Triple offset butterfly valves 1

[Ferralm]

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?

 

[JimCasey]

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.

 

[Ferralm]

Thanks, all you say (on the surface) seems to be correct but I have more than one problem not only the viton issue. I could encapsulate the needed memory of any kind inside the felfon seat but the polymer seeps by the TFE seat causing a build up behind the seat causing it to protrude in differnt spots.

 

[NGiLuzzu]

Ferralm,
how about the shaft bush bearings? Is there polymer build-up too?

Thanks, 'NGL

 

[Ferralm]

No problem with the bearings I am using nitr. 60 bushings w/doge bearings also avoid mounting in the vertical position w/gear operator.

 

[farfarvalve]

I cant support the issue with process reaction against the soft seat materils you have selected in the past. With graphite in the triple offset, this is prefered for firesafe applications. Triple offset metal seated have graphite in the body seat to allow movement during torque seal for metal to metal contact. Again using the flow in the prefered direction would help the seal where as you would push the disc into the cone assiting the sealas well as the torque for tight metal to metal shutoff.

 

[GeoSmith]

Anyone know the graphite in body seat can survive in the high pressure class (such as ANSI 900)and the high temperatue cases.

 

[farfarvalve]

Dear GeoSmith, Yes the graphite would be used on high temp applications with Class 900 not being a problem in-fact TTL have valves on high temp applications in Class 1500 they also have class 2500 on 12" and above. The TTL body seat which has graphite laminated, this allows some flex when the disc seat contacts with the body seat. So for high temp this design has track record on success!
Bruce

 

[NGiLuzzu]

Ferralm,
I would suggest you to try a valve with a static seat on the body and a seal ring on the disc.
In that way, the seat may be hardened, for example, by means of a Stellite weld overlay (Grade 6 is often used, even if Grade 21 may be a better choice... in any case, compatibility with the specific application should be checked).
In addition, the seal ring may be built as a "solid" piece (instead of the "lamellar" construction) of a selected metallic material, and also properly treated (nitrided, hardened or coated, etc.) and/or shaped with a rounded profile, if necessary; then a stainless steel + graphite spiral wound gasket may work in the groove on the disc, under the seal ring itself, without direct contact with the medium.

For possible Suppliers of such valves, please refer to Thread408-126483 and Thread408-139775 (for instance) within this Forum.

In the end, it is recommended to install the valve with the stem axis in horyzontal position, the more inclined side of the conical seat above and the "flatter" side below (in order to allow the removal of possible solid particle accumulation or build-up by stroking the obturator...).

Hope this helps, 'NGL

 

[GeoSmith]

Thanks Bruce,

It seems the graphite is strong for the high pressure case. How about in the cryogenic condition? The graphite in triple offset valve is still working? My client find his valve is leaking for the liquid nitrogen condition, extremem low temperature.

 

[NGiLuzzu]

GeoSmith,
what's the entity of the leakage at cryogenic temperature?

Most common helium testing standards (such as BS 6364) allow for leak rates up to 150 ml/min per in of ND: in this case (36"), that would sum up to 5.4 l/min...

Thanks, 'NGL