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PWHT, NDT and HT
- Thread starter Angsi
- Start date
It really depends on the application and Standards you are required to follow. Why would you heat treat (HT) and perform a PWHT?
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?
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?
By HT do you mean Heat Treat or something else like Helium Leak Test? Just a further note, if customer specs or the code you're working to stipulate NDE after PWHT, you'd be well advised to perform and clear all such NDE before PWHT to avoid a situation where repairs are necessary after PWHT.
lostsailor
Structural
I suspect HT is meant to denote hydrostatic test
If HT relates to hydrostatic testing; I would prefer option 2. NDT before PWHT is something that is optional, and depends on various circumstances. As a purchaser of equipment, I may not want to spend the money to have NDT performed before PWHT. NDT, if required by the particular code or standard, should be performed after welding and before hydrostatic testing.
I suspect HT means hardness test.
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
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
Too much guessing about meaning of HT. Santhuru... what do you mean by HT?
Steve Braune
Tank Industry Consultants
Steve Braune
Tank Industry Consultants
- Thread starter
- #8
I am terribly sorry. By HT I meant hydrotest, PWHT=Post Weld Heat Treatment and NDT=Non-Destructive Testing.
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?
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?
As I stated earlier, the codes do not provide specific fabrication detail or guidance that you are looking for, only requirements for NDT, PWHT and hydrostatic testing for new construction. I believe one of the ASME power piping codes does mandate NDT after PWHT but not ASME B&PV code. Once the welding is completed, one can take credit for NDT before PWHT or after. If you choose to perform NDT before PWHT to satisfy code requirements, I would perform a wet fluorescent MT of the weld joint after PWHT. If for some reason hydrogen cracks were to develop prior to PWHT, in most cases the cracks would probably open to the surface (as a means of allowing dissolved hydrogen to diffuse out of the weld or base metal), and would be detected by a surface exam. Weld defects, on the other hand, will be detected by NDT performed after welding is completed – regardless of PWHT. The rationale is that PWHT does not cause LOF, IP, slag or weld metal shrinkage cracks.
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.
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.
metengr,
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
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
Steve Braune;
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.
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.
Santhuru
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.
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.
metengr,
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
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
- Thread starter
- #16
Santhuru,
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.
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.
- Thread starter
- #18
weldtek,
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
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
adrianviorel
Mechanical
Steve is right. We are doing NDT before PWHT, simply to avoid this operation to be done for improper welds(let's just say it is an assumed extra cost).
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.
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.
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