Investigating the Effects of Cyclic Thermo-Mechanical Loading on Cyclic Plastic Behavior of a Ninety-Degree Back-to-Back Pipe Bend System

Abstract

Pipe bends are generally employed for routing piping systems by connecting to straight pipes but back-to-back pipe bends are often necessary for confined space applications. In order to achieve safe operation under complex loading, it requires a thorough pipeline integrity assessment to be commenced. This paper investigates the effects of cyclic thermo-mechanical loading on cyclic plastic behavior of a 90-deg back-to-back pipe bend system, including temperature-dependent yield stress effects. Structural response interaction boundaries are determined for various different combinations of cyclic and steady loading. Constructed structural responses are verified by full cyclic incremental, step-by-step, finite element analysis. The numerical studies provide a comprehensive description of the cyclic plastic behavior of the pipe bends, and semi-empirical equations for predicting the elastic shakedown limit boundary are developed to aid pipeline designers in the effective assessment of the integrity of the pipe bends without a requirement for complex finite element analysis.