If you x-ray after PWHT and you have a defective weld that needs re-work then you will have to re-heat treat that weld. Not sure what the benefit of that would be.
Some specifications call for NDE (pick your favorites) before and after PWHT. The intent of this is to find issues and fix them prior to the PWHT while still discovering cracks which may occur days after the welding is completed or as a result of the stress redistribution during PWHT. For example, you might see RT and PT prior to PWHT and PT again after the PWHT.
Just depends on how critical the vessel is perceived to be. Or if it's fabricated of V-modified materials. Though I hear claims that the cracking issues of a few years ago have been resolved.
But... the OP's question was strictly Code requirements, not "good practice" or owner's specification related.
jte, our concern is is how do you certify PWHT is satisfactory. Or the normal procedure is only to PT after PWHT?
My initial question was: If the code orders or not to RT after PWHT?
You either read the PWHT charts to understand what time and temperature was applied to the pressure retaining item or you can use hardness testing to check if the weld and surrounding base metal heat affected zone have been tempered from PWHT.
Well, for example several weeks ago I was reviewing a project heavy wall spec which is being proposed by an E&C for use on one of my company's projects which called out substantial pre- and post- PWHT NDE. Sorry - don't want to get more specific about which companies and which project. The point is that they do exist. At least one of our generic reactor spec's requires RT prior to PWHT and more NDE post-PWHT.
Would that job you currently have be fabricated of a PWHT limited material - perhaps one for which the welding procedures are only qualified to three or four PWHT cycles?
That's typically where I'd expect pre-PWHT RT requirements. When you perform pre-PWHT RT, then it is not unreasonable to ask for post-PWHT NDE - whether thats RT, PT, MT, shear wave, etc. is up to the spec writer. As mentioned, if its in the spec, then the owner is willing to pay for the extra effort in order to receive a more reliable / maintainable vessel.
According to ASME Sec VIII,DIV-1,welds have to be radiographed,as a part of the design efficiency, e.g RT-1,RT-2.... and others. No code will specify at what point of fabrication NDE (such as RT) has to be done, if so that becomes too binding. Often clients spefication, which is more suited to service conditions, specify if RT shall be done before or after PWHT.
Usually from codes perspectives for steels which are not prone to serious cracking (e.g P1,P3,P4,P5A) RT shall be done on completion of fabrication, prior to PWHT. For steels which may develop cracking upon PWHT, through secondary hardening, such as P5B, P5C additional NDE (RT/UT or others) should be done following PWHT, to safeguard the components.
From ASME perspectives, for PI materials RT shall be done prior to PWHT. If there is any additional project requirement of RT after PWHT it is above the code requirements.
