TABLE OF CONTENTS Many different types of corrosion exist (Pourbaix, 1973; Snoeyink and Wagner, 1996), and only a few of the most significant to the corrosion of drinking water systems will be covered here. Specialized corrosion texts should be consulted for more comprehensive discussions.
The kind of attack depends on the material, the construction of the system, the scale and oxide film formation, and the hydraulic conditions. Corrosion forms range from uniform to intense, localized attack. The different forms of corrosion are primarily influenced by the distribution of anodic and cathodic areas over the corroding material. If the areas are microscopic, and very close to each other, corrosion may be relatively uniform over the entire surface. If the areas are scattered, however, and especially if the potential difference is large, pits may form, sometimes covered with the irregular and sometimes voluminous deposits called tubercles, which can greatly impede water flow.
According to one model, when uniform corrosion of a single metal occurs, any one site on the metal surface may be anodic at one instant and cathodic the next. Anodic sites shift or creep about the surface, so rate of loss of metal becomes relatively uniform over the metal surface.
An alternative model for uniform corrosion is that oxidation at a metal surface is accompanied by electron transport through an adherent film (see Snoeyink and Wagner, 1996, Figure 1.7). Reduction of oxygen occurs at the film surface, and transport of ions to and away from the...
