The Influence of Bourdon Effect and Ovalization Effect on The Stress Distribution on Pipe Elbows
Proceedings Publication Date
Pipe bends are frequently used to change the direction of a pipeline. The surface geometric characteristics of elbow fittings and bends may lead to a host of unbalanced thrust forces caused by the internal pressure and temperature. The internal pressure causes unbalanced thrust forces tending to open up the elbow fitting or bend depending on its stiffness and surrounding constraints. These forces tending to cause ovalization of the cross section and causing the tendency of pipe bends to open up are termed the "Bourdon effect". If these unbalanced thrust forces are not taken into consideration, unanticipated deformations and high stress levels could occur at the elbow location that may not be accounted for in traditional stress analysis. Applying an external bending moment may cause ovalization of the cross-section leading to an increase in the flexibility and stress levels on bends. Past studies considered the ovalization effect using factors based on closing in-plane bending moment only for unpressurized pipes. In this paper, the influence of Bourdon effect and ovalization effect on the stress levels of pipe bends are investigated. 90-degree elbows with fixed-free ends are analyzed. Three nominal pipe sizes (12, 24, and 42) are selected. The effect of bending moment direction is studied and its interaction with internal pressure loading is investigated. The bending moment direction was found to have a significant effect on the stress distribution. Different bends with different bend angles were investigated and it is concluded that the bend angle affects the stress level. A comparison between the FEA results and the current codes is presented.