Corrosion failure of 20^# steel in the complicated environment

In order to understand deeply the corrosion failure of 20^# steel in the complicated environment and define the main factors of corrosion failure, failure analysis was carried out on the oil and gas mixed pipeline section in Tahe oilfield by means of macroscopic analysis, chemical composition analysis, tensile property and metallographic analysis, scanning electron microscopy and energy spectrum analysis and X-ray diffraction analysis (XRD). It is indicated that the main cause of corrosion perforation in this pipeline section is the electrochemical corrosion caused by the corrosive medium. The main corrosion products are FeCO₃, FeOOH, FeS, FeOH·H₂O and so on. The Cl^-, H₂S, CO₂ and O₂ in the medium of pipeline transportation are the main compositions that lead to corrosion perforation. Among them, H₂O is the carrier of corrosion, and CO₂ has the most significant effect, followed by H₂S. Besides, stronger corrosion scaling is presented on the pipeline due to the characteristics of high content of Cl^-, H₂O, CO₂ and H₂S, high mineralization degree and low pH of the produced liquid in this oilfield. Finally, the effects and laws of pipeline sediments on pipeline corrosion failure were further determined by performing point corrosion tests with/without the coverage of sediment in the laboratory. It provides technical support for the corrosion control of metal pipelines in the future.