by Pneumatic cylinder fitted on the Vice actuated electrically The Vice will be very rigid and sturdy in design Machine will be supplied with single clamping vice

BEVELLING HEAD -

A special Beveling Head will be provided with the machine Two Tools of HSS will be used One for Beveling and second for Root Face The Beveling Tool will be mounted in a special Spring Loaded Tool Holder with a Roller device It is fitted on the main spindle that is then mounted in the traveling Sleeve

Note - One set of Round Type Clamping Jaws will be provided with the machine Other Round Type Clamping Jaws are Optional and will be supplied at an extra Cost

83

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Fig 12 Pipe beveling machine

15 Ultrasonic testing

Basic Principles of Ultrasonic Testing

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements Ultrasonic inspection can be used for flaw detectionevaluation dimensional measurements material characterization and more To illustrate the general inspection principle a typical pulseecho inspection configuration as illustrated below will be used

84

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

A typical UT inspection system consists of several functional units such as the pulserreceiver transducer and display devices A pulserreceiver is an electronic device that can produce high voltage electrical pulses Driven by the pulser the transducer generates high frequency ultrasonic energy The sound energy is introduced and propagates through the materials in the form of waves When there is a discontinuity (such as a crack) in the wave path part of the energy will be reflected back from the flaw surface The reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen In the applet below the reflected signal strength is displayed versus the time from signal generation to when a echo was received Signal travel time can be directly related to the distance that the signal traveled From the signal information about the reflector location size orientation and other features can sometimes be gained

Wave Propagation

Ultrasonic testing is based on time-varying deformations or vibrations in materials which is generally referred to as acoustics All material substances are comprised of atoms which may be forced into vibrational motion about their equilibrium positions Many different patterns of vibrational motion exist at the atomic level however most are irrelevant to acoustics and ultrasonic testing Acoustics is focused on particles that contain many atoms that move in unison to produce a mechanical wave When a material is not stressed in tension or compression beyond its elastic limit its individual particles perform elastic oscillations When the particles of a medium are displaced from their equilibrium positions internal (electrostatic) restoration forces arise It is these elastic restoring forces between particles combined with inertia of the particles that leads to the oscillatory motions of the medium

In solids sound waves can propagate in four principle modes that are based on the way the particles oscillate Sound can propagate as longitudinal waves shear waves surface waves and in thin materials as plate waves Longitudinal and shear waves are the two modes of propagation most widely used in ultrasonic testing The particle movement responsible for the propagation of longitudinal and shear waves is illustrated below

85

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Fig 13 wave propagation

In longitudinal waves the oscillations occur in the longitudinal direction or the direction of wave propagation Since compressional and dilational forces are active in these waves they are also called pressure or compressional waves They are also sometimes called density waves because their particle density fluctuates as they move Compression waves can be generated in liquids as well as solids because the energy travels through the atomic structure by a series of compressions and expansion (rarefaction) movements

In the transverse or shear wave the particles oscillate at a right angle or transverse to the direction of propagation Shear waves require an acoustically solid material for effective propagation and therefore are not effectively propagated in materials such as liquids or gasses Shear waves are relatively weak when compared to longitudinal waves In fact shear waves are usually generated in materials using some of the energy from longitudinal waves

Ultrasonic Inspection is a very useful and versatile NDT method Some of the advantages of ultrasonic inspection that are often cited include

It is sensitive to both surface and subsurface discontinuities The depth of penetration for flaw detection or measurement is superior

to other NDT methods Only single-sided access is needed when the pulse-echo technique is

used It is highly accurate in determining reflector position and estimating

size and shape Minimal part preparation is required Electronic equipment provides instantaneous results

86

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Detailed images can be produced with automated systems It has other uses such as thickness measurement in addition to flaw

detection

As with all NDT methods ultrasonic inspection also has its limitations which include

Surface must be accessible to transmit ultrasound Skill and training is more extensive than with some other methods It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen Materials that are rough irregular in shape very small exceptionally

thin or not homogeneous are difficult to inspect Cast iron and other coarse grained materials are difficult to inspect due

to low sound transmission and high signal noise Linear defects oriented parallel to the sound beam may go undetected Reference standards are required for both equipment calibration and

the characterization of flaws

The above introduction provides a simplified introduction to the NDT method of ultrasonic testing However to effectively perform an inspection using ultrasonics much more about the method needs to be known The following pages present information on the science involved in ultrasonic inspection the equipment that is commonly used some of the measurement techniques used as well as other information

History of Ultrasonics

Prior to World War II sonar the technique of sending sound waves through water and observing the returning echoes to characterize submerged objects inspired early ultrasound investigators to explore ways to apply the concept to medical diagnosis In 1929 and 1935 Sokolov studied the use of ultrasonic waves in detecting metal objects Mulhauser in 1931 obtained a patent for using ultrasonic waves using two transducers to detect flaws in solids Firestone (1940) and Simons (1945) developed pulsed ultrasonic testing using a pulse-echo technique

Shortly after the close of World War II researchers in Japan began to explore the medical diagnostic capabilities of ultrasound The first ultrasonic instruments used an A-mode presentation with blips on an oscilloscope screen That was followed by a B-mode presentation with a two dimensional gray scale image

Japans work in ultrasound was relatively unknown in the United States and Europe until the 1950s Researchers then presented their findings on the use of ultrasound to detect gallstones breast masses and tumors to the

87

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

international medical community Japan was also the first country to apply Doppler ultrasound an application of ultrasound that detects internal moving objects such as blood coursing through the heart for cardiovascular investigation

Ultrasound pioneers working in the United States contributed many innovations and important discoveries to the field during the following decades Researchers learned to use ultrasound to detect potential cancer and to visualize tumors in living subjects and in excised tissue Real-time imaging another significant diagnostic tool for physicians presented ultrasound images directly on the systems CRT screen at the time of scanning The introduction of spectral Doppler and later color Doppler depicted blood flow in various colors to indicate the speed and direction of the flow

The United States also produced the earliest hand held contact scanner for clinical use the second generation of B-mode equipment and the prototype for the first articulated-arm hand held scanner with 2-D images

Beginnings of Nondestructive Evaluation (NDE)

Nondestructive testing has been practiced for many decades with initial rapid developments in instrumentation spurred by the technological advances that occurred during World War II and the subsequent defense effort During the earlier days the primary purpose was the detection of defects As a part of safe life design it was intended that a structure should not develop macroscopic defects during its life with the detection of such defects being a cause for removal of the component from service In response to this need increasingly sophisticated techniques using ultrasonics eddy currents x-rays dye penetrants magnetic particles and other forms of interrogating energy emerged

In the early 1970s two events occurred which caused a major change in the NDT field First improvements in the technology led to the ability to detect small flaws which caused more parts to be rejected even though the probability of component failure had not changed However the discipline of fracture mechanics emerged which enabled one to predict whether a crack of a given size will fail under a particular load when a materials fracture toughness properties are known Other laws were developed to predict the growth rate of cracks under cyclic loading (fatigue) With the advent of these tools it became possible to accept structures containing defects if the sizes of those defects were known This formed the basis for the new philosophy of damage tolerant design Components having known defects could continue

88

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

in service as long as it could be established that those defects would not grow to a critical failure producing size

A new challenge was thus presented to the nondestructive testing community Detection was not enough One needed to also obtain quantitative information about flaw size to serve as an input to fracture mechanics based predictions of remaining life The need for quantitative information was particularly strongly in the defense and nuclear power industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as a new engineeringresearch discipline A number of research programs around the world were started such as the Center for Nondestructive Evaluation at Iowa State University (growing out of a major research effort at the Rockwell International Science Center) the Electric Power Research Institute in Charlotte North Carolina the Fraunhofer Institute for Nondestructive Testing in Saarbrucken Germany and the Nondestructive Testing Centre in Harwell England

Fig 13 Ultra sonic

testing

Present State of Ultrasonicrsquos

Ultrasonic testing (UT) has been practiced for many decades Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today Through the 1980s and continuing through the present computers have provided technicians with smaller and more rugged instruments with greater capabilities

89

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Thickness gauging is an example application where instruments have been refined make data collection easier and better Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a scribe Some instruments have the capability to capture waveforms as well as thickness readings The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection Also some instruments are capable of modifying the measurement based on the surface conditions of the material For example the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface This has led to more accurate and repeatable field measurements Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws when performing shear wave inspections Cathode ray tubes for the most part have been replaced with LED or LCD screens These screens in most cases are extremely easy to view in a wide range of ambient lighting Bright or low light working conditions encountered by technicians have little effect on the technicians ability to view the screen Screens can be adjusted for brightness contrast and on some instruments even the color of the screen and signal can be selected Transducers can be programmed with predetermined instrument settings The operator only has to connect the transducer and the instrument will set variables such as frequency and probe driveAlong with computers motion control and robotics have contributed to the advancement of ultrasonic inspections Early on the advantage of a stationary platform was recognized and used in industry Computers can be programmed to inspect large complex shaped components with one or multiple transducers collecting information Automated systems typically consisted of an immersion tank scanning system and recording system for a printout of the scan The immersion tank can be replaced with a squirter systems which allows the sound to be transmitted through a water column The resultant C-scan provides a plan or top view of the component Scanning of components is considerably faster than contact hand scanning the coupling is much more consistent The scan information is collected by a computer for evaluation transmission to a customer and archivingToday quantitative theories have been developed to describe the interaction of the interrogating fields with flaws Models incorporating the results have been integrated with solid model descriptions of real-part geometries to simulate practical inspections Related tools allow NDE to be considered during the design process on an equal footing with other failure-related engineering disciplines Quantitative descriptions of NDE performance such as the probability of detection (POD) have become an integral part of statistical risk assessment Measurement procedures initially developed for metals have been extended to engineered materials such as composites where anisotropy and inhomogeneity have become important issues The rapid advances in digitization and computing capabilities have totally changed the faces of many instruments and the type of algorithms that are

90

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

used in processing the resulting data High-resolution imaging systems and multiple measurement modalities for characterizing a flaw have emerged Interest is increasing not only in detecting characterizing and sizing defects but also in characterizing the materials Goals range from the determination of fundamental microstructural characteristics such as grain size porosity and texture (preferred grain orientation) to material properties related to such failure mechanisms as fatigue creep and fracture toughness As technology continues to advance applications of ultrasound also advance The high-resolution imaging systems in the laboratory today will be tools of the technician tomorrow

Wavelength and Defect Detection

In ultrasonic testing the inspector must make a decision about the frequency of the transducer that will be used As we learned on the previous page changing the frequency when the sound velocity is fixed will result in a change in the wavelength of the sound The wavelength of the ultrasound used has a significant effect on the probability of detecting a discontinuity A general rule of thumb is that a discontinuity must be larger than one-half the wavelength to stand a reasonable chance of being detected

Sensitivity and resolution are two terms that are often used in ultrasonic inspection to describe a techniques ability to locate flaws Sensitivity is the ability to locate small discontinuities Sensitivity generally increases with higher frequency (shorter wavelengths) Resolution is the ability of the system to locate discontinuities that are close together within the material or located near the part surface Resolution also generally increases as the frequency increases

The wave frequency can also affect the capability of an inspection in adverse ways Therefore selecting the optimal inspection frequency often involves maintaining a balance between the favorable and unfavorable results of the selection Before selecting an inspection frequency the materials grain structure and thickness and the discontinuitys type size and probable location should be considered As frequency increases sound tends to scatter from large or course grain structure and from small imperfections within a material Cast materials often have coarse grains and other sound scatters that require lower frequencies to be used for evaluations of these products Wrought and forged products with directional and refined grain structure can usually be inspected with higher frequency transducers

Since more things in a material are likely to scatter a portion of the sound energy at higher frequencies the penetrating power (or the maximum depth in a material that flaws can be located) is also reduced Frequency also has an effect on the shape of the ultrasonic beam Beam spread or the

91

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

divergence of the beam from the center axis of the transducer and how it is affected by frequency will be discussed later

It should be mentioned so as not to be misleading that a number of other variables will also affect the ability of ultrasound to locate defects These include the pulse length type and voltage applied to the crystal properties of the crystal backing material transducer diameter and the receiver circuitry of the instrument These are discussed in more detail in the material on signal-to-noise ratio

16A Procedure for the Hydrostatic Pressure Testing of Marine Facility Piping

SCOPE

The purpose of this methodology is to provide a useful alternative that a marine facility operator can implement to facilitate hydrotest planning performance and interpretation Providing precise and complete test data will allow the facility operator and California State Lands Commission (CSLC) to more effectively assess the validity of hydrostatic pressure tests

This methodology is intended for use in conjunction with the recently developed CSLC testing calculation (spreadsheet) applicable to testing of marine facility piping and pipelines under the jurisdiction of the California State Lands Commission as defined in Article 55 of the California Code of Regulations This is not regulation however using these tools may help to improve the consistency and quality of data collected during the test

CODES AND STANDARDS

The following codes and standards are referenced or provide additional information and guidelines for conducting pressure testing of pipelines or piping

1048707 California Code of Regulations Article 55 Marine Terminal Oil Pipelines

1048707 Department of Transportation 49 CFR Part 195 Transportation of hazardous liquids by pipeline

92

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

1048707 American Society of Mechanical Engineers B314 Pipeline Transportation Systems For Liquid Hydrocarbons and Other Liquids

1048707 American Petroleum Institute Recommended Practice 1110 Pressure Testing of Liquid Petroleum Pipelines

PLANNING THE TEST

Test Pressure

Prior to the hydrotest the pipeline operator should determine the minimum and maximum test pressure ranges These test pressures should take into account the current status of the pipe maximum operating pressures and the applicable federal state and local regulations In accordance with Article 55 the pressure during the test must be maintained to be at least 125 of the maximum allowable operating pressure (MAOP) for that pipeline In general the lowest pressure reading during the test period will be one factor in limiting the maximum allowable operating pressure in the system Both flange ratings and the presence of pressure relief devices must be considered when setting the test pressure Pressure ratings for flanges located with the tested pipeline must be identified and recorded Pressure relief devices must also be identified and recorded These devices should be removed or isolated as necessary

Test Mediums

It is recommended that the test be conducted in water However liquid hydrocarbons with a flashpoint greater than 140 degrees Fahrenheit or 60 degrees centigrade can also be used as the test medium Fluid properties for these test mediums should be obtained prior to the test for pre-test and post-test calculations Data for common hydrocarbon test mediums are provided in the spreadsheet however these should be compared to specific fluid properties obtained from the terminal or refinery

NOTE Liquid hydrocarbons typically expand more due to temperature changes than does water and it may be more difficult to obtain satisfactory test results especially when aboveground pipeline segments are tested Another drawback to using hydrocarbon as a test medium for pipelines that are located either over water or are submerged is that product may spill into the water if a leak occurs during the test

Test Segments

93

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

The facility operator shall provide an accurate description of the piping section to be tested It is recommended that the facility operator develop an isometric drawing showing the piping section with accurate pipe lengths locations of fittings and valves pipe diameters wall thickness and pipe grade (elevation) information Also the drawing should show the lengths of the aboveground and belowground sections that will be tested Accurate as possible pipeline lengths shall be determined prior to the test (from a scale drawing or by direct measurement using a tape measure or walker wheel)

It is recommended that a pipeline undergoing test be segmented so that the test is conducted against blind flanges This eliminates the chances of fluid bypass through valves which reduces the accuracy of the results When a full blind flange cannot be inserted to isolate the pipeline segment consider using a pan blind 333 If testing against blinds is not possible the pipeline operator could consider performing a static test to assess the integrity of the valve(s) that will be used for sectioning The pipe section could be pressurized to a pressure below the Maximum Operating Pressure (MOP) and each valve checked by visual audible or remote means for fluid bypass Any fluid bypass through a valve can drastically reduce the accuracy of the test data collected and may cause test results to fall outside the acceptance criteria calculated from the spreadsheet

Line Fill

To obtain accurate results it is important that the entire piping system and especially any elevated piping sections be reasonably free of air or other entrapped gas If testing with water the facility operator should prepare a line fill plan that removes product completely and reduces the amount of air in a test section Eliminating air increases the accuracy of the test results and too much air may ldquomaskrdquo leaks during the pressure test A common method for filling a piggable line involves using a pig to displace fluid with water If this is not feasible the water flush should be at a fast enough rate appropriate for the pipe size volume and fluid displaced that will ensure a completely turbulent interface between the water and displaced fluid If eliminating trapped airgas from the tested pipeline is problematic it is strongly recommended to install high point vent valves If high point vents are installed bleed trapped airgas completely from the valves The spreadsheet calculates an estimated line fill volume based upon the theoretical ratio of volume change to pressure change (DVDP) as discussed in the following section This value can be used for line fill planning and verification purposes

Pre-test Calculations

94

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

DVDP Definition DVDP is defined as the change in volume for an associated change in pressure of a known volume under pressure Two DVDP calculations are used in these guidelines a theoretical and a field value A theoretical DVDP will give the expected volume change for an associated change in pressure for the specified volume under test assuming that the volume under pressure is free of entrained gas The field value of DVDP is the actual volume change for an associated change in pressure for the specified volume under test If air exists within the line under pressure this value will be different that the theoretical value This procedure provides guidelines for calculating both DVDPrsquos and acceptable differences between the theoretical and field values of DVDP 351 Theoretical DVDP Prior to start-up of test activities the facility operator should perform a pre-test calculation to obtain a theoretical value of the DVDP for the verified volume of pipe under test and the appropriate test medium This information can be used to determine whether entrained gas exists in the line under test The theoretical DVDP for aboveground (unrestrained) pipe is calculated through the following equation

The theoretical DVDP for buried (restrained) pipe is calculated through the following equation

where V = volume of the segment for the individual pipe diameter D (gallons) D = outside diameter of pipe (in) E = elastic modulus of steel pipe (psi) t = wall thickness of pipe (in) ν = poissonrsquos ratio of steel pipe

C = compressibility of test media (in3in3psi)

95

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

NOTE For a test segment with multiple diameters sum the individual DVDPrsquos of each pipe diameter to obtain a total DVDP for the entire test section NOTE The DVDP constant provides useful data with which to predict how much fluid will be required to bring up a test segment to pressure For example for a fully packed line at 0 psi with a desired pressure of 100 psi and DVDP constant of 050 gallonspsi the amount of fluid which will be required to bring the segment to test pressure will be 100 psi x 050 gallonspsi = 50 gallons This will be the minimum amount if trapped air is present the required amount of fluid to reach test pressure could be much larger See Section 44 of this procedure for information about field DVDP The spreadsheet can be used to calculate the theoretical value of DVDP

Test Sensitivity

During a hydrotest several factors will affect the accuracy of test results An overview of these factors follows

Fluid Temperature

Fluid temperature is affected by a variety of factors including ambient temperature weather conditions pipe location test media source pipe color etc For buried pipe the expected fluctuation due to ambient temperature effects should be small due to the insulation provided by soil For aboveground pipe external conditions will have the greatest impact As fluid temperature increases the hydrotest pressure should be expected to increase As fluid temperature decreases the hydrotest pressure should be expected to decrease Pressure data that does not trend with temperature changes in fluid data should be carefully analyzed Data that does not trend correctly may indicate the existence of a leak or poor placement of the temperature recording instrumentation

The following table provides some calculated data for the expected fluid temperature increase over a four-hour period for standard pipe diameters and wall thickness Table 1 below is provided to show the relative sensitivity of fluid (water) temperature to ambient temperature for highly idealized cases In this case ambient temperature is held constant assuming a four-hour test period and initial water temperature of 60degF

Entrained Air

96

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Entrained air may prevent stabilization of the testing fluid during a test or may mask the presence of an actual leak The first indication of significant amount of entrained air will usually occur during pressurization Pressurization will not be immediate since water injected into the test section must displace a significant volume of highly compressible air Also expanding air may prevent the detection of an actual leak in the test segment If a small leak is present the expected pressure loss due to the leak may not be apparent since expanding air within the pipeline will tend to keep the pressure constant This is the primary reason for using DVDPrsquos to determine the percentage of air that is present and for eliminating air in the test section

Chart 1 shows the effect of pipeline pressure versus volume injected for various quantities of trapped air for 1000 ft of 8625rdquo pipe The chart shows how air can effect the volume required to reach full test pressure

Coefficient of Thermal Expansion

The coefficient of thermal expansion of the test medium effects the calculated volume and pressure changes versus a change in temperature (DVDT amp DPDT) Mediums with high thermal coefficients are very sensitive to changes in temperature Therefore for the same temperature recording accuracy a product test would potentially show a higher volume or pressure change when compared with water as a test medium This is the primary reason for using water as a test medium and for taking accurate temperature data

97

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Test Accuracy

98

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

The PassFail criteria that has been developed is dependent upon three variables that effect the calculated volume loss or gain during a hydrotest These variables are the change in pressure during the test the change in temperature experienced by the fluid during the test and the change in fluid volume (though bleeding injecting or leaks) during the test This section discusses the recommended accuracy of the instrumentation to be used in the hydrotest

Pressure Recording

Pressure recording devices should have an accuracy of +- 1 psi A typical deadweight tester has this accuracy and shall be used for the test A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing actual pressure data that will be used in post-test calculations Electronic pressure recorders with higher resolution may provide more frequent and accurate data sampling to enable pressure trending during the test

Temperature Recording

Regardless of the test medium used the temperature recording device should have a high accuracy The output resolution for a water test should be 01degF and for a hydrocarbon test the recommended resolution is 001degF A typical ldquoclockrdquo type chart recorder can be used for documentation purposes but should not be relied upon for providing the temperature data that will be used in post-test calculations

Volume Measurements

Accurate determination of fluid volumes bled or injected should be accounted for during a test Volumes should be measured using the most precise graduations available As a rule of thumb if the theoretical DVDP in gallonspsi is greater than 01 gallonpsi then measurements should be taken to the nearest gallon If the DVDP is between 01 and 001 gallonpsi then the measurements should be taken to the nearest pint (18 gallon) For DVDPrsquos less than 001 gallonspsi the measurements should be taken to the nearest ounce (this can be done by using a standard measuring cup)

PERFORMING THE TEST

Ambient Conditions

99

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

Ambient conditions may have great impact on fluid temperature and the accuracy of hydrostatic test results Certain ambient conditions may not only provide improved test results but may actually make the hydrotest operations easier The following guidelines can be used for assessing ambient conditions

1048707 Hydrostatic tests should not be conducted in rainy or wet conditions since visual leak detection may not be possible

1048707 Aboveground pipe tests should be conducted on cloudy overcast or cool days to minimize thermal heating of the fluid This will reduce the amount bleeding that will be required which may be significant for large sections of aboveground pipe exposed to the sun on hot days

1048707 Types of weatherexternal conditions that should be avoided are very hot (summer) extremely windy rainy and wet (due to condensate dew mist salt water spray etc) conditions

Pressure Recording Equipment

The following pressure recording equipment shall be used during a hydrotest in accordance with Article 55 a calibrated deadweight tester with 1 psi increments and a calibrated pressure chart recorder Pressure recording equipment should be installed so that localized surges from the test pump or bleed lines do not interfere with the readings A dedicated test manifold that allows each instrument to be blocked in separately is recommended Pressure transmitters or other type of pressure recording device with the required or better accuracy can also be used but for record keeping purposes a chart recorder should be provided

100

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

17 X-Ray Test and Fluoroscopy

This is an effective means of testing welds where one can continuously view the weld seam on video monitor Real Time Radiography is done essentially on the first pipe from production for setting up the welding and other inspection parameters It is done every time the pipe sizewall thickness are changed However it may be done as per the clientrsquos requirementsspecification

Final Inspection Visual Checking Weighing and Measuring

Each pipe is finally inspected after all the required tests inspections are carried out on the same by works inspectors third party inspection agency depending on the

Fig 14 x-ray testing machine

customerrsquos requirement for the following within the acceptance norms or not The inside amp outside surface end welds are checked Dimensional checks

101

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

like outside diameter wall thickness length straightness joviality out of square ness etc

Bevel ends of the pipe for Bevel angle Bevel root face and workmanship Finally when the pipe is acceptable then the pipe is marked stamped and coated as per the requirement governing specification

Each pipe is weighed on a digital weighing scale and measured for the exact meter age also which also helps to compare it with theoretically calculated weight of pipe Physical measurement helps to find whether it is within the tolerance of clients requirement

Final Marking

Each pipe is marked and given a specific serial no which helps to get the complete details or history of the particular pipe such as Raw Material details date of manufacturing its U T RT reports and other quality checks

102

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

18APPLICATION OF SPIRAL- WELDED PIPE

The robust design and durability aspects of spiral welded pipes enables their wide applicability across many important areas Water wastewater hydropowerand industrial are application where spiral-welded steel pipes are often utilized Common uses within this application include the following

Transmission Mains Treatment Plant Piping Pump Station Piping Force Mains Intakes and Outfalls Oil and Gas Aqueducts etc

BENEFITS OF SPIRAL- WELDED STEEL PIPES

Basically casters to onshore applications Durability Robustness Uniform stress distribution through the entire pipe higher rigidity

than L-seam pipes

103

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

19 CONCLUSION

Spiral welded pipe offers cost benefits over UOE pipe and is used in utility duties successfully but acceptance of this product form for oil and gas applications is markedly varied Industry requires better information on the technical issues related to specification and production of spiral welded pipe for oil amp gas applications so that cost savings can be realized wherever possible without compromising safety

It is proposed that a global review of the state-of-the-art of spiral welded pipe for oil and gas applications be undertaken similar to a successful TWI review of ERWHFI line pipe This will collate experience and concerns worldwide from pipe manufacturers pipeline installation companies and operators producing a single source document to provide guidance on appropriate use of spiral welded pipe and identify areas where additional data is required to increase confidence

BENEFITS

The benefit of wider adoption of spiral welded pipe for oil amp gas service will result in reduced capital expenditure for pipeline development replacement The specific savings will depend heavily upon the project pipeline length location etc but may be about 10-15 of material cost for a typical application

104

• 17 X-Ray Test and Fluoroscopy
• Final Marking

• 17 X-Ray Test and Fluoroscopy
• Final Marking