Versatile heavy-lift system - Brief Article - Statistical Data Included

Generally, companies offering heavy-lift and transport services all use and buy the same equipment from the same manufacturers. As market developments increasingly demand lifting and transporting ever-heavier components, heavy-lift companies simply buy the bigger cranes being developed by crane manufacturers.

Currently, the world's largest single-bodied crawler cranes can lift up to 1,400 t. Rigging and de-rigging time, transportability and transport economics are claimed to be the forces driving crane R&D, but that may be questionable.

Transport challenge. Today, load-outs of 12,000 t using the Self Propelled Modular Transporter (developed in 1984) are considered quite normal, and module-weight constraints are now determined by offshore lifting rather than load-out capability. Recognizing the inherent disadvantages of traditional, heavy crawler cranes, Mammoet Transport took the challenge of developing a new lifting system that would:

* Be easy and economical to transport on a global scale

* Realize a significant increase in lifting capacity

* Be flexible and versatile

* Use an alternative counterweight source

* Require less investment per ton of lifting capacity.

One of the first things examined was transportability. The outcome was clear almost before starting. The standardized transport dimension in use today is the container. This allowed only two choices: either a 20- or 40-ft container to be used as the dimensional basis for the new machine. After consideration, the company chose a standard 20-ft container.

The final outcome was far from being just a crane. Called the Mammoet Sliding Gantry (MSG), it is a fully integrated system that can be configured to tackle virtually any heavy-lift or transport problem that can arise. Principal components are discussed below.

Mast sections were specially designed so that when purpose-built end frames are attached, they are the same size as a standard 20-ft container. Twistlocks were incorporated into the design to simplify lashing. These mast sections can be used to build: 1) one or more free-standing portals; 2) A-type, MSG portal or double MSG A-frames; 3) several free-standing towers; or 4) a boom for the MSG in a "crane type" lifting configuration.

Strand lifting units came from the civil engineering industry where they were used to tension steel cables in pre-stressed-concrete structures. These high-pressure, 900-t hydraulic jacks formed the basis for the new lifting system.

For lifting and lowering operations, compact 18-mm-dia. strands were used; each strand can be locked in the lower and upper anchor head using a built-in wedge-grip mechanism. As the upper anchor head closes and grips the strands, the piston of the jack extends and raises the closed, upper anchor head, including the strands. When the jack is fully extended, the lower anchor head closes to grip the strand. Then, the upper head opens, and the piston retracts to its starting position. For lowering, the procedure is reversed.

In the event of hose breakage or hydraulic failure, integral safety valves are built into the strand lifting units to stop cylinder movement. A unique feature of the system is the integrated control system for continuous monitoring of stroke, hydraulic pressure, wedge position and applied load. All operations are controlled using a Windows-based program developed in-house.

Hydraulic skid system. Skidshoes with built-in, 600-t-capacity hydraulic jacks, combined with the push-pull system and skidtracks, are the latest way to move ultra-heavy loads. Once the skidshoe has been installed beneath the load, the jack can be extended up to 600 mm to pick up the load, automatically compensating for any differences in the load's surface profile.

Alternative for steel counterweight. The system can be configured in endless combinations. One way of rigging the system looks much like a conventional large crane, but there are certain aspects that are very unconventional. Engineers identified that a major problem was the need for counterweight, which is inherent to any crane. Instead of traveling around the world with "dead steer' as counterweight, they decided to use whatever was locally available. Open-top, 20-ft containers can be filled with locally available sand, steel, concrete, etc., until the required counterweight is achieved.

New opportunities. The greatest potential for savings is at the conceptual design/planning stage. By the time the project has moved forward to procurement and the construction method chosen, the scope for potential savings is greatly diminished.

Considering the MSG system early in the process allows for full cost savings. Structures can be fabricated in heavier components before final assembly or installation; alternative mating procedures can speed up projects; yards lacking in lifting capacity, load-out facility or water depth can now compete in the marketplace.

The heavy-lift engineering and application of this system was the responsibility of Mammoet Engineering & Innovation B.V. Its construction was audited, tested and certified by Lloyd's.

COPYRIGHT 2000 Gulf Publishing Co.
COPYRIGHT 2000 Gale Group