Buckling phenomenon for straight and curved pipe under pure bending

Not only straight pipes, but also the curved ones are used in an actual pipeline. In designing such a pipeline, it is important to know the buckling strength of the pipe under various kinds of loads. Especially, it is well known that the buckling moment will be reduced by increasing the pipe’s length. However, comprehensive studies for the buckling strength of straight and curved pipe under bending loads are still limited. In this research, the previous research for the buckling strength of pipe under bending moments was reviewed. It is well known that the cross-sectional oval deformation takes place and the buckling strength of pipe is reduced due to this deformation. Therefore, secondly, the buckling phenomenon for a straight pipe under a pure bending moment was investigated by nonlinear FEA, considering the effect of a cross-sectional oval deformation by changing the varying of pipes, that is, the length-to-diameter ratio (L/D) varying from about 5 to 20 and the diameter-to-thickness ratio (D/t) varying from about 50 to 200. Thirdly, the buckling phenomenon for curved pipe was also investigated by changing the R/D from 50 to 200 where R is the curvature radius of curved pipe. From the results of the calculations for the straight pipe, the reduction rate of the buckling moment due to the oval deformation of pipe was clarified for various values of L/D and D/t, not only in elastic buckling, but also in elasto-plastic buckling. For the curved pipe, it was explained that the buckling moment will be reduced by lowering the value of R/D.