Flexible rough bore pipes are widely used in the oil and gas industry. One application is their use as risers and jumpers for gas production, transport and injection. In the past, some flexible pipes have been experiencing high amplitude tonal pressure fluctuations above critical velocities. These pulsations can cause mechanical vibrations at topside and subsea platforms, resulting eventually in topside/subsea piping failures [Swindell 2007].A Joint Industry Project, sponsored by BP, Bureau Veritas, ExxonMobil, Shell, StatoilHydro, TNO and the UK Health & Safety Executive, has addressed the technical issues associated with this singing phenomenon. A good understanding of the phenomenon has been achieved, by combining actual offshore measurement data, laboratory test results at low, medium and high pressures and numerical acoustic and flow simulations. The JIP has recently been completed and the final results are now available.The singing behaviour is strongly influenced by the corrugation geometry, the operating process conditions and the characteristics of the upstream and downstream connecting piping. Another critical parameter is the liquid content of the gas. Small amounts of liquid already increase the critical velocity significantly. Guidelines have been developed on practical assessment and mitigation measures for existing assets and precautionary design measures for planned assets.This paper describes the influence of the topside and subsea piping and of the liquid content of the gas on the critical velocity to trigger the singing phenomenon. Furthermore, it describes the operational and design guidelines that have been developed.
For catenary mooring lines, the relationship between excursion of the point of suspension and the length of suspended line is highly nonlinear. If the point of suspension is then set in motion, the velocity of the line resulting from a change in catenary profile induces additional nonlinear hydrodynamic loading components. The sensitivity of the mooring line to initial and oscillatory conditions results in a complicated tension history at the point of suspension, with line tensions possibly greatly exceeding those predicted by static analyses. This paper presents results from an experimental investigation into the response of a large (1:16) and small (1:70) scale single-chain catenary model mooring line when subject to a comprehensive, and equivalent, range of excitation parameters. Tests were performed at purpose-built test facilities. Small-scale model tests were carried out at University College London (UCL). Large-scale model mooring line tests were completed at the Ship Dynamics Laboratory, Canal de Experiencias Hidrodinamicas de El Pardo (CEHIPAR), Madrid, Spain. Funding for the model tests performed in Spain was provided through the European Union Access to Large Scale Facilities—Training and Mobilisation of Researchers Program.
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