The Modeling and Measurement of Boundary Conditions for Pit Size on Stainless Steels under Atmospheric Exposure Conditions

Abstract

Literature values prove the existence of maximum pit size. Values from exposures to natural environments exist for a range of materials in which exposure times of 10 y or more clearly show a plateau in the size of the largest pits. A recently published model uses the conditions that result from atmospheric exposures to place a bound on the size to which a pit can grow. Although this approach has been shown to compare well to data collected from exposures of stainless steels over long times (> 25 y) at coastal locations, laboratory validation is required in which salt loading density, RH and temperature can be rigorously controlled. After three months, the laboratory exposures of four stainless steel alloys, with 240 and 600 µg/cm 2 of NaCl and 90 and 95% RH, were found to have little pit damage, and all pit sizes were correctly bounded by predicted model values.