You should first determine what the code of construction is. The code will lay out PWHT and NDE requirements. Engineering design usually includes reference to the appropriate code of construction. If one isn't specified, I recommend ASME B31.3.
As a general rule, required NDE must be performed after PWHT.
When we have to do PWHT on a weld; we do NDE before the PWHT for info. When the PWH is completed we do the final NDE. We do this in order to find out if there is a known defect present before going through the costly practice of doing the PWHT only to have to do it agian if a repair is needed.
Charles.
jm812,
You have mentioned normal fluid service so I presume you mean B31.3.
If this is the case you will find Section 331 and Table 331.1 will give you all the information you require,
Regards,
Shane