Cathodic protection is a method for preventing metal dielectric ( water, fresh water and soil media ) electrochemical corrosion protection technology , the basic principle of this technique is applied to the metal surface to be protected certain DC current to produce a cathode polarization, when the potential of the potential value of a metal is lost , the anodic dissolution process of corrosion will be effectively suppressed. Depending on the way to provide a cathode current cathodic protection anodes is divided into two sacrificial and impressed current method, the former is a more negative potential of a metal ( such as magnesium , aluminum, zinc, etc. ) with a metal structure to be protected electrically connected , by continuously dissolving electronegative metal or alloy is consumed , to provide a protective current to be protected , the metal structure for protection . The latter is an external AC power into low-voltage direct current through the auxiliary anode current is passed to the protective metal structure to be protected , so that corrosion is suppressed. Whether sacrificial anode or impressed current method, the effective and rational design application can get a good protective effect.
Joint application of cathodic protection and coating , can make the underground or underwater metal structures to obtain the most economical and effective protection . Good coating layer can protect the outer surface of the structure is not more than 99% of the corrosion of metal structures is generally in the underground or underwater use before coating the metal with a protective coating to electrically insulate the dielectric environment . If the metal structure can be completely electrically insulate the metal corrosion in the dielectric forming the battery is suppressed, and the corrosion current can not be generated , thereby preventing corrosion of metals . However, the coating layer is preferably completely does not exist , since the construction in the transport , installation and mending , treated soil stress and thermal stress , aging , and the presence of the coating the coating tiny pinholes , metal structures layer is always some defects, these defects ultimately result in localized corrosion of metal produced . Cathodic protection and coating combination can effectively solve this problem. Aspect cathodic corrosion protection coating is effective to prevent breakage resulting prolong the life of the coating , but also significantly reduce the protective coating on the other hand the current requirement to improve the distribution of the protection current , increasing the radius of protection , the protection of the cathode become more cost-effective for underground or underwater metal structures , cathodic protection corrosion coating poorly exposed or even the only alternative means of corrosion protection . Cathodic protection costs usually account for only 1% to be protected 5% of the cost of the metal structure , and the life of structures can thus be doubled or even several times extended , therefore, this technology has been widely recognized by the people , and has been more widely used in ships, harbor facilities engineering , marine engineering , petrochemical, power , municipal and other areas , the prospects are very broad.