what could happen with a P91 pipe and welds on service without PWHT 3

[Eduardo1982]

Dear guys.
I know it is a crazy question, but what could happens with a P91 pipe and welds on steam service what is working under pressure and without PWHT? Even if it is a temporal pipe (and probably it can be used for a couple of weeks on use) are there any "method" to follow to assure that those welds can work without damage or rupture?
My apologies if this forum is not the correct one for my crazy question.

 

Your question indicates that you should not be allowed anywhere near P91 steel (and probably any other steel). Any AI with a pulse would stop you in your tracks.

And the answer is 'hard no, don't even think about it'.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

What could happen is catastrophic rupture. P91 welds have been known to develop stress corrosion cracks without stress releiving post weld heat treatments when exposed to moisture. Delayed hydrogen cracking due to welding can also occure.

 

[EdStainless]

In the best case (no cracking) you will have much lower creep strength in the weld or HAZ leading to early failure.
There are special HT for different service conditions.

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P.E. Metallurgy, consulting work welcomed

 

[DVWE]

This is not safe, even in steam service, and for temporary use. P91 welds will crack without PWHT, and anyone standing near that steam line would be put in jeopardy when there is loss of primary containment.

The devil is in the details; she also wears prada.

 

DVWE,

P91 is pretty much only used for steam service. Where P91 is used (2500 psi) anyone in the same building could be in jeopardy when it breaks, never mind standing near a break.

I consider P91 so problematic that if we knew in the 1990s what we know now, it would probably not have entered the Code. Most career WEs aren't even familiar with how to handle it. EPRI is certainly concerned.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[DVWE]

P91 is pretty much only used for steam service. Where P91 is used (2500 psi) anyone in the same building could be in jeopardy when it breaks, never mind standing near a break.

Yes, I am very much aware of that. Thank you.

The devil is in the details; she also wears prada.

 

[weldstan]

I've also seen it used in petrochemical plants and services where P9 was specified in the past.

 

[MJCronin]

In light of the comments above, I found kind of a fun article ..... from 2016

P91 Piping: A Panacea-Turned-Nightmare for Power Plants ? Victor Rodgers | March 01, 2016

https://insights.globalspec.com/article/2215/p91-piping-a-panacea-turned-nightmare-for-power-plants

It is important to remember that the P91 push for High Energy Piping came about because of the rash of spectacular steam failures with ASTM A335 P11 and P22 materials in the 1990s.

P91 was attractive to the Combined Cycle crowd because of additional cost savings (for high temperature steam systems) because of the superior strength at higher temperatures AND superior creep performance versus P11/P22. P91 systems could be constructed with significantly thinner piping wall thicknesses .............. but ONLY IF THE ASME PIPING CODE REQUIRED HEAT TREATMENTS WERE PERFORMED !!!!

CC powerplant people have found that hardness testing and detailed analysis are required to determine if a suspect P91 weldment is acceptable.

Another fun read:

https://www.ccj-online.com/2q-2010/p91-commands-respect/

https://www.powermag.com/inspecting-aberrant-p91-components-for-integrity/

Interestingly, as I recall, Europe and I (think) China have NOT been using P91 materials in High Temperature Service ... They Specify the even higher alloy P122 materials.

There are many old posts on these eng-tips fora about usage of P91 materials.....

But this is the seminal paper that tell you everything that you must know

https://www.lincolnelectric.com/en-us/industries/Documents/P91_and_Beyond.pdf

MJCronin
Sr. Process Engineer

 

[MJCronin]

https://www.steamforum.com/steamforum_tree.asp?master=984

MJCronin
Sr. Process Engineer

 

[EdStainless]

Some interesting reading. Some from fairly recently and some from 25 years ago.

https://www.epri.com/research/products/1024718

https://www.epri.com/research/products/000000003002006390).

https://www.epri.com/research/products/TR-103617

https://www.scribd.com/doc/246144971/EPRI-Best-Practice-Guidelines-for-P91-1023199

https://becht.com/becht-blog/entry/grade-91-steel-how-did-we-get-here-part-2/

https://pdfslide.net/documents/etd-epri-p91-failures.html

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P.E. Metallurgy, consulting work welcomed

 

EPRI was so concerned about safety issues related to P91 that in 2014 they took the extraordinary step of releasing this document free of charge to the public, when they normally would have charged a hefty fee to non-members.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

p.s., don't take this document as a license to weld P91; considerable experience and knowledge is still required.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

I've also seen it used in petrochemical plants and services where P9 was specified in the past.

Because of the Type IV creep cracking issues, P91 is often not used near it's base metal property limits, thereby negating much of the theoretical advantage. It's a net loss in many situations.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[XL83NL]

Off-topic, and solely out of curiosity, does anyone know which material(s) is (are) considered to be potentially good successor(s) for P91? 740H?

Huub
- You never get what you expect, you only get what you inspect.

 

[MJCronin]

This 2007 document gives you a peek into the future for CSEF steels from a welding standpoint

"P91 and Beyond" ---Welding the new-generation Cr-Mo alloys for high-temperature service
BY KENT K. COLEMAN AND W. F. NEWELL JR

EPRI Manager, Kent Coleman is the author for many significant papers on P91 issues and Type IV Cracking

https://www.lincolnelectric.com/en-us/industries/Documents/P91_and_Beyond.pdf

This 2017 document provides important information about P91, P92 and P93 alternatives in possible high temperature USC boiler applications:

https://cdn.ymaws.com/

http://www.vma.org/resource/resmgr/2017_tech_seminar_presentations/Henley_Specifications_for_Po.pdf

The end of the evolutionary path for high temperature steam system alloys seems to be HR6W (UNS N06674).... developed by Japanese metallurgists.

Based on the amount of chrome and nickel in HR6W, it will be very expensive

The fine engineers at Black and Veatch are the Gold Standard in both Powerplant Design and Materials Selection .... IMHO

USC power plant applications were expected to be a huge market for new and exotic CSEF steels .... But, the world has changed

Importantly, reliable and ubiquitous Combined Cycle Powerplants (and cheap natural gas) will probably kill all plans for new coal USC power stations

(See the chart entitles "ESTIMATED COSTS AND THERMAL EFFICIENCIES OF VARIOUS PLANT TYPES" on page 42 of the B&VP Presentation)

MJCronin
Sr. Process Engineer

 

P91 has reached a dead end; all we can do is mitigate Type IV risk through lower operating temperature and advanced UT methods. EPRI has developed techniques for non-PWHT repair methods (but do not try those at home).

P92 has different alloy design and shows a bit more promise; the long-term results from service are not yet in I don't believe.

P93 - I have not followed developments there.

Supercritical and USC dreams and schemes rely on exotic ferritic alloys (and the metallurgy is complex) for efficiency gains, but there are serious problems of alloy instability arising from (i) welding; (ii) heat treatment; and (iii) high-temperature service.

As I like to say, "live by the carbides, die by the carbides".

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[XL83NL]

Some time ago I read about 740H, I think in this book (which I don’t have at hand right now). Not sure if this reference is older than what’s previously posted, or which authority is considered leading though.

Huub
- You never get what you expect, you only get what you inspect.

 

[MJCronin]

Ironic talks about "Supercritical and USC dreams and schemes..." I agree ...

It is sad in many ways that there has been so much research, money and long careers spent trying to advance the science of high temperature metallurgy...... while at the same time the world turns away from coal power plants and rushes headlong into Natural Gas fired Combined Cycle plants.

To me, the state of the art seems a lot like a final group of 1890 blacksmiths perfecting the ultimate horseshoe .... as a fleet of Ford Model "Ts" crowd the streets ...

Does anyone really think that these new materials will have a role in future power generation ?



MJCronin
Sr. Process Engineer

 

[XL83NL]

I’m not in the power plant business, my interest is different. Any materials which are likely interesting may have more spin off and as such become interesting for other applications (for example due to better availability). One of the reasons why 617 has become quite popular for some of our applications.

Huub
- You never get what you expect, you only get what you inspect.