Cathodic protection is a method of protecting metal, especially steel, from corrosion by electrochemically making it the cathode of an electrical circuit, so that it no longer corrodes.
Characteristics
Corrosion is an electrochemical process in which metal gives up electrons and dissolves. Cathodic protection turns this to advantage by ensuring the metal to be protected receives electrons rather than losing them. There are two main forms:
- Sacrificial anodes: galvanic anodes made of a more reactive metal, such as zinc, magnesium or aluminium, are connected to the steel. They corrode away in its place, sacrificing themselves to keep the steel intact.
- Impressed current: a direct current is supplied from an external source through a rectifier, driving the protective effect and allowing larger or more demanding structures to be covered.
Both approaches achieve the same end: the protected steel becomes the cathode, and corrosion is halted or greatly slowed.
Application
Cathodic protection is widely applied to metal that is buried or submerged, where coatings alone cannot be relied on. Typical uses include steel pipelines underground or underwater, sheet piles, storage tanks and the reinforcement within concrete. By extending the service life of these structures, it saves both money and the disruption of premature replacement.
Related terms
- Corrosion
- Reinforcement
- Sheet pile
- Rust
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