Cryogenic Gate Valve trim material - soft vs hard seat

[Gorman3]

Hi,

I have an engineer asking for large diameter 600# class CF8M API 600 gate valve. Service is Butane or Propane at -200 degrees. Valve will be operated annually during shutdown at which time the pipe would be drained downstream and removed thus exposing the downstream seat while upstream is under pressure with a differential of 300 psi. Usually I'd quote an extended bonnet with Trim 10 or Trim 12, but considering the line will be open downstream I think soft seats for zero leakage might be best. Thoughts on seat materials?

To be frank a DIB valve or DBB setup would be best but they're just looking for a single gate.

thanks for your thoughts

 

[gerhardl]

More details will probably give you a better answer, but your question is interesting. There is an ongoing development regarding non-metallic sealing materials for cryogenic purposes. This will give you a far wider choice of soft sealing materials than only a few years ago.

Personally (note: without much experience in cryogenics) I would go for an approved valve for the purposes, perhaps preference for soft sealing if exsisting certified/tested. This arises some important issues, as your technical question is only part of the total application requirements.

Are you constructing or buying on the open market?
Is the valvetype best for the solution?
What is the size of the valve (Large??? Could be 2 inch or much more, this will tell you about exsisting competitors and solutions)
Safety rules or safety considerations at the plant or generally (country, area, type of plant, associations)?
Is two valves in series needed for safety?
Certifications needed?

 

[Gorman3]

I just found out there will be some kind of check valve and then a blind valve this gate valve which is 14" diameter. I would use a different valve but the users design calls for a API 600 gate. The valve will be closed but not at a low enough temp for the gas to remain liquid.