Welding Metallurgy

A: A feels right because hydrogen cracking is the usual headline risk, but low‑hydrogen practice directly targets that mechanism, not ignores it. C tempts people who’ve seen overheated welds fail Charpy, yet grain growth isn’t addressed by hydrogen control at all — it’s heat input and time at temperature. D sounds subtle and very field‑real, but underbead cracking still needs hydrogen as the trigger. Solidification cracking happens while the weld pool freezes; diffusible hydrogen after solidification doesn’t touch segregation‑driven hot cracking, so B is the hole in the safeguard.

A: A borrows logic from stainless overlays where dilution matters, but D1.1 interpass limits aren’t about chemistry balance. C sounds practical — wet shops exist — yet hydrogen risk increases at low temperatures, not high interpass. D is a shop‑floor pain, but distortion is managed by sequencing, not code temperature caps. The code writers are guarding the quenched and tempered structure; too much time hot between passes over‑tempers the HAZ and drops strength and toughness, which is B.

A: B is seductive because FN control is drilled into stainless welding, but solidification cracking would show up during fabrication, not months in service. A borrows from carbon steel logic; austenitic stainless doesn’t crack that way without extreme conditions. D requires temperatures far above the operating envelope. Residual stress from welding plus warm chlorides is the classic recipe for transgranular cracking in 300‑series stainless, making C the mechanism that fits the timeline and environment.

A: A and B are explicitly defined by the symbol geometry and dimensions, even without a tail. D is handled by arrow and symbol placement. The tail is where process notes live; leaving it blank pushes GTAW vs GMAW and filler choice back to a WPS or tribal knowledge, which is exactly what escaped control here.