High Temperature Ball Valve Seat with DEPG (Selexol) 2

[hwilson]

Hey Everyone,

I have about 30 6"-12" ball valves through which DEPG/Selexol (dimethyl ethers of polyethylene glycol) passes. We currently use teflon seats but a few of the valves have started leaking (process, not externally). The highest temperature these valves see is 250 F. Any suggestions on a valve seat material or kits?

Thanks,

Heather

 

[hsbcn]

PTFE in and of itself should handle the 250F temperature, so something else might be amiss.

What pressure are you dealing with? Problematic medium (abrasive/corrosive/other)? And how long have these valves been on the line and what is the diagnostic of the reason why some valves are leaking and others not?



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[hwilson]

The highest pressure is 600 psig. Some valves only see 30 psig. I'll have to get more information from the plant manager, but I believe the high temperature and use of DEPG/Selexol is causing the seats to be ineffective.

 

[gerhardl]

Hsbcn: I agree!

In addition: History? How long in operation before leaks? Possibillity of crack-openings(99,9% ???) giving cavitation or drawing of sealing material? Check of position, adjustment of limit and torque switches if any. Slack and precision and adjustment of any mechanical connection and operator. Best tip: to replace one of the worst valves including operator, and inspect directly, valve inside included, this will tell you a lot. Pictures of damage?

PTFE should in itself be OK, as far as I can see, both for fluid and temperature. However, as there is a multitude of PTFE fillers and other details of fabrication details giving again a multitude of 'PTFE's', there could be an unfortunate mismatch for this particular PTFE's fabrication or application.

 

[moltenmetal]

"Valves have started leaking". OK, all valves leak, even soft seated ball valves. They leak more after they've been in service a while. Whether or not there's a problem that you can do anything about, depends on how MUCH they leak.

250 F doesn't need anything other than reinforced Teflon. Unreinforced PTFE creeps too easily to use in a big valve like these.

 

[hwilson]

The leaking valves have been replaced recently, so length of service is not an issue. I suggested the plant just switch to RTFE. Thanks for your input.