AWS Certified Welding Inspector — FundamentalsWelding MetallurgyEasy
A welding inspector is performing an inspection on a newly welded structural steel component and observes a discontinuity that is a groove melted into the base metal adjacent to the toe of the weld, which has not been filled by weld metal. This discontinuity is a common defect that can reduce the effective thickness of the base metal. What is this discontinuity called?
- AUndercut
- BLack of Fusion
- COverlap
- DConcavity
Show answer & explanationAnswer & explanation
Correct answer: A. Undercut
Undercut is a groove melted into the base metal adjacent to the toe or root of a weld and left unfilled by weld metal. It reduces the base metal thickness and can act as a stress concentrator.
Why the other options are wrong
- B. Lack of fusion is the failure of the weld metal to fuse with the base metal or with a previous weld bead, not a groove in the base metal.
- C. Overlap occurs when weld metal extends beyond the weld toe or root without fusing to the base metal, which is excessive weld metal, not a groove.
- D. Concavity is a concave profile of the weld face, which is a shape issue, not a groove melted into the base metal.
Undercut (Weld Discontinuity)
A groove melted into the base metal adjacent to the toe or root of a weld and left unfilled by weld metal. It reduces the effective thickness of the base metal at the weld joint.
- Caused by excessive current, too long an arc, or incorrect electrode angle.
- Acts as a stress concentrator, potentially leading to fatigue or brittle fracture.
- Can be detected by visual inspection.
- AWS D1.1 (Structural Welding Code – Steel) specifies limits for undercut.
Memory trick: Undercut: A 'cut' (groove) 'under' the weld.