A review of literature for the structural assessment of mitred bends

Abstract

This paper presents a state-of-the-art review of literature available for the structural assessment of all types of mitred pipe bends. Compared with smooth bends, the volume of literature available for mitres is less extensive and its scope is not as wide. Historically, this reflects a reduced application level, as well as a less demanding range of applications, such as non-high temperature use. There is also the issue that an analysis of a mitred bend is complicated by discontinuity stresses, as well as those due to cross-section ovalisation. This fact delayed the development of non-linear analysis of mitred bends. Nevertheless, there is now a substantial body of work on mitred bends. This review tabulates and characterises all publications to date in chronological order. The details of experimental specimens are highlighted, with a view to these perhaps providing useful verification data for any future finite element analysis for example. Issues of particular interest to pipework designers are discussed, including the effects of combinations of loading, out-of-circularity, tangent pipe length and flanges. Failure characteristics and loads are discussed where relevant. Topics for further research are also noted. For example, comprehensive design curves do not exist for the elastic and plastic behaviour of all mitre types, over a practical range of geometry and loading parameters. Similarly, there is still scope for further work on the effect of combined loading, end effects and out-of-circularity. Limit, collapse and burst loads are not yet available across the entire spectrum of bends and loading parameters either. Creep and optimisation represent virgin territory as far as mitred bends are concerned and given that unforeseen vibration is a common source of high-cycle fatigue failure in pipework, there must also be scope for vibration-induced fatigue studies

Numerical simulation of ratcheting and fatigue behaviour of mitred pipe bends under in-plane bending and internal pressure

“…The summary of material properties used is presented in Table 1. Cyclic strength coefficient and cyclic strain hardening exponent were obtained through Equations (6)(7)(8) and also included in this table.…”

“…Wood [8] conducted a review of mitred bend publications to date, referencing the structural behaviour of all types of mitred pipe bends. Post yield literature available discusses either limit or bursting pressure tests and collapse or limit bending moment tests, both in plane and out of plane or for a combination of pressure and moments.…”

A comparison of plastic collapse and limit loads for single mitred pipe bends under in-plane bending

“…Wood [2] presents an up-to-date and comprehensive list of almost all references relating to the structural behaviour of mitred pipe bends of all types. The post-yield information available in the literature relates to either limit/burst pressure tests or limit/collapse bending moment testseither in-plane or out-of-plane.…”

Stresses in the vicinity of an unreinforced mitre intersection: An experimental and finite element comparison

“…Possibly the earliest reference to the actual use of finite elements, for the study of a mitred bend, is due to Edwards [12] in 1974. A comprehensive review of mitred bend publications from 1952 to date, is presented in reference [13]. This review contains reference to 93 publications, many of which detail the development of analytical solutions by Kitching and others.…”