A Simplified Method for Predicting Creep Collapse of a Tube Under External Pressure

Abstract

A simplified method is proposed to predict the creep collapse behavior of a long tube subjected to external pressure. The shape of the cross section of a tube is assumed to be quasi-elliptical characterized by a single variable, often called as shape factor in the literature. The growth of the displacement field is represented by the change of shape factor which is governed by an ordinary differential equation. A general class of creep constitutive equations can be employed with an accompanying elasticity whose effect is crucial under higher external pressure. Plane strain condition is assumed. Nonlinearity of stress distribution through the wall of the tube is allowed according to the creep constitutive equation in general, while the strain distribution is assumed to be linear. The method is applied to the analyses of heat tubes, which are typical for heat exchangers of high-temperature gas-cooled reactors, and is compared with the computer solution by the finite element method based on a finite deformation theory, as well as solutions by other simplified methods.