A generalised Monkman-Grant relation for creep life prediction: An application to 1CrMoV rotor steel

A generalised Monkman-Grant relation, which can be derived from the 4-Theta projection technique, is proposed and then used to predict creep properties at non accelerated test conditions. In this generalisation, creep rates at low strains are used to predict minimum creep rates that are then used in the Monkman-Grant relation to predict times to failure. Predictions of creep properties for 1CrMoV from this generalisation and from the 4-Theta projection technique were assessed using the mean absolute percentage error (MAPE) and mean square error (MSE)-which was further decomposed into systematic and random components. When considering the accuracy with which minimum creep rates were predicted, all but the generalised Monkman-Grant relation using 0.1% strain had a lower MAPE compared to the 4-Theta projection technique. The generalised Monkman-Grant relation using 0.5% and 1% strains had larger random components of the MSE compared to the 4-Theta projection technique. When considering the accuracy with which times to failure were predicted, all of the generalised Monkman-Grant relations produced lower MAPE compared to the 4-Theta projection technique. However, only when creep rates were measured at 0.2% strain, did the generalised Monkman-Grant relation produce prediction errors that had a significantly higher random component. (c) 2006 Springer Science + Business Media, Inc.