A subsea umbilical consists of electrical cables, fiber optic cables, steel tubes, and thermoplastic hoses. It may also include two or three of these four components for executing specific functions. The umbilical components are designed and manufactured to meet the umbilical functional and technical requirements. Proper materials are chosen to manufacture the components, and verification and acceptance tests are done to demonstrate the conformance to the component functional and technical requirements. The functions and characteristics of the four umbilical components are described and specified in the following sections.
The electrical cables are divided into two types: power cables and signal/ communication cables. Usually the power cable and signal cable are combined into one cable, which is called a power and control umbilical.
Power cables are used for the power supply of offshore platforms and subsea production equipment, such as control pod, pilot control valve, and electric pumps. According to Section 188.8.131.52 of ISO 13628-5 , power cables voltage ratings are selected from a range of 0 V up to the standard rated voltages U0/U(Um) ¼ 3.6/6 (7.2) kV RMS, where U0, U, and Um are as defined in IEC 60502-1 and IEC 60502-2.
Signal/communication cables are usually used for the remote control/ monitoring of subsea production equipment, such as operation of a pilot control valve, feedback of wellhead status, and operating parameters. According to Section 184.108.40.206 of ISO 13628-5 , signal/communication cables are selected from a range of 0 V RMS up to U0/U (Um) ¼ 0.6/1.0 (1.2) kV RMS, where U0, U, and Um are as defined in IEC 60502-1 and IEC 60502-2.
Fiber Optic Cable
Fiber optic cables are capable of continuous operation when immersed in a seawater environment. The fiber type is of either single-mode or multimode design. The design is as given in the manufacturer’s/supplier’s specifications. Individual fiber identification is by means of fiber coloring. The fibers are contained within a package that prevents water and minimizes hydrogen contact with each fiber. The carrier package for mechanical protection and its contents are designed to block water ingress in the event that the fiber optic cable in the umbilical is severed.
Umbilical steel tube referred to as super duplex steel tube is capable of continuous operation when immersed in a seawater environment and when it meets the requirements of ASTM A240 for either UNS S32750 or S39274 chemistries and the additional requirements specified herein and listed below:
- The tube is made by the pilger or cold-drawn process from tube hollows that should be 100% visually inspected prior to processing. Hollows should be demonstrated to meet the product chemistry requirements.
- The tube is in-line batch or continuously furnace or induction annealed in a nonoxidizing annealing atmosphere at a temperature and quench rate to be determined by the manufacturer.
- The tube may be built up on reels to the specified length by automatic orbitalwelding in accordance with preprogrammed and approved procedures.
- The tube meets all of the applicable material and process requirements of NACE MR-01-75.
- All tube lengths are cleaned to NAS 1638 Class 6 and measures taken to ensure contamination do not occur during transport and storage prior to
incorporation into umbilical lengths.
Thermoplastic hose is capable of continuous operation when immersed in a seawater environment.
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