Xelcor - Redefining Foundation Connections
Offshore wind turbines are growing, and projects are moving into deeper waters. This increases the demands on foundation design, fabrication and offshore installation. Water depth, salinity, currents, wind and seabed conditions add further complexity. Current foundation connection systems lack scalability, adaptability, and pose high HSE risks during installation.
Xelcor is a polyurethane (PU)-based slip-joint connection system designed for scalable offshore foundation concepts and enables efficient offshore installation.
What Xelcor is
A Slip Joint connects two conical steel sections through an overlapping interface. Xelcor adds an engineered PU layer between the two steel sections.
The system can connect monopile-to-transition-piece (MP–TP), monopile-to-monopile (MP–MP) and similar offshore foundation interfaces. Xelcor is designed for a wide range of water depths, including 40 m and beyond. It supports applications above water, in the splash zone and in submerged conditions.
How Xelcor works
In a Xelcor foundation connection system, the outer conical steel section, such as a transition piece or upper split monopile, is lowered over the inner section. The resulting overlap forms the connection between the two components.
Before offshore installation, high-performance PU plates are bonded to the anti-corrosion coating on the inside surface of the outer section. When the steel sections are joined offshore, the plates form an engineered PU layer between the two steel surfaces.
The PU layer distributes loads evenly across the overlap, reduces local stress concentrations and reduces fatigue, and compensates for standard fabrication tolerances and steel imperfections. Because the plates are integrated onshore as part of the foundation manufacturing workflow, the system supports a plug-and-work approach during offshore installation.
The five pillars of advantage
Xelcor is scalable to larger turbine sizes, i.e. from 15 MW, and deeper waters through modular foundation segmentation, multiple connection concepts and standardized, repeatable production. Flexible MP–TP, MP–MP, splash-zone and subsea concepts support project-specific applications, while modular plate engineering enables consistent production quality across different geometries and tolerances.
Xelcor supports cost efficiency through reduced total EPCI cost, faster installation and lower vessel requirements. The use of existing vessels, manufacturers and ports broadens access to available infrastructure and supports competitive, lower-cost execution. Independent cost analysis from Ramboll (2025) indicates potential foundation CAPEX savings of 5-15% in water depths of 30-60 meters, depending on project configuration, and installation time reductions of up to 35%.
Xelcor supports reliable structural performance and integrity through optimized loads, a protected interface and tolerance-optimized designs. Loads are distributed evenly to reduce stress concentrations and fatigue risk at welds, while coatings are preserved and steel-to-steel corrosion risk at the connection is reduced. Independent validation includes extensive testing and DNV C-Level certification of the 1:10 prototype.
Xelcor strengthens resilience in deployment by reducing dependence on heavy-lift vessels and enabling localization of the supply chain. The system supports the use of existing installation fleets, regional manufacturing and local execution capabilities. This can help minimize bottlenecks in installation logistics, improve planning certainty and enhance overall project robustness.
Xelcor supports safety and re-usability through plug-and-work installation with no bolting or grouting, enabling faster installation while reducing HSE risk. Fewer offshore work steps reduce personnel exposure to hazardous activities and lower noise impact due to reduced installation intensity. Maintenance-free operation and PU plate re-use support circularity and end-of-life value.
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Scope of Work
Design. Production. Integration. Seamlessly Delivered.
Xelcor is designed to integrate into existing offshore wind project workflows and reduce complexity and offshore installation effort. Rosenxt provides an integrated scope covering three key areas. The result is a buildable foundation connection concept prepared for subsequent offshore installation.
Design of the PU, Slip Joint and overlap region
We develop the project-specific design of the steel overlap region and PU plate layer to control load transfer and stress distribution. We evaluate relevant load cases and align tolerances early with monopile and transition piece manufacturers.
Production of Xelcor PU plates
We manufacture project-specific PU plate sets entirely in-house, matching approved dimensions, tolerances and specifications. Series production ensures consistent quality and throughput, with plates designed for demanding offshore conditions.
Integration into the foundation structure
We integrate the PU plates into monopiles or transition pieces onshore, directly in the port area. Our fully automated, modular and scalable process ensures high-quality integration and fits existing EPCI workflows, fabrication processes and project schedules.
Engineered Polyurethane for Harsh Offshore Environments
Rosenxt builds on decades of experience with polyurethane solutions for applications in harsh environments. Our material expertise covers performance requirements including high abrasion resistance, chemical resistance and material flexibility.
For Xelcor, the PU plates, adhesive layer and integration process are engineered for the specific foundation configuration and its structural and environmental conditions.
Development and Validation Evidence
Xelcor’s current readiness is supported by physical testing, simulation-test correlation and material and process validation. Further qualification activities are ongoing, including long-term material validation, production-process qualification and installation readiness.
Physical Testing
- 1:10-scale prototype test campaign – functional integrity and performance of the design principle, the PU and the adhesive layer system
- Large-scale PU layer test scale 1:4 – test scalability integrity and capacity of the layer system
- Mechanical properties testing – PU & adhesive
- Interface testing – friction & wear
- PU plate production – process & manufacturing feasibility testing
- PU Integration – bonding process trials, plate manufacturing trials
Independent Verification / Confirmation
- DNV C-Level Certification (1:10 prototype)
- Ramboll Cost Comparison Report (2025)
- Production equipment and process confirmed by supplier
- Seamless integration of PU Plate integration process confirmation by foundation manufactures
- Offshore installation verification statement
Let’s take Xelcor offshore
We are looking for the right industry partner to advance Xelcor towards a 1:1 offshore prototype.
Joint Case Study
Develop a foundation concept tailored to a specific offshore wind project.
Joint Research Program
Jointly validate Xelcor and advance its technology readiness.
Development Partnership
Develop a 1:1 onshore or offshore prototype as the next step towards offshore validation.
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News
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