Re: [MW:36162] RT before PWHT for P1 (NACE/ H2 service)

Dear Mr. Chatterjee,

You have not indicated whether it is an H₂S service or a general type. PWHT can itself introduce or reveal 

problems such as

reheat/stress-relief cracking in susceptible weldments,

dimensional distortion,

cracking associated with high hardness/microstructural conditions and 

defects that were not detectable before PWHT.

So, if it is an NACE/H₂S service line, the project specification may require a final NDE after PWHT, even though 

B31.3 itself does not mandate it for P-No. 1.  

Welding → RT/UT → PWHT → final RT/UT → hardness check, where hardness control is an important means of 

controlling SSC susceptibility in carbon and LA steel weldments.

The first RT/UT is useful for finding weld defects. PWHT changes the weld metallurgy and residual stress condition. 

Final RT/UT (for a sour-service line with mandatory PWHT) could be an additional project/engineering requirement. 

Hence, you can decide based on your needs.

C. Sridhar.

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On Wed, 9 Sept 2026 at 11:26, Bhavani Prasad Emani <emanibhavani@gmail.com> wrote:

Hi KG,

Here is my reason for your question;

The reason to do NDT after PWHT for alloy steel is to verify the weld after the heat treatment has finished, because PWHT itself can create or reveal defects that were not visible right after welding.

Main reasons:

- Reheat/stress-relief cracking: Alloy steels, especially Cr-Mo types, can develop cracks during PWHT.

- Delayed cracking: Hydrogen-related cracks or other delayed defects may appear after welding and only become apparent later.

- Defect growth or opening: Existing small discontinuities may grow or become detectable during thermal cycling and stress relief.

- Final acceptance condition: The inspection must ensure the component is fit for service before it is put into operation. 

So, in practice, post-PWHT NDT is done to catch defects caused by the heat treatment itself and to confirm final code acceptance of the finished weld.

Thanking you,

With best regards,                                            

           

Bhavani Prasad Emani,
Associated Engineering Services
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On Tuesday, September 8, 2026 at 06:50:57 PM GMT+5:30, Kannayeram Gnanapandithan <kgpandithan@gmail.com> wrote:

What is the reason to do NDT after PWHT for alloy steel. 

THANKS & BEST REGARDS,

KG.PANDITHAN, BE, IWE,  

ISO 9712 Level 2 in VT,

ASNT-Level II in PT,MT,RT & UT,

LA ISO 9001-2015, ISO 3834, EN 1090 & EN 15085, 

International Welding Engineer. 

CONSULTANT-WELDING & QUALITY

Mobile no: +919940739349

On Tue, 8 Sept 2026, 17:00 Bharath Kumar, <vbmkumar1988@gmail.com> wrote:

Hi 

The requirement for examination after PWHT usually comes from the construction code/specification, service requirements, or project specification, not simply from the P-No. designation.. in my understanding the material like Pno 3/5A,5B,5C basically a alloy materials it's metallurgical behaviour during welding and followed by heat treatment will be different than normal carbon steel material. These material may occur delayed cracks unlike carbon steel it could be a one of reason for NDT after PWHT . But normally carbon steel material it's not mandatory to do RT/UT before PWHT unless specified by client requirement. You can perform after PWHT but you should ensure the weld free from surface defects ( by PT/MPI) before PWHT. 

BR

V.Bharathkumar

On Tue, Sep 8, 2026, 8:34 AM 'ranajit chatterjee' via Materials & Welding <materials-welding@googlegroups.com> wrote:

Dear Sirs,

As per ASME B31.3 clause no.341.3.1(a) mentioned P Nos.3,4,5A,5B,5C AND 15 materials examination(RT/UT) shall be performed after completion of heat treatment. But no information for P1 material whether NDT performed before or after PWHT.

Please advise can we perform NDT(RT/UT) before PWHT activity for P1(NACE/H2 service) material or not.

Regards,

Ranajit Chatterjee

9995018265

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