thePetroStreet

We are using a carbon steel pipe 12" schedule 120 pipe for fabrication of a small heat exchanger shell.
Now what should be the code need to be followed for PWHT requirements? As per ASME B31.3, the qualifying thickness is 20mm and ASME VIII div. 1 requires PWHT for thickness greater than 38mm. Our pipe thickness is 25mm.

What's the pipe ASTM?
Design code?

I believe if you have used the material as allowed by the design code than all other requirements would also be applied from the same code.
In your case, you must have designed the exchanger shell as per ASME VIII Div.1 so you may not perform any PWHT.

it should be asme sec 8, div 1. In our plant also, such exchangers r there and not post weld heat treated. By the way, one query id there: what is the logic behind difference between governing thickness for pwht in sec 8 div 1 & b31.3 for same material?

Thanks all.
Ben: It's A-106 Gr. B pipe and we have done the design calculations as per ASME VIII div. 1.

Octane: You have to follow the requirements as in ASME VIII Div. 1. No need to PWHT.
Jiteshvk: Pressure vessels only face the circumferential and longitudinal stresses however piping due to its lay-out / routing undergoes torsional stresses also. That's the reason in piping code for carbon steel material PWHT is mandatory when thickness exceeds 20 mm.

thanks, ben. now its clear to me

Thanks everybody.