Installation Load Consideration in Ultra-Deepwater Pipeline Sizing

Abstract

The design of ultra-deepwater offshore pipeline is often based on the wall thickness and material grade selection to resist the local buckling due to bending, axial tension, and external pressure. Typically, this load combination occurs at the sagbend region during pipeline installation. With the economics of ultra-deepwater pipeline systems being highly dependent on the installation considerations, it remains difficult to see how this design methodology with no reference to installation loads, can lead to an economical solution. By means of extensive numerical studies, over a range of pipe diameters and water depths, it is shown that installation parameters are sensitive to wall thickness and the level at which the maximum allowable bending strain is set. By appropriately combining pipe strength and stiffness characteristics with the pipelay installation parameters, a bending strain limit is defined that is shown to lead to the most economical solution.