13 - Development in materials for ultra-supercritical and advanced ultra-supercritical steam turbines

Abstract

Enhancement of steam conditions is very effective in raising the efficiency of steam turbines; therefore, considerable efforts have been made to enhance steam conditions in the past. This enhancement has been achieved owing to a variety of technology improvements such as steam path design, rotor dynamics, sealing technology, cooling methods, etc. However, the most important technology for achieving the advancement of steam conditions is material development. As it is well known, the strength of materials under high-temperature conditions, typically represented by creep-rupture strength, becomes lower. In order to have better creep-rupture characteristics in the high-temperature region, stepwise improvements, for instance, those in chemical composition, heat treatment, and so on, have been made in the major components of steam turbines such as moving blades, rotors, casings, steam valves, etc.