Wis5 welding defects 02
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Transcript of Wis5 welding defects 02
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Welding InspectionDefects/Repairs
Course Reference WIS 5
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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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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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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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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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Process Cracks Process 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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Copyright © 2003 TWI LtdTransverse crack Longitudinal crack
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LACK OF SOLID METALSLACK OF SOLID METALS
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POROSITYPOROSITYDescription : 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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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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Copyright © 2003 TWI LtdIncomplete filled groove
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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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Elongated slag linesInterpass slag inclusions
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Inter- run ImperfectionsInter- run ImperfectionsIrregular 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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Lack of FusionLack of Fusion
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Incomplete root penetrationIncomplete root penetrationFailure 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 fusionLack 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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Lack of Smoothly Lack of Smoothly Blended SurfacesBlended Surfaces
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Surface porositySurface porosityGas 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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Copyright © 2003 TWI LtdExcess cap reinforcement
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Excessive PenetrationExcessive PenetrationProjection 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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Excessive root penetration
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UndercutUndercutAn 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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Cap UndercutCap Undercut
Measured in both Length & DepthMeasured in both Length & Depth
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Cap undercutRoot undercut
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OverlapOverlapAn 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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Profile DefectsProfile Defects
Poor stop/starts
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MiscellaneousMiscellaneous
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MisalignmentMisalignmentThe 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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Arc strikesArc strikesRandom 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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SpatterSpatterSmall 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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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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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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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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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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Plate LaminationPlate Lamination
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Any Questions?Any Questions?
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QuestionsQuestionsQU 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 defectsa. Lack of root wall fusion b. Lack of root penetrationc. Incomplete filled groove d. Concave root
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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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Faisal Yusof
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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
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Arc air gouging