Casting stainless steel / forged stainless steel for cryogenic valves.

[viki100]

I have problem, that supplier offers me a cryogenic ball / gate valves ASME class 300 / 600 (BW welding ends) body / bonnet made of casting CF8M. When I asked them, CF8M, doesn't problem with sensitization (intergranular corrosion, postweld heat treatment) cast stainless steel after welding for cryogenic application.
They confirmed that CF8M/ 316SS (with Charpy impact test) is ok, even for the body welding ends. Yes, we have good experience the CF8M.
I think that, to my knowledge, good engineering practice should be used CF3M / 316L SS (carbon below 0,035 %) instead CF8M / 316SS for cryogenic applications, and not only.
Many manufacturers of valves (the cryogenic valves) offer valves made of CF8M for welding.
According to ASME B16.34 ASTM A351 CF8M and CF3M are the same group materials 2.2.
Could you help me in this topic, explain to me about it.

Thanks a lot.

Viki

 

[hsbcn]

CF8M is actually quite common in cryogenic valves.

I work with valves in exotic alloys at The Alloy Valve Stockist. This is our blog, and this is me on Twitter and LinkedIn. Let's connect!

 

[EdStainless]

The convention is to use the straight grade designation, for ease and convenience.
The last set of valves that I bought that were marked CF8M all have C that was less than 0.03%.
As long as they are below 0.05% for all practical purposes they will behave as if they were L grade.

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Plymouth Tube

 

[TOVmania]

Sensitization and IGC are related and usually applicable to higher temperature application(300-500C) but not for cryogenic valves.

If proper welding technique is used, PWHT is not required for stainless steel grade for cryogenic application in terms of impact strength or controlling ferrite number within P-No. 8 and Group No. 1.

If the valve application temperature must cover cryogenic to high temperature, then using CF3M or CF3 will be the choice.