Pitting Corrosion

Pitting Corrosion

Pitting corrosion is an example for  a localized and accelerated corrosion. When a small particles of dust or water etc are get deposited on a metal (like steel). The portion covered by the dust will not be well-aerated area compared to the exposed surface hence the covered surface becomes anodic with respect to the surface exposed. In presence of an conducting medium (moisture) corrosion starts below the dust part and forming a pit. Once pit is formed the ratio of corrosion increases, because of the formation of smaller anodic and larger cathodic area intense corrosion takes place.

Pitting corrosion is one of the most destructive forms of corrosion. It causes equipment to fail because of perforation with only a small percent weight loss of the entire structure. Because of the small sizes of the pits it is highly difficult to identify the pitting corrosion. Pitting corrosion is an autocatalytic process, and once the corrosion products are formed, it further provides the condition for differential aeration below the corrosion product and surrounding metal parts. The pit grows and ultimately may cause failure of the metal.