How Cathodic Protection Works in Water

The basic principle of all CP techniques is that the unwanted anodic corrosion reactions are suppressed by the application of an opposing current forcing the local anodes to be polarized to the potential of the local cathodes therefore stifling corrosion cells. If less than this amount of cathodic current is supplied some corrosion would still occur, but the level of corrosion would be less without any CP. From a thermodynamics point of view, the application of a CP current basically reduces the corrosion rate of a metallic structure by reducing its corrosion potential toward its immune state (see Figs. 4.14 and 4.17). The two main methods of achieving this goal are by either  

These simple schematics are neglecting one important component that may be a useful monitoring tool for sacrificial CP systems but is a must for ICCP for which controlling the potential applied to a protected structure is essential. This tool called a reference electrode is mentioned in the next sections, but details of its usage and functionality are described in Sec. 13.5.1. 

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