This article is part of the series about tools and equipment specifically designed by Temporary Works Design (TWD) to enable the safe and efficient installation of offshore wind turbines in deeper waters from floating installation vessels.
Although many offshore wind farm projects will select monopile foundations in the future the number of projects where jacket foundations are selected also looks set to increase.
To maintain the ever-increasing efficiencies and, therefore, cost reduction achieved with monopile foundation installation in recent years, TWD has designed a successful jacket lifting tool which connects to the same flange on to which the tower will later be placed.
However, the flange is designed to withstand downward and over-turning forces over the whole flange for more than 20 years in a hostile environment. To use the flange with a lifting tool TWD was faced with the challenge to apply lifting forces at 3 specific clamping points on the flange, while minimizing any structural changes to the original design.
As a result of the clever geometry of the design of the tool the clamps are mechanically locked during the lift. This design also ensures flange integrity when lifting, with a pad which provides downward pressure to the upper side of the flange directly above the lifting clamp.
A remotely operated hydraulic piston holding the clamp in position when lifting, also withdraws the clamp when the weight is taken off the tool and holds the clamp away from the flange allowing the tool to disengage.
A smooth, safe lift and installation is ensured taking jacket’s centre of gravity into consideration in the design of the tool and the interface with the flange. Small additional fixtures, mounted on the jacket during construction, include guides to position the clamps and bumpers to prevent any damage to the jacket.
The tool is not made for just one set of jackets. The flange dimensions on jackets for one wind farm are likely to be the same on each jacket, however this tool is also designed to fit different sized flanges on jackets for other wind farms. On each of the three arms of the tool there is a spliced connection. Filler blocks can be added here providing an increase of up to 1m in the diameter. Changes in the centre of gravity can also be compensated to guarantee a vertical lift by adjusting a turn-buckle attached between the clamp section and the framework.
To ensure that the foundation is aligned correctly over the pre-installed pin piles, tugger lines fitted to a triangular frame on the tool and connected to winches on the crane boom can be remotely operated for small and accurate movements.
The TWD Jacket Lifting Tool is a lightweight tool, being less than 1% of the jacket weight, allowing the installation crane to make maximum use of its lifting capacity. It enables lifting jackets off from the deck of an installation vessel and installing them safely, quickly and accurately without involving personnel being on the jacket at any time during installation, including connection and disconnection, adding to the safety factor.
In the coming weeks we will share updates on these individual developments through our website and LinkedIn channel, so stay tuned!
Triggered your interest? Visit our stand, 1.502 at Offshore Energy Amsterdam on 8 and 9 October 2019, and learn more about our Transport & Installation Engineering in Offshore Wind.
#Jacket, lifting tool, Offshore, Wind farm, monopile