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　　Insulated joints Uses: buried steel oil, gas, water pipelines are often damaged due to corrosion, not only reduce life expectancy, serious also cause accidents. Effective measures to prevent corrosion of buried pipelines are to adopt cathodic protection technology. In the cathodic protection project, it is required to cut off the electrical connection between the protected pipe and some of the devices, equipment and tributaries connected to it, and to avoid the loss of the negative protection current to the unconnected parts. To ensure the success of cathodic protection technology.