Study On The Fast Detection System For Coating Defects Of Buried Pipelines

Because of its unique advantages of transporting gas, liquid and slurry, pipeline transportation has become the vitals of modern industry and national economy, playing a more and more important role in the economic construction and national defense industry. The corrosion of metal is one of the critical factors that affect the reliability and the service life of buried steel pipelines. The integrated application of anticorrosive coating and cathode protection performs an effective protection function to the buried steel pipeline, thus preventing the external corrosion of the pipeline. It is indicated in the related data that more than half of the pipelines in the world have served for over 30 years and most of the long-transferred oil and gas pipelines in China have also been in production for more than 20 years. As a matter of experience, the anticorrosive coating has already stepped into the stage when the accidents happen most frequently. Therefore, it is imperative to carry out the detecting and servicing of the anticorrosive coating of pipelines systematically.Although there are a variety of detection techniques for the anticorrosive coating defects of buried pipelines, none of them could provide the whole information about the anticorrosion state of pipelines. Both CIPS (close interval potential survey) and DCVG (direct current voltage gradient) techniques are quite advanced coating detection techniques in the world and are good examples of portable coating detection instruments that have high efficiency. At present the detection techniques in China for pipeline coating defects are still being developed and the research and exploration on the instrument based on the above techniques is at a relatively backward stage. As a result of the complexity and necessity of the buried pipeline detection, it is of significant importance to study the detection techniques and instruments for the anticorrosive coating defects of pipelines, as well as to evaluate the quality of the coating accurately and effectively.The existing detection techniques for coating defects of buried pipelines have been compared and analyzed with their advantages and disadvantages summarized in this paper, meanwhile the integrated detection technique of CIPS and DCVG is proposed to be the study object of this paper. The principle of the cathode protection of buried pipelines as well as the distribution rule of impressed electric potential along the pipeline has been analyzed, and using the instantaneous power cut method to eliminate the soil IR drop during the potential measurement is specially pointed out.