I am having problems with 36" soft seated butterfly valves. When the valves were disigned for vent gas compressor suction valves the styrene content was not taken into consideration so the TFE seat ring with viton o-ring are not compatable. Polymer builds up behind the seat ring and also causes swelling to the viton backup o-ring. I know the charts imply they or compatable but they are not. We also have problems with graphite packing in styrene service. I have chosen a triple offset design butterfly with laminated sst & graphite seat. Does anyone know if I may experience problems with the graphite seat?

Graphite is normally only attacked by very strong oxidizers.  

Why don't you replace the viton O-Ring with another elastomer? I'm surprised that Viton is attacked: Usually amines and acetate radicals attack viton.  Water swells Viton a little.  

 Nitrile is resistant to most HCs but limited to around 180F, Silicone is pretty easy to get and operates at higher temps--susceptible to some solvents, tho'.   Or if you have significant funding there is Kalrez.  It still won't be as expensive, though, as a new valve.  

If you can use a Fluorocarbon seal ring you can use PTFE packing. Usually the first ring in a Graphite packing set is a braided junk ring-your monomer is probably building up in this porous ring and causing you the problems.  At least TFE is not porous and it's famous for being slippery.   

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