Given the strong reliance on long-term datasets containing multiple heats of the same material (i.e., different bathes), there is a pressing need to obtain reliable predictions of creep properties that are representative of all such batches. This paper presents a new estimation framework for the theta methodology which enables a distribution of creep properties to be predicted which should be representative of any batch of … Continue reading Accounting for Batch to Batch Variation when Predicting the Safe Life of Materials Operating at High Temperatures: An Application to 1Cr-1Mo-0.25V Steels Using the Theta Methodology

Recently there has been renewed interest in assessing the predictive accuracy of existing parametric models of creep properties, with the recently develop Wilshire methodology being largely responsible for this revival. Without exception, these studies have used multiple linear regression analysis (MLRA) to estimate the unknown parameters of the models, but such a technique is not suited to data sets where the predictor variables are all … Continue reading A partial least squares solution to the problem of multicollinearity when predicting the high temperature properties of 1Cr–1Mo–0.25V steel using parametric models

The existing length of the materials development cycle is currently far too long. Validation of a new methodology to reduce this time requires evidence of its applicability to a wide range of materials. This study focuses on 18Cr–12Ni–Mo steel because of its importance to future power generation. The methodology is shown to accurately predict the strengths of numerous batches of this material obtained from different … Continue reading Prediction of long-term creep rupture data for 18Cr–12Ni–Mo steel

The creep and creep rupture properties of 18Cr–12Ni–Mo steel tubes have been analysed using the Wilshire equations. The observed behaviour patterns are then briefly discussed in terms of the dislocation processes governing creep strain accumulation. A suitable statistical framework for analysing both the single and multi batch data available on this material is then specified. It is shown that ignoring the hierarchical nature present in … Continue reading Obtaining confidence limits for safe creep life in the presence of multi batch hierarchical databases: An application to 18Cr-12Ni-Mo steel

This paper develops a modification of the shared frailty model that allows for the distribution of the response and the random effects to be determined by the data (from within the exponential family of distributions). A simulated maximum likelihood and a computationally simpler simulated linear least squares approach to estimating this model are also presented. These generalizations are important for modelling high-temperature deformation because they … Continue reading A frailty model for the analysis and prediction of creep and creep fracture: with application to high temperature plant life assessment using 1Cr–1Mo–0.25V

Designers of new power-generation plants are looking to make use of new and existing high-strength austenitic steels so that these plants can operate with much higher steam and, therefore, metal temperatures. However, this article shows that the Wilshire–Scharning methodology is incapable of producing accurate long-term-life predictions of these materials from short-term data. This article puts forward a modification of this approach that should enable existing … Continue reading A Novel Approach to the Prediction of Long-Term Creep Fracture, with Application to 18Cr-12Ni-Mo Steel (Bar, Plate, and Tube)