We come across bolting seating failure while performing Flange Leakage/Stress Calculations mainly for Outlet flanges in Safety valves which are of lower rating. This failure is independent of piping loads.Can we neglect this failure when the flange is safe in all other conditions?

Regards
Krishnendu Bhattacharya

Read this posting , it may answer your questions.

Using the Taylor Forge method (As in ASME VIII which Caesar uses)I recall calculated bolt loads being too high for 150# flanges when a spiral wound gasket is used. The flange stresses came out OK. This is because this gasket requires a high seating stress.
Although gasket sizes are the same for 150# to 2500# this calculation suggested to me these gaskets should not be used for the 150# rating. B16.5 rating tables make no reservations on gaskets of course. If your equivalent pressure (from pressure + moments) is within the rating then flange is acceptable to B16.5.
Note also Caesar Flange leakage allows you to double (sometimes treble) the bolt allowables. The problem never occurred with 300# which have more and bigger bolts.

Michael