Background

Met Mast Removal (Decommissioning): Amrumbank West Wind Farm

Background

The client required a solution for the removal of a met mast within the Amrumbank West wind farm field located in the North Sea, German Sector. In order to complete the work scope Proserv designed bespoke tooling solutions and modified an existing suite of tooling to overcome the engineering challenges offshore within a tight timeframe.

Background

Solution

Proserv provided a decommissioning solution by utilising and implementing design modifications to a suite of existing tooling. These included extending water depth capabilities from 10-13 metres to a 50 metre depth and amending a cutting tool so it could detect and cut around a steel channel obstacle within the pile. An aluminium external guide band was also designed in-house to fit one of the largest diameter monopiles to date in Proserv’s history (4.3m).  A series of trials were carried out in one of Proserv’s test tanks within the timeframe prior to mobilisation.

Scope

The met mast decommissioning operations were carried out in two stages and included excavation and cutting operations. The first stage consisted of internal airlifting within the met mast utilising Proserv’s augmented soil plug tool, airlift tool  and a high flow/high  lift submersible pump, ensuring the internals of the met mast remained flooded. The cutting operations in the second stage utilised a modified Internal Pipe Cutter (IPC09) to perform a subsea internal severance cut completing the scope of work.

The cutting operations were carried out in two stages. Topside cutting was completed in the first phase followed by subsea cutting operations concluding the work scope. The topside module was reused, as an extra safety precaution in case of adverse weather conditions following topside severance where angled cuts of 20 degrees were performed. The method ensured no damage occurred internally to the stabbing cones.

Background

Conclusion

The required design modifications were executed within the short timeframe and the offshore work scope was completed on schedule. The client received a fit-for-purpose solution necessary for the decommissioning works using a safe cutting system with no ROV or diver intervention required.

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