Vent: A flange weld cracked on a pressure vessel at the power plant in Joliet.

We were doing a hydro test on a new boiler section, and I heard a sharp ping from the far end. Found a hairline crack running about three inches along a main steam outlet flange. The preheat was right, but the fit-up must have been off by a fraction. We had to drain the whole thing, grind it out, and re-weld under full supervision. Anyone ever have a weld pass visual and dye pen but still fail under pressure?

2 comments

2 Comments

rileyfox9h ago

Heard about a similar thing happening on a pipeline job, was it just residual stress?

paige_ellis598h ago

We had a 16 inch header weld on a turbine bypass line at the Calpine plant that did the exact same thing. Passed every NDE check on the floor, then popped a tiny leak during the final steam blow. The engineers blamed it on locked-in stress from the original fit up, just like rileyfox said. It's the worst feeling, thinking you're done and then having to cut out a huge section.