Plastic Collapse Loads for Pipe Elbows Using Inelastic Analysis

The results of an inelastic analysis are used to predict plastic collapse loads for in-plane bending of several pipe elbows. The analysis is made using a nonlinear finite element computer program which takes into account the effects of material strain hardening, stress redistribution, and ovalization of the elbow cross section. Various methods are used to determine plastic collapse loads based on the calculated load-deformation curves. The predicted collapse loads are compared to collapse loads determined by limit analysis and the method described for plastic analysis in Section III, Appendix F, of the ASME Boiler and Pressure Vessel Code. It is concluded that the current Code definition of collapse load is overly conservative for structural materials typical of high temperature application, and that the 0.2 percent offset method or the 2 times the angle of linear response method produce more realistic results.