By various manufacturing techniques straight pipes with initially circular cross sections can be processed into smooth bends but usually with noncircular cross sections and with variations in thickness. These changes from the ideal are normally referred to as “ovality” and “thinning”; their influence on the subsequent behaviour of curved pipes is not yet fully understood. Here theoretical work on constant thickness circular and elliptical cross sections has been extended to cope with typical variations in thickness. The theory which is based on a classical energy approach is outlined for in-plane bending loading and is easily extended to cover out-of-plane bending. Linear elastic small displacement limitations apply. It is concluded that normally accepted values of thinning have virtually no effect on the flexibility due to bending of smooth pipe bends with or without initial ovality. Similarly, the peak meridional bending stresses were found to be insensitive to thickness variations.

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