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metal dusting - crude vacuum service

  • 1.  metal dusting - crude vacuum service

    Posted 05-20-2020 07:01 PM

    All,

    I am having metal dusting issues in my 5 chrome crude vacuum furnace roof tubes and I was curious if any others have experienced this in their plants in crude service. From reading the MTI Awareness Bulletin 33 and several papers from RT Jones's work I have a good enough understanding of the mechanism and history in other services, but I have not seen much discussion about it happening in crude vacuum service.

    We have verified the mechanism through a failure analysis and UT points showing short term corrosion rates up to 888mpy. The furnace is approximately 50 years old and has not shown any significant wall loss from carburization until 2018. No pitting found, more of a general wastage. The sulfur is currently low less at less than 50 ppm.

    I appreciate any thoughts on trying to prevent the metal dusting. We replaced the tubes with 9 Chrome, but I was curious if anyone had any advice on preventing the 9 chrome tubes from metal dusting as well or if there are any other known cases in industry.



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    Elyssa Okkelberg
    Materials, Corrosion, and Welding Engineer
    Chevron Corporation
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  • 2.  RE: metal dusting - crude vacuum service

    Posted 05-21-2020 10:08 AM

    Hi Elyssa,

     

    Was there a change in the sulfur content of the gas in 2018, or shortly before?  Sulfur can protect against metal dusting at high enough levels, and maybe a change in the presence of sulfur contributed to your sudden experience of carburization.

     

    Best,

     

    Stephanie Britton

    Lead Materials Engineer

     

    Air Products

    7201 Hamilton Blvd

    Allentown, PA 18195

    610-481-3397

    brittosl@airproducts.com

     






  • 3.  RE: metal dusting - crude vacuum service

    Posted 05-21-2020 02:30 PM
    Stephanie,

    Yes, starting in 2012 the feed has been significantly changed to a lower and lower sulfur. We currently do not specify a minimum sulfur for crude feed. Thank you for your input.

    ------------------------------
    Elyssa Okkelberg
    Materials, Corrosion, and Welding Engineer
    Chevron Corporation
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  • 4.  RE: metal dusting - crude vacuum service

    Posted 05-22-2020 09:37 AM

    Greetings Elyssa 

    I am not aware of metal dusting case in crude and vacuum heaters even the same is not listed as damage mechanism in API 573 of CDU heaters. However, Carburization may occur in crude and vacuum heaters which is a known step that precede most of reported metal dusting failure cases.

    In CCR units, DMDS are injected to minimize metal dusting since adsorption of sulfur, obtained from the decomposition of DMDS on metal, allow to minimize metal dusting (0.3 ppm found by experience necessary to prevent metal dusting in CCR). In contrast this option is not viable in many

    processes due to the increased use of catalysts which are sensitive to sulfur content. (EX. Syngas Industry)

     

    The same context of sulfur role, the influence of H2S on metal dusting of pure iron has been investigated at T 500 ̊C. The presence of sulfur retards the start of metal dusting. With increasing H2S content the onset of metal dusting can be retarded for longer times.

    Hence, I believe that you need to review the change in process conditions and temperature and define a limit of sulfur content (i.e. IOW) necessary to protect your heater tube.

    Hope this can help


    Attached are some interesting papers for your kind info.


    Ahmed Eissa

    Senior Materials and Corrosion Engineer

    ENPPI



    ------------------------------
    Ahmed Eissa
    ENPPI
    Engineering
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  • 5.  RE: metal dusting - crude vacuum service

    Posted 05-24-2020 11:09 AM
    Dear Elyssa:

    Metal Dusting has been investigated for a long time, and in my opinion and experience, with confusion and uncertainty. The following are some academic investigators that have done significant work and may be of value. MTI has a number of reports on metal dusting that you should be able to access thru the MTI Website.

    Good luck with resolving your specific problem in identification metal dusting in your specific unit.

    Ken Natesan at Argonne
    David Young
    Hans Grabke
    Michael Schutze
    Christine Geers

    Emory Ford
    MTI Fellow