The current at the defect of pipeline anticorrosion coating enters into cathodic protection and forms cathodic voltage cone in soil. For anticorrosive coating with strong mechanical strength, there are only a few defects of anticorrosive coating occasionally, and they are far away from each other.
In the vicinity of these defects, the shape of the potential line is similar to that of the grounding plate, and at a further distance, the potential is similar to that of the buried earth. If there are many defects in the anticorrosive coating of pipeline, and these defects are close to each other, these single voltage cones are combined to form a cylindrical voltage field around the pipeline. It is usually due to the lack of anti-corrosion coating for old pipe fittings, poor insulation weld quality, no anti-corrosion coating for electrical connection and external pipe or bushing, etc. the old pipeline needs high protection current. The bare steel surface in cathodic protection soil may require a protection current density of up to 500 mA. M-2, especially in well ventilated conditions, produces a voltage cone of several hundred millivolts.
Through the buried pipeline in the voltage cone area of cathodic protection pipeline, the protection current outside the voltage cone is detected. When the pipeline leaves the cathode voltage area, the unprotected pipeline will have anodic corrosion. The potential of the affected pipeline measured by the reference electrode on the cross point surface is mainly the resistance voltage drop caused by the protection current flowing from the soil to the defective part of the cathodic protection pipeline.
Since the voltage cone of cathodic protection pipeline will disturb the external pipeline, it can be evaluated by measuring the voltage drop on the soil surface. Therefore, it is not necessary to establish measurement points at each intersection to determine the interference of cathodic protection devices on external pipelines.
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.
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