Effects of the dissolved oxygen and slurry velocity on erosion-corrosion of carbon steel in aqueous slurries with carbon dioxide and silica sand

Carbon dioxide corrosion is one of the important degradation mechanism for carbon steel pipelines in the oil sands, oil and gas industries. Such type of corrosion has attracted considerable attention due to the increased tendency to inject CO2 into oil wells to reduce the viscosity of oil for increased production. When erosion is involved, the synergy of corrosion and erosion can significantly accelerate the failure of steel pipelines. It has been noticed that CO2 corrosion of carbon steel is influenced by the level of dissolved oxygen (DO) in solution. Since DO level in the sections of pipeline at distance from inlets can be considerably lowered due to the oxidation of substances in the transported solutions, the damage to pipelines caused by erosion-corrosion varies in different sections. In this study, erosion-corrosion of a pipeline steel (X65) in aqueous slurries containing silica sand and CO2 at different dissolved oxygen (DO) levels was investigated. It was demonstrated that the damage to the steel was increased when CO2 was blown into the slurry. However, when CO2 was blown at a much higher pressure, which significantly reduced the DO level of the slurry, the weight loss was lower than that in open air without CO2, indicating that the dissolved oxygen considerably enhanced the CO2 corrosion and the erosion-corrosion synergy. Thus, CO2 could play a more destructive role in the vicinity of pipeline inlets. Besides, the destructive effect of CO2 on the steel was stronger at lower slurry velocities. Efforts were made to clarify relevant mechanisms responsible for the observed phenomena.