Hydraulic strand jacks can raise very large loads without taking up a large footprint. These attributes make them ideal for lifting vessels in the narrow confines of refineries—although the other end of the vessel will need to be tailed by another crane, or in some kind of a skidding frame. The jacks themselves only provide the force; the lift height comes from the modular towers that they sit on. These structures have to be as strong and rigid as possible to support lifted loads, while being as light and as small as possible to keep transport costs low.
Modular lifting towers are generally used with strand jacks held on top of the towers, or to support strand jacks or heavy hoists on beams straddling across the towers. They can raise lifting beams and hold climbing jacks. They usually set up in groups of two or four, with or without guy lines. They pack up in shipping containers for shipping worldwide.
California, USA-based lifting contractor and crane supplier Bigge markets its new Lift Tower System, which it designed, built and used, as an alternative to mobilising super-lift cranes. The LTS can be rigged in three-column or four-column legs, and has a lifting capacity of up to 3,500t.
It recently used the LTS for a job for a northern California refinery to lift and set three hydrocarbon-cracking reactor vessels. By the time that the Bigge team offloaded, barged and delivered the vessels, which weighed up to 603t and 30m, the LTS was ready to pick them up. It was assembled with two three column legs and two four column legs with top-mounted Hydrospex HSL5000 strand jacks on a jacking trolley, which moved the load in the longitudinal and transverse directions. The strand jacks were rigged to Bigge’s 900t-capacity powered swivel.
The vessels were delivered to the site using a hydraulic platform trailer, which was also used to tail each vessel as the strand jacks lifted the vessels to vertical. Once vertical, the trailer was removed and the jacks held the full load while it trolleyed down the girders and set into final position.
As of mid-October, UK-headquartered heavy lift and jack manufacturer Dorman Long was preparing the second job for its DL-TS3000 Mk1 modular tower, lifting a 3,520t aircraft maintenance hangar roof at Hong Kong International airport for client HAECO, scheduled for November. After that, it will lift 12 vessels measuring up to 100m long and 1,400t in weight for a client in India.
Although the tower is stick-built, it rises in identical 11.4m-high sections that resemble large tower crane mast sections and pin together. Dorman Long says that the system can also self-erect and self-dismantle. A 24.8m high tower has a gross strand jack lifting capacity of 3,000t when guyed with four cables, or 2,600t without guys, using two or four strand jacks powered by a diesel engine-powered hydraulic power pack. The same system in the same configuration can lift 3,600t using the company’s own-manufactured climbing jacks. The same climbing jacks can also lift a heavy lifting beam. At maximum height of 173m, the system (which requires four guy lines) can lift 1,300t with strand jacks, or 3,600t with climbing jacks. A wholly owned subsidiary of Dorman Long in Shanghai, China, manufactures the tower.
In the system’s first job, from October to December 2007, Dorman Long was sub-contracted to design, supply and operate a skidding and jacking system to erect a wellhead platform jacket that measured 26m x 22m x 140m high, and weighed 2,800t for the Maari Field, Malaysia. The jacket was erected in eight sections, weighing up to 660t each. The bottom section was erected on to the platform base by crane and used to support a skidding system and jacking tower system for erection of the top seven sections.
Rigging International’s modular tower, called a Vertical Pole System, is completely stick-built from standard units: 3m, 6m and 12m-long main chords, 3m and 6m diagonal braces and 3m and 6m horizontal braces. The main chords bolt together while the diagonal and horizontal braces pin to the main chords. All of these pieces can assemble a 400t triangular tower with three chords (3m x 2.6m), a 600t square tower (3m x 3m) and a 800t rectangular tower (3m x 6m) with four main chords. Box-frame top girders can span up to 100ft (30m) and link to the tower with 3m-high transition frames.
Switzerland-based VSL Heavy Lifting developed a modular tower system in 1993 and has used it to raise vessels in the CCR Aromatics Plant, in Jurong, Singapore, including a 910t 95m tall vessel. The company also makes strand jacks from 10t-500t pulling capacity.
International heavy lift contractors Sarens and Mammoet also use heavy modular towers for heavy rigging.??
