Lateral Walking and Feed-In of Buckled Pipelines Due to Interactions of Seabed Features

The increasing demand for subsea pipeline tie-back systems operating at high temperatures and pressures has introduced new challenges for pipeline design. In particular, a pipeline designed to buckle laterally, may displace both laterally and axially over time when subjected to repeated heat-up and cool-down cycles. Depending on changes in local seabed slopes and the direction and severity of passing thermal transients, a combination of pipeline walking drivers with differing responses may occur along the pipeline route. In this case, both lateral and vertical features such as buckles, spans or route bends may act as sites which: • Accumulate axial feed-in over heat-up and cool-down cycles (‘collectors’). • Experience decreasing axial feed-in over heat-up and cool-down cycles (‘givers’). • Maintain buckle shape with little change in axial feed-in during heat-up and cool-down cycles. To̸rnes et al. [1] explained the mechanism in which thermal transients can lead to axial creep or walking and Carr et al. [2] demonstrated how global seabed slope and tensile loads can also cause walking as a result of repeated heat-up and cool-down cycles. This paper discusses the complex interactions of multiple features potentially present along a pipeline route, including thermal transients, slope, route bends and tensile load effects. The resultant combinations may manifest themselves in the through-life distribution of axial movement along the pipeline.