welding techniques and inspections final

ScopeSection-I Welding Terminology

Section-II Welding Safety

Section-III Welding PPEs and Hand Tools

Section-IV Welding Joints and symbols

Section-V Important Arc Welding Processes

Section-VI Welding Consumables

Section-VII Welding Imperfections

Section-VIII Duties of Welding Inspector

Section-IX Inspection and Testing of Welds

Welding Terminology1: Welding:Welding may be described as a metal working process in which metals are joined by heating to the melting point and allowing the molten portions to fuse or flow together.

2: WeldabilityThe capacity of a metal to be welded easily is called weldability.

3: ARCA comparatively low voltage electrical discharge through a gas, between spaced electrodes.Basically there are three kinds of Arc1) Arc due to direct current2) Arc due to alternating current3) Arc due to pulse currentDirect current is further divided into DCSP and DCRP.

Section-I

Welding Terminology4: DCRP:In this case electrode is negative and base metal is positive.2/3 heat is produced at the base metal and 1/3 at the electrode.

5: DCSP:In this case electrode is positive and work piece is negative.2/3 heat is produced at the electrode and 1/3 at the base metal.

6: ARC Welding:A group of welding processes which produce coalescence of metals by heating with Arc or Arcs, with or without the application of pressure and with or without the use of filler.

7: Gouging & Air Carbon Arc CuttingAn arc cutting process that melts base metal by the heat of a carbon arc and removes the molten metal by a blast of air.

Section-I

Welding Terminology8: Arc Blow:An electric current flowing through the electrode sets up magnetic field in a continuous series of circles in a plane perpendicular to the axis of the rod. Similarly magnetic lines are also formed around the work piece and ground cables. When the fields around the work piece or around the electrode are unbalanced, the arc bends away from the greater concentration of the magnetic fields. This deflection of the arc from its intended path is called Arc Blow.

9: Arc Force:The axial force developed by an Arc plasma.

10: Electrode Force:The force between the electrodes in making spot, seams, or projection welds by resistance welds.

Section-I

Welding Terminology11: Deposition Rate:Deposition rate is the weight of metal deposited in a given period of time, usually expressed in kg/hr.

12: Deposition Efficiency:Electrode deposition efficiency is defined as the ratio between deposited and melted weight of the electrode.

13: Shielding Gas:Protective gas used to prevent atmospheric contamination. Argon, Helium & Carbon dioxide are commonly used as shielding gases. ‘.

14: Operation Factor:It is defined as the proportion of the total welding time an operator is actually fusing electrodes.

Section-I

Welding Terminology

Process Deposition Rate%

Operation Factor%

SMAW 60-75 20-30

GTAW 90-100 20-30

GMAW 90-95 50 for Semi Auto m/c100 for Auto m/c

FCAW 85-90 50 for Semi Auto m/c100 for Auto m/c

SAW 95 50 for Semi Auto m/c100 for Auto m/c

Section-I

Welding Terminology15: Dilution:Thus the dilution is defined as a change in composition of a welding filler metal caused by the admixture of the base metal or previously deposited weld metal in the deposited weld bead.

16: Residual Stress:Stress remaining in a structure or member as a result of thermal or mechanical treatment. In fusion welding, stress arises because of the contraction of the metal during cooling from the solidus temperature to room temperature.

17: Peening.The mechanical working of metals by means of impact blows.

18: Pre-heating.The application of heat to the base metal prior to a welding or cutting operation.

19: Post-heating:The application of heat to a weldment after welding.

Section-I

Welding Terminology20: Inter-pass Temperature:In a multiple-pass weld, the temperature minimum or maximum, (as specified) of the deposited weld metal before the next pass is started.

21: Puddling:If welding is done without filler rod, it is called puddling. Normally this is used for plates of less than 3 mm thickness.

22: Forehand WeldingA welding technique in which the welding torch or gun is directed towards the progress of welding. The forehand welding technique adopted for thin sheets.

23: Backhand WeldingA welding technique in which the welding torch or gun is directed opposite to the progress of welding. A backhand welding is used for the thickness greater than 3 mm.

Section-I

Welding Terminology24: Weaving.A type of weld bead made with transverse oscillation, and consequently wider than the stringer bead.

25: Stringer.A type of weld bead made without appreciable transverse oscillation.

26:Duty Cycle.Duty cycle Is defined as the percentage of a 10 minute period that an equipment can be operated at a rated amperage without over heating or suffering other damage.

27: ButteringA form of surfacing in which one or more layers of weld metal are deposited on the face of a joint. The buttering provides a, metallurgically compatible transition weld deposit for subsequent completion of the weld joint.

28: KERF.The width of a cut produced during a cutting process.

Section-I

Welding Terminology29: Brazing And Soldering Brazing and soldering are joining processes involving a filler metal with a melting temperature below the solidus temperature of the base metal. If the filler metal melts above 450 °C, the process is called brazing.If the melting temperature is below 450 °C, it is called soldering.Brazing Alloys -Aluminum silicon Alloy, Copper phosphorous alloy, Silver, Gold, Copper, Copper - zinc alloy, Magnesium, Nickel.Soldering Alloy - lead and tin

30: Open Circuit VoltageIt is the voltage at the output terminals of a welding power source, when it is energized but has no current out put.

Section-I

Welding Safety

Introduction: Normally welding are not hazardous but a completely safe work-place is something non-existent in the world. Because welding generally requires the use of current. The hazards which are more or less peculiar to welding are;

1=Electric Shock2=Arc Radiation3=Fumes and dust4=Compressed gases5=Fire and explosions6=Noise

Section-II

Welding Safety

1: Electric Shock:

• Electric shock may occur in welding if current happens to pass through the welder’s body; the magnitude of the current will depend upon the resistance offered by the body.

• A current of 0.1 A or above is taken to be lethal to humans.

• Human body resistance is a of 600 ohm, the lethal current will be provided by voltage of just 60V.

• Generally it is taken that currents up to 0.002 A do not produce pain, those between 0.002 and 0.05 A do so and are dangerous, and those higher than 0.05 A can cause heavy shocks and can be lethal at 0.01A.

• Therefore necessary precautions must be taken to minimize electrical risk. This can best be done by ensuring proper insulation of cables, and reliable earthing of welding equipment. The grounding circuits, sanitary sewers and water pipes, should never be used as earth or return for welding circuit.

Section-II

Welding Safety

2: Arc Radiation:

• An electric arc gives off visible light (wavelength 0.4 to 0.75 lam) of high intensity with a 10,000 times the safe glare level of the eyes. The intensity of emitted light depends upon the current level, and the presence of flux.

• Welders should always warn others nearby before striking an arc by shouting ‘mind your eyes’.

• Welders operating SAW units do not need shields but they should use goggles to protect their eyes from accidental flashes through the flux.

Section-II

Welding Safety

3: Fumes and Dust:

Many welding processes generate dust and particulate fumes, which when inhaled regularly over long periods may result in serious effects on the welder’s health. The fumes and dust generated during arc welding may be carried into the zone around the welders face by convection currents rising from the arc. Metallic vapors, mostly oxides and silicates of metals, react with atmospheric oxygen resulting in the formation of fine dust. Especially dangerous are the oxides of zinc, lead, beryllium, and copper formed during welding of copper, brass, and bronze.

Section-II

Welding Safety

4: Compressed Gases:

• Whether in use or stored, the cylinders should be kept vertical and secured toprevent falling by means of chains and clamps.

• Hammers or wrenches should not be used to open cylinder valves.• Proper trolleys should be used for moving cylinders from one point to another in• the workshop. A cylinder should never be carried on shoulders because in case

it falls it can not only injure the person but may also explode.• Compressed gas cylinders should not be exposed to sunlight or heat as this may

to increase of pressure leading to explosion.• The temperature of gas cylinder should never be allowed to exceed 54 0C.• A cylinder valve should be opened gradually without jerk otherwise it may

damage regulator diaphragm.• Cylinders should be provided with their caps during storage and transport.

Section-II

Welding Safety5: Fire and Explosions:

• Never keep inflammable or combustible materials in the vicinity of welding operation.

• Cylinders for gas welding and cutting should never be used when they are lying in horizontal position.

• Never use copper couplings to join hoses carrying acetylene as this could cause the formation of the potentially explosive copper acetylide.

• Never use oxygen for blowing out or cleaning pipes and vessels.

• Hot work-pieces after preheating or welding should he guarded and clearly marked in bold letters.

• Fire-fighting equipment must be installed in the welding workshop areas. The fire fighting equipment must be checked at regular intervals.

• No smoking should be allowed in the welding area where inflammable goods are being used.

Section-II

Welding Safety6: Noise Hazard:

• Normal welding operations do not cause much noise but air carbon-arc gouging and plasma arc with high currents can create excessive noise requiring ear protection.

• Noise above 80 db is considered harmful and above 120 db outright dangerous, therefore workers exposed to such high level noise must he provided proper ear plugs.

Section-II

Welding Safety

Safety Precautions during Welding:

• No oil, grease should be present at work piece.

• Never use acetylene at pressures above 15 psi.

• Never use torches, regulators or other equipment that is in need of repair.

• Always use the operating pressures recommended by the manufacturer.

• Always wear goggles when working with a lighted torch.

• Do not use matches for lighting torches.

• Wear clothing suitable for the work to be done.

• NEVER do welding or cutting without adequate ventilation.

Section-II

Welding PPEs & Hand ToolsIntroduction:

• Proper use of Personnel Protective Equipment (PPE) greatly reduces the risk of injury and minimizes the effects of toxins.

• Different types of hand tools are used in the welding processes.

Section-III

Personnel Protective Equipments (PPEs).

Section-III

Welding Caps:

A welder’s cap should be worn to protect the head from hot metal and slag splatter. In addition, long hair should be tied back and tucked inside the welding jacket. Hats that are mainly polyester or have significant plastic content are not allowed.

Recommended: Cotton welding caps

Welding PPEs & Hand Tools

Welding PPEs & Hand ToolsPersonnel Protective Equipments (PPEs).

Section-III

Eye Protection:

Approved eye protection must be worn at all times while in the lab. This can be safety glasses or goggles. Eye protection must fit properly, and be in good condition. It must be properly worn, protecting the user’s eyes at all times.

Recommended:

ANSI 87.1 compliant safety glasses made of polycarbonate must be worn.

Personnel Protective Equipments (PPEs).

Section-III

Face Shield:

Additional eye protection is required over safety glasses for certain tasks. For processes that will produce high velocity particles, a full-face shield is required. A face shield is required for using portable grinders, pedestal grinders, abrasive cut-off saws, and sanders. .

Welding PPEs & Hand Tools


Section-III

Hearing Protection:

There are many noise-generating devices in the welding shop that can damage your hearing, and there are circumstances in which debris can penetrate the ear canal. Earplugs are required to protect your ears from both loud noises and foreign object damage. Ear muffles can be worn to provide even greater noise reduction.

Recommended:

Silicon earplugs on a string.


Section-III

Hand Protection:

Leather welding gloves are required to protect the hands while welding. They should match the welding process that you are performing.

Recommended:

•Thick leather welding gloves are recommended for SMAW and FCAW.•Medium-weight welding gloves are recommended for GMAW. •Thinner welding gloves are recommended for GTAW.


Section-III

Breathing Protection:

There are many fumes and gases produced from welding and associated processes. It is highly recommended that a filter mask or a ½-mask respirator be worn for welding and grinding. FCAW, SMAW and grinding are processes that produce fumes and particulates.

Highly Recommended:

half-mask Respirator with a P100 filter and charcoal filter.

Recommended:N95 or N100 mask.


Section-III

Body Protection:

Proper clothing can provide a great amount of protection. A welding jacket is highly recommended. Polyester fibers or nylon jackets or pants are not allowed. Pants should not have cuffs that can catch sparks or hot slag.

Recommended:Natural fiber such as cotton or leather


Section-III

Feet Protection:

Proper shoes will protect your feet from hot sparks or falling objects. The protective footwear you choose should comply with ASTM.i.e.ASTMF2413-05 or M/I/75/C/75M=Footwear designed for a male.F=Footwear designed for a female.I/75=Impact rating of 75 (foot pounds)C/75=Compression rating of 75 (2500 lbs. of pressure)05= 2005

Recommended:•Closed-toed shoes are required.•Leather shoes are recommended.•Metal-toe safety shoes are highly recommended.


Section-III

Welding Helmet:

A limited number of welding helmets are provided for use. SMAW, FCAW, GMAW, GTAW and plasma cutting require a welding helmet with a welding approved shaded lens.

Recommended:•Use approved welding shaded lens according to the process

Welding PPEs & Hand ToolsWelding Hand Tools:

Section-III

Ball peen hammer Needle Nose Pliers

Lineman’s Pliers Measuring Tape

Welding PPEs & Hand ToolsSection-III

Try Square Wire Brush

Chipping Hammer Torch Tip Cleaner

Welding Hand Tools:

Welding PPEs & Hand ToolsSection-III

Files Hand Shear

Hand Grinder Soap Stone or Scribe

Welding Hand Tools:

Welding Joints and Symbols

A Weld:

A union between materials caused by heat, and or pressure

A Joint:

A configuration of members

Section-IV

Welding Joints and SymbolsBasics Types of Weld Joints:

Butt Joint

Tee Joint

Edge Joint

Corner Joint

Lap Joint

Section-IV

Welding Joints and SymbolsAngular Limits of Different Joints:

Type of Weld Joint Angular Limits (Degree)

Lap Joint 0 ~ 5

Tee Joint 5(Excl.) ~ 90

Edge Joint 0 ~ 30

Corner Joint 30(Excl.) ~ 135

Butt Joint 135(Excl.) ~ 180

Section-IV

Welding Joints and SymbolsTypes of Welds:

1) Fillet weld,

2) Groove weld

3) Back or backing weld

4) Flange weld,

5) Plug or slot weld,

6) Spot or projection weld

7) Seam weld,

8) Surfacing weld.

Section-IV

Welding Joints and SymbolsWeld and Welding Symbols:A weld symbol indicates the required type of weld while the welding symbol includes the weld symbol and supplementary information.

Section-IV

Welding Joints and SymbolsWeld and Welding Symbols:

Section-IV

Welding Joints and Symbols

NDT Symbols:

NDT symbol will consists of the following elements:

1- Reference line2- Arrow3- Examination method letter designations4- Dimensions, areas and number of examinations5- Supplementary symbols6- Tail7- Specifications, code, or other references

Section-IV

Important Arc Welding Processes

The inspector should understand the basic arc welding processes most frequently used in the fabrication and repair of refinery and chemical process equipment. These processes include:

1) Shielded metal arc welding (SMAW)

2) Gas tungsten arc welding (GTAW)

3) Gas metal arc welding (GMAW)

4) Flux cored arc welding (FCAW)

5) Submerged arc welding (SAW)

Section-V


1: SHIELDED METAL ARC WELDING (SMAW)

• SMAW is the most widely used of the various arc welding processes.

•SMAW uses an arc between a covered electrode and the weld pool. It employs the heat of the arc, coming from the tip of a consumable covered electrode, to melt the base metal.

•Shielding is provided from the decomposition of the electrode covering.

•Either alternating current (ac) or direct current (dc) may be employed, depending on the welding power supply.

•A constant-current (CC) power supply is preferred.

•SMAW is a manual welding process.

Section-V


1: SHIELDED METAL ARC WELDING (SMAW)

Section-V

Important Arc Welding ProcessesSection-V


Advantages of SMAW:

Some commonly accepted advantages of the SMAW process include:

a. Equipment is relatively simple, inexpensive, and portable.b. Process can be used in areas of limited access.c. Process is less sensitive to wind and draft than other welding processes.d. Process is suitable for most of the commonly used metals and alloys.

Limitations of SMAW:

Limitations associated with SMAW are:

a. Deposition rates are lower than for other processes such as GMAW.

b. Slag usually must be removed at stops and starts, and before depositing a weld bead adjacent to or onto a previously deposited weld bead.

Section-V


2: GAS TUNGSTEN ARC WELDING (GTAW)

•GTAW is an arc welding process that uses an arc between a non-consumable tungsten electrode and the weld pool.

•The process is used with shielding gas and without the application of pressure.

•GTAW can be used with or without the addition of filler metal.

•The CC type power supply can be used with either dc or ac, the choice depends largely on the metal to be welded.

•Direct current welding is typically performed with the electrode negative (DCEN) polarity.

•Alternating current is mainly used for welding of Aluminium and Magnesium.

Section-V

Important Arc Welding Processes2: GAS TUNGSTEN ARC WELDING (GTAW)

Section-V

Important Arc Welding ProcessesAdvantages of GTAW:

Some commonly accepted advantages of the GTAW process include:

a. Produces high purity welds, generally free from defects.b. Little post-weld cleaning is required.c. Allows for excellent control of root pass weld penetration.d. Can be used with or without filler metal, dependent on the application.

Limitations of GTAW:

Limitations associated with GTAW process are:

a. Deposition rates are lower than the rates possible with consumable electrode arc welding processes.

b. Has a low tolerance for contaminants on filler or base metals.c. Difficult to shield the weld zone properly in drafty environments

Section-V


3: GAS METAL ARC WELDING (GMAW):

• GMAW is an arc welding process that uses an arc between continuous filler metal electrode and the weld pool.

• The process is used with shielding from an externally supplied gas and without the application of pressure.

• GMAW may be operated in semiautomatic, machine, or automatic modes.

• It uses either the short circuiting, globular, or spray methods to transfer metal from the electrode to the work.

Section-V


3: GAS METAL ARC WELDING (GMAW)

Section-V

http://images.google.com/imgres?imgurl=www.pacmig.com/images/sa_1.jpg&imgrefurl=http://www.pacmig.com/sa.html&h=285&w=285&prev=/images%3Fq%3Dmig%2Bwelding%26svnum%3D10%26hl%3Den%26sa%3DG

Important Arc Welding ProcessesAdvantages of GMAW:

Some commonly accepted advantages of the GMAW process include:a. The only consumable electrode process that can be used to weld most commercial metals and alloys.b. Deposition rates are significantly higher than those obtained with SMAW.c. Minimal post-weld cleaning is required due to the absence of a slag.

Limitations of GMAW:

Limitations associated with GMAW process are:a. The welding equipment is more complex, more costly, and less portable than that for SMAW.b. The welding arc should be protected from air drafts that will disperse the shielding gas.c. When using the GMAW-S process, the weld is more susceptible to lack of adequate fusion.

Section-V


4 :FLUX CORED ARC WELDING (FCAW)

• FCAW is an arc welding process that uses an arc between continuous tubular filler metal electrode and the weld pool.

•The process is used with shielding gas evolved from a flux contained within the tubular electrode, with or without additional shielding from an externally supplied gas, and without the application of pressure.

Section-V


4 : FLUX CORED ARC WELDING (FCAW)

Section-V

Important Arc Welding ProcessesAdvantages of FCAW:

Some commonly accepted advantages of the FCAW process include:a. The metallurgical benefits that can be derived from a flux.b. High deposition and productivity rates than other processes such as SMAW.d. Shielding is produced at the surface of the weld that makes it more tolerant of stronger air currents than GMAW.

Limitations of FCAW: Limitations associated with FCAW process are:a. Equipment is more complex, more costly, and less portable than that for SMAW.b. Self-shielding FCAW generates large volumes of welding fumes, and requires suitable exhaust equipment.c. Slag requires removal between passes.

Section-V


5: SUBMERGED ARC WELDING (SAW)

• Submerged arc welding is an arc welding process that uses an arc or arcs between a flux covered bare metal electrode and the weld pool.

•The arc and molten metal are shielded by a blanket of granular flux, supplied through the welding nozzle from a hopper.

•The process is used without pressure and filler metal from the electrode.

•The process can be applied in semiautomatic, automatic and machine modes.

Section-V

Important Arc Welding Processes5: SUBMERGED ARC WELDING (SAW)

Section-V


Advantages of SAW:

Some commonly accepted advantages of the SAW process include:a. Provides very high metal deposition rates.b. Produces repeatable high quality welds for large weldments and repetitive short welds.

Limitations of SAW:

Limitations associated with SAW process are:

a. A power supply capable of providing high amperage at 100% duty cycle is recommended.b. Weld is not visible during the welding process.c. Equipment required is more costly and extensive, and less portable.d. Process is limited to shop applications and flat position.

Section-V

Welding Consumables

Introduction:

• Welding consumables are materials used up during welding such as electrodes, filler rods, fluxes and externally applied shielding gases.

• Welding consumables can be grouped in to;

1: Coated electrode2: Fluxes3: Filler wires/ filler rods4: Shielding gases

Section-VI

Welding Consumables

Selection of Electrodes:

• Base Metal Strength Properties

• Base Metal Composition

• Welding Position

• Joint Design and Fit-up

• Thickness and Shape of Base Metal

• Production Efficiency and Job Conditions

Section-VI

Welding Consumables

Fluxes:

Flux is a material used during welding, brazing or braze welding to clean the surfaces, the joint chemically, to prevent atmospheric oxidation and reduce impurities or float them to the surface.

Fluxes are used in

1: SMAW2: SAW3: FCAW

Section-VI

Welding Consumables

AWS Filler Metal Specification:

More Electrodes standards:

AWS:American Standards

DIN:German Standards

JIS:Japanese Standards

Section-VI

Welding ConsumablesSection-VI

Welding ImperfectionsIntroduction:

This section is concerned mainly with discontinuities, which may or may not be classified as defects (rejectable) depending on requirements of individual specifications or codes.

Discontinuity:

A discontinuity is defined as an interruption of the typical structure of a weldment, such as a lack of homogeneity in the mechanical, metallurgical, or physical characteristic of the material, or weldment.

A discontinuity is not necessarily a defect. Discontinuities are rejectable only if they exceed specification requirements in terms of type, size, distribution, or location. A rejectable discontinuity is referred to as defect.

Defect:

By definition, a defect is a discontinuity whose size, shape or location makes detrimental to the useful service of the part in which it occurs. Discontinuities may be found in the weld metal, heat affected zone, or base metal of many elements.

Section-VII

Welding Imperfections

Welding Discontinuities/Defects:

Discontinuities/defects can be divided into following categories.

3) Solid Inclusions

4) Lack of fusion

1) Cracks

7) Mechanical or Surface damage

6) Dimensional Discontinuities

2) Gas Pores & Porosity

8) Misalignment

5) Incomplete Joint Penetration

Section-VII


1: Cracks

Cracks form in the weld and base metal when localized stresses exceed the ultimate strength of the material.

Cracking may occur at elevated temperatures during weld metal solidification or after solidification when the weldment has equalize in temperatures.

Cracks can be classified as either hot cracks or cold cracks. Hot cracks develop at elevated temperatures. Cold cracks develop after solidification is complete. Hot cracks propagate along grain boundaries. Cold cracks propagate both along grain boundaries and through grains.

Section-VII

Section-VII


Causes of Cracks;

1. Highly rigid joint

2. Excessive dilution

3. Defective electrodes

4. Poor fit-up

5. High sulfur base metal

6. Crater cracking

Section-VII

Welding Imperfections 2: Porosity:

Porosity is characterized by cavity type discontinuities formed by gas entrapment during solidification.

Surface breaking porosity

Fine cluster porosity Blow hole > 1.6 mm Ø

Hollow root bead

An isolated internal porosity

Coarse cluster porosity

Section-VII


Causes of Porosity:

1.Excessive hydrogen, nitrogen, or oxygen in welding atmosphere

2.High solidification rate

3.Dirty base metal

4.Dirty filler wire

5.Volatilization of zinc from brass

Section-VII

Welding Imperfections3: Solid Inclusion:

Entrapment of solid particles results into solid inclusion

Internal solid inclusion causing a lack of sidewall fusion

Surface breaking solid inclusionInternal solid inclusion causinga lack of inter-run fusion

Solid inclusions caused by undercut in the previous weld run

Internal solid inclusion

Section-VII


Causes of Solid Inclusion:

1.Failure to remove slag

2.Improper joint design

3.Slag flooding ahead of the welding

4.Poor electrode manipulative technique

5.Entrapped pieces of electrode covering

Section-VII

Welding Imperfections4: Incomplete Fusion:

Incomplete fusion is termed as fusion which does not occur over the entire intended for welding and between all adjoining weld beads.

Section-VII


Causes of Incomplete Fusion:

1. Insufficient heat input

2. Wrong type or size of electrode

3. Improper joint design

4. Inadequate gas shielding.

5. Incorrect electrode position

Section-VII

Welding Imperfections5: Incomplete Joint Penetration:

Incomplete joint penetration is defined as “penetration by weld metal that does not extend for the full thickness of the base metal in a joint with a groove weld.

Section-VII


Causes of Incomplete Joint Penetration :

1. In correct electrode position2. Weld metal running ahead of the arc3. Trapped oxides or slag on weld groove or weld face.

Section-VII

Welding Imperfections6: Dimensional Discontinuities:

Production of satisfactory weldment requires staying within specified sizes and shapes of welds and finished dimensions of an assembly. Dimensional data with tolerances may be found on drawings and in specifications and codes. Assemblies not meeting the requirements must be corrected before final acceptance.

a) Distortion

b) Incorrect Joint Preparation

c) Incorrect Weld size and profile

a) Incorrect Final dimensions

Section-VII


6 (a): Distortion

A change, permanent or temporary, in shape or dimensions of a part as a result of heating and welding.It may be;

I. LongitudinalII. TransverseIII. AngularIV.Bowing

Section-VII


Causes of Distortion

I. The Heat Input

II. Restraint

III. Inherent Stresses in the Parent Metal

IV.Parent Metal Properties

Section-VII


Prevention of Distortion

Rule-1 (Reduce the effective shrinking force)

Rule-2 (Making shrinkage works to reduce distortion)

Rule-3 (Balance shrinkage forces with other forces)

Section-VII



Rule-1 (Reduce the effective shrinking force)

• Do not Over weld

• Use Proper weld fit up

• Use few passes

• Use intermittent welds

• The use back step technique

• Skip welding technique

Section-VII



Rule-2 (Making shrinkage works to reduce distortion)

• Locating part out of position

Section-VII



Rule-3 (Balance shrinkage forces with other forces)

• Balance one shrinkage force with another

• Peening

• Use jigs and fixtures

Section-VII


6 (b): In correct Joint Preparation

• Established welding practice requires proper joint dimensions for each type of joint, consistent with the thickness of the material being welded.

• Failure to meet these criteria may result in a greatly increased tendency to produce discontinuities in the weld, in addition to the possibility of creating distortion.

• Therefore, it is important that joint preparation is the same as shown in the applicable drawings and within specified limits of the specification.

Section-VII

Welding Imperfections6 (c): In correct weld size and profile:

Section-VII


6 (d): In correct final Dimensions:

• Weldments are fabricated to meet certain dimensions, whether specified on detailed drawings or hand-written sketches. The fabricator must be aware of the amount of shrinkage to be expected at each weld joint. This will affect the final overall dimensions of the product.

• Weldments that require rigid control of final dimensions usually must be by machining or grinding after welding or after post weld heat treatment to stay within limits.

Section-VII


7: Mechanical or Surface Damage:

Mechanical or surface damage may be caused by;

• Grinding

• Hammering/ chisel marks

• Slag chipping hammer marks

• Torn cleats

• Arc strikes/spatter

Section-VII


8: Misalignment:

Linear misalignment measured in mm 3 mm

Angular misalignment measured in degrees*

15

Excess weld metal heightLowest plate to highest point

Linear

Angular

Section-VII

Duties of Welding Inspector

It is the duty of all welding inspectors to ensure that welding operations are carried out in accordance with written, or agreed practices or specifications

BeforeDuringAfter

Section-VIII

Duties of Welding Inspector

Before Welding:

1) Safety:Ensure that all operations are carried out in complete compliance with local, company, or National safety legislation (i.e. permits to work are in place).

2) Documentation: Check Specifications, Drawings, Procedures etc.

3) Welding Process and ancillaries: Check equipment ,Cables, Regulators, Ovens etc.

4) Incoming Consumables: Materials/welding consumables (Size. Condition. Specification. Storage)

5) Marking out preparation & set up: Check Angles/Root face/gap values. Distortion control. Pre-heat prior to tack welding if applicable.

Section-VIII

Duties of Welding InspectorDuring Welding:

1) Pre-Heating.

2) In process distortion control

3) Consumable control

4) Welding process

5) Welding run sequence and inter-pass cleaning

6) Minimum/maximum Inter-pass temperatures

7) Full compliance with all elements given on the WPS.

Section-VIII

Duties of Welding InspectorAfter Welding:

1) Visual Inspection

2) Non Destructive testing

3) Repairs

4) Repair procedures (NDT/Excavation/Welding/Welder approval)

5) PWHT

6) Hydro-static testing

7) Submission of all inspection reports to QC departments

Section-VIII

Inspection & Testing Of WeldsIntroduction:In general the inspection and testing of welds may include one or more of the following procedures depending upon the type of structure and the importance of its service.

1. Visual inspection and measurement

2. Destructive tests for mechanical strength and toughness

3. Non-destructive tests for hidden or sub-surface flaws

4. Tightness tests i.e., pressure and leak tests.

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Inspection & Testing Of Welds1: Visual Inspection:Visual examination is the most extensively used NDE method for welds. It includes either the direct or indirect observation of the exposed surfaces of the weld and base metal.

• Direct visual examination is conducted when access is sufficient to place the eye within 6”~ 24” of the surface to be examined and at an angle not less than 30 degrees to the surface.

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Inspection & Testing Of WeldsOptical Adds of Visual Inspection:

Lighting:The inspection surface illumination is of extreme importance. Adequate illumination levels shall be established in order to ensure and effective visual inspection. Standards such as ASME Section V Article 9 specify lighting levels of 100 foot-candles (1000 Lux) at the examination surface.

• MirrorsValuable to the inspector allowing them to look inside piping, threaded and bored holes, inside castings and around corners if necessary.

• MagnifiersHelpful in bringing out small details and defects.

• Fiberscopes & Boroscopes:Widely used for examining tubes, a deep hole, long bores, and pipe bends, having internal surfaces not accessible to direct viewing.

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Inspection & Testing Of WeldsOptical Adds of Visual Inspection:

Mirror Magnifier

Fiberscope Boroscope

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Inspection & Testing Of Welds

Mechanical Adds of Visual Inspection:

Steel Rule:

Available in a wide selection of sizes and graduations to suit the needs of the inspector.

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Vernier Scale:A precision instrument, capable of measuring in decimal units to a precision factor of 0.0001 in. The Vernier system is used on various precision measuring instruments, such as the caliper, micrometer, height and depth gages etc

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Combination square set:

Consisting of a blade and a set of three heads: Square, Center and Protractor. Used universally in mechanical work for assembly and layout examination.

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Thickness gauge:

Commonly called a “Feeler” gauge is used to measure the clearance between objects.

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Levels:Tools designed to prove if a plane or surface is truly horizontal or vertical.

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Inspection & Testing Of WeldsWeld Examination Devices:

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Inspection & Testing Of Welds2: Destructive Testing Of Welds:

Tests are conducted for the qualification of welding procedures, the qualification of welders and welding operators and for quality control.The destructive tests are usually of following types.1: Chemical Tests2: Metallographic Tests3: Mechanical Tests

i)- Hardness Test (Brinell, Rockwell, Vicker)ii)- Tensile Testiii)- Impact Testiv)- Bend Testv)- Fatigue Test

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Inspection & Testing Of Welds3: Non Destructive Testing Of Welds:

The methods with which defects and imperfections can be detected in a product without affecting the serviceability of the product are known as non-destructive methods.The Commonly used NDT methods that are applicable to the inspection of weldments are;

1: Liquid Penetrant Testing (PT)2: Magnetic particle Testing (MT)3: Radiography Testing (RT)4: Ultrasonic Testing (UT)5: Acoustic Emission Testing (AET)

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4: Tightness Testing:

i: Pressure testing:Pressure (Hydrostatic) Testing is carried out after all work has been completed and all examinations have been performed.

A suggested test procedure could be as follows;

• Ensure adequate venting of the vessel during filling to prevent air pockets and during draining to prevent the formation of a vacuum. • After filling examine the vessel to see that it is not leaking.

• Gradually apply pressure to approximately 50% of the specified test pressure and then in stages of 10%, until the specified test pressure is reached.

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Inspection & Testing Of Welds4: Tightness Testing:

i: Pressure testing:

• Maintain the specified test pressure for not less than 30 minutes prior to close visual inspection

• Observe the vessel for general yielding or other forms of visible distortion which could occur.

• If close visual inspection is to be undertaken, the test pressure should be reduced to about 2/3 of its value or to its deign pressure limit, but even then the vessel should not be subjected to shock loading such as hammer testing

•After the agreed test time and examination, the pressure should be gradually released through the top vent valve.

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Inspection & Testing Of Welds4: Tightness Testing:

ii: Pneumatic Testing

This testing could be carried out as a substitute for hydraulic testing when the use of a liquid testing medium is not practicable when;

•The vessel cannot be safely and practicably filled with a liquid test medium due to overloading, and over stressing.

•The vessel cannot be readily dried out and any traces of test medium remaining cannot be tolerated by subsequent processes.

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welding techniques and inspections final

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