Hydraulic Flying Leads and Couplers

3.3.8. Hydraulic Flying Leads and Couplers

The hydraulic flying leads deliver hydraulic and chemical services from the SUTA to the tree or from the SDA to the tree, as shown in Figure 3-8. The HFLs are made up of three main components: the tubing bundle, the steel bracket assembly heads, and the MQCs. The bundle is terminated at both ends with an MQC plate, which is used to connect the HFL to the trees, or the UTA. These assemblies have padeyes for handling and deployment purposes.

3.3.8.1. Construction

Tubes are bundled and jacketed for protection and to prevent kinks in the tubes. End terminations from the tubes to the MQC assemblies and to the couplers are welded and NDE (None Destructive Examination) examined. Termination assemblies are structurally sound and capable of withstanding all transportation, installation, and operation loads.

3.3.8.2. Connection Plates

The hydraulic flying leads are supplied with MQC plates designed for a number of couplers. All tubes and coupling assignments need to match UTA and tree assignments. All couplers and the HFL are capable of withstanding full design pressure and test pressure. The design takes into consideration the fact that all couplers will be energized to a full test pressure of 1.5! design pressure during a FAT (Fabrication Assemble Testing) proof test. Design of all MQCs and couplers also considers the potential for leakage due to the external pressure being higher than the internal pressure. All seals are compatible with the chemicals, methanol, and hydraulic control fluid used. Hydraulic couplers are leak free in the unmated condition with high pressure of full working pressure or low pressure of 1 psi. MQCplates on the HFL haveROV-operable attachment means in order to connect to the inboard MQC plates at the UTAs, trees, and manifold. Makeup at depth must be achieved with all positions pressurized or only one side pressurized. Breakout at depth must be achieved with no positions pressurized. No special tooling is required for installation or removal of the terminations. Hydraulic couplings must be qualified for the duty and be capable of mating and unmating at worst case angles after coarse alignment, without failure. The MQC must be capable of mating and unmating 50 times on land and 30 times at design water depth without seal replacement and without leakage when made up and subjected to internal pressures between 0 psi and the system working pressure, and maximum hydrostatic pressure. The following potential misalignments should be considered in MQC design:
• Linear misalignments: 1.5 in. in each direction;
• Axial misalignment between male and female connector limited to 3 degrees;
• Rotational misalignment limited to 5 degrees.

MQCplates are outfittedwith an emergency release device. The design also prevents the MQC plates from engaging if they are not aligned properly. The couplers are not engaged prior to proper alignment. The emergency release mechanism makes provision for the separating forces necessary at depth. MQC plates are visible for ROV inspection. This visibility must be capable of indicating full engagement of the MQC plates and means to verify that installation was properly made. It must be possible to inspect for leaks during operation.

3.3.8.3. Installation

All circuit paths in theHFL are proof tested to 1.5!maximumdesign pressure. HFLs are visible to the ROV at the design water depth and in installed configurations. HFL assembly design incorporates the means for offshore deployment. The design also incorporates the capability for HFLs to be lifted and installed by ROVs subsea. Maximum weights in air and water (for empty and filled tubing) and any buoyancy/flotation requirements must be defined. Methods for handling, installation, and retrieval and for providing any necessary permanent flotation must be specified. Offshore test/verification procedures and long-term storage procedures must be provided. All assembly drawings, list of materials, and interface drawings to ROV oper- ation and installation must be provided. HFLs are outfitted with ROV API-17F Class 4 buckets or as referenced in ISO 13628-8 [3] for handling purposes. The type of fluid that is required inside the HFL during shipping and deployment must be defined. Storage fluids must be compatible with chemicals and hydraulic fluid. HFLs are outfitted with MQC protection caps during shipping. The maximum allowable pull on a termination and the minimum bend radius for assembled HFLs must be specified. HFLs have clear permanent markings visible to an ROV during design life at service subsea.

3.3.8.4. Hydraulic Couplers

The hydraulic couplers for deepwater applications need a spring strong enough to seal against the external pressure head in order to prevent seawater from contaminating the hydraulic fluid, and need to be designed such that only a low-pressure force is required for makeup. Figure 3-9 and Figure 3-10 illustrate female and male hydraulic coupler structures, respectively.

Couplings are available that require a low force for makeup, and these are available with dual redundant resilient seals and with a combination of resilient and metal seals. For deepwater applications a fully pressure-balanced coupling is pref- erable. These are fairly new concepts, but are available in single coupler pair design and also the four coupler hydraulic circuits design. The single pair is a resilient seal with a porting design that allows for inherent pressure balancing across the poppets, which provides pressure assistance to the spring closure force when the coupling is disconnected. The design uses a combined metal and resilient seal arrangement acting in a shear seal arrangement as the coupler mates and disconnects. Both designs use the principle that the flow path is radial and hence produces no resultant separation force. It is important for hydraulic couplers to have adequate flow paths to ensure that adequate hydraulic response times are achievable. The poppets are balanced to prevent them being driven hydraulically from the central open position and sealing against one of the seal faces. The female couplers are usually assembled into a hydraulic jumper stab plate so that they can be retrieved and the seals replaced if necessary. The female couplers are assembled so that they are floating on the plate to allow for any manufacturing tolerances. The backs of the connectors have to be terminated by screw-on hose termination couplers or by screw seal or welded assemblies for the termi- nation of steel tubing. Joint Industry Conference (JIC) hose terminations, which swage inside the central core tube of a standard thermoplastic hose, can only be used when the hose can be maintained full of fluid of a specific gravity equal to or similar to the specific gravity of seawater. This is to prevent collapse of the hose in deepwater applications. Alternatively, high collapse resistance (HCR) hose with a spiral flexible metal former under the core tube must be used. The flexible inner core is designed to withstand the external seawater pressure and to prevent the hose core from collapsing. The HCR hose requires a different type of coupling that has a welded construction. The metal former inside the coupler slides inside the spiral hose support and seals by swaging onto the outside of the thermoplastic liner. When stab plates are densely populated, it can be difficult to turn and orient all of the hoses through 90 degrees and into the hose/cable restraint. Right-angled connectors are used to orient the hoses into the clamp. It may also be necessary to have these connectors of stepped heights in order to allow hose makeup and to avoid tight bends or kinking of the hoses. The basic design requirements for hydraulic couplers should follow ISO 13628-6 [3] and ISO 13628-4 [4]; However, some specific design requirements may vary according to its applications, such as subsea production control modules, junction plate assemblies, flying lead connectors, and etc. The following requirements cover different types of hydraulic couplers, but not limited to, (1) a coupler with poppet, (2) a coupler without poppet, (3) a male blank coupler, and (4) a female blank coupler.

• The couplers include inboard and outboard MQC plates that provide the mechanism for mating, demating, and locking multiple coupler connections within a single assembly.
• The hydraulic coupler system is configured to ensure that the replaceable seals are located in the hydraulic flying leads.
• Design of the hydraulic system should consider water hammer, high-pressure pulses, and vibration on couplers. This includes external sources, for example, chokes.
• Where high cyclic loads are identified, the design and manufacturing should be reviewed to mitigate associated risks, for example, the use of butt-weld hydraulic connections.
• The designs minimize ingress of external fluid during running and makeup operation.
• The couplers are designed for reliable and repeatable subsea wet mating under turbid environmental conditions.
• The couplers have a minimum of two seal barriers to the environment unless the barrier is seal welded.
• All chemical and hydraulic circuits within the same component are rated to the same design pressure.
• All hydraulic and chemical tubing circuits are NAS 1638-64 Class 6 [5] (or equivalent ISO 4406 Code 15/12) [6].
• The couplers are designed for operation and sealing under the maximum torque and bending moment applied to mated couplers through MQC engagement and misalignment.
• The couplers have metal-to-metal seals with elastomeric backup seals. Elastomeric seals must be compatible with the operating fluid.
• Couplers are furnished with necessary protection equipment in order to protect the equipment when being unmated and in-service and to prevent calcareous buildup and marine growth.
• Poppet couplers are to be used on all hydraulic and low-flow chemical services.
• Poppetless couplers are to be used on full-bore and high-flow chemical injection lines to reduce pressure losses and eliminate trash buildup through the poppet area (i.e., methanol supply and annulus vent lines).
• Spare umbilical tubes have poppet couplers.
• Consideration must be given to the ability to bleed trapped pressure in poppet circuits when recovered to surface (i.e., residual operation pressure or head pressure once disconnected from system).
• Special consideration is given to scale buildup prior to connection.