Finally got that flange gap right on my third try at the Marathon Petroleum job

I kept seeing guys leaving a 1/4 inch gap between the flange face and the pipe end on those 6 inch lines in Gary. That's way too much for a raised face flange, you want maybe 1/16 inch max so the gasket doesn't blow out under pressure. I checked with my foreman and he confirmed it after I showed him the manufacturer spec sheet. Has anyone else noticed this being a common mistake on refinery turnarounds?

3 comments

3 Comments

brooke_murray3d ago

1/16 is asking for trouble on a hot service line where the flange studs will stretch under thermal expansion. A little extra gap gives you room to retorque without pulling the gasket out of shape.

gray3143d ago

Totally feel you on this one, @brooke_murray. I've been burned by that exact same thing on a few jobs where I thought a tight gap would save time and it just backfired on the retorque. Nothing worse than watching a gasket squirm out of shape when you're trying to get the flange right. Leaving a little breathing room is one of those things you learn the hard way, but once you know it you never go back.

oliviabutler3d ago

Wait, have you ever tried cheating it by using a thicker gasket with that tight gap? That's what I did on a job last year and the damn thing blew out at 200 psi before we even got the line hot. Learned real quick that gap isn't just for show, it's there for the studs to stretch and the gasket to settle without getting pinched. Even on low temp stuff, I've seen flanges pull gaskets out of shape when you bolt them up too tight with no room. The worst part is you think you're saving time by not having to shim or adjust, but then you end up tearing it all down anyway. Now I leave at least 1/8 on anything that's gonna see any heat or pressure, no exceptions.