PWHT, NDT and HT
PWHT, NDT and HT
(OP)
Do you,
1. NDT, PWHT and HT or
2. PWHT, NDT and HT or
3. NDT, PWHT, MPI and HT?
Any help will be much appreciated.
Thanks.
1. NDT, PWHT and HT or
2. PWHT, NDT and HT or
3. NDT, PWHT, MPI and HT?
Any help will be much appreciated.
Thanks.





RE: PWHT, NDT and HT
Normally, after welding you either re-heat treat or perform a local PWHT. It makes no sense to do both.
Regarding NDT before or after PWHT. This depends on the application. Some Standards require NDT after all weld repairs, which includes PWHT.
What is your application?
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
Typically PWHT, MPI And NDE then HT.
Volumetric NDE prior to PWHT can be done to substantiate the quality of the weld prior to heat treatment however usually you want to complete PWHT prior to NDE and hardness testing.
MPI on the other hand will cover all arc strikes and thermocouple removals after PWHT. In view of this there should be a comprehensive visual weld inspection to assure that the weld is fully filled and acceptable for any required NDE. This can reduce the possibilities of having to perform repairs which may need to be PWHT ....again.
Best of luck.
STEVE
RE: PWHT, NDT and HT
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: PWHT, NDT and HT
The HT naturally comes last. The real question I had was should the NDT be performed after or before the PWHT.
If the NDT is performed prior to the PWHT, isn't there a need to verify the weld condition after the heat treatment process? I have heard of weld defects following the PWHT.
If the NDT is performed after the PWHT, then any defects detected in the welds during the NDT, wont it call for another PWHT? Can a localised PWHT be performed in this case?
I thought it might be a good idea to NDT prior to the PWHT and following that a MPI/DPI, though cost can be an issue here (maybe even the real necessity for it).
How would the people in this forum choose to do it?
RE: PWHT, NDT and HT
Performing NDT before PWHT is really up to the purchaser, if it is not required by a code or standard. For certain materials and applications it is not necessary or you can perform some level of NDT before PWHT with the final NDT after PWHT as meeting code requirements. With the availability of low hydrogen electrodes and care during welding, the chances of developing problems during PWHT are minimal.
For heavy wall butt weld joints, we have used radiographic testing (RT) to shoot the root and at 1/4 wall thickness of weld deposit to assure no rejectable weld defects before completing the weld and going into PWHT. The highest probability of developing weld defects is during the early stages of welding where access or the control of preheat could be a problem for heavy wall material. The reason for having the NDT before PWHT was to avoid the cost and time to perform a second PWHT if we need to excavate weld defects.
RE: PWHT, NDT and HT
ASME VIII requires that NDE be performed after PWHT, but brfore HT. Most manufacturers will also do NDE before PWHT too.
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: PWHT, NDT and HT
Could you provide or site a specific location in Section VIII where this is required, not after welding, but after PWHT - does it pertain to a class of material for fabrication? I am more familiar with Section I, and I know there is no reference to NDT that must be performed after PWHT.
I am less familiar with Section VIII, and I don't recall a specific reference to NDT that must be performed after PWHT, only that NDT shall be performed of welds in accordance with the applicable sub paragraphs or parts.
RE: PWHT, NDT and HT
What is the base metal? Sec VIII does not require any NDE after PWHT except for certain alloys, notably straight chromium, see UHA 33. If your working with carbon steels or Cr Mo alloys, there is no requirement in Sec VIII for NDE after PWHT.
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
I am not in my office until late next week. I do not have access to ASME VIII at this time. Upon return I will advise relavent Code paragraph for you.
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
I should have asked you previously which division you're working to, however, per ASME Sec VIII, Div 1, there is absolutely no reason to perform NDE after PWHT on SA516-70 material. If you're working to Div 2 I can check tomorrow, 3-11-05.
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
I believe that there is absolutely every reason to perform NDE after PWHT as it is not unheard of to find weld cracks after cooling. I will cite the ASME VIII paragraph when I get back to my office and dig out my ASME Code.
Steve Braune
Tank Industry Consultants
www.tankindustry.com
RE: PWHT, NDT and HT
The conformity certificate should be issued for a material that was subject to all tehnological operations, (PWHT included). Therefore, the only results that are taken into consideration by inspectors are the ones for post-PWHT NDT.
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
In your case above there is no Code requirement to perform PWHT after heat treatment. However, as I already stated, there are many client specs that do and if so the manufacturer is pretty much obligated to do it before and after in case of repair.
RE: PWHT, NDT and HT
RE: PWHT, NDT and HT
In cases where NDT before PWHT is not specified it is up to the fabricator but it would seem prudent to apply NDT before PWHT as an insurance. It is an expensive excercise to repair and re-do a PWHT due to cracks, etc which could have been found before the equipment was put in the furnace.