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ASME - POWER AND PROCESS PIPING Practical Definitions

I. Introduction:

Pipe is a pressure tight cylinder used to convey a fluid or to transmit a fluid pressure in applicable material specifications. Tube or tubing in the specifications are treated as pipe when intended for pressure services, under ASME B31.1 - Power Piping and ASME-B31.3 - Process Piping. Piping is an assembly of piping components used to convey, distribute, mix, separate, discharge, meter, control or stop fluid flows. Piping also includes pipe-supporting elements but does not include support structures, such as building frames, foundations, or any equipment excluded from Code definitions. Piping components are mechanical elements suitable for joining or assembly into pressure-tight fluid containing piping systems. Components include pipe, tubing, fittings, flanges, gaskets, bolting, valves and devices such as expansion joints, flexible joints, pressure hoses, traps, strainers, tie-ins, loops, unions, couplings, spools, in-line portions, instruments, separators, etc.

II. Pipe General Considerations: A vast array of materials for the manufacturing of pipes are employed today. Only A.S.T.M (American Society for Testing and Materials) specifies more than 500 different types of materials. Below is a summary of the main materials used:



III. Tube Manufacturing Processes: There are two types of industrial processes for the manufacture of pipes:

2) Welded Pipe The welding process consists of two phases: In the first one the contact surface of two elements is heated using currents of high frequency. Next, the two welded elements are clenched. 1) Seamless pipe manufacturing: Seamless steel pipe is made from a solid round steel billet which is heated and pushed or pulled over a form until the steel is shaped into a hollow tube. The seamless pipe is then finished to dimensional and wall thickness specifications in sizes from 1/8 inch to 26 inch OD. 1.1) Rolling Process:

The methods of manufacturing seamless steel pipe vary slightly from manufacturer to manufacturer, but these are the basic stages.

a) Cast Round Billets: High-quality steel round bars are required for seamless tubular products (Fig. 1/8).

Figure 1/8:Casting Process



b) Round Reheating: The rounds are cut to the required length and weighed prior to being reheated in a furnace (Fig. 2/8).

Figure 2/8:Round Reheating

c) Rotary Piercing Mill: The round billet is gripped by the rolls, which rotate and advance it

into the piercer point, which creates a hole through its length (Fig. 3/8).

Figure 3/8:Rotary Piercing Mill (RPM)

d) Mandrel Pipe Mill: The pipe is rolled using several stands over a long, restrained

mandrel (Fig. 4/8).

Figure 4/8:Mandrel Pipe Mill (MPM)

e) Shell Reheating: The MPM shell is transferred to a reheat facility, where it can be

cropped and weighed prior to reheating (see Fig 5/8).



Figure 5/8:Shell Reheated in a Furnace

f) Stretch Reducing Mill: The reheated and descaled pipe is conveyed through a stretch

reducing mill, which utilizes up to 24 stands to reduce the diameter to the required finished size (Fig. 6/8).

Figure 6/8:Stretch Reducing Mill

g) Cooling Bed: The pipe lengths are placed on cooling bed (Figure 7/8).

Figure 7/8:Pipe on a Cooling Bed

h) Batch Saws: After cooling, batches of the as-rolled mother pipe are roller conveyed in

parallel to carbide tipped batch saws for cropping into specified lengths (Figure 8/8).

Figure 8/8:Batch Saws.

1.2) Extrusion Process: Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section. The main advantages of this process are the ability to create very complex cross-sections, work brittle materials, because the material only encounters compressive and shear stresses and form finished parts with an excellent surface finish.



a) Hot extrusion: Hot extrusion is a hot working process, which means it is done above the material's recrystalli-zation temperature to keep the material from work hardening and to make it easier to push the material through the die. Most hot extrusions are done on horizontal hydraulic presses that range from 230 to 11,000 metric tons (250 to 12,000 short tons). Pressures range from 30 to 700 Mpa (4,400 to 100,000 psi), therefore lubrication is required, which can be oil or graphite for lower temperature extrusions, or glass powder for higher temperature extrusions. The biggest disadvantage of this process is its cost.

b) Cold extrusion: Cold extrusion is done at room temperature or near room temperature. The advantages of this over hot extrusion are the lack of oxidation, higher strength due to cold working, closer tolerances, good surface finish, and fast extrusion speeds if the material is subject to hot shortness. Materials that are commonly cold extruded include: lead, tin, aluminum copper, zirconium, titanium, molybdenum, beryllium, vanadium, niobium and steel. Examples of products produced by this process are: collapsible tubes, fire extinguisher cases, shock absorber cylinders and gear blanks.

c) Warm extrusion: Warm extrusion is done above room temperature, but below the recrystallization temperature of the material the temperatures ranges from 800 to 1800 F (424 to 975 C). It is usually used to achieve the proper balance of required forces, ductility and final extrusion properties. Metals that are commonly extruded include: Aluminum: is the most commonly extruded material. Aluminum can be hot or cold extruded. If it is hot extruded it is heated to 575 to 1100 F (300 to 600 C). Examples of products include profiles for tracks, frames, rails, mullions, and heat sinks. Brass: is used to extrude corrosion free rods, automobile parts, pipe fittings, engineering parts. Copper: (1100 to 1825 F (600 to 1000 C)) pipe, wire, rods, bars, tubes, and welding elec-trodes. Often more than 100 ksi (690 MPa) is required to extrude copper. Lead: and tin (maximum 575 F (300 C)) pipes, wire, tubes, and cable sheathing. Molten lead may also be used in place of billets on vertical extrusion presses. Magnesium: (575 to 1100 F (300 to 600 C)) aircraft parts and nuclear industry parts. Magnesium is about as extrudable as aluminum. Zinc: (400 to 650 F (200 to 350 C)) rods, bar, tubes, hardware components, fitting, and hand-rails. Steel: (1825 to 2375 F (1000 to 1300 C)) rods and tracks. Usually plain carbon steel is extruded, but alloy steel and stainless steel can also be extruded. Titanium: (1100 to 1825 F (600 to 1000 C)) aircraft components including seat tracks, engine rings, and other structural parts. Obs.: Magnesium and aluminum alloys usually have a 0.75 m (30 .in) RMS or better surface finish. Titanium and steel can achieve a 3 micrometres (120 .in) RMS.

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The aspect ratio of the part to be cast is what determines which of the techniques can be used. When the diameter of the desired part is larger in comparison to the overall-length (ring shaped), vertical casting is most commonly used. Likewise, when the length is larger compared to the diameter (tube shaped), horizontal casting setups are used.

ASTM A660 - Standard Specification for Centrifugally Cast Carbon Steel Pipe: This specification covers carbon steel pipe made by the centrifugal casting process intended for use in high-temperature, high-pressure service, suitable for fusion welding, bending, and other forming operations. Centrifugal castings use directional solidification and pressure from the centrifugal force to create castings with a denser sound structure, with superior physical properties in comparison to statically poured castings. It has been made clear that centrifugal casting is a versatile process with benefits in the areas of mechanical properties and overall process cost-effectiveness. The utilization of this process can be beneficial when producing a variety of products. Size Limitations of Centrifugal Castings: 2. Diameter: Up to 3 m (10 feet) 3. Length: 15 m (50 feet) length 4. Wall Thickness: 2.5 mm to 125 mm (0.1 - 5.0 in) 5. OD Tolerance: as fine as 2.5 mm (0.1 in) 6. ID Tolerance: can be 3.8 mm (0.15 in) 7. Surface Finish: from 2.5 mm to 12.5 mm (0.1 - 0.5 in) rms 2) Cast Iron Pipes: Historically are used as pressure pipes for transmission of water, gas and sewage, and as a water drainage pipe, during the 19th and 20th centuries. The material is predominantly gray cast iron, frequently used uncoated, although later developments did result in various coatings and linings to reduce corrosion and improve hydraulics. Gray cast iron pipes were gradually superseded by ductile iron pipes, which is a direct development, with most existing manufacturing plants transitioning to the new material during the 1970s and 1980s. There is currently almost no new manufacture of gray cast iron pipe. Iron is melted in the cupola furnace at approx. 1,550C (~2820F) using scrap steel and recycled materials. In order to obtain ductile cast iron, the iron is injected in the converter with a magnesium alloy. The pipes are manufactured from the injected iron using the centrifugal casting process. The centrifugal cast pipes are annealed at 960C (1760F) in a continuous furnace, so that the cementite can be broken down into ferrite and graphite. All pipes are then given a zinc or zinc-aluminium casing, cleaned in the sleeve area, spray-galvanised and pressure-tested at up to 50 bar (725 psi) , followed by a visual, dimensional and material check.



The Cast Iron Soil Pipe Institute (CISPI), organized in 1949, is the leading American of cast iron soil pipe and fittings for most of manufacturers. The Institute is dedicated to aiding and improving the plumbing industry. 3) Welded Pipe Manufacturing: The manufacturing process generally involves the following stages in a step by step procedure, as shown below.

a) Slitting: is a process in which a coil of material is cut down into a number of smaller coils of narrower measure, selectively thin (0.001 to 0.215 in.) and can be machined in sheet or roll form.

The illustration that follows provides a two-dimensional look at a typical coil slitting process. Note how the metal workpiece is drawn past the upper and lower slitting blades, leaving two coils the same length as the original wide coil.

b) Rolling: is ametal formingprocess in which metal stock is passed through a pair of rolls, according to the temperature of the metal rolled. Hot rolling is when temperature of the metal is above recrystallization temperature. Cold rolling is when temperature of the metal is below its recrystallization temperature. Hot Rolled (HR) Coils are slitted to pre-determined widths for each and every size of pipes.



c) Uncoiling, End Shearing: The slitted coil is uncoiled at the entry of edge mill. The leading end of the coil is precisely cut to provide an edge that can be effectively joined with the trailing end of the previous coil being processed. This allows for a continuous pipe making operation.

d) Forming: The edge milled coil is introduced into the three roll edge pre-bending

assembly and then into the forming assembly, which consists of three forming roll banks and several outside cage rolls. This forming assembly combines the strength and precision to form the exact outside diameter and the other dimensional properties of the desired pipe for tack welding at a rate of up to 40 feet per minute.

e) ERW Welding: This operation provides a continuous weld seam, strong enough to keep the desired pipe OD end shape. In this stage, the future pipe open edges are heated to the forging temperature through a high-frequency, low-voltage welding system, and welded by forge rolls, making perfect and strong butt weld without filler materials.

f) Final Welding Station: The pipe is then taken to the final welding station, where the full

length of the tack welded seam is completed by a Submerge Arc Welding (SAW). Superior SAW quality is achieved first by precise tracking of the weld seam, in order to maintain the alignment of the pipe ID and OD.

g) De beading: In this stage, the weld flash on top and inside of the pipe, is trimmed out

using the carbide scarfing tools. Hydrostatic Testing: During this testing procedure, the pipe is filled with water and subjected to the specified pressure for a minimum of 10 seconds. The testing is accomplished by a 5,000 psi ultra-modern testing unit, performed to ensure the welding integrity of the pipe. Ultrasonic Testing: Non-destructive tests are performed to further ensure the integrity of the pipe weld and pipe body. An ultrasonic shear wave inspection of the full length of the weld zone and the heat affected zone is made. After ultrasonic evaluation is complete, pipe ends are inspected by X-Ray in a separate operation. Seam Normalising: When required, the welding portion and the heat affected zones, are put to normalizing treatment and then cooled down in a air cooling bed. Quenching and Tempering: When also required, the quenching and tempering of tubes include a number of variables that can have a big effect on the process and the finished product. The process of quenching and tempering carbon steel tubulars, is heated to about 1,600 F, cooled rapidly, and reheated to a temperature less than about 1,300 F. The exact temperatures and times are dictated by the steel chemistry and the desired mechanical properties.



Sizing: After water quenching, slight reduction is applied to pipes with sizing rolls. This results in producing desired accurate outside diameter. Laser Length Measuring Device provides precision accuracy of pipe lengths and automatically records the length, to a pipe computer record. Cutting: In cutting stage, the pipes are cut to required lengths by flying cut off disc/saw cutter.The traveling Cutoff and Length Optimization equipment, optimize and maximize pipe lengths, resulting in fewer field girth welds. End Facing And Bevelling: The pipes ends are faced and bevelled by the end facer by automatic arrangements, controlled through touch screen operator interface panels. Each pipe end is beveled to the specified profile bevel (bevel angle -30 to 35 degrees and root face of 0.031 to 0.904). If required, the plain ended tubes go for processing, such as galvanizing, threading, black varnishing and more. Galvanizing Line: Continuous Hot-Dip galvanizing mill roll out galvanized coils are supported with on line tension leveling, trimming lines and skin pass mills, to take care of special requirements of customers, in terms of coating mass, width, thickness etc. Bar Code Labeling: When also required, bar codes are attached to the I.D. surface of each pipe for tracking. The conventional bar code consists of the traceable Pipe ID number. The two-dimensional bar code is encoded with all of the pipe data that is printed on the label. The label is in addition to required paint markings. Pipe Corrugation: At customers request, the pipe go to a corrugator machine (sheet-to-sheet type) capable of profiling galvanized sheets up to 3 meters (10 ft) length with maximum dimen-sional accuracy. OCTG Piping: OCTG is abbreviated from Oil Country Tubular Goods, which refer to a special kind of seamless steel pipes, mostly welded ones, used for oil and gas exploitation and production.The common OCTG products are: tubing, drill pipes, associated tubular products and accessories to the Oil & Gas related projects. 4) Design Temperature: The design temperature is assumed to be the same as the fluid temperature, unless calculations or tests support use of other temperatures. If a lower temperature is determined by such means, the design metal temperature is not permitted to be less than the average of the fluid temperature and the outside surface temperature. ASME B31.1 Power Piping - does not have a design minimum temperature for piping, as it does not contain impact test requirements. This is perhaps because power piping generally does not run cold. Certainly, operation of water systems below freezing is not a realistic condition to consider. 4.1) Material Allowable Stress: The Code provides allowable stresses for metallic piping in Appendix A, the lowest of the follo-wing with certain exceptions:

1/3.5 times the specified minimum tensile strength (which is at room temperature); 1/3.5 times the tensile strength at temperature (times 1.1); Two-thirds specified minimum yield strength (which is at room temperature); Two-thirds minimum yield strength at temperature; Average stress for a minimum creep rate of 0.01%/1,000 hr.; Two-thirds average stress for creep rupture in 100,000 hr.; 80% minimum stress for a creep rupture in 100,000 hr.



4.2) Internal Pressure Design: The ASME B31.1 (Power Piping) and ASME B31.3 (Process Piping) codes provides the basic methods for design of components for internal pressure. (1) The ASME B16.5 for flanges, are considered suitable for the pressure rating specified in the standard. Other methods of pressure design provided in ASME B31.1 and ASME B31.3 can be used to determine pressure ratings above the maximum temperature. (2) The ASME B16.9 for pipe fittings, state that the fittings have the same pressure rating when matching seamless pipes. The components are considered to have the same allowable pressure as seamless pipes of the same nominal thickness. Design calculations are not usually performed for these components, but are performed for straight pipes and matching fittings. (3) Design equations for straight pipes and branch connections are provided in ASME B31.1 and ASME B31.3 to determine the required wall thickness with respect to internal pressure of components. (4) Special components may be designed in accordance, since the procedure provides accepted methods, such as burst testing and finite element analysis, to determine the pressure capacity of these components. (5) The equations in the Code provide the minimum thickness required to limit the membrane and, in some cases, bending stresses in the piping component to the appropriate allowable stress. To this thickness must be added the mechanical and corrosion/erosion allowances. (6) The ASME B31.1 code for power piping (boiler external piping) have ASME stamp scheme, that is, the construction contractor must be certified by ASME organization and hold the PP stamp. This is the reason in the ASME B31.3 code you can not see the words of Authorized Inspector, but you can see the words owner inspector. 5) Carbon Steel Pipes: Due to its low cost, excellent mechanical properties and ease of welding and forming, carbon steel is called "material commonly used" in industrial piping, ie, only if it fails to employ the carbon steel when there is any circumstance special banning. Thus, all other materials are used in some specific cases. In processing industries, more than 80% of the tubes are of carbon steel, which is used for fresh water, low pressure steam, condensate, compressed air, oil, gas and many other low corrosive fluids, at temperatures from - 45C (-113F), and at any pressure. Some tubes are galvanized carbon steel, ie with an inner lining and outer hot-zinc deposit in order to give increased corrosion resistance. The mechanical strength of carbon steel begins to suffer a sharp drop in temperatures above 400C (752F), mainly due to the phenomenon of permanent creep deformation (creep), which begins to be observed from 370C (698F), and must be considered mandatory for any service at temperatures above 400C (752F). The creep deformations will be much larger and faster the higher the temperature the greater the tension material and the longer the time during which the material was subjected to temperature. At temperatures above 530C (986F) carbon steel undergoes intense oxidation surface (scaling) when exposed to air, with the formation of thick oxide crusts, which makes it unacceptable for any continuous operation.



Prolonged exposure of steel carbon at temperatures above 440C (824F) can also cause a precipitation of carbon graphitization, which makes the material get brittle. For all these reasons it is not recommended the of use of carbon steel pipe working continuously over 450C (842F), although any temperature may be permitted up to 550C (1022F), provided they are of short duration and not coincident with large mechanical stresses. The greater the amount of carbon in the steel, the greater is the hardness and the greater is the yield and tensile stress, to compensate the increase in carbon, affecting the ductility and weldability of the steel. Therefore, in steel pipes the amount of carbon to 0.20% and 0.25% C, the weld is very easy, and up to 0.35% C the pipes can easily be bent cold. Carbon steels can be killed with addition of up to 0.1% Si, to remove gas, or "effervescent" (rimed-steel), which contain no Si. Low carbon steels (up to 0.25% C) have the tensile strength of the order 31.0 to 37.0 kg/mm (~44000 to 52600 psi), and yield strength between 15.0 to 22.0 kg/mm (~21000 to 31000 psi). Medium-carbon steels (up to 0.35% C) are respectively 37.0 to 54.0 kg/mm (~44000 to 76700 psi) and 22.0 to 28.0 kg/mm (~21000 to 39800 psi). At very low temperatures, carbon steels have a brittle behavior and subject to sudden brittle fracture. This effect is enhanced when low carbon steels are standardized to obtain fine grains. Therefore, to work at temperatures below 0C (32F) should be steels with have a maximum content of 0.3% C and normalized to a fine grain. Piping operating in this temperature range, should be required the "Charpy" impact test to verify its ductility. The minimum temperature for the standard carbon steel conform to ANSI.B.31.3 is below -6C (-20F), but not lower than -10C (-50F); the coincident pressure should not exceed 25% of the design pressure and the combined longitudinal stresses should not exceed 6 ksi. Carbon steels when exposed to the atmosphere undergoes uniform corrosion (rust), which is mo-re intense the higher the humidity and air pollution. Direct contact with the ground, causes a pe-netrating rust pitting, which is more severe in wet acid soil, so that contact should be avoided. The carbon steel is violently attacked by mineral acids, especially when diluted or hot. The service alkali is possible up to 40C (104F), however, for temperatures above 70C (158F), should be done a heat treatment of stress relief. Higher temperatures cause a serious problem of corrosion in carbon steels. In general, residuals from these corrosions are not toxic, but can affect the color and taste of the contained fluid. 5.1) Commercial Carbon Steel Pipes:

a) ASTM A-106 - Specification for seamless pipes of 1/8" to 24" nominal diameter, high-quality carbon killed steel, for use at elevated temperatures. This specification sets out the requirements for chemical composition and mechanical properties testing.



Note: Grade "A" pipes for services where there are cold bending tubes. Grade "B" pipes, should only be used up to 200C (392F). The use of grade C are recommended with temperatures up to 600C (~1100F) at maximum pressure of 150 psi.

b) ASTM A-53 - Specification for carbon steel pipes, medium quality, with or without seam, 1/8" to 24" nominal diameter, for general use.This specification also sets the requirements for chemical composition and mechanical properties testing.

Grade "A": low carbon steel, TS= 33 kg/mm (~46900 psi), YS= 20 kg/mm (~28000 psi. Grade "B": medium carbon steel, TS= 41 kg/mm (~58000 psi), YS= 24 kg/mm (~34000 psi). The carbon steel by this specification is not always killed.The pipes may be black; i.e unfinished, or galvanized. The specification distinguishes two grades of material for pipes manufactured by welding or electrical resistance. For cold bending tubes should be used "A" range.Although the maximum temperature allowed by ANSI.B.31 to pipes A-53 grades A and B are the same of the pipes A-106 (A and B grade), the materials of this specification should not be used in permanent service above 400C (752F). The pipes according to the ASTM A-53 are cheaper than pipes according to the ASTM A-106, and thus, represent most of the carbon-steel pipes from industrial installations in general.

c) ASTM A-120 - Specification for carbon steel pipes, with seam or seamless black or galvanized, structural quality of 1/8" to 16" nominal diameter.This specification, does not prescribe requirements for complete chemical composition, then, this material specifi-cation has no quality assurance. The A-120 steel pipes, should not be bent cold and not used at temperatures above 200C (392F) or below 0C (32F).

OBS.: The standard ANSI.B.31.3 only allows the use of A-120 pipes for fluids known as "Cate-gory D", which includes not inflammable fluids, non-toxic, at pressures up to 10 kg/cm (150 psi) and temperatures up to 180C (356F).These pipes, are cheaper than the former, however, widely used for water, compressed air, condensate and other services of low responsibility.

d) ASTM A-333 (Gr. 6) - Specification for seamless carbon steel pipes, special for low temperature use.This specification has a rate up to 0.4% C and 1.0% Mn, always nor-malized to refinement of grain and is subjected to "Charpy" impact test at -46C (-15F).

e) API-SL - Specification of the "American Petroleum Institute" for carbon steel pipes of

medium quality. It covers pipe from 1/8" to 64" nominal diameter, black, seam or seam-less.The requirements of chemical and mechanical properties are similar to specifi-cation ASTM A-53.

f) API-SLX - Specification for tubes and seamless, made of carbon steels of high strength, special pipelines. Distinguished below, in a table, are the six degrees of material, all of me- carbon steels:



OBS.: According to the standard ANSI.B.31, the pipes of this specification should not be used at temperatures above 200C (392F). The ANSI B .31.1, prohibits the use of these tubes for steam application. 5.2) Specifications for Welded Pipes:

a) ASTM A-134 - Specification for pipes manufactured by protected welding arc, for diameters above 16" and wall thicknesses up to 3/4", with longitudinal or spiral weld.

b) ASTM A-135 - Specification for pipe manufactured by electrical resistance welding for diameters up to 30". Pipes grade "A" have a tensile strength up to 33 kg/mm (~46900 psi) and grade "B" up to 41 kg/mm (58000 psi).

The standard pipes specifications A-134 and A-135 are allowed for fluids "Category D".

b) ASTM A-671 - Specification pipe manufactured by protected welding arc to be used at room temperature and low temperatures, with diameters of 12" or larger. The specification covers nine classes, depending on the requirements of stress relief heat treatment.

c) ASTM A-672 - Specification for pipes for moderate temperatures. The manufacturing

process and diameter range for carbon-steel pipes are the same ASME A-671. Obs: The pipe specification A-671 and A-672 were previously covered by the specification A-155 which was suppressed. The pipes are made from killed carbon steel plates (ASTM A-515 or A-516) or not killed (ASTM-A-285 Gr C), with standard radiograph and total pressure testing.

d) ASTM A-211 - Specification for spiral welded pipes from 4" to 48" nominal diameter, alloy and stainless steels. Alloy steels have any number of other elements in addition to enter in the composition of carbon steels.

5.3) Alloy Steel Pipes: There are three general classes of alloy steels pipes, molybdenum, chromium-molybdenum and nickel alloy steels. The molybdenum alloy steel and chrome-molybdenum contain 1% Mo and up to 9%Cr, in various proportions, as shown in the table below. Stainless ferritic mate-rials (magnetic), are specific for use in high temperatures.

Chromium mainly causes a significant improvement in oxidation and corrosion resistance at high temperatures, particularly to oxidizing, whose effects are more pronounced when is larger the amount of chromium. Up to the amount of 2.5% Cr, there is a slight increase in creep resistance, but larger percentages of Cr reduce sharply this resistance (except in austenitic stainless steels containing nickel). For this reason, the alloys up to 2.5% Cr are specific for services of high temperature, with large mechanical loads and low corrosion and where the main concern is the creep resistance.



While the most amount of chromium steels are specific for services in high temperature, with reduced mechanical strength and high corrosion, where is most required, oxidation or corrosion resistance, molybdenum is the most important element for improvement of the creep resistance of steel, contributing also to increase corrosion alveolar resistance. In the same way that carbon steels, alloy steels are also subject to sudden brittle fracture when subjected to very low temperatures, and thereby being employed in any services with temperature below 0C (32F). Mo and Cr-Mo alloy steels also oxidate, although more slowly than carbon steels. The behavior of these steels, in relation to acids and alkalis, is similar to carbon steels. Materials with up to 2.5% Cr are specific to services at high temperatures, such as superheated steam pipes. Materials with more than 2.5% Cr are very used in services with hot oil. Due to its high resistance to corrosion by sulfur compounds contained in hydrocarbons. All of these services are still employed to steels with hydrogen. 5.4) Process Application: The stainless steels are those containing at least 12% of chromium, which confers the property of not rust, even in prolonged exposure to a normal atmosphere. The main cases that justify the use of these special steels (stainless and alloy steels) are as follows: a) High Temperatures - temperatures above the limits of use of carbon steels, or even below these limits, when it required great mechanical strength, creep and corrosion resistance. b) Low Temperatures - temperatures below 0C (32F) for carbon steels which are subject to brittle fracture. c) High Corrosion - Services with corrosive fluids, even within the range of use of carbon steels. In general, the alloy steels and stainless steels have better corrosion resistance qualities than carbon steels. However, there are numerous cases of exception: the salt water, for example, destroys the special steels as fast as carbon steels. d) Need for non-contamination - Services that can not be allowed contamination of the circulating fluid (food and pharmaceuticals, for example). Corrosion can cause contamination of the circulating fluid, when rust is loaded by the current flowing. For this reason, is often employed special alloy steels. e) Safety - Services with hazardous fluids (hot, flammable, toxic, explosive, etc.), where required safety against possible leaks and accidents. For these cases not normally need special steels. d) Types of alloys - Depending on the total amount of alloying, the elements are distinguished from the low alloyed steels with up to 5% of alloying elements, intermediate alloy steels containing between 5% and 10 %, and high alloy steels, with more than 10%. 5.5) Steam Pipes,Hydrocarbons and Hydrogen: Alloy steels containing nickel are special materials for use in very low temperatures, the temperature lower limit both the greater the amount of nickel, as shown in the table below. The main specifications of ASTM alloy steels for pipes are:

a) Seamless Pipes: A-335 Cr-Mo alloy steels, A-333 Ni alloy steels.

b) Seamed Pipes (great diameters):A-671 up to the 2.5% Ni alloy steels,



A-672 up to the 0.5% Mo alloy steel, A- 691 Cr-Mo alloy steels.

5.6) Stainless Steel Pipes Application: There are two main classes: the austenitic stainless steels (non-magnetic), containing 16% to 26% Cr, and the ferritic stainless steels (magnetic) containing basically 12% to 30% Cr in austenitic condition. All austenitic steels retain the ductile behavior even in extremely cold temperatures, and some were employed to near absolute zero. These steels are all easy welding materials. The table below shows the more employed types of stainless steels:

Obs.: The austenitic stainless steels have an extraordinary resistance to oxidation and fluency with high temperature values, except the low carbon (AISI 304L and 316L), where the limit is 400 C (752F) due to the lower mechanical strength of these steels. The ASME types 304, 316 steels and other so-called "non-stabilised", are subject to a precipi-tation of carbides of Cr (sensitisation) when subjected to temperatures between 450C and 850C (840F to 1560F), which diminishes the corrosion resistance of the material, and shall be subject to a severe form of corrosion (corrosion intergranular) in acidic media. This phenomenon can be controlled by adding Ti or Nb (for "stabilized" steels, ASME types 321 and 347), or by reducing the amount of carbon (very low carbon steels, ASME 304L and 316L). The presence of even the tiniest quantities of HCI, chlorides, hypochlorites, etc., (chlorine ions), can cause severe corrosion in all intro-cellular austenitic stainless steels, and should therefore be avoided. The austenitic stainless pipes are more used for very high temperatures and very low temperatures (cryogenic services), oxidizing and corrosive services, food and pharmaceutical and other services of non-contamination, hydrogen in high temperatures and pressures etc. Ferritic and martensitic-austenitic steels, have much less resistance to creep and corrosion in general, as well as lower temperature oxidation start, so it is more low temperatures usage limits.

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The main lines for the manufacturing of pipes are:

a) Seamless Pipes: - Black, smooth edges, beveled, 1/2 " to 10", ASTM A-106, ASTM A-53, API-5L, 5LX, ASTM A- 333A (grades 1, 3, 6, 7), ASTM A-335 (grades Pl, P2, P5, P7, P11, P12, P21, P22). - Black or galvanized, with thread, 1/2" to 10", Sch. 40 and 80, ASTM-A-120. - Black, heavy-duty for steam, with thread, 3/8" to 8", according to DIN-2441. - Black or galvanized, for water, air or gas, with thread, 3/8" to 8", according to DIN-2440.

b) Welded Pipes with Longitudinal Welding Arc: -Black, beveled ends, 12" to 64", according to the API-5 L, API-5LX, ASTM A-134, ASTM A-139, ASTM A-155 and ASTM A-252.

c) Welded Pipes with Longitudinal Electrical Resistance Seam: - Carbon steel, black, smooth beveled ends, up to 64", according to API-5L, API-5LX, ASTM A- 53, ASTM A-120, ASTM A-135 and ASTM A-252. - Carbon steel, black, galvanized, with threaded ends, up to 12", ASTM A-120. - Stainless steel, ASTM A-312, up to 4".

d) Welded Pipes with Spiral Seam: - Carbon Steel, black, beveled ends, from 18" to 80", API-5LS, ASTM A-134, ASTM A-139, ASTM A-211, ASTM A-252, with different specifications of AWWA (American Water Works Association). 6) Cast and Wrought Iron Pipes: Cast iron pipes are used for water, gas, sewage and sea water, in low-pressure services, room temperature, and where there is large mechanical loads with good resistance to corrosion, mainly to corrosion of soil. Good quality types are commonly manufactured by centrifugal foundry. Wrought iron pipes known as "galvanized iron pipes" (almost always galvanized), employed in secondary applications, low pressures and temperatures used for water, compressed air, condensate and commonly used in soil water and gas installations. Cast iron pipes are manufactured from 2" up to 24" diameters, smooth edges, threaded with

integral flanges, tested to pressures up to 400 psi. Wrought iron pipes are manufactured by pressure welding and electrical resistance, up to 4", with the same diameters and wall thicknesses of steel pipes. Wrought iron pipes have lower mechanical strength, but good corrosion resistance, equivalent to iron and much better than carbon steel. The ferro-silicon is the most common of these alloys, containing up to 14% Si, very resistant to attack from most acids and with exceptional abrasion resistance. The ASME B.31 only allows use of iron pipes for oil and other flammable fluids in soil buried piping, temperatures up to 150C (300F) and maximum pressures up to 150 psi.

In remote locations, in case of refineries, the allowable pressure may go up to 400 psi. The ASME B.31 prohibits the use of iron piping for toxic fluids into any further conditions, ("category M1"), as well as to services in temperatures below 0C (32F).



7) Non-Ferrous Piping: Making a comparison between the non-ferrous metals and carbon steels, we can say that the non-ferrous metals have better corrosion resistance. However, has lower mechanical strength and lower resistance to high temperatures, presenting better behavior at low temperatures. Due mainly to its high cost, the application of non-ferrous metals is little used. To almost all corrosive services, the non-ferrous metals have been replaced by plastics, with price advantages and much better physical and chemical properties. The main types are: 7.1) Copper and Alloys: A wide variety of materials, including commercially pure copper, and various types of brass and cupro-nickel, have excellent resistance to corrosion from air, water (including sea water), dilute acids, alkalis, many organic compounds and of numerous other corrosive fluids. Copper alloys are subjected to severe effects of corrosion when in contact with ammonia, amines and other nitro compounds, to be used in continuous operations, from -180C (-350F) up to 200C (~400F. Due to the high heat transmission coefficient, the brass and copper piping are much employed in coils, and as cooling and heating tubes. In small diameters (up to 2"), the copper tubes are also very used to water, compressed air, oils, low-pressure steam, refrigeration services, and for transmitting instrumentation signals. Pipes made of copper and alloys should not be used for food or pharmaceutical, because can carry toxic residues. The main specifications are: Copper pipe: ASTM B-88 Brass pipe: ASTM B-111Copper-nickel pipes: ASTM B-466 7.2) Aluminum and Alloys: These metals are very light (about 1/3 of the weight of steel), with a high coefficient of heat transmission, very good corrosion resistance to atmosphere, water and many organic compounds, including organic acids. The waste resulting from corrosion is not toxic. The mechanical strength of aluminum is low, however, can be improved by the addition of small amounts of Fe, Si, Mg and other metals. Both the aluminum and its alloys can work in continuous operation since -270 C (-518F) up to 200C (~400F), employed for heating systems, refrige-ration, cryogenic services and non-contamination processes. The main specifications are pipes for conduction, ASTM B-241-10 (Standard Specification for Aluminum and Aluminum Alloys). 7.3) Lead and Alloys: Lead pipes are soft, heavy, with low mechanical strength, but exceptional corrosion resistance, used in the atmosphere, soil, water (including sea water and acids), alkalis, halogenous and other various corrosive media.



The lead is one of the rare metal materials that can work with sulfuric acid in any concentration. The temperature limit of work, depending on the alloy goes from up to 200 C (~400F). Lead pipes are employed primarily for sewer piping, atmospheric pressure. 7.4) Nickel and Alloys: The materials of these classes are: Nickel, Monel (67% Ni, 30% Cu) and Inconel (80% Ni, 13% Cr), with exceptional corrosion and temperature resistance, both high as too low, excellent mechanical qualities and can also be applied in services with various dilute acids and alkalis. The most usual is the Monel metal, used for salt water piping, dilute sulphuric acid, hydrochloric acid, alkali and other corrosive services with non-contamination. The temperature limit is 550C (~1020F) for Monel, 1,050C (~1920F) to 1,100C (~2000F) for Inconel. The high costs restrict the use to a few special cases. 7.5) Titanium, Zirconium and Alloys: Considered until recently as rare metals, almost laboratory curiosities. Currently, these metals have been used in industrial application, although prices are still extremely high. These materials have extraordinary properties for corrosion resistance, with excellent mechanical qualities. Specific gravity is about half the weight of steels. The behavior with many strongly corrosive media is better than stainless steels and nickel alloys. 7.6) Non-Ferrous Piping - Diameters and Thicknesses: 1. Brass pipes and tubing, copper-nickel, aluminum and its alloys are manufactured with diameters of 1/4" to 12", gauged by the outside diameter, with thicknesses according to BWG sizes or decimals of an inch. The brass tubes and aluminum, are found in usually rigid bars with 6 m (~20 ft) long. 2. The copper pipes and tubing are manufactured commonly in 3, usually known as K, L and M, beeing the K the heavier, found in rigid bars with 6 m (~20 ft) long or in coils.

3. Lead pipes and tubing are manufactured in diameters from 1/4" to 12", gauged by the internal diameter with various thicknesses and sold in rolls. 8) Nonmetallic Pipes: Manufacturing of pipes and tubing with a wide variety of nonmetallic materials, as follows: 8.1) Plastic Materials: Currently is the most important group of nonmetallic materials. The employment of these materials has grown a lot in recent years, mainly as a substitute for stainless steels and non-ferrous metals. Some plastics can be translucent, allowing a visual observation of the movement of fluids through pipes. Plastics can be used in direct contact with the ground, even in the case of humid soils and rarely can be found acids or contamination of the circulating fluid, since plastics do not produce toxic waste. Most plastics is attacked by highly concentrated mineral acids. The behaviour in the presence of organic compounds is vari-able: hydrocarbons and organic solvents dissolve some plastics.



Plastics usually resist corrosive, being unnecessary to apply over thicknesses to corrosion. The destruction of plastic materials occurs by dissolution or by direct chemical reaction. Almost all plastics suffer a slow decomposition process when exposed to sunlight for a long time, due to the action of ultraviolet rays, becoming brittle (wheatering). Advantages: - Light weight, density varying between 0.9 and 2.2. - High resistance to corrosion- Very low friction coefficient- Manufacturing facilities and handling (can be cut with a hacksaw)- Low electrical and thermal conductivity- Colour and permanent painting, gives good looking, - Allows to adopt color codes for identification of pipelines. Disadvantages: - Low heat resistance is the biggest disadvantage. Despite the great strides the majority of these materials cannot work at temperatures higher than 100C (212F). - Low mechanical strength. The tensile strength limit is on the order of 2.0 to 10.0 kg/mm (~2800 to 14000 psi) for most plastics. Some thermostable plastics, laminated in successive layers of plastic resins and glass fibres have better mechanical strength, though lower than iron or carbon steel. - Poor dimensional stability, subject to deformation by fluency in any temperature (cold creep). - Uncertain mechanical behaviour, chemical and physical data. The margin of error is much greater than in relating to metals. - High coefficient of expansion, up to 15 times than carbon steels. Some plastics are fuels or at least capable of powering slowly combustion. The general classes of plastics are: thermoplastics and thermosettings. 8.2) Thermoplastics: A thermoplastic (sometimes written as thermo-plastic) is a type of plastic made from polymer-resins that becomes a homogenized liquid when heated and hard when cooled. When frozen, however, a thermoplastic becomes glass-like and subject to fracture. The RTP (reinforced thermoplastic pipe) is a high pressure plastic pipe system, which consists of three layers, the outer and inner layers are made of PE, and the middle layers is made of aramid fiber reinforced tape. With the application of heat, may be repeated times softned, formed and replaced, however, the thermosettings cannot be molded by heat. Resist diluted mineral acids, alkalis (even when hot), halons, saline solutions and acidic, the salt water and the numerous other chemicals. The addition of dark pigments greatly improves the plastic resistance and is recommended that when plastics are to be permanently exposed to the sun and rain have pigments of black carbon. Plastic materials can not be used for fire protection piping. ASME B.31 allows the use of plastics for fluids "category D", water pipes and non-flammable chemicals in vapor generation plants. Thermoplastic materials are usually employed for small and medium diameters, while the thermostable are preferred for large diameter pipes.



8.3) Main Plastic Materials: a. Polyethylene:is the lightest and simplest of the thermoplastic materials, with excellent resis-tance to mineral acids, alkalis and salts. It is a combustible material, with low mechanical strength (2800 to 5000 psi), whose temperature limits range from 38 to 80(100 to 176F), depending on the specification. Polyethylene is used for moderate pressure. Flexible pipes are manufactured with diameters of 1/2" to 4", common classes, 6.0 to 10.0 kg/cm (85 to 150 psi). b. Polyvinyl Chloride (PVC):one of the most common industrial thermoplastics, corrosion resis-tance equivalent to polyethylene, very good mecha-nical qualities, temperature from 20 to 130C (68 to ~270F). Although this material can be burned, the flame is extinguished spontaneously. Rigid PVC pipes are very used in water piping, sewer, acids, alkalis and other corrosive fluids. Covers manufacturing diameters from 1/2" to 10" according to Sch. 40 and 80, with smooth or threaded ends and external cladding in successive layers of polyester resin and glass fibre wounds ("filament winding"), from 25 to 400 mm in diameter, to severe corrosive fluid services. Can also be manufactured in two classes (class 300 psi and class 450 psi), with smooth ends with bags, or integral flanges. c. Acrylic Butadiene-Styrene (ABS), Cellulose Acetate: thermoplastic qualities, similar to those of PVC used for rigid pipes, with small diameters. Both are combustible materials. d. Fluorinated Hydrocarbons: known as "Teflon", used for coatings of steel tubes and joints or in high corrosion services. Thermoplastics of the non-fuels group, with exceptional qualities for corrosion resistance and with a wide range of temperature application, up to 260C (500F). 8.4) Asbestos-cement: Asbestos-cement pipes (transits) are made of cement and sand mortar with frameworks of asbestos fibres. Mechanical strength is small, and may only be used for low pressure and where they are not subject to major external efforts. The asbestos-cement has excellent resistance to air, soil, alkaline, neutral water, salt water, oils and organic compounds. For the most of these, the material is completely inert, resisting indefinitely. The cement-asbestos should not be used for services with acids or acidic water solutions. The main job of the cement-asbestos pipes is for sewerage piping. Asbestos-cement pipes are manufactured in two main types: - Conduction pipes 2 to 16 classes for pressures 100 and 150 psi respectively. There are asbestos-cement pipes diameters up to 36", for pressures up to 200 psi. - Sewer pipes 2 to 20, lightweight types, buried, for services without pressure. 8.5) Reinforced Concrete: Reinforced concrete pipes, used mainly for important piping (large diameters) for water and sewage. Corrosion resistance, equivalent to asbestos-cement pipes, but the mechanical resistance is greater. There are three types of reinforced concrete pipes:

1) Framed with steel bars, with longitudinal or transversal steel screens for low pressures (up to 100 psi) and small overloads.



2) Framed with steel plates embedded in concrete, for pressures up to 150 psi or smaller, for services where is necessary to guarantee better tightness.

3) Framed with wire in prestressed concrete with high strength spiral wound steel, under

strong tension, to put the concrete pipe in permanent compression. These pipes have also secondary steel plate frames, to ensure tightness, employed for pressures up to 600 psi, and liability in strong overloads. The reinforced concrete pipes are manu-factured by centrifuged and vibrated cement, diameters from 10 to 150 and 3 to 6 ft length. 8.6) Glaze Clay or Ceramics: The glaze pottery pipes or tubes, also called "manilhas", have excellent resistance to corrosion, being inert in relation to the ground, to the atmosphere and to most corrosive fluids. The mechanical strength is low, however, a little better than the cement-asbestos pipes, employed almost exclusively for sewering, manufactured in short lengths (1.0 m approx.) with nominal diameters from 50 to 500 mm, and with tips and socket edges. 8.7) Glass: Are rare manufacturing pipes and tubes, for special services only employed for high corrosion or when it requires absolute purity of the circulating fluid. Glass is the best material for corrosive media all in small diameters, applied up to 3/8 at most. 8.8) Rubber: Rubber pipes or tubes are manufactured with many types of natural and synthetic elastomers for various ranges of pressures and temperatures, generally flexible applications (hoses and sleeves). For severe services and high pressure, the pipes usually have multiple rubber and canvas reinforce-ments, often vulcanized with steel wire spiral frames, up to 400 mm nominal diameter. Although these materials have different properties and often have extraordinary specific elasticity, causing rupture with a very large elastic deformation (300 to 700%), without any permanent deformations, the normal service temperature limits range from 25C to 100C. Some rubbers are good fuels, others burn slowly. In the same way as most plastics, rubbers suffers a deterioration as a result of long exposure to sunlight, making it brittle. The addition of black carbon improves resistance to light and also increases the resistance to surface wear. Natural rubber resists well to acidic waters (and alkaline), dilute acids, salts and the numerous other corrosive media, but is attacked by oil products and all several solvents and organic compounds. The most important of the synthetic types are called Neoprene and SBR (styrene-butadiene). The Neoprene is resistant to oil products, while SBR is an economical synthetic rubber, with properties similar to natural rubber.



8.9) Epoxy: Thermoestable material used for pipes of large diameter (up to 900 mm), with smooth ends and integral flanges. The pipes or tubes are of laminated construction, in successive layers of plastic resin and glass-fibre wounds, to improve mechanical strength, called "FRP"- Fiberglass Reinforced Plastic). The epoxy is a plastic material with very good corrosion resistance, it burns slowly, and can be used at temperatures up to 150 C. 8.10) Polyester and Phenolic Compounds: Thermostable materials, epoxy-like characteristics. The phenolic compounds may work up to 150 C, with a wide range of diameters, manufactured in a laminated construction way, with a glass fiber frame (FRP) reinforcing PVC externally. 9) Steel Pipes with Internal Coatings: When the nature of the service requires a high resistance to corrosion and abrasion, mechanical strength and high pressure, the best application is the use of steel pipes with an inner lining. In general, it is better to use steel pipes or tubes with internal coatings, specific for abrasion resistance, than integral tubes with a need of more wall thickness to withstand a high pressure. However, should be also evaluated, the fluid to be handled, the air environment or application in soil; in these cases, the pipes with internal coatings do not apply. In extreme corrosion cases, the coating materials are: concrete, plastics, rubbers, graphite, porcelain, rubber, asphalt, etc. Pipes with concrete coating are very used in salt water pipes with a concrete layer between 0.6 cm to 1.2 cm thick, automatically placed inside with a centrifugal way. In most piping diameter of 20" is welded a steel screen internally to improve the adhesion of the concrete to prevent cracks or extrication of lining pieces. Other important types of internal coating in steel pipes, are the plastic coatings and rubbers. Plastic coatings (teflon, epoxy, phenolic compounds, etc.), and hard rubbers are used for pipelines carrying salt, acids, alkalis, salts and other chemicals, while the soft rubber coverings are used for pipelines of abrasive fluids. High corrosion services requires that the coating is perfect and continuous because any flaw (crack, bubble, scratch etc.), may result in localized corrosion point, which can pierce the wall of the pipe more rapidly than an uniform corrosion. 10) Pipe Connections: The primary means of connecting pipes are: - Threaded connections (screwed joints). - Welded connections (welded joints). - Flanged connections (flanged joints). - Tips and sockets (bell and spigot joints). - Other systems of compression connections: special, proprietary connections, etc.



The choice connections to use depends on many factors such as: material and diameter of the pipe, purpose and location, degree of security required, work pressure and temperature, fluid contained, whether or not dismantling, etc. The most often used connection purposes are: a) The current connections are weldings along the pipe, where the main concern is low cost and safety from leaks; b) Threading and flanging are used to connect the ends on pumps, valves, tanks, vessels and other equipment, where is a necessary ease of disassembly. 11) Threaded Connections: Threaded connections are one of the oldest means of binding pipes. The nominal diameter maximum current usage is 2", although there is manufacturing of pipes with threaded ends, with connections up to 4" or larger yet. For connecting pipe fittings together for easy desassembly, is employed three types of pieces; couplings, nipples and unions, with internal threads for screwing with the internal or external threads of the pipe ends.

The threads of the pipes, as the unions, nipples and couplings are conical, with the grip there is an interference between the screw threads, ensuring the tightness. For sealing, there are closure sealants, sealing out completely. It is important that the sealant used does not contaminate or be attacked or dissolved by circulating fluid. For services with water or gas, typically using red lead as a sealant. The unions are employed when you want the piping easily dismountable, where arrangements without the existence of unions the threading would be impossible. However, the threading weakens the wall, for this reason, when there are threaded connections use always thick-walled pipes (Sch. 80 minimum). Threaded connections are only used for hot-dipped galvanised steel tubes or wrought iron. Although, not exclusively, may be threading on carbon steel pipes, alloy steels, cast iron and plastic materials, always limited to the nominal diameter of 4 ". The American standards for pipe threads are according to ASME.B.2.1. The threaded connections are limited to the nominal diameter of 2", but not for services cyclical heavily. Except for pipes "Category D" is required the minimum thickness for Sch. 80 up to 1 1/2" and Sch. 40 for larger diameters. For thermoplastics, the minimum thickness should be Sch. 80, any diameter.

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As a general rule, the flanged connections should be used in the smallest possible number, because they are always points of possible leaks, and because are expensive and heavy. The flanges can be integrals, i.e., fused or forged together, welded or threaded with the pipe. The flanges of valves, pumps, compressors, turbines and other machines are almost always integrals with such equipment. Although the standardized series of ASME B.16.5 covers nominal diameters from 1/2" to 24", are not used flanges for pipes or tubes less than 1/2".

13.1) Common Types of Flanges: The most common types of flanges, according to ASME B.16.5 are: a. Integral Flange: used only in some cases to cast iron pipes. It is the oldest type of flanges and also what is proportionally more resistant. b. Welding-neck-WN): is the most often used in industrial pipes for all pressures and tempera-tures, for diameters from 1/2'' to 24. The welding neck flanges are the most resistant, provides an important reinforcement for use in several applications involving high pressure and elevated temperatures, giving conditions to lower residual stresses. This flange is connected to the pipe with a single butt weld, with the inner surface of the pipe perfectly smooth and seamless to facilitate the concentration of efforts or corrosion. The assembly with these flanges is expensive because each piece of pipe shall have beveled edges for welding, and must be cut square in the right measure, with very small tolerance in length. c. Slip-on-OS):is cheaper and easier to install than the previous one, because the tip of the tube fits into flange, facilitating the alignment, avoiding the need to cut the pipe in the exact measure. The flange is connected to the tube by two welds on internal and external angle. This flange can only be used for pipes in severe, because the services are not permissible grip is much less, residual stresses are high and the section discontinuities result in the concentration of efforts and facilitate erosion and corrosion.

Should not also be used for services with hydrogen and discouraged for cyclical services, subject to wide variation in temperature and crevice corrosion. The overlapping flanges are always weakness points into the pipe, because the mechanical strength is lower than the pipe itself. d. Screwed-SCR): used only for non-weldable metal pipes (iron for example), and for some types of non-metallic pipes, such as those of plastic materials. Can also be employed for carbon steel and wrought iron in secondary pipes applications (water, compressed air, etc.) and proper processes. The ASME B.31 recommends sealing welds between the flange and the pipe, for flammable, toxic, hazardous or great piping responsibilties. The permissive grip with these flanges is small, and tensions developed are high as the screw acts as an intensifier of efforts, and also as a permanent cause of leakage. e. Socket Weld-SW):similar to overlapping flanges, but more resistant with a full socket on the tip of the pipe for internal welding. This type is used for most steel pipes of small diameter, up to 2". Due the internal discontinuity these flanges are not recommended for services subject to corrosion under contact. f. Lap Joint:also called "Van Stone" and different from others, do not stay attached or welded on the pipeline, but, able to slide freely released on the pipe. At the end of the pipe there is a rebound or ledge (stub-end), which will serve as a stop for the flange.

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The face of these flanges has a circular deep slot, which fits a metallic ring, to a better sealing with the same degree of tightness of the screws, not only because of the actions of wedge ring, but the internal pressure tends to dilate the squeezing ring seal against the slot walls. The hardness of the face of the flanges should always be higher than the metallic ring and the minimum values according to material: - Carbon Steels: 120 Brinell; - Alloy and Stainless Steels, 304, 316, 347 types and 321: 160 Brinell; - Stainless Steels 316 L and 304 L types: 140 Brinell. d. Male & female-tongue & groove: These type of face is used for special services with corrosive fluids, because the metallic joint can be confined, in the absence of the fluid contact. It should be noted that, with these facings, the couples between flanges are different from one another. 14) Materials, Manufacturing, Classes and Diameters: Forging is the most common system for manufacture of steel flanges of any type. In practice, due to the high cost and the difficulty of obtaining large forgings, for 20 largest flanges, are the following alternative process for manufacturing: - Hot rolled steel flanges. These flanges can be accepted as equivalent to quality forged: - Flanges made of rolled sheet metal (or pressed), in two halves welded at the ends, when observed that all inspection and manufacturing requirements (ASME, sec. Vlll, div. 1, par. UA-46), must be accepted without restrictions. The main specifications of ASTM forged flanges are: - A-181: carbon steel forged flanges for general use. - A-105: carbon steel flanges calmed with itself for high temperatures. - A-182: steel flanges-Mo, Cr-Mo alloy and stainless steels. - A-351: carbon steel flanges and Ni alloy steels for low temperatures. The ASME B.16.5 sets the classes with nominal pressure: 150 psi, 300 psi, 400 psi, 600 psi, 900 psi, 1,500 psi 2,500 psi. The "primary non-shock rating" is the allowable pressure without a certain temperature. The carbon steel flanges are for temperatures up to 260 C (500 F) for class 150 psi and 455 C (850 F) for the other classes. For alloy steel and stainless steel flanges these temperatures may vary according to the material, being higher than the corresponding to the carbon steel. Allowable pressures for any material and any class, decrease with increasing temperature. Thus, for example, carbon steel flanges for class 150 psi, we have the following correspondences between permissible temperatures and pressures: 38C (100F): 19 kg/cm (275 psi);150C (300F): 14 kg/cm (210 psi) 260C (500F): 10 kg/cm (150 psi) 370C (700F): 7.5 kg/cm (110 psi) 480C (900F): 5 kg/cm (70 psi). The number that represents the nominal pressure, does not mean the allowable pressure with which the flange can work, as is erroneously interpreted. The allowable pressure for each nominal pressure, depends on the temperature and flange materials.



For each class of nominal pressure, an allowable pressure variation curve as a function of temperature. In the ASME B.16.5 these curves are transformed into tables giving the permissible pressure for all temperatures and for all usual materials. 14.1) Pressure/Temperature of Carbon Steel Flanges: The ASME B.16.5 Pipe Flanges and Flanged Fittings, sets for each nominal diameter and pressure class all dimensions of flanges: inner and outer diameters, length, thickness, circle, diameter drilling, number of screws, etc. The nominal diameter flanges with same pressure class are exactly alike and will adapt to the same pipe. The nominal pressure classes cover all types of flanges from 1/2" to 24", with the following exceptions: - Class 2,500 psi is manufactured up to 12" diameter. Socket flanges are manufactured to 150 psi and 600 psi classes. Threaded flanges class 1,500 psi, manufactured up to 12" in diameter. - Flanges of 3", nominal diameters or smaller up to 400 psi class, are the same as those of the class 600 psi. Flanges 2 1/2" nominal diameters or smaller up to 900 psi class, are the same for those of the class 1,500 psi. Carbon steel flanges more than 24", according to MSS-SP-44 or according to API-605 (up to 60" diameter nominal), or according to the standards of some manufacturers. Stainless steel flanges have the face and machining patterns often lighter than the standard flanges, for economy of materials. Example: Flange welding neck, 6", ASME B.16.5, face with RF finishing, 300 psi, ASTM A-181 Gr. I, for Sch. 40 piping (ASME B.36.10). 15) Flanges with Other Materials: Flanges are also of malleable iron, non-ferrous metals and various plastic materials. Cast iron flanges (ASME B.16.1) are manufactured in nominal pressure classes 125 psi and 250 psi, 1" to 24", threaded and blind. Drilling of cast iron flanges class 125 psi is the same of the steel flanges 150 psi class, which can be engaged with each other; the same for cast iron flanges class 250 psi and 300 psi class steel. Brass flanges, bronze and aluminum are manufactured in 150 psi 300 psi classes and, from 1/2" to 4" in diameter. Plastic PVC flanges are manufactured in class 150 psi (ASME B.16.5), 1/2" to 8" in diameter, threaded, blind and socket weld with the appropriate adhesive to the piping. Flanges for tubes "FRP" are manufactured in glass fibre reinforced plastics and these pipes diameters range according to standard class 150 psi, ASME B.16.5; these flanges can be integral to pipe or loose as lap joints. 15.1) Flange Joints or Gaskets: For all flanged connections there is a joint which is the sealing element. The joint is subject to a strong clamping screw compression and a shear stress due to internal pressure of circulating fluid. It is necessary that the pressure exerted by screws is higher than the internal pressure of the fluid, so that there is no leakage through the joint. For this reason, the greater the fluid pressure harder and resistant is the joint to resist the dual effort of compression and shear by the pressure screws. The joint must also be sufficiently deformable and elastic to model irregularities of the surfaces of the flanges, ensuring the sealing. The material of the joints should also resist the corrosive action of the fluid, as well as, the whole possible range of temperature variation.

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