Abstract

Flow-induced pulsations in flexible risers and flowlines (FLIP) has been the subject of ongoing research roughly over the last two decades. This phenomenon, also called singing, can cause high vibration and cyclic stress levels in the attached up- and downstream pipe systems, thereby imposing serious limitations on the flowrates through the pipes. FLIP occurs when the flow velocity along the flexible is above a certain onset flow velocity. Large pressure pulsations can appear as a result of a feedback loop mechanism established between vortex shedding at the inner cavities and longitudinal acoustic standing waves. Since FLIP is recommended to be avoided in all cases, the main focus of the research has been to understand the phenomenon and build models to predict the onset velocity. An overview of the experiences in the behavior and prediction of onset data on a large number of field cases is given. Recent advances on the theory and prediction of the onset and behavior of flow induced pulsations are discussed. This ranges from new advanced test methods for acoustic source allocation to full large scale experiments. In addition, new and upcoming anti-FLIP technologies as well as possible mitigation actions available to operators are discussed, by introducing recent field experiences as well as large scale tests.

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