Punktkorrosioon

Punktkorrosioon, also known as pitting corrosion, is a localized form of corrosion that leads to the formation of small holes or pits in a metal surface. This type of corrosion is particularly dangerous because it can rapidly penetrate the material, leading to structural failure even when the overall corrosion is minimal. It most commonly occurs on passive metals, such as stainless steels, aluminum, and titanium, which form a protective oxide layer.

The initiation of pitting is often attributed to the breakdown of this passive film. This can be caused by the presence of aggressive ions, such as chloride ions (Cl-), which can adsorb onto the metal surface and disrupt the protective layer. Once a pit initiates, the local environment within the pit becomes more aggressive than the surrounding surface. This is due to the accumulation of metal ions and the formation of an acidic solution, further accelerating the corrosion process.

Factors that promote punktkorrosioon include the presence of contaminants on the metal surface, variations in the metal's microstructure, and certain environmental conditions, such as high concentrations of chlorides and low pH. Identifying and preventing punktkorrosioon often involves controlling the environment, using corrosion-resistant materials, and maintaining surface cleanliness. Inspection methods like visual examination and non-destructive testing are crucial for detecting the presence of pits.