The Contrast between the Pitting Corrosion of 316 SS in NaCl and NaBr Solutions: Part I. Evolution of Metastable Pitting and Stable Pitting

This paper contrastsmetastable and stable pitting of 316 austenitic stainless steel in chloride and bromide bearing solutions. Metastable and stable pitting characteristics were evaluated by potentiostatic and potentiodynamic polarization experiments, respectively. Results revealed that for a given concentration of halide anions, pitting and repassivation potentials rise by increasing the Br-:Cl- concentration ratio in the environment. Increasing the relative concentration of Br- also leads to a decrease in the values of metastable pit stability product. Furthermore, higher concentration of bromide in the solution reduces the growth kinetics of metastable pits. Using pencil electrodes, it was also found that hindrance of the dissolution reactions in presence of bromide anion could be responsible for the lower aggressivity of bromide and the observed decrement in metastable growth kinetics. (C) 2019 The Electrochemical Society.