Seal material

[jrmc]

Hello,

because of leaks in emergency vent´s we are thinking of change the seal material from Teflon to Viton.
The Viton allows better seal, but i think it can have the problem of stick
Anyone with similar problem?

 

[JimCasey]

Viton is rubbery and much softer than Teflon. It will seal with lower contact pressures.

Viton is resistant to many chemical but it is attacked by ammonia, and anything with acetate radicals. Also water makes it swell.

 

[jrmc]

hello
but what about the stick of viton, after some time with in contact to aromatic components

 

[micalbrch]

Viton isn't good for aromatic hydrocarbons but only for halogen and aliphatic hydrocarbons.

 

[jrmc]

but why? because the stick problem??

 

[Latexman]

I looked at two references I have and they said Viton is excellent/satisfactory in aromatic HC service. One was the Parker O-ring Handbook.

Stick problem? You mean the o-ring is chemically attacked, swells, absorbs the solvent, and gets sticky/tacky? Yeah, that'll happen if the elastomer is not compatible with the chemical.

Teflon is very hard and waxy and chemically resistant to almost everything, so it's unlikely to get tacky/sticky.

Good luck,
Latexman

 

[jrmc]

We actually use teflon.
because i´m not sure of the stability of viton, i will keep teflon and do some tests with viton.
After i will report where.

 

[JimCasey]

Most any elastomer will cold-flow and conform to microscopic (or larger) surface irregularities if it is compressed against a surface for a long time. We have all had to scrape gaskets.

The possible consequence of that in a safety-relief valve would be that the valve would not pop at its calibrated relief pressure.

If the seat/seal is designed properly the elastomer o-ring of choice would not be so highly loaded that it would bond against the surface of the nozzle. Marketing buzzword: "Controlled Compression". The disc is designed to seat against the nozzle with metal-to-metal, and the elastomer seal fits in a cavity in the disc so it is gently squeezed against the surface of the nozzle. The Parker O-ring handbook has specific guidelines for the appropriate amount of compression.

It's probably appropriate to remember that the SRV is only there to protect personnel and property. If the operators are doing their jobs correctly and there is not an equipment failure, then the SRV will never pop. If the valve does lift in response to an overpressure and the o-ring is destroyed, the valve will reseat but it will leak. That's OK, because it has saved the component from overpressure and it's time to shut down the system and verify that nothing was damaged by the pressure excursion.

Viton, Hypalon, Neoprene, Buna-N are all used for hydrocarbons and there are individual selecton criteria-most notably the maximum service temperature each withstands.