The PWHT requirements are normally specified by the code of construction. For your case, I would presume you would be working under ASME B31.3. If so, the PWHT requirements are specified by material composition and thickness of the pipe.
Welding procedures can be downloaded from AWS web site, go to publications look for procedures starting with letter "B" (B2.1-1-16 is the procedure for SMAW) these are pre-qualified procedures.
zishan 99,
If the governing Code is B31.3, the PWHT required based on thickness could be deleted per 331.2.2 (a) with acceptance of the Owner. PWHT is neither required nor is it prohibited per API 1104.