Explosive Decompression of O-Rings 3

[Sircrashalot]

I have a client asking about the AED resistance of an O-Ring in a 4" 150" Ball Valve (client is conservative Supermajor). Everything I have ever seen on ED is that it only affects valves in high pressure gas service, and I have as a general rule only been concerned with it in valves over 600# class. I know that the o-ring cord size is also a factor, as cords less than 5mm in diameter are generally not susceptable to ED damage. I KNOW that the O-ring in the valve is OK, but how do it PROVE it. Is there a paper somewhere that states "ED is only an issue for valves in gas service above XXX psi pressure and for seals that have a cord diameter greater than Y".

Any help appreciated...

Thanks,

Andy

 

[MikeHalloran]

It's not clear if this developmental software ever actually became available:

http://www.reinforcedplastic.com/WZ/WorldPumps/productnews/productupdate/000083/show/

Mike Halloran
Pembroke Pines, FL, USA

 

[zdas04]

I was talking with the chief engineer for a ball valve manufacturer once and he was describing a problem with his valves in dense-phase CO2 service. It seems the o-rings would become permeated with CO2 during normal operation and when they depressurized the system for maintenance every o-ring in every valve shredded (he described it as popping trap doors in the rubber) and none of them held when the system was brought back up. They solved the problem with a different o-ring material. The point of the story is that any elastomer can be subject to explosive decompression in the right fluids/conditions. It is important to know that your seals are compatible with your fluids.

David

 

[dcasto]

Ditto to zdas, not only do the elastomers "pop" they can swell greatly. We used oring seal in our orifice meters in ethylene. When we changes plates, we would hang to oring up to let it expand and expell the ethylene. If it didn't blister and pop, we would use it again.

To solve the problem, viton was a vast improvement over butyl-n. Next came Kalrez and a combination viton and teflon (teflon is not flexible enougn by itself.

 

[SJones]

http://www.hse.gov.uk/research/rrhtm/rr485.htm

http://www.hse.gov.uk/research/rrhtm/rr320.htm

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[unclesyd]

The two treatises discussing O-rings in the post SJones are excellent in that they cover nearly all aspects of using O-rings.

The only thing they seem to have left out is the purchasing department's substitutions.

 

[Sircrashalot]

Steve,

Many thanks. This is what I was looking for!

Pressure greater than than 35 bar, section greater than or equal to 5.35mm.

Andy