Resistance test method for cathodic protection

2022-01-18 09:48
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Insulating connectors for buried pipelines generally refer to insulating joints or insulating flanges. For assembled insulating flanges or integral insulating joints, electrical insulation performance tests should be carried out before installation into the pipeline. Generally, a megohmmeter can be used to directly measure the insulation resistance value. The megohmmeter method is only suitable for insulation resistance measurements of insulation joints that are not installed on the pipeline.


      The Jueyan joint installed on the buried pipeline, the pipelines on both sides have formed a closed loop through the soil, which can be regarded as a grounding body and is in a conducting state, so the insulation resistance can no longer be measured by the megohmmeter method. At this time, its insulation performance can be tested by potentiometric method.


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


      When using the potential method, it should be noted that when the grounding resistance value of the pipeline on the unprotected side is very small, even if the leakage of the insulation joint is serious, since the leakage resistance is much larger than the grounding resistance of the pipeline on the unprotected side, the ground potential of the pipeline on the unprotected side will not be significantly negative. shift, resulting in an error in the judgment of the potentiometric method. In addition, if the arrester of the anode lead-out line is broken down, or the auxiliary anode is too close to the insulating joint, the potential of the insulating joint will be significantly moved forward when the protection side is powered. There will also be a significant negative shift, resulting in a misjudgment by the potentiometric method.




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