ROV

  1. Subsea


ROV at work in an underwater oil and gas field. The ROV is operating a subsea torque tool (wrench) on a valve on the subsea structure.
ROV whale encounter!

A remotely operated vehicle (ROV) is a tethered underwater vehicle. They are common in deepwater industries such as offshore hydrocarbon extraction. An ROV may sometimes be called a remotely operated underwater vehicle to distinguish it from remote control vehicles operating on land or in the air. ROVs are unoccupied, highly maneuverable and operated by a person aboard a vessel. They are linked to the ship by a tether (sometimes referred to as an umbilical cable), a group of cables that carry electrical power, video and data signals back and forth between the operator and the vehicle. High power applications will often use hydraulics in addition to electrical cabling. Most ROVs are equipped with at least a video camera and lights. Additional equipment is commonly added to expand the vehicle’s capabilities. These may include sonars, magnetometers, a still camera, a manipulator or cutting arm, water samplers, and instruments that measure water clarity, light penetration and temperature.

History

A Royal Navy ROV (Cutlet) first used in the 50s to retrieve practice torpedoes and mines

In the 1950s the Royal Navy used "Cutlet", a remotely operated submersible, to recover practice torpedoes.

The US Navy funded most of the early ROV technology development in the 1960s into what was then named a "Cable-Controlled Underwater Recovery Vehicle" (CURV). This created the capability to perform deep-sea rescue operation and recover objects from the ocean floor, such as a nuclear bomb lost in the Mediterranean Sea after the 1966 Palomares B-52 crash. Building on this technology base; the offshore oil & gas industry created the work class ROVs to assist in the development of offshore oil fields. More than a decade after they were first introduced, ROVs became essential in the 1980s when much of the new offshore development exceeded the reach of human divers. During the mid 1980s the marine ROV industry suffered from serious stagnation in technological development caused in part by a drop in the price of oil and a global economic recession. Since then, technological development in the ROV industry has accelerated and today ROVs perform numerous tasks in many fields. Their tasks range from simple inspection of subsea structures, pipeline and platforms to connecting pipelines and placing underwater manifolds. They are used extensively both in the initial construction of a sub-sea development and the subsequent repair and maintenance.

ROV on its way to work

Submersible ROVs have been used to locate many historic shipwrecks, including that of the RMS Titanic, the Bismarck, USS Yorktown, and SS Central America. In some cases, such as the SS Central America, ROVs have been used to recover material from the sea floor and bring it to the surface.

Much work remains to be done. More than half of the earth’s ocean is deeper than 3000 meters, which is the current working depth of most of the ROV technology. As of the writing of this article, the deeper half of the ocean has never been explored. This vast area has the potential to meet much of humanity’s needs for raw materials. As the industry advances to meet these challenges, we will undoubtedly see further improvements in these complicated robots.

While the oil & gas industry uses the majority of ROVs; other applications include science, military and salvage. Science usage is discussed below, the military uses ROV for tasks such as mine clearing and inspection. Approximately a dozen times per year ROVs are used in marine salvage operations of downed planes and sunken ships.

Construction

Conventional ROVs are built with a large flotation pack on top of an aluminium chassis, to provide the necessary buoyancy. Syntactic foam is often used for the flotation. A tool sled may be fitted at the bottom of the system and can accommodate a variety of sensors. By placing the light components on the top and the heavy components on the bottom, the overall system has a large separation between the center of buoyancy and the center of gravity: this provides stability and the stiffness to do work underwater.

Electrical cables may be run inside oil-filled tubing to protect them from corrosion in seawater. Thrusters are usually in all three axes to provide full control. Cameras, lights and manipulators are on the front of the ROV or occasionally in the rear to help in maneuvering.

The majority of the work class ROVs are built as described above; however, this is not the only style in ROV building. Specifically, the smaller ROVs can have very different designs, each geared towards its own task.

Classification

Submersible ROVs are normally classified into categories based on their size, weight, ability or power. Some common ratings are:

  • Micro - typically Micro class ROVs are very small in size and weight. Today’s Micro Class ROVs can weigh less than 3 kg. These ROVs are used as an alternative to a diver, specifically in places where a diver might not be able to physically enter such as a sewer, pipeline or small cavity.
  • Mini - typically Mini Class ROVs weigh in around 15 kg. Mini Class ROVs are also used as a diver alternative. One person may be able to transport the complete ROV system out with them on a small boat, deploy it and complete the job without outside help. Occasionally both Micro and Mini classes are referred to as "eyeball" class to differentiate them from ROVs that may be able to perform intervention tasks.
  • General - typically less than 5 HP (propulsion); occasionally small three finger manipulators grippers have been installed, such as on the very early RCV 225. These ROVUs may be able to carry a sonar unit and are usually used on light survey applications. Typically the maximum working depth is less than 1,000 metres though one has been developed to go as deep as 7,000 m.
  • Light Workclass - typically less than 50 hp (propulsion). These ROVs may be able to carry some manipulators. Their chassis may be made from polymers such as polyethylene rather than the conventional stainless steel or aluminium alloys. They typically have a maximum working depth less than 2000 m.
  • Heavy Workclass - typically less than 220 hp (propulsion) with an ability to carry at least two manipulators. They have a working depth up to 3500 m.
  • Trenching/Burial - typically more than 200 hp (propulsion) and not usually greater than 500 hp (while some do exceed that) with an ability to carry a cable laying sled and work at depths up to 6000 m in some cases.

Submersible ROVs may be "free swimming" where they operate neutrally buoyant on a tether from the launch ship or platform, or they may be "garaged" where they operate from a submersible "garage" or "tophat" on a tether attached to the heavy garage that is lowered from the ship or platform. Both techniques have their pros and cons; however very deep work is normally done with a garage.

Naming conventions

ROVs that are manufactured following a standardized design are commonly named by a brand name followed by a number indicating the order of manufacture. Examples would be Sealion 1 or Scorpio 17. The design of a series of ROVs may have changed significantly over the life of an ROV series, however an ROV pilot will often be familiar with the idiosyncrasies of a particular vehicle by name.

ROVs that are one-off or unique designs may be given a unique name similar to the style used for ships. ROVs are not normally referred to in the female gender as ships may be, but in the neutral gender.

References

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