INFLUENCES OF TiN INCLUSION ON CORROSION AND STRESS CORROSION BEHAVIORS OF ALLOY 690 TUBE IN HIGH TEMPERATURE AND HIGH PRESSURE WATER

TEM and SEM were used for studying the existing forms and distribution states of TiN inclusions in alloy 690. The corrosion and stress corrosion behaviors of alloy 690 were investigated through high temperature high pressure electrochemical measurement and immersion tests. TiN particles are the main inclusion in alloy 690 and randomly distribute in austenitic matrix. Corrosion experiments showed that pitting corrosion occurs preferentially at the inclusions containing Ti with high potential in simulated primary water of pressurized water reactor (PWR). In high temperature high pressure alkali solution containing lead, the region near TiN inclusion and close to the side of matrix is the preferred position for corrosion, and TiN inclusions at grain boundary can subsequently cause local stress concentration on grain boundary, both of which lead to intergranular stress corrosion cracking in alloy 690.