Erosion-corrosion Behavior And Numerical Simulation Of Typical X65 Steel Pipes In Simulated Formation Water

Pipeline is an important conveying equipment for industrial production and erosion-corrosion failure is a common failure form in various pipeline failure cases.During the oil and gas transportation process,the cross-section or shape of the pipeline material often changes,such as reducer,elbow,etc.The transporting corrosive medium and solid particles will cause severe erosion-corrosion on pipeline steel material,which will cause early damage of the pipes.Therefore,it is of great significance to study the erosion-corrosion behavior of typical pipes in simulated formation water with sand particles to predict the corrosion degree of pipelines and effectively prevent pipeline leakage and fracture.In this paper,the erosion-corrosion behavior of X65 carbon steel reducer and elbow in simulated oilfield formation water was studied by tube flow experimental device using weight loss method and electrochemical test.Pure corrosion rate,pure erosion rate,corrosion-enhanced erosion rate,erosion-enhanced corrosion rate and their percentages accounting for total erosion-corrosion rate at different locations of the tube were determined.The morphology after erosion-corrosion was characterized by SEM,EDS and XRD techniques.The flow characteristics and erosion distribution of pipe under liquid-solid two-phase flow conditions were obtained by computational fluid dynamics simulation.The experimental and simulation results indicated that with the decreasing of reducer tube diameter the erosion-corrosion rate,erosion rate(total erosion rate,pure erosion rate and corrosion-enhanced erosion rate)and their percentages in erosioncorrosion rate are increased.And the total corrosion rate and erosion-enhanced corrosion rate are also increased with the decreasing of tube diameter,but their percentages in erosion-corrosion rate are reduced.From the location of tube top,tube side to the tube bottom,a similar erosion-corrosion behavior could be obtained except for the reduction of corrosion-enhanced erosion rate and its percentage in erosioncorrosion rate.This erosion-corrosion behavior of the reducer is result from the distribution of flow velocity and sand particle concentration and the synergistic interaction between erosion and corrosion,especially the erosion-enhanced corrosion rate.At the position of the elbow inlet,the inside erosion-corrosion rate is higher than outside.At the rear position of the elbow,the erosion-corrosion rate increases as the axial angle θ increases,and decreases as the annular angle Ф increases(from outside to inside of elbow).The maximum erosion-corrosion rate occurs at the outside of elbow outlet and downstream straight pipe.The distribution of total corrosion rate,total erosion rate,pure erosion rate and erosion-enhanced corrosion rate are the same as total erosion-corrosion rate.The inside corrosion-enhanced erosion rate is higher than outside.The percentages of total corrosion rate,pure corrosion rate,erosion-enhanced corrosion rate and the corrosion-enhanced erosion rate accounting for total erosioncorrosion rate decrease as the axial angle θ increases and increase as the annular angle Ф increases.The percentages of total erosion rate and pure erosion rate increase as the axial angle θ increases,and decrease as the annular angle Ф increases.A high erosioncorrosion rate is associated with a high impact of sand particles.