Pile Gripper for installation of wind turbines

A novel level-adjustable and retractable passive pile gripper has been developed by Ørsted.

The installation of offshore monopiles is typically performed using specialized jack-up vessels (JUVs) or floating platforms. In this process, the monopile is positioned and driven into the seabed using methods such as hydraulic impact, vibration, jetting, electro-osmosis, or a combination of these techniques. Accurate positioning and effective stabilisation during driving are essential to ensure the monopile achieves the installation tolerances post installation.
The pile gripper is a hydraulic clamping device mounted on the installation vessel. Its role is to hold the monopile in place while being driven into the seabed, ensuring it remains stable and vertical. Pile grippers are essential due to the challenging offshore environment, where waves, wind, and currents can cause the monopile to shift during installation. By securing and stabilizing the pile, the gripper ensures accurate alignment, reduces the risk of structural misalignment, and enhances the efficiency and safety of the installation process.

Traditionally, pile grippers are static components that allow a monopile to move along the vertical axis while remaining stationary. This fixed height on the JUV or platform is a drawback and can limit their ability to stabilise monopiles of varying lengths, especially for use with shorter monopiles (for example, those using slip joints or monopile & transition piece arrangements). This height constraint can lead to difficulties in maintaining stability, requiring additional handling or equipment adjustments.

During the installation of offshore wind turbine MP foundations, stability over a greater range of motion is key to successfully lowering the monopile into place.

Ørsted has developed a pile gripper concept that has two axes of freedom: one horizontal and one vertical. Consequently, the pile gripper can provide adjustable height, facilitating the successful installation of shorter monopiles, and it can retract inboard during transit or relocation.
The figure shows a level-adjustable and retractable passive pile gripper
The adjustable pile gripper comprises a monopile gripping section and two sets of rails. This design allows the pile gripper to remain initially in a retracted configuration, where the gripping section is drawn back onto the JUV or platform. During monopile installation, the pile gripper transitions to an operational configuration, where the gripping section extends along the horizontal set of rails, enabling it to reach over the side of the JUV or platform. Additionally, the pile gripper can operate at various elevations, where the gripping section is lowered along the vertically aligned sets of rails, positioning it below the deck of the JUV or platform.

This concept enhances the vertical adjustment potential of this technology, enabling it to grip significantly lower than the current deck-level single horizontal axis retractable pile grippers presently available on the market. This improvement helps to avoid potential instability issues that may arise if not guided correctly during penetration.

Jonathan Foster
Lead IP Specialist
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