The Effect of Scan Rate on Pitting Potentials of High Performance Alloys in Acidic Chloride Solution

Abstract

Abstract The effect of potential scan rate on the pitting potential determination of several high performance alloys in acidic chloride solution at 70 C was documented. Materials from several alloy classifications were examined including austenitic stainless steel, duplex stainless steel, 20-type stainless steel, and nickel base alloys. The functional relationship of pitting potential versus scan rate was dependent on the material studied. Results at intermediate and rapid scan rates were dependent on the material studied and on the experimental procedure. The response of the pitting potential of a given alloy to intermediate and rapid scan rates appears to be a function of the kinetics of passive film formation at the corrosion potential and at applied potentials. Therefore, the most promising accelerated electrochemical tests for localized corrosion resistance are the slow scan rate and constant potential pitting tests. Hastelloy alloy G was found to be resistant to pitting corrosion at all applied potentials in this environment. Additionally, the microstructural sites most susceptible to stable pit initiation were determined for the alloys investigated.