In the strive of the Offshore Wind industry to become competitive with other forms of energy generation, KCl is determined to invent new solutions to bring this goal closer. When in 2012, KCl was approached by a Dutch utility for grouting issues at one of the Dutch Offshore Wind park, KCl provided and implemented a good remedy but placed the topic on the R&D agenda in order to develop a structural solution. Grouting or bolting of the connection between monopile and transition price are time consuming operations. Grouting issues have cost the industry a fortune up to now and the alternative of bolting, which implies the use of hydraulic tools offshore, is complicated and time consuming. They are heavy and difficult to handle. Moreover the installation of pre-tensioned bolts requires complicated procedures and the bolts need to be periodically inspected and tightened during service intervals. With above problems in mind, KCl was determined to find a better solution for the foundation connection which moreover had to contribute to the industry's goal of reducing CAPEX and OPEX. In KCl's Double Slip Joint (DSJ) concept, two sets of steel rings with matching conical surfaces are integrated in the standard cylindrical tubes of the monopile and the transition piece (TP). The TP is installed by lifting it inside the monopile. Contact is made concentrated at two sets of rings, which have a small tapered angle of about 2 degrees and an exact fit. This provides a well-defined self-locking steel on steel connection after installation of the TP. The TP will automatically settle under the gravity loads and operational turbine loads within a short period of time, to reach a final stable locked condition, rigidly connected to the pile, as if 'welded' together.
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