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16837 views
00:59 Jun-19-2007

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
NDT before and after PWHT low carbon steel

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.


 
03:24 Jun-19-2007

Mark Badrick

Inspection
Bahrain Petroleum Co,
Bahrain,
Joined Oct 1999
11
Re: NDT before and after PWHT low carbon steel ----------- Start Original Message -----------
: 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.
------------ End Original Message ------------

Nigel, this was the subject of a recent discussion here and I can make the following comments, which are my personal views – others may add or disagree:

1. In our case PWHT on carbon steel is generally service related e.g. Carbon steel pipe work in Amine and Caustic service.
2. The code says that NDT should be performed after welding and as heat treatment is a part of the welding technology, it should be performed after heat treatment.
3. Many sites will want to perform NDT before heat treatment as this saves the time and money of having to repair welds and again perform heat treatment on the repair. As the owner we are willing for the contractor to do the NDT before heat treatment, but at his own cost.
4. The NDT carried out before heat treatment should be the same as the NDT carried out after heat treatment. Generally the NDT before heat treatment has been radiography, but as the owner we have substituted this for UT after heat treatment. The theory being, that the only repairable defects likely after heat treatment (if this has not been performed correctly) is cracking and the preferred method for crack detection in this instance would be UT.

Hope this helps.

Mark





 
06:44 Jun-19-2007

Dent McIntyre

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
247
Re: NDT before and after PWHT low carbon steel ----------- Start Original Message -----------
: : 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, this was the subject of a recent discussion here and I can make the following comments, which are my personal views – others may add or disagree:
: 1. In our case PWHT on carbon steel is generally service related e.g. Carbon steel pipe work in Amine and Caustic service.
: 2. The code says that NDT should be performed after welding and as heat treatment is a part of the welding technology, it should be performed after heat treatment.
: 3. Many sites will want to perform NDT before heat treatment as this saves the time and money of having to repair welds and again perform heat treatment on the repair. As the owner we are willing for the contractor to do the NDT before heat treatment, but at his own cost.
: 4. The NDT carried out before heat treatment should be the same as the NDT carried out after heat treatment. Generally the NDT before heat treatment has been radiography, but as the owner we have substituted this for UT after heat treatment. The theory being, that the only repairable defects likely after heat treatment (if this has not been performed correctly) is cracking and the preferred method for crack detection in this instance would be UT.
: Hope this helps.
: Mark
------------ End Original Message ------------


As the NDE manager of a large fabrication company for many years I have had this discussion many times.

Bottom line is RT and UT do not find the same discontinuities so the same test needs to be performed before as is performed after PWHT.

Second issue is particular to UT since PWHT is not likely to change response to indications you have to make sure your UT repeatability is as good as can be expected. We always were a little more conservative in our calls before PWHT because of the repeatability issue. Also make sure that you do not significantly change the surface finish after PWHT.



 
08:55 Jun-20-2007

Mark Badrick

Inspection
Bahrain Petroleum Co,
Bahrain,
Joined Oct 1999
11
Re: NDT before and after PWHT low carbon steel ----------- Start Original Message -----------
: : 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, this was the subject of a recent discussion here and I can make the following comments, which are my personal views – others may add or disagree:
: 1. In our case PWHT on carbon steel is generally service related e.g. Carbon steel pipe work in Amine and Caustic service.
: 2. The code says that NDT should be performed after welding and as heat treatment is a part of the welding technology, it should be performed after heat treatment.
: 3. Many sites will want to perform NDT before heat treatment as this saves the time and money of having to repair welds and again perform heat treatment on the repair. As the owner we are willing for the contractor to do the NDT before heat treatment, but at his own cost.
: 4. The NDT carried out before heat treatment should be the same as the NDT carried out after heat treatment. Generally the NDT before heat treatment has been radiography, but as the owner we have substituted this for UT after heat treatment. The theory being, that the only repairable defects likely after heat treatment (if this has not been performed correctly) is cracking and the preferred method for crack detection in this instance would be UT.
: Hope this helps.
: Mark
------------ End Original Message ------------

Further to my answer above, the problem with a change of NDT method after PWHT as with point 4 above - you may find original unacceptable defects with the UT that were missed or misinterpreted by the radiography. So as a general rule it would be better to do the NDT after PWHT, but as we all know, at the end of the day, if it is within the scope of the code, it is the financial/time implications that will dictate when and what NDT method is used.

Mark


 
05:23 Jun-20-2007

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
Re: NDT before and after PWHT low carbon steel Mark and Dent

Thank you both for your valuable responses. I have already written one lengthy response which unfortunately crashed on me so I think this one will be shorter!

We actually have a Russian code requirement (SNiP) for RT before PWHT followed by 20% UT after PWHT specifically to search for cracks, which I suppose is the perceived PWHT problem especially with higher alloy materials, groups P3, 4 and 5.

Many fabricators radiograph welds before PWHT and make any necessary repairs prior to performing PWHT followed by RT and film presentation to the client. This prevents the need for repeat HT cycles. I think most of our WPS's are done at 3 cycles.

Now its our Construction QC Supevisor's contention that he has never known a case where an acceptable indication pre PWHT becomes unacceptable post-PWHT. Especially for low carbon steels, where hardenability and hydgogen cracking are of little concern, I agree with him, I have not know it happen, however I would not extrapolate that to a definitive "It never happens". I am certain it has done or it will do. And of course there is no insurance policy of the NDT if before PWHT only NDT is approved.

And the bottom line is about finance - extra shutdown days to complete radiography being embarrassing for all.

Thanks again for your replies


----------- Start Original Message -----------
: : : 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, this was the subject of a recent discussion here and I can make the following comments, which are my personal views – others may add or disagree:
: : 1. In our case PWHT on carbon steel is generally service related e.g. Carbon steel pipe work in Amine and Caustic service.
: : 2. The code says that NDT should be performed after welding and as heat treatment is a part of the welding technology, it should be performed after heat treatment.
: : 3. Many sites will want to perform NDT before heat treatment as this saves the time and money of having to repair welds and again perform heat treatment on the repair. As the owner we are willing for the contractor to do the NDT before heat treatment, but at his own cost.
: : 4. The NDT carried out before heat treatment should be the same as the NDT carried out after heat treatment. Generally the NDT before heat treatment has been radiography, but as the owner we have substituted this for UT after heat treatment. The theory being, that the only repairable defects likely after heat treatment (if this has not been performed correctly) is cracking and the preferred method for crack detection in this instance would be UT.
: : Hope this helps.
: : Mark
: Further to my answer above, the problem with a change of NDT method after PWHT as with point 4 above - you may find original unacceptable defects with the UT that were missed or misinterpreted by the radiography. So as a general rule it would be better to do the NDT after PWHT, but as we all know, at the end of the day, if it is within the scope of the code, it is the financial/time implications that will dictate when and what NDT method is used.
: Mark
------------ End Original Message ------------




 
10:36 Jan-25-2017
B.GOPI KRISHNA
Re: NDT before and after PWHT low carbon steel In Reply to Nigel Armstrong at 00:59 Jun-19-2007 (Opening).

After heat treatment NDT-RT is required or not. If required please suggest me through IBR code or ASME code with reference clause.

 
14:27 Jan-30-2017

Steven Doc

Other, Quality Manager
Siemens Energy,
Egypt,
Joined Feb 2011
187
Re: NDT before and after PWHT low carbon steel In Reply to B.GOPI KRISHNA at 10:36 Jan-25-2017 .

ASME I it is entirely up to you, ASME B.31.1 it shall be carried out after PWHT for material groups P3,4,5A,5B & 15E, as prescribed in para 136.4.1.

 
07:43 Feb-02-2017

Shane Feder

, Quality Co-ordinator (SubSea)
Thailand,
Joined Dec 2014
76
Re: NDT before and after PWHT low carbon steel In Reply to Steven Doc at 14:27 Jan-30-2017 .

B31.3
341.3 Examination Requirements
341.3.1 General.
For P-Nos. 3, 4, 5A, 5B, 5C, and 15E materials,
examinations shall be performed after completion of
heat treatment.

 


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