Distinguishing between the pitting corrosion behaviour of 316L(N) and316 stainless steels using shot noise analysis

Abstract

In the present work, an attempt has been made to analyze Electrochemical Noise (EN) data obtained from 316 Stainless Steel (SS) and 316L(N) coupons exposed to aerated 0.5M NaCl solution for 30d. The analysis of the data was based on the principle of stochastic process like pitting corrosion. Initially, the cumulative probability of the frequency of pitting corrosion events was numerically calculated which was transformed from the domain of the frequency of events to the mean free time domain. Thereupon, Weibull probability plot was constructed by fitting Weibull distribution function to the calculated cumulative probability. From the slopes and the intercepts of the Weibull plots, the pit embryo generation rate was calculated. The data analysis was conducted after the exposure of 10, 15 and 20d respectively so as to examine the distinguishing features that could be obtained from the Weibull probability plots. It was observed that, 316SS showed ever growing pitting corrosion events which was reflected in the Weibull probability plots. However, 316L(N) showed passivation after a few events of metastable pitting (10d exposure) which was reflected in the Weibull probability plots. The pit embryo generation rate was found to be suppressed in 316L(N) which signified the true reason for its showing enhanced pitting corrosion resistance.