Understanding Subsea Umbilical Cable and its Usage
What Is a Subsea Umbilical Cable?
A subsea umbilical cable is more than a submersible power cord. It is generally a multi-function hose or cable. For example, many subsea umbilical cables carry data cables as well as electrical lines. They can supply other “consumables” to a subsea or underwater apparatus. That is why they’re compared to human umbilical cords.
How Are Subsea Umbilical Cables Used?
Subsea umbilical cables are used in diving, robotics, the military, and some aerospace applications. The subsea cable connects a ship, floating oil rig, subsea flow station, or other off-shore facilities with a logistical source. This could be anything from a well-equipped ship to facilities onshore.
The cables can also connect various items underwater. This includes underwater sensor stations, pumping stations, and subsea compressor units. It is similar to a power grid because it typically delivers electrical power, but anything else you want can be put into the thermoplastic hose or steel umbilical cable.
What Are the Most Common Uses of Umbilical Cables Used?
The biggest users of subsea umbilical cables are marine operations and the oil and gas industry. The cable might carry power to an offshore drilling rig or deliver hydraulic fluid while removing wastewater. Or it may deliver power, clean water, and a fast internet connection to people working on a floating oil rig. The same cable or another may remove wastewater and send raw crude oil to tanks onshore. The hoses can carry pressurized gases including air mixtures and industrial gases. Yet they can be used to connect almost any sort of equipment that’s been installed underwater to each other, ships, or control stations on land.
Factors That Affect Subsea Umbilical Design
Subsea umbilical cables are by definition designed to withstand seawater. These same cables can be used in freshwater applications, as well. However, there are many other factors that affect their design. They need to be made to withstand the water pressure they’ll be subjected to. This is why cables that are used for oil rigs and ships a short distance offshore are not as strong as those laid in the deepest part of the Gulf of Mexico. This is why the hose design will vary wildly based on water depths.
Another factor to consider is what is flowing through the pipe. A rugged 10 to 20-inch thermoplastic hose may be used to carry fiber optic cables and electrical power lines to an offshore destination. Fiber optics is only practical for shorter cable lengths. Expect steel tube umbilicals to be used to deliver hydraulic fluid for fracking and carrying the resulting natural gas or raw crude to a waiting holding tank. Subsea umbilical cables used to deliver chemicals for a chemical injection well will obviously need to resist erosion on exposure to said chemical, as well as resist corrosion to whatever is outside of the pipe.
Another factor that affects subsea umbilical cable design is the intended application. A straight line connection akin to a water hose connecting is far simpler than subsea trees, where there are “trunks” that branch off of the main line to secondary stations. The subsea umbilical cords generally connect to the surface facility or a floating vessel via a topside umbilical termination unit or TUTU. The subsea equivalent is called a subsea umbilical termination unit or a SUTU. Flying leads are used to lay the umbilical cable along a planned route.
Subsea umbilical cables tend to be lighter than permanently installed metal pipelines since they will be carried on board of ships or even helicopters. And they may roll it back up when they’re ready to pull up stakes and move on. Or they may be a flexible connection to submersible vehicles. This gives the vehicle a greater range than an independent craft since it doesn’t have to carry batteries. Subsea umbilical cables for mobile craft will generally be thinner and lighter than those used to carry chemicals to and from an oil well.
What Are the Benefits of Using Subsea Umbilical Cables?
Let’s use the example of underwater oil and gas exploration. A network of subsea umbilicals connects several drilling sites. All of these connect to a single ship that accepts and holds the crude oil pumped up by the drilling stations, while the ship or floating oil rig supplies power and consumables to the many smaller underwater drilling sites. You only need a single control hub, instead of having half a dozen ships overseeing an oil-producing area covering several hundred square kilometers. This dramatically reduces the cost of subsea oil and gas production. This is especially true when you’re sending chemical injection fluids to an underwater unit or supplying power to heat it up to prevent the formation of waxes that slow the hydrocarbon flow. You can install heating elements in the pipes to prevent the formation of ice on it, too. That makes umbilicals invaluable for maximizing output from oil and gas production systems.
Furthermore, the subsea cables and related infrastructure are literally flexible. If you move the equipment, you can take the cables with you. This reduces the environmental impact of the project relative to alternatives like installing permanent steel pipes like an underwater version of the Alaskan Pipeline. When you’re using steel pipes in an umbilical cable, they will be connected with flexible sections that continue to protect the lines and hoses inside.
The subsea umbilical cable network is also flexible from a design perspective. Simply add additional trunks to the network to grow it, whether you extend it in one direction or add new branches. There will be limits such as how much power can flow through the cables or the safe internal pressure of gasses and fluids flowing through the pipes.
Fiber optic cable connections give you high speed, high accuracy, and private communications. That’s invaluable when you’re sending proprietary sensor data back to your control center or letting people in the field have video conferences with peers without relying on expensive satellite internet. The challenge of communicating underwater is universal. Even military submarines have problems using radio in saltwater.
The more important use of the built-in fiber optic cable in most subsea umbilical cables is the data connection required to control subsea equipment. You can use the same cable to deliver hydraulic fluids required to control valves and send signals to the controller along with electrical power to drive the system. You need a wired connection because most radio signals aren’t going to work in a subsea environment. Furthermore, it gives you incredibly tight control over the submersible or equipment, something you need when dealing with a leaking well or underwater craft navigating choppy waters. Or use the submersible connected to the surface by an umbilical cable for underwater surveying. Take samples with robotic arms or go in for a closer look with video cameras. Your craft is only limited by the length of the subsea umbilical cable, though that same cable reduces the risk of losing it.
If you would like to learn more about subsea umbilical cables, reach out to the professionals at Geospace Technologies. Since 1980, we have stayed at the forefront of engineering and manufacturing innovation. Contact us or submit a form about your inquiry.