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Weld Defect Identification Chart

Common weld discontinuities, how to spot each one, and the usual causes, using AWS A3.0 terms, with acceptance left to the governing code.

Ref WG-0209AWS A3.0AWS D1.1

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

AWS A3.0 defines the terms. A discontinuity is any break in the normal structure of a weld. It becomes a defect only when it exceeds the acceptance criteria of the governing code, such as the visual inspection table in AWS D1.1 for structural steel. This chart helps name what you see and trace the likely cause. It does not decide whether a weld passes.

How to use it

Clean the weld and look at it in good light from several angles.
Match what you see to a row.
Check the usual causes against the setup: gas, wire, parameters, technique, joint fit-up.
Judge acceptance only against the governing code and the inspector's call.

Defect chart

Discontinuity	What it looks like	Common causes
Porosity	Round or elongated holes on the surface or inside the bead	Low or excess gas flow, drafts, leaks, dirty or wet metal, damp electrodes
Undercut	Groove melted into the base metal at the toe, left unfilled	Too much current or travel speed, wrong angle, long arc
Overlap (cold lap)	Weld metal rolled over the base metal without fusing at the toe	Too slow travel, low heat, wrong angle
Cracks	Lines along, across or at the end of the weld (crater cracks)	High restraint, hydrogen, high carbon or sulfur, fast cooling, crater not filled
Incomplete fusion	Weld metal not fused to the base metal or the previous bead	Low heat, wrong angle, fast travel, dirty joint
Incomplete joint penetration	Root of the joint not filled through	Tight root opening, low current, large electrode
Slag inclusion	Trapped slag, seen on cross section or X-ray, sometimes at the surface	Poor cleaning between passes, wrong angle
Excessive reinforcement (convexity)	Bead too high or crowned	Too slow, too much wire feed, low voltage
Underfill	Weld face below the base metal surface	Too fast, too little filler
Burn-through	Hole melted through thin material or root	Too much heat, wide root opening
Spatter	Metal droplets stuck to the base metal	Wrong voltage, CO2 gas, long stickout
Arc strike	Small spot or crater outside the weld	Striking the arc on the base metal; poor ground

Key points

Cracks are generally rejectable under structural codes regardless of size. Check the code.
Hidden discontinuities need NDT (UT, RT) to find.
Fixing the cause beats grinding out repeat defects.

Common mistakes

Calling every discontinuity a defect, or the reverse.
Grinding a weld to hide undercut without checking minimum thickness.
Turning up gas flow to cure porosity caused by a leak.

Governing standards: AWS A3.0; AWS D1.1; AWS B1.10 (visual examination guide).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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