Cathodic protection is a kind of used to prevent the metal dielectric (seawater, fresh water and soil, etc) in the erosion of the electrochemical protection technology, the basic principle of this technology is to protect metal surfaces exert a certain dc current, make its produce cathodic polarization, the potential of occurring when the metal was a potential value, the erosion of the anodic dissolution process can effectively bay.

According to different cathodic current, cathodic protection is divided into two sacrificial anode and impressed current method, the former is a more negative potential of metal (such as aluminum, magnesium, zinc, etc.) and the protected metal structure of the electrical connections, through the electronegative metal or alloy melting consumption, provide protection to be protected from electrical current, make the metal structure to be protected. The latter is the external alternating current into low voltage direct current, through the auxiliary anode will be the protection of the current to the protected metal structure, so that erosion can be inhibited.

Whether the sacrificial anode method or the impressed current method, its effective and reasonable design and application can obtain good protection effect. The combination of cathodic protection and coating can provide the most economical and effective protection for underground or underwater metal structures. A good coating protects more than 99% of the outer surface of the structure from erosion. Underground or underwater metal structures are usually coated with a protective coating before use to provide an electrical insulation of the metal from the dielectric environment. If metal structures can achieve complete electrical insulation isolation, metal in the dielectric erosion battery formation will be inhibited, erosion current will not be generated, thus preventing metal erosion. However, there is no such thing as a completely ideal coating, because there are always some defects in the outer coating of metal structures due to transportation, installation and filling, thermal stress and soil stress, the aging of the coating and the existence of tiny pinholes in the coating, and these defects will eventually lead to local erosion of the metal.

The combined application of cathodic protection technology and coating can effectively solve this problem. Cathodic protection on the one hand can effectively prevent the erosion of lesions of coating, prolong the service life of coating, coating on the other hand, can greatly reduce the requirement of protection current, improve the protection of current distribution, increase the protection radius, has made it more economic and effective, for the cathodic protection on bare or poor anticorrosion coating of underground or underwater metal structures, Cathodic protection is even the only means of choice for erosion protection. Cathodic protection measurements are usually only protected metal structure cost 1% ~ 5%, and the service life of the structure can be double or even several times to extend because of this, therefore, the technique to get general recognition of the people, and has set up a ship, in port engineering measures measures, Marine engineering, petrochemical, electric power, municipal, and other fields to get more and more widely used, the vision is very broad.