Fillet Weld Leg and Undercut Acceptance
A 3/8 in A36 plate girder has a 5/16 in fillet weld specified on the drawings. The joint is statically loaded and is a primary member. Visual inspection of a 10 in length shows a measured leg of 9/32 in on one side. Along the same length, there is a continuous undercut on the plate edge that measures 3/64 in deep over a 2 in segment. The weld surface is convex and otherwise sound; no cracks or visible porosity are seen. The fabricator argues that the weld is acceptable because the leg is only 1/32 in under and the undercut is shallow. The inspector must apply AWS D1.1 visual acceptance criteria.
1. Evaluate the fillet weld leg size against AWS D1.1.
Read the worked answer
Specified leg = 5/16 in = 0.3125 in. Measured leg = 9/32 in = 0.281 in. Undersize = 0.031 in, or 1/32 in.
AWS D1.1 permits a fillet weld undersize of 1/16 in for sizes less than 5/16 in and 1/8 in for sizes 5/16 in and greater. A 5/16 in specified fillet falls in the 5/16 in and greater category, so a 1/32 in undersize is within the permitted tolerance. The leg size alone is acceptable, assuming the effective throat and length meet the design requirement.
2. Evaluate the undercut against AWS D1.1 for a statically loaded primary member.
Read the worked answer
Undercut depth = 3/64 in = 0.047 in. For statically loaded primary members, AWS D1.1 limits undercut to 1/32 in (0.031 in) for material less than 1 in thick. The plate is 3/8 in thick, so the limit is 1/32 in. The measured 3/64 in undercut exceeds that limit and is rejectable. If the member were cyclically loaded, the limit would be tighter still, about 0.01 in, and the undercut would also fail. The fabricator’s argument that the undercut is “shallow” does not override the measured depth.
3. What repair and reinspection should be required?
Read the worked answer
The leg size does not require repair, but the undercut does. Grind the undercut to sound metal, blend the profile, and rewelding if the ground depth reduces the required section. Use a qualified welder and procedure; for 3/8 in A36, preheat is normally not required, but the surface must be clean and dry. After repair, perform visual inspection of the blended or rewelded area and confirm that the undercut has been removed and the fillet profile is acceptable. Document the measured undercut, the repair location, and the reinspection results.