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COOPERATIVE STOCHASTIC-BEHAVIOR; STAINLESS-STEEL; PITTING CORROSION; SULFIDE INCLUSIONS; FITTING CORROSION; INITIATION
Abstract:
Interactions among local pit sites were investigated using a 5×5 array of 25 electrodes consisting of closely spaced, flush-mounted 316 stainless steel wires. Three types of interactions occurred when actively corroding pits existed while the remaining electrodes were initially passive in 0.05 M NaCl solution. Suppression of pitting on nearby electrodes occurred due to ohmic potential drop near pre-existing pits. Enhancement of pitting at initially passive electrodes was observed and attributed to both temporary alternations in the local solution composition and a more persistent effect attributed to some action of the locally altered solution composition on nearby passive surfaces. The exact origin of the damage on the nearby passive surface is unknown. Each of these effects exhibited different periods of persistency after pit deactivation. A phenomenological model was developed and used to simulate some of the features of the experimental findings. The model included stochastic pit initiation and interactions promoted by surface damage and concentration effects or inhibited by ohmic drop. The model successfully reproduced some of experimental observations and illustrated the formation of nonrandom corrosion damage patterns even on a simulated homogeneous surface.
