The Impact of Slugs on Pipe Response - Physical Testing and Numerical Correlation

Abstract

Subsea systems that transport multiphase flow such as wellhead and manifold jumpers, tie-in spools, free-spanning pipelines and risers can all be subject to slug and turbulence loading and response, depending on the characteristics of the reservoir fluids, the pipe geometry and the flow conditions. As part of the SLARP (slug loading and response in pipelines) joint industry project (JIP), a series of tests were undertaken to provide experimental measurements at field-realistic scale dimensions for an investigation into the interactions between slug flow and the dynamics of subsea pipeline jumpers. Advanced numerical methods were validated for simulating the effects of slug flow on subsea pipe structures. The test campaign, pipe configurations, sample test results and numerical correlation of slug flow characteristics with measured pipe dynamics are presented in this paper. The test section consists of a U-bend constructed from 4-inch pipe. Liquid slugs were propelled through the piping by gas pressure and the structural response of the test section was measured as the slugs traversed a series of 90° pipe bends. As a basis for the test programme, slug lengths and velocities of up to 30m and 15m/s, respectively, were used. Frictional slides and wire rope slings were employed to provide differing restraint and damping conditions for the test section. The experimental data during the test campaign were compared to numerical simulations that accounted for load contributors of slugs travelling through the test section. Strong correlations were observed between the slug speed and pipe deflections from the physical tests. The system response was shown to be sensitive to slug velocity, pipe system restraint, pipe system stiffness and the evolution with time of the slug characteristics. The numerical methods employed are shown to be suitable for use in the prediction of dynamic response of subsea pipelines to slug loading where flow conditions are well understood. The novel aspect of this work relates to the successful development of a test piece which has features particular to subsea jumpers and the passing of high velocity slugs through the system combined with the simulation of the test conditions using finite element (FE) software that accounts for all key load contributors. These tests provide key insight to the interaction between slug flow conditions and the dynamics of pipe jumpers at field-realistic scale and in part formed a basis for industry guidelines developed as part of the JIP.