The prediction of long-term creep-rupture strength values for mod. 9Cr –1Mo ferritic steel and 316L(N) austenitic stainless steel is made using several life prediction methodologies at 773, 823 and 873 K. Creep-rupture strength values have been predicted following the Larson –Miller parameter, the Orr – Sherby –Dorn parameter, artificial neural network, and Wilshire approaches for rupture lives up to 60 years (5.2566105 h) using creep-rupture data available in the literature. It has been demonstrated that the prediction of creep-rupture strength values using these approaches are comparable. Creep-rupture strength values have been also evaluated using linear extrapolation of average creeprupture strength values given in French Nuclear Design Code RCC-MR for durations more than 36105 h. Predicted creep-rupture strength values using the literature data are found to be higher than those obtained from RCC-MR for both 9Cr –1Mo steel and 316L(N) SS. This suggested that the RCC-MR data are conservative and can be safely used for a design life of 60 years.