Development and Qualification of Materials for Indian Advanced Ultra-Supercritical Coal-Fired Power Plant

Abstract

Abstract India has embarked on an ambitious program of setting up efficient advanced ultra-supercritical (AUSC) technology with steam temperature and pressure of 993 K and 31 MPa, respectively. This article deals with the testing and qualification of indigenously produced materials for the Indian AUSC mission project, the research and development phase of which is currently in the advanced stage of completion. As part of this, exhaustive database pertaining to various mechanical properties including creep, low cycle fatigue (LCF), creep-fatigue interaction (CFI), high cycle fatigue (HCF), fracture toughness, and crack growth has been generated covering important candidate materials such as alloy 617M tubes and forgings, 304HCu stainless steel tubes, and alloy 625 castings. Tubes of both alloy 617M and 304HCu stainless steels are to be used in the boilers, whereas alloy 617M forgings would be used as turbine rotor and alloy 625 castings as turbine casings. The data have been subsequently used to establish design curves identifying safe regimes of operation with respect to creep, LCF, HCF, CFI, and fatigue and creep crack growths. The properties were seen to be comparable with those derived from internationally developed equivalent grades. The bimetallic weld joints between alloy 617M and 10Cr steels were also evaluated to derive the appropriate strength reduction factors under creep and cyclic loadings. Additionally, the influence of thermal aging at service temperature on the microstructural evolution and mechanical properties was investigated based on tensile and fracture properties to account for the service exposure induced degradation and associated embrittlement.