Handling of 9 Cr 1 Mo Material
Handling of 9 Cr 1 Mo Material
(OP)
Hi, I working on HRSG Fabrication with 9 Cr material, I have customer specification state that "If the assembly is not PWHT within 24 hours of the completion of welding, it shall be enclosed or covered and be stored 5 degrees above ambient temperature" I wonder what is the reason to store work piece at 5 degrees above ambient temperature? Also, spec require to Hold at 200 F for minimum 1 hrs before PWHT, What's the reason for that? Is all of this for allow hydrogen escape and keep hydrogen (Humid) away from weld?
Thanks for all answer.
Pook
Thanks for all answer.
Pook
RE: Handling of 9 Cr 1 Mo Material
Is it for some Gulf customer namely Kuwait?
Actually the requirement was there to prevent hydrogen ingress as you have correctly thought of.
But I do feel the code needs to be changed as enclosing and covering is enough. No point in holding 5 degree above ambient.
Regards.
DHURJATI SEN
Kolkata, India
RE: Handling of 9 Cr 1 Mo Material
No, This is Vogt Power spec. Thanks for the answer!
Pook
RE: Handling of 9 Cr 1 Mo Material
Bob
RE: Handling of 9 Cr 1 Mo Material
RE: Handling of 9 Cr 1 Mo Material
RE: Handling of 9 Cr 1 Mo Material
Hydrogen per se is not the problem. Stress corrosion cracking has been encountered in welded P91 parts allowed to sit at room temperature after welding and before PWHT. I am not up on the very latest research but I am not sure the mechanism is well understood yet. It does seem to involve moisture, and empirically it is known that the problem can be avoided by PWHT as soon as possible after cooling to below a sufficiently low temperature (200°F; to ensure full metallurgical transformations are completed).
EPRI and CCJ websites will have information about this phenomenon.
p.s., do not confuse post-weld soaking with heat treatment, which has specific Code meanings.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Handling of 9 Cr 1 Mo Material