Chapter 11 - Effects of the Reel Vessel Installation Method on Pipe Structural Performance

Abstract

In recent years, the Reel Vessel pipeline installation method has become increasingly preferred in offshore operations due to the efficiencies it provides and its cost effectiveness. The reeling/unreeling process, however, induces repeated plastic bending to the pipe, altering its material properties and ovalizing its cross section, thus reducing the collapse pressure. The tension applied during reeling is an important factor that amplifies ovalization but is required to prevent catastrophic local buckling by bending. In this chapter the effects of reeling are first studied experimentally using a model reeling test facility, and then analytically using a large-scale 3-D finite element shell model, and an efficient 2-D analysis similar to that in Chapter 10. Both analyses utilize nonlinear kinematic hardening models to account for the cyclic bending due to winding and unwinding. Two sets of experiments are performed. In the first, the pipe is wound and unwound for three cycles under constant tension, while monitoring the evolution and accumulation of ovality and axial strain at different levels of tension. Ovality grows during winding, partially recovers during unwinding, but a permanent amount is left behind. The axial strain grows during both winding and unwinding. Both ovality and axial strain increase significantly as the tension increases, and accumulate with each cycle. In the second set of experiments, tubes undergo a single wind/unwind cycle at different levels of tension, and the specimens are subsequently collapsed under external pressure. The collapse pressure is shown to decrease significantly with tension, demonstrating the degrading effect of the reeling/unreeling-induced ovality. Both analyses produce results that are in good agreement with all aspects of the experimental measurements, with the 3-D full simulation providing more details about the reeling/unreeling process. Overall, the methods and results in this chapter help the designer better understand the reeling/unreeling process, its modeling challenges, and its consequences on pipelines installed by reeling.