•
A list of weld defects and their causes is given
below.
•
Other defects not listed are mainly those of
geometry and include misshapen and incorrectly sized welds, variable cap width
and height, weld face roughness, incomplete weld fill and asymmetry of fillet
welds.
• These are all welder-induced problems, requiring improved shop-floor discipline and/or welder retraining.
Defect Name: Lack of side wall fusion
ISO 6520 Defect No: 4011 (Fig – 11.1)
Description of Lack of side wall fusion: Failure of
Weld Metal to fuse to weld preparation.
Causes of Lack of side wall fusion:
- Current too low,
- travel speed too high,
- incorrect torch angle,
- oxide film on prep. Surfaces,
- inadequate join cleaning,
- weld preparation too narrow.
Defect Name: Lack of inter-run fusion
ISO 6520 Defect No: 4012 (Fig – 11.1)
Description of Lack of inter-run fusion: Failure of
weld metal to fuse to preceding run
Causes of Lack of inter-run fusion:
§ Current too low,
§ travel speed too high,
§ incorrect torch angle,
§ inadequate inter-run cleaning
Defect Name: Lack of root fusion
ISO 6520 Defect No: 4013 (Fig – 11.1)
Description of Lack of root fusion: Root bead fully
penetrated but not fused to root face
Causes of Lack of root fusion:
§ current too low
§ voltage too low
§ travel speed too high
§ root face too thick
§ root gap too wide
§ incorrect torch angle
§ inadequate cleaning
Remedies of Fusion Related Weld Defects:
§ use a sufficiently wide joint preparation
§ select welding parameters (high current level, short arc length, not too high a welding speed) to promote penetration into the joint side wall without causing flooding
§ ensure the electrode/gun angle and manipulation technique will give adequate side wall fusion
§ use weaving and dwell to improve side wall fusion providing there are no heat input restrictions
§ if arc blow occurs, reposition the current return, use AC (in MMA [SMA] welding) or demagnetize the steel
Defect Name: Poor restart (Cold start)/Lack of fusion
ISO 6520 Defect No: 517
Description of Poor Restart: Lack of fusion beneath
weld start position.
Causes of Poor Restart:
§ Incorrect welder technique
§ Poor earthing
Defect Name: Lack of Penetration
ISO 6520 Defect No: 402
Description of Lack of Penetration: Failure to
achieve the minimum penetration specified by design.
Causes of Lack of Penetration:
§ Current too low
§ Travel speed too high
§ Incorrect torch angle
§ Incorrect weld prep.
Defect Name: Insufficient (lack of) root penetration
ISO 6520 Defect No: 4031 (Fig – 11.2)
Description of Insufficient (lack of) root penetration:
Failure of weld metal to penetrate fully root faces.
Causes of Insufficient root penetration:
§ Current too low
§ Travel speed too fast
§ Root face too thick
§ Root gap too small
§ Incorrect torch angle
§ Misalignment
Defect Name: Excess Penetration
ISO 6520 Defect No: 504 (Fig – 11.3)
Description of Excess Penetration: Unacceptable
protrusion of the root bead.
Causes of Excess Penetration:
§ Current too high
§ Travel speed too slow
§ Root gap too wide
§ Root face too thin
Defect Name: Root or face undercut
ISO 6520 Defect No: 501 (Fig – 11.4)
Description of Root or Face Undercut: Notch parallel
to weld at weld toe. Prevalent at top edge of PB fillet.
Cause of Root or Face Undercut:
§ Current too high
§ Travel speed too fast
§ Incorrect torch angle
§ Inadequate cleaning
Defect Name: Excess Convexity
ISO 6520 Defect No: 502 (butt) (Fig – 11.5)
Description of Excess Convexity: Excess weld metal on the face of a butt or
fillet weld. Excess convexity can produce notch effect in the welded area and
consequently , concentration of stress under load.
Causes of Excess Convexity:
§ Incorrect welding technique
§ Current too high
§ Travel speed too low
§ Incorrect torch manipulation
Defect Name: Excess Weld Metal (Excess cap Height)
ISO 6520 Defect No: 503 (fillet) (Fig - 11. 5)
Description of Excess Weld Metal: Excess weld metal on the face of a butt or
fillet weld.
Causes of Excess Weld Metal:
§ Incorrect welding technique
§ Current too high
§ Travel speed too low
§ Incorrect torch manipulation
Defect Name: Incomplete fill (face concavity of missed edge). Insufficient
throat in fillet welds
ISO 6520 Defect No: 511 (Fig - 11. 6)
Description of Incomplete fill: Insufficient weld metal fill giving groove on
weld face resulting in insufficient throat.
Causes of Incomplete fill:
§ Poor welder technique
§ Travel speed too fast
§ Current too low
§ Incorrect torch positioning
Defect Name: Root Concavity
ISO 6520 Defect No: 515 (Fig – 11.7)
Description of Root Concavity: Root pass ‘sucked back’ to give a shallow groove.
Causes of Root Concavity:
§ Current too high
§ Root gap too wide
§ Root face too thin
Defect Name: Burn – through
ISO 6520 Defect No: 510
Description of Burn-through: Localized loss of weld pool in root.
Causes of Burn-through:
§ Current too high,
§ Travel speed too slow
§ Root face too thin
§ Root gap too large
Defect Name: Overlap (roll-over)
ISO 6520 Defect No: 506 (Fig – 11.8)
Description of Overlap: Weld metal that has rolled over at the edges
and not fused to the parent metal. May be face or root.
Causes of Overlap:
§ Weld bead too large
§ Current too high
§ Travel speed too slow
§ Prevalent in horiz.-vert. welds
§ Inadequate cleaning
Defect Name: Porosity
ISO 6520 Defect No: 201
Description of Porosity: Gas entrapped in weld metal giving a cavity.
May be localized, uniformly distributed or aligned.
Causes of Porosity:
§ Dirty consumables
§ Poorly cleaned or dirty weld preparations
§ Contaminated shield gas
§ Contaminated ((hydrogen containing) parent metal – especially castings
§ Oxide film on parent metal
§ Porous gas hoses
§ Leaks in gas delivery system
§ Condensation
§ Poor join design trapping gas
Defect Name: Worm-hole(piping)
ISO 6520 Defect No: 2016
Description of Worm-hole: Elongated gas cavity formed by solidification
of large weld pool.
Causes of Worm-hole:
§ Excessive current
§ Travel speed too slow
Defect Name: Crater pipe
ISO 6520 Defect No: 2024
Description of Crater pipe: Elongated cavity in the weld finish crater.
Causes of Crater pipe:
§ Incorrect welder technique
§ Lack of crater fill
Defect Name: Solidification Cracking
ISO 6520 Defect No: 100
Description of Solidification Cracking: Cracks in weld produced during welding.
Causes of Solidification Cracking:
§ Incorrect choice of filler metal
§ Failure to control dilution
§ Incorrect edge preparation
§ Crack susceptible parent metal
§ High restraint
§ High heat input
Defect Name: Crater cracking
ISO 6520 Defect No: 104
Description of Crater Cracking: Short longitudinal or star shaped crack in
finish crater.
Causes of Crater Cracking:
§ Incorrect welder technique
§ Lack of crater fill
Defect Name: Liquation Cracking
ISO 6520 Defect No: 100
Description of Liquation Cracking: Cracking in the HAZ or in previously deposited
weld metal.
Causes of Liquation Cracking:
§ Incorrect filler metal
§ Crack sensitive parent metal
§ High restraint
§ High heat input
Defect Name: Oxide Entrapment
ISO 6520 Defect No: 303
Description of Oxide Entrapment: Oxide films are trapped within the weld metal.
Causes of Oxide Entrapment:
§ Oxide films in or on parent metal
§ Oxide films in or on filler metal
§ Oxygen in shield gas
§ Poor gas shielding
§ Inadequate cathodic cleaning
Defect Name: Puckering
ISO 6520 Defect No: 3034
Description of Puckering: Excessive Oxide entrapment from weld pool turbulence.
Causes of Puckering:
§ Poor gas cover
§ Very high weld current
Defect Name: Tungsten or copper inclusions
ISO 6520 Defect No: 3041 (tungsten), 3042 (copper)
Description of Tungsten or Copper Inclusions: Accidental contact of the electrode (TIG) or
contact tip (MIG)
Causes of Tungsten or copper inclusions:
§ Poor welder technique
§ Incorrect mechanized set-up
Defect Name: Stray arc strike
ISO 6520 Defect No: 602
Description of Stray arc strike: Accidental arcing outside weld prep..
Causes of Stray arc strike:
§ Welder carelessness.
Defect Name: Spatter
ISO 6520 Defect No: 602
Description of Spatter: Droplets of weld metal expelled from weld pool.
Causes of Spatter:
§ Poor welder technique
§ Incorrect weld parameters
Defect Name: Under flushing
ISO 6520 Defect No: 606
Description of Under flushing: Thinning below design thickness.
Causes of Under flushing:
§ Excessive Grinding
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