Undersized Fillet Weld on a Load-Bearing Bracket
A 6 mm fillet weld is specified on a bracket-to-column T-joint. The weld is 200 mm long and was made in one pass with a 3.2 mm electrode. The inspector uses a fillet weld gauge and finds the leg size is 4.0 mm at the start, 4.5 mm at mid-length, and 4.0 mm at the end over the 200 mm weld. The throat is correspondingly about 2.8–3.2 mm. The drawing requires a 6 mm fillet, continuous, with no undercut greater than 0.8 mm. The inspector also finds 0.5 mm undercut at two locations and a 10 mm long crater at the end. The welder says the gauge is 'just a reference' and the weld 'looks strong.' The project specification references AWS D1.1. The bracket carries a calculated load.
1. How should the inspector evaluate the fillet weld size with the gauge, and what does the reading indicate?
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Use a fillet weld gauge that measures leg length or throat. For an equal-leg fillet, throat = 0.707 × leg. A 6 mm specified fillet should show about 6 mm leg and about 4.2 mm throat. The readings of 4.0, 4.5, and 4.0 mm leg, with throat about 2.8–3.2 mm, are a 25–33% shortfall. Measure at several points along the 200 mm weld, not just one, and check for convexity or concave profile. The gauge is not 'just a reference' when the drawing specifies a size and the code has acceptance criteria. The consistent undersize indicates the welder likely used a smaller electrode, lower current, or faster travel than the WPS requires.
2. What is the disposition under a typical structural acceptance standard such as AWS D1.1?
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The weld is rejectable on size. AWS D1.1 requires fillet welds to meet the specified size; only limited undersize is permitted, and a 1.5–2.0 mm shortfall on a 6 mm fillet is not a minor tolerance issue. The 0.5 mm undercut is within the 0.8 mm allowed by the drawing, so undercut alone would not reject the weld. The 10 mm crater at the end is a separate discontinuity and should be evaluated; a crater that reduces the throat is not acceptable. The calculated load on the bracket makes the size deficiency more serious because the weld capacity is proportional to throat. Record the readings, locations, and gauge type.
3. What repair and documentation should follow?
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Mark the undersized areas, clean them to bare metal, and add weld passes to build the leg to 6 mm, or remove and re-weld if the profile is poor. Use the qualified WPS and the correct electrode size and current; do not simply cover the weld with a cosmetic pass. Re-inspect the repaired area with the gauge, check for undercut at the toes, and evaluate the crater. Document the nonconformance, the locations, the gauge readings before and after repair, the WPS used, and the reinspection result. If the bracket is already loaded or coated, obtain engineering approval before repair. The welder should be briefed on the size requirement and the WPS parameters.