P91 TO STAINLESS STEEL GR304

[qualitypro]

What are the constraints while welding P91 to stainless steel small bore pipes? What should be the minimum preheat, maximum interpass temp and post weld heattreat temperature? Is an Inconel wire/ rod appropriate for producing a quality weld?

 

[ijzer]

preheat 200 Deg. C
max . interpass 250 Deg. C
Cool down to ambiant before PWHT 750-760 Deg. C
Inconel wire type ER NiCr-3 is adviced.

 

[jonford]

I don't think you have given enough information for anyone to give you a adequate response. The preheat is given by the code of record and the P91 will govern here. For ASME B31.1, P91 requires a 400 degree preheat(ref. 131.4.5). You then need to concern yourself about interpass for the stainless. Whatever value you choose, you need to qualify your procedure to Section IX and have it pass the tensile tests. As for PWHT, again the code will give you requirements. For B31.1 it is 1300 to 1400 degrees for P91.

My company's procedure uses a 400 degree preheat, interpass max of 600, PWHT of 1350 +/- 25, and ER NiCr-3 wire.

I gave you the information not knowing which code you are fabricating to. Most ASME codes are similar (but not exact) in their numbers.