RE: Flange Failure Images

From: <Steve>
Date: Fri Jan 30 2004 - 05:40:00 EST

Paul
guess I didnt explain clearly. I think it is probably a lap flange or similar stub end with a plate flange fitted. If the plate flange does not have a correctly dimensioned chamfer or bevel on its inner bore, it will bind on the stub end fillet radius, preventing the flange inner face from bearing on the outer face of the stub end. But with some big spanners we can crank it up (as we do) which will crush the flange bore onto the stub fillet, and bend the flange into a cone shape. The tension on the flange bore could easily cause the cracks shown provided the stub end doesnt collapse first. Diagnosis - wrong flange for the job. Obviously, because the bloody thing broke.

Hows that for a stack of interdependent assumptions based on a couple of happy snaps?

I wonder what the real cause was..........

Cheers

Steve

-----Original Message-----
From: Paul Bowers [mailto:pbowers@pipingdesign.com] Sent: Friday, January 30, 2004 11:17 AM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Flange Failure Images

Assuming this is 10", 12" or 14" line size (12 bolts) and it's a Van Stone/lap joint assembly (as Steve considered and then dismissed), the stub end should be at least 5" long, meaning we should see a butt weld close to where it's written "SX" with an arrow and "6" underneath. That's why I speculated that it might be a butt type angle ring, which is only 1.5" face-to-face - the butt weld would be almost totally obscured.

Or maybe it's this: http://www.ipp-inc.com/rev3/sose.htm

The flanges definitely appear to be of different material and this looks like a spec change interface.

Paul

> >except I dont see any
> >welding on the failed flange and i dont see where the welding
relates.
> You may be right. I thought I was seeing the remains of a fillet
towards
> the bottom of the pipe in slide 2. There's nothing on the ring itself
> that I can see. Wonder if this is a lap joint ring mated to an
ordinary
> slip-on or weld neck.
>
> > (i cant see the flange ring welded to the pipe being the case
because the
> >flange ods line up and the bolt position has not changed radially (no
> >stretch) and the pipe hasnt "shrunk").
> If it were a lap ring , overtightening would produce the radial cracks
at
> the bolt holes. There would be a gap between the ring ID and the pipe
> wall which would open up under tightening as the the ring ID rotates
out
> and away from the pipe OD.
>
> >It strongly appears to be an illegitmate slip on ring flange. if made
out of
> >improper material the failure would occur as seen at the stress
raisers of
> >the holes.
> Bang on. Looks like cast iron maybe with a coat of primer. I wonder if
> that light-colored stuff at the OD is caulk, laid in as a desperation
> measure.

---

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