RPTFE seat shows swelling with glycol water mix 1

[hp1996]

Hello,

I have an application where the media is 50/50 water-GLycol, using a buttefly valve, with RPTFE seat. Temp is 232F, 35 psi and the seat is showing swelling, the valve has been in operation less than a year.

I can't find a chart that would give me temp ratings for Reinforced teflon and glycol, any idea why the seat may be swelling?


Thanks so much,

 

[StoneCold]

hp1996
Teflon lined butterfly valves have a backing material behind the teflon that makes it a resiliant seat. Fluid can permeate the teflon and cause the backing material to swell. Check with your vendor about what the material is in your valve. We have had similar problems in other services so we went to a viton backing material. That worked for us.

Regards
StoneCold

 

[hp1996]

Thanks StoneCold, forgot to mention that this is a High Performance valve, the RPTFE seat doesn't have a backing material on it that I am aware of. I was thinking on that way, that the glycol may have permeate the seat somehow, but didn't know that it would do that to the reinforced teflon.

 

[btrueblood]

You shouldn't double post. Probably too late now.

 

[hp1996]

Thanks btrueblood,

I saw the post on the other thread, and tried to move that thread to this forum, or try to close that one... any idea how to do that?

 

[btrueblood]

Well, you could RF one or the other, but as there have been substantive replies in both fora, it's probably too late.

 

[MikeHalloran]

Users can't edit or delete stuff here. Only management can.
A Red Flag gets management's attention.
A polite detailed request in the resulting dialog box can cause most anything to happen to a message. Remember you are talking to a caring intelligent nonengineer person.


Bear in mind that PTFE is a sintered product, inherently porous, and that reinforcement makes it more porous. So the glycol will eventually reach whatever the reinforcement is, and whatever is behind the seal also.



Mike Halloran
Pembroke Pines, FL, USA

 

[moltenmetal]

I'd be truly shocked if reinforced PTFE was actually swelled by glycol/water. That would be quite the discovery.

Teflon isn't resilient enough to serve as a particularly good seat material for a butterfly valve. The so-called "high performance" designs are many, and vary greatly in just how well they work with non-resilient seat materials. Are you sure what you're observing is swelling, rather than creep/cold flow of the seat material? The reinforced teflon creeps less and creeps at higher temperatures than unreinforced PTFE, but neither are anything like rubber.

232 F, 35 psig is an easy service. You should be able to find a truly resilient seat material which will work fine under those conditions with glycol/water.

 

[btrueblood]

"I'd be truly shocked if reinforced PTFE was actually swelled by glycol/water."

I have seen glass reinforcement go away in superheated water/steam service. Like molten says, this results in higher rates of creep in the teflon than would be expected for the reinforced material. Either way, teflon by itself is not a very good seal material.

A better idea would be an EPDM rubber seal, probably a peroxide cured EPR for those temperatures.

 

[gerhardl]

I am in the position of a German 'internal for a company/for larger customers' technical paper describing materials allowed and recommended for solenoid valves for different fluids and temperatures. I have found this, through some decades, very reliable.

For glycoel (note: ethylen glycol ( C2 H6 O2) 100% concentration, at 120 deg C, this paper recommends for dynamic sealing elements FKM, EPDM, Kalrez and PTFE. Not recommended is NBR, CR CSM and Delrin. Not recommended for static sealing is PP, PVC; PVDF, NR, NBR and CSM.

As a fact any elastomere will absorb and swell any fluid on a microscopic level, the question is only how much and how fast under the given circumstances, from not measurable to bothersome and disturbing the functionality of the component.

Anything varying from the 'norm' could influence your RPTFE status: porosity or composition of your reinforcement of PTFE, or the PTFE itself, additives and impurities or variances in the 'glycol' (unknown additives?), unknown factors in the process ( cleaning agents, impurities etc?), mechanical faults etc.

Conclusion: RPTFE should be a reasonable choice. Given that it obviously does not work, I will agree with btrueblood for try of alternative materials.

A good idea would also be to check the valvetype itself, and that the 'swelling' is not a result of drawn out material by improperly closed valves (cracked open, or damaged seal with hairline opening giving underpresurre over the sealing and leaking (cavitation conditions?)).

 

[hp1996]

Hello all,

Thanks so much for the responses.

We are thinking on something else was in the mix, that may have cause the swelling. We are also reviewing the conditions that the valve was operating, to check if cavitation occurred.

Thanks again,

 

[rmw]

Did you mix the glycol or did you purchase a prepared mix prepared by the glycol vendor. If the former, did you use DI or pure water? If not what could have been in it that might be part of the equation. If the latter, know that 100% glycol is not 100% glycol. The manufacturers of glycol put 5-6-7% other things, stabilizers, etc. into the mix to insure the long life of the glycol.

rmw

 

[moltenmetal]

RPTFE is used routinely with commercial glycol/water/inhibitor coolant mixtures at temperatures beyond your service limit.

Again, if RPTFE is actually swelling in this service, it'd be a huge surprise.

That it would creep sufficiently to interefere with the operation of a butterfly valve would not surprise me at all.

 

[btrueblood]

Again, agree with molten. The number of chemicals out of all the billions of them, that would attack ptfe, are very few.

 

[hp1996]

Thanks so much for all the posts, I really appreciate all the information.

We are exploring on the creep possibility, haven't gotten all the information from the site on cycles and operating times.

Thanks again,

HP