Anodic film properties determined by EIS and their relationship with caustic stress corrosion cracking of Alloy 600

The properties of the anodic films formed on Alloy 600 at different applied potentials in 10 wt.% NaOH solution at 315 °C were studied using in situ electrochemical impedance spectroscopy. Relaxation times for passivation and semiconductivity of the films were determined from EIS measurements. The results were correlated with the stress corrosion cracking (SCC) behavior obtained from the C-ring tests under the same conditions. The changes of the semiconductive properties and the peak of relaxation time were observed around 0.20 V where the SCC rate showed a maximum. These results were also consistent with the prediction parameter for SCC obtained from fast and slow polarization scans.