ROV-based pipeline recovery system developed for such an event
- A diverless ROV-based system recovers a pated pipeline off Brazil in three steps.
The Stena Apache supported the recovery of a pipeline from 2,700-ft water depths.
During the completion of a deepwater pipeline in 2,000-3,000 ft water depths off Brazil last year, a pipe joint weld failed, sending the pipeline to the seabed in 2,700 ft water depths. Stena Offshore of Aberdeen recovered the 12-in. pipeline using its ROV-based recovery system shortly afterward and continued laying the line.
The pipelay vessel, Stena Apache, conducted the operation. The recovery of the dropped pipeline involved a series of steps:
- The ROV (remotely operated vehicle) located the end of the parted pipeline and dredged out the area under the recovery end.
- The pipe cutter was lowered and docked to the ROV. Both were lowered to the seabed and the pipeline cut was managed by the ROV.
- The cutter was raised to the surface and a connector lowered and mated to the pipeline.
- The ROV connector and pipeline were raised to the surface.
A Stena spokesman pointed out the pipeline parting event was the first test of the intervention system, which had been previously developed by Stena upon contracting for laying the deepwater line for Petrobras, the Brazilian national oil company.
Previous pipeline recovery operations have involved reconnection with a lay down wire or having a diver burn a hole in the pipeline to connect a shackle and pull up wire. The lay down wire is standard for abandonment operations. The latter is usually undertaken when a pipeline parts. However, the depths at which the pipeline was to be installed precluded use of a diver, so Stena had to develop a diverless recovery system.
Components of the recovery system include the following:
- ROV unit: The research group chose Slingsby Engineering's MRV unit to transport and support the work packages on the seabed.
- Dredging/support: The dredging unit and pipeline support systems are off-the-shelf items.
- Pipe cutters: After evaluation of a number of pipe cutting packages, a system employing a continuous loop of diamond impregnated wire was selected.
The Stena design group had to develop a specialized unit to deploy the wire cutting machine. The attaches to the ROV for deployment and depends on the ROV for hydraulic power and signal conductors. The cutting unit is small and contains its own valve pack, telemetry system, and surface control panel.
The ROV clamps the cutter onto the pipeline, and the wire loop is lowered onto the pipeline at a controlled rate. Pipe cutting is monitored by a camera. Cutting times average one hour for a 10-in. diameter, 1/2-in. wall thickness pipe.
- Connector: The pipeline recovery connector is also an off-the-shelf item, but had never been deployed below water before. Stena chose a version of the Ball Grip, designed by BSW Engineering, which has been used often to lift drill pipe and other tubulars topside. The system relies on a wedge surface engaging ball bearings against the internal pipe wall and is held in place by the recovery line pull. The ROV inserts the assembly into the pipeline and actuates a latch. Recovery connectors with a proof load of 80-200 tons have been fabricated for use on 10-in. and 12-in. pipelines, but the unit can be designed to fit inside 2-in. ID pipes.
- Dewatering: Dewatering of the flow is provided by a pig launcher, that is part of the initiation assembly deployed with the ROV.
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