Corrosion Allowance and Elastomers

[Angsi]

Can someone please advise the following:

- Is a CS body valve with 10mm corrosion allowance readily available for all pressure classes or if they need to be specially manufacturered? Or is the 10m corrosion allowance OTT (over the top)??
- The following valve elastomers specifications, are they correct w.r.t. to the application temperature limitations:
a.PTFE shall be limited to 230 deg C, Viton A to 200 deg C, Buna N to 120 deg C and Neoprene to 90 deg C

Thanks.

 

[SJones]

Has an analysis been performed to ascertain whether a 10 mm corrosion allowance is an economic option. With expected corrosion rates of this magnitude the valve may fall apart. Is CRA overlay not a viable option?

As for seals, take a look at:

http://www.hse.gov.uk/research/rrht...uZ292LnVrL3Jlc2VhcmNoL3JyaHRtLzMwMS00MDAuaHRt

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[JimCasey]

If you expect 10mm corrosion in CS you would be well advised to look at a different, corrosion-resistant, alloy. You're not saving money if the valve corrodes so much that it cannot perform its intended function and your products are out of specs. It's not economical either if the valve blows and shuts the process down, or worse: if somebody is injured and you have to pay a bajillion dollars to his family and the cost of a cleanup for the spill.

O-ring information:

http://www.marcorubber.com/compatibility.htm

Material Web:

http://www.matweb.com

The temperatures you listed look to be about right for those elastomers. Viton can get really hot for a short period of time.

 

[Elvie]

The WO is by far the correct choice but the WO material must be selected to fit your corrosion conditions.If you were looking for 10mm of CA I doubt your Neoprene or Buna N seal material fit into equation .The seal material selection is as tough as body material selection and shall also meet fluid service on its full operating temp range.
Then be sure the valve rating covers your press/temp application.