Flushing and pigging of subsea flowlines generally requires traditional vessel-based operated pigging and testing systems that are equipped with large high-pressure pumps and long umbilicals. In deepwater, these systems become extremely large, heavy, and awkward to handle and to operate.
Cybernetix is developing Sapps, a cost-effective, compact, light weight subsea flowline flushing and pigging system that is operable by ROV and that does not require a dedicated umbilical to the surface.
Artist's impression of a Sapps system in operation on the seabed.
After the flowline has been laid in an air-filled mode, the Sapps module is installed adjacent to the pipeline lay-down head, and the flexible connection is made up using a work ROV. The ROV is connected to the Sapps control module to allow data transmission and commands between the surface and the seabed through the ROV umbilical.
The Sapps system filters seawater at ambient pressure and feeds it into the air-filled pipeline, thereby flooding the line and pushing the pig forward. A flow meter and a hydraulically operated flow control valve ensure a controlled manner of flooding of the pipe, and a backwash system can be activated in the event of filter blockage.
If seawater has to be treated, the chemicals that are to be injected are pre-mixed on the surface and stored in elastomer reservoirs inside the Sapps structure. These reservoirs are fitted with an injection pump that is controlled by an injection flow meter to ensure a correct water/chemicals ratio.
Sapps is equipped with a booster pump to provide additional pressure to complete pigging of the full length of the line or to send additional pigs through the line. The system is being designed for deployment by the vessel's crane; alternatively, the system can be connected onto the ROV as a tool-skid.
The system is designed for high precision remote control and data transmission through the telemetry of a standard work ROV via a simple interface of the Sapps' PC surface control with the ROV's control system. In air, the Sapps is expected to weigh 3 tons, and variable buoyancy allows it to be handled by a work ROV. The depth rating will be 3,000 m, and the frame support allows it to be installed on very soft seabeds (5 Kpa). Commissioning of an operational system is scheduled for completion in mid-2003.