Can PVC be NACE approved for Sour Service?

[Foxtrap]

I was told to research butterfly valves to put in a PVC piping system. I was also asked to make sure that the valve was sour trimmed. I never thought that PVC would be able to be used in sour conditions. Is that right?

 

[rustbuster]

Have never heard of PCV in sour service. Nace MR-01-75 addresses the properties of alloy steels and CRA's.

 

[SJones]

But can you even get PVC butterfly valves? ISO 15156 does only address metallic materials because it is looking at crack resistance.

Steve Jones
Materials & Corrosion Engineer

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

 

[Foxtrap]

I have a few different types of PVC butterfly valves that I have looked at, but I am unaware of what sour gas does to PVC. Is there a NACE or ISO standard for other materials besides metallic for H2S? Is this a corrosion or cracking issue?

Thank you for the help so far.

 

[Burdy]

An excert from the NACE web site reads -'NACE International was originally known as "The National Association of Corrosion Engineers" when it was established in 1943 by eleven corrosion engineers in the pipeline industry. These founding members were involved in a regional cathodic protection group formed in the 1930s, when the study of cathodic protection was introduced'.
Cathodic corrosion involves the flow of a current, as the majority of plastics are largely insulators it can be seen that PVC is a material which would come into this catagory. Many manufacturers protect thier valves by coating with PTFE, rubber, nylon etc to provide an insulator between the media and the valve body.
It can therefore be seen that PVC is not a material which will appear in any NACE document.
Br
Berni

 

[danw2]

How long, do you suppose, would a PVC valve last in a fire?

 

[Burdy]

Whilst I've made no reference to the melting point of PVC, I know it is low. My experience from firetesting Polymer seated valves as against lined would say that (size dependant, because a large body would not get to temperature in 1/2 hour) a 6 inch valve would last less than a rubber one, say 15 minutes at best before a collapse of the liner. I would suspect however that the seal between the flanges(in all sizes, where the liner forms part of the flange face) would fail very quickly causing a failure of the firetest.
We actually use a very ols standard known as DOT Rule 54, which is a fire test for fittings. This is used for offshore fire main rubber lined valves. Your PVC valve may pass this if the burners are kept away from the flanges.
Br
BH