Gas liquid slug flow can induce vibrations in process piping and large scale slugging can cause some oscillations of subsea flexible pipes. Pipe movements should be avoided, as fatigue can lead to pipe failure. Flow transients can also cause pipe failure, water slugs have lifted geothermal pipelines off support, and runaway hydrate plugs have caused fatalities. The flow – structure interaction is therefore of interest to study and to incorporate in dynamic simulators.

Several cases of dynamic slug flow-structure interactions have been studied in small scale laboratory. A two way coupling has been established between a pipe structure model and a slug tracking model.

A pigging case of a submerged flexible pipe is presented here. An initially liquid filled hose is hanging freely in a 4m long water tank. A pig is inserted at the inlet, and subject to a backpressure of air which drives the pig and the liquid out of the pipe. The subsequent pipe dynamics is video recorded and compared with the coupled flow-structure simulations. At high flow rates the initially U-shaped pipe rises above the water level and falls back to the surface. The experiments and the coupled models are described as well as key aspects of the numerical solvers.

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