Cathodic protection of direct-buried insulated pipe is an electrochemical protection method in metal anti-corrosion. Unlike other anti-corrosion processes for direct-buried insulated pipe, it applies current to the protected metal body so that the electrode potential of the protected metal shifts in the negative direction, reducing the metal’s spontaneous tendency to change from the atomic state to the ionic state, thereby fundamentally suppressing corrosion. However, this process must be carried out in an electrolyte, so buried steel pipes are well suited to cathodic protection. Cathodic protection is a supplement to the anti-corrosion coating of the direct-buried insulated pipe itself. The presence of the anti-corrosion coating can greatly reduce the current consumed by cathodic protection, and cathodic protection can compensate for deficiencies of the anti-corrosion coating, thereby improving safety and economy. Achieving a perfect combination is the preferred anti-corrosion solution for practitioners.

　　The anti-corrosion grade of the steel casing of direct-buried insulated pipe shall be determined according to the local soil corrosivity grade. When soil corrosivity is high, the anti-corrosion grade shall be taken as extra-reinforced. When soil corrosivity is medium, the anti-corrosion grade shall be taken as reinforced. When the grade is low, a standard anti-corrosion grade may be used. It is therefore necessary to know the corrosivity level of the pipeline route in order to optimize the anti-corrosion grade.