WHPS Structure Decommissioning & Recovery

The Challenge

All three structures had to be safely recovered and seafastened on the vessel while maximising the available deck space.

The structures had originally been piled approximately 6 m into the seabed. For recovery, the piles were to be cut 3 m below mudline, leaving around 3 m of pile projecting beneath each structure. This introduced additional constraints for recovery, lifting and seafastening.

Very limited original design information was available due to the age of the structures, so the lift and structural assessments had to be developed from the available project information and engineering assumptions.

Geotechnical assessment was also required to estimate breakout loads during recovery following cutting of the pile sections.

The Solution

Working closely with the Maersk Supply Services project engineering team, Elgenio developed a detailed recovery, lifting and seafastening solution around the vessel layout and project constraints.

The seafastening arrangement was deliberately kept simple and robust, reducing the amount of fabricated steelwork required while allowing all three structures to be recovered and secured on deck in a single trip.

Structural and lift assessments were developed using the available geometry and project data, with appropriate assumptions applied where original design information was unavailable.