Inhibition of stress corrosion cracking of alloy 600 in 10% sodium hydroxide solution at 315°C

The effect of inhibitors on the electrochemical behavior and stress corrosion cracking resistance of Alloy 600 (UNS N06600) was evaluated in 10% sodium hydroxide (NaOH) solution at 315degreesC. The specimens, which were of a C-ring type for stress corrosion cracking tests, were polarized at 150 mV above the corrosion potential for 120 h with and without inhibitors such as titanium oxide (TiO2), titanium boride (TiB2), and cerium boride (CeB6). The chemical compositions of the films formed on the crack tip in the C-ring specimens were analyzed using scanning Auger electron spectroscopy. Cerium boride, which was the most effective, was observed to decrease the crack propagation rate by more than a factor of 3 compared with that obtained with no inhibitor. It was found that changes of the active-passive transition potentials and film compositions were related to the resistance to stress corrosion cracking in high-temperature caustic solution.