Resistance test method of cathodic protection

The insulated connector of buried pipeline generally refers to insulated joint or insulated flange. For the assembled insulation flange or integral insulation joint, the electrical insulation performance test shall be conducted before installation into the pipeline. Generally, megger can be used to directly measure the insulation resistance. The megohmmeter method is only applicable to the insulation resistance measurement of insulated joints not installed on the pipeline.

For the gorgeous joint installed on the buried pipeline, the pipeline on both sides has formed a closed loop through the soil, which can be regarded as the grounding body and is in the conduction state. Therefore, the megohmmeter method can not be used to measure the insulation resistance. At this time, the potential method can be used to test the insulation performance.

The principle of the potential method is as follows: if the insulation performance of the insulated joint is good, there will be no cathodic protection current flowing from the protected pipe side through the insulated joint to the unprotected side. After the cathodic protection station supplies power to the pipeline on the protected side, the pipe ground potential of the protected side moves negatively under the action of the cathodic protection current, but the pipe ground potential of the deep well anode is almost unchanged due to no current inflow at the unprotected side. If the insulation performance of the insulated joint is not good, the cathodic protection current will flow through the insulation flange, and the pipe ground potential on the unprotected side will also move negatively.

When using the potential method, it should be noted that when the grounding resistance of the unprotected side of the pipeline is very small, even if the insulation joint has serious leakage, because the leakage resistance is far greater than the grounding resistance of the pipeline on the unprotected side, the pipe ground potential of the unprotected side will not be significantly negative shifted, which leads to the misjudgment of the potential method. In addition, if the arrester of the anode outlet is broken down, or the auxiliary anode is too close to the insulation joint, the local potential of the insulated joint will be significantly positive when the power is supplied to the protection side. Even if the insulated joint does not leak electricity, the measured value of the pipe ground potential on the non protection side will also be significantly negative, which will lead to misjudgment of the potential method.

Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing cathodic protection technology, engineering design, installation and technical services.