right and bottom left corners of Figure 9 provide better views of the two lateral buckles that form in this segment of the flowline. The distance between the nodes shown on the flowline is approximately 75 feet; not all nodes are shown in Figure 9. The element length is approximately 3 ft in this model.


The design approach often used at Technip to satisfy the fatigue requirements in deepwater flowlines is to trigger controlled lateral deflections intentionally at appropriate intervals along the flowline route. Doing so provides greater confidence that Technip’s flowline designs will achieve the reliability needed to operate safely for their design life, which may be 20 years or more. The controlled lateral deflections help ensure that the stress range during each loading cycle is minimal, thus limiting the fatigue damage. With uncontrolled buckling of a deepwater flowline, curvatures of the pipeline in the buckle can be much larger/sharper, increasing the stress and fatigue damage experienced.


Various methods exist for perturbing the flowline geometry so that lateral deflections reliably form at designated locations. “Sleepers” (short vertical upsets) can be placed under the flowline or a distribution of buoyancy module can be placed around the flowline to “lift” it off of the seafloor.


The effective axial force profiles along a flowline simulation are plotted in Figure 10. In this model, a buoyancy module is placed at a distance of 1500 meters from one end of the flowline. The flowline does not effectively buckle during the first operational cycle. However, the lateral deformations during the hydrotest and the early operational cycles accumulate and trigger a large global buckle in the third cycle. The buckle relieves much of the compressive force in the middle of the flowline. Ideally the buckle control measures used in a deepwater pipeline system lower the


Figure 9. Changes in the slope of the seafloor trigger lateral buckles. 10 2009 SIMULIA Customer Conference


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