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In situ etchant for P91 steel

  • 1.  In situ etchant for P91 steel

    Posted 09-18-2020 08:12
    I am looking for a suitable etchant for field replication of the P91 steel. The picric acid and its reagents are restricted. I would appreciate if you can share some of your experience.


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    Waleed Khalifa
    Principal and CEO
    Arabic Consultancy Center for Engineering Materials, Inspection
    Maadi, Cairo
    01098163293
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  • 2.  RE: In situ etchant for P91 steel

    Posted 09-22-2020 10:15
    Waleed,

    It has been a while since I worked with P91, but I believe for field work we used a strong nitric acid - something around 5-7%. You had to continually swab it for quite some time. Unfortunately I don't remember the details, but hopefully that can be a starting point for you.

    -Lindsay

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    Lindsay Malloy
    Staff Materials Development Engineer
    DePuy Synthes
    West Chester PA
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  • 3.  RE: In situ etchant for P91 steel

    Posted 09-23-2020 08:02
    Hi Lindsay

    Thank you. It is good to have a start point.

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    Waleed Khalifa
    Principal and CEO
    Arabic Consultancy Center for Engineering Materials, Inspection
    Maadi, Cairo
    01098163293
    ------------------------------



  • 4.  RE: In situ etchant for P91 steel

    Posted 09-23-2020 13:32
    What do you want to reveal? If you want to reveal fresh martensite, you could use 20% ammonium persulfate. The fresh martensite will be silver color.

    Sent from my iPhone




  • 5.  RE: In situ etchant for P91 steel

    Posted 09-23-2020 11:25
    I agree with Lindsay, use the strongest safest store-able Nital you can.

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    Rodney Bentz
    Mager Scientific, Inc.
    Fenton MI
    (734) 476-5224
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  • 6.  RE: In situ etchant for P91 steel

    Posted 09-25-2020 07:42
    Rodney makes a good point, that Nital does have its own issue of slow gas build-up.  In the lab one can get around this by leaving the cap not fully tightened, or by storing in plastic bottles.  For field work the bottles are generally being opened and closed so often that pressurization is not an issue even with glass bottles, as long as you don't store them for long periods.  The higher the nitric percentage, the faster the gas build-up.

    While one has to decide on one's own goals for etching, for P91 and field metallography one is generally only looking for proper heat treat (more often measured with hardness testing anyway) or grain boundary cavitation from service-induced high temperature creep.  While I had very little experience with P91, I evaluated possibly a thousand replicas of the lower Cr-Mo and Cr-Mo-V steels, and depending on the metallographer mostly 3 or 5% Nital was used.

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    Paul Tibbals
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  • 7.  RE: In situ etchant for P91 steel

    Posted 10-23-2020 16:38
      |   view attached
    I used 9% nital as in-situ etchant for boiler tubes T91, and the replica micrographs showed clearly the grain boundaries, the carbides and precipitates (see the attached images). Thank you for your valuable advice.

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    Waleed Khalifa
    Principal and CEO
    Arabic Consultancy Center for Engineering Materials, Inspection
    Maadi, Cairo
    01098163293
    ------------------------------

    Attachment(s)

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    replica images T91.pdf   173 KB 1 version