ROV-operable pipeline
flushing and pigging
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.
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.
05/01/2003
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