Dissimilar metal bayonet connection

[MENEF]

Hi,

Does anyone has good or bad experience with dissimilar metal bayonet connections with secondary 0-ring seal at the flange and V-band clamp?

Our company is used to specify Double seal bayonet type end connections with flange.

Application: Liquid Nitrogen at 50 psi (design 150 psi) Pipe: 1 1/2'' x 3 1/2'' VJ pipe.

Thank you.

 

[iainuts]

Hi MENEF,
All the bayonet connections I’ve seen are made from 300 series stainless steel. I’ve not seen any dissimilar metals used, with the exception of a case in the launch industry that had an Invar inner line.

The bayonet should be rated for cryogenic temperature, and generally, only 300 series is used. Leakage would result in very cold temperatures at the flange which is a safety concern for metals that become brittle such as carbon steel.

The primary concern with bayonets is to have the male end pointed down or at an angle. Male bayonets that are horizontal or pointing upwards will allow liquid to travel along the annular space between the male and female halves and boil off at the flange, the warm gas going back into the line. This results in a relatively large heat leak and a very cold flange and O-ring seal which results in leakage. Leakage results in harder O-rings and more leakage… snowball affect.

A nose seal is intended to reduce or eliminate the problem with liquid getting between the male and female bayonets but I wouldn’t rely on them.

So to answer your question, dissimilar metals, as long as the metals don’t result in interference, would be ok, but that is a secondary issue to ensuring the materials are good for cryogenic service and the bayonet orientation is correct.