STP - The Basic Concept

STP is developed from the basis of our proven STL system which has been successfully utilized on several fields in the North Sea.

The core of the STP system is the buoy moored to the seabed. Pulled into and secured in a mating cone, the buoy is connecting the vessel to the mooring system. Internal in the buoy is the turret with connection to the mooring and riser systems. The outer buoy hull can rotate freely with the vessel around the turret by means of internal turret bearings.

The STP swivel (Rotating Connector) is transferring well streams, water, gas, signals and power from the geo-stationary risers to the piping/ cabling system of the freely weather-vaning vessel towards the process plant onboard.
Riser accommodation

The STP application requires that several risers and umbilicals can be connected to the turret. To give space for the multiple risers and umbilicals, the STL turret shaft has been extended in diameter.

By utilizing the largest available opening in the standard buoy design, a space with an inside diameter of 2700 mm can be used for arranging riser termination's etc. This allows for a typical no. of risers in the range from 7 - 10 dependent on riser size. APL also has also proven that the concept is scalable upwards, and has designed STP buoy able to accommodate 15-20 risers.
Multi-path swivel

The high pressure multi-path swivel is a key component in the STP system. In addition to the multi- path swivel for fluids and gas, both power and signal/ utilities utility swivel arrangement may be required.
Geometrical standardization

All STL/STP systems today are based on the same mating cone geometry in the vessel leading to standardization of the specialized steelwork in the vessel as well as an excellent basis for utilization and reuse of both buoys and vessels.
Flexible mooring system

The STL installations operative are installed in water depths from 85 to 350m and with design significant wave heights of up to 15.5m. Systems in construction will have design significant wave heights up to 18.4m. Verification of mooring systems through ocean basin tests have verified the feasibility of the STL/STP mooring systems for water depths ranging from 40 to 900m. Mooring system analysis have demonstrated the suitability of the STL/ STP mooring system for water depths ranging from 20 to more than 2000meters.
Mooring system verification

Correspondence between analyzed and model tested data versus real life full scale mooring line tension measurements on have demonstrated very good accuracy. In normal operation excursion from system centre will be monitored using either DGPS OR HPR systems.

STP References