The paper deals with the effect of pressure, temperature and time on corrosion rate of pipeline steels in CO2 saturated water and in humid saturated CO2 gas in the range from 25 to 60°C and pressure from 20 to 145 bar, up to 400 hours of exposure. The results of weight loss tests show very high rates in the aqueous phase, one or two order of magnitude higher than the values obtained in CO2 saturated with water. Depending on temperature and pressure, cementite and iron carbonate scales can grow on metallic surface reducing corrosion rate. SEM and metallographic analysis evidenced the evolution of scale from defective cementite-based layer to protective compact carbonate scale. An experimental setup has been designed, taking various measures from different references to get an idea about corrosive effect due to flow of waste gases under higher pressure. Material grade was selected same as used for CO2 capture, transport and storage.