Effect of Flow on the Corrosion Behavior of Pipeline Steels under Supercritical CO₂ Environments with Impurities Available to Purchase

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 on the corrosion of carbon steels in the high-pressure environments associated with CO₂ transmissions 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 condition (8 MPa and 35°C). The corrosion rate of samples was determined by weight loss measurements. The surface morphology and the composition of the corrosion product layers were analyzed by using surface analytical techniques (SEM and EDS). 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 of water, 50 ppm SO₂, and 100 ppm NO, but corrosion occurred when SO₂ concentration was increased to 4500 ppm and 40,000 ppm 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.