Study On The Drag Reduction Internal Coating Performance For Serviced Gas Pipeline

Study and application of the internal coating for pipeline in our country have been started relatively late. From the trunk of pipeline first use internal coating technology to now, the coating has gone through eight or nine year service. Because it is unable to directly inspect the internal coating of serviced pipeline, so the reliability and timeliness of inner coating can not make clearly. The internal coating of serviced pipeline has not been studied in our country. However, understanding and mastering the inner coating performance and failure process have an impotant significance to ensure the quality of transported gas, safety of the gas transmission system, the social and economic effect of the internal coating. Therefore, the present work will be focused on the research within internal coating of serviced pipeline.The main results of the present paper are achieved from a piece of pipeline which is cut from the pipeline in a high-risk areas and having been serviced nearly 5 yesrs. Using conventional coating experiments and electrochemical impedance test the performance of the inner coating has been studied. Using fuzzy theory to the comprehensive evaluation model has been established for internal coating life influence analysis and the evaluation results have been obtained. The results include the following aspects:(1) Using conventional coating experiments, the performance of the inner coating has been studied. The results showed that, because the weld reinforcement is eroded and abroded by the dust particles of the medium transported in long-term, making the coating spalling seriously where in weld position; the anti-stripping, wear resistance, adhesion of the coating is good, but the corrosion resistance is poor.(2) Using fuzzy theory, according to the hierarchical method proposed comprehensive evaluation index system for inner coating life of pipeline, the comprehensive evaluation model has been established and the fuzzy evaluation results have been obtained through to expert scoring. The results showed that, no one think the inner coating comprehensive life is excellent,51 percent of people think coating comprehensive life is good, about 40 percent of people think coating comprehensive life is medium,6 percent of people think coating comprehensive life is poorer, and 3 percent of people think coating comprehensive life is very poor.(3) Electrochemical impedance spectroscopy testing of surface complete coating. The results showed that, after 24h immersion, the coating resistance from 109Ω·cm2 quickly reduced to less than 106Ω·cm2, show that the surface of the coating have a lot of micro-defects that make electrolyte solution easily work into coating/basic metal cause by corrosion of base metal; after 408 h immersion, the coating resistance is reduced to 104Ω·cm2, coating surface appeared with visible minimal bubbling, coating performance has deteriorated.(4) Electrochemical impedance spectroscopy testing of surface with defects coating. The results showed that, after 0.5h immersion, coating system has a low impedance values of low frequency (from 103 to 104Ω·cm2); then the coating/basic metal system appears rising trend; With the immersion time prolong, the corrosion products increase, make the coating adhesion decrease, the coating protective performance is degradation, After 424h immersion, the low-frequency impedance values of the coating specimen as low as X70 steel.