Origins of persistent interaction among localized corrosion sites on stainless steel

The origins of persistent interactions among localized corrosion sites were investigated using multielectrode arrays (MEA). MEAs consisted of one hundred 250 mum diam AISI 316 stainless steel wires configured into 5 x 20 close-packed rectangle and 5 x 5 far-spaced configurations. Experiments were conducted in dilute chloride solutions and elevated temperatures to accentuate interactions. Interactions between early dominating pits and the adjacent electrode surface were found to develop as regions of enhanced or suppressed pitting susceptibility triggered by concentration and potential fields developed during growth of large pits, respectively. Transient aggressive species accumulation around active pits was also found to cause "surface damage'' to electrodes that persisted for long periods after primary pits were repassivated and solutions extensively stirred. Oxide film alteration, mixed metal sulfide inclusion damage, and surface contamination were all considered to be possible origins of persistent interactions. Mn(Fe,Cr) S inclusions were implicated to be the origin of such persistent interactions. Persistent interactions were completely suppressed by nitric acid treatment, which is believed to remove or modify susceptible Mn(Fe,Cr) S inclusions. (C) 2004 The Electrochemical Society.