A CRITICAL APPRAISAL OF SOME POPULAR LABORATORY ELECTROCHEMICAL TESTS FOR PREDICTING THE LOCALIZED CORROSION RESISTANCE OF STAINLESS ALLOYS IN SEA WATER

Evidence is presented to demonstrate that although the critical pitting potential is qualitatively related to the resistance of a material to passivity breakdown by pit initiation, it is of questionable value in predicting the corrosion performance of a structure containing crevices. Experiments conducted on a 30Cr-3Mo-Fe alloy indicated total immunity to passivity breakdown by pit initiation during anodic polarization in 1M NaCl and under freely corroding conditions in acidified 10% FeCl3. However, on specimens containing an artificial crevice, passivity breakdown by crevice corrosion initiation was observed in the same two media. The long term implications of these data were confirmed by 16 month immersion tests in sea water, where severe crevice attack was noted equal in extent to that observed on AISI Types 304 and 316 stainless steels whose pit initiation properties were considerably inferior to those of the 30Cr-3Mo-Fe alloy. The results of cyclic potentiodynamic anodic polarization experiments conducted on AISI Type 430 stainless steel are presented to demonstrate that the so called protection potential, E sub p, is not a unique material parameter. It is shown that E sub p varies in a semilogarithmic manner with the amount of localized attack induced by polarization; that is, with the chemistry changes in the growing pit caused by hydrolysis of corrosion products and chloride ion buildup in the pit cavities. On this basis, it is concluded that E sub p data (however determined) cannot be used alone as a criteria for protection against the propagation of pre-existing pits or crevices in an engineering structure. Based on cyclic polarization procedures, a method of assessing the susceptibility and resistance of an alloy to crevice corrosion is suggested. It is shown that, for alloys which initiate pits during anodic polarization, the magnitude of the "difference potential" is related to the crevice corrosion weight loss. For alloys that have no critical pitting potential, the presence of hysteresis during cyclic polarization with an artifical crevice indicates susceptibility to crevice corrosion.

  • Availability:
  • Corporate Authors:

    National Association of Corrosion Engineers

    2400 West Loop South
    Houston, TX  USA  77027
  • Authors:
    • Wilde, B E
  • Publication Date: 1972-8

Media Info

  • Pagination: p. 283-292
  • Serial:
    • CORROSION
    • Volume: 28
    • Issue Number: 8
    • Publisher: NACE International
    • ISSN: 0010-9312

Subject/Index Terms

Filing Info

  • Accession Number: 00035984
  • Record Type: Publication
  • Source Agency: United States Merchant Marine Academy
  • Files: TRIS
  • Created Date: Oct 20 1973 12:00AM