Plastic collapse of pipe bends under combined internal pressure and in-plane bending

A.C. Robertson, H. Li, D. Mackenzie

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Plastic collapse of pipe bends with attached straight pipes under combined internal pressure and in-plane closing moment is investigated by elastic–plastic finite element analysis. Three load histories are investigated, proportional loading, sequential pressure–moment loading and sequential moment–pressure loading. Three categories of ductile failure load are defined: limit load, plastic load (with associated criteria of collapse) and instability loads. The results show that theoretical limit analysis is not conservative for all the load combinations considered. The calculated plastic load is dependent on the plastic collapse criteria used. The plastic instability load gives an objective measure of failure
and accounts for the effects of large deformations. The proportional and pressure–moment load cases exhibit significant geometric strengthening, whereas the moment–pressure load case exhibits significant geometric weakening.
Original languageEnglish
Pages (from-to)407-416
Number of pages9
JournalInternational Journal of Pressure Vessels and Piping
Issue number5
Publication statusPublished - May 2005


  • pipe bend
  • plastic collapse criterion
  • plastic instability
  • geometric non-linearity

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