Difference between ASME B31.3 and B31.1 for P4 to P4 GTAW

[K K]

Dear All,

I have query regarding PWHT,

I have qualified WPS and PQR, some lines class are belongs to as per B31.3 and B31.1, but the WPS and PQR are as per B31.3.

Regarding PWHT and Preheat, what is the difference between these two standards.

( I understand that 1) PWHT temperature for ASME P number 04 material is different from ASME B31.3 (process) : range 704-746°C to ASME B31.1 (Power) : range 650-700°C.)

Below I am mentioning WPS parameters for PWHT, please clarify me whether the parameters are correct or Not. 

Material : ASTM A 335 P11 to ASTM A 335 P11 - ( PNo-4; G.No-1 to PNo-4; G.No-1 )

Process : GTAW

Test coupon Thickness :  19.05 mm

PWHT- Temp range - 690°C- 705°C

Heating range : 200°C/hr

Cooling range : 200°C/hr

Interpass temp : 315°C

Post Heating : 300°C -350°C ; holding thickness 10mm to 20mm -30 min / 20mm to 30mm - 90min.

And regarding Backing -  PQR is qualified with Argon, can we use Nitrogen in WPS.

Please clarify me the above my doubts.

Thanks

Kiran