Copper will be passivated naturally in aerated water through the formation of a thin layer of Cu2O; nevertheless, there are three types of corrosion.
type I pitting corrosion
This corrosion is promoted by two factors :
- a low residual oxygen content and a low bicarbonate content;
- the presence of carbonated films (and to a lesser extent, harmful oxides such as the CuO oxide) on the surface of the pipe. This last factor tends to disappear when applying standards that restrict the quantity of carbon per surface area unit.
type II pitting corrosion
Far less common, this type of corrosion occurs in hot, sparsely mineralised water at temperatures above 60°C. Pitting is less visible on the inner pipe surfaces and covered by a film that most frequently has a copper sulphate base.
This type of corrosion is mainly linked to excessive circulation velocities created by individual geometries (bends, necks, etc.).
other types of corrosion
There are other types of corrosion. In particular, considerable uniform corrosion can occur in aerated water containing ammonium (industrial water) through solubilisation of the protective layer.