Lochfraßkorrosion

Description: In the case of pitting corrosion, very small Corrosion sites first occur on the surface. This is particularly common in materials with a surface that is passivated as a result of general corrosion. Chloride or bromide ions remove oxygen from the oxide layer and take its place. As a result, the relevant location is no longer protected by the oxide layer. If favourable environmental conditions do not ensure repassivation of these areas, corrosion occurs. Only isolated corrosion points are initially visible on the surface. In deeper layers, these increasingly develop into craters or troughs. Due to the minor surface damage, pitting corrosion often goes unnoticed for long periods. It is made more likely by: A lack of oxygen at the corrosion sites - this impairs repassivation and increases the formation of concentration cells Electrochemical potential Low pH values and high temperatures Steel alloys with molybdenum or chromium are resistant to pitting corrosion but can lose their protection as a result of Annealing.