Corrosion on laminated seat of butterfly valve 2

[monaco8774]

We have been experiencing some failures in a sea water system of some triple offset hard metal seated laminated butterfly valves, the laminate is described as ASTM A479 type 316 Ti/Graphite and you can see various layers.

We know we have had some failures of rubberlined butterfly valves upstream and it apears that some iron oxide (brown rusty powder) is sticking into particular layers of the laminate, and has started some kind of corrosion.The rest of the valve looks new.

My question is can the carbon steel contaminant in the system cause corrosion on the stainless parts of the laminate, and if so how do we get out all this contamination to stop the failures continuing to happen. Apologies I have no lab analysis as the guys through the seat away when they replaced it.

 

[EdStainless]

stainless + graphite in seawater, sound like galvanic corrosion to me. I doubt that your upstream issues were a factor.

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Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[joeswoes]

what about Teflon lined to stop the oxide adhesion ?

 

[monaco8774]

Guys thanks for the quick responses, I have asked for an upgrade on the seat to the vendor,no answer yet. I think that the problem with the adhesion is the triple offset design of butterfly needs to torque into the seat in order to seal so the laminate is made soft enough to do this. If any material is in the valve at the time of closure it will be squashed into the soft seat by the torquing of the valve. We have had much better experience with the double offset type where there is a sealing PTFE ring.