Environmental performance analysis of coated austenitic steels for their use in supercritical steam turbines

The environmental performance of two austenitic steels and the correspondent coating was analyzed. Austenitic steels are materials usually employed for the construction of steam turbines in the coal-fired power plants with supercritical and ultra-supercritical conditions of temperature and pressure, about 700 ℃ and 37,5 MPa. The mechanical properties of these materials, together with protective coatings, confer corrosion and oxidation resistance to the turbine components, as research has proved. Nevertheless, the environmental impacts associated to the substrate-coating system have not been deeply investigated to choose the best option in terms of sustainability. This study presents two types of austenitic steels, as well as a coating with its corresponding deposition process, which are normally employed in these supercritical conditions. The designated materials are AISI 347 and AISI 321 austenitic steels, while the selected protective coating is slurry aluminide applied by painting and diffusion heat treatment. In this situation, a comparative life cycle assessment (LCA) for several combinations analyzes the environmental behavior of both material and coating. Besides that, an economic review is carried out. This work aims to make a contribution to better understanding to the environmental damages as well as the significance of considering the technical and environmental assessment when conducting material and coating choice. The results obtained indicated that the AISI 321 austenitic steel coated with slurry aluminide had the best environmental behavior, showing lower impacts and costs.