Cryogenic service
cryogenic valves, please consider following points:-
- Body(Austenitic SS) and trim material selection(Austenitic SS)
- Soft seat(PCTFE) and seal(Lip seals-PTFE+SS/Elgiloy) material for the ball valves.
- Material of seal ring(Solid seal ring is generally selected) for triple offset butterfly valves
- Extended Bonnet requirement for the valves to protect the valve packing from freezing. Extended bonnet length in accordance with BS 6364/MSS SP-134/ ISO 28921/Shell SPE 77/200.
- Cryogenic testing in accordance with standards/client documents stated in point no. 4 above.
- Cavity relief mechanism for valves with inherent cavity. This is a common requirement for valves with flashing service. Triple offset butterfly and Eccentric ball valve are cavity free.
These are some of the main requirements.- The purpose of extended bonnet is to provide a insulating vapor column and to protect the packing from cryogenic temperatures. at cryogenic temperatures, the graphite packing will freeze and will render the valve in operable. So, extended stem is not a alternative to extended bonnet. So, for cryogenic valves, we have to provide extended bonnet only
Source: Linkedin-Cryogenic service