Comparison of plastic collapse moment for different angled non-circular pipe bends under bending moments and internal pressure

Pipe bends are a crucial component of the pipeline industry because they experience more stresses and deformations than straight pipes of the same dimensions and material properties under the same loading conditions. For a reliable and safe piping system, the plastic collapse moment of pipe bends must be estimated accurately. The current study aims to find which bending mode is critical to failure for pipe bends; for that, the collapse moment under in-plane closing (IPC), in-plane opening (IPO) and out-of-plane (OP) bending moments are compared using finite element (FE) analysis. The comparison accounts for various values of internal pressure, bend angle and initial geometric imperfection. The FE analysis considers elastic-perfectly plastic (EPP) and strain-hardening (SH) material models. Twice-elastic-slope (TES) method is implemented to evaluate plastic collapse moment for all considered cases. The comparison of collapse moment shows that under unpressurized conditions, pipe bends are critical to IPC bending moment. However, it is difficult to identify which bending mode is critical under pressurized conditions. Therefore, plastic collapse moment under all three bending modes should be known and for that plastic collapse moment equations under all bending modes should be proposed.