Micro subsea vehicles cut duration, cost of offshore inspections
Micro-sized remotely operated vehicles are set to slash inspections costs for offshore foundations by reducing the need for heavy equipment and labor and shortening subsea check-ups.
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Technology developers are looking to bring micro-remotely-operated vehicles (Micro-ROVs) used to inspect oil and gas platforms, into the offshore wind sector.
Micro-ROVs can cut underwater inspection costs by over 70% by avoiding the need for diving support vessels (DSVs), according to a study by MDB Marine, a provider of Micro-ROV services.
MDB Marine's day rate is about GBP£5,000 ($7,700) and the company’s cost comparison is based on ballast tank inspections for the oil and gas industry.
The company says it can carry out an inspection program of an equivalent quality to using divers. Using the smaller vehicles requires less man-hours and there are clear benefits to human safety.
“The biggest risk is to the man inside the tank,” said Derek Bond, MDB Marine co-director. “We completely eliminated the need for manned entry and that made it not just the safest but also the most efficient method as well.”
Using Micro-ROVs more than halved the visual inspection time compared with using divers, according to a study in the oil and gas sector, Bond said.
At the same time, “[the diver operation was] operating with a six-man team and we were operating with a two-man team.”
In this particular application, the use of micro-ROVs led to a 73% reduction in man-hour requirements, compared to the traditional method of diver based inspections, he said.
Super size
So far, micro-ROVs have been somewhat overlooked by the renewable energy sector. Instead, developers and operators tend to rely on larger remotely operated machines: filing cabinet-sized inspection units, for example, or work-class machines that are the size of a small car.
These devices offer safety benefits over the use of divers for subsea inspections, but still require specialist support teams and heavy lifting equipment that in practice is only usually found on DSVs.
Micro-ROVs, which have already been used in the oil and gas sector, are much simpler to deploy and operate.
One of the more popular models, the VideoRay Pro 4, weighs about 6 kilos and can be packed along with its control systems into two suitcases totaling less than 40 kilos. The device can be operated by a single person.
Depth-wise, the VideoRay Pro comes with a 40-meter tether but can operate at up to 305 meters below water. The small size of micro-ROVs means they can survey locations where space is limited and mobility is key.
Chart source: WEU Offshore Foundations & Supporting Structures Report 2015
Safety first
Reducing the risk to workers is a key advantage of the micro-ROV technology, said Michael Dusher, marine supervisor at Maersk’s Floating Production Storage and Offloading vessels division.
“The ROV’s main selling point is in controlling risk,” he said.
The vehicles can also aid diver-assisted projects, Dusher said.
“An ROV can pinpoint areas of interest to direct the rope access team towards. Due to the ROV, the timeframe is reduced drastically and therefore the potential for harm is also reduced.”
These safety and cost improvements are leading to growing interest in micro-ROVs in the oil and gas sector.
“Micro-ROVs are capable of completing a great deal of the inspection work scopes carried out by larger, more costly systems currently being used,” Dusher noted.
“They are small plug-and-play systems that in the hands of a skilled ROV pilot have the ability to produce extraordinary results. I have witnessed systems such as the VideoRay Pro series using a great deal of attachments, making them incredibly versatile.”
Flexibility
Proponents of the micro-ROVs also point out the technology can be more agile underwater than larger devices, since they present a lower surface area to oncoming currents.
Dusher believes a greater awareness of the potential of micro-ROVs would benefit the renewable and fossil fuel energy industries alike.
“Where I see the benefit of these micro systems, above all others, is as a rapid response service,” he said. “The system can be loaded into the back of any car with and operator and driven country-wide at short notice.”
A micro-ROV could also be easily shipped to offshore locations by helicopter, he said, making it easy to carry out on-the-spot foundation inspections following rough weather or other incidents that might be a cause for concern.
Another advantage of Micro-ROVs is that they can be launched and operated from multi-purpose vessels, which widens the choice of available vessels and lessens the likelihood of vessel shortage.
Number of vessels equipped for offshore wind installations
Chart source: WEU Offshore Foundations & Supporting Structures Report 2015
Smaller Micro-ROV units will have to demonstrate their cost-effectiveness as technology firms are also working to lower the cost of using larger remotely operated vehicles.
The European Marine Energy Centre (EMEC), a tidal and wave power research base in Orkney, UK, has been studying the potential of seabed shelters where the machines can recharge without have to be brought up.
Trials of the concept indicate that seabed-based charging could double the operation time for inspection-class ROVs.
“That doubling of ROV time I think in itself is a significant and useful a step forward,” said EMEC’s managing director, Neil Kermode.