Plastic collapse loads in shape-imperfect pipe bends under in-plane opening bending moment

• Collapse loads for shape-imperfect pipe bends is determined.
• Ovality and thinning are the shape imperfections considered.
• Finite element limit analysis uses large geometry change effects.
• Twice-elastic-slope method was used to obtain plastic loads.
• Ovality needs to be considered to determine collapse load while thinning produces negligible effect.

The combined effect of ovality and thinning/thickening on collapse load of pipe bends under in-plane opening bending moment was investigated using finite element limit analysis considering large geometric change effect. The material is assumed to be elastic-perfectly plastic. Twice-elastic-slope method is used to obtain collapse moment from moment–rotation curves drawn for each bend. Variation of thickness due to thinning in the cross section of pipe bend produces negligible effect on collapse load. The effect of ovality is significant except for pipe ratio 20 with λ = 0.5. A new closed-form solution is proposed to determine collapse moment of pipe bends with ovality and it is validated with existing experimental data.