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Demag PC 6800-1 lifts foundation piles for windfarm
Unique operating conditions require unique approaches – this phrase perfectly sums up the project currently being carried out by crane service provider Sarens NV with a Demag® PC 6800‑1 pedestal crane. The job, which involves a whole series of challenges, consists of lifting 89 steel piles from a barge on The IJsselmeer on behalf of customer Van Oord Offshore Wind.
The first challenge revolves around the platform from which the crane is doing its work: More specifically, all the lifts are being carried out from a barge on open water. “And since the IJsselmeer is very shallow, this meant that we had to build a special barge that would have a small draft thanks to its dimensions of 62 x 53 meters. This is how we were able to make sure that the work platform would not run aground,” reports Sarens project manager Mart van Hoorn. With its dimensions, the platform is roughly half the size of a soccer field, and has been as such baptized the “Sarens Soccer Pitch” (SSP) internally.
However, despite the enormous dimensions, it would have been practically impossible to set up a lattice boom crawler crane on the barge due to the latter’s rugged construction. Because of this, the Sarens team decided to instead use a Demag PC 6800-1 pedestal crane, as setting it up would be much easier given the conditions at hand. Moreover, as a powerful representative of the 1,250-tonne class, it met all requirements regarding the relevant load weights, lifting heights, and the ability to work at angles of inclination of up to two degrees.
The crane was transported directly from its previous place of use in Hungary to the Dutch coast, where it was subjected to a technical check before being set up. Due to the tight space conditions on the barge, the setup was carried out with an extremely meticulous plan. “We first pre-assembled the crane on the shore and then put together and tested the larger components on the barge. This way, we minimized the potential risks of assembly on the water and at height,” Mart van Hoorn explains. It took the six-person Sarens assembly crew a total of around one and a half weeks to set up the crane, including the application of a protective coating to prevent saltwater corrosion. The PC 6800-1 was set up with an SSL/LSL S1 configuration, a 72-meter main boom, and a 40.5-meter Superlift mast with a radius of 24 meters. The superstructure counterweight came in at 250 tonnes, while the Superlift counterweight at a radius of 27 meters came in at 360 tonnes that were placed on a Demag counterweight carrier. Finally, a double hook block with nine-part reeving was installed in order to pick up the loads.
The goal: Two piles per day
“With this configuration, our Demag PC 6800-1 was perfectly prepared to lift the 89 foundation piles with the help of a floating sheerleg,” Mart van Hoorn reports. The piles, each weighing up to 250 tonnes and measuring up to 40 meters, are picked up directly from a transport ship, placed in an upright position with the help of the sheerleg, moved to the intended location, and driven into the IJsselmeer’s lakebed. “The fact that these operations have to be carried out in a sort of floating arrangement in between a bunch of ships makes the whole operation particularly challenging,” Van Hoorn points out. This is why at least ten experienced employees are always out there on the water for each lift. “The plan is to drive two foundation piles per day depending on the weather, with the process of lifting and positioning a pile upright taking somewhere between 30 and 90 minutes,” Mart van Hoorn explains. Consequently, this project will take about three months all in all.
Adjusted crane specifications in line with on-site conditions
One particularly tough challenge consisted of the constant, and sometimes strong, winds at the work site at open waters. “This is why we needed Demag to look at the specific conditions of this job and adjust the permissible wind conditions for the crane together with us. In addition, we needed new charts for the maximum lifting capacities at angles of inclination of up to two degrees from Demag,” reports Hendrik Sanders, who works at the Sarens Research & Development department. Moreover, Demag conducted a failure modes and effects analysis to identify the crane components subject to particularly large loads and describe the effects of a potential failure – this will make it possible to respond as fast as possible in the event of a failure so as to minimize any downtimes. And last, but not least, new software had to be loaded onto the crane’s control system. “This was done by Demag Service technicians, who came to the work site with the sole purpose of loading the new software,” explain Hendrik Sanders and Mart van Hoorn, who expect the rest of the project to go smoothly given not only the optimal preparation, but also Demag PC 6800-1´s power and structural strength.