RE: Flange Failure Images

From: <Al>
Date: Thu Jan 29 2004 - 15:02:00 EST

because of the dark gap between the flange ring and the pipe, the nature of the failures (Mostly radial inward cracks) and the suspiciously different "greyed" and speckled color this looks like a "slip on flange ring" of illegitimate material.

I had the same thoughts that chris expressed ....except I dont see any welding on the failed flange and i dont see where the welding relates. If that Failed ring is really welded to the pipe theres a huge undercut or separation between the inner ring diameter and the pipe. If this was originally joined the hub is inadequate and the (non existing hub) stress would be huge. In a slip on there is no hub stress.

  (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").
it doesnt look like the ring broke away from the pipe (circumferentially).

the gap is too big. it looks like a fig 2-4 type 1a flange was intended and messed up.

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.

-----Original Message-----
From: Christopher Wright [mailto:chrisw@skypoint.com] Sent: Thursday, January 29, 2004 12:22 PM To: ?
Subject: Re: [PipingDesign] Flange Failure Images

I'm not sure what I'm looking at in these pictures. It's not clear that the assembly is a real flange or simply a ring made up to substitute for a real flange. The ring OD's don't appear to match.

The cracked circumferential weld looks like it broke without any yielding, and the first thing I'd look at is whether the weld meets the ASME Code requirements for such a welded assembly and Appendix 2 of Section VIII Div 1. I'd also check the welding procedure. Sound welds of the proper size don't usually break like this. Can you supply the weld detail?

The cracks at the bolt holes also occurred without any evidence of yielding. I'm inclined to doubt that the material is suitable for a flange. If it were cast iron or something notoriously unductile, it shouldn't be welded. I've never seen radial cracks like this in a flange. The circumferential stress in the flange ring is usually non-governing, but the cracks are located and oriented properly for failure from overtightening. The multiple failures show significant overstress and not just a local flaw at one of the bolt holes.

I don't mean to slander anyone but it looks a bit like this connection was cobbled together in a hurry either to save the cost of a real flange or because a 'quick fix' was needed. Overall the appearance is very much non-typical of the failure of a forged flange. My first guess is that the flange is made from unsuitable material and not welded or designed properly for the bolt-up loads.

I hasten to add that this is a first-pass assessment without any real examination, but I the main points--proper welding practice, material specification and suitable weld design and the first things I'd look at.

Christopher Wright P.E.    |"They couldn't hit an elephant at
chrisw@skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw

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