The vehicle in use underwater.Click here to enlarge the image
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Thousands of kilometers of submarine pipelines are inspected each year using towed systems or remotely operated underwater vehicles equipped with sonar, video and magnetic sensors. ECA is aiming for a similar capacity for the Alistar.
When operating near structures, AUVs require advanced maneuvering capabilities. They must be able to respond quickly when given the command to move up, down, right or left. According to the ECA, this can only be achieved with a vehicle equipped with two thrusters that provide three degrees of freedom.
In pipeline inspection, the difficulty for an AUV is mainly that as-built reports indicating pipeline locations are not precise enough to pre-program a flight path with waypoints above the pipeline (i.e. about 5-10 m). For a correct video inspection of a pipeline, the AUV must fly directly above the line, with a tolerance of about 50 cm on either side and about 1 m above the line.
This is where pipeline tracking sensors and real-time processing of sensor data come into play. ECA has been working on these capabilities since early 2004, culminating in a recent pipeline tracking test over 500 m off Toulon. The pipeline was a 50 cm diameter steel section. The resulting tracking showed that the position – which ECA had pre-programmed from the map for the search phase – was incorrect. By following the pipeline's track, the AUV was able to determine the true position of the line and correct the error.
ECA's future studies for the Alistar 3000 include extending its capabilities to include monitoring pipeline touchdown points and inspecting anchor lines, subsea booms and manifolds. This will require improvements to side-scan sonars, multibeam profilers and 3D cameras, as well as adapting the automatic control algorithms to the different shape of the vehicle.
Once these changes are implemented, the vehicle should be able to check that the pipeline is being laid on the correct path and store data so that it “knows” where the pipeline is on a later revisit. The technology should significantly reduce the time needed to inspect a pipeline, claims ECA, taking into account the current limitations of tugboats and ROVs due to the umbilicals. The specifications of the escort vessel should also change, as the typical total weight of 75 tonnes for a deep-sea ROV can be reduced to 15 tonnes for the Alistar.
Further demonstrations for potential customers are planned before the end of this year to allow for further technical and commercial evaluation. Work to date has attracted interest from subsea contractors in Houston and the North Sea.
Intervention studies
Last autumn, the autonomous light emergency vehicle Alive completed its sea trials off the coast of southern France. Project coordinator Cybernetix is currently in talks to advance development with new partners.
The tests in the deep waters off the coast of Bandol in Provence were the culmination of a three-year development programme partly funded by the European Commission. Other partners included the French oceanographic research institute Ifremer, Norway's Hitec Framnaes, the European Joint Research Centre in Italy and the Ocean Systems Laboratory at the University of Edinburgh.
Following a series of tank and shallow water tests in the summer of 2003, the goal of the sea trials was for the AUV to autonomously dock with a pre-installed ROV panel and perform pre-programmed tasks, namely opening and closing valves using the vehicle's hydraulic manipulation arm. The Alive was launched from the Ifremer research vessel Europe and subsequently monitored via an acoustic link that also transmitted telemetry data and images from the AUV to the surface.
The AUV's maneuvers were controlled via video and sonar image processing onboard Europe and matched with a computer-aided design image of the underwater environment. After a 10-minute transit time to the seabed and subsequent approach to the target, successful docking and telemanipulation of the panel was confirmed by an observation ROV monitored by a second vessel, the Cupidon.
During this program, three dives were successfully conducted. According to Cybernetix, these confirmed the functionality of each of the vehicle's subsystems and also demonstrated the Alive's ability to perform in difficult sea conditions. The vehicle was designed to perform autonomous light intervention tasks on offshore installations in water depths of up to 3,000 m, without the need for long umbilicals or a dedicated supply vessel, which can account for 90% of the cost of a deep-water intervention operation.
Marseille-based Cybernetix claims that these results pave the way for extending the AUV to new tasks beyond traditional seabed surveys. They also prove that AUVs can perform interventions on fixed underwater structures such as wellheads for inspection, maintenance or repair work. Alive's open frame is designed to integrate different combinations of sensors and actuators.
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