Study on the evolution mechanism and influencing factors of CO2 corrosion product film under pipe flow

CO₂ corrosion constitutes a common form of corrosion in oil and gas pipelines. The presence of elevated concentrations of CO₂ in produced water from oil and gas fields has the potential to cause significant corrosion of pipelines and associated equipment, resulting in substantial economic losses. This paper presents the findings of an experimental study of CO₂ corrosion at different flow rates and times. It analyses the mechanism by which CO₂ corrosion products evolve over time at various flow rates, utilizing a combination of characterization techniques, including electrochemical testing, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The experimental setup is an independently designed gas-liquid two-phase flow loop system. The results demonstrate that the flow rate exerts a significant influence on the integrity of the corrosion products. As the flow rate increases, the corrosion rate of the 20# steel initially rises before subsequently declining. The formation and evolution of CO₂ corrosion products under static conditions can be divided into four main stages: the diffusion of the corrosive medium, substrate dissolution, the formation of the product film and continued corrosion. Nevertheless, the flow rate exerts an influence on the formation and integrity of the corrosion product film. At 0.75 m/s, the corrosion behavior is characterized by accelerated corrosion. At 1.2 m/s, the corrosion behavior is characterized by alternating cycles of accelerated corrosion product deposition → erosion damage → accelerated corrosion product deposition → erosion damage.