Origins of Persistent Interaction among Localized Corrosion Sites

Interactions amongst localized corrosion sites were investigated using multi-electrode arrays. The 5x20 array consisted of one hundred 250 μm AISI 316 stainless steel wires configured into a close packed rectangle. Experiments were conducted in 0.05 M NaCl to investigate interactions triggered by the presence of active pits. Interactions between primary pits and the adjacent electrode surface were found to develop as regions of enhanced or suppressed pitting susceptibility originating from concentration and potential fields developed during growth of large pits, respectively. Aggressive species accumulation around active pits was also found to cause surface damage to electrodes that persisted for long periods of time after primary pits were repassivated. Oxide film alteration, inclusion damage, and surface contamination were all considered to be possible origins of persistent interactions. Persistent interactions were completely suppressed by nitric acid treatment. Sulfide inclusions were implicated to be the origin of such persistent interactions.