Study on Corrosion Mechanism of N80 Steel Pipe Columns and Threads by CO2-Cl- in Shale Gas

The entire research reveals the corrosion mechanism by comparing the corrosion morphology of the threads and pipe columns, as well as simulating their flow conditions. The experimental findings indicate that primarily localized corrosion occurred at pipeline connections. The corrosion product layer consists mainly of iron oxide and ferrous carbonate. Through electrochemical experiments, the corrosion resistance of the threads and pipe columns was tested and evaluated. According to research using CFD software to simulate fluid flow, there is evident turbulence at the pipe column connections. This turbulence is due to the local pipe diameter change between the two column connections. Additionally, the fluid convection phenomenon in the threaded joints creates local pressure, leading to the accumulation of corrosive media in the fluid and accelerating the corrosion rate. Based on the above characterizations, the primary cause of severe corrosion at the threaded joints is CO2, while the high content of Cl- in the environment and fluid turbulence are the main factors that destroy the dense corrosion product film and expedite corrosion. Together, these factors reveal the corrosion failure mechanism of the threaded joints caused by CO2-Cl- environmental fluids in turbulent flow conditions.