A re-assessment of elastic follow-up in high temperature piping

Abstract

Despite the availability of detailed inelastic finite element analysis, the design of complex pipework systems operating at high temperature, where creep has to be taken into consideration, can be problematic. Design can be based on elastic analysis alone provided the effect of ‘elastic follow-up’ – the possibility of large inelastic strain concentration at some locations due to elastic behaviour of the rest–is somehow taken into account. Over the years it has become common to adopt an ‘elastic follow-up factor’, based on simplified methods, which can provide some estimate of the accumulated strain. This type of approach was developed over the years from numerous studies (including the author's) of the phenomenon of elastic follow-up in various structures. In all of these studies the constitutive model for creep was based on the simple power law. However, it has recently been shown by the author that stress-range dependent constitutive creep models can lead to significantly different predictions for follow-up. This paper applies this finding to the author's previous results on elastic follow-up in high temperature: it is demonstrated that consequently there could be a need to re-assess current design practice.