5. Other generalized degradation modes

5.1 Generalized corrosion

In the presence of moisture, steels corrode and tend to revert to their natural state of iron oxides and hydroxides.

The balance between the oxidation of iron and the reduction of oxygen and water leads to differences in electrical potential between the anodic (iron oxidation) and cathodic (oxygen and water reduction) zones. This can happen in two ways:

• the reaction sites are very close to each other. The thickness of the metal decreases uniformly, causing widespread corrosion;

• the reaction sites are clearly separated and related to heterogeneities in the metal visible to the naked eye, which is characteristic of pitting corrosion.

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