Dear Faruk,
NO CODE WILL ALLOW P-91 STEEL TO BE WELDED WITHOUT PWHT.
Further to the recommendations of John, I would like to add a few points. P-91 is classified as P 5B Gr2 material in ASME Sec-IX. Often in the past people thought this steel to be “just another Chrome Moly” steel, till the “lessons were learnt”. P-91 steel is never used in ambient temperature or typically for 15psi (very low) design pressure ranges. This material is recommended for design and pressure ranges where any mishap (minor or major) could cause human fatalities. If you do a google search with these keywords “ p-91 steel, failure, fatalities”, you will see tons of articles.
The attached article would provide a good general guidance on P-91 steel and understand the need for PWHT.
Let me know if it helps.
Thanks.
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of John Henning
Sent: Monday, August 30, 2010 10:01 AM
To: materials-welding@googlegroups.com
Subject: [MW:6787] RE: 6769] Any WPS for P91 Material without PWHT
Not a good idea. Not only is 91 in the as welded condition rather brittle but it has been shown to be subject to stress corrosion cracking in the presence of water (condensation, dew, rain, etc.). You can find recommendations sprinkled throughout open literature that discuss the need to keep as welded 91 warm and dry between welding and PWHT. (A tedious Google search should reveal at least four good references – a task left to you). There have been several 91 failures traced back to SCC due to improper handling of 91 in the as welded condition. Some recommendations not only restrict storage conditions but also time duration.
As previously pointed out, all ASME codes require PWHT for all welded 91 without any exemptions.
John
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Mohamed Farook
Sent: Sunday, August 29, 2010 11:00 PM
To: materials-welding@googlegroups.com
Subject: [MW:6769] Any WPS for P91 Material without PWHT
Dear friends,
Greetings to all,
Please advise me if you have WPS for P91 material without PWHT….
PWHT is time consuming..
Thanks and Regards,
asfaruk
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