About the cathodic protection design of urban pipelines, people seem to enter a misunderstanding. For example, the sacrificial anode method is adopted in Tianjin. It is considered that this method has the advantages of small interference, simple management and uniform current distribution. However, this method also has some limitations, such as high cost, limited by soil resistivity and limited life. At present, 3PE tube is widely used, so that the cathodic protection current needs very little, voltage is small, basically will not cause interference to the adjacent device. In the aspect of management, sacrificial anodes are buried in many groups, and the phenomenon of human damage and loss is very serious in urban construction, which is difficult to manage. For example, 45 zinc anodes were used in Shaanxi-Tianjin pipeline 8Km into the city, and 18 of them were lost after 14A operation, along with many test piles. The applied current cathode protection in the suburbs of 54Km is normal until now, the grounding resistance is less than 1ω, and the output current is 0.2A. The management personnel only need to maintain an auxiliary anode ground bed and ensure the normal operation of the power supply. It is much simpler than sacrificing the anode in management. This EXAMPLE SHOWS THAT THE APPLIED CURRENT HAS the ADVANTAGES of long SERVICE life OF the device, not limited by soil resistivity, and adjustable current output. In addition, the applied current can also adjust the potential arbitrarily when the stray current is large. When forced discharge is used, it is a cathodic protection of applied current.
At present, Tianjin will popularize energy-saving and environmental protection in five years, and use natural gas to burn coal to improve urban environmental quality. Since the beginning of 2012, the natural gas pipeline DN600-700 3PE has been re-laid under the road. In order not to affect the traffic, the construction is carried out at night, and all the anode protection is adopted. Because of the city pipeline branch, into each boiler also need to add insulation, resulting in a lot of insulation joint consumption, the project cost is very high.
In view of this scheme, the applied current protection method is recommended for partitioning. The advantages of the system are that it can adjust the output, build branch lines, expand and build new pipelines in the zoned area, and can be incorporated into the original protection system in most cases. In addition, this method can avoid overprotection, not limited by soil resistivity, reduce the number of insulation joints, and the cost will be greatly reduced.
The anode ground bed has two ways: (1) low output applied current protection, in the area as the unit, in this device, each anode bed is installed only 1 ~ 2 anodes, the output current is less than 1A, because the voltage is small interference, can greatly reduce the number of anode ground bed. (2) Deep well Yang stage ground bed, the protection current flows from deep to the surface, there is no external pipeline in the way of the flow current, will not cause interference, different parts of the protected structure are independent end, can reduce the shelter, resulting in uniform current distribution. One anode hole can protect a large area without causing interference problems. In addition, the anode bed can be located anywhere, which requires the least number of holes and occupies the least space, especially suitable for urban and industrial areas. Since 2007, Beijing Gas has used 7 ~ 8 deep well anodes to protect the pipe network in different areas of the city to realize additional cathodic protection.