Cathodic Protection (CP) is one of the main and the most effective method to prevent most types of corrosion on a metal surface. In some cases CP can even stop damage arising due to corrosion. Metals, especially ferrous metals, corrode in the presence of oxygen, water, and other impurities such as sulfur. Without CP, metals act as the anode and easily lose their electrons and thus, the metal becomes oxidized and corroded. CP simply supplies the metal with electrons from an external source, making it a cathode.
Let’s understand the basic terminologies
- Oxidization: Loss of Electrons
- Reduction: Gain of electron
- Anode: Where oxidization reaction takes place
- Cathode: Where reduction reactions take place
- Types of Cathodic Protection:-
- Galvanic Cathodic Protection
Galvanic cathodic protection involves protecting metal surfaces of an equipment using another material that is more reactive. The latter also called as the sacrificial anode has less electrochemical potential compares to metal component being protected. Therefore the sacrificial metal undergoes oxidization rather than the metal component that is being protected.
The figure above illustrates how the galvanic cathodic protection
Sometimes, steels are galvanized rather than connected to galvanic anodes. Galvanized steels are steels that are coated with a protective zinc layer. The zinc layer acts to cathodically protect steel against corrosion in most underground and marine environments.
Impressed Current Cathodic Protection (ICCP)
ICCP is the more economical method of CP when underground pipelines are long or offshore equipment is too large to protect via one or few galvanic anodes. In ICCP electrons are supplied to cathodic structure via an external DC source (Rectifier). The steel component is connected to the negative terminal of the power source and the impressed current anodes are connected to the positive terminal of the power source.
Industry application of cathodic protection
Cathodic protection is used routinely for protecting equipment operating in aggressive environments. The 2 most common applications of cathodic protection are for buried pipeline systems & vessels as well as off shore platforms.
Cathodic protection is not used to protect equipment in atmospheric condition or protect components internally.