Had a flange weld fail on a shutdown job in Gary, Indiana

We were doing a full pressure vessel inspection on a Tuesday morning. The old weld on a 12-inch steam flange just gave way during the hydro test, right at the root. The foreman, a guy named Carl, had me grind it all out and showed me his trick with a tighter arc gap on the first pass. I've been using that method ever since. Anyone else pick up a small trick from a failure that stuck with you?