Sif has expended ifs offshore wind services by adding so-called bolting tests to their scope. This test checks the bolted flange connection between a monopile and transition piece by fitting and torquing all 128 bolts before both parts are shipped out to sea.

Sif’s customer DEME had requested the Dutch company to carry out such tests for the SeaMade wind farm, which DEME is building off the coast of Belgium. Previously, these tests were executed by third parties, but now, Sif can provide this as additional service as well.

Sif prepared the engineering and arranged a monopile section and transition piece section to be manufactured with all required lifting points. These sections were tilted straight up in Roermond and then transported to the Sif Maasvlakte 2 area. Using SPMTs, these sections were transported from the inner harbour to the quayside. With a 1300T crawler crane, the monopile was lifted onto the foundation followed by the transition piece section on top.

After four days of successful testing by our client, the monopile and transition piece were disassembled and returned to Roermond, where they will return into the normal production process.

Slip joint connection

Sif is currently involved in an innovation project that investigates the use of slip joint connections on monopiles. In contrast to a flanged connection, the slip joint connection does not use bolts to connect the monopile foundation and the transition piece.

Instead, the foundation will be equipped with conical-shaped end pieces of the monopile and transition piece, which are stacked like coffee cups in a cupboard. The ultimate goal of this connection is to save installation time offshore.  While this technique has been applied successfully onshore, it was only used in offshore projects on a test basis.

This particular test is part of the Two Towers Borssele V innovation site, where a number of innovations will be applied in the project such as a slip joint connection, seabed protection and a full aluminium sprayed coating.

Sif director Fred van Beers said: “Sif considers it important to be part of innovations such as the ones being applied by our client Two Towers at Borssele V. These innovations are aimed at either saving costs on the manufacturing of the products and/or the installation and its maintenance at sea or at ensuring an improvement of the environmental impact on sea life. The offshore wind industry is still young and innovations such as these help to further decrease the costs of energy from offshore wind.”

Two Towers is the consortium for the Borssele V project that comprises Van Oord, Investri Offshore and Green Giraffe. Grid connection is scheduled for 2021.