Overlap / Cold Lap — Always Rejected

What is Overlap (Cold Lap)?

Overlap occurs when the weld bead flows over and extends past the weld toe onto the base metal surface without properly bonding. The weld metal "laps" the base metal like shingles on a roof, but there is no fusion at the interface.

• Typical appearance — A visible ridge or ledge where the weld edge extends past the base metal toe. The weld metal overhangs the base metal surface.
• Lack of fusion — The overlapped area is a separation. If pulled, the weld metal will separate from the base metal at that point.
• Stress concentration — Overlap creates a sharp corner where crack initiation occurs under tensile stress or vibration.
• Common in fillet welds — More likely when welding a vertical leg (uphill or downhill) or when welder drifts laterally.

AWS D1.1 Table 6.1 Acceptance Criterion

Why Overlap is Unacceptable

• Unbonded area under stress — The base metal under the overlap is not fused to the weld. Shear stress concentration at the sharp corner initiates fatigue cracks, especially under cyclic loading.
• Crack initiation site — The sharp corner (toe of the overlap) is a stress riser. Cracks grow from there into the base metal.
• Reduced joint strength — The overlapped region contributes no strength to the joint. The weld may look larger, but it's defective.
• NDT reveals it easily — Dye penetrant or magnetic particle testing shows the lack of fusion under the overlap clearly.

Common Overlap Causes

• Poor welder control / technique — Lack of lateral control when advancing along the joint. Bead drifts sideways, away from the joint line.
• Wrong gun/torch angle — Electrode angled away from the joint corner. Weld puddle flows sideways and overrides the base metal surface.
• Excessive stick-out (GMAW) — Long contact tip-to-work distance creates a longer arc, wider puddle that spreads beyond the joint.
• Too-wide weaving pattern — In a weave pass, the lateral movement extends past the base metal edges, creating overlap at the extremes of the weave.
• Downslope fillet welds — Gravity pulls the weld puddle downward; if bead is too large or angle is wrong, metal flows past the toe onto the lower member.

How to Inspect & Document for the Report

• Visual examination at magnification — Use 10x magnifying glass to identify the overlap ridge. Look for a visible step where the weld extends past the base metal toe line.
• Dye penetrant (PT) test — Apply penetrant over the suspected overlap area. The lack of fusion will trap penetrant under the overlapped weld, showing clearly under black light.
• Magnetic particle (MT) inspection — For ferrous materials. MT is very sensitive to the lack of fusion discontinuity under overlap.
• Document location and extent — Note which leg (in a fillet), which side (in a groove weld), and approximate length of the overlap.
• Mark for rejection clearly — OVERLAP – REJECT. No conditional acceptance; this is a zero-tolerance defect.

CWI Prevention & Repair Strategy

• Require welder training on fillet weld technique, especially toe control. High-quality fillets have consistent width with no overlap.
• Enforce WPS limits on bead width and wire size. A 3/8" fillet should not be made in a single 1/8" wire pass — that creates insufficient lateral control and risk of overlap.
• For repair, grinding removes the overlap. However, if multiple overlaps appear, it indicates a systemic welder skill or setup issue. Address the root cause.
• On critical structures, use PT or MT supplementary inspection on all fillet welds as a quality check.