Unified Model of Steady-State and Transient Creep and Identification of Its Parameters

Defining equations are proposed that provide correct description both of steady-state and transient creep on the basis of a unified relation accounting for nonlinearities inherent in each of the examined stages to improve creep prediction accuracy for long periods of time (300,000 h or more). The Levenberg-Marquardt algorithm was used for effective two-level identification of six parameters of the model. The identification is shown to be effected with creep and relaxation curves. The values of model parameters were obtained for different steels employed in the manufacture of steam lines.