Figure 3457 shows the effects of Cr and Al content on the weight gain of ODS ferritic steels after exposure to SCPW at 500 °C with 8 ppm of dissolved oxygen. Increasing the Cr content from 14 to 17 wt % does not affect corrosion resistance if ODS ferritic steels contain 4wt % Al. For 16wt% Cr, the addition of A1 increases corrosion resistance in 16Cr-ODS steels. As shown in Figure 35,43 tested at SCPW (510°C, 25 MPa) for 600 h, the addition of 4wt% Al did not significantly influence corrosion resistance in 19Cr — ODS steel, though a rather dense chromia film was observed on the specimen surface. The 16wt% Cr is not large enough to form homogeneous and stable chromia on the entire surface of the specimen, whereas a very thin alumina film covers the entire surface of the specimen with the Al addition of 2 wt%. Thus, the addition of Al effectively improves corrosion resis­tance in 16Cr-ODS steel. As shown in a comparison with 9Cr-ODS steel in Figure 35, its weight gain is much larger than 16Cr-ODS steel, indicating that 9Cr-ODS steel is not adequate for application to SCWR. The suppression of SCPW corrosion by the addition of Al to 16Cr-ODS steel is due to the for­mation of a very thin alumina film on the surface.