Jeremy Beckman Editor, Europe
Early in July, ECA's Alistar autonomous underwater vehicle (AUV) undertook its first significant autonomous pipeline inspection task. In a trial mounted off-shore Toulon, southern France, the AUV tracked a pipeline and recorded video images over a distance of 500 m.
Alistar first demonstrated its autonomous inspection capabilities to the industry last November at the Deep Offshore Technology conference in Marseille. The Alistar 3000 AUV is the successor to ECA's shallow water vehicle, the Alistar 300 demonstrator. ECA built the latter to provide experimental data needed to refine the current version for operations to 3,000 m water depth.
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During the DOT trials, the company proved that it could pre-program its vehicle to search for, find, and inspect a structure (a vertical pipeline) without operator commands. Having located the pipeline, the AUV adjusted its offset (by around 1 m) before starting vertical inspection of the pipe while recording video. Finally, ECA towed a vertical pipeline to demonstrate the vehicle's ability to follow it, simulating the fist steps of pipeline touch-down monitoring.
Close approach
ECA has proven its AUVs' efficiency and reliability for deepwater seabed survey work. To take the technology a step further – i.e., surveying and inspection of underwater structures – the company has developed an architecture that allows the Alistar to approach structures within a sub-meter distance, which it says is not possible with the current generation of high-flying "mono-thruster," torpedo-shaped AUVs.
The Alistar provides close-up hovering capability by means of eight thrusters configurable in three axes. These also allow the vehicle to perform non-manipulative tasks that only ROVs previously achieved. Another advantage, compared with existing AUVs, is the vehicle's ability to autonomously interpret its payload sensor information in real time and to adjust its position automatically in order to undertake acceptable close video inspection.
The vehicle in action underwater.
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Thousands of kilometers of submarine pipelines are inspected each year using towed fish systems or ROVs equipped with sonar, video, and magnetic sensors. ECA aims to achieve similar capability for the Alistar.
AUVs require advanced maneuvering skills when operating close to a structure. They must be able to react quickly when an order is sent to move up, down, right, or left. ECA claims this can only be achieved by a vehicle fitted with a set of two thrusters providing three degrees of freedom.
For pipeline inspection, the difficulty for an AUV lies mainly in the fact that "as-built" reports giving the positions of the pipeline are not precise enough to allow pre-programming of a trajectory with way points above the pipeline (i.e., around 5-10 m). Correct video inspection of a pipeline involves flying the AUV directly above the line with a tolerance of around 50 cm on either side and around 1 m above the line.
This is where pipeline tracking sensors and real-time processing of the sensors' data comes into play. ECA has been working on these capabilities since early 2004, culminating in the recent 500-m pipeline tracking trial off Toulon. Here, the pipeline was a 50-cm-diameter steel section. The resultant tracking showed that the position – pre-programmed by ECA from the map for the search phase – was incorrect. By following the pipeline's track, the AUV allowed the line's actual position to be determined, thereby correcting the error.
ECA's future studies for the Alistar 3000 include broadening its capabilities to pipeline touch-down monitoring and inspecting anchor mooring lines, subsea trees, and manifolds. This necessitates refinements to side-scan sonar, multi-beam profilers, and 3D cameras, and adjusting the automatic piloting algorithms to the different shape of the vehicle.
Once these changes have been implemented, the vehicle should be able to check that the pipe is being laid on the right track, and also store data so that it "knows" where the pipeline is during a subsequent return visit. The technology should reduce substantially the time taken to inspect a pipeline, ECA maintains, taking into account the current limitations of towed fish and ROV due to the umbilicals. The specification of the support vessel should also change, as the typical spread weight of 75 tons for a deepwater ROV can be cut to 15 tons for the Alistar.
Further demonstrations to potential clients should be mounted before the end of this year, allowing further technical and commercial evaluation. Work to date has attracted interest from subsea contractors based in Houston and the North Sea.
Intervention trials
Last fall, the autonomous light intervention vehicle, Alive, completed sea trials off southern France. Project coordinator Cybernetix is now in discussions to take development forward with a new set of partners.
The trials in deepwater offshore Bandol, Provence, were the culmination of a three-year development program part-funded by the European Commission. Other partners were French oceanographic research institute Ifremer, Norway's Hitec Framnaes, the European Joint Research Center in Italy, and Edinburgh University's Ocean Systems Laboratory.
Following a series of tank and shallow-water tests in summer 2003, the aim of the sea trials was for the AUV to dock autonomously onto a pre-installed ROV panel and perform pre-programmed tasks, namely opening and closing valves with the vehicle's hydraulic manipulating arm. The Alive was launched from the Ifremer research vessel Europe, with subsequent supervision via an acoustic link, which also relayed telemetry data and images from the AUV to the surface.
The AUV's maneuvers were controlled via video and sonar image-processing onboard the Europe and matched with a computer-aided design image of the underwater environment. Following a transit time of 10 min to the seabed and the subsequent approach to the target, successful docking and telemanipulation of the panel was confirmed by an observation ROV supervised from a second vessel, the Cupidon.
During this program, three dives were successfully executed. According to Cybernetix, these validated the functionality of each of the vehicle's sub-systems and also proved the Alive's ability to perform in difficult sea conditions. The vehicle has been designed for autonomous light intervention duties on offshore installations in water depths to 3,000 m without the need for long umbilicals or a dedicated support vessel, which can consume 90% of the cost of a deepwater intervention operation.
Marseille-based Cybernetix claims these results open the way for extension of the AUV to new tasks other than conventional seabed surveys. They also prove that AUVs can perform intervention of fixed subsea structures such as wellheads for inspection, maintenance, or repair operations. Alive's open frame is designed to allow integration of different combinations of sensors and actuators.
The ROV-deployable deepwater pipeline pigging system, Sapps, is closer to a commercial launch, following successful tank tests this summer.
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Recently, Cybernetix was invited to join SeaBee, another EC-funded project, this time led by Hannover University. Here, the objective is to develop an autonomous vehicle – a progression of Alive – that would combine core sampling and environmental data-gathering capabilities. The other three partners are based in scientific marine laboratories based in the Baltic Sea (Marilim), Porto (Cimar), and the Corsican Sea (Corsicologie).
According to Cybernetix's Offshore Division Director Alain Fidani, the program will involve mechanical and electronic integration of a seabed corer, developed by Challenger Oceanic, into the vehicle. the AUV will also be equipped with skis in an attempt to cushion landings on the seabed. Test campaigns are planned next summer in the Baltic, Atlantic, and Mediterranean (off Corsica seas).
Hybrid studies
Cybernetix has also been approached to join the EC-supported Soave project. Soave aims to develop a hybrid ROV/AUV for deep-sea inspection, maintenance, and repair work. Another Maridan- designed vehicle was to be the focus of this scheme, but work was halted when the Danish contractor went out of business.
Swimmer, Cybernetix's first ROV/AUV prototype, was a three-year development, which again climaxed in sea trials of southern France. Soave provides an opportunity to move the R&D further toward development of a commercial unit. Until recently, Statoil was seriously interested in taking the Swimmer for subsea interventions in the Norwegian sectors. Cybernetix was also in discussions with numerous US oil companies about potential applications.
For Soave, a new prototype vehicle would be built, with Oceaneering working on the ROV part of the hybrid system. Other partners would be the University of Hannover, as project coordinator; Fugro, in charge of sea trials; and Shell Technology in Norway as a possible future user. The test program will ideally get under way by 1Q 2006.
In May, Cybernetix presented another new development at OTC, its miniature ROV Junior, weighing 35 kg. This ROV is designed to be fitted onboard a work-class ROV, providing the pilot with an extra pair of "eyes" in water depths to 3,000 m. Junior incorporates advanced capabilities that include a digital display of up to three video sources with sensor feedback overlay. Digital images or video sequences can be recorded by the surface control unit. The vehicle also provides 17 kg of vectorized thrust and can maneuver well even in strong currents. There has been strong interest from several ROV service contractors, in particular Oceaneering and Sonsub, according to Fidani.
In another development, Cybernetix has started commercialization of Sapps, its deepwater pipeline flushing, pigging, and hydrotesting system, following the completion of extensive trials this summer. The tests were the result of a two-year development program designed to deliver the first subsea pigging system for commissioning deepwater pipelines in water depths of up to 2,500 m. The compact Sapps system is deployed and connected by a work ROV through a skid.
