Stability of oxide layer formed on high-chromium steels in LBE under oxygen content and temperature fluctuation

The behavior of protective oxide layers on P122 and its welds and of ODS steel in LBE is examined under conditions of changing temperatures and oxygen concentrations. P122 steel (12Cr) and its welded joints are exposed to LBE at 550 degree C for 4,000 h with oxygen concentrations of 10-6 and 10-8 wt% which change every 800 h. It is found that like in case of constant oxygen concentration of 10-6 wt%, a protective spinel layer was maintained on P122 and also on its welded joint. Two experiments are conducted on ODS steel, both with temperatures changing from 550 to 650 degree C and back every 800 h, one experiment with 10-6 wt%, the other with 10-8 wt% oxygen in LBE. Like in the former test with constant temperature at 550 degree C no dissolution attack could be observed in experiments with temperature fluctuation. Contrary to this results is the observed dissolution attack on ODS with a constant temperature of 650 degree C at 10-6 wt% oxygen in which formation of a protective layer was not allowed before reaching 650 degree C LBE temperature. (authors)