Swivel

Swivel Stack

The swivel stack can, with the aid of a number of hydraulic systems, utilizing either cylinders or geared pinion systems, be manipulated in all planes to facilitate its connection / disconnection. The swivel can be retracted to its stowed position by a transverse travel. The swivel is finally connected to the DRB when the QCDC coupling is engaged. The QCDC includes the risers ESD (emergency shut down valves).

The Swivel stack consists of several independent sub assemblies:

• Production Swivel
• Hydraulic Utility Unit
• Electric Slip Ring Unit

Production Swivel

The Production Swivel provides the fluid transfer between the risers and the FPSO. When in operation, it is located centrally in the moonpool directly above the buoy and QCDC (Quick Connect Disconnect Coupler). As the buoy is deployed and retrieved by a pull-in winch hawser that demands the same central position, the swivel is mounted on a transit frame that allows it to be deployed or retracted when necessary to permit buoy deployment and retrieval operations.

The Production Swivel unit is located at the bottom of the stack and comprises one or more (by request) toroidal flow paths. Each flow path can be utilized for the transference of production fluids from the reservoir, gas lift or gas injection or for water injection/re-injection to the reservoir. Each flow path has a rated design pressure, max. 5000psi (345bar). All flow paths are designed for sour service.

The Swivel consists of an inner part and an outer part. The outer part (swivel rings or casings) are locked to the ships movement by torque arms. The geostationary inner part is turned by the buoy rotating system controlled by the DP system of the ship to avoid twisting the geostationary risers when the vessel changes heading. The swivel rings houses a unique triple dynamic seal system arrangement either side of the flow path. The Inner part ( core)  is manufactured from 22% Cr Duplex Stainless Steel then HIP coated with Tungsten Carbide and ground to a very smooth surface finish. The casings are manufactured from 22% Cr Duplex Stainless Steel.

The flow-paths through the core into the risers are piggable through insertion of ball valves at the top of the core, which permit access to the pig launcher/receiver supplied by others.

For transfer of utilities there are utility swivels mounted at top of the production swivel, one for electrical supply (control and power), one for hydraulical supply and one additional fluid swivel.