Duplex stainless steel has better corrasion resistance than 304L and 316L. How much the difference is it? However, is it worth for the extra cost?

    To rust on not of the stainless steel not only influences the appearance but also needs to consider the mechincial properties. For example, the rust may cause the valve sticking, not to run. Or, the rust and corrosion may cause the pressure vessel leak, and even perforation. When stress corrision occurs, it may cause the safety problem in structure break.  Great caution is necessary.

    When comparing the corrision resistance in different materials, we can test by standard specification ASTM G48. The easier way is to calculate the material compositions to compare the corrision resistance.

    PREN（Pitting Resistance Equivalent Number）can be used as the corrision of stainless steel containing chromium. The formula is as followig:

PREN=1×(Cr％)+3.3×(Mo％)+16×N％

    In general, the steel with higher PREN  has better corrision resistance. When PREN >32, it usually has the corrision resistance to sea water.  Please take following as the reference.

   

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