Exploration • Drilling • Field Services
Smaller, lighter cables simplify shipboard deployment by reducing the space required for winching equipment and cable storage. Since deepwater umbilical cables are several thousand metres long, a 10 per cent reduction in a cable’s diameter can significantly reduce the required deck space.
A high-performance umbilical cable typically contains multiple types of elements to handle power, control, video, and telemetry. Tus you will find a mixture of larger conductor power cables, twisted-pair and multi-conductor elements, coaxial cable, and fibre-optic cable in various combinations to meet the specific needs of the application. An umbilical cable is typically constructed in
several concentric layers. Fig. 2 shows a type of construction designed by TE Connectivity that combines power, multimode and single-mode fibre- optic cables, and a shielded quad cable in a double- armoured cable. As you can see this is a complex design and it
is important that all elements work together in harmony to provide the required power, data and mechanical criteria. Each layer is defined not by function, but by the diameter of each cable element to maintain concentricity. Some cables, for example, may have power cables near the core’s centre, while others have them in outer layers. Maintaining concentricity is important both to clean, efficient winching and to achieving rugged flexibility. Each layer is wrapped with a tape, typically an aluminium/polymer tape, and voids are typically filled with water-blocking materials. Not called out in Fig. 2 are drain wires and fillers. Tese are added as necessary.
Te outer armouring serves as both strength members and core protection; it functions to disengage the cable elements from the overall tensile load placed on the cable.
Te cable is 1.670 inches (42.42mm) in
diameter. Its weight in water is 2771 pounds per 1000 feet (4123kg/km). It has a working load 35,000 pounds (156kN) and a bend radius of 33 inches (84cm). Te bend radius is most important to the diameter of the sheave. Using the cable at smaller bend radii can increase fatigue resistance and shorten the service life. Given the challenges of creating robust umbilical cables, designers use advanced simulation tools to analyze the mechanical and electrical performance. It is impractical to build multi-kilometre prototypes, so expertise in design and simulation are essential. Current efforts in umbilical innovation are focusing on the cable’s core, looking for ways to pack more functionality into the same or
Enabling optical communications Optical fibres are finding increased use in umbilical cables because of the increased bandwidth they offer over long distances. While fibres have high tensile strength to withstand longitudinal pulling, they can be easily broken or damaged if not protected correctly. As a result, fibre-optic cables typically have their own armouring. While aramid yarn - the same strength members common with other fibre- optic cables - are used, more robust designs also use metallic armouring. Te high hydrostatic application pressures can increase attenuation in a fibre. TE Connectivity offers three different
approaches:
● Fibre in Steel Tube (FIST), which places the fibre in a solid stainless-steel tube to protect against hydrostatic pressures, high temperature effects and corrosive environments. FIST packaging is a loose- tube design, which can accommodate several fibres loosely held within the tube and encapsulated in gel. Because the fibres ‘float’ within the tube, the length of the fibre is slightly longer than the tube to ensure low strain. FIST technology is the simplest and lowest cost approach. It maintains low strain on the fibre by decoupling stress on the tube from that on the fibre. If the cable stretches during installation or use, the excess fibre can accommodate the stretching without being strained. Loose tube designs also are very forgiving of extreme temperature excursions, but are less suited to the most rugged applications, such as extreme depths and extreme cable lengths. FIST also offers high density packaging of multiple fibre in the tube and, of the three options, is the easiest to terminate.
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Fig. 2. A typical umbilical cable is an armoured assembly containing signal conductors, power conductors, and optical fibres.
Source: TE Connectivity
smaller space. Te Rochester Cable group of TE Connectivity, for example, is working with thin-wall insulation and fibre-optic packaging as key to next- generation cables.
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