A mechanistic and quantitative study of pipeline materials (X65) degradation due to erosion-corrosion in saturated CO2 environment under solid-liquid impingement was performed using a combined electrochemical and acoustic emission techniques. Electrochemical Impedance Spectroscopy (EIS) was used to characterise the evolution of the dissolution mechanisms of the steel surface and the acoustic emission (AE) technique was used to capture the mechanical damage due to plastic deformation cutting and ploughing mechanisms of the sand impacts. Results indicate that the combined techniques can be very useful in understanding the mechanisms of the erosion-corrosion process and the quantification of the overall damage individual and synergistic contributions.