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Stainless Steal Corrosion Vs pH

  • 1.  Stainless Steal Corrosion Vs pH

    Posted 10-23-2019 06:19
    Could you share a paper on 316L corrosion vs pH. Is it affected by alkali pH?

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    Catalina Zurano

    GlaxoSmithKline
    Buenos Aires
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  • 2.  RE: Stainless Steal Corrosion Vs pH

    SENIOR MEMBER
    Posted 10-24-2019 02:16
    Ferric chloride corrodes stainless steel  (definitely SUS304 from actual experience in wastewater treatment where ferric chloride is a common treatment chemical) due to chloride attack and possibly catalyzed by the ferric ion.
    Flash mixers and/or agitators usually have SUS316 or SUS316L wetted parts(shaft and impellers) but we have not noted any significant corrosion in the flash mixing tanks - possibly due to the dilute concentration of ferric chloride and often basic (or alkaline) conditions.
    No, we don't have a paper or article on 316L vs pH.

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    Manuel Gloria PE
    Principal Consultant
    Aquatreat Environmental Systems Inc
    Mandaluyong
    Philippines
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  • 3.  RE: Stainless Steal Corrosion Vs pH

    SENIOR MEMBER
    Posted 10-24-2019 02:58
    Probably you can find such diagrams about resistance of 316L material against different agents and pH values on the homepage of steal makers like Sandvic. If you don't find it directly you can call customer service. They will be happy to provide you with information. Also here resistance against pH is temperature dependent.

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    Reinhard Michel
    Mechanical Engineer
    Retired Head of Static Equipment Group, Fertilizer Division
    thyssenkrupp Industrial Solutions AG
    Dortmund, Germany
    Reinhard
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  • 4.  RE: Stainless Steal Corrosion Vs pH

    SENIOR MEMBER
    Posted 10-24-2019 09:19
    ​Hi Catalina,

    316L is generally good with most alkali pH solutions however, pH isn't really the best way to look at a material's compatibility. There are various aspects that play into a materials resistance to a chemical. The most important aspect is generally the chemical's composition. For instance, sodium hypochlorite or bleach has a pH of 11, but the chlorine molecule is very aggressive to most metals including 316L. 316L is more resistant to chlorine and chlorides than 304 SS, but it's still not resistant enough to make it a good suggestion. I would suggest googling resistance of 316L SS to your specific chemical. Cole Palmer has a database on their website that you can look up a decent amount of chemicals on and see various materials resistance to that chemical (I've found it to be overall pretty accurate and at least a good starting point). If the chemical your working with is a more exotic chemical then you'd likely need to do some more research or break down the molecular formula and see if there's any specific molecule that may not be good with 316L.

    There are 2 more factors to also consider when you're looking at chemical resistance and they can make a big difference on a material being OK or NOT OK to use with a chemical. The other two factors are the chemicals concentration, and the temperature at which it's going to be stored or processed at. The higher the temperature the chemical is being processed or stored at, generally the more aggressive it will be towards a material. Depending on the chemical, it can be more aggressive or less aggressive at higher concentrations (Nitric and sulfuric acid are good examples for concentration dependence).

    Sorry that doesn't provide a yes or no answer, but there's far more than just pH that plays into material selection and applicability. Hope that helps!
    ​​

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    James Burtnett-Grigsby PE
    Chemical Process Engineer
    Maumee OH
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  • 5.  RE: Stainless Steal Corrosion Vs pH

    SENIOR MEMBER
    Posted 10-25-2019 21:43
    Your question seems to relate to the performance of 316L austenitic stainless in high pH environments.  As others have indicated, performance is not a simple function of pH.  Chloride contamination can be especially detrimental in many solutions; and temperature is a particularly important factor.  Chlorides can cause multiple forms of corrosion, including pitting, crevice corrosion, and stress corrosion cracking.  With regards to temperature, carbon steel is normally adequate for the storage of 50% sodium hydroxide, but any heating coils to prevent freezing would need to be nickel - 316L would not be sufficient.  Also, assuming your equipment is welded (the L grade is normally specified to prevent chromium carbide segregation during welding), the impact of your solution on the weld area should be considered.  Much more would need to be known before predicting performance in your particular environment; and even then, you may need to perform tests to confirm expected performance.

    Good sources of information as to the performance and testing of 316L (and other alloys) in various environments (books, conference papers, etc.) include the websites of NACE International (the corrosion society formerly known as the National Association of Corrosion Engineers), MTI (the Materials Technology Institute of the chemical process industries), ASM International (formerly the American Society for Metals) and NiDi (the Nickel Development Institute).

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    Roger Turcotte PE,Corrosion,CathodicP
    Scarborough ME
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  • 6.  RE: Stainless Steal Corrosion Vs pH

    SENIOR MEMBER
    Posted 10-29-2019 04:17

    Dear Catalina Zurano,

    Corrosion Vs. pH for SS316 is very complex. Others factors are also influenced on pH. Acidic attack on stainless steels is very complex and depends not just on the pH but what acid is present, whether the acid is weak or strong, the type of acid (non-oxidizing versus oxidizing), the temperature, and level of dissolved oxygen. At low pH Ferric chloride corrodes SS 316 stainless steel. This ferric chloride formed at low pH and that ferric chloride attack on Ni which is present in SS more nickel more corrosion. If the temperature considered then The corrosion rate of 316L SS increases with increasing pH in hydrogenated high temperature water at 300 °C. Higher pH reduces the stability of the oxide films and accelerates the dissolution process of the oxides. With increasing pH, the corrosion rate decreases, being highest at pH 4 and lowest at pH 9. The number and depth of pits increase with increasing Cl concentration. From the results of cyclic polarization is inferred that the pitting potential, Epit is shifted to a more negative potential with increasing Cl concentration and temperature and decreasing pH .At low pH, high Cl content and stagnancy are the conditions most suitable for initiation and propagation of pitting in AISI 316L stainless steel.

    https://www.researchgate.net/publication/238739911_Effect_of_ph_and_chloride_concentration_on_the_corrosion_of_duplex_stainless_steel

     

    https://www.researchgate.net/publication/332572120_Stress_Corrosion_Cracking_in_Co_2_Compressor_Intercooler?_sg=nt9MDM3tA9DBSnC5XWAfScOnIkKc88OPrxC3JxFsA_eBdFe6axaGrYCzMMuYDKX3w6KLp1nzUfJSQ4ZD9UEFXCqjVR6BhBHnaKH1pnVc.2P6N1KyeimpEpmwRCYFK6q8yK56VORH_JRQqfI9Cv23m1cJAab2zeNbbYqyaPr7vn2IdtEXv9zjgpyhcARzxOw

     

     Regards,
    Prem Baboo

     

     



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    [Prem ] [Baboo] [DGM]
    [Mr.]
    [Dangote Fertilizer Projects]
    [Lekki] [Lagos]
    [Nigeria]
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  • 7.  RE: Stainless Steal Corrosion Vs pH

    Posted 10-29-2019 05:08
    Thank you very much for the explanations

    ---------------------------------
    Catalina Zurano

    GlaxoSmithKline
    Buenos Aires
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