Wis5 welding defects 02

Faisal Yusof
TE
Copyright © 2003 TWI Ltd
Welding Inspection
Defects/Repairs
Course Reference WIS 5

Faisal Yusof
TE
A perfect butt weld joint, when subjected to an external
force, provide a distribution of stress throughout its
volume which is not significantly greater than parent
metal.
DefinitionDefinition

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TE
DefinitionDefinition
This is achieved as long as the following features
apply :-
• Welds should consists of solid metal throughout a cross
section at least equal to that of parent metal.
• All parts of a weld should be fully fused to the parent
metal.
•Welds should have smoothly blended surfaces.

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TE
Defects which may be detected by visual inspection can
be grouped under five headings
 Cracks
 Lack of solid metals
 Lack of fusion
 Lack of smoothly
blended surfaces
 Miscellaneous
Weld DefectsWeld Defects

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TE
CracksCracks

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Classified by Shape
 Longitudinal
 Transverse
 Branched
 Chevron
Classified by Position
 HAZ
 Centreline
 Crater
 Fusion zone
 Parent metal
CracksCracks
Cracks that may occur in welded materials are caused
generally by by many factors and may be classified by
shape and position, cracks are classed as planar.

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TE
Process CracksProcess Cracks
HAZ hydrogen cracking
 Weld metal hydrogen cracking
Solidification cracking (Hot Tearing)
Lamellar tearing

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CracksCracks
HAZ hydrogen cracking
Weld metal hydrogen cracking
Solidification cracking Lamellar Tearing

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Transverse crack Longitudinal crack

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LACK OF SOLID METALSLACK OF SOLID METALS

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POROSITYPOROSITY
Description : Gas pores trapped within the weld metal
Causes :
• Damp fluxes/ corroded electrode
•Grease/hydrocarbon/water
contamination of prepared surface
•Air entrapment in gas shield
•Too high arc voltage/arc length
•Incorrect/insufficient deoxidant
in electrode, filler or parent metal
Preventation :
• Use dry electrodes in good
condition
•Optimise gas flow
•Use electrode with sufficient
deoxidation activity
•Reduce arc voltage or arc length

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Gas CavitiesGas Cavities
Root pipingRoot piping
PorosityPorosity

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Cluster porosity Herring bone porosity

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Crater PipeCrater Pipe
A shrinkage cavity at the end of a weld run where the arc is
terminated
Causes :
•Lack of welder skill due to using
processes with too high current.
•Inoperative crater filler ( GTAW )
Preventation :
• Retrain welder
•Use correct crater filling
technique

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TE
Crater Pipe/CracksCrater Pipe/Cracks
Crater pipeCrater pipe
Crater CracksCrater Cracks

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RootRoot concavityconcavity
A shallow groove, which may occur in the root of a butt weld
Causes :
•Insufficient arc power to produce
positive bead
•Excessive backing pressure ( GTAW )
•Lack of welder skill
•Slag flooding in backing bar groove
Preventation :
• Raise arc energy
•Reduce gas pressure
•Retraint welder
•Tilt work to prevent slag
flooding

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root concavity

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UnderfillUnderfill
A weld with thickness less than that of the parent metal
Causes :
•Insufficient weld metal
•Irregular weld bead surface
Preventation :
• Increase number of weld run
•Retrain welder

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TE
Incomplete filled groove

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TE
Slag InclusionsSlag Inclusions
Slag or other matters trapped during welding. The imperfection is of
an irregular shape and thus differs in appearance from a gas pore
Causes :
•Heavy millscale/rust on work surface
•Incomplete slag removal from
underlying surface of multipass weld
•Slag flooding ahead of the arc
•Entrapment of slag in work surface
•Unfused flux due to damage coating
Preventation :
• Grind surface prior welding
•Improve interun slag removal
•Position work to gain control of
slag
•Dress work surface smooth
•Use electrode in good condition

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TE
Elongated slag linesInterpass slag inclusions

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Inter- run ImperfectionsInter- run Imperfections
Irregular along the fusion line between weld beads
Causes :
•Low arc current resulting in low
fludity of weld pool
•Too high travel speed
•Inaccurate bead replacement
Preventation :
• Increase current
•Reduce travel speed
•Retrain welder

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TE
Lack of FusionLack of Fusion

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Incomplete root penetrationIncomplete root penetration
Failure of the weld metal to extend into root of a joint
Causes :
•Excessively thick root face, insufficient root gap
or failure to cut back sound metal in a ‘back
gouging’ operation
•Low heat input
•Excessive inductance in GMAW dip transfer
•SMAW electrode too large( low current density )
•Use of vertical down welding
Preventation :
• Improved back gouging and edge
preparation
•Increase arc power or decrease travel
speed
•Improve electrical settings and possibly
switch to spray transfer
•Reduce electrode size
•Switch to vertical up procedure

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Root DefectsRoot Defects
Lack of root fusion Lack of root Penetration

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Lack of root penetration Lack of root fusion

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Lack of sidewall fusionLack of sidewall fusion
Lack of fusion between weld metal and parent metal at one side of weld
Causes :
•Low heat input to weld
•Molten metal flowing ahead of arc
•Oxide or scale on weld preparation
•Excessive inductance in GMAW dip transfer
welding
Preventation :
•Increase arc energy or increase travel
speed
•Improve electrode angle and work
position
•Improve edge preparation procedure
•Reduce inductance, even if this increase
spatter

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TE
Lack of SmoothlyLack of Smoothly
Blended SurfacesBlended Surfaces

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Surface porositySurface porosity
Gas pores which break the surface of the weld
Causes :
•Damp or contaminated surface of electrode
•Low fluxing activity
•Excess sulphur ( particularly free – cutting steels)
producing sulphur oxide
•Loss of gas shield gas due to long arc or high
breezes ( GMAW )
Preventation :
•Clean surface and dry electrodes
•Use a high activity flux
•Use high manganese to produce MnS,
note free cutting should not normally be
welded
•Reduce arc length

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Excess Weld Metal ( Reinforcement )Excess Weld Metal ( Reinforcement )
Reinforcement is the extra metal which produces convexity in fillet
welds and a welds thickness than the parent metal plate in butt welds.
Causes :
•Excess arc energy ( GMAW,SAW )
•Shallow edge preparation
•Faulty electrode manipulation
•Incorrect electrode size
Preventation
•Reduction of energy input
•Deepen edge preparation
•Improve welder skill
•Reduce electrode size

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Excess cap reinforcement

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Excessive PenetrationExcessive Penetration
Projection of the root penetration bead beyond a specified limit
Causes :
•Weld input energy too high
•Incorrect weld preparation i.e excessive
root gap, thin edge preparation, lack of
backing
•Use electrode unsuited to welding position
•Lack of welder skill
Preventation
•Reduce arc power/increase weld speed
•Improve work piece preparation
•Use correct electrode position
•Retrain welder

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TE
Excessive root penetration

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UndercutUndercut
An irregular groove at the toe of a run in the parent metal or in
previously deposited welding, cause by welding
Causes :
•Melting of top edge due to too high welding
current ( especially at free edge) or high
travel speed
•Attempting an HV fillet weld leg length
>9.0 MM
• Excessive/Incorrect weaving
•Incorrect electrode angle
Preventation
•Reduce power input,especially
approaching a free edge where overheating
can occur
•Weld in a flat position or use multirun
technique
•Direct arc towards thicker member

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TE
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 of a weld caused by metal flowing on to the
surface of the parent metal without fusing to it
Causes :
• Poor electrode manipulation
• High energy input/low travel speed
causing surface flow of fillet weld
• Incorrect positioning of weld
• Electrode having too high a fluidity
Preventation
•Retrain welder
•Reduce the heat input or limit size of
fillet weld to 9.0 mm leg by using multi
run weld
•Change the flat position
•Change to less fluid weld metal

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TE
Profile DefectsProfile Defects
Poor stop/starts

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MiscellaneousMiscellaneous

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MisalignmentMisalignment
The non – alignment of two abutting edges in a butt joint
Causes :
• Inaccuracies in assembly procedures or
distortion from other welds
• Excessive ‘out of flatness' in hot rolled
plate or sections
Preventation :
•Adequate checking of alignment prior to
welding coupled with the use of clamps
and wedges
•Check accuracy of rolled section prior to
welding

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TE
Arc strikesArc strikes
Random areas of fused metal where the electrode, the holder, or
current return clamp accidentally touched the work and produced a
short duration arc
Causes :
• Poor Access to work
• Missing insulation on electrode holder
or torch
• Failure to provide an insulated resting
place for the electrode holder or torch
when not in use
• Loose current return clamp
Preventation :
•Improve access ( modify assembly
sequence )
•Institute a regular inspection scheme for
electrode holders and torches
•Provide an insulated resting place
•Regularly maintain current return clamp

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TE
SpatterSpatter
Small droplets of electrode material can be projected clear of the weld
and may fused to the parent metal
Causes:
• High arc power
• Magnetic arc blow
• Incorrect setting for GMAW process
• Damp electrodes
Preventation :
•Reduce arc power
•Reduce arc length or swith to AC power
•Modify electrical settings ( but be careful
to maintain full fusion
•Use dry electrodes

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TE
Burn ThroughBurn Through
 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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TE
Burn through
Burn
Through
Root Defects

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Root Coking/Oxidized RootRoot 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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TE
Mechanical DamageMechanical Damage

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Mechanical DamageMechanical Damage
Mechanical damage can be defined as any surface material
damage 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

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TE
Parent Material DefectsParent Material Defects
A welding inspector should also inspect the parent
material for any visible defects
Lamination
Mechanical damage Lap
Segregation line

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TE
Plate LaminationPlate Lamination

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Any Questions?Any Questions?

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TE
QuestionsQuestions
QU 1. Give two main causes for the occurrence of a burn through
QU 2. Give two main causes for the occurrence of excessive root
penetration on a single-V butt weld
QU 3. Give five defects, which may occur when welding carbon
steel using the MMA welding process with the current setting
to low
QU 4. Give three possible causes for the occurrence of lack of
side wall fusion
QU 5. Sketch the following defects
a. Lack of root wall fusion b. Lack of root penetration
c. Incomplete filled groove d. Concave root

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TE
Weld RepairsWeld Repairs

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Welding RepairsWelding Repairs
 Authorization for repair
 Removal and preparation for repair
 Testing of repair - visual and NDT
In the event of repair

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 A weld repair may be used to improve weld profiles or
extensive metal removal
 Repairs to fabrication defects are generally easier than
repairs to service failures because the repair procedure may
be followed
 The main problem with repairing a weld is the maintenance
of mechanical properties
 During the inspection of the removed area prior to welding
the inspector must ensure that the defects have been totally
removed and the original joint profile has been maintained
as close as possible

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TE
The specification or procedure will govern how the defective
areas are to be removed. The method of removal may be
 Grinding
 Chipping
 Machining
 Filing
 Oxy-Gas gouging
 Arc air gouging
Arc air gouging

Wis5 welding defects 02

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