Effect of Flow on the Corrosion Behavior of Pipeline Steel in Supercritical CO₂ Environments with Impurities

Corrosion is a major concern in transmission pipelines that transport captured CO₂. While dry CO₂ is noncorrosive, significant corrosion has been reported in dense-phase CO₂ with trace amounts of water and impurities such as O₂, H₂S, SO_x, and NO_x. The aim of this work is to improve our understanding of the physicochemical aspects of the corrosion of carbon steels in the high-pressure environments associated with CO₂ transmission pipelines. The effect of flow on the corrosion of X65 carbon steel was investigated in a series of autoclave tests with different combinations of impurity concentrations in supercritical CO₂ conditions (8 MPa and 35°C). The corrosion rate of specimens was determined by weight loss measurements. The surface morphology and composition of the corrosion product layers were characterized using surface analytical techniques (scanning electron microscopy, eneregy dispersive x-ray spectroscopy, and Raman microscopy). Localized corrosion was measured via surface profilometry after corrosion products were removed. Results showed that no corrosion was observed in the supercritical CO₂ with 650 ppm_v of water, 50 ppm_v SO₂, and 100 ppm_v NO, but corrosion occurred when SO₂ concentration was increased to 4,500 ppm_v and 40,000 ppm_v of O₂ was added to the system. The presence of flow significantly accelerated the corrosion of carbon steel. Furthermore, localized corrosion was observed in the presence of both O₂ and flow.