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, SOx, and NOx. 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 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 condition (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 (SEM, EDS 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 ppmv of water, 50 ppmv SO2, and 100 ppmv NO, but corrosion occurred when SO2 concentration was increased to 4500 ppmv and 40,000 ppmv 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.