Fillet Weld Rejection on Contaminated A36
A fabricator is attaching 1/4-inch A36 clip angles to a 1/2-inch A36 beam with 1/4-inch fillet welds. The beam has tight mill scale, a film of water-soluble cutting fluid, and patches of surface rust. The welder wipes each area with a rag, runs a wire brush over it, and begins welding with gas-shielded FCAW. The first 20 welds pass visual, but the 21st is bent in a shop bend test and opens up with clustered porosity and incomplete fusion on the beam side. The inspector also finds 3/64-inch undercut on several welds. The project specification states a 1/32-in maximum undercut on this joint. The welder says the machine "was running fine yesterday" and wants to turn up the wire feed speed. The shop is unheated and the plate feels damp.
1. Separate the defects and identify the most probable root causes. Which defect is a surface preparation issue and which is a process/technique issue?
Read the worked answer
These are not one defect. Clustered porosity is most likely contamination: the water-soluble cutting fluid, rust, and damp plate were smeared by the rag and wire brush rather than removed. Wire brushing over oil can push it into the surface and does not remove mill scale. Incomplete fusion on the beam side is a preparation and heat/angle problem: mill scale melts at a much higher temperature than steel, so the arc does not wet the beam; increasing wire-feed speed alone may just make a bigger, colder bead. The 3/64-in undercut exceeds the 1/32-in project limit and is a technique/current/travel-angle problem. Separate the defects before changing one variable.
2. Give the preparation and fit-up sequence you would require before welding resumes, including how to handle the cutting fluid and rust.
Read the worked answer
First degrease with a clean solvent and rags, and let the surface dry; do not grind oil into the metal. Then grind the weld zone and at least 1 in beyond it to bright metal, removing mill scale, rust, and any contaminated layer. Use a clean grinding wheel and keep the area dry; warm damp or cold plate to at least about 70°F and keep it dry before welding. Refit and check gap, angle, and cleanliness. Use a qualified FCAW procedure and run a test coupon before restarting production. If the wire or gas is suspect, verify gas flow and liner condition.
3. How should the failed weld and the undercut welds be dispositioned and repaired?
Read the worked answer
The bend-test failure is a rejected weld. Gouge or grind out the entire defective area, including the incomplete fusion, to sound metal; do not just cover it. Confirm removal with visual and, if required, PT/MT, then re-weld with the qualified procedure and re-test. The undercut welds that exceed 1/32 in must also be repaired by grinding and depositing new metal, then blended and inspected. A cover pass over porosity or slag traps the defect and is not a repair. Record the repair and the parameters.