PWHT of P5 group B material

Date 07-30-2004 09:29

ASME B31.3 – 2002 paragraph 331.1.3(b)(2) does not require PWHT for socket welded pipe connections of NPS 2 and smaller when the fillet throat is 13mm (1/2 in) and smaller, with the recommended preheat applied and specified minimum tensile strength is 71 ksi and less, for P 3, 4, 5 and 10A. This means P5 B’s such as 5Cr, 9Cr can be welded without PWHT within the about constraints. I was always under the impression that these materials, containing more than 3% Cr should be PWHT regardless; does anybody have experience with this?

Cheers
Joe

By GRoberts (***)

Date 07-30-2004 14:36

The ASME codes provide the minimum requirements for providing for safe operation of a weldment. (i.e. avoiding brittle failure) There are lots of things that are advisable that are not required by the code, such as the PWHT you mention. There are also factors that the code does not attempt to address, such as creep life performance, fatigue, or corrosion resistance. The lack of PWHT is not considered critical by the code as the thin materials involved do not lend themselves to brittle failure, but it sure wouldn’t do any good for creep or fatigue life if you don't PWHT.