Integrity Assessments of Components in the Creep Range

Robust methods for the predictions of deformations and lifetimes of components operating in the creep range are presented. The ingredients used for this are well-tried numerical techniques, combined with the concepts of continuum damage and so-called reference stresses. The methods described are derived in order to obtain the maximum benefit during the early stages of design where broad assessments of the influences of material choice, loadings, and geometry need to be made quickly and with economical use of computers. It is also intended that the same methods will be of value during operation if estimates of damage or if exercises in life extension are required. Results of the suggested method are amenable to tabular or graphic representation. To illustrate the use of these in parametric studies, three brief case studies are included. These involve a notched rod, a perforated plate, and a pipe for which lifetime estimates based upon failure criteria involving different degrees of conservatism are calculated. In addition, an illustration is given of the use of the charts presented in deciding inspection intervals and lifetime extensions. Finally, a brief excursion into the possibility for using the suggested methods for the mapping of designs within given regional constraints is given.