Postweld heat treatment for P91

[Dlew]

What are the requirements to perform PWHT for P91 material?

[arcpro]

Please specify under which construction code this material has been used?
It is for ASME B31.3?

[Dlew]

Yes, considered for ASME B31.3.

[mechcolor]

31.3 recommends to apply PWHT from 732-774C and maintain that for 1 h per 25 mm.
Minimum holding time is 2 hrs.

[Dlew]

Yeah, however following exactly the mentioned details we have been suffering with the resulting hardness not matching the requirements.
Are there are other precautions needed to be taken during PWHT?

31.3 recommends to apply PWHT from 732-774C and maintain that for 1 h per 25 mm.
Minimum holding time is 2 hrs.