Ageing high temperature power plant components needs to be periodically assessed for their remaining creep life to prevent unforeseen failures and for their life extension beyond the design life. Creep is a time-dependent deformation phenomenon occurring at stresses well below the yield stress and at temperatures in excess of 0.4 times melting temperature (Tm) in degrees absolute. Due to thermal activation, materials slowly and continuously deform even under constant load (stress) and eventually fail. Hence, one of the most critical factors determining the integrity of elevated-temperature components is their creep behaviour.