Behaviour of cold bend pipes under combined loads.

摘要

Cold bends are frequently required in energy pipelines in order to change the vertical and horizontal orientation of the pipeline route. Deformations caused by ground movement along the pipeline tend to accumulate at the site of cold bends, which often causes local buckling at these locations. Little is currently known about the behavior of cold bend pipes under applied loads, accordingly this research program was conducted to investigate their local and global load-deformation relationships.; Full-scale tests were conducted on seven large diameter cold bend pipes and one straight pipe that were loaded under axial load, bending, and internal pressure. The specimens were tested until local buckling occurred, and the curvature of several of the pipes was increased until they fractured at the wrinkle location. It was demonstrated though these tests that the critical strain of cold bend pipes is lower than that of a straight pipe, and that the central bend angle of the specimens could achieve up to 49 degrees without fracturing.; Several ancillary tests were conducted on the specimens to better understand the effects of cold bending on the pipe properties. The residual strains, initial imperfections, and material stress-strain properties were measured for several of the specimens. It was revealed that cold bending causes a distribution of imperfections that is similar in shape to a sine function. It was also determined that there is a considerable degree of work hardening that occurs on the material in the region of the cold bend.; A finite element model was also created to validate the behaviour of the test specimens. The model incorporated the geometry, imperfections, and material properties that were measured from the cold bends. The model demonstrated reasonable accuracy in predicting both the global and local load deformation behaviour of the specimens during testing. A parametric study was subsequently conducted to assess the influence of the diameter to thickness ratio, internal pressure, material grade, imperfection magnitude, and bending degree/diameter length on the behavior of cold bend pipes under applied loads.