Reiäkkökorroosio

Reiäkkökorroosio, also known as pitting corrosion, is a localized form of corrosion that creates small holes or pits in a metal surface. This type of corrosion is particularly dangerous because it can severely weaken a material with relatively little loss of total mass, making it difficult to detect in its early stages. It typically occurs in environments that contain aggressive ions, such as chloride ions, which can break down the passive film that usually protects the metal.

The mechanism of pitting corrosion often begins with a small defect or imperfection in the metal's surface, or at an inclusion within the material. Once initiated, the anodic reaction (metal dissolution) occurs within the pit, while the cathodic reaction occurs on the surrounding passive surface. The geometry of the pit, being small in area but deep, leads to a concentration of aggressive ions within the pit and an accumulation of corrosion products. This self-sustaining process can lead to rapid penetration of the metal.

Common materials susceptible to pitting corrosion include stainless steels, aluminum alloys, and nickel alloys, especially in environments like saltwater, acidic solutions, or industrial atmospheres containing corrosive species. The presence of certain contaminants, variations in temperature, and flow conditions can also influence the initiation and propagation of pits.

The consequences of pitting corrosion can range from aesthetic damage to catastrophic failure of components, particularly in critical applications such as pipelines, chemical processing equipment, and marine structures. Detection methods often involve visual inspection, dye penetrant testing, eddy current testing, and ultrasonic testing. Prevention strategies focus on controlling the environment to reduce the concentration of aggressive ions, selecting appropriate corrosion-resistant materials, and maintaining protective coatings.