Weld overlap: what it is and how to spot it

Use this diagram

Copy this HTML to show the diagram with a credit link<img src="https://filletgauge.com/charts/weld-discontinuities/weld-overlap.svg" alt="A T-joint fillet weld in cross-section whose face spills past the toe as a rounded lip, with a thin white line under the lip showing it is not fused to the plate" width="100%"><p><a href="https://filletgauge.com/guides/weld-overlap?utm_source=embed&amp;utm_medium=referral&amp;utm_campaign=figure_embed&amp;utm_content=weld-overlap.svg">The lip looks like extra weld; the line under it is the problem. Original drawing, not to scale. by Fillet Gauge</a></p>

How to recognize overlap

1. Look at the toe angle. A sound toe blends smoothly into the plate. An overlapped toe meets the plate at a sharp angle, close to or past square, with the weld bulging out over the plate.
2. Look for a line under the lip. Low-angle light shows a dark seam where the lip sits on the plate. A thin feeler or the edge of a gauge blade can slip under it.
3. Check the size on each leg. On a fillet, overlap often makes one leg look oversize, because the lip extends the apparent toe. The real toe is where fusion stops.
4. Think about the pool. Overlap is common where the pool sags: the lower toe of a horizontal fillet, or the toes of a vertical weave that didn't pause at the sides.

How it is confirmed

Visual inspection is the main method, helped by light and magnification. Where the lip is borderline, a surface method such as penetrant or magnetic particle testing can show whether there is an open seam under it. Record the length and location. Many documents treat overlap as part of the weld profile requirements, so you find it with the profile rules rather than in a separate limit. Acceptance always comes from the governing document.

Common mix-ups

• Overlap or undercut. Both sit at the toe. Undercut takes metal out of the plate. Overlap adds unfused metal on top of it. Ask which way the metal went.
• Overlap or convexity. A convex fillet bulges but its toes still fuse and blend. Overlap has an unfused lip beyond the toe.
• Overlap or incomplete fusion. Overlap is a surface condition at the toe. Incomplete fusion is the same failure to bond, but buried on a sidewall or between passes.

Why it forms

The weld pool runs onto plate that isn't hot enough to melt. Typical causes are too slow a travel speed, so the pool piles up, too low a current for the electrode size, an electrode angle that pushes metal toward one toe, and a long arc that spreads heat without melting the plate. A pool too large to control in the position does the same.

Overlap on the CWI exam

On Part B, overlap fits Welding Inspection and Discontinuities, at least 34% of the practical, where weld profile is judged on replicas. On Part A it fits Visual Examination and Welding Application and Control, since the causes are technique. On Part C, the weld profile rules are where to look, Clause 7 of D1.1 for the D1.1 endorsement, read in your own copy.

Practice it

Tell overlap from undercut and its other look-alikes in the weld discontinuities quiz. Then read its opposite at the toe, undercut, and the face condition it sits next to, excessive reinforcement and convexity. Every type is in the weld discontinuities guide.

Check the rest of Part B

Take the free 10-question check. It's weighted to the Part B outline, scored by domain and needs no signup, so you see which Part B domain to tackle first.

Sources

Show the list

• A general review of geometric shape imperfections, Part 1 (Job Knowledge 67), TWI. Retrieved 25 Oct 2026.
• CWI Part B Practical Examination Information, American Welding Society, Rev. 03.01.2024. Retrieved 20 Oct 2026.
• Discontinuity names follow AWS A3.0, Standard Welding Terms and Definitions. Every description here is our own wording.