O-ring for cryogenic service (-200F)?

[rave426]

Hello everyone! This is my first post on this forum and I am looking for a bit of help.

I'm working on improving a mechanical seal design for a cryogenic service (methane) pump. The process temp is -200F (Yes i said -200F). For some reason I have not been able to find any sources that reference information about o-rings for a temperature this low.

We are currently using grafoil o-rings in the mechanical seal, but we have many issues with leak by when the pump is first started and sometimes even during chill down. The grafoil o-rings are also a pain in the rear to install as they are fairly sensitive.

Does anyone have ANY recommendation on a different type of o-ring to use. There are indeed other issues with the service, such as us using liquid gas lower/upper seals, but that is being improved as well. Right now I want to figure out how to get away from grafoil o-rings.

Opinions? Thanks!

Seal design improvement ideas are welcomed as well!

 

[btrueblood]

Spring loaded teflon (PTFE) seals. There are versions made to fit "standard" o-ring grooves. Slightly more temperamental than o-rings, but much less temperamental than grafoil.

Few, if any, elastomer materials retain any resilience at temperatures below about -50 F, so forget about finding a standard o-ring that will work at -200F.

 

[rave426]

^^ Thanks for the response. Directly after I posted I found this site.

http://www.creavey.com/materials.html

I'll look into what you mentioned!

 

[btrueblood]

Um, no. The ptfe-encapsulated o-ring you posted a link to, is encapsulating a typical elastomer (rubber), which (again) will lose resilience at -50F or so. I.e., this seal will be no better than a piece of solid teflon or PFA at cryo. temperatures. It would likely seal through one or maybe a few thermal cycles, but will start to leak shortly after that due to creep (relaxation in compression) of the teflon. The spring (metallic flexible element) loaded seals do not have the problem of lost resilience at very cold temperatures.

 

[rave426]

Yes, the elastomer will not be of much use. The link I posted also contains a reference to their "astra" seal, which is indeed a SS ring loaded design. That is the one I will do a bit of research on. Temp range is -420 to 500 F!

Thanks for the help!

 

[hydtools]

Look here, too.

http://www.seals.saint-gobain.com/omniseal-seals.aspx

Ted

 

[rave426]

Thanks Ted. I'll look into that as well.

 

[flexibox]

Try this site

http://www.huhnseal.no/pdf/advanced.pdf