Statistical Distribution of Critical Pitting Temperature of Stainless Steels

Abstract

The range of Critical Pitting Temperature (CPT) for five different stainless steels is measured to determine whether it is wide or narrow. The impact of bulk solution composition and surface passivation on CPT was also measured in order to evaluate the relative importance of pit initiation and pit propagation on CPT. The results of the study revealed that CPT can be measured within a narrow range (±1.3 °C) regardless of the alloy and bulk solution composition. It is also shown that experimental error caused by crevice corrosion can lead to a wider range of CPT values. These results are explained using the Salinas-Bravo and Newman CPT model. It is shown that, for the conditions studied herein, CPT is not dependent on pit initiation, but rather, it is a transition phenomenon, i.e., CPT is determined by the transition from metastable to stable pit growth.