Application of Electrochemical Impedance Spectroscopy for Monitoring Stress Corrosion Cracking

The present study investigated whether electrochemical impedance spectroscopy (EIS) could be used to monitor stress corrosion cracking (SCC). First, a model was developed that interpreted the impedance response of a cracked surface (i.e., the model could distinguish between a flat electrode surface and a surface with cracks). Experiments on stainless steel (SS) electrodes with artificial “cracks” (electrically drilled small holes) in 0.1 M sodium sulfate (Na2SO4) showed that the influence of the artificial “cracks” on the impedance response was reflected mainly in the phase shift at frequencies between 100 Hz and 1 Hz. To generate real stress corrosion cracks, slow strain rate tests (SSRT) were performed with a sensitized Type 304 SS (UNS S30400) specimen in a 5-N sulfuric acid (H2SO4) + 0.1-M sodium chloride (NaCl) solution at room temperature. Analysis of the fracture surface clearly showed intergranular attack, suggesting that stress corrosion cracks were formed. Impedance measurements were performed twice an hour during experiments with stress (SSRT) and without stress. Phase shifts at frequencies 100 Hz and 10 Hz showed a clear difference between the results with stress and without stress, suggesting that stress corrosion cracks were detected by the impedance measurements.