Examination of the Theories for Calculating the Stresses in Pipe Bends Subjected to in-Plane Bending

Abstract

Much theoretical and experimental work has been published on the flexure of pipe bends. Examination of the results to date show considerable differences between certain measured results and the predicted behaviour. The theoretical works relate mainly to long radius bends and all make many simplifying assumptions. This paper presents a more detailed theoretical study, for bending in the plane of the pipe bend. Examination of both typical and extreme cases and a comparison with the experimental evidence shows which of the various theoretical simplifications can be accepted for a given pipe bend. It is concluded that although complete stress distributions calculated by previous theories may be seriously in error over particular ranges of the variables, the peak stresses and flexibilities are, by a combination of circumstances, unlikely to be more than 5-10 per cent in error if certain factors introduced in the more recent of these theories are used. Manufacturing and other variations between nominally similar pipe bends, however, seem to preclude the possibility of predicting the behaviour of a particular bend to closer than ±20 per cent.