New Lifting Technique Lowers Costs In Construction Of Drilling Rigs

A new technique, which utilizes a multipurpose hydraulic system for constructing the main deck structures of offshore drilling rigs, has been announced by Hydranautics, Inc. The technique has been applied successfully by Chicago Bridge & Iron Company (CBI) at Pascagoula, Miss., and Ingleside, Texas, in fabricating a semisubmersible rig for World Drilling Company of Tulsa.

The technique allows complete deck fabrication and installation of truss c o n n e c t o r s at nearground level, thereby saving on crane work and other costs associated with high c o n s t r u c t i o n.

Using part of a multipurpose hydraulic tool designed and built by Hydranautics for translating the finished drilling rig by skidding, CBI was able to lift the 1,050-ton ground-level-fabricated deck section approximately 100 feet in the air in less than eight hours, and lock the structure on oil at that height for approximately 10 weeks.

With the suspended structure locked on oil, CBI was able to monitor in real time the weight of the total load as well as the actual load of each support point, and easily made the adjustments in height to compensate for support settlement and to accomplish part fittings.

The lift was started on a weekend at 7:35 am and by 3:20 pm the total deck structure had been lifted to the elevation required for assembly of trusses under the platform by the regular work crew on Monday morning. The time required to accomplish the ground-level work staging prior to the actual lift was included in the eight-hour period.

The components used to lift the triangular deck (200 foot/ side) were later used as part of the Hydranautics transfer system to skid the entire 5,000-ton drilling rig. According to Hydranautics, the lift tool may be acquired as part of the combination liftskid system or as a single-functional unit with the capability for additions at a future date.

The components of the lift-skid system that were used by CBI during the lift operation consisted of the following: six chain jacks, each rated 175 tons at 3,500 psi; 12 balance cylinders (borrowed from the Gripper Jack portion of the complete system), each rated at 21.86 gpm at 5,000 psi; and 12 length (each 120 feet long) of 214-inch stud link GR3 chain with a total minimum breaking strength of 342 tons.

Key advantages offered by the Hydranautics equipment used to lift main deck structures are numerous.

Use of the equipment allows construction from the top down at yard level, minimizing high time, its problems and cost.

Hydraulic load e q u a l i z a t i o n is provided between load points.

Real time load readouts are possible for each lift point as well as the total deck weight. There is an inherent stiffness of chain support with the safety of steel to steel positive lockout at each chain pitch. The load can be lifted any distance from a fraction of an inch to hundreds of feet, then stopped and held as long as required.

Hydranautics points out that there are two primary advantages to purchasing the complete multipurpose system. The cylinders are interchangeable between lift, positioning, and transfer modes of operation. The same power units may be used for lift, positioning, and transfer functions.

Maritime Reporter Magazine, page 20,  May 15, 1981

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Maritime Reporter

First published in 1881 Maritime Reporter is the world's largest audited circulation publication serving the global maritime industry.