Effects on PWHT on P22 and A106B 1

[Liao DH]

I am currently working on a new PQR for P22 and A106B welding. I am using a A335 P22 pipe on one side and A106B pipe on the other. Pipe size is 3" sch80. I have done an X-ray before and after the PWHT process and there was no visible defects. My PWHT procedure is as follows, preheat till 230 degrees C before an inclination and declination of 100 degrees C per hour till it reaches 690 degrees C. As per section XI and ASME B31.1, I have held the temperature for 1hr. When the mechanical tensile test was performed, it cracked at the A106B base metal. The minimum tensile strength of the metal is 415 Mpa, however results show that it became 403 after PWHT at the 6 o'clock position and 440Mpa at the 12 o'clock position. Could there have been something wrong with the PWHT procedure which led to the decrease in tensile strength? On the mill certificate the tensile strength of the A106B material is 515Mpa.

 

[0707]

What was your cooling rate? At what temperature did you shut off the heating resistences. What had been your hardnesses in both base metals, and on the seam weld in the end of the PWHT? Did your weld during the cooling be covered with ceramic blankets?

luis

 

[weldstan]

B31.1 does not require PWHT for this thickness and diameter of the P22 alloy. Furthermore the PWHT temp does not meet the minimum required for P22 (1300F min) unless B31.1 has changed.

PWHT at 690 C will adversely affect tensile strength of A-106B but in almost all cases that I have performed such PQR tests after PWHT at 1320F, I have not seen reduction below the minimum specified tensile requirements. But it can happen. Note that the MTR is not indicative of the actual strength of your A-106B coupon.

 

[r6155]

Repeat the PQR and stay present during welding test coupon. Only preheat, no PWHT.
Put your stamp and check them before and after machining the test pieces.

Regards

 

[Liao DH]

@0707 Cooling rate is 100 degrees per hour as well. Max hardness is at welding seam of value 240Mpa, base metal hardness is 198Mpa.HBR values. While cooling it was covered with blanket until 200 degrees C then it was removed.

@weldstan and @r6155 are you guys able to show me the section which shows that it is not required. From table 132 of section B31.1 i see that there is a min PWHT temperature for group 1 and group 5B(P22). Moreover, P22 requires mandatory PWHT.

 

[r6155]

P22 is P-Number 5A (not 5B)
See Table 132.2-1 Exemptions to Mandatory Postweld Heat Treatment

Regards