Investigation Of Corrosion And Inhibition Effect For N80 Steel In Supercritical CO₂/H₂O System

The supercritical CO2 is widely applied in the fields of carbon capture and storage(CCS), oil and gas exploration. The carbon steel will be excessively corroded in supercritical CO2 when the presence of water. The most practical and convenient way to solve the problem is to use the inhibitors, however, there are only few reports about the research of corrosion and inhibition effect in the supercritical CO2-H2 O conditions.This paper aimed at the corrosion and inhibition effect for N80 carbon steel in supercritical and non-supercritical CO2-H2 O conditions. A self-designed weight-loss apparatus and a home-made in-situ dynamic electrochemical measurement system were established. The corrosion behavior of N80 carbon steel and the inhibition effect in supercritical CO2-H2 O conditions were investigated by the weight-loss method, surface analysis method and electrochemical measurements including the EIS and potentiodynamic polarization measurement. The results of weight-loss experiments without inhibitors indicate that the corrosion rate of N80 steel increases with increasing CO2 partial pressure and the rotation rate. There is significant difference in the inhibition effect between non-supercritical and supercritical CO2-H2 O conditions especially under dynamic conditions. Comparing SEM graphs of the surface morphology of test samples, we can see that the corrosion product layers on the surface of N80 carbon steel break off when the CO2 partial pressure and the rotation rate increased. The results of electrochemical measurements indicate that the electrochemical impedance spectroscopy consist of a capacitive semicircle in the high frequency range and an inductive loop in the low frequency range when the absence of inhibitors, while the inductive loop gradually disappeared and turned into a capacitive semicircle with the addition of the inhibitor which significantly increase the value of the Rct and reduce the corrosion rate. The differential capacity curve in supercritical and the non-supercritical CO2-H2 O conditions demonstrate that the potential of zero charge(PZC) shift to the negative direction which result in theresidual positive charge increased on the surface of N80 carbon steel when the CO2 partial pressure changed from non-supercritical to supercritical state. The results of the Uv-Visible Spectrophotometer measuremnets indicate that the concentration of the dissolved inhibitor in the water phase decreased in the supercritical CO2 conditions. The inhibition efficiency increased by enlarging the volume ratio of the test solutions which implied that the concentration of the inhibitor in water phase increased by decreasing the volume ration of supercritical CO2. The computational fluid dynamics(CFD) simulation of the dynamic electrochemical measurement system indicated that the speed, shear stress and turbulent kinetic energy increased by reducing the gap between the rotor and samples. Comparing the non-supercritical CO2 condition, the speed, shear stress and turbulent kinetic energy reduced, but it's distribution on the sample surface change to more inhomogeneously under supercritical CO2 conditions.