Evaluation on quality of anticorrosive coating and effect of cathodic protection for crossing pipeline

The coating may be damaged during the back dragging of horizontal directional drilling crossing pipeline, and inadequate cathodic protection may exist because the distribution law of cathodic protection potential of the crossingpipeline section is different from that of the straight section and it is difficult to test. All these conditions bring the risk ofcorrosion to the crossing pipeline. Hence, evaluation was carried out to the quality of the anticorrosive coating and theeffect of cathodic protection for the in-service crossing pipeline. During the evaluation, feeding test was conducted withtemporary anode groundbed, in-line current test was carried out with current loop, and tests based on surface potential, soilresistivity and cathodic polarization behavior were conducted for the crossing section. On this basis, the conductivity of theanticorrosive coating of the crossing pipeline was calculated, and the quality of the anticorrosive coating was evaluated.Additionally, by estimating the cathodic protection potential of the damaged point, a method was formed for the evaluationof the quality of the anticorrosive coating and the effect of cathodic protection of the crossing pipeline. For the two crossingpipeline sections in the case study, the quality of the anticorrosive coating was evaluated as excellent for both, and for thesection with lower quality, the cathodic protection at the damaged point was estimated, with the most positive potentialof －0.845 V_CSE. Therefore, it can be recommended to appropriately increase the cathodic protection current or to adopt the100 mV polarization criterion. As indicated by the test results, the method is applicable to the evaluation of the anticorrosivecoating quality of the in-service crossing pipeline and it also provides suggestions to the operation and maintenance ofcathodic protection.