A list of weld defects and their causes is given in Table 11.1. 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.

If the required acceptance level for the defects listed above is not con­tained within a relevant application standard then it is the responsibility of the designer to select the appropriate quality level. A readily available specification to which the designer may refer for guidance is BS EN 30042 ‘Arc Welded Joints in Weldable Alloys, Guidance on Quality Levels for Imperfections’. This document contains three quality levels, B stringent, C intermediate and D moderate, the choice of which depends upon design considerations, subsequent fabrication activities such as rolling or pressing,


Defect Name


ISO 6520 Defect no.


(Fig. 11.1)

Lack of inter-run fusion Failure of weld metal to fuse to

preceding run


(Fig. 11.1)


(Fig. 11.1)

Lack of root fusion

Poor restart (cold start) Lack of fusion beneath weld start


Lack of penetration Failure to achieve the minimum

penetration specified by design

Insufficient (lack of) root Failure of weld metal to penetrate




(Fig. 11.2) 504

(Fig. 11.3)


(Fig. 11.4)

501 (butt)

Lack of side wall fusion

penetration Excess penetration Root or face undercut Excess convexity

Failure of weld metal to fuse to weld preparation

Root bead fully penetrated but not fused to root face

fully root faces

Unacceptable protrusion of the root bead

Notch parallel to weld at weld toe. Prevalent at top edge of PB fillet

Excess weld metal on the face of a

Current too low, travel speed too high, incorrect torch angle, oxide film on prep. surfaces, inadequate joint cleaning, weld preparation too narrow

Current too low, travel speed too high, incorrect torch angle, inadequate inter-run cleaning

Current too low, voltage too low, travel speed too high, root face too thick, root gap too wide, incorrect torch angle, inadequate cleaning

Incorrect welder technique (see Section 7.4.1), poor earthing

Current too low, travel speed too high, incorrect torch angle, incorrect weld prep.

Current too low, travel speed too fast, root face too thick, root gap too small, incorrect torch angle, misalignment

Current too high, travel speed too slow, root gap too wide, root face too thin

Current too high, travel speed too fast, incorrect torch angle, inadequate cleaning

Current too high, travel speed too low,

503 (fillet) Excess weld metal

(Fig. 11.5) (excess cap height)

511 Incomplete fill (face

(Fig. 11.6) concavity or missed

edge). Insufficient throat in fillet welds

515 Root concavity

(Fig. 11.7)

510 Burn-through

506 Overlap (roll-over)

(Fig. 11.8)

201 Porosity

2016 Worm-hole (piping)

2024 Crater pipe

100 Solidification cracking butt or fillet weld

Insufficient weld metal fill giving groove on weld face resulting in insufficient throat

Root pass ‘sucked back’ to give a shallow groove

Localised loss of weld pool in root

Weld metal that has rolled over at the edges and not fused to the parent metal. May be face or root

Gas entrapped in weld metal giving a cavity. May be localised, uniformly distributed or aligned

Elongated gas cavity formed by solidification of large weld pool

Elongated cavity in the weld finish crater

Cracks in weld produced during welding

incorrect torch manipulation

Poor welder technique, travel speed too fast, current too low, incorrect torch positioning

Current too high, root gap too wide, root face too thin

Current too high, travel speed too slow, root face too thin, root gap too large

Weld bead too large, current too high, travel speed too slow, prevalent in horiz.- vert. welds, inadequate cleaning

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 joint design trapping gas (see Chapter 2)

Excessive current, travel speed too slow

Incorrect welder technique — lack of crater fill

Incorrect choice of filler metal, failure to control dilution, incorrect edge preparation, crack susceptible parent

ISO 6520 Defect no.

Defect Name



metal, high restraint, high heat input (see Chapter 2)


Crater cracking

Short longitudinal or star-shaped crack in finish crater

Incorrect welder technique, lack of crater fill


Liquation cracking

Cracking in the HAZ or in previously deposited weld metal

Incorrect filler metal, crack sensitive parent metal, high restraint, high heat input (see Chapter 2)


Oxide entrapment

Oxide films trapped within the weld metal

Oxide films in or on parent metal, oxide films in or on filler metal, oxygen in shield gas, poor gas shielding, inadequate cathodic cleaning



Excessive oxide entrapment from weld pool turbulence

Poor gas cover, very high weld current

3041 (tungsten)

3042 (copper)

Tungsten or copper inclusions

Accidental contact of the electrode (TIG) or contact tip (MIG)

Poor welder technique, incorrect mechanised set-up


Stray arc strike

Accidental arcing outside weld prep.

Welder carelessness



Droplets of weld metal expelled from weld pool

Poor welder technique, incorrect weld parameters



Thinning below design thickness

Excessive grinding

Lack of Inter-run Fusion

11.1 Defects 4011 lack of side wall fusion, 4012 lack of inter-run fusion, 4013 root fusion.

11.2 Defect 4021.

11.3 Defect 504.


(a) Butt



11.6 Defect 511.

Root concavity (RC) 11.7 Defect 515.

static or dynamic loading, temperature and corrosive conditions and the consequences of failure.