Basic Welding.pptx

8/10/2019 Basic Welding.pptx

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BASIC W ELDING

YASREF Project Quality Management DivisionEPC-1

Prepared By: Biplab Pal


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Welding

An operation in which two or more parts are united by means of heator pressure or both, in such a way that there is continuity in thenature of the metal between these parts.

Welding Conditions Smooth joint surfaces that match each other Surfaces clean and free from oxides, grease and dirt. Metals to be joined have same microstructure The metals should be good quality (no internal impurities)

Welding Preparation Before starting a weld, the joint edges should be carefully prepared.

Bevelling large edges Cleaning (Chemical/Mechanical)


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Type of joint Butt Joint

A connection between the ends or edges of two parts making an angleto one another of 135 to 180 inclusive in the region of the joint. T joint

A connection between the end or edge of one part and the face ofthe other part, the parts making an angle to one another of morethan 5 up to and including 90 in the region of the joint


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Corner Joint:

A connection between the ends or edges of two parts making an angleto one another of more than 30 but less than 135 in the region of the

jointEdge Joint:

A connection between the edges of two parts making an angle to oneanother of 0 to 30 inclusive in the region of the joint


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Cruciform Joint

A connection in which two flat plates or two bars are

welded to another flat plate at right angles and on thesame axis T joint. Lap Joint

A connection between two overlapping parts making anangle to one another of 0 to 5 inclusive in the region ofthe weld or welds


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Features of Completed Weld (Butt Weld)

Weld Face

Parent Metal

HAZ

Weld Metal

Root Fusion Line

Excess Weld Metal

Toe

Weld Zone


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Features of Completed Weld (Fillet Weld)

Parent Metal

HAZWeld Metal

Root

Fusion Line

Excess WeldMetal

Parent Metal

Toe

Weld Zone

Weld Face


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Parent metal : Metal to be joined or surfaced by welding. Filler metal : Metal added during welding. Weld metal : All metal melted during the making of a weld and retainedin the weld. Heat-affected zone (HAZ) : The part of the parent metal that ismetallurgic ally affected by the heat of welding or thermal cutting, but notmelted. Fusion line : The boundary between the weld metal and the HAZ in afusion weld. This is a non-standard term for weld junction. Weld zone : The zone containing the weld metal and the HAZ. Weld face : The surface of a fusion weld exposed on the side from

which the weld has been made. Root : The zone on the side of the first run furthest from the welder. Toe : The boundary between a weld face and the parent metal orbetween runs. This is a very important feature of a weld since toes arepoints of high stress concentration and often they are initiation points fordifferent types of cracks (eg fatigue cracks, cold cracks). In order toreduce the stress concentration, toes must blend smoothly into the

parent metal surface. Excess weld metal : Weld metal lying outside the plane joining thetoes.Other non-standard terms for this feature: Reinforcement, overfill.


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Included angleThe angle between the planes of the fusion faces of parts to be welded. Inthe case of single V or U and double V or U this angle is twice the bevelangle. In the case of single or double bevel, single or double J bevel, theincluded angle is equal to the bevel angle.

Root faceThe portion of a fusion face at the root that is not beveled or grooved. Itsvalue depends on the welding process used, parent material to be weldedand application; for a full penetration weld on carbon steel plates, it has avalue between 1-2mm (for the common welding processes).

GapThe minimum distance at any cross section between edges, ends orsurfaces to be joined. Its value depends on the welding process used andapplication; for a full penetration weld on carbon steel plates, it has a valuebetween 1-4mm.

Root radiusThe radius of the curved portion of the fusion face in a component preparedfor a single J or U, double J or U weld. In case of MMA, MIG/MAG and oxy-fuel gas welding on carbon steel plates, the root radius has a value of 6mmfor single and double U preparations and 8mm for single and double Jpreparations.

LandThe straight portion of a fusion face between the root face and the curvedpart of a J or U preparation, can be 0. Usually present in weld preparationsfor MIG welding of aluminum alloys.


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Basic Welding PositionFlat

Horizontal-vertical

Horizontal


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Vertical-up & Vertical-down

Overhead

Horizontal overhead


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Basic components of a WELDING SYMBOL


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Types of Electric Arc Welding

Manual Metal Arc (MMA)

Metal Arc Gas Shielded (MAGS) MIG

Tungsten Arc Gas Shielded (TAGS) TIG

Submerged Arc Welding (SAW)


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Manual Metal Arc (MMA) Most widely used of all the arc welding processes

Commonly calledstick

welding

ApplicationsWeld Work, repair work, structural steelwork,


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Touch electrode against work withdraw electrodeto establish arc . Heat of arc melts base metal,the electrodes metal core , and any metal

particles in electrodes covering.Heat also melts, vaporises, or breaks downchemically non-metallic substances in covering forarc shielding. Mixing of molten base metal and

filler metal from electrode produces coalescencerequired to effect joining.


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Advantages Used with many electrode types & sizes

Used in all positions

Used on great variety of materials

Flexibility in operator control makes it the most versatile of all weldingprocesses

Low cost of equipment

Dis-advantages Rod becomes shorter & periodically needs replacing

Slows production rate (% time welder welding)


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The Electrode and Coating Coating is a combination of chemicals

Cellulosic electrodes contain cellulose

Rutile electrodes titanium oxide (rutile)

Basic electrodes contain calcium carbonate (limestone) andcalcium fluoride (fluorspar)


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Function of Electrode Coating

Produce gas to shield weld pool from oxidising effects ofatmosphere

Fluxing elements help weld pool to form

Helps slag to form-removes impurities

Slag slows down cooling preventing Brittleness

Can contain alloying elements or additional fillermetal


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Equipment used in MMAAC power source

Takes power directly from mains power supply. It usea transformer to supply the correct voltage to suit thewelding conditions.


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DC power sourceTwo types

1. DC generator2. Transformer-rectifier

DC Generator An electricity generator is driven by a motor. Themotor can be electric, petrol or diesel. The generatorprovides DC current for the arc


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Transformer-rectifier

A transformer with an electrical device to changeAC to DC , this is known as a rectifier. It has theadvantage of being able to supply both DC and AC


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Basic Transformer-rectifier circuit (AC to DC)

On/Off

switch

Step Down Transformer Bridge Rectifier

SmothingCapacitor

High ACVoltage

230V

Low AC

Voltage10-50V

DCoutput

+

_

A B C D


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A B

C D


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MIG is similar to MMA in

that heat for welding isproduced by forming anarc between a metalelectrode and the workpiece; the electrode meltsto form the weld bead.

The main difference is that the metal electrode is a small diameter wire fedfrom a spool and a shielding gas is used. As the wire is continuously fed, theprocess is often referred to as semi-automatic welding.


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Advantages

Large gaps filled or bridged easily Welding can be done in all positions No slag removal required High welding speeds High weld quality Less distortion of work piece


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Equipment used in MAGS

Three major elements are :

Welding torch and accessoriesWelding control & Wire feed motor

Power Source

Shielding Gas


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Welding torch and accessories

The welding torch guides the wire and shielding gas to theweld zone.

Brings welding power to the wire also Major components/parts of the torch are the contact tip,

shielding gas nozzle, gas diffuser, and the wire conduit

NOZZLE

CONTACT TIP

GAS DIFFUSER


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Welding control and wire feedmotor

Main function is to pullthe wire from the spooland feed it to the arcControls wire feed speed

and regulates the startingand stopping of wire feed


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Sheilding Gas

Purpose of shielding gas is to protect the weld area from thecontaminants in the atmosphere

Gas can be Inert, Reactive, or

Mixtures of both Argon, Helium, and Carbon

Dioxide are the main three gasesused in MAGS


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Tungsten Arc Gas Shielded (TAGS)

TIG TIG is similar to MMA in that heat forwelding is produced by forming anarc between a metal electrode andthe workpiece

Applications

Used in joining magnesium and Aluminium, stainless steels

for high quality weldingThin sheet material


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Advantages Superior quality welding

Can be used in mechanised systems Used to weld aluminium and stainless steels Free of spatter Low distortion


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Equipment used in TAGS

Power source

Electrodes

TIG must be operated with a constantcurrent power source - either DC or

AC

Electrodes for DC welding are normally pure tungsten. In AC welding, as the electrode will be operating at a muchhigher temperature, It should be noted that because of the

large amount of heat generated at the electrode, it isdifficult to maintain a pointed tip and the end of theelectrode assumes a spherical or 'ball' profile.


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Sheilding Gas

Argon Argon + Hydrogen Argon/Helium

Helium is generally added to increase heat input(increase welding speed or weldpenetration). Hydrogen will result in cleaner looking

welds and also increase heat input, however,Hydrogen may promote porosity or hydrogencracking.

Shielding gas is selected according to the material being welded.


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Equipment used in SAW

SAW is normally operated with a single wire on either AC orDC current. Common variants are: twin wire

triple wire single wire with hot wire addition metal powdered flux addition

All contribute to improved productivity through a marked

increase in weld metal deposition rates and/or travel speeds.

Wire


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Flux

Fluxes used in SAW are granular fusible mineralsThe flux is specially formulated to be compatiblewith a given electrode wire type so that thecombination of flux and wire yields desiredmechanical properties. All fluxes react with the weldpool to produce the weld metal chemicalcomposition and mechanical properties


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Gas Welding (Oxy-acetylene)

A number of welding processes use a flame producedby burning a mixture of fuel gas and oxygen . The gasusually used is Acetylene but other gases are alsoused.Separate cylindersand a hose pipefrom each cylindertransports the gasesto a torch.

Gas and fuel mix inthe torch

burns @ 3100 C.


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During the welding heat from the flame is concentratedon the joint edges until the metal melts and starts to flow.When the molten metal from both sides melts it starts to fuse,when the metal cools down the two parts becomePermanently joined.

Additional FillerMetal is fed in byhand into theweld pool, atregular intervals

where it becomesmolten and joinswith the parentmetal.


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The Oxy-acetylene weldingFlame

Oxidizing Excessoxygen (1.5:1) (Brasses,Bronzes, copper)

Neutral Equalacetylene & oxygen (low carbonsteel, mild steels).

Reducing or CarburizingExcess acetylene (0.9:1)(Alloy steels and aluminiumalloys)

Inner Cone

SecondaryCombustion

envelope

Acetylenefeather

Max. Temp.Zone


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Carburizing Neutral Oxidizing



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Primary Combustion zone

The oxy-acetylene flame has two distinct zones.

The inner zone (Primary combustion Zone) is the hottest partof the flame. The welding should be performed so as the point

of the inner zone should be just above the joint edges.

C2H2 + O 2 2CO + H 2


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Equipment used in O-A welding

The oxygen and acetylene hose pipes

Gases used

Gas pressure Regulators

Flashback arrestor

Welding torch/Welding nozzle

Filler rods and fluxes


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The oxygen and acetylene hose pipesReinforced rubber hoses.

Acetylene hose has left hand thread couplings and colour coded red.

Oxygen hose has right handed thread couplings and colour coded blue

Gases usedOxygen extracted from air and compressed into cylinders at highpressure. Cylinder is black. Oil should never be brought into contactand should not be used on fittings

Acetylene (C 2H2) is a fuel gas. Cannot be compressed directly asexplodes at high pressures. Cylinders are packed with porousmaterial which is filled with acetone Acetone absorbs acetylene.Cylinder colour coded maroon


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Welding torch

Oxygen and acetylene are delivered to the torch by separate hoses.Each gas is controlled by a valve on the torch. The two gases mix in thetorch and after they are ignited burn at the nozzle.

Mixer Needle valves


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Flashback Arrestors

These are positioned on both the fuel gas and oxygen supplybetween the hose and the regulator. Their purpose is to prevent thereturn of a flame through the hose into the regulator.


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Filler Rods and fluxes

Filler rods are used when additional filler metalis required in the weld area they come indifferent diameters.

Fluxes protect the weld pool from contaminationby oxygen and nitrogen, they are normally inpaste form placed on a heated filler rod beforewelding begins


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Resistance welding

Resistance welding uses the application of electriccurrent and mechanical pressure to create a weldbetween two pieces of metal. Weld electrodes conductthe electric current to the two pieces of metal as they areforged together . The welding cycle must first developsufficient heat to raise a small volume of metal to themolten state. This metal then cools while under pressureuntil it has adequate strength to hold the partstogether. The current density and pressure must be

sufficient to produce a weld nugget, but not so high as toexpel molten metal from the weld zone.


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Spot welding

Seam Welding


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Spot welding

Ideal for joining light sheet metal. The electrodesare made from copper. Pressure is applied to theelectrodes and an electric current is passedthrough the circuit. The high resistance betweenthe joint faces causes rapid heating and fusing ofa small globule of metal from both faces.


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Seam welding

The rollers allow the workpiece to move through thewelder continuously. A streamof electrical pulses passthrough the rollers and weldsthe joint


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Resistance Welding Benefits High speed welding Easily automated

Suitable for high rate production

Economical

Resistance Welding Limitations Initial equipment costs

Lower tensile and fatigue strengths

Lap joints add weight and material


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Friction welding

One part is held stationary while theother part is rotated

When the parts are hot enough therotation is stopped and the parts forgedtogether


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Robotic welding

Robots are driven using actuators which

control the robotic arm from an input signal.They can use hydraulic (large robots),pneumatic(small actuators with simple controlmovements) or electrical principles ofoperation.

A computer sends instructions inelectrical signals or pulses. An interfaceconverts these digital pulses intoanalogue electricity for the motors. The

robot is fitted with sensors which cansend feedback on the position of therobot.


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Advantages of Robotic welding

Faster production rates Efficient continuous operation Safe working practice Reliable and consistent welds Full automation Cost effective

Examples Automated welding of motor vehiclesskeletal frames and bodies.


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Robotic welding Terms

Lead through programming Teaching robot movements through

guiding it manually through a sequence of operations. These arerecorded to memeory

Machine Vision Area of vision robot has, limits which robot sensorscan operate

Working enevelope The area within which a robot can operate.Where the work is caried out by robotic arm

Yaw left and right movment of robotic arm

Roll rotation of robot about one of its axis

Degrees of freedom These are the number of independentmovements of the arm joints( or actuators) the robot has.


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Welding Safety

Working in a safe manner, whether in the workshop or


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on site, is an important consideration in any welding operation.The responsibility for safety is on the individual not only fortheir own safety, but also for other peoples safety. The Visual/WeldingInspector has an important function in ensuring that safe workinglegislation is in place and safe working practices are implemented. The

Inspector may be required to carry out safety audits of weldingequipment prior to welding, implement risk assessment/permit to workrequirements or monitor the safe working operations for a particular task,during welding.There are a number of documents that the inspector may refer to forguidance:

Government legislation The Health & Safety at Work Act.

Health & Safety Executive COSHH Regulations, Statutory instruments. Work or site instructions permits to work, risk assessment documents

etc. Local Authority requirements.

There are four aspects of arc welding safety that the Visual/WeldingInspector needs to consider:

Electric shock. Heat and light. Fumes and gases. Noise.

Electric Shock


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The hazard of electric shock is one of the most seriousand immediate risks facing personnel involved in thewelding operation.Contact with metal parts, which are electrically hot, can causeinjury or death because of the effect of the shock upon thebody or because of a fall as a result of the reaction to electricshock.The electric shock hazard associated with arc welding may bedivided into two categories:

Primary voltage shock 230 or 460V Secondary voltage shock 60 to 100V

Primary voltage shock is very hazardous because it is muchgreater than the secondary voltage of the welding equipment.Electric shock from the primary (input) voltage can occur bytouching a lead inside the welding equipment with the powerto the welder switched on while the body or hand touches thewelding equipment case or other earthed metal. Residualcircuit devices (RCDs) connected to circuit breakers ofsufficient capacity will help to protect the welder and otherpersonnel from the danger of primary electric shock.

Secondary voltage shock occurs when touching a part


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Secondary voltage shock occurs when touching a partof the electrode circuit perhaps a damaged area onthe electrode cable and another part of the body touchesboth sides of the welding circuit (electrode and work, or weldingearth) at the same time.

Most welding equipment is unlikely to exceed OCVs of 100V.Electric shock, even at this level can be serious, so the weldingcircuit should be fitted with low voltage safety devices, to minimizethe potential of secondary electric shock.

A correctly wired welding circuit should contain three leads: Welding lead from one terminal of the power source to the

electrode holder or welding torch. Welding return lead to complete the circuit, from the work to the

other terminal of the power source. Earth lead from the work to an earth point. The power source

should also be earthed. All three leads should be capable of carrying the highest welding

current required.To establish whether the capacity of any piece of current carrying

equipment is adequate for the job, the Visual/ Welding Inspectorcan refer to the duty cycle of the equipment.

All current carrying welding equipment is rated in terms of:


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All current carrying welding equipment is rated in terms of:Duty cycle

All current carrying conductors heat up when welding current ispassed through them. Duty Cycle is essentially a measure of thecapability of the welding equipment in terms of the ratio ofwelding time to total time, which can be expressed as:

Duty cycle = Welding time 100/Total time

By observing this ratio the current carrying conductors will not beheated above their rated temperature. Duty cycles are based ona total time of 10 minutes.For example: A power source has a rated output of 350A at 60%duty cycle. This means that this particular power source willdeliver 350A (its rated output) for six minutes out of every ten

minutes without overheating.Failure to carefully observe the duty cycle of equipment canover-stress the part, and in the case of welding equipment causeoverheating leading to instability and the potential for electricshock.

Heat


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In arc welding, electrical energy is converted intoheat and light energies, both of which can have serious healthconsequences.The welding arc creates sparks, which have the potential to cause

flammable materials near the welding area to ignite and cause fires. Thewelding area should be clear of all combustible materials and is goodpractice for the Inspector to know where the nearest fire extinguishers areand the correct type of fire extinguisher to use if a fire does break out.Welding sparks can cause serious burns, so protective clothing, such aswelding gloves, flame retardant coveralls and leathers must be worn aroundany welding operation to protect against heat and sparks.

LightLight radiation is emitted by the welding arc in three principal ranges:

Type Wavelength (Nanometers)

Infra Red (Heat) > 700

Visible Light 400-700

Ultra Violet Radiation < 400


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Ultra Violet Radiation (UV)

All arc processes generate UV and excess exposure causes skininflammation, and possibly even skin cancer or permanent eye damage.However, the main risk amongst welders and Inspectors is inflammation ofthe cornea and conjunctiva, commonly known as arc eye or flash.

Arc eye is caused by UV radiation which damages the outmost protectivelayer of cells in the cornea. Gradually the damaged cells die and fall off thecornea exposing highly sensitive nerves in the underlying cornea to thecomparatively rough inner part of the eyelid. This causes intense pain,

usually described as sand in the eye. The pain becomes even more acute ifthe eye is then exposed to bright light. Arc eye develops some hours after exposure, which may not even havebeen noticed. The sand in the eye symptom and pain usually lasts for 12-24hours, but can be longer in more severe cases. Fortunately, arc eye isalmost always a temporary condition. In the unlikely event of prolonged andfrequently repeated exposures, permanent damage can occur.

Treatment of arc eye is simple: rest in a dark room. A qualified person orhospital casualty department can administer various soothing anestheticeye drops which can provide almost instantaneous relief. Prevention isbetter than cure and wearing safety glasses with side shields willconsiderably reduce the risk of this condition.

Ultra violet effects upon the skin


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The UV from arc processes does not produce the browning effect of sunburn; butdoes result in reddening and irritation caused by changes in the minute surfaceblood vessels. In extreme cases, the skin may be severely burned and blisters mayform. The reddened skin may die and flake off in a day or so. Where there hasbeen intense prolonged or frequent exposure, skin cancers can develop.

Infra red radiationInfra red radiation is of longer wavelength than the visible light frequencies, and isperceptible as heat. The main hazard to the eyes is that prolonged exposure (overa matter of years) causes a gradual but irreversible opacity of the lens. Fortunately,the infra red radiation emitted by normal welding arcs causes damage only within acomparatively short distance from the arc. There is an immediate burningsensation in the skin surrounding the eyes should they be exposed to arc heat.The natural human reaction is to move or cover up to prevent the skin heating,

which also reduces eye exposure.Fumes

Because of the variables involved in fume generation from arc welding and alliedprocesses (such as the welding process and electrode, the base metal, coatingson the base metal and other possible contaminants in the air), the dangers ofwelding fume can be considered in a general way. Although health considerationsvary according to the type of fume composition and individual reactions, thefollowing holds true for most welding fume. The fume plume contains solid particles

from the consumables, base metal and base metal coating. Depending on thelength of exposure to these fumes, most acute effects are temporary and includesymptoms of burning eyes and skin, dizziness, nausea and fever.

For example, zinc fumes can cause metal fume fever, a temporary illness


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p p ysimilar to flu. Chronic, long-term exposure to welding fumes can lead tosiderosis (iron deposits in the lungs) and may affect pulmonary function.Cadmium, however, is a different story. This toxic metal can be found onsteel as a coating or in silver solder. Cadmium fumes can be fatal evenunder brief exposure, with symptoms much like those of metal fume fever.These two should not be confused. Twenty minutes of welding in thepresence of cadmium can be enough to cause fatalities, with symptomsappearing within an hour and death five days later.

GasesThe gases that result from arc welding also present a potential hazard.

Most of the shielding gases (argon, helium and carbon dioxide) are non-toxic, when released, however, these gases displace oxygen in thebreathing air, causing dizziness, unconsciousness and death the longerthe brain is denied oxygen.Some degreasing compounds such as trichloroethylene andperchlorethylene can decompose from the heat and UV radiation toproduce toxic gases. Ozone and nitrogen oxides are produced when UVradiation hits the air and can cause headaches, chest pains, irritation ofthe eyes and itchiness in the nose and throat.To reduce the risk of hazardous fumes and gases, keep the head out ofthe fume plume. As obvious as this sounds, it is a common cause offume and gas over-exposure because the concentration of fumes andgases is greatest in the plume.

In addition, use mechanical ventilation or local exhaust at the arc to direct the


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fume plume away from the face. If this is not sufficient, use fixed or moveableexhaust hoods to draw the fume from the general area. Finally, it may benecessary to wear an approved respiratory device if sufficient ventilationcannot be provided. As a rule of thumb, if the air is visibly clear and the

welder is comfortable, the ventilation is probably adequate. To identifyhazardous substances, first read the material safety data sheet for theconsumable to see what fumes can be reasonably expected from use of theproduct.

Refer to the Occupational Exposure Limit (OEL) as defined in the COSHHregulations which gives maximum concentrations to which a healthy adult canbe exposed to any one substance. Second, know the base metal anddetermine if a paint or coating would cause toxic fumes or gases. Particularattention should also be made to the dangers of asphyxiation when welding inconfined spaces. Risk assessment, permits to work and gas testing are someof the necessary actions required to ensure the safety of all personnel.

Noise

Exposure to loud noise can permanently damage hearing, cause stress andincrease blood pressure. Working in a noisy environment for long periods cancontribute to tiredness, nervousness and irritability. If the noise exposure isgreater than 85 decibels averaged over an 8 hour period then hearingprotection must be worn, and annual hearing tests carried out.

Normal welding operations are not associated with noise level problems with two


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exceptions: Plasma arc welding and air carbon arc cutting. If either of these twooperations is to be performed then hearing protectors must be worn. The noiseassociated with welding is usually due to ancillary operations such as chipping,grinding and hammering. Hearing protection must be worn when carrying out, or

when working in the vicinity of, these operations.

Welder Qualification (Issuing JCC)

The use of qualified Welding Procedure Specification (WPS) is the acceptedmethod for controlling production welding but this will only be successful if thewelders are able to understand and work in accordance with them.

Welders also need to have the skill to consistently produce sound welds (freefrom defects).

Welding Standards have been developed to give guidance on what particulartest welds are required in order to show that welders have the required skillsto make particular types of production.

The qualification process for welders

Qualification testing of welders to European Standards requires test welds tobe made and subjected to specified tests to demonstrate that the weldersable to understand the WPS and to produce a sound weld.

For manual and semi-automatic welding the emphasis of the tests is to


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demonstrate the ability to manipulate the electrode or welding torch andwelds in particular materials.For mechanized and automatic welding the emphasis is ondemonstrating that welding operators have the ability to control particulartypes of welding equipment.

American Standards allow welders to demonstrate that they can producesound welds by s

Welder qualification and Issuing JCCThe welder is allowed to make production welds within the range ofqualification recorded on his Welder Qualification Certificate (JCC).The range of qualification is based on the limits specified by the WeldingStandard for welder qualification essential variables defined as: Avariable that if changed beyond the limits specified by the Weldingby Standard may require greater skill than has been demonstratedby the test weld.Some welding variables that are classed as essential for welderqualification are the same types as those classified as essential forwelding procedure qualification, but the range of qualification may besignificantly wider.Some essential variables are specific to welder qualification. objectingtheir first production weld to NDT.

C W ldi Di ti it & th i C &


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Common Welding Discontinuity & their Causes &Prevention

Cracks Cavities

Solid inclusions Lack of fusion and penetration Imperfect shape and dimensions Miscellaneous imperfections

CRACK


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CRACK

Definition : An imperfection produced by a local rupture in the solid state, which mayarise from the effect of cooling or stresses. Cracks are more significant than othertypes of imperfection, as their geometry produces a very large stress concentration atthe crack tip, making them more likely to cause fracture.Types of crack: Longitudinal. Transverse. Radiating (cracks radiating from a common point). Crater.

Branching (group of connected cracks originating from a common crack). These cracks can be situated in the: Weld metal HAZ Parent metal Exception: Crater cracks are found only in the weld metal.

Depending on their nature, these cracks can be: Hot (ie solidification cracks liquation cracks) Precipitation induced ( ie reheat cracks, present in creep resisting steels). Cold ( ie hydrogen induced cracks). Lamellar tearing.

Hot cracks


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Hot cracks

Depending on their location and mode of occurrence,hot cracks can be: Solidification cracks: Occur in the weld metal(usually along the centerline of the weld) as a resultof the solidification process Liquation cracks: Occur in the coarse grain HAZ, inthe near vicinity of the fusion line as a result ofheating the material to an elevated temperature, highenough to produce liquation of the low melting point

constituents placed on grain boundaries.

Solidification cracks


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Generally, solidification cracking can occur when:

The weld metal has a high carbon or impurity (sulphur etc) elementcontent.

The depth -to-width ratio of the solidifying weld bead is large (deep andnarrow).

Disruption of the heat flow condition occurs, eg stop/start condition

The cracks can be wide and open to the surface like


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pshrinkage voids or subsurface and possibly narrow.Solidification cracking is most likely to occur incompositions, which result in a wide freezingtemperature range. In steels this is commonly createdby a higher than normal content of carbon and impurityelements such as sulphur and phosphorus. Theseelements segregate during solidification, so thatintergranular liquid films remain after the bulk of the

weld has solidified. The thermal shrinkage of the coolingweld bead can cause these to rupture and form a crack.It is important that the welding fabricator does not weldon or near metal surfaces covered with scale or whichhave been contaminated with oil or grease. Scale can

have a high sulphur content, and oil and grease cansupply both carbon and sulphur. Contamination with lowmelting point metals such as copper, tin, lead, and zincshould also be avoided.

Hydrogen induced cracks


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y g

Hydrogen induced cracking occurs primarily in the grain-coarsenedregion of the HAZ, and is also known as cold, delayed or underbead /toecracking. Underbead cracking lies parallel to the fusion boundary, and itspath is usually a combination of intergranular and trans granularcracking. The direction of the principal residual tensile stress can, for toecracks, cause the crack path to grow progressively away from the fusionboundary towards a region of lower sensitivity to hydrogen cracking,when this happens, the crack growth rate decreases and eventuallyarrests.

A combination of four factors is necessary to cause HAZ hydrogen


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A combination of four factors is necessary to cause HAZ hydrogencracking:

1. Hydrogen level > 15ml/100g of weld metal deposited

2. Stress > 0.5 of the yield stress3. Temperature < 300C

4. Susceptible microstructure > 400HV hardness


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Lamellar tearing


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Lamellar tearing occurs only in rolled steel product (primarily plates) and its maindistinguishing feature is that the cracking has a terraced appearance.Cracking occurs in joints where:

A thermal contraction strain occurs in the through -thickness direction of steel plate Non -metallic inclusions are present as very thin platelets, with their principal planesparallel to the plate surface.Contraction strain imposed on the planar non-metallic inclusions results in progressivede-cohesion to form the roughly rectangular holes which are the horizontal parts of thecracking, parallel to the plate surface. With further strain, the vertical parts of thecracking are produced, generally by ductile shear cracking. These two stages create theterraced appearance of these cracks.

Two main options are available to control the problem in welded joints liable to lamellartearing: Use a clean steel with guaranteed through -thickness properties (Z grade). A combination of joint design, restraint control and welding sequence to minimize therisk of cracking.

Gas pore


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Gas pore

Causes Prevension

Damp fluxes/corroded electrode (MMA) Use dry electrodes in good condition

Grease/hydrocarbon/watercontamination of preparedsurface

Clean prepared surface

Air entrapment in gas shield (MIG/MAG, TIG) Check hose connections

Incorrect/insufficient de oxidant in electrode,filler or parent metal

Use electrode with sufficient de oxidationactivity

Too high an arc voltage orlength Reduce voltage and arc length

Gas evolution from priming paints/surfacetreatment

Identify risk of reaction before surfacetreatment is applied

Too high a shielding gas flow rate whichresults in turbulence (MIG/MAG, TIG)

Optimize gas flow rate

Worm holes


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Causes Prevention

Gross contamination ofpreparation surface

Introduce pre weld cleaningprocedures

Laminated work surface Replace parent material

with an un laminated pieceCrevices in work surfacedue to joint geometry

Eliminate joint shapeswhich producecrevices

Surface porosity


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p y

Causes Prevention

Damp or contaminated surface orelectrode

Clean surface and dry electrodes

Low fluxing activity (MIG/MAG) Use a high activity flux

Excess sulphur (particularly free cuttingsteels) producing sulphurdioxide

Use high manganese electrode to produceMnS, note free-cutting steels (highsulphur) should notnormally be welded

Loss of shielding gas due to long arc orhigh breezes (MIG/MAG)

Improve screening againstdraughts and reduce arc length

Too high a shielding gas flow rate whichresults in turbulence (MIG/MAG,TIG)

Optimize gas flow rate


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Slag inclusions


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g

Cause Prevention

Incomplete slag removal fromunderlying surface of multi passweld

Improve inter-run slag removal

Slag flooding ahead of arc Position work to gain control ofslag. Welder needs to correctelectrode angle

Entrapment of slag in worksurface

Dress/make work surfacesmooth

Flux inclusions


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Oxide Inclusion

Cause Prevention

Unfused flux due to damagedcoating Use electrodes in goodcondition

Flux fails to melt andbecomes trapped in the weld(SAW or FCAW)

Change the flux/wire. Adjustwelding paramtres iecurrent, voltage etc toproduce satisfactory weldingconditions

Cause PreventionHeavy mill scale/rust on worksurface

Grind surface prior to welding

Tungsten Inclusion


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g

Cause Prevention

Contact of electrode tip with weld pool Keep tungsten out of weld pool; use HF start

Contact of filler metal with hot tip of electrode Avoid contact between electrode and filler metal

Contamination of the electrode tip by spatter from the weldpool

Reduce welding current; adjust shielding gas flow rate

Exceeding the current limit for a given electrode size or type Reduce welding current; replace electrode with a largerdiameter one

Extension of electrode beyond the normal distance from thecollet, resulting in overheating of the electrode

Reduce electrode extension and/or welding current

Inadequate tightening of the collet Tighten the collet

Inadequate shielding gas flow rate or excessive winddraughts resulting in oxidation of the electrode tip

Adjust the shielding gas flow rate; protect the weld area;ensure that the post gas flow after stopping thearc continues for at least 5 seconds

Splits or cracks in the electrode Change the electrode, ensure the correct size tungsten isselected forthe given welding current used

Inadequate shielding gas (eg use of argon-oxygen or argon-carbon dioxide mixtures that are used for

MAG welding)

Change to correct gas composition

Lack of sidewall fusion


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Lack of sidewall fusion

Cause Prevention

Low heat input to weld Increase arc voltage and/orwelding current; decreasetravel speed

Molten metal flooding ahead of

arc

Improve electrode angle and

work position; increase travelspeed

Oxide or scale on weldpreparation

Improve edge preparationprocedure

Excessive inductance in MAGdip transfer welding

Reduce inductance, even if thisincreases spatter

Lack of inter-run fusion


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Cause Prevention

Low arc current resulting inlow fluidity of weld pool

Increase current

Too high a travel speed Reduce travel speed

Inaccurate bead placement Retrain welder

Lack of root fusion


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Cause Prevention

Low heat input Increase welding current and/or arc voltage;decrease travel speed

Excessive inductance in MAG dip transfer welding, Use correct induction setting for the parent metalthickness

MMA electrode too large(low current density)

Reduce electrode size

Use of vertical down welding Switch to vertical up procedure

Large root face Reduce root face

Incorrect angle or incorrect electrode manipulation Use correct electrode angle. Ensure welder is fullyqualified and competent

Excessive misalignment at root Ensure correct alignment

Small root gap Ensure correct root opening

Incomplete penetration


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Cause Prevention

Excessively thick root face,insufficient root gap or failure to cutback to sound metal in a backgouging operation

Improve back gouging technique andensure the edge preparation is as perapproved WPS

Low heat input Increase welding current and/or arcvoltage; decrease travel speed

Excessive inductance in MAG diptransfer welding, pool flooding aheadof arc

Improve electrical settings andpossibly switch to spray arc transfer




Incomplete root penetration


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Cause Prevention

Low heat input Increase welding current and/or arc voltage;decrease travel speed

Excessive inductance in MAG dip transfer welding, Use correct induction setting for the parent metalthickness




Large root face Reduce root face

Incorrect angle or incorrect electrode manipulation Use correct electrode angle. Ensure welder is fullyqualified and competent

Excessive misalignment at root Ensure correct alignment

Small root gap Ensure correct root opening

Undercut


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Undercut

Cause Prevention

Melting of top edge due to highwelding current (especially at freeedge) or high travel speed

Reduce power input, especially approaching a freeedge where overheating can occur

Attempting a fillet weld inhorizontal vertical (PB) position withleg length >9mm

Weld in the flat position or use multi-run techniques

Excessive/incorrect weaving Reduce weaving width or switch to multi-runs

Incorrect electrode angle Direct arc towards thicker member

Incorrect shielding gas selection(MAG)

Ensure correct gas mixture for material type andthickness (MAG)

Excess weld metal


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Cause Prevention

Excess arc energy (MAG, SAW) Reduction of heat input

Shallow edge preparation Deepen edge preparation

Faulty electrode manipulation orbuild-up sequence

Improve welder skill

Incorrect electrode size Reduce electrode size

Too slow a travel speed Ensure correct travel speed is used

Incorrect electrode angle Ensure correct electrode angle isused

Wrong polarity used (electrodepolarity DC-VE (MMA, SAW )

Ensure correct polarity ie DC +VE Note DC-VEmust be used for TIG

Excess penetration


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Cause Prevention

Weld heat input too high Reduce arc voltage and/orwelding current; increasewelding speed

Incorrect weld preparationie excessive root gap, thin

edge preparation, lack ofbacking

Improve work-piecepreparation

Use of electrode unsuited towelding position

Use correct electrode forposition

Lack of welder skill Retrain welder

Overlap


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Cause Prevention

Poor electrode manipulation(MMA)

Retrain welder

High heat input/low travelspeed causing surface flow of

fillet welds

Reduce heat input or limit leg size to 9mm maxleg size for single pass fillets.

Incorrect positioning of weld Change to flat position

Wrong electrode coating typeresulting in too high a fluidity

Change electrode coating type to a moresuitable fast freezing type which isless fluid

Linear misalignment


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Cause Prevention

Inaccuracies in assemblyprocedures or distortionfrom other welds

Adequate checking ofalignment prior to weldingcoupled with the use of

clamps and wedgesExcessive out of flatness inhot rolled plates or sections

Check accuracy of rolledsection prior to welding

Incompletely filled groove


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Cause Prevention

Insufficient weld metal Increase the number ofweld runs

Irregular weld bead surface Retrain welder

Irregular width


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Cause Prevention

Severe arc blow Switch from DC to AC, keepas short as possible arclength

Irregular weld bead surface Retrain welder

Root concavity


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Cause Prevention

Insufficient arc power toproduce positive bead

Raise arc energy

Incorrect prep/fit-up Work to WPS

Excessive backing gaspressure (TIG) Reduce gas pressure


Slag flooding in backing bargroove

Tilt work to prevent slagflooding

Burn-through


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Cause Prevention

Insufficient travel speed Increase the travel speed

Excessive welding current Reduce welding current


Excessive grinding of root face More care taken, retrain welder

Excessive root gap Ensure correct fit-up

Arc Strike


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Cause Prevention

Poor access to the work Improve access (modify assemblysequence)

Missing insulation on electrode holder ortorch

Institute a regular inspection scheme forelectrode holders and torches

Failure to provide an insulated restingplace for the electrode holder or torchwhen not in use

Provide an insulated resting place

Loose current return clamp Regularly maintain current return clamps

Adjusting wire feed (MAGwelding) without isolatingwelding current

Retrain welder

Spatter


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Cause PreventionHigh arc current Reduce arc current

Long arc length Reduce arc length

Magnetic arc blow Reduce arc length or switch to AC power

Incorrect settings for GMAW process Modify electrical settings (but be careful tomaintain full fusion!)

Damp electrodes Use dry electrodes

Wrong selection of shielding gas(100%CO2)

Increase argon content if possible,however too high a % may lead to lack ofpenetration

WELDING INSPECTION METHOD &


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WELDING INSPECTION METHOD &INVOLVEMENT

Checking before Weldingh f ll b h k d b f d ld


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The following are to be checked before proceeding any welding:

Item to be checked Action

1. Material In accordance with drawing/WPSIdentified and can be traced to a test certificateIn suitable condition (free from damage and contamination)

2. WPS Have been approved and are available to welders (andinspectors)

3. Welding equipment In suitable condition and calibrated as appropriate

4. Weld preparations In accordance with WPS (and/or drawings)

5. Welder qualifications Identification of welders qualified for each WPS to be used. Allwelder qualification certificates are valid (in date)

6. Weldingconsumables

Those to be used are as specified by the WPSs are beingstored/controlled as specified by the QC procedure

7. Joint fit-ups In accordance with WPS/drawings tack welds are to goodworkmanship standard and to code/WPS

8. Weld faces Are free from defects, contamination and damage

9. Preheat (if required) Minimum temperature is in accordance with WPS

Checking During Welding


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The following are to be checked during welding:

Item to be Checked Action

1. Site/field welding Ensure weather conditions are suitable/comply with Code ( conditions will notaffect welding)

2. Welding process In accordance with WPS

3. Preheat (if required) Minimum temperature is being maintained inaccordance with WPS

4. Interpasstemperature Maximum temperature is in accordance with WPS

5. Weldingconsumables

Inn accordance with WPS and being controlled asprocedure

6. Welding parameters Current, volts, travel speed are in accordance with WPS

7. Root run Visually acceptable to Code (before filling the joint) (for single sided welds)

8. Gouging/ grinding By an approved method and to good workmanshipstandard

9. Inter-run cleaning To good workmanship standard

10. Welder On the approval register/qualified for the WPS being used

Checking After WeldingTh f ll i b h k d Af ldi


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The following are to be checked After welding:

Item to be Checked Action

1. Weld identification Each weld is marked with the welder's identification and isidentified in accordance with drawing/weld map

2. Weld appearance Ensure welds are suitable for all NDT (profile, cleanness etc)Visually inspect welds and sentence in accordance with Code.

3. Dimensional survey Check dimensions are in accordance withdrawing/Code

4. Drawings Ensure any modifications are included on as-built drawings

5. NDT Ensure all NDT is complete and reports are available for records

6. Repairs Monitor in accordance with the procedure

7. PWHT (if required) Monitor for compliance with procedure (check chart record)

8. Pressure/load test (ifrequired) Ensure test equipment is calibratedMonitor test to ensure compliance with procedure/ Code.Ensure reports/records are available

9. Documentationrecords

Ensure all reports/records are completed and collated asrequired

Welding of On-Plot Piping Inspection Check List


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Sl No Document Name DocumentNumber

1.Review WPS & Process Control Procedure(Plant Piping) SAIC-W-2001

2. Review of Procedure for Weld Repair (PlantPiping)

SAIC-W-2002

3. Review Post Weld Heat Treatment (PWHT)Specification, Procedure, & Table for On-Plot

Piping

SAIC-W-2003

4. Post Weld Heat Treatment (PWHT) for On-Plot Piping

SAIC-W-2004

5. Pre-Welding Inspection (Shop & Field) ofPlant Piping

SAIC-W-2005

6. In-Process Welding Inspection SAIC-W-2006

7. Post-Welding Visual Inspection (Plant Piping) SAIC-W-2007

8. Review Procedure - Weld ID & Traceability,Process Control Tracking (SAEP-1160Database)

SAIC-W-2008

9. Review Procedure - Control of WeldingConsumables (Storage, Handling, Issuance,

SAIC-W-2009


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Conditioning) - Plant Piping10. Receiving Inspection of Welding

ConsumablesSAIC-W-2010

11. Validation of Welding Equipment (PlantPiping)

SAIC-W-2011

12. Review Hardness Testing Procedure - All Applications (Plant Piping, Pipelines, Vessels& Tanks)

SAIC-W-2012

13.Inspection of Repair on Weld Joints or BaseMetal by Welding (Prior to Weld Acceptance) SAIC-W-2013

14. Verify Hardness Testing - All Applications(Plant Piping, Pipelines, Vessels & Tanks)

SAIC-W-2014

15. Selection of Welds for NDE (On-Plot Piping &Structures)

SAIC-W-2015

16 Production Weld & Welder Repair Rate Assessment for On-Plot Piping SAIC-W-2016

17. Control of Welding Consumables - PlantPiping (Site Storage, Handling, Conditioning &Issuance)

SAIC-W-2032

18. Buttering and / or Weld Build-up SAIC-W-2033

19 Welder & Welding Operator Certification (Plant SAIC-W-2035


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19. g p (Piping)

SAIC W 2035

20. Inspect/Verify Piping & Weld Modifications* After

Initial Welding Acceptance (Rework & WeldRepairs)

SAIC-W-2036

21. Procedure & Inspection of Socket & Seal WeldedThreaded Joints (Gap Control, See also SAIC-L-2015)

SAIC-W-2037

22. Review of Positive Material Identification

Program and Testing Procedure

SAIC-L-2004

23. Positive Material Identification (PMI) of AlloyPiping & Alloy Components (All Applications)

SAIC-L-2010


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Thank You

Basic Welding.pptx

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