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NDT before or after the PWHT

NDT before or after the PWHT

Postby zirsald » Tue Nov 05, 2013 2:03 pm

Dear forum members,
Could you please let me know if the NDT's shall be done before or after the PWHT and kindly indicate to me specific paragraph(s) of welding code(s)
Thanks
zirsald
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Re: NDT before or after the PWHT

Postby arweldcon » Mon Nov 11, 2013 12:09 pm

Dear Zirsald,
Please let me consider that question as a non complete question since you have not specified the material, the welding code, etc.
In general, if it is for carbon steel, NDT shall be performed after welding but if PWHT is a part of the welding technology, then it should be performed after PWHT. Nevertheless, in order to save time and money it’s better to do an extra NDT after welding and before PWHT because in case of defect you can repair before PWHT and thus to avoid an extra PWHT cycle.
regards
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Re: NDT before or after the PWHT

Postby wefel » Mon Nov 11, 2013 5:04 pm

For carbon and low alloy steels ASME VIII-1 doesn't define that RT (and thus all other NDTs) shall be performed after PWHT. Instead if it is for some high alloy steels (please have a look at UHA-33 of ASME VIII-1) then the RT/NDTs shall be made after PWHT has been performed. That is because a delayed hydrogen cracking could happen. For the same reason the par. 341.3.1(a) of ASME B31.3 states that "for P-numbers 3,4 and 5 materials, examination shall be performed after completion of any heat treatment".

Nevertheless, I suggest you always perform dual NDT (before and after PWHT). Perform before PWHT in order to save time and money avoiding an extra PWHT cycle as claimed by arweldcon and perform after PWHT since, except the reason already mentioned regarding some high alloy steels, the heat cycle of PWHT may cause degradation and/or distortion of microstructure and thus unacceptable defect(s) may emerge.
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