Mechanism verification of severe corrosion caused by local oil-water slippage of X65 pipeline steel in an offshore oil field

Purpose In 2020, an oilfield in the South China Sea conducted a corrosion test on a sea pipeline laid on the seabed made of X65 pipeline steel and found that serious internal corrosion occurred inside. The Purpose of this study is to ensure the safety and stable production of the oilfield, the oilfield proposed to verify the leading factors and mechanisms of severe corrosion of the X65 pipeline steel. Design/methodology/approach Based on the actual working conditions and environmental parameters of X65 pipeline steel, the corrosion rate of X65 pipeline steel was studied by a laboratory corrosion immersion experiment. The mechanical parameters of X65 pipeline steel were studied by tensile testing. The mechanical-electrochemical corrosion model was established according to the sea pipeline’s environmental parameters and working conditions. The parts of the sea pipeline prone to corrosion were simulated and analyzed by ANSYS software, and the high-risk positions of corrosion were predicted. Findings The results of laboratory simulation corrosion tests, mechanical properties tests and finite element simulation have shown that severe two-phase turbulence will occur in the oil-water mixed multiphase flow inside the X65 pipeline, which will produce fluid impact force on the inner wall of the pipeline, increasing local moisture content, with the local moisture content exceeding 30 Wt.%, resulting in an area prone to corrosion appearing at the oil-water phase decomposition interface. Considering the field data and the actual working conditions, the oil-water slippage phenomenon and the prediction of a high risk of corrosion in the X65 pipeline steel offshore pipeline were analyzed by the finite element simulation method. Originality/value The study on the main corrosion factors of X65 pipeline steel can provide guidance for the oil production process and material selection in the oilfield. In this work, the corrosion mechanism of X65 pipeline steel was studied comprehensively by finite element analysis simulation and laboratory simulation corrosion tests.