RI 4 Defect Causes

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Copyright © 2003 TWI Ltd

RadiographyDefects/Processes

Course Reference WIS 20

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Defects which may be detected by visual inspection can be grouped under five headings

Cracks

Surface irregularities

Contour defects

Root defects

Miscellaneous

Weld DefectsWeld Defects

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Other associated defects

Cavities

Solid inclusions

Set up irregularities

Parent material defects


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Classified by Shape Longitudinal

Transverse

Branched

Chevron

CracksCracksClassified by Position HAZ Centreline Crater Fusion zone Parent metal


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CracksCracks

Longitudinal parent metal crack Transverse weld metal crack

Longitudinal weld metal crack Lamellar tearing

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Copyright © 2003 TWI LtdTransverse crack Center line crack

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Surface IrregularitiesSurface Irregularities

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UndercutUndercut An irregular groove at the toe of a weld run in the

parent metal

Excessive amps/volts

Excessive travel speed

Incorrect electrode angle

Excessive weaving

Incorrect welding technique

Electrode too large

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Cap UndercutCap Undercut

Measured in both Length & DepthMeasured in both Length & Depth

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Cap undercutRoot undercut

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OverlapOverlap An imperfection at the toe or root of a weld caused by

metal flowing on to the surface of the parent metal without fusing to it

Contamination

Slow travel speed

Incorrect welding technique

Current too low

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OverlapOverlap

Toe OverlapToe Overlap

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Crater PipeCrater Pipe

Crater pipe is a shrinkage defect and not a gas defect, it has the appearance of a gas pore in the weld crater

Too fast a cooling rate

Deoxidization reactions and liquid to solid volume change

ContaminationCrater crack(Star crack)

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Crater PipeCrater Pipe

Crater pipeCrater pipe

Weld craterWeld crater

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Crater Pipe/CracksCrater Pipe/Cracks

Crater pipeCrater pipe

Crater CracksCrater Cracks

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Copyright © 2003 TWI LtdSpot weld gas Spot weld crack

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Contour DefectsContour Defects

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Incomplete filled groove Poor cap profile

Excessive cap heightIncomplete filled groove + Lack of sidewall fusion

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Poor stop/starts

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Copyright © 2003 TWI LtdIncomplete filled grooveExcess cap reinforcement

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Root DefectsRoot Defects

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Incomplete root fusion

Incomplete root penetration

Low Amps/volts

Large Root face

Small Root Gap

Fast Travel Speed

Incorrect Electrode Angle

Contamination

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Lack of root fusion Lack of root Penetration

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Lack of root fusionLack of root penetration

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Concave root


Root faces too large

Root gap too large

Excessive back purge pressure during TIG welding

Excessive root bead grinding before the application of the second pass

A shallow groove, which may occur in the root of a butt weld

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Concave RootConcave Root

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Excessive root penetration


Root faces too small

Root gap too large

Excessive amps/volts

Slow travel speed

Root penetration bead in excess in accordance with the relevant specification being used

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Excessive Root PenetrationExcessive Root Penetration

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Concave root Excessive root penetration

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Shrinkage groove


Insufficient weld metal deposited in the root pass

Too fast a cooling rate during the application of the root bead pass

Poor welding technique

A shallow groove caused by contraction in the weld metal along each side of the penetration bead

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High Amps/volts

Small Root face

Large Root Gap

Slow Travel SpeedBurn through

A localized collapse of the weld pool due to excessive penetration resulting in a hole in the root run

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Copyright © 2003 TWI Ltd Burn through

Burn Through

Root Defects

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Root Coking/Oxidized Root Root Coking/Oxidized Root

Loss or insufficient back

purging gas

Most commonly occurs

when welding stainless

steels

Purging gases include

argon, helium and

occasionally nitrogen

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Miscellaneous DefectsMiscellaneous Defects

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Accidental striking of the arc

onto the parent material

Faulty electrode holder

Poor cable insulation

Poor return lead clamping

Arc strike

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Spatter

Excessive current

Damp electrodes

Contamination

Incorrect wire feed speed

when welding with the MAG

welding process


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InclusionsInclusions

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Gas CavitiesGas Cavities

Root piping

Cluster porosityGas pore

Blow holeHerringbone porosity

Loss of gas shield

Damp electrodes

Contamination

Arc length too large

Damaged electrode flux

Moisture on parent material

Welding current too low

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Gas CavitiesGas Cavities

Root pipingRoot piping

PorosityPorosity

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Single gas poreCluster porosity

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Solid InclusionsSolid Inclusions

Slag originates from welding flux

MAG and TIG welding process produce silica inclusions

Slag is caused by inadequate cleaning

Other inclusions include tungsten and copper inclusions from the TIG and MAG welding process

Slag inclusions are defined as a non-metallic inclusion caused by some welding process

Slag inclusions

Parallel slag lines

Lack of sidewall fusion with

associated slag

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Elongated slag linesInterpass slag inclusions

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Set-up IrregularitiesSet-up Irregularities

Plate/pipe Linear Misalignment (Hi-Lo)

Poor fit-up

Angular Misalignment

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Linear MisalignmentLinear Misalignment

Plate Linear Misalignment

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ProcessesProcesses

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Welding ProcessesWelding Processes

Welding is regarded as a joining process in which the work pieces are in atomic contact

Common Fusion welding processes Oxy-acetylene

MMA (SMAW)

MIG/MAG (GMAW)

TIG/TAG (GTAW)

Sub-arc (SAW)

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Manual Metal Arc Process (MMA)Manual Metal Arc Process (MMA)

Parent material

Electric Arc

Gas shield

Molten weld pool

Solidified slag

PenetrationBuild up of weld metal

Electrode covering

Electrode core wire

USA: SMAWUSA: SMAW

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Tungsten Inert Gas (TIG)Tungsten Inert Gas (TIG)

Filler wire

Gas inlet

Deposited weld metal

Cap

SwitchHandle

Shielding gas

Switch power cable

Electrode

USA: GTAWUSA: GTAW

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Parent material

Electric Arc Gas shield

PenetrationBuild up of weld metalMolten weld pool

Shielding gas in

Wire electrode

Contact tip and electrode wire guild

Metal Active/Inert Gas (MAG/MIG)Metal Active/Inert Gas (MAG/MIG)

USA: GMAWUSA: GMAW

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Plain top roller

Half grooved bottom roller

Wire guide

MAG/MIG Internal Wire DriveMAG/MIG Internal Wire Drive

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Sub-arc (SAW)Sub-arc (SAW)

- +

Power supply

Filler wire spoolFlux hopper

Wire electrode

Flux

Slide rail

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Submerged-arc (SAW)Submerged-arc (SAW)

- +

Power supply

Filler wire spoolFlux hopper

Wire electrode

Flux

Slide rail

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RI 4 Defect Causes

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