Subject and Keywords:
Cathodic Protection (CP) was first applied in 1824, before its theoretical foundation was known. Corrosion of metals is caused by potential difference and metal surface with lower potential becomes an anode in the circuit and gets consumed by corrosion. The principle of cathodic protection is to force the protected metal to become the cathode, by introducing a less noble metal (with higher potential) to be consumed or by introducing an external power source. In principle, cathodic protection is very simple but in practice there are many considerations that need to be addressed. Too low current may not protect the structure while too high current may lead to coating disbonding and hydrogen embrittlement. CP is widely used for pipelines, since corrosion is omnipresent in soil, coating repair is troublesome and expensive, and a gas/oil pipeline failure may be catastrophic. CP is also used to protect oil rigs and ships against corrosion in harsh marine environments. Soil-steel bridges also are prone to corrosion from soil and water, and are difficult to repair, thus CP shows great promise in extending their lifetime. The article presents the principles of CP and the main issues that need to be taken into account in its design. One case study of CP used for a culvert is also discussed.