PWHT Requirement for piping materials in Hydrogen Service and Wet Sour Service 1

[ATUL KHATRI]

Hydrogen Service
ASME 31.3 gives exemption from PWHT for P.No 1 (carbon steel piping material) irrespective of thickness with a clause of Preheating above 25mm nominal thickness . So still "carbon steel with PWHT" curve shall be applicable as per API RP 941 ?

If yes than will there be any governing thickness for the same?

Wet Sour Service
Requirement of PWHT for SSC (Sulfide stress cracking) and associated crackings HIC,SOHIC is not clearly mentioned in NACE MR0103 for piping material. What should be the criteria for the same ? Though MR0175 does exempt the requirement of PWHT if CS, LAS comply the hardness requirement as mentioned in Table A.1 of MR0175.Please clarify

 

[SJones]

1.
No. Without the specific application of the requisite PWHT, the benefit cannot be accounted for.

2.
The criterion will be the specification directive of the purchasing party as to which elements of NACE SP0472 they wish to apply to CS. For LAS, again the particular approach vis a vis PWHT or hardness testing needs to be specified.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[Dhurjati Sen]

Dear Atul,

B 31.3 gives "Exceptions to Basic Requirements" regarding heat treatment not only for P No 1 but for all materials. That does not mean you skip PWHT for Hydrogen Service for any thickness of CS material.

Same logic holds for Wet Sour Service.

It is always better to follow the code rather than to focus on its exemptions.

Regards.



DHURJATI SEN

 

[pradipgoswami]

B-31.3 exemption clause does not mean that one can walk away from PWHT by application of preheat. According to Table 331.1.3 :-With respect to exemptions From PWHT [Notes (3)–(5)] has also to be referred.
Refer applicable Note(4):- No exemptions are permitted for PWHTs required by the designer or the WPS.
For wet Hydrogen service "PWHT" is a mandatory requirement. You may refer NACE International Publication 8X194 for clarifications.

API RP-941 applies more to safeguard against HTHA, not for wet H2S environments.
Hope it clarifies your query.


Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[weldstan]

For hydrogen piping review B31.12.

 

[ATUL KHATRI]

Thanks to all for sparing time to respond.

@pradipgoswami (Materials)
NACE 8X194 clearly exclude piping and atmospheric tanks from its scope. So i believe this may not govern the Heat treatment requirements for piping in WET H2S service.

I didn't mention API RP-941 for wet H2S service.

Dhurjati Sen (Materials)

I am still looking for clear guidelines for hydrogen service (applicable to HTHA) and Wet H2S service.

weldstan (Materials)

Table GR-3.6.1-1 (Requirements for Post Weld Heat Treatment of Weldments) of ASME B31.12 also exclude PWHT requirement till 20 mm nominal thickness.
Than should it be criteria for PWHT for hydrogen service ?

 

[weldstan]

Brfore I retired, a few Owners defined B31.12 to be used on some of our/their projects. Others defined B31.3.

 

[Dhurjati Sen]

Dear Atul,

Check API RP 571 for clear guidelines for wet H2S service.

Regarding HTHA, it was not mentioned in your original post.

Regards.

DHURJATI SEN

 

[pradipgoswami]

Hi Atul ,

Some rationales from API-RP-571 on materials/damage mechanisms in wet H2S service are as below.Note while providing the exemption clauses, ASME B-31.3 clearly states:- Note(4):- No exemptions are permitted for PWHTs required by the designer or the WPS.

Hence the exemption is not across the board. A good understanding of wet H2S service damages definitely would be helpful.

According to API RP-571, Wet H2S Damage could be of many types
• Blistering
• HIC
• SOHIC
• SSC

The effects of PWHT as defined by RP-571 are as follows:-

• Blistering and HIC damage develop without applied or residual stress so that PWHT will not prevent them from occurring.
• High local stresses or notch-like discontinuities such as shallow sulfide stress cracks can serve as initiation sites for SOHIC. PWHT is highly effective in preventing or eliminating SSC by reduction of both hardness and residual stress.
• SOHIC is driven by localized stresses so that PWHT is also somewhat effective in reducing SOHIC damage.
Prevention / Mitigation:-
• SSC can generally be prevented by limiting the hardness of welds and heat affected zones to 200 HB maximum through preheat, PWHT, weld procedures and control of carbon equivalents. NACE RP0472 provides additional details.
• PWHT can also help to minimize susceptibility to SOHIC.
• PWHT has limited value in preventing blistering and HIC damage from initiating but is beneficial in reducing residual stresses and strength levels that might otherwise contribute to crack propagation,
Additional Resources:-
1.

https://www.ogj.com/articles/print/...-with-wet-h2s-cracking-revealed-by-study.html

2.

https://www.eng-tips.com/viewthread.cfm?qid=406131

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[pradipgoswami]

Hi Atul ,
Please find the section of the HTHA curve for Carbon Steels, as in Appendix-F, RP-941.You may refer the compete curve in Fig-1 of the same RP.
Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[ATUL KHATRI]

@pradipgoswami (Materials)
Thanks for sharing
it helped me a lot

 

[IFRs]

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