“ROV” stands for remotely operated vehicle working subsea.
These systems are used to perform tasks such as drill support; subsea construction; inspecting pipelines, structures and cables; operating and maintaining valves and other moving parts on subsea manifolds; trenching for submarine cables and pipelines; seabed surveys; inspection and maintenance of platforms; and enabling video observation of both divers and underwater equipment.
The communication between the operator and the vehicle is controlled by an umbilical/tether cable. Nexans Norway AS designed and manufactures both ROV umbilicals and tethers, and they are designed according to our customer’s specifications and requirements.
ROV cables are exposed to dynamic cycling, thermal and electrical stress, currents and rough seas. The main purpose of the cables is the transmission of power, signal, communication and tensile loads to a remote location.
The industry is constantly going deeper, and Nexans supports the industry by offering products qualified for operations below 7000 meter water depth with a voltage rating up to 6.6kV.
An ROV umbilical is typically installed topside on a winch and is the physical connection between the control unit and the vehicle.
The cable core is built up by combining copper conductors for power and signaling, and fiber optic elements for communication. The cable core is protected by sheaths and high tensile armoring such as steel wires or synthetic yarns.
For an ROV system operated with a TMS (tether management system), the chosen strength member is typically steel wires to support the total weight of the system submerged in water. For extreme depths and for free flying systems (no TMS) synthetic armoring is the preferred option.
The main challenge of the industry, as the operations go deeper, is to reduce the total weight of the system and at the same time increase power transmission. Nexans supports this challenge by constantly developing new designs including improved technology.
A typical work class ROV has a tether cable installed between the vehicle and the TMS (tether management system), to transmit electrical power, optical signals and mechanical payloads through a light and highly flexible and robust cable.
ROV tether cables are exposed to repeated bending at small diameters and low tension, followed by occasional snap loads. High performance polymer yarn handles hydrostatic pressure at great depths, and is resistant to fatigue and friction damage. It is also chemically stable in seawater, oils and other fluids used in the oil & gas industry.
Boosting the flexibility and extending the life time of a tether cable, Nexans Norway has chosen to use new bending-optimized polymer Dyneema ® yarns called Enable™ to ensure prolonged service life on existing systems. Less termination work on vessels, shorter shutdown times, more flexibility in design, and lower weight to accommodate more copper conductors in a smaller diameter are all advantages. This proven technology leads to less voltage loss, longer excursion lengths, and lower failure and replacement costs for customers. The Enable™ designs have been in operation in harsh environments and have been successfully tested by third parties.
The length of a tether is determent by the type of work being performed and the available space on the TMS drum. Typical excursion is between 450 meters and 1600 meters, and the tether is typically designed and manufactured to be either neutrally buoyant or heavy in water.