Pitskorrosion

Pitskorrosion is a localized form of corrosion that results in small holes or cavities in a metal surface. It is a particularly insidious form of corrosion because it can cause significant structural damage with relatively little loss of overall metal mass. The initiation of pits typically occurs at a defect in the passive film that protects the metal, such as a scratch, inclusion, or grain boundary. Once initiated, the pit acts as an anode, while the surrounding passive surface acts as a cathode, creating a galvanic cell.

The corrosive environment within a pit is often more aggressive than the bulk environment. This is due to the accumulation of corrosive species, such as chloride ions, and the buildup of metal ions that hydrolyze, producing acidic conditions. This self-sustaining electrochemical process can lead to rapid pit propagation, even in environments that might otherwise be considered non-corrosive. Pits can deepen and widen, eventually perforating the metal component, leading to failure.

Factors that promote pitskorrosion include the presence of aggressive ions like chlorides, low pH environments, stagnant conditions, and surface contaminants. Common materials susceptible to pitskorrosion include stainless steels, aluminum alloys, and nickel alloys. Prevention strategies involve maintaining a protective passive film through proper material selection, surface treatment, and controlling the corrosive environment. Regular inspection and maintenance are also crucial for detecting and mitigating pitskorrosion before it leads to catastrophic failure.