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Question on Intergranular Corrosion of Low Carbon 304 stainless

  • 1.  Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-21-2021 17:20
    Does anyone have any technical literature they can point me to for the study of intergranular attack of "non-sensitized" (eg., austinitized) 304 stainless steel.

    I have an interesting case of severe intergranular corrosion of 304 stainless with low carbon. Chemical Analysis shows compliance with UNS S30400. Elemental analysis shows 0.02% carbon. 

    Other elements are:
    Cr - 18.61
    Ni - 8.23
    Mn - 1.36
    P - 0.027
    S - 0.001
    Si - 0.28

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    Ana Diaz
    Principal Consultant
    APV Consulting
    Chadds Ford PA
    (610) 388-2027
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  • 2.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-22-2021 07:51
    You should check for sensitization per ASTM A262.

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    Ronald Parrington
    Director of Industrial Services
    ESI
    MAPLE GROVE MN
    (607) 342-3103
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  • 3.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-30-2021 23:37
    Hello Ana
    assuming this is a storage tank or similar, was the surface of the stainless steel cleaned by surface grinding or grit blasting before passivation treatment?  It's common for the steel surface to pick up small particles of iron from manufacture, handling or hot work that can subsequently initiate corrosion pitting.  In the presence a stress (such as a tank wall), you might see this transition to SCC due to hydrogen embrittlement of the grain boundaries.

    Hope this helps.

    Regards

    Michael

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    Michael Henderson
    CONSULTANT METALLURGIST
    EASTHAM ENGINEERING CONSULTANCY PTE LTD
    SINGAPORE
    6591849574
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  • 4.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-22-2021 18:55
    The carbon content you show is certainly low.  Without more details on the application, here is a shotgun approach of things to look into.  Some are unlikely but all are at least possible:
    Is there any chance of other alloy content that is relevant?  The other interstitials that can tie up Cr include N, B, and O.  A heat treatment in a nitrogen atmosphere could result in some nitride formation.
    Chloride SCC (and probably all of the other causes of SCC) is temperature dependent.  Was the service greater than ~150F / 65C?  Did conditions result in a concentrating effect such as drying of a solution on the surface?
    Were there additional 304SS components exposed to the same environment that did not have attack?
    Were there other species than sodium chloride present?  For instance, MgCl2 is much more aggressive than NaCl.  Liquie metal embrittlement from Hg?
    Was the surface possibly in a different condition than expected, for instance a too-aggressive pickling solution that attacked the surface before service?
    Has the presence of other intermetallic compounds been ruled out, such as sigma phase?
    Was the actual service environment the same as design, for instance were other corrodent species or unexpected temperature excursions documented?
    I hope these questions are useful. 
    Paul T.





  • 5.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-23-2021 10:03
    Is the effect of sensitization just observed near the surface? Was the carbon measured from core material? I am wondering if the surface could have been unintentionally carburized.

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    Ken Kirby
    Snap-on, Inc.
    Kenosha WI
    (262) 748-3836
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  • 6.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-27-2021 10:01
    Edited by Ana Diaz 06-27-2021 10:02
    Thanks to all who have replied.  To answer some questions.....

    1. The service is potable water service
    2. The temperature is ambient temperature
    3. The elemental analysis was done on the bulk material to check for compliance with 304 composition
    4. Carbon steel is not attacked
    5. I have no history on the thermomechanical processing of the items
    6. There were no tests done on the failure other than SEM/EDS

    So, it is a puzzle.

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    Ana Diaz
    Principal Consultant
    APV Consulting
    Chadds Ford PA
    (610) 388-2027
    ------------------------------



  • 7.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-22-2021 12:29
    We got the ASTM A-262 tests covered and are starting with Method A.  I may do some of the other methods in A-262 or an EPR test.

    Since the material was 0.02% Carbon, I was surprised to find IGA and was wondering if anyone had done any studies or published papers rather than just running tests. 

    Since "low carbon" is considered a method to mitigate sensitization and "low" is less than 0.03% carbon, I was curious if there were any studies investigating how low in carbon do you need to go before you don't get sensitization.  I have the ASM Time-Temperature curves for sensitization as a function of carbon levels....but this work dates from the 1980's and really doesn't address sensitization at low carbon levels.

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    Ana Diaz
    Principal Consultant
    APV Consulting
    Chadds Ford PA
    (610) 388-2027
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  • 8.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Posted 06-27-2021 22:42
    Hi Ana,
    For further free advice, you could try to entice responses with further specifics.  Product form, wall thickness, exposure environment details (indoor, outdoor, presence of cleaning chemicals, temperature range), how was the failure detected, what was the length of service.
    Another idea that came to mind is that I have seen flexible stainless and also flexible brass connectors which were corroded externally, where the final determination was that animal excretions had been deposited repeatedly and left to dry and concentrate.  These contain various salts, possibly ammonia, organic acids, etc.
    Regards,
    Paul Tibbals, P.E.







  • 9.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Dayton Chapter Admin
    Posted 06-29-2021 21:23
    Anna,

        I used to perform ASTM A262 on 316 alloy and found that IGA can form when the cooling rate was too slow.   This was usually due to a large batch of material in a furnace and the center portion of the load cooled too slowly.  When cooled too slow, the hardness was near 90 HRB and above; occasionally exceeding 23 HRC.  A simple hardness check may be in order.

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    Emil Lesner
    Senior Metalerials Engineer
    Collins Aerospace
    Fletcher OH
    (937) 541-6201
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  • 10.  RE: Question on Intergranular Corrosion of Low Carbon 304 stainless

    Pune Chapter Admin
    Posted 07-03-2021 08:50
    If it's not sensitised, then you should check for loss of passivation.
    Also check out for stray currents.
    Regards
    Rahul Gupta