Global warming due to carbon dioxide emissions is a major threat facing humanity. Thermal power plants contribute significantly to the carbon dioxide emission. One way to reduce carbon dioxide emissions by thermal power plants is to increase the operating efficiency of boilers employed in thermal power plants. Towards this, coal-fired power plants employ supercritical (374 ℃ and 22.1 MPa) and ultra-supercritical (600 ℃ and 27 MPa) operating conditions for steam generation. Advanced ultra-supercritical (AUSC) power plants operating at 710 ℃ and 31 MPa can provide further increase in thermal efficiency. The rise in temperature pressure threatens materials’ stability due to creep and steam and gas oxidation. This requires detailed research on these topics. As part of the national mission project on the development of AUSC technology, our laboratory has undertaken steam oxidation studies under AUSC conditions. We built a test loop to simulate the temperature and pressure in an autoclave and studied nickel base super alloys such as 740H and 617 and austenitic stainless steels such as 304HCu and Sanicro 25. Complementary techniques were employed to understand the oxidation behavior of the alloys. The alloys 617, 740H, and Sanicro 25 showed significantly low oxidation kinetics due to the formation of inner Cr2O3 scales and outer (Mn,Fe,Ni)Cr2O4 spinels. On the contrary, 304HCu suffered severe oxidation as it suffered chromium volatilization and steep chromium depletion in the alloy oxide interface. This talk will bring out the interplay among the alloy chemistry, microstructure, and corrosivity of the steam to give a perspective for alloy development against AUSC steam oxidation.
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