SDS COMPONENT DESIGN REQUIREMENTS
Contents
SDS Component Design Requirements
Topside Umbilical Termination Assembly (TUTA)
The Topside Umbilical Termination Assembly (TUTA) provides the interface between the
topside control equipment and the main umbilical system. This fully
enclosed unit incorporates electrical junction boxes for the electrical power
and communication cables, as well as tube work, gauges, and block and
bleed valves for the appropriate hydraulic and chemical supplies.
The TUTA will typically be located near the umbilical J-tube on the
host. Basically, it includes an electrical enclosure in a lockable stainless steel
cabinet certified for its area of classification with ingress protection to fit its
location. Additionally the valves in the TUTA comply with requirements for valves in flammable services as stated on fire testing standards. The termination unit at the topside end of the umbilical is designed for hang-off and includes a bull-nose suitable for pulling the umbilical up through the host guide tube onto a termination support. For a free-flooded umbilical, it is sufficient to seal off the individual ends of the conductors and tubes and use an open bull-nose. Tubes must be individually sealed to prevent hydraulic oil loss and water ingress during the pulling operations. Electrical conductors must be sealed to prevent water ingress along the insulation. If the umbilical is intended for temporary laydown, pressure relief during retrieval is considered. Basically, the J-tube seals can withstand a 100-year maximum wave and maintain its differential pressure capability during service life. Free span corrections between the J-tube bell mouth and seabed are also be designed according to the project’s specific design basis.
Subsea Umbilical Termination Assembly (SUTA)
The SUTA is the subsea interface for the umbilical and
may serve as the distribution center for the hydraulic and chemical services
at the seabed. The SUTA is connected to the subsea trees via HFLs.
SUTA is typically composed of the following:
• UTH;
• Flying leads to connect the UTH and HDM;
• HDM if available;
• Mudmat foundation assembly with stab and hinge-over mechanism;
• MQC plates to connect to HFLs.
The type of SUTA to be used is determined by field architecture consid-
erations, and is further defined during detailed design.
The SUTA is designed with the following flexibilities:
• Provision for possible links to additional umbilicals;
• Provision for spare header included in case of internal piping failure;
• Demonstration of design that allows flexible installation;
• Retrievability and reconfiguration options;
• Redirection of any umbilical line to any tree service via flying leads.
SUTAs are installable with or without drilling rig assistance. The mudmat includes attachment points for adjusting the subsea position, with application of external horizontal forces, when direct vertical access for installation is not possible. A SUTA’s dimensions allow for ground transportation from the fabri- cation facility to the final destination. The umbilical is permanently terminated in the UTH. The infield first end SUTA is a smaller unit, its purpose is to link the electrical of hydraulic/chemical lines. HFLs are used to connect hydraulic/chemical lines between SUTAs and subsea trees/manifolds. EFLs are used to connect electrical power/communication from the umbilical termination assembly (UTA) to the manifold and tree-mounted SCM. The UTH, HDM, and EDMs are each independently retrievable from the UTA’s mudmat. Each of the electrical quads (umbilical cables with four conductors) is terminated in electrical connectors at the UTH. The EFL interconnects between these UTH connectors and the EDM connectors, routing power and communication from the UTH to the EDM. Subsea electrical distribution is done from the EDM to the subsea trees and production manifolds. Two flying leads provide the hydraulic/chemical interconnections between the UTH and the HDM.
Umbilical Termination Head (UTH)
The UTH consists of a structural frame, hinging stab, MQC plates, super-duplex tubing, and bulkhead style ROV electrical
connectors. Umbilical services are routed to the MQC plates and electrical
connectors for distribution to subsea production equipment.
The SUTA terminates the hydraulic subsea umbilical and provides
a flange connection to attach the umbilical termination. The umbilical is
composed of super-duplex tubes.
All tubing in the UTH and HDM is welded to the hydraulic couplers
located within the MQC plates. The number of welded connections
between the couplers and the tubing is kept at a minimum. Butt-weld joints
are preferred over socket-welded connections. The design allows for full
opening through the tubing and the welded area. The design also avoids any
area where crevice corrosion may occur.
The termination flange connection between the SUTA and the
umbilical is designed to accomplish the following condition:
• Because the SUTA is installed with its stab and hinge-over stinger, the
flange is capable of supporting the weight of the SUTA as well as all
installation loads.
• After installation, the SUTA may need to be lifted from its mudmat and
stab and hinge-over funnel. As the SUTA is lifted and brought back to
the surface, the flange is capable of supporting the “unsupported”
umbilical weight with a 50% safety factor.
The UTH at minimum complies with the following requirements:
• At minimum, the UTH is designed to allow termination of a minimum
of nine umbilical steel tube lines and two electrical quads.
• The structural frame is designed to securely attach to and support the
umbilical and end termination as well as provide mounting locations for
the MQC plates and bulkhead electrical connectors.
• The hinging stab is attached to the frame and is the interface between the
UTH and mudmat structure.
• The UTH frame size is minimized in order to simplify handling and
overboarding.
• TheUTHare kept small to fit inside most umbilical overboarding chutes,
and can be maneuvered through most vessel umbilical handling systems.
• The recovery padeyes are designed to take the full recovery load of the
UTH and the umbilical.
• The UTH, combined with the umbilical split barrel (supplied by
the umbilical manufacturer), is designed to sit on the umbilical reel of
an installation vessel at the end and/or at the beginning of the umbilical.
• Tubing connections and other possible points of failure are reduced as
much as possible in the UTH to avoid having to retrieve the umbilical to
repair a failed component.
Subsea Distribution Assembly (SDA)
The SDA distributes hydraulic supplies, electrical power supplies, signals, and injection chemicals to the subsea facilities. The facilities can be a subsea template, a satellite well cluster, or a distribution to satellitewells. The SDA connects to the subsea umbilical through the SUTA.
Construction
The SDA frame is fabricated from carbon steel coated in accordance with a subsea paint specification. The frame is designed for lifting and lowering onto a location on a Subsea production system. Alternatively, the SDA can be located on a mudmat, simple protective frame, or monopile.
Interface with the Umbilical
The SUTU can connect to the SDA with a vertical/horizontal stab and hinge-over/clamp connection. Alternatively, it can connect via electrical and hydraulic jumpers at a seabed level pull-in location or manifold structure pull-in location using an ROV or diver connectors. If the field layout demands, the jumpers can route through a weak link breakaway connector.
Interface with SCM
The jumpers from the SDA to the Subsea Accumulator Module (SAM) mounting base (SCMMB) are connected using an ROV.
Electrical Distribution
The electrical distribution is usually contained in an oil-filled, pressure- balanced, fabricated and coated carbon steel housing called an electrical distribution unit(EDU). (Non–pressure-balanced, resin-filled junction boxes are sometimes used, but these do not allow future maintenance and require the encapsulated components to be suitable for use at depth; designs requiring current-limiting devices may be housed in a one-atmosphere enclosure.) Entry and exit of the EDU is by flange-mounted electrical controlled environment-type connectors. The connectors are configured so that any connections that may be accidentally disconnected live have the live conductors protected from the seawater. Cable tails from the back of the electrical connectors within the oil-filled housing are connected for distribution as required by the control system architecture and the system redundancy capability. The requirement for fault protection is dependent on the system design and the number of wells that could potentially be disabled by a subsea cable fault. Three types of electrical protection are used: fuses, circuit breakers, and thermal resetting trip devices. Fuses are not effective, as slow-blow fuses are necessary in order to cater to the inrushing current while charging up the umbilical. This makes fuses ineffective in isolating a fault in the distribution system without overloading the remainder of distribution outlets and, generally, a fuse would not blow before the line insulation fault trip in the EPU is activated. Circuit breakers have been used subsea in EDUs, but are not commonly used because the circuit breaker reset mechanism has to penetrate through the EDU housing using O-rings, which introduces a potential fault path. The thermal resetting devices are semiconductor devices and due to the technology required, they are not available from all suppliers.
Hydraulic and Chemical Distribution
The hydraulic distribution is by tubing from the incoming interface connection routed around the structure to the distribution outlets. The stab connections and the tubing are generally made of type 316 stainless steel. The tubing terminations are all welded for integrity. The tubing, which is usually installed at a fabrication site, has to be flushed and cleaned to the integrity required by the subsea control system. Chemical injection systems generally require larger volume flows during normal operation, and are also subject to increased viscosity at lower seabed temperatures. Therefore, larger bore tubing or piping is generally used, again welded to maintain integrity. Multiple stab plate hydraulic connections must have some movement in order to allow for alignment during makeup. Also tubing is often installed on structures using clamps with plastic inserts. This can leave the tubing and end connections floating without cathodic protection. It is essential that these items be electrically bonded to the main structure cathodic protection system to avoid rapid corrosion of the system. Other material that may be considered for the distribution piping or tubing is carbon steel for the chemical injection system, or more exotic materials such as Duplex or Super Duplex stainless steel. To ensure correct mating of the respective parts, guide pins are used on stab plates, and single connections may have different size quick-connect couplings or may be keyed for proper orientation.
ROV Connection
The access of an ROV to the SDU has to be carefully considered. It is not necessary to have a docking station for ROV makeup, but docking may make certain tasks easier. If the field survey shows strong currents at the seabed and changeable directions, then ROV docking is necessary. With multiwell applications where the ROV must remove connectors from parking positions and hook up at positions on the SDU, it is essential that the ROV does not get entangled in any of the other flying leads. This can cause damage to the flying leads or may entangle the ROV where it would need to cut flying leads in order to free itself. Clear marking of the connection point is essential to ensure that the ROV pilot can orient the ROV at the desired location and to ensure that the correct hookup in low-visibility subsea.
