Characterization of iron carbonate scales developed under carbon dioxide corrosion conditions

Carbon steel CO₂ corrosion is a common and very serious problem in the oil industry. It often results in severe damage to pipes and equipment. Besides controlling direct costs associated with loss of production and replacement or repair to the equipment damaged by corrosion, life and environmental safety must be protected with the thorough study of this type of corrosion.; For a given type of steel, the CO₂ corrosion rates are strongly influenced by many mechanical and environmental factors, such as flow velocity, temperature, gas-liquid ratio, oil-water ratio, CO₂ partial pressure, and the chemical composition of the produced water. Under specific conditions, a corrosion product, the iron carbonate (FeCO₃), can deposit over the corroding metal as a scale and dramatically reduce the CO₂ corrosion rates on carbon steels. The ability to reliably predict the protective characteristics of such scales so that this knowledge may be used to mitigate the CO₂ corrosion problem is the main objective of this research.; CO₂ corrosion tests performed under various CO₂ corrosion flowing conditions in a flow loop were used to generate and study FeCO₃ scales. In situ Electrochemical Impedance Spectroscopy (EIS) techniques were successfully used to monitor the development of the scales throughout the duration of the tests. The EIS monitoring enabled the identification of the type of scales being formed and the quantification of the protection they give.; A procedure using EIS, SEM and X-ray diffraction was developed to electrochemically and morphologically characterize the scales formed. In this work, morphology of the scales was proved to be the most important characteristic related to CO₂ corrosion protection, and temperature was found to be the main environmental parameter controlling the morphology of the scales.; For the environmental conditions tested, a correlation was developed to predict the type of iron carbonate scales that would be formed and the amount of CO₂ corrosion protection these scales would provide to carbon steels.