Learned something wild about boiler tube thickness tolerances today

I was looking through some old ASME specs last night and found out that boiler tubes can have a wall thickness that's 15% thinner than what's stamped on them and still pass inspection. That blew my mind. I always figured if it said 1/4 inch wall, that's what you got. Turns out there's a whole range of acceptable variance built into the standards. That makes me wonder how many failures out there are from tubes that were technically within spec but just barely. Any other guys ever run into tubes that measured way under but the paper said they were good?

2 comments

2 Comments

derek6564d agoMost Upvoted

Tbh that's terrifying to hear. 15% under and still passes inspection feels like a recipe for disaster down the line. Makes you wonder how many near misses were actually just standard practice.

ray_miller413d ago

Did you see that write-up from the National Board a few years back about the 15% variance rule? They said it dates back to when boiler tubes were made way less precise, and the tolerance was basically a carryover nobody ever updated.