When international steel construction company Iemants constructed an offshore oil module for Fabricom at the company’s Hoboken facility in Antwerp, Belgium, it required a cost-effective and efficient lifting solution to lift and mount a large spreader bar used to perform offshore lifting on top of the module. These massive modules, critical for the oil and gas production process, range in sizes reaching 25m high, 30m wide and 40m long and weigh up to 2200 tonnes.
The company turned to its lifting partner, The Sarens Group, to develop the solution.
The spreader bar measured 13.5m long, 5m wide, and 6m high and weighed 145t. It had to be lifted from ground level to a placement height of 32m, and the crane would have to work at a maximum 24-m radius during the lift. “We considered a number of options from using a single crawler crane to performing a tandem lift using two all-terrain cranes,” says Erik Van der Elst, Key Account Manager for Sarens.
The advantage of the single crane option would have been that it required only one crane and crew to be mobilised. However, a crawler crane would require multiple days and more than 20 loads to transport the crane components necessary to configure it to meet 145t lift capacity at a 24m radius. “It would need at least 10 days to complete the entire project from mobilisation to completing the lift with the single crane option,” says Van der Elst. This was too long and costly for the module lift project.
Sarens’ project managers focused on a more efficient dual crane option, using the 700t capacity class Terex AC 700 all-terrain crane. To meet required lifting capacity and working radius, while minimising loads to improve mobilisation efficiency, planners went with a 20.5m main boom option, using a 4m variable adapter to connect the 30m luffing fly jib to the telescopic boom.
“In this configuration, each AC 700 crane offers 86.5t capacity at the 24m radius, ample capacity to safely lift the 145-t spreader bar,” says Michael Klein, Product Marketing Manager for Terex and Demag All Terrain Cranes. Even though this option required two cranes to be mobilised, it offered significant time and money savings.
The nine-axle AC 700 all-terrain crane is quickly driven to the jobsite with its complete 60m main telescoping boom installed, while meeting 12tonne per-axle load limits to reduce the number of loads required for transport. Even using the two cranes, this option would cut the number of loads approximately in half compared to mobilising a crawler crane.
“We calculated a week’s time savings by using the two Terex all terrain cranes, which represented significant labor and cost savings for our customer,” explains Van der Elst. “This is critical for the construction of an oil module in a depressed oil price market.”
Sarens mobilised its first Terex AC 700 crane from its Belgium headquarters in Wolvertem plus eight trailers of supporting material, jib segments and counterweight to make the 27km trip to the Hoboken jobsite. The large but nimble Terex crane reaches highway speeds of 75km/h to quickly get from the yard to the project, and, once on site, its 8-axle steering allows the crane to quickly maneuver into position for lifting.
Within a day, Sarens’ four-person work crew transported the first all-terrain crane to the jobsite, rigged it with 160 t of counterweight and the 30-m luffing fly jib, and had it ready for the lifting project. On day two, the crane went to work lifting and positioning supporting equipment in preparation for placement of the spreader bar.
“The first crane on site placed the lifting supports, rigging for the platform and a radar mast,” says Van der Elst. “At the same time, we moved our second crane to the jobsite and had a different four-person crew prepare and position that AC 700 for the spreader bar lift.”
Bboth cranes were in position for completing the critical lift the morning of day three. To avoid the potential of weight overload on one of the cranes, Sarens’ lift plan included positioning a 160t capacity swivel beam in between the spreader bar and cranes’ hook blocks. “This provided perfect weight distribution of the load between the two cranes,” says Van der Elst.
To start the spreader bar lift, the two crane booms worked at a 22m radius, and, as the lift progressed, the boom radius decreased to 17m as the two cranes swiveled the load into position. While placing the spreader bar atop the module, both cranes were operating at a 24m radius, and the two booms were less than a couple of meters apart. “The responsive controls of the AC 700 cranes give our operators very precise movements of the boom and load, which allows us to confidently complete intricate tandem lifts like this,” Van der Elst explains.
With the lift complete, both four-person crews derigged their respective AC 700 cranes, and the lifting equipment convoy traveled back to Sarens’ Wolvertem yard. In just three days, the dual crane option safely and efficiently placed the spreader bar plus supporting equipment onto the oil module, seven days faster than what was estimated for the single crane option. More importantly, going with a tandem approach saved Sarens’ customer money.
