Abstract
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 the galvanic coupling period on the temporal evolution of localized corrosion 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 breakdown potential distributions were determined. Visual and microscopic observations were compared with the localized corrosion risk evaluated from the superimposition 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 galvanic coupling was removed. Galvanic coupling with zinc anodes in seawater led to growth of a light layer of aragonite, and the protection persisted for > 3 weeks after the coupling was removed. Galvanic coupling with magnesium anodes in seawater led to growth of thick calcareous deposits of a different composition. Protection persisted for > 1 year after the galvanic couple was removed.
