PW.39 P15 E Lowered Minimum Temp for PWHT

[rmillercwi]

I noticed in the 2017 edition the minimum temp for PWHT of P15 E materials has been lowered from 1350 to 1300.

Does this indicate a trend that lowering PWHT temp is desirable for 15E materials? It would seem by doing so it would effect hardness numbers somewhat. Just wondering what was driving this change.



I also see that non mandatory appendix C is now mandatory for P15 E materials if using electrical resistance heating pads. Also wondering what was driving that requirement.

 

[metengr]

The revision was to allow a larger spread in PWHT range to enable the pipe ID to reach 1300 deg F in lieu of 1350 deg F without exceeding the lower critical trasformation temperature for Grade 91 on the pipe OD surface. The rational was early work by Oak Ridge that performed PWHT at 1300 deg F. I was the project manager for this revision to BPV I.

 

[metengr]

For the non mandatory Appendix, BPV I wants to share best practices with PWHT of Grade 91 CSEF steel. You will be seeing more non mandatory appendices as part of the modernization program for BPV I.

 

[rmillercwi]

THanks Met..

It would also seem a step foward in joining grade 91 to 2.25 cr. by reducing carbon migration when using the lower temp. Or not?

Back in the day the reccomendation for welding grade 91 to itself was to use the higher range 1375/1425 and run it out for a minimum of 2 hrs. I have heard rumors that EPRI has trended away from that but cannot find the actual document to support that hypothosis. Was thinking perhaps the drop in temp to 1300 was related to it.

The latest read I can find free from EPRI is from 2015. In that document they state going down to as low as 1247F ( I realize not acceptable to BPV1)

 

[metengr]

rmillercwi
No, the lower PWHT temperature is unrelated to carbon migration. There is a new non mandatory appendix that you will see in the 2019 edition of ASME B&PV Code Section I. It is related to dissimilar metal welding guidance for Grade 91 steel.