Experimental investigation of stress corrosion on supercritical CO2 transportation pipelines against leakage for CCUS applications

Carbon Capture, Utilization and Storage (CCUS) is one of the key technologies that will determine how humans address global climate change. For captured CO2, in order to avoid the complications associated with two-phase flow, most carbon steel pipelines are operated in the supercritical state on a large scale. A pipeline has clear Stress Corrosion Cracking (SCC) sensitivity under the action of stress and corrosion medium, which will generally cause serious consequences. In this study, X70 steel was selected to simulate an environment in the process of supercritical CO2 transportation by using high-temperature high-pressure Slow Strain Rate Tensile (SSRT) tests and high-temperature high-pressure electrochemical test devices, with different O2 and SO2 contents. Studies have shown that 200 ppm SO2 shows a clear SCC sensitivity tendency, which is obvious when the SO2 content reaches 600 ppm. The SCC sensitivity increases with the increase of SO2 concentration, but the increase amplitude decreases. With the help of advanced microscopic characterization techniques such as scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), through the analysis of fracture and side morphology, the stress corrosion mechanism of a supercritical CO2 pipeline containing SO2 and O2 impurities was obtained by hydrogen embrittlement fracture characteristics. With the increase of SO2 content, the content of Fe element decreases and the corrosion increases, demonstrating that SO2 plays a leading role in electrochemical corrosion. This study further strengthens the theoretical basis of stress corrosion of supercritical CO2 pipelines, plays an important role in preventing leakage of supercritical CO2 pipelines, and will provide guidance for the industrial application of CCUS.