The degradation of carbon mild steel under cavitation erosion-corrosion exposure was studied by means of a 20 kHz ultrasonic device with a piezoelectric inducer. Possibilities of estimation of material failure by current measurement techniques are presented and discussed. The effect of cavitation exposure of the mild steel has been investigated in situ with the dynamic electrochemical impedance spectroscopy technique. Estimation of the surface degradation rate is enabled by an adequate equivalent circuit selection. A dynamic impedance method was used to verify the impedance parameters online during the measurement. These measurements are assisted by estimation of the weight loss function commonly used for the evaluation of erosion-corrosion resistance of materials. (C) 2008 The Electrochemical Society.