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Corrosion - Passive films on 304/316L s/s?

  1. Dec 1, 2007 #1
    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?

    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. Presumably this is because of the complicated nature of alloy passive film behavior?

    Further info: Operating temperature 140 - 160 deg C, with off-line period once a week for steam cleaning.

    Any assistance most welcome!



  2. jcsd
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