Umbilical and Hose Analysis
Electric and Hydraulic power are transferred from the topside to the subsea equipment via control Umbilicals and hoses.
The Umbilical and hose lines are flexible pipes with very low bending and axial stiffness which can result in high deflection under environmental current loading. High deflections in the umbilical and hose lines can cause interference with adjacent equipment or the riser. Furthermore, large deflections may cause the Minimum Bend Radius (MBR) limits of the umbilical and hose lines to be compromised especially under additional dynamic wave loads and the corresponding vessel motions. Exceeding recommended MBR criteria can cause damage to the lines with a potential loss of power or control to the subsea equipment. This is very critical to the safe functioning of barriers especially when working on live wells.
Numerous solutions exist for each system configuration. If compensated tension is available on the vessel then the umbilical deflection can be stabalised by a tensioned podline. However, if no compensation is available then it is necessary to provide stabalising tension to the umbilical via a clump weight suspended above the seabed away from the subsea equipment. The clump weight must have sufficient free travel to accommodate the worst-case vessel heave motion. Furthermore, connection must be made from the Umbilical Termination Assembly (UTA) to the subsea control package and this is done using a flying lead which itself is a flexible pipe with low stiffness. The flying lead must also accommodate the vessel heave motion and this can be achieved using buoyancy to provide an ‘S’ bend which is carefully configured so not to overload the anchor or compromise the MBR requirements.
AS Mosley performs design optimisation and assessment of umbilical and hose system configurations using global finite element analysis. The global model of the umbilical and hose lines incorporates accurate mechanical properties (mass, bending, axial and torsional stiffness) and includes a representation of the vessel and its motion response.
Field specific environmental loads are applied to the global model combined with vessel excursions for the following design conditions:
- Normal operations
- Extreme environmental conditions
- Accidental Vessel Excursions (i.e. Drift Off during DP failure)
The load combinations fully capture the dynamic deflections of the Umbilical and Hose lines and this is used to optimise the variables within the system configuration.
Optimisation of the following variables is performed:
- Mass of clump weights
- Elevation of Clump weights above seabed
- Length of jumper hoses
- Buoyancy configuration on jumper hoses
- Umbilical overpull tension to disconnect from UTA
The operating limits (i.e. seastates, vessel heave, and offset) are assessed throughout the optimisation process in order to meet the operability requirements ensuring efficient, safe and cost-effective operations.
For more information on umbilical and hose analysis, please contact us directly.
