Localized corrosion probability in stainless steels after cathodic protection in seawater

Growth of calcareous deposits on stainless steels (SS) exposed to seawater under cathodic protection (CP) conditions was examined. CP was performed by galvanic coupling with iron, zinc, or magnesium anodes. The influence of t he galvanic coupling period on the temporal evolution of localized corrosio n susceptibility was examined for various SS with CP removed. The study was carried out using a statistical approach with 33 SS samples from the same group. Temporal evolutions of corrosion potential distributions and breakdo wn potential distributions were determined. Visual and microscopic observat ions were compared with the localized corrosion risk evaluated from the sup erimposition of corrosion potential distributions with breakdown potential distributions. Galvanic coupling of SS with iron anodes in seawater did not lead to growth. of calcareous deposits, and protection failed soon after g alvanic coupling was removed. Galvanic coupling with zinc anodes in seawate r led to growth of a light layer of aragonite, and the protection persisted for > 3 weeks after the coupling was removed. Galvanic coupling with magne sium anodes in seawater led to growth of thick calcareous deposits of a dif ferent composition. Protection persisted for > 1 year after the galvanic co uple was removed.