Cathodic protection for PCCP pipeline

Electrical continuity requirement

According to the requirements of NACE RP 0100 [8], electrical continuity shall be made between the prestressed reinforcement and the steel cylinder in the PCCP pipe to ensure the electrical continuity of the cathodic protection current between the prestressed reinforcement and the steel cylinder. At the same time, to ensure the electrical continuity between THE PCCP pipes, each PCCP pipe should be electrically continuous bonding.

In the protection section of THE PCCP pipe, in order to ensure the service life and protection range of the sacrificer anode, each 20 PCCP pipes (about 100 m) are used as a protection unit for electrical continuity bonding; There is no electrical continuity bonding between each protection unit.

If the PCCP pipe protection section contains steel pipe fittings such as (manhole) exhaust valve well, drain valve well and connected facility, electrical continuity bonding shall be carried out at both ends of (manhole) exhaust valve well, drain valve well and connected facility steel pipe fittings to ensure continuity of cathodic protection current.

Both cathodic protection and stray current protection measures for reinforcement assume an electrical continuity extending through the reinforcement. This is the case for most reinforced concrete structures with steel bars, but this is verified by measuring the resistance of the reinforced mesh. To this end, the measuring cables are connected to the reinforcing bars after the concrete has been removed from the remote points. To avoid the influence of contact resistance, rust should be completely removed from the contact points. If measured resistance value & GT; 1 ω, indicating that electrical continuity is not fully achieved. The steel bar should then be short-circuited to the rest of the reinforcing steel bar of the mesh which has achieved complete electrical continuity.

Electrical insulating

In order to prevent the interference of stray current and the loss of the protection current of THE PCCP pipe, insulation facilities are installed at the head and end of the protection pipe, branches and the connection with the external pipe for electrical insulation.

Cathodic protection criterion

As early as 1984, in the study of the cathodic protection of the Gaeping-Yingkou water supply line, the literature indicated that the protection potential was -0.50V(CSE) when the concrete protective layer was not damaged. When chloride has been applied to the steel bar, the value is -0.71V. Has corroded steel bar, using -0.77V; Japan stipulated in the "Guidelines for the Prevention of Corrosion of Concrete Structures in the Ocean" that the protection potential is -0.77V~-0.85V; To sum up, negative offset -0.10V is adopted for cathodic protection of Geping-Yingkou water supply line; And -0.77V~-0.85V. The maximum protective potential was below the hydrogen evolution potential, which was -1.170V.

According to NACE RP 0100-2004 standard, the polarization potential difference of PCCP pipeline should not be less than 100mV after the cathodic protection system of PCCP pipeline is put into operation. The minimum negative potential should be no less than -1000mV(minus the IR drop). This code applies to cathodic protection and corrosion control of PCCP pipelines. This standard is derived from laboratory test results and successful cathodic protection experience data. During the design, the cathodic protection method and detection period can be determined according to the experience to meet the similar standard requirements.

The above text is quoted from "Cathodic Protection of Concrete Pipe of Prestressed Steel Cylinder" by Hu Shixin et al.

PCCP pipe water supply and drainage engineering provides high quality and long life pipe materials, has great advantages for large diameter and long distance, in recent years in China has made rapid progress in the development, but due to the SHORT application time of PCCP pipe in China, the corrosion of this kind of pipe has not caused people's attention. The practice in foreign countries tells us that cathodic protection is an effective corrosion prevention technology for buried PCCP pipe, which has been vigorously promoted in foreign countries. For example, the Great artificial river project in Libya adopted cathodic protection on the basis of summarizing the experience and lessons of the first phase project. Although the domestic PCCP pipe technology started late, the starting point is relatively high. The CATHOdic protection has been designed for the PCCP pipe in the south-to-North water transfer project and is being put into practice, which is the first time in China. Its experience will bring a qualitative leap to the construction of THE DOMESTIC PCCP pipe in the future.