Effects of Reeling on Pipe Structural Performance-Part I: Experiments

The winding and unwinding of a pipeline in the reeling installation process involve repeated excursions into the plastic range of the material, which induce ovality, elongation, and changes to the mechanical properties. The reeling/unreeling process involves some back tension required to safeguard the pipe from local buckling. This study examines the effects of winding/unwinding a pipe on a reel at different values of tension on the induced ovality and elongation and the resulting degradation in collapse pressure. In Part I, a model testing facility is used to simulate the reeling/unreeling process in the presence of tension. The combination of reel and tube diameters used induces a bending strain of 1.89%. A set of experiments involving three reeling/unreeling cycles at different levels of tension is performed on tubes with diameter-to-thickness ratios (D/t) of 20 and 15.5 in which the progressive changes in cross-sectional geometry and elongation are recorded. Both ovalization and elongation are shown to increase significantly as the back tension increases. A second set of experiments on the same two tube D/ts is performed in which following a reeling/unreeling cycle at a chosen level of tension, the tubes are collapsed under external pressure. The collapse pressure is shown to decrease significantly with tension, which is primarily caused by the reeling/unreeling-induced ovality. Part II presents models for simulating reeling and the induced structural degradation. The experimental results in Part I are used to evaluate the performance of the models.