Stress Corrosion Cracking on geothermal turbine blades made of nickel-based superalloy

Geothermal power plants provide a particularly competitive alternative to other renewable energy sources, owing to their ability to ensure continuous energy production with low environmental impact and independence from climatic factors. However, the critical operating conditions, both mechanical and environmental, demand a careful analysis and selection of materials, especially for highly stressed components such as turbine rotors. These elements are exposed to high temperatures, severe mechanical loading, and aggressive chemical species that can promote severe degradation phenomena, including erosion-corrosion and stress corrosion cracking. This study, developed within the framework of a failure analysis, compares the corrosion behaviour of turbine rotor blades manufactured from nickel-based superalloys 718 and 725 after service in a geothermal environment. Samples were extracted from steam turbine stages operating under the most corrosive conditions, specifically in the dew-point region. The analyses allowed the identification of the corrosion mechanisms affecting the nickel-based superalloys and provided insights into the relationship between crack propagation and the material microstructure.