Processes occurring during cathodic disbonding of unpigmented and pigmented epoxy coated mild steel with a linear defect fully immersed and semi-immersed in simulated seawater (3.5 wt.% NaCl solution) have been investigated by using a combination of Scanning Acoustic Microscopy (SAM) and Scanning Kelvin Probe (SKP).Disbonding and blisters were detected by SAM and localised electrochemical information of the disbonded region also inside the blisters was obtained from SKP potential maps.