This book highlights the qualitative and quantitative sequential changes in microstructure of P91 steel under various stress and temperature conditions. The P91 alloy is an established material used under elevated temperature and stress in the components of thermal power plants. Temperature and stress levels for laboratory experimentation have been selected based on the true operating condition of a boiler. This book describes both full length as well as interrupted tests that were performed under given parameters. Subsequently, the microstructures, bulk hardness and NDE parameters...