Research On DC Potential Detection Technology For Buried Steel Pipeline

As a secure and economical means of transporting crude oil and gas, pipelines have been used all over the world. The industry of pipeline transporting is one of the five biggest industries including railway, highway, air, water transportation, and it plays more and more important role in the economic construction and the industries of national defense.Due to the increase of running time of pipelines, the detriment, defect during construction, corrosion, the coating of pipeline is severely invalidated. Consequently, the accidents, such as break and perforation, cause great losses of economy and lives of people. So the external corrosion of steel is one of the most key factors that influence the reliability and life of the buried pipeline system. To mitigate corrosion, a combination system of protective coating and cathodic protection is widely utilized. These protection techniques have been widely put into use in long-distance pipeline domestically.Normally cathodic protection is acquired by sacrificial anodes and impressed current. Based on studying home and abroad documents and the existing theory of sacrificial anodes. The mathematical model of potential distributing protected by sacrificial anodes is established. Research about distribution of protect potential influented by soil enviroments and the distribution when coating is damaged. Based on this research, laboratory model is estabished. Ansys is used to do finite element analysis for proving the correctness of theory model and laboratory model. By referring to 850mV rule and experiment, the evaluation of effectiveness protected by sacrifying anodes was put forward .The theory of wavelet transform is applied to process the detection signals of ON potential and OFF potential. Pipeline-soil voltages detected by instruments, are processed by wavelet threshold de-noising method, and the noise effects to the pipeline–soil voltages are eliminated. Thus the real signal data is restored. The fixed detection of damaged point on the coating is researched and the manner has been experimented in the engineering, All the results mentioned have been approved pretty well by engineering experiments.The operational software has been developed that can be used for evaluating quality condition of the burial steel pipe coating protected by sacrificial anodes. Its main functional modules are introduced in detail as well as their implementation manners. The software system is applied in the engineering and the system is convenient to operate, the damaged position is accurate to locate and the result of analysis and evaluation is reliable, which can meet the needs of engineering application.