Marine paints are complex polymeric systems containing layers of different nature that significantly delay the corrosion failures. In order to obtain a rapid ranking in the corrosion protection provided by the paints, it is important to apply sensitive and non-invasive methods for early detection of under paint corrosion. Scanning Kelvin Probe (SKP) was used to determine the mechanism(s) of corrosion and paint de-adhesion. This technique is sensitive to the metal-polymer interface and gives a quick assessment of cathodic delamination or anodic undermining. Depending on the type of exposure the mode of corrosion de-adhesion was evaluated and compared with SKP data obtained under polarization experiments by impressed current in aqueous electrolyte. After exposure, pull off test and Scanning Electron Microscopy – Energy Dispersive X ray Spectrometry (SEM-EDX technique) were applied to determine the paint adhesion stability around the defect and to analyse the steel-paint interface.