Anodic protection. Cathodic protection

The title of this study clearly indicates that, in the technique under consideration, a metal structure will be protected against corrosion either cathodically or anodically, throughout its entire service life. However, the latter condition may be too restrictive in some cases, and we shall see 4.1.7 that intermittent protection may sometimes be considered.

The types of protection studied here are limited to the many practical cases where the metal structure is in contact with a liquid or solid electrolyte, whether it is immersed, itself constitutes a container containing an electrolyte, or is buried in damp soil. Respectively, this would be the case for a sheet-pile curtain lining a quay or the hull of a ship, a phosphate degreasing tank or water reservoir, and a buried pipeline.

Apart from the much rarer cases where the electrolyte is not aqueous (e.g. sulphuric acid), we will almost always be dealing with water to which salts have been added to a greater or lesser extent. We also know , the essential role played by adsorbed or imbibed water in the electrical conductivity of soils. As a result, the resistivity of liquid or solid electrolytes, expressed in Ω · m, is a key physical factor in problems of corrosion or corrosion protection.