Corrosion Behavior of X65 Steel in Simulated Gathering Pipeline Environment

The corrosion behavior of X65 steel in the CO₂/oil/water environment in gathering pipeline was investigated by mass loss method, SEM and XRD. The results show that the corrosion rate of the X65 steel increased at first and then decreased with the increase of flow rate and CO₂ pressure, and critical velocity and critical pressure existed, below the critical value, the corrosion products formed on the steel surface were loose, porous and unstable, higher than the critical value, the product films were dense and had strong adhesion with a certain protective effect. When the flow rate increased to more than 1 m/s, the oil film adsorbed on the sample surface more evenly, the active points of corrosion reaction were reduced and the substrate was protected from being corroded, thus the corrosion rate decreased. With the increase of CO₂ partial pressure, the solubility of CO₂ in crude oil increased, the viscosity of crude oil decreased, the mobility of the crude oil became better and the probability of oil film adsorption increased, these factors led to the reinforcement of corrosion inhibition to X65 steel, and the corrosion rate decreased.