Modelling pitting corrosion of stainless steel in atmospheric exposures to chloride containing environments

Abstract

We describe work in modelling pitting corrosion of 300 series stainless steel during exposure to chloride containing environments, with a focus on atmospheric conditions. It is well known that, under certain conditions of temperature and humidity, pitting corrosion can initiate on stainless steel if sufficient quantities of chloride containing salts are deposited on its surface. One of the key hypotheses that this work intended to test is the existence of bounds on maximum pit depths in the presence of fixed and possibly limited amounts of cathodic current. In the presence of the relatively high cathodic currents associated with high relative humidity and high surface contamination by hygroscopic salts, which are most likely to be representative of outdoor environments, maximum pit depths are predicted to be of the order of 150-300 μm, developed over periods of several months. In conditions more likely to be representative of indoor conditions with corrosion occurring under thin moisture layers, pit propagation is severely inhibited and very high chloride concentrations are required that favour the development of shallow, dish shaped pits.