Limit-Load Analysis of Pipe Bends Under Out-of-Plane Moment Loading and Internal Pressure

Abstract

The purpose of this work is to study the load-carrying capacity of pipe bends, with different pipe bend factor (h) values, under out-of-plane moment loading; and to investigate the effect of internal pressure on the limit moments in this loading mode. The finite element method is used to model and analyze a standalone, long-radius pipe bend with a 16-in. nominal diameter, and a 24-in. bend radius. A parametric study is performed in which the bend factor takes ten different values between 0.0632 and 0.4417. Internal pressure is incremented by 100 psi for each model, until the limit pressure of the model is reached. The limit moments were found to increase when the internal pressure is incremented. However, beyond a certain value of pressure, the effect of pressure is reversed due to the additional stresses it engenders. Expectedly, increasing the bend factor leads to an increase in the value of the limit loads. The results are compared to those, available in the literature, of a similar analysis that treats the in-plane loading mode. Pipe bends are found to have the lowest load-carrying capacity when loaded in their own plane, in the closing direction. They can sustain slightly higher loads when loaded in the out-of-plane direction, and considerably higher loads under in-plane bending in the opening direction.