Operating Range of RTFE seats in a Butterfly valves 1

[ashwanikaul4]

Hi All,

I shall be grateful for your help in selection of seat material for 4 inch double-offset, leakage Class VI, firesafe butterfly valve of SS-304 MOC.

The valve is required to operate at design temperature of 182 deg C ( 360 F) and pressure of 400 psig to modulate flow of gas stream containing O2, H2, N2 and water (as steam) The seat material offered in 600 Class rating is RTFE ( glass reinforced PTFE) with inconel backup. Supplier is informing that seat material can work till 374 deg F although designer has suggested inconel metal to metal seat.

I shall be grateful if you could kindly share your operating experience with RTFE seat material at similar temperatures and pressures. Our concerns are mainly regarding the damage to seat due to creep at high temperature and high pressure, especially in presence of gas stream. For example, shold we expect damage to seat even when valve is operating with about 35% opening as velocity at seat shall be low in such case?

Lookig forward to your views / experince
Ashwani

 

[gerhardl]

I have limited experience in the range you mention, but I find it reasonable to compare with valves produced for high-pressure/high temperature steam. Theoretically RTFE should be OK for the range, but I would as you sought for improved solutions.

Suggestions are FFKM (for instance Kalrez from du Pont) or probably better, as used for steam-valves, sealings reinforced with graphite (carbon) for soft sealing, or pure metal or sintered metal sealings.

 

[ashwanikaul4]

Thanks Gerhardtl for our valuable inputs.

Ideally the seat material is OK as it falls just near suppliers limit. The concern was long term deterioration due to creep at high presure and temperature during normal operation when valve is to operate at 35% opening.

Regards,
Ashwani

 

[CKchi]

RPTFE has a range of operation temperature of -100 degreeC to 200 degreeC, i guess it shoul be ok for the case of 180 degreeC and pressure rating 600#.

A double offset butterfly valve with firesafe design, I guess the primary seat is PTFE and secondary seat seal is metal.

 

[ashwanikaul4]

Thanks CKChi for your input. We have now acepted Leakage class IV valve with metal to metal seat suitable for P, T conditions instead of relying on RPTFE seat. We felt that leakage class of valve with damaged RPTFE seat and secondary metal seat would be similar to IV class valve with metal to metal seat in long run. We are also modifying SOP to ensure upstresm isolation valve is always closed manually to ensure zero leakage.
Regards

 

[qdzung]

How much oxygen content by volume in the fluid?
Did you consider the oxygen service for this valve if the fluid contains more than ~20% oxygen by volume?

 

[valvit]

@CKchi...

RPTFE may have a maximum temperature range of 200C, and it may also be suitable for Class 600 pressure....but not at the same time. Many manufacturers will answer each question independent of the other...and ignore the fact that because of creep, RPTFE cannot handle higher pressures at high temperatures. You should really be looking to a nylon or PEEK seat if you need a thermoplastic, for this operating condition.

 

[ashwanikaul4]

Thanks Qdzung and Valvit,

The stream has no oxygen and OP should read CO2 instead of O2.Sorry for the mistake.

And yes, Valvit, the simultaneous ocurrence of extreme conditions was the reason why we chose not to useRPTFE seat.

Regards