Code requirement/valid reason why NDE MUST be done after PWHT 1

[ndeguy]

PWHT is approx 1 hour @ 650 deg Celsius on P1 (low carbon) steels. Is there a Code requirement (ASME/ANSI/API/EN/SNiP) that such NDT MUST be done after PWHT?

What do forum members think of a suggestion for NDT before PWHT only. If all unacceptable RT indications are repaired prior to stress relief (1 hour @ 650 deg), is there any likelihood/possibility of stress relief of P1 materials causing metallurgical problems or acceptable/undetected indications to open up which may then be detected by RT and be cause for rejection. Is the latter realistic or is NDT after PWHT on low carbon materials just a convention.

Thanks in advance for your comments.


Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[metengr]

ndeguy;
For P-No 1 materials, NDT can be performed prior to or after PWHT. There is nothing in the Code that mandates NDT after PWHT for P-No 1 base materials, only NDT after the completion of welding.

Keep in mind that most Codes and Standards provide only minimum requirements. The Engineer nor Owner can always specify above and beyond these requirements.

Here is my opinion for what it's worth;
For P-No 1 and P-No 3 base materials, if proper welding practice is followed (using low hydrogen electrodes specified minimum preheat and interpass temperatures), I will permit volumetric NDT to be performed (if required by Code) prior to PWHT provided a surface NDT is performed after PWHT.


For P- 4 and P-No 5 base materials, I normally specify NDT after PWHT. In most cases, mechanical contractors will perform volumetric NDT during welding and certainly before PWHT because they have to assure a final (after PWHT) NDT.

 

[metengr]

An additional comment to the above because I did not state my rationale for mandating NDT after PWHT; welding of P-No 4 and P-No 5 base materials requires more caution, because of the higher alloy content in these materials, versus carbon steel. With higher alloy content comes increased hardenability and hydrogen cracking becomes more of a concern. So, this is my rationale for specifying NDT after PWHT (ASME Power Piping Code provides similar guidance of NDT after PWHT, versus ASME B&PV Code) for these groups of air hardening steels.

 

[stanweld]

ASME B31.3 requires examination after PWHT for P Nos. 3, 4 and 5. Ref. 341.3.1(a).

 

[JoeTank]

API-650 requires MT after PWHT

Joe Tank