P91 joints left as-welded for a long period: how to proceed?
P91 joints left as-welded for a long period: how to proceed?
(OP)
I am involved with a project where the plant owner 'lost sight' of the site welding contractor for a few months (a wise man used to say: "you get what you inspect, not what you expect!).
As a result, hundreds of P91 welds (1.2 to 2in thick) have been left as-welded for months in an uncontrolled environment and I guess exposed to the elements. I am aware of the risks associated with as-welded P91 (SCC, hydrogen cracking). The plant owner asked how they should inspect the joints to detect any damage occurred, check the microstructure and decide whether they can proceed to PWHT or reject the joints.
In my opinion, if any SCC has developed this should be detectable by surface inspection (PT or MT). Hydrogen cracks may be embedded, so volumetric inspection should also be applied.
The owner asked if they should also do replicas, to verify that the microstructure is fully martensitic, but I do not see how it would not be 100% martensitic, as the joints have been cooled to ambient temperature after welding.
Any suggestions will be appreciated.
As a result, hundreds of P91 welds (1.2 to 2in thick) have been left as-welded for months in an uncontrolled environment and I guess exposed to the elements. I am aware of the risks associated with as-welded P91 (SCC, hydrogen cracking). The plant owner asked how they should inspect the joints to detect any damage occurred, check the microstructure and decide whether they can proceed to PWHT or reject the joints.
In my opinion, if any SCC has developed this should be detectable by surface inspection (PT or MT). Hydrogen cracks may be embedded, so volumetric inspection should also be applied.
The owner asked if they should also do replicas, to verify that the microstructure is fully martensitic, but I do not see how it would not be 100% martensitic, as the joints have been cooled to ambient temperature after welding.
Any suggestions will be appreciated.





RE: P91 joints left as-welded for a long period: how to proceed?
Early in my career, I had a similar situation with a fabricator inexperienced with CSEF's. Not only did the welds sit for months outdoors before PWHT, but they were even lifted from the prefab area and rigged into place before the PWHT was performed in-situ (including 30+ foot spools). NDE confirmed the absence of cracking, and it became a non-issue with no problems during service.
RE: P91 joints left as-welded for a long period: how to proceed?
RE: P91 joints left as-welded for a long period: how to proceed?
Did not have the same luck with some P22 welds. 11 of 12 welds revealed delayed cracking with RT performed prior to final PWHT after being welded 9 m0s prior. Original RT of welds performed immediately after welding proved sound.
RE: P91 joints left as-welded for a long period: how to proceed?
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
RE: P91 joints left as-welded for a long period: how to proceed?
As has been said, if they cooled gently from the weld you are fairly safe.
Are you really worried about the creep properties? If so then some micros are in order.
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P.E. Metallurgy, Plymouth Tube
RE: P91 joints left as-welded for a long period: how to proceed?
Metallography can give useful information, but CSEF alloys can fail prematurely even when all composition, NDE and mechanical property indicators are normal and within spec. There may be damage mechanisms going on that cannot be detected by any kind of physical examination or testing (short of fully destroying the part). With CSEF steels it is imperative to know the full history of every raw material input and of how every weld was made, and be able to apply metallurgical knowledge as well as Code rules, to be able to do a meaningful risk assessment. For example, PWHT hold temperature must be tailored to composition.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."