Onsite Offshore Machining | Hornsea Wind Project | EEW Offshore Structures

The Challenge

Reekie was commissioned to deliver a specialist in-situ machining solution to rectify non-conforming monopile flanges on the Hornsea Wind Project for EEW Offshore Structures. The flanges had been fabricated outside specification, resulting in the sealing groove and sealing face exceeding acceptable tolerances.

The original sealing groove, manufactured at 6.6 mm width, required precision onsite machining back to the design depth of 4 mm. As the monopiles were already installed offshore, traditional workshop machining or component removal was not possible, making offshore in-situ machining the only viable solution.

Technical Constraints

The project presented several challenges typical of offshore onsite machining operations:

• All machining had to be carried out in situ offshore

• Equipment needed to be:

  • Easily broken down into man-handleable components

  • Suitable for deployment from a support vessel using lift bags

• The solution had to perform precision machining on a 6 m diameter flange

• The existing groove exhibited ovality, requiring the machining system to accurately follow the profile without removing material from the groove width

The Solution

Reekie designed and developed a bespoke compact in-situ milling machine, based on the company’s proven MHDR32 machining platform, and re-engineered it for large-diameter onsite flange machining using a curved circular track matched precisely to the groove radius.

A 30-degree segmented track system was developed to support efficient and accurate offshore machining, enabling the system to:

• Allow rapid onsite setup and alignment

• Use dowels located in the existing groove to position the machine accurately at each segment

• Follow the local ovality of the flange while maintaining tight machining tolerances

The segmented design ensured negligible blending between passes, allowing:

• Accurate restoration of the sealing groove depth

• Minimal material removal across the original 6.6 mm groove width

• A consistent surface finish around the full flange circumference

Delivery

As part of the offshore in-situ machining project, Reekie:

• Designed and manufactured the curved track and slideway system

• Delivered all required engineering and project documentation within the agreed 4-week timeframe

• Mobilised the machining system offshore to complete the onsite machining works

The Result

• 15 monopile towers successfully machined in situ back to specification

• Sealing grooves and faces restored within required tolerances

• Offshore rework completed without removal or replacement of installed structures

• Significant time and cost savings achieved for the client through onsite machining

Key Capabilities Demonstrated

• Onsite machining and in-situ machining solutions

• Bespoke offshore machining system design

• In-situ flange and sealing groove machining

• Precision machining of large-diameter offshore structures

• Rapid engineering development under tight project schedules