7.8.1 General
7.8.1.1 Equipment covered
In 7.8 are covered the tree and tubing head connectors that attach the tree or tubing head to the subsea wellhead. In addition, tubing heads are also covered in 7.8.
7.8.1.2 Tree/tubing head spool connectors
Three types of tree/spool connectors are commonly used:
⎯ hydraulic remote operated;
⎯ mechanical remote actuated;
⎯ mechanical diver/ROV operated.
All connectors shall be designated by size, pressure rating and the profile type of the subsea wellhead to which they will be attached (see Table 15). Tree/spool connectors shall conform to maximum standard pressure ratings of 34,5 MPa (5 000 psi), 69 MPa (10 000 psi) or 103,5 MPa (15 000 psi), as applicable. Body proof testing shall be conducted at 1,5 times the pressure rating. The design and installed preload should give consideration to possible higher pressure from an SCSSV seal-sub leakage in the gallery inside the tree connector.
The tree connector may be a separate unit or may be integral with the XT valve block.
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© ISO 2010 – All rights reserved 69 Table 15 — Wellhead systems — Standard sizes and types
System designation High-pressure housing working pressure
Minimum vertical bore
mm – Mpa (in; psi) MPa (psi) mm (in)
476 – 69 (18 3/4; 10 000) 69,0 (10 000) 446 (17,56) 476 –103 (18 3/4; 15 000) 103,5 (15 000) 446 (17,56) 425 – 35 (16 3/4; 5 000) 34,5 (5 000) 384 (15,12) 425 – 69 (16 3/4; 10 000) 69,0 (10 000) 384 (15,12) 527 – 540 – 14 (20 3/4; 21 1/4; 2 000) 13,8 (2 000) 472 (18,59) 346 – 69 (13 5/8; 10 000) 69,0 (10 000) 313 (12,31) 540 – 35 (21 1/4; 5 000) 34,5 (5 000) 472 (18,59) 346 – 103 (13 5/8; 15 000) 103,5 (15 000) 313 (12,31) 476 – 69 (18 3/4; 10 000) 69,0 (10 000) 446 (17,56) 346 – 103 (13 5/8; 15 000) 103,5 (15 000) 313 (12,31)
7.8.1.3 Tubing heads 7.8.1.3.1 Uses
Tubing heads are commonly used to
⎯ provide a crossover between wellheads and subsea trees made by different equipment manufacturers;
⎯ provide a crossover between different sizes and/or pressure ratings of subsea wellheads and trees;
⎯ provide a surface for landing and sealing a tubing hanger if the wellhead is damaged or is not designed to receive the hanger;
⎯ provide a means for attaching any guidance equipment to the subsea wellhead.
7.8.1.3.2 Types, sizes and pressure rating
The tubing head shall be designated by size, pressure rating, and the profile types of its top and bottom connections. Top connections are commonly either hub- or mandrel-type connections that shall match the tree connector. The bottom connection shall match the wellhead. The tubing head and connector may be manufactured as an integral unit. Tubing heads shall conform to standard pressure ratings of 34,5 MPa (5 000 psi), 69 MPa (10 000 psi) or 103,5 MPa (15 000 psi), as applicable. Body proof testing shall be conducted at 1,5 times the pressure rating. When the tubing head and connector are manufactured as an integral unit, then the pressure rating shall apply to the unit as a whole.
7.8.2 Design
7.8.2.1 Loads/conditions
As a minimum, the following loading parameters/conditions shall be considered and documented by the manufacturer when designing the tree connector and tubing head:
⎯ internal and external pressure;
⎯ pressure separation loads, which shall be based on worst-case sealing conditions (leakage to the largest redundant seal diameter shall be assumed);
Copyright International Organization for Standardization Provided by IHS under license with ISO
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⎯ mechanical preloads;
⎯ riser bending and tension loads (completion and/or drilling riser);
⎯ environmental loads;
⎯ snagging loads;
⎯ fatigue considerations;
⎯ vibration;
⎯ mechanical installation (impact) loads;
⎯ hydraulic coupler/flowline stab connector thrust and/or preloads;
⎯ thermal expansion (trapped fluids, dissimilar metals);
⎯ BOP loads;
⎯ tree loads;
⎯ flowline loads;
⎯ installation/workover;
⎯ overpull;
⎯ corrosion.
7.8.2.2 Load/capacity
The manufacturer shall specify the loads/conditions for which the equipment is designed.
7.8.2.3 Actuating pressures
Hydraulically actuated tree and tubing head connectors shall be capable of containing hydraulic release pressures of at least 1,25 times hydraulic RWP in the event that normal operating pressure is inadequate. The manufacturer shall document both normal and maximum operating pressures. The connector design shall provide greater unlocking force than locking force. It is the responsibility of the manufacturer document the connector locking and unlocking pressures and forces.
7.8.2.4 Secondary release
Hydraulically actuated tree and tubing head connectors shall be designed with a secondary release method, which may be hydraulic or mechanical. Hydraulic open- and close-control line piping shall provide either a ROV/hot stab/isolation valve, or be positioned with a cut-away loop (for cutting the lines by diver/ROV) to vent pressure, if needed, to allow the secondary release to function.
7.8.2.5 Position indication
Remotely operated tree connector and/or tubing head connectors shall be equipped with an external position indicator suitable for observation by diver/ROV.
7.8.2.6 Self-locking requirement
Hydraulic tree and tubing-head connectors shall be designed to prevent release due to loss of hydraulic locking pressure. This may be achieved by the connector self-locking mechanism (such as a flat-to-flat locking segment design) or backed up using a mechanical locking device or other demonstrated means. The design
© ISO 2010 – All rights reserved 71 of mechanical locking devices shall consider release in the event of malfunction. The connector and mechanical locking device design shall ensure that locking is effective with worst-case dimensional tolerances of the locking mechanism.
7.8.2.7 Overlay of seal surfaces
Seal surfaces for tree and tubing-head connectors that engage metal-to-metal seals shall be inlaid with corrosion-resistant material that is compatible with well fluids, seawater, etc. Overlays are not required if the base metal is compatible with well fluids, seawater, etc., e.g. if the material is a CRA. Design is in accordance with the manufacturer’s specifications.
7.8.2.8 Seals testing
Means shall be provided for testing all primary seals in the connector cavity to the rated working pressure of the tree/spool connector or tubing hanger, whichever is lower.
7.8.2.9 Seal replacement
The design shall allow for easy and safe replacement of the primary seal and stab subs.
7.8.2.10 Hydraulic lock
The design shall ensure that trapped fluid does not interfere with the installation of the connector.
7.8.2.11 Materials
Materials shall conform to 5.2.
For forged material used for pressure-containing and high-load-bearing parts, forging practices, heat treatment and test coupon (QTC or prolongation) requirements should meet those of API RP 6HT. In addition, the test coupon shall accompany the material it qualifies through all thermal processing, excluding stress relief.
7.8.3 Testing 7.8.3.1 General
The test procedure in 7.8.3.2 applies to both mechanical and hydraulic connectors.
7.8.3.2 Factory acceptance testing
After final assembly, the connector shall be tested for proper operation and interface in accordance with the manufacturer’s written specification using actual mating equipment or an appropriate test fixture. Functional testing shall be conducted in accordance with the manufacturer’s written specification to verify the primary and secondary operating and release mechanisms, override mechanisms and locking mechanisms. Testing shall verify that the actual operating forces/pressures fall within the manufacturer’s documented specifications.
Connectors that are hydraulically operated shall have its internal hydraulic circuit, piston(s), and cylinder cavity(s) subjected to a hydrostatic test to demonstrate structural integrity. The test pressure shall be a minimum of 1,5 times the hydraulic RWP of the connector. No visible leakage shall be allowed. Minimum hold period for the connector’s hydraulic actuator hydrostatic test is 3 min.
Copyright International Organization for Standardization Provided by IHS under license with ISO
Not for Resale No reproduction or networking permitted without license from IHS
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