Re: 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)