On the corrosion mechanism of CO_2 transport pipeline steels caused by impurities: Roles of each impure components and benchmarks

摘要

Carbon Capture, Utilization and Storage (CCUS) has been proposed as a promising technology for the mitigation of CO_2 emissions into the atmosphere from fossil-fuel-operated power generation plants. As the reliability and cost effectiveness of the pipeline transport network is crucial to the overall operability and resilience of the CCUS system, it is vital to realize the possible corrosion risks of the employed pipeline steels corresponding to the impurity level of the gas source. Recent studies have shown that even the high alloyed materials might be susceptible to general and/or localized corrosion by the condensates forming from the impurities such as SO_x, NO_x, CO, O_2 and water [1]. Up to now, however, there is no regulation procedure which defines the maximum acceptable level of impurities and the combination of them for each employed pipeline steels. Herein, systematic experiment series were conducted by mixing pure CO_2 gas with varying concentration of each impurity and with the varying combination of them. Each time, the mixture was then fed (1 L/min) into the reactor containing 12 specimens for 120-600 h at 5°C (to simulate the sub-level pipeline transport). The resulted condensate was collected and analyzed by ionic chromatography and atomic absorption spectroscopy to determine the chemical composition. In this study, the "worst-case scenario" gas mixture, containing 2.5 % H_2O, 1.8 % O_2, 1000 ppm NO_2, and 220 ppm SO_2 as impurities, resulted in the condensate containing H_2SO_4 0.114 M and HNO_3 0.0184 M (pH 2.13). This "original" condensate was then re-produced to carry out exposure tests and electrochemical characterization including corrosion potentials and impedance spectroscopy in CO_2 saturated condition for 7-14 days at the same temperature. The corrosion rate was also measured by mass loss method.