Borssele V slip joint connection: design, certification and installation of the world's first full‐size submerged slip joint

Abstract

In April 2020 the world's first full-size submerged slip joint connection was installed at the Borssele Site V offshore wind farm. This event marked the launch of a new, alternative transition piece/monopile (TP/MP) connection for the offshore wind market. An extensive qualification programme in terms of numerical modelling and testing was set up prior to installing the slip joint. This process was witnessed, reviewed and accepted by DNVGL. It led to a certified slip joint design for Borssele V, with a 9.5 MW wind turbine generator (WTG) on top of the foundation as well as an A-level component certificate for the slip joint in general. The installation of the slip joint for Borssele V was the first use of this connection in a commercial full-size wind turbine. The implementation of the slip joint connection at Borssele V demonstrated the benefits of the slip joint in terms of simple, safe and fast installation as well as the option for using the slip joint submerged, thus allowing a more optimized weight/length split between MP and TP and the use of smaller installation vessels. A monitoring campaign was executed during and after installation to provide lessons for future slip joint designs. Reducing the levelized cost of energy (LCoE) requires big steps in technology innovation. The Borssele V offshore wind farm offered a unique opportunity to demonstrate to the industry that the slip joint connection is fully feasible and ready for practical implementation. The slip joint: simple connection, ingenious design.