Welding ASME P5A to P5B 1

[nnlpba]

I am joining ASME A335 grade P22(2-1/4 Cr 1 Mo) to A335 grade 5b(5 Cr 1/2 Mo). Which electrode should be used E9018-B3 or E8018-B6? Should the preheat and PWHT be performed in accordance with the P5b or the P5a material?

 

[metengr]

I would use the E9018 B3 electrode. The preheat and post weld heat treatment should follow the P-No 5B requirements without exceeding the lower critical transformation temperature for P-No 5A (which is 1480 deg F). I believe the PWHT range is similar for P-No 5A and P-No 5B, per B31.1, with minor overlap in temperatures for ASME Section I PWHT requirements.