A systematic method was established to determine the upper limit of moisture content for supercritical CO2 pipeline transport. In the corrosion experiments, the weight-loss method was applied to measure the corrosion rate of X70 steel exposed to a supercritical CO2/SO2/O-2/H2O mixtures for different relative humidity, aiming to explore the critical relative humidity point for X70 steel corrosion under such conditions, which is a crucial point for setting the upper limit of moisture content. The critical relative humidity was estimated to be between 50% and 60% on the basis of the experiment results. The microstructure and chemical composition of the corrosion products were examined employing SEM and XRD. Based on the estimated critical relative humidity combining with the solubility consideration of H2O in CO2 at various temperatures and pressures, the pipeline thermodynamic model was used to determine the upper limit of moisture content for supercritical CO2 pipeline transport. (C) 2012 Elsevier BM. All rights reserved.