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P91 (9Cr-1Mo) ferritic alloy steel

  • 1.  P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-21-2020 07:58

    The ASM Journal of Materials Engineering and Performance has seen an increase in the publication, citation, and download of articles related to P91 (UNS K91560), a 9Cr-1Mo ferritic alloy steel. What are some possible explanations for the growing research interest in this alloy?



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    Scott Henry
    Senior Content Engineer
    ASM International
    Materials Park OH
    (440) 338-5401
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  • 2.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-22-2020 11:25
    P91 alloy exhibits high resistance to creep and has better steam oxidation resistance than lower chromium alloys. It also has lower thermal expansion than the austenitic stainless steels. This combination of desirable properties has made it a workhorse material for higher efficiency fossil power plants. Although it is an old alloy, it still presents many issues associated with welding, heat treatment (it is a tempered Bainitic material with strengthening precipitates) and creep/rupture resistance.

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    John Grubb FASM
    New Kensington PA
    (724) 448-5272
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    Original Message


  • 3.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-22-2020 11:26
    This grade is no where near new on the street, whether in the form of pipe (A335 P91), Tubes (A213 - T91), forgings (A182 - F91) or castings (A217 C12A).  Originally developed at Oak Ridge National Labs as part of the fast breeder reactor program, it has become the workhorse of the power generation industry.  It has replaced the 2.25Cr-1Mo (A335 P22) ​for boiler tubes, high temperature piping, and heat recovery steam generators.  With the support of the Electric Power Research Institute (EPRI) and the ASME Boiler and Pressure Vessel Code, it has gained widespread use due to the excellent elevated temperature properties.   But as the adage goes, there is no free lunch.  The alloy is metallurgically complex and was unfortunately treated like the very robust Cr-Mo steels it replaced during manufacturing, fabrication, and erection.  In addition, the steam side oxidation characteristics were not well understood and are a departure from other Cr-Mo steels.  This has led to local hot spots and premature failures as well as down stream solid particle erosion and blockages.

    Welding and heat treatment of this alloy also has to be approached with caution.  There have been many dramatic failures of weldments, especially dissimilar metal welds. The fine grained heat affected zone of the Grade 91 material is the life limiting location of weldment for similar metal welds and carbon migration of a dissimilar metal weld using an 2.25Cr-1Mo filler metal can result in a much lower than anticipate creep performance. 

    The complexity of the Grade 91 steel weld filler metals is further exemplified by the effects of Ni and Mn on the lower critical temperatures.  The AC1 can be suppressed to a point that partial solid state phase transformation to austenite is possible during post weld heat treatment resulting in untempered martensite. 

    The material has been in widespread use for long enough now that the material challenges are causing enough of a disturbance in the industry that it is receiving the financial funding to support further research.

    The second generation alloys like A335 P92 and A213 T23 have been deployed in sufficient quantity and have been in service long enough for long term effect to start manifesting.  That will likely be the heavy research area in the next 5 to 10 years.

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    DAVID SEGLETES
    Structural Integrity Associates
    York SC
    (803) 487-2368
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    Original Message


  • 4.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-22-2020 11:27
    The utility industry has used P91 extensively in natural gas fired power plants.  Initially there were issues with understanding the need to precisely control the microstructure in these applications.  Plants may now be looking for additional information as these systems may be nearing their end of design life.

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    Frank Watson
    SAFE LABS
    Sanford NC
    (919) 464-1817
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    Original Message


  • 5.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-25-2020 10:45
    P91 has been known for its creep resistance and has evolved from Cr-Mo steel types. Fission reactors use P91 grades. Research on fusion tokamak devices have taken this as surrogate to develop 9Cr steels with reduced activation elements. Since energy driven systems are more investigated, this alloy becomes inevitable to be discussed.

    Regards, nirav.

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    Nirav Jamnapara
    Scientific Officer (F) & Head - PTTS
    Institute for Plasma Research
    Gandhinagar
    91 79 23964039
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    Original Message


  • 6.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-27-2020 09:24
    John, David, Frank, and Nirav,
    Thanks very much for the information about P91. I did some searches in the ASM Handbook and other ASM Digital Library and did not , and I did not find much information. I wonder if it would be useful for ASM to gather and publish some additional information about this alloy? Possibilities might include:
    • Feature article in Advanced Materials & Processes magazine
    • Review article in the Journal of Materials Engineering and Performance or International Materials Reviews
    • Case histories for the Journal of Failure Analysis and Prevention
    • ASM technical book on the properties, selection, processing, and characterization of this alloy (or alloys in this family)
    Feedback or additional ideas are welcome. I would be happy to speak with any authors who might want to tackle one of these projects.
    Thanks,
    Scott




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    Scott Henry
    Senior Content Engineer
    ASM International
    Materials Park OH
    (440) 338-5401
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    Original Message


  • 7.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-28-2020 08:44
    Scott,

    I would think that there are probably hundreds if not thousands ​of articles, papers and presentations on the "creep strength enhanced ferritic" (CSEF for short) alloys.  I think a feature article or review article would not do the topic justice.  I think there are plenty of examples for several case history articles in the Journal of Failure Analysis and Prevention.  In my opinion, a technical book on CSEF steels in general (now in third generation with Thor 115) would be useful.  I did a quick search and there does not seem to be a comprehensive text on the topic.  People like Jeff Henry (ATC, Inc), Johnathan Parker (EPRI), Terry Totemeier (Structural Integrity Associates) would make a great editorial panel. There is a whole four hour long working group session at the ASME Boiler and Pressure Vessel code meeting every quarter to discuss CSEF steels on Sunday afternoon.

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    DAVID SEGLETES
    Structural Integrity Associates
    York SC
    (803) 487-2368
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    Original Message


  • 8.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-30-2020 07:42
    David,
    Thanks. We did have some conversations a couple of years ago with Jonathan Parker and others at EPRI about a potential book on CSEF alloys. ASM is still interested in this possibility. Perhaps a small working group could be assembled to move the project forward.
    Scott

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    Scott Henry
    Senior Content Engineer
    ASM International
    Materials Park OH
    (440) 338-5401
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    Original Message


  • 9.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-28-2020 12:14
    Scott,

    I agree with what David said in his reply - there's a lot of content out there already and has been for some years.  EPRI and ASM have organized a large conference every three years since the 1990's covering Grade 91 and other advanced steels and nickel-base alloys for high-temperature applications - "Advances in Materials Technology for Fossil Power Plants" - the most recent one was in Nagasaki, Japan this past October.  So I'm not sure that a simple feature article or case histories would do the topic justice.  But I think adding content on these materials to the ASM Handbook Volume 1 would be helpful (as a section under "Specialty Steels and Heat-Resistant Alloys).  Also maybe a technical book on creep-strength enhanced ferritic steels - there was a book published back in 2008 "Creep Resistant Steels", eds. F. Abe, T.-U. Kern, R. Viswanathan, but there has been a lot of research and practical experience since then.

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    Terry Totemeier
    Structural Integrity Assoc.
    Boulder CO
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    Original Message


  • 10.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 01-30-2020 07:42
    Terry,

    Thanks. ASM has partnered with EPRI to publish the last several Advances in Materials Technology for Fossil Power Plants proceedings volumes. We plan to move these volumes into the ASM Digital Library within the coming months. This should create a nice searchable repository of information.

    It's a good idea to add some information to the ASM Handbook series. We have been piloting some "digital first" content projects--this might a good topic area for such a project.

    Scott

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    Scott Henry
    Senior Content Engineer
    ASM International
    Materials Park OH
    (440) 338-5401
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    Original Message


  • 11.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 02-27-2020 08:23

    Dear Scott,

    I agree with David & Terry that a lot of literature is available on 9Cr steels and its variants. For example a book on Cr-Mo steels is already published by R. L. Klueh with ASTM, wherein 9Cr steels have been discussed. But as you said, there is still room for considering a book on 9Cr steels and its future variants. For example, new alloys such as EUROFER, F82H, CLAM, IN-RAFMS etc. are similar 9Cr steels developed for fusion applications and further more is being investigated. In fact, the ODS alloy development and the FeCrAl alloy developments are also taking this knowhow further. My doctoral student has recently submitted his thesis on weldability of aluminized P91 steels, which again is a separate topic.

    In my opinion, different applications (sector wise, e.g. nuclear fission, nuclear fusion, high temperature reactors, petrochemical plants etc.) followed by what would be its future variants (e.g. ODS alloys as discussed, or say, altered composition alloys etc.).

    I would be willing to support for contributing in an ASM book with whatever data I have. You can consider me as a volunteer !

    best regards,

    Nirav.



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    Nirav Jamnapara
    Scientific Officer (F) & Head - PTTS
    Institute for Plasma Research
    Gandhinagar
    91 79 23964039
    ------------------------------

    Original Message


  • 12.  RE: P91 (9Cr-1Mo) ferritic alloy steel

    Posted 02-28-2020 08:44
    Scott,
    All these subsequent posts are spot-on as I understand the subject, also. Speaking to your inquiry, as an Owner/Operator I have noticed increased number of proposals to use CSEF in pressure vessel fabrication, which may be related to claims to lower purchase cost (stronger material = thinner wall = potentially lower cost). The use of these materials may force the consideration of new damage mechanisms when in corrosive service, and so close consultation with corrosion and material specialists is required before committing to procurement. In the oil industry, API publication TR-938B has been helpful guidance.

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    Josh Yoakam
    Corporate Mechanical Integrity Engineer
    HollyFrontier
    Tulsa OK
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    Original Message