P91 Interpass temperatures

By worgz01 Date 03-06-2008 02:48

Can anyone tell me the range of interpass temperatures that should not be exceeded when welding P91 with SMAW process? Our WPS and subsequently PQR had ranges upto 650 deg F, however we have had a resent incident where the material temperature reached 780 deg F during the welding process. Would this be deemed as detrimential to the joint integrity. Ken

By js55

Date 03-06-2008 14:25

No. The idea to interpass maximums with Grade 91 (of any process) is to allow for some martensitic transformation so that subsequent weld passes can participate in the stress relief process of the passes below them.

By js55

Date 03-06-2008 17:08

Let me clarify a bad choice of words. I did it again. Interpass max is imposed on Grade 91 at a level below the Ms (martensitic start) temp of Grade 91 (standard IP max's are ~750-Ms is slightly higher) in order to get at least a partial transformation of the microstructure to martensite. Then as subsequent beads are run they will participate in tempering the previous martensitic beads. Simliar to what PWHT will accomplish.
Yes. This sounds much better.
Thanks Al.

By worgz01 Date 03-07-2008 01:50

Thanks. This has made it all clear.
Appreciated