Discussion on chloride pitting failure and preventive measures

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Pitting corrosion generally occurs easily in stationary media. Erosion holes generally develop along the direction of gravity or horizontally; once formed, pitting erosion accelerates automatically as it goes deeper. In an aqueous solution containing chloride ions, the oxide film on the stainless steel surface dissolves, resulting in the formation of small pits with a diameter of 20μm to 30μm on the base metal; these small pits are the nuclei for pitting corrosion. As long as there is a certain amount of chloride ions in the medium, it is possible for an erosion nucleus to develop into an erosion hole. Common preventive measures: Adding elements such as molybdenum, nitrogen, and silicon to stainless steel, or increasing the chromium content while adding these elements. Reduce the concentration of chloride ions in the medium. Adding a corrosion inhibitor increases the stability of the passivation film or facilitates the repassivation of a damaged passivation film. External cathodic current protection is employed to suppress pitting.