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Drilling Operations
Wellhead Connectors
Wellhead connectors are hydraulically actuated connectors that lock a subsea BOP stack to the wellhead housing, and the LMRP to the top of the lower stack. This Category covers complete wellhead and LMRP connectors, actuator rings, locking dog and collet segments, pistons, seal kits and gaskets. Profile, bore and pressure rating decide fit before condition does.
How the connector locks
The connector lands over the wellhead's high-pressure housing or a mandrel on the lower stack. Hydraulic pistons drive an actuator ring that forces locking dogs or collet fingers into a matching profile. The locking geometry preloads the joint, and a metal ring gasket seals the bore. Unlock pressure retracts the ring and frees the segments. Most designs carry a secondary unlock circuit and an ROV override for when the primary circuit fails.
Variants
- Wellhead connectors, which join the lower stack to the subsea wellhead
- LMRP connectors, which join the LMRP to the lower stack and release during an emergency disconnect
- Dog-type and collet-type designs
- High-angle release versions that can unlatch with the riser at an angle
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Bore and pressure rating | Must match the stack | 18-3/4 in. at 10,000, 15,000 or 20,000 psi |
| Profile and mandrel | Must match the wellhead or LMRP mandrel | OEM profile and size |
| Load capacity | Bending and tension limits at pressure | OEM load envelope chart |
| Lock and unlock volume | Draws on the BOP accumulators | US gal or litres |
| Gasket type | Must match the wellhead's seal prep | VX, VT or equivalent |
| Upper connection | Mates to the stack above | API flange, studded or hub |
Standards and certification
API 16A covers hydraulic connectors as drill-through equipment, in design verification, material and testing. API 16AR covers their repair and remanufacture. API Standard 53 sets connector function and pressure tests in service. In US waters, 30 CFR 250.734 requires the subsea system to unlatch the LMRP through ROV intervention and in an emergency disconnect sequence, so the LMRP connector's secondary circuits matter as much as its primary one.
Failure modes and inspection
- Wear, galling and cracking of locking dogs, collet fingers and the actuator ring
- Piston, cylinder and seal wear, which slows locking or causes leaks between circuits
- Damage to the gasket seal surfaces and any corrosion-resistant inlay
- Position indicator failures, which leave the latch status unknown
- Preload loss from worn profiles
An inspection includes dimensional checks against OEM limits, magnetic particle testing of locking parts, a function test recording lock, unlock and secondary unlock pressures, a pressure test against a test mandrel and a check of the position indicator through its full travel.
Documentation
Ask for the certificate of conformity with the API 16A edition and PSL, the OEM load envelope chart for that model and configuration, function and pressure test records, the repair or 16AR remanufacture report and the seal kit dates.
Integration
Check the profile against the wellhead systems you will run, and the gasket against their seal prep. Lock and unlock volumes add to the accumulator demand on the BOP control system. Hydraulic stab plates and ROV panel positions must match your stack frame. Load capacity must cover the riser analysis loads at the wellhead.
Refurbishment and the used market
Recertification replaces seals and gaskets, re-dresses seal surfaces, inspects locking parts and retests the connector against a mandrel. A spare identical to the connector already on your stack keeps seal kits and procedures the same. Well-known families include the Vetco Gray H-4, now from HMH, Cameron collet connectors from SLB, and the Dril-Quip DX series, now from Innovex. These connectors complete BOP stacks, and production and intervention connectors sit under subsea connectors.
FAQ
Frequently asked questions
Is an H-4 connector compatible with other wellheads?
An H-4 connector fits wellheads and mandrels that carry a matching H-4 profile of the right size. Several makers build wellheads with an H-4 compatible profile. Always confirm the profile, mandrel size, gasket prep and pressure rating against the wellhead drawings.
What is the difference between a wellhead connector and an LMRP connector?
A wellhead connector locks the BOP stack to the subsea wellhead. An LMRP connector locks the lower marine riser package to the top of the lower stack, so the rig can disconnect and leave the stack shut in on the well. LMRP connectors are often high-angle release designs.
What should I check on a used subsea wellhead connector?
Check the locking dogs or collet segments, the actuator ring, the pistons and seals, and the gasket seal surfaces. Ask for a function test with lock and unlock pressures, the last pressure test, the API 16A edition it meets and the OEM load envelope chart.
Why does a wellhead connector need a load envelope chart?
The load envelope chart shows the combinations of tension, bending and pressure the connector holds without separating or leaking. Riser and stack loads at the wellhead must sit inside it. The chart is specific to the model, size and wellhead profile.
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