Application of the Wilshire Stress-Rupture and Minimum-Creep-Strain-Rate Prediction Models for Alloy P91 in Tube, Plate and Pipe Form

Abstract

There exists a challenge in predicting the long-term creep of materials (3 105 hours) where 11+ years of continuous testing is required to physically collect creep data. As an alternative to physical testing, constitutive models are calibrated to short-term data (< 104 hours) and employed to extrapolate the long-term creep behavior. The Wilshire model was introduced to predict the stress-rupture and minimum-creep-strain-rate behavior of materials and the model is well-accepted due to the explicit description of stress- and temperature-dependence allowing predictions across isotherms and stress levels. There is an ongoing effort to determine how alloy form affects the long-term creep predictions of the Wilshire model. In this study, stress-rupture and minimum-creep-strain-rate predictions are generated for alloy P91 in tube, plate, and pipe form. Data is gathered from the National Institute of Materials Science (NIMS) material database for alloy P91 at multiple isotherms. Following the establish calibration method for the Wilshire model, post-audit validation is performed using short-term data from NIMS to vet the extrapolations accuracy of each form at different isotherms. The Wilshire model demonstrates successful extrapolative techniques for the stress-rupture and minimum-creep-strain-rate of tube, plate, and pipe forms across multiple isotherms. Overall the form with the highest extrapolative accuracy for both stress-rupture and minimum-creep-strain-rate is the plate and the lowest one is the pipe. Stress-rupture design maps are provided where stress and temperature are axes and rupture-time is in contour. The design maps can be applied to: (a) given the boundary conditions, determine the design life (b) given the design life, determine the acceptable range of a boundary conditions. The latter is more useful in turbomachinery design.

Probabilistic creep with the Wilshire–Cano–Stewart model

“…Typical creep models are applied deterministically where scatter is not considered; rather, the best-fit through the data is the target of calibration. Deterministic calibration is performed for creep models such as the MPC-Omega, 10 theta-projection, 11,12 Wilshire, 13 Hiu-Liu parameter (HLP), 14 Riedal, 15,16 Wilshire-Cano-Stewart (WCS), 17,18 and sine-hyperbolic (Sinh) 19 models among others. Herein, it is desired to transform deterministic models into probabilistic models by introducing uncertainty.…”

“…The WCS model, a CDM-based version of the Wilshire model, is a combination of the Wilshire and Sinh models to predict creep deformation, damage, and rupture. 13,18 The WCS model is advantageous because of an explicit description of temperature dependency from Wilshire and the ability to model secondary and tertiary creep and creep damage given by Sinh. 13,18,43,44 Deterministically, the model has been calibrated and validated for alloy P91 13 and applied to model the accelerated creep test data of Inconel 718.…”

“…13,18 The WCS model is advantageous because of an explicit description of temperature dependency from Wilshire and the ability to model secondary and tertiary creep and creep damage given by Sinh. 13,18,43,44 Deterministically, the model has been calibrated and validated for alloy P91 13 and applied to model the accelerated creep test data of Inconel 718. 43 The WCS model was applied for rupture prediction of alloy P91 and exhibited superior accuracy compared to Larson-Miller (LM) model.…”