Research Of Defect Detection & Evaluation Method For Protective Coating Of Buried Steel Pipeline Based On Cathodic Protection

Pipeline, a secure and economic means of transporting oil and gas in large scale,is more and more widely used in China.The industry of pipeline transporting is one of the five biggest industries railway, highway, air, ship transporting, and it plays more and more important role in the economic construction and the industries of national defense.Due to the increase of age of pipelines, the detriment, defect during construction, corrosion, the coating of pipeline is severely invalidated in China. The subsequent accidents, such as break and perforation, cause great losses of economy and lives of people.The detection technology of pipeline coating is the import mean for the safe operation of pipelines, but the detection technology is still backward in China, especially in the precise location of coating defects, evaluation of coating defects and quality evaluation of coating. The defect detection and evaluation of pipeline coating is researched, based on the DCVG and CIPS technology, one of the best coating detection technologies in the world. The research purpose is to provide the scientific basis for the work of repairing the coating of pipelines.The detection methods of DCVG and CIPS is deeply studied and practiced on the detection project, which is proved highly effective. The standard of the damaged degree of protective coating of pipeline based on voltage gradient is put forward.The theory of defect location for protective coating of buried steel pipeline based on Wavelet Transform is put forward. The theory of wavelet transform is used to process the detection signals of ON potential,OFF potential and voltage gradient, and the breaking position of protective coating is located accurately according to the theory that the extreme modulus value of wavelet transform responds to the singular point of signals. The engineering experience shows that the defect position is accurate to locate, which can meet the needs of engineering application.Pipeline-soil voltages which are detected by the instrument are processed by wavelet threshold de-noising method,and the noise effects to the pipeline–soil voltages are eliminated. The fixed detection of protective coating is researched and experimented in the engineering. The engineering experiment shows that the protective coating defect can be evaluated by the combined detection technique of DCVG and CIPS.The experiment platform is set up in the laboratory.The protective coating defect is imitated in the pipeline cathodic protection system.The influence that protective coating defect opposes to parameters of cathodic protection system is mainly analyzed.A defect detection and evaluation system of protective coating for buried steel pipeline is developed. Its main functional modules are introduced in detail as well as their implementation techniques. The software system is applied in the engineering,and it shows that the system is convenient to operate, the defect position is accurate to locate and the result of analysis and evaluation is reliable, which can meet the needs of engineering application.