Crevice experiments with small bore Alloy 600 and Type 304 stainless steel tubing demonstrated that specific ion effects and heat treatments which change the microstructure of exposed surfaces, can counteract the charge transport/metal hydrolysis mechanism of crevice acidification. The results suggested that competition between the macroscopic electrochemical cell or “macrocell” mechanism, and direct reduction of water, hydrogen ions, or anions by the alloy, established the direction and extent of changes in pH. A simple uniform dissolution model correctly predicted the relationship among metal ion concentrations and the pH in a crevice when only macrocell corrosion occurred.

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