Inhibition of caustic induced stress corrosion cracking of Alloy 600 by inhibitors

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