grey cast iron for sour gas? 1

[gustorf]

Is there any technical reason not to use grey cast iron material inside a valve (not pressure containing) for sour gas applications?

 

[Elvie]

1)Gray cast iron is prohibited by NACE MR0175 for use in sour services "as a pressure-containing member" due to its susceptibility to SSC( sulfide stress cracking).
2)However you should check whether NACE MR0175 applies to your case as it is mentioned in its para 1.3.2.1 "MR0175 need not apply for LP gas when total system pressure is less than 65psia (0.448MPa)".
Bottom line:I should avoid the use of a gray cast iron material in any gas application where a SSC is a potential risk be it a very tiny one.

 

[gustorf]

Elvie, thanks for your reply.
The parts i am thinking of are non pressure containing parts inside a valve (a flow diffuser which does not handle any pressure). Please have a look at

http://www.noreva.de,

check on products "NRV-Z" and look at the green coloured item inside the valve.
gustorf

 

[jsummerfield]

The Texas Railroad Commission issued a law about 25-years ago that clarifies when NACE MR0175 must be applied based upon the pressure and hydrogen sulfide content. Require NACE compliance and obtain certification from the equipment supplier.

John

 

[Elvie]

Gustorf,
I suppose the "NRV-Z" is an axial check valve the "green cloured " stuff being the trim.When valve is closed the trim is going to face the differential pressure so the stress will be there there;subsequently the SSC risk is high.If my guessing is correct I shall never accept the trim in gray cast iron.