ASME Section III-D PWHT/NDE question

[lostsailor]

Gentlemen,
I am also posting this question on the Nuclear Engineering forums but since this one seems to get more traffic I hope
you will excuse my presumption.
A pressure vessel is to be constructed in accordance with ASME III-D requirements and will be constructed of P-4X material, radiographed in accordance with Code requirements, and subjected to a PWHT of 725 degrees F (the purpose of which has not yet been ascertained ).
As the PWHT is neither required nor prohibited by the Code, per Table ND-4622.1-1, it has been suggested that the vessel can be subjected to RT prior to the PWHT being done with no additional NDE after PWHT, as stipulated in ND-5120.
My read on this is regardless of whether or not PWHT is mandated by the Code, RT should always be performed after PWHT, unless specifically exempted by the Code, due to the possible complications arising from the PWHT process.
Just looking for some additional opinions.

Regards,
RLS

 

[ApC2Kp]

lostsailor,
Code requires an RT after PWHT on specific materials. Examinations done after PWHT will detect flaws that might open up or appear after the thermal expansions of high temperature.
Some examinations are done before and after a PWHT in order to catch and repair flaws before PWHT, so that it could save a second PWHT of weld repairs detected on first round. It depends on how involved and cost of the PWHT.
A 316 SS vessel of 10 ft diameter and 60 ft length was heat treated to 1800F (red hot) in the large oven of CBI shop in Jasper, AL. The P-8 material is not required by Code to be PWHT, but we wanted to minimize welds sensitivity to chlorides. Since fabrication was done in Knoxville, it made sense to RT before PWHT, and then repeat RT when it was returned to fabricator's shop before the hydro test in Knoxville.
If it was a small vessel or item handled in same shop with a local PWHT, then the consequences of finding flaws after the PWHT are minimal, even with a repeated PWHT.

 

[Kerhin]

Most Codes allow RTs either before or after PWTH. I typically opt for after PWHT since the PWHT may have relieved stresses to the point of initiating a crack. However, at the temperature you are using I cannot imagine that this would be an issue, so prior to PWHT would be fully acceptable. The only heat treatment I know of for Inconel type alloys is called stress equalizing for work hardened nickel alloys. Performed in the range of 500 to 700 deg.F results in a partial recovery of coldworked material.

 

[metengr]

Unless required by a particular Code or Standard, NDT after PWHT is good engineering practice. As I have stated in the past, the Code provides minimum requirements.

If the customer so chooses, NDT can be added prior to and after PWHT for those materials where delayed cracking or stress relief cracking is a concern.

Now back to your specific case, with such a low stress relief temperature of 725 deg F, I would not bother to perform any NDT for this P-4X series material. From a metallurgical viewpoint, NDT after welding is fine and meets the Code requirements. Adding another layer of NDT after this low temperature stress relief will serve no useful purpose for this class of material.