Moonpool Systems

The moonpool and what moves through it

The moonpool sits under the well centre. On a dual-activity drillship it is long enough for two well centres, so the crew can run a BOP or tree on one while drilling or running casing on the other. The BOP stores on a set-back area beside the moonpool. A gantry crane or BOP handling system lifts it, a carrier moves it over the well centre, and guidance gear steadies it through the splash zone. Doors close the opening when nothing is running, and gates guard the edge when it is open.

The three sub-Categories

How to choose comes down to the interfaces. Most moonpool equipment is designed for one hull. Rail gauge, opening size, BOP or tree footprint and the height to the drill floor set what fits. Equipment from a sister rig built by the same yard is the most likely to drop in. Anything else usually needs new rails, adaptor plates or structural work.

Standards and certification across the group

• Load-carrying equipment is usually certified as lifting or handling equipment. Depending on class and flag, that means the class society's lifting appliance rules, such as DNV-ST-0378 or the ABS guide for certification of lifting appliances. On the Norwegian shelf, NORSOK R-002 also applies.
• These rules call for design approval, a proof load test above the safe working load (SWL) on installation and after major repair, and periodic thorough examination.
• Moonpool doors and their supports form part of the hull structure, so class approves their design and surveys them with the hull.
• Hydraulic systems follow the OEM's fluid cleanliness targets, usually stated as ISO 4406 codes.

Integration questions

• Load path from the BOP or tree weight, through the cart and rails, into deck structure designed for it.
• Interlocks between doors, carts, guidance and the drill floor so nothing moves into an occupied or open well centre.
• Hydraulic supply pressure and flow from the rig's power units, or electric supply for rack and pinion drives.
• Control system integration with the drilling control network, where carts and doors are run from the driller's chair.

Records that make used moonpool equipment credible

• General arrangement drawings with rail gauge, opening size and interface dimensions.
• Design approval and the last proof load test for every load-carrying item.
• Thorough examination records from the source rig.
• Hydraulic schematics, cylinder data and the last fluid cleanliness result.
• Interlock and control logic descriptions.
• Preservation records for the time the rig sat stacked.

Without drawings, you cannot judge fit before the equipment reaches your yard. Without load test records, expect a full proof load test before first use.

Sourcing used moonpool equipment

Weight comes first. Modern 18-3/4 in 15,000 psi BOP stacks with six or more rams weigh much more than older stacks, so a cart or guide from an older rig may be under-rated. Moonpool equipment lives in spray, so seized pins, corroded rails and leaking cylinders are common on equipment from cold-stacked rigs. Ask for the general arrangement drawings, load test certificates and preservation records first. Naventr can share the Seller's drawings with you and arrange an inspection on request.