O-Ring Between Flat Face Flanges? 3

[Slagathor]

I have a manufacturer telling my client to use a 7mm o-ring to seal between two 16" 125# cast flanges. There is no o-ring groove. The manufacturers sales rep is saying to just put the O ring between the flange faces, even though there is nothing to locate it. This seems absurd to me. Has anyone ever heard of this being proper piping practice?

The joint in question is between a pump suction nozzle, and a special pump suction elbow, both supplied by the mgf. I am concerned about cracking a flange in the short term, and the o-ring failing longer term as it creeps out. I am tempted to over rule the recommendation, and use a proper gasket (cloth inserted rubber, 1/16th thick). This is at a wastewater plant, so no ASME standards...all the standards are AWWA. Pressure is in the range of 20 psig, digester sludge service.

 

[rconner]

Also, while I'm kind of partial to steel and ductile iron myself, considering that some gray cast iron flanged joints and seals have provided remarkable service (and in some cases continually) for centuries, and that some folks since have at least attempted to make flanges out of much cheesier materials I'm not sure I'd necessarily so single out same. I kind of like the summary statement by the seemingly erudite folks at

http://europeansealing.com/uploads/...-FSA-Guidelines-Flange-Gaskets-009_98_ENG.pdf

, "The behaviour of a flanged joint in service depends on whether or not the tension created in the fasteners will clamp the joint together with a force great enough to resist failure of the seal, but small enough to avoid damage to the fasteners, joint components, gasket etc."