TWI Defects

7/21/2019 TWI Defects

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Copyright © 2005 TWI Ltd

WI 3.1

M.Rogers

Welding Imperfections

Course notes section reference 3

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Weld Defect ClassificationWeld Defect Classification

Defects can be grouped under three mainclassifications

Planar Defects: linear from at least one dimension

• Cracks

• Lack of fusion

Linear Volumetric Defects: Linear in length with volume

• Slag lines

• lack of fusion with associated slag

• Piping.

Non-planar defects: rounded indications without significat length

• Slag inclusions

• Gas pores/blow holes.

• Other matallic and non-matallic inclusions





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Classified by Shape

Longitudinal

Transverse

Branched

Chevron

Classified by Position

HAZ

Centreline

Crater

Fusion zone

Parent metal

Cracks that may occur in welded materials are causedgenerally by many factors and may be classified byshape and position, cracks are classed as planar.

CracksCracks

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M.Rogers

Longitudinal parent metal crack

Longitudinal weld metal crack Lamellar tearing

Transverse weld metal crack

CracksCracks



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Transverse crack Longitudinal crack

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InclusionsInclusions



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Root piping

Cluster porosityGas pore

Blow hole

Herringbone porosity

Loss of gas shield

Damp electrodes

Contamination

Arc length too large

Damaged electrode flux

Moisture on parent material

Welding current too low

Gas pore <1.5mm Blow hole.>1.6mm

Gas CavitiesGas Cavities

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M.Rogers

Root piping

Porosity

Gas CavitiesGas Cavities



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Cluster porosity Herringbone porosity

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Slag originates from weldingflux

MAG and TIG weldingprocess produce silica

inclusions

Slag is caused byinadequate cleaning

Other inclusions includetungsten and copperinclusions from the TIG andMAG welding process

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

Slag inclusions

Parallel slag lines Lack of interunfusion + slag

Lack of sidewallfusion with

associated slag

Solid InclusionsSolid Inclusions



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Solid InclusionsSolid Inclusions

Lack of interun fusion + slag

Lack of sidewall fusion + slag

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Elongated slag linesInterpass slag inclusions



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Lack of FusionLack of Fusion

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Incomplete filled groove+ Lack of sidewall fusion

1

2

1. Lack of sidewall fusion2. Lack of inter-run fusion

Poor welder skill

Incorrect electrode

manipulation

Arc blow

Incorrect welding

current/voltage

Incorrect travel speed

Incorrect inter-run cleaning

Lack of Fusion Lack of Fusion



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Lack of Fusion Lack of Fusion

Lack of sidewall fusion + incomplete filled groove

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An imperfection at the toe or root of a weld caused bymetal flowing on to the surface of the parent metal

without fusing to it

Contamination

Slow travel speed

Incorrect welding technique

Current too low

OverlapOverlap



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Toe OverlapToe OverlapFillet weldFillet weld

Toe OverlapToe OverlapButt weldButt weld

OverlapOverlap

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M.Rogers

Lack of root fusion

Incomplete root penetration

Low Amps/volts

Large Root face

Small Root Gap

Fast Travel Speed

Incorrect Electrode Angle

Contamination

Arc blow

Weld Root DefectsWeld Root Defects



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Lack of root fusion Incomplete rootPenetration

Weld Root DefectsWeld Root Defects

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Lack of root penetration Lack of root fusion



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Surface & ProfileSurface & Profile

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Incomplete filled groove Poor cap profile

Excessive cap height

Poor cap profiles and excessive

cap reinforcements may lead to

stress concentration points at

the weld toes and will also

contribute to overall poor toe

blend

Weld Profile DefectsWeld Profile Defects



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Poor Cap Profile & Poor Toe Blend

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Incomplete filled grooveExcess cap reinforcement



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Poor stop/starts


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Miscellaneous DefectsMiscellaneous Defects



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Spatter

Excessive current

Damp electrodes

Contamination

Incorrect wire feed speed

when welding with the MAG

welding process

Arc blow

Miscellaneous Defects Miscellaneous Defects

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WI 3.1

M.Rogers

Accidental striking of the arc

onto the parent material

Faulty electrode holder

Poor cable insulation

Poor return lead clamping

Arc strike

Miscellaneous Defects Miscellaneous Defects



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An irregular groove at the toe of a weld run in theparent metal

Excessive amps/volts

Excessive travel speed

Incorrect electrode angle

Excessive weaving

Incorrect welding technique

Electrode too large

Cap & Root Undercut Cap & Root Undercut

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Intermittent Cap Undercut

Cap Undercut Cap Undercut



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Cap undercutRoot undercut

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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 weldmetal along each side of the penetration bead

Weld Root Defect Weld Root Defect



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M.Rogers

Concave root

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 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 rootpenetration



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Concave root Excess root penetration

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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 excessivepenetration resulting in a hole in the root run




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Burn Through

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Loss or insufficient back

purging gas

Most commonly occurs

when welding stainless

steels

Purging gases include

argon, helium and

occasionally nitrogen

Oxidized Root (Root Coking)Oxidized Root (Root Coking)



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M.Rogers

Crater pipe

Weld crater

Crater PipeCrater Pipe

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

Too fast a cooling rate

Deoxidization

reactions and liquid to

solid volume change

Contamination

Crater cracks

(Star cracks)

Crater pipe

Crater PipeCrater Pipe



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M.Rogers

Mechanical DamageMechanical Damage

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Mechanical damage can be defined as any surface materialdamage cause during the manufacturing process.This can included damage caused by:

Grinding

Hammering

Chiselling

Chipping

Breaking off welded attachments (torn surfaces)

Using needle guns to compress weld capping runs

Mechanical Damage Mechanical Damage



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Mechanical Damage Mechanical Damage

Mechanical Damage/Grinding Mark

Chipping Marks

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SetSet--up Irregularitiesup Irregularities



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A variation of leg lengths on a fillet weld

Note: Unequal leg lengths on a fillet weld may be specifiedas part of the design, in which case it will not beconsidered as a defect.

Unequal Leg LengthsUnequal Leg Lengths

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Plate/pipe Linear Misalignment

(Hi-Lo)

Angular Misalignment

Linear misalignment is

measured from the lowest

plate to the highest point.

Angular misalignment is

measured in degrees

Set Set --up Irregularitiesup Irregularities



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Linear Misalignment


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Linear Misalignment


TWI Defects

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