All-electric ROV designed for ultra-deepwater applications

Transitioning from hydraulic fleet

Th 0300osrov
Th 0300osrov
Oceaneering's new E-Magnum work class ROV.
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An all-electric remotely operated vehicle (ROV) is being developed by Oceaneering International in preparation for the industry push into water depths where hydraulic-based systems lack efficiency. Dick Frisbie, Oceaneering's Senior Vice-President of Deepwater Technology, said he is pragmatic about the product - it will compete directly with the Magnum fleet of workclass ROVs Oceaneering builds and markets.

These vehicles have attained a reliability rating above 99%, and Frisbie said the challenge to introducing the new all-electric version of the vehicle is to avoid impacting this hard-won reliability. "The worst thing you can do is cause a rig down-time," Frisbie said.

The concept of an all-electric ROV is not new. Frisbie said all smaller ROVs are electric and early ROV designs of every description relied on established electronic technology. In fact, the first ROV, the US Navy's CURV, used to recover a hydrogen bomb off the coast of Spain in the 1950s was all electric.

Early on, the problem with the all-electric design was that as ROVs got larger, so did the thrusters. When hydraulics became a practical alternative, the industry quickly shifted to hydraulic thrusters. In addition to control issues, these units could generate more useable horsepower for less weight than their electric counterparts. There is another major advantage to hydraulics: The power can be diverted to specific thrusters to provide a boost in power for a certain task. This is not possible with electric thrusters.

Because the hydraulic thruster configuration, including work capability, was more efficient than electric thrusters development work on an improved electric thruster system slowed. An electric-thrustered ROV is more efficient, but because hydraulics seemed to provide a solution to the same problem, this line of development was not followed until new technologies came along.

Back to the future

The standard for workclass ROVs is to use electrical power, from the umbilical, which is converted to hydraulic power. This is an inefficient process that requires a lot of electric power to deliver an acceptable amount of hydraulic power.

Frisbie said electric thrusters could increase the reliability of an individual ROV, but that is not really the driver. Frisbie said his company looks to better training of personnel to keep reliability high (around 99.7%).

The electric ROVs have fewer moving parts so they should be easier and cheaper to maintain over the long term. But Frisbie said these advantages are not nearly valuable enough to justify the expense of developing a new propulsion system. The chief reason Oceaneering has developed a new all-electric workclass ROV is the industry interest in ultra-deepwater. Frisbie said there are depths where drilling will occur in the future that current hydraulic ROVs cannot efficiently access.

Traditionally, deepwater ROV designs were beefed-up versions of shallow water designs. What is needed now, Frisbie said, is a step change in technology that will generate all-electric ROVs with the power and versatility of the current fleet and the added ability to operate in ultra-deepwater. Frisbie said it is ironic that this step to the future is really a return to the past, when hydraulics was not an option.

Deepwater applications

The primary reason all-electric ROVs will be used in ultra-deepwater has to do with the umbilical. The umbilical connects the ROV cage to the winch and control equipment on the surface. The umbilical provides power to the unit and communications back and forth between the operator and the ROV. The umbilical also hoists and lowers the ROV and its cage.

To handle this strain, and protect the power and communication lines inside, the umbilical is armored by a steel coating. This coating is protective, but also very heavy. The larger the diameter of the umbilical, the heavier the armor. At a certain depth, the size umbilical needed to transmit power to a hydraulic workclass ROV would require an umbilical that is too heavy to support its own weight. The steel would no longer do the job. That means switching to a lightweight alloy such as titanium, or to Kevlar.

Titanium would work, but is prohibitively expensive, as is Kevlar. Also, both have significant technical issues. Looking forward, the long-term solution would be an ROV that can operate on less power to maintain an umbilical that can be armored by steel. Frisbie said an all-electronic ROV would fit this bill.

Such an ROV should have a 30% efficiency advantage over a comparable hydraulic vehicle. The problem is, this would mean a revolutionary design change. Frisbie said his company is building a number of its E-Magnum ROVs but not enough to guarantee a replacement if something were to go wrong. Until there is a major shift from the use of hydraulics to all-electric ROVs, Frisbie said Oceaneering has to use its hydraulic fleet to back up its smaller number of all-electric vehicles, should one be lost or damaged.

This new design is an all-electric workclass ROV that uses the same system as the hydraulic vehicles already in the market place. This means the tether, cage, umbilical, winch, and console are the same for both units. Frisbie said if the E-Magnum were to stop working or be lost, it could be replaced by a hydraulic model in 12 hours plus shipping time. This unit would simply hook into the tether of the all-electric unit and be ready to go.

More power

Not only does this interchangeability give customers a safety net, it also gives them an option for a more powerful work capability. Because the hydraulic unit can divert most of its power to individual tasks, it is much more versatile than its all-electric counterpart. Frisbie said in cases where an operator needs more power to perform a specific task, a hydraulic unit can be shipped out. Once the work is complete, the E-Magnum can take over again.

Frisbie said areas of future interest in ultra-deepwater, such as suction pile installation, fluid injection, subsea completions, dredging, subsea separation support, and riserless drilling support, will require more power than the current all-electric ROV could produce.

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