Dutch offshore contractor Van Oord has successfully installed the world’s first submerged slip joint
The project was completed on 25 April 2020 on the Borssele V offshore windfarm in the Netherlands. The Borssele Site V project consists of two 9.5-MW wind turbines. Van Oord was awarded the balance of plant scope for the project.
This was the first time a submerged slip joint had been used on a full-sized offshore wind turbine on a fully commercial basis.
After years of developing the system in co-operation with its technology partners, Van Oord used the installation vessel Aeolus to install the slip joint foundation.
Design and production of the slip joint was certified by DNV GL in Q3 2019 with Mott McDonald assessing its ‘bankability.’
A slip joint is a connection between a monopile foundation and a transition piece. It consists of two conical sections placed on top of each other. The concept is based on friction, using the weight of the components fitted to a monopile to ensure firmness and stability. Installation takes place by sliding the wind turbine’s foundation over the monopile, without having to use grout or bolts.
Unlike standard solutions, the slip joint makes a submerged connection possible, allowing for a more balanced weight distribution between monopile and transition piece.
It therefore opens up the possibility of manufacturing larger foundations for the next generation of wind turbines with existing manufacturing facilities and installing them at deepwater locations using existing vessels. The conical sections used in the connection are produced using standard manufacturing methods.
“The slip joint provides a rapid, simple and safe installation solution in combination with reduced maintenance for the duration of the project,” Van Oord said.
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