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An offshore oil platform is no place to take chances with machinery, especially when it's sitting in the middle of the ocean. Between the rough weather, the long travel distance, and the huge costs of downtime, only the best equipment can be trusted to work on time, every time in the offshore world. Allied's Lantec planetary winch proved its mettle on a recent project in the Gulf of Mexico.
Versabuild LLC, an offshore equipment and heavy lift specialist in Belle Chasse, Louisiana, recently had a challenging assignment for Shell's Nakika platform, which sits about 150 miles off the US coast in the Gulf of Mexico. This platform is connected to subsea wells about two miles away by several submersed pipelines. The pipelines are linked to the platform by steel catenary risers. The installation of the platform risers requires the simultaneous vertical lifting and lateral steering to position the top of the risers into their respective hang-off porches. For the Nakika platform the very high weights of the risers required the use of a hydraulic chain jack to provide the lift.
To steer the pipe laterally, Versabuild placed two Lantec planetary winches side-by-side on the platform. Each winch was outfitted with 500 feet of 1-1/4-inch EEIP wire rope. The winch lines were fleeted through underwater snatch blocks located on the hull pontoons and connected to rigging on the riser pull head. An ROV (remotely operated vehicle) with camera allowed the winch operator to observe the pipe position at the pull head. The operator adjusted the cable positions on the two winches to maneuver the pipe into position, which had to be accurate to within about 1 inch. As the riser was pulled up, the winches reeled in wire rope to maintain the pipe position.
The winches did not need high line speed, but did need to provide load and displacement control. A minimum line pull of 50 tons was required for each winch. Allied's engineers worked closely with their counterparts at Versabuild to refine a standard winch design with a twist—put on two sets of motors and drives to power one drum. The dual-drive winch uses the same drum as a standard single-drive winch, but has a complete set of reduction gears and hydraulic drive motor on each side of the drum. This doubles the torque supplied to the drum, which doubles the line pull over a single-drive model. This dual-drive Lantec 750 winch was able to generate over 50 tons of line pull.
Versabuild designed and built the complete power package and winch mounting arrangement. The HPU was driven by a Caterpillar 185 HP diesel engine. It produces hydraulic power of 75 gpm at 2500 psi. The flow was split between the two winches, and was more than adequate to provide the power needed.
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The winch mounting was creative. Versabuild needed to handle the installation of several risers without relocating the winches and HPU multiple times. The solution was to mount each winch on a rotating pedestal that could be locked into place with a locking pin. To steer a different riser, the winches could be rotated to the most favorable angle quickly.
The winches were initially on the platform for about eight months, and then returned to shore. They will soon go back to the Shell Nakika for another two to three months of hard duty.
Project Manager Jason Fabre of Versabuild reports that "the winches worked perfectly. We had some other small problems, but none at all with winches."
Tough job. Tough winch. Problem solved.
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