RT before PWHT for P1 (NACE/ H2 service)

[ranajit chatterjee]

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

[Bhavani Prasad Emani]

Hi Ranajit, 

Here are some suggestions regarding your requirement,

Yes. For P-No. 1 carbon-steel materials, ASME B31.3 does not impose the same mandatory “examine after heat treatment” requirement that it explicitly imposes on P-Nos. 3, 4, 5A, 5B, 5C and 15E.

1. What B31.3 clause 341.3.1(a) actually requires

In the current B31.3 wording, Clause 341.3.1(a) states that for P-Nos. 3, 4, 5A, 5B, 5C and 15E, examinations are to be performed after completion of heat treatment. P-No. 1 is deliberately not included in that list.

Therefore:

| Material          | B31.3 clause 341.3.1(a) specific post-heat-treatment requirement |

| ------------      | ---------------------------------------------------------- |

| P-No. 1           | No   |

| P-No. 3           | Yes |

| P-No. 4           | Yes |

| P-No. 5A/B/C  | Yes |

| P-No. 15E       | Yes |

So, from B31.3 clause 341.3.1(a) alone, RT/UT of a P-No. 1 weld may be performed before PWHT.

This interpretation is also consistent with the historical ASME interpretation addressing P1/P2 materials, which concluded that the B31.3 post-heat-treatment examination requirement does not apply to them. 

2. But your NACE/H₂S service changes the practical recommendation

This is the important part.

If your P-No. 1 piping is NACE/H₂S sour service, I would not recommend treating pre-PWHT RT/UT as the final examination unless the project specification/design document explicitly permits it.

The reason is not clause 341.3.1(a) itself. It is the sour-service/material specification and project requirements.

For example, PWHT can alter:

* weld-metal and HAZ hardness

* residual stresses

* hydrogen-related susceptibility

* microstructure

* potential crack behavior

Therefore, if PWHT is specified for the sour-service system, the conservative and technically preferable arrangement is:

Welding → preliminary NDE → PWHT → final NDE

For example:

VT → PT/MT as applicable → RT/UT (pre-PWHT if desired) → PWHT → final RT/UT → hardness examination

The pre-PWHT examination can be useful for detecting weld defects before PWHT, while the post-PWHT examination provides the final acceptance examination.

3. Can RT be performed before PWHT?

Yes — for P-No. 1 under B31.3

There is no prohibition in clause 341.3.1(a) requiring P-No. 1 RT to wait until after PWHT.

However, if you perform RT before PWHT and subsequently carry out PWHT, I would distinguish between:

Pre-PWHT RT = preliminary/control examination

and

Post-PWHT RT = final examination, where required by the project specification, client specification, sour-service specification, or engineering design.

This is particularly advisable where the line is designated NACE MR0175 / ISO 15156 sour service.

4. What about UT?

The same basic principle applies.

For P-No. 1, B31.3 clause 341.3.1(a) does not mandate that UT be performed after PWHT.

However, if the project requires final UT after PWHT, or if the engineering specification says NDE shall be performed after PWHT, that requirement takes precedence.

Also, the UT technique itself must be suitable for the material, thickness, weld configuration and examination stage. Some UT procedures may be affected by PWHT condition and calibration requirements.

Thanking you,

With best regards,                                            

           

Bhavani Prasad Emani,
Associated Engineering Services
#3-5-944/205-206 & 220-221,
2nd Floor, Panchavati Mall,
Narayanaguda, Hyderabad, India.
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[pradip kumar Sil]

For P -1 material , there is no restriction, you can conduct either before or after. Check the client spec if anything mentioned

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[SENTHILKUMAR SWAMINATHAN]

Before is not mandatory, but to make sure no any defects. 

After PWHT if any not acceptable defects you have do again PWHT

Before PWHT Volumetric NDT Accepted then 95% sure except Crack After PWHT Volumetric NDT will get accepted.

After PWHT Surface NDT should perform as a good practice.

Thank you, 

Regards, 

S.SENTHILKUMAR

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[venkateswara reddy Desireddy]

Most of clients specifications after PWHT NDT only consider as final NDT.

Code , client spec shall be meet the testing requirements.

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[Bharath Kumar]

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

--

[Kannayeram Gnanapandithan]

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

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[Bhavani Prasad Emani]

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
#3-5-944/205-206 & 220-221,
2nd Floor, Panchavati Mall,
Narayanaguda, Hyderabad, India.
Mob.No: +91 9032585485
Website: www.aesinspections.in,
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[pradip kumar Sil]

It's a because present stabilizing element as well high content of alloying element like Cromium.

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[sridhar cn]

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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[Hareesh K V]

Dear Sir,

Yes you can do it if your other specifications is not restricting the same. That will not be a code violation.

Regards 

Hareesh K V

Mechanical Engineer 

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