PWHT Wall Thickness

By jon20013 (*****)

Date 05-05-2007 12:00

Shane, that certainly does sound rediculous and I'm wondering if they would be permitted (by design) to reduce the wall thickness so much? You're talking nearly 25%... if you look to your material specification, it would likely prohibit this... I'm not sure which material you're dealing with, but that would be one method to stop them. If acceptable by design and within material specifications governing minimum wall thickness then I guess you would be stuck with permitting it but there seems to be a few avenues for you to review in order to keep it from happening. Regards, Jon

By MBSims

Date 05-05-2007 13:32

Assuming that the 19 mm is equal to or greater than the minimum wall thickness (including corrosion allowance) specified by the designer, it could be acceptable. It depends on what code you are working to and how that code defines "thickness" or "nominal thickness" for postweld heat treatment. The ASME B31.1 definition of nominal thickness for PWHT is the lesser of either the thickness of the weld or the thicker of the materials being joined at the weld. The thickness of a groove weld is defined as "the thicker of the two abutting ends after weld preparation, including I.D. machining." So if the design engineer says that 19 mm meets the minimum required wall thickness and has no other issues with the machining details, then this could be acceptable.

By js55

Date 05-07-2007 14:27

I concur with Marty's assessment, and could not say it better. The crude assumtion is thickness at the weld, from a practical standpoint. This used all the time with C-bore situations an the like. Though I do not remember being involved in using it to purposely avoid PWHT. But in the end, if the thickness at the weld is under tolerance, its essentially the same result, as long as the HAZ (and most specifically the HTHAZ (speaking predominantly of ferritics, and bainitics)) is contained within the reduced thickness as well.
In fact, avoiding imposing another heat treat on the BM could actually be, and probably will be beneficial. If the weldment can be produced without PWHT (emphasis on the W) the unnaffected BM certainly can.