Power plant components are subjected to high temperature and cyclic loadings causing them to operate near or beyond the yield limit of the material, hence residual stresses will be produced that are going to be critical to their life. As a result, accurate residual stress characterisation is often crucial for the design and analysis of high-reliability mechanical components. The aim of this study is to investigate the evolution of residual stress in two power plant materials using neutron diffraction. The results of this study are going to be used to develop and validate a mathematical material model.