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The Corrosion Forum: Corrosion - Passive films on 304/316L s/s?

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    • CommentAuthorCrispin
    • CommentTimeDec 2nd 2007
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    Hi All,

    In acidic conditions (pH not known, but do know there is presence of formic & sulphuric acid, chlorides + free water), is is possible for NiO to form in preference to CrO on Austenitic stainless steel - grade 304 or 316L operating at ~ 150/160 deg C?

    I have a sample analysis from within 304/316L stainless material system of NiO, with traces of Mo & Fe formate. Additionally, Ni, Fe, Cr, Cl & S elements are picked up in the analysis.

    I understand all the other analysis components, but re: NiO, my thoughts where that chromium oxide is not stable in low pH environments, and this may be the reason for NiO being found instead? I cannot find any text books with Pourbaix diagrams for alloys to look at stability of oxide films formed on s/s, only the pure metals. I see that CrO is not stable in pH lower than 3, but cannot find a nickel diagram to compare.

    Further info: Cyclic operating conditions, 6 days operation with 1 day off-line for steam cleaning.

    Any assistance most welcome!

    Thanks

    Crispin
    • CommentAuthorzee
    • CommentTimeFeb 8th 2008 edited
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    The formation and stability of passive layers should be investigated by AES and electrochemical polarization techniques. Stability diagrams do not provide info on presence or the rate of dissolution of passive layers.
    • CommentAuthorCrispin
    • CommentTimeMar 16th 2008
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    Zee, thanks.

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