Switching to lightweight lifting slings saves days on wind farm installation
Speed, safety and lower operational costs
Offshore wind farms are booming in Europe. Installation and operational costs are falling fast, and the amount of power generated is growing thanks to the advent of bigger turbines. The downside is that bigger also means heavier. Advances in lifting and installation technology are playing a significant part in further driving down costs. Gleistein slings made with Dyneema® SK78 helped reduce transshipment time by 3.5 days.
Heavier turbines demand stronger slings
Over the last few years, slings made with synthetic fibers have become the norm in offshore and wind farm installations. This has been driven by their advantages over the once dominant steel wire lifting slings. Steel wire slings are heavy, hard to handle, potentially dangerous, and can damage high value loads.
The well-known alternative to steel wire lifting slings are polyester slings. These are lighter, but their downsides become more significant as the weight and size of payloads increase. The latest offshore wind turbines are pushing polyester slings to their practical limits as the slings are becoming too thick to handle.
Dyneema® goes where polyester cannot
The new generation of larger wind installations pose no problem for Dyneema®. Slings made with Dyneema® SK78 are significantly stronger than polyester, at one fifth of the weight. They are also easy to maintain, inspect, and repair, which increases uptime and reduces costs. Lifting slings with Dyneema® SK78 can also be recertified, allowing them to be used on multiple projects, so lowering the cost per lift. Further advantages include their softness and flexibility, as this makes them safer for crews, loads, and structures. The fact that they are also torque-free and show similar elongation to steel wire rope, gives full control to the crane operator. Lastly, they float on water and are resistant to chemicals and salt.
World’s biggest offshore wind farm
Walney Extension, off the UK coast, in the Irish Sea, is a good example of the current state of the wind farm industry. Built, owned and operated by Dong Energy, it is the first wind farm to employ turbines rated at over 8 MW (actually 8.25 MW). It highlights the speed at which the industry is developing.
The original wind farm, known as Walney 1 and 2, dates back to 2011 and 2012. At that time, it was the world’s largest operational offshore wind farm. Its 102 turbines max out at 3.6 MW each, providing 367 MW of total power. Walney Extension, by comparison, has fewer turbines – 87 of them. However, these turbines are rated at 7 MW and 8 MW, and the new wind farm can produce 660 MW of power – enough for more than 460,000 homes. It looks set to reclaim the world’s biggest title once on-stream.
Heavy lifting at Walney Extension
Walney Extension employs two types of turbines. The larger MHI Vestas V164-8.0 account for 40 of the 87 turbines at Walney Extension (the remainder are Siemens). It has 80-meter blades, a swept area of 21,124 m2, and each one rises 220 meters above the seabed. The monopiles weigh up to 970 tons each, and have a diameter of over 8 meters. Luckily, lifting technology is keeping pace.
Problems with polyester slings
Construction projects always involve multiple partners. In the case of Walney Extension, the owner/operator is Dong Energy, marine specialist Van Oord won the contract to install the seabed foundations and monopiles, and chose SAL Heavy Lift to transport 87 monopiles, from Germany.
SAL initially considered polyester slings, but soon decided that these would be too heavy, too slow to rig, and simply too thick. The company therefore decided to replace its polyester slings with Gleistein DynaOne® slings. These would be significantly lighter, while their small diameter (120 mm) would allow SAL to stow two monopiles next to each other. This would have been impossible with polyester slings because their bigger diameter would have left too little space between the monopiles and the vessel’s board wall.
Saving time and money using Gleistein DynaOne® slings with Dyneema®
The reality lived up to the promise. SAL found that using Gleistein slings made with Dyneema® reduced the loading and unloading time of each monopile by 60 minutes – equivalent to 3.5 days for the complete project. With 87 monopiles to move, the costs of the slings were amortized very quickly through faster loading and unloading, and lower shipping costs. And there was another bonus: crews loved the way the lightweight slings handled.
“We were extremely pleased with the Gleistein slings,” says Sebastian Wenzel, Project Engineer SAL Heavy Lift. “The quality and the ability of the slings proved key in our project, and I can recommend them. Outstanding quality and performance!”
Lightweight lifting slings for a heavyweight operation
For the Walney Extension, SAL employed Gleistein DynaOne® slings. These are made with Gleistein DynaOne® rope with Dyneema® SK78 fiber. The slings can lift up to 325 tons each. The Gleistein slings as configured for SAL weighed five times less than a polyester sling of the same strength and show less than 1% elongation at work load. In total, the lifting configuration was capable of lifting 1,300 tons (with a safety factor of 3.72), comfortably exceeding the 970-tons weight of each monopile. Further plusses included being soft, making them less likely to damage whatever was being lifted, while a replaceable protection sleeve over the rope, also made with Dyneema®, extends the slings’ service life and speeds up makes rope inspections.