The Challenge
As offshore wind turbines continue to increase in size, the demands placed on bolted flange connections become increasingly stringent.
For manufacturers of monopiles, transition pieces, and tower foundations, achieving the required flatness on large-diameter flanges has become a growing challenge. Traditional correction methods such as heat straightening can struggle to deliver the tolerances required on today’s eight-plus meter flanges, where even small geometric deviations can impact bolt preload, structural integrity, and long-term reliability.
CS Wind Offshore, a leading manufacturer of offshore wind foundations and transition pieces, sought a manufacturing solution capable of delivering the precision required by next-generation offshore wind projects.
The Solution
To address this challenge, CS Wind Offshore incorporated CNC Onsite’s Goliath flange milling machine into its manufacturing process.
Designed specifically for large offshore structures, Goliath performs precision milling of tower base, monopile, and transition piece flanges up to 10 meters in diameter. By machining flange surfaces after welding, the process creates the flatness and surface geometry required for critical bolted connections.
Unlike traditional correction methods, Goliath provides a controlled and repeatable machining process capable of handling increasingly complex flange designs, including tilted and double-tilted flanges, while maintaining the required tolerances.
The Results
By integrating precision milling into production, CS Wind Offshore established a manufacturing process capable of meeting the tightening tolerance requirements of the offshore wind industry.
Key benefits include:
- Improved flange flatness on large-diameter structures
- Reduced reliance on heat straightening and manual correction methods
- Increased consistency and quality control throughout production
- Improved conditions for correct bolt preload and structural integrity
- Reduced risk of bolt loosening and fatigue-related issues
- Greater flexibility in future flange and foundation designs
- Support for the increasing dimensions of next-generation offshore wind turbines
Perspectives
CS Wind Offshore
“We constantly develop our manufacturing to ensure we can deliver the right products with the right tolerances that the industry requests. With larger flanges, integrating Goliath into our manufacturing process will allow us to continue to do just that. We are proud to support the development of the industry and, by securing the tolerances, we contribute to securing the integrity of these large structures and thereby the production of green power for many years.”
– Klaus Munck Rasmussen, Senior Vice President, Bladt Industries
CNC Onsite
“Obtaining a global flatness of a couple of millimeters on a four to five meter diameter flange can be challenging enough, but obtaining the same result on today’s eight-plus meter flanges is simply not possible with previous methods.”
– Søren Kellenberger, Sales Director, CNC Onsite
Long-Term Value
Flange connections are among the most critical mechanical joints in offshore wind structures. Their performance directly influences bolt integrity, maintenance requirements, and the operational reliability of the asset throughout its lifetime.
By introducing precision milling as a standard manufacturing process, CS Wind Offshore has taken an important step toward meeting the increasing tolerance demands of larger offshore wind turbines while reducing process variability and supporting the long-term integrity of critical bolted connections.
The project demonstrates how precision machining can help manufacturers transition from traditional correction methods to controlled, repeatable production processes capable of supporting the next generation of offshore wind foundations and towers.
