3. Localized corrosion

Localized corrosion always results from uniform corrosion, due to galvanic coupling between heterogeneous zones. All it takes is a small anode and a large cathode to generate very high local penetration speeds. These local heterogeneities may be pre-existing, in the metal or in the corrosive medium, with a well-identified origin external to corrosion. They will then give rise to a large number of "derived" types of corrosion, i.e. interactions between corrosion and all these third-party phenomena. This will be discussed in 4