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The first application of CP dates back to 1824, long before its theoretical foundation was established. The principle of CP is simple. A metal dissolution is reduced through the application of a cathodic current. Cathodic protection is often applied to coated structures, with the coating providing the primary form of corrosion protection. The CP current requirements tend to be excessive for uncoated systems. Cathodic protection has probably become the most widely used method for preventing the corrosion deterioration of metallic structures in contact with any forms of electrolytically conducting environments, i.e. environments containing enough ions to conduct electricity such as soils, seawater and basically all natural waters. Cathodic protection basically reduces the corrosion rate of a metallic structure by reducing its corrosion potential, bringing the metal closer to an immune state.
The basic principle of all CP techniquesis that the unwanted anodic corrosion reactionsare 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 lessthan that 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 towards its immune state as shown for iron and steelor for aluminum and its alloys.
The basic principle of CP is simple. A metal dissolution is reduced through the application of a cathodic current. Cathodic protection is often applied to coated structures, with the coating providing the primary form of corrosion protection. The CP current requirements tend to be excessive for uncoated systems. The two main methods of achieving this goal are by either:
Using sacrificial anodes with a corrosion potential lower than the metal to be protected (see the seawater galvanic series)
Using an impressed currentprovided by an external current source
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