Corrosion investigations on ferritic materials in light-water reactor environments

Failures of pressurized components of power plants which are exposed to the environment, such as boiler drums, elbows and tube branches, are due to corrosion. Experimental investigations were carried out at 240 C on the low-alloy ferritic steels 20 MnMoNi 5 5 (similar to A 533) containing two different sulfur contents (0.009 and 0.020 weight-% S), 22 NiMoCr 3 7 (similar to A 508) containing 0.006% S, and 17 MnMoV 6 4 (WB 35) containing 0.017% S, in deionized oxygenated high temperature, high pressure, water (0.4 ppm and 8 ppm O2, 7 MPa). Detailed investigations of corrosion process on these material show that the corrosion behaviour of the material in governed by yield and creep processes at the crack tip which are responsible for a corrosion-assisted crack advance due to the rupture of the protective oxide layer (magnetite), competing with the repassivation of this layer. (J.S.). 20 refs., 8 figs., 1 tab