Use of Rapid-Scan Potentiodynamic Techniques to Evaluate Pitting and Crevice Corrosion Resistance of Iron-Chromium-Nickel Alloys

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Abstract
Rapid-scan potentiodynamic polarization techniques were utilized to determine pitting potentials (Ep) for Types 304 and 316 stainless steel in 25°C, 4 percent sodium chloride. Decreasing the test time by increasing the potential scan rate prevented the development of crevice attack, thereby permitting Ep to be measured accurately and reproducibly. A close examination of the rapid-scan polarization curve for Type 304 stainless steel in the potential region above Ep revealed two distinct linear segments. Static potential test results indicated that the more active linear segment was a response due to pitting attack, and the more noble linear segment was a response due to crevice attack. These observations suggest that if a rapid-scan potentiodynamic technique is employed, then pitting and crevice corrosion resistance might be measured by a single test procedure. In addition to the effect of potential scan rate, it was found that the test electrode surface finish is an important consideration in the determination of pitting resistance or crevice resistance or both.