Floating offshore wind is progressing from individual demonstrators towards projects requiring large numbers of foundations. Delivering these projects will depend not only on turbine and foundation design, but also on how efficiently foundations can be manufactured, transported and assembled. The scale up challenge is therefore not simply to design larger floating platforms. It is to produce foundations at a repeatable rate that supports the offshore installation program. Welding remains the established method for joining steel floating foundations, with a long record in shipbuilding and offshore construction. Completing major structural welds at the assembly port, however, requires qualified personnel, controlled procedures, detailed inspection and coating repair. These activities increase the time each foundation occupies the assembly area. 

Compared with completing large structural welds at the quayside, bolting could shorten assembly cycles, reduce yard occupancy and simplify some equipment and personnel requirements. Bolting does not eliminate welding. Flanges and other connection components will normally still be welded to tubular members during fabrication. The difference is that these welds can be completed, inspected and coated in a controlled facility before final assembly.  

At commercial scale, a floating wind farm could require hundreds of connections between primary structural members. Reducing the time required for each connection could reduce the number of assembly lines and help ports maintain the production rate required for offshore installation. Depending on the design, bolted assembly may also reduce coating repair and allow individual components to be replaced more readily. 

This article is part of our Frontiers in Power publication. Download to get the full issue.

This article covers:

• The scale-up challenge
• Why bolted connections?
• Reliability considerations: loosening, corrosion and fatigue
• Conventional ring flanges may not be enough
• Compact flange connection
• Additional measures to address specific failure mechanisms
• Remaining challenges and gaps