The corrosion behavior in CO2 medium of 20# steel under the (CO2/aqueous solution) gas-liquid two-phase stratified flow condition

The corrosion rate, morphology, and composition of corrosion products of 20# seamless steel in CO2 medium under gas-liquid two-phase stratified flow conditions (CO2/aqueous solution) have been investigated using the weight loss method, scanning electron microscopy with energy-dispersive x-ray spectroscopy, and x-ray diffraction. The forming mechanism of corrosion products has been discussed. Results showed the irregular zigzag trend of the corrosion rate curve with the gradual extension of corrosion time. The corrosion rate peaked at corrosion times of 4 and 8 h, with the values reaching 1.49 and 0.647 mm/a, respectively. At the beginning of the corrosion process, a layer of special iron oxide formed rapidly on the 20# steel surface. The local corrosion products with cell shape precipitate and grow on the special iron oxide surface with the extension of corrosion time, and the initial corrosion product is mainly strip-shaped along the CO2 gas flow direction. The local cellular corrosion products extended along the perpendicular direction of gas flow to gradually form an entire covering product layer with the extension of corrosion time. The main phases of corrosion products include FeCO3 and iron oxides. The loose inner layer mainly comprised Fe3C and little amount FeCO3, whereas the dense outer layer was mainly composed of FeCO3 and a few iron oxides. The loose corrosion product layer presented a period of densification after formation.