What Is an Offshore Wind Turbine Monopile?
The wind turbine monopile refers to a monopile used as the offshore wind turbine foundation. AGICO also offers wind turbine anchor cage foundation solution for customers, which consists of high-strength anchor bolts and anchor ring plates. It consists of a single large-diameter steel pipe, manufactured from high-strength low-alloy marine steels mainly by plate rolling and welding processes. Monopiles are typically manufactured in large sizes, with diameters ranging from 5 to 10 meters and lengths that can exceed 100 meters. They feature a simple structural configuration, high load-bearing capacity, well-established manufacturing and installation techniques, and relatively low overall cost. It is an economic solution that is most widely used in offshore wind turbine foundations.
How does it work? After being embedded into the seabed, the monopile provides foundation stability through the monopile’s substantial self-weight and the frictional resistance between the pile shaft and seabed soils. Monopile is primarily designed and applied in shallow to medium water depths of approximately 20 to 50 meters.
Main Components of a Wind Turbine Monopile
Wind turbine monopile foundation consists of a steel pipe pile, a transition piece and foundation connection components, here are the details:
- Steel Pipe Pile (Main Shaft):
Steel pipe pile in large diameter (3–4.5 m) is the main shaft of the foundation system, it is formed by rolled and welded steel plates; the length is determined by water depth and seabed conditions. - Transition Piece (Optional):
A transitional piece is a steel structure member connecting the tower and the monopile, it has a cylindrical shape and designed to facilitate load transfer and installation. - Foundation Connection Components:
Wind turbine tower shall be installed directly on the monopile or through a transition piece, the connection part include flanged connections and grouting materials, to ensure rigid bonding between the tower and monopile.
Where to find an offshore wind monopile supplier? In the past, offshore wind monopile is only manufactured and supplied by large steel mills in Western countries. While in recent years, steel mills in China have significantly enhanced competitiveness in the production of extra-large monopiles for wind turbines, with exports to the European and American market accounting for over 20% market share.
Offshore Wind Monopile Specifications
AGICO can manufacture and supply a wide size-range of monopiles tailored for wind turbine foundation requirements. The monopiles are manufactured by thick steel plates in optional high class marine structural steel grades to provide high-strength and corrosion resistance.
For offshore wind turbines in the 8–15 MW+ class, monopile diameters typically range from 6.0 m to over 11.5 m, with wall thicknesses up to 210 mm. Offshore-grade steels such as S355, S420, and S460 (EN 10225) are selected based on turbine capacity, water depth, and fatigue requirements to ensure structural integrity and long-term performance.
Monopile Parameters
- Steel Standards: EN 10025, EN 10225, ASTM A572, ASTM A709
- Steel Grades: S355J2 / S355G8+M, S355ML / S355G10+M, S420ML / S420G2+M, S460ML / S460G2+M, ASTM Gr.50 / Gr.60
- Welding Method: SAW / LSAW
- Maximum Diameter: Ø6.0–11.5 m (customizable)
- Maximum Wall Thickness: 50–210 mm
- Section Length: 20–35 m
- Total Monopile Length: 60–100 m and above
- Monopile Weight: 600–2,500 tons
Choose Monopile Size according to Turbine Capacity
| Turbine Capacity | Typical Water Depth | Monopile Diameter | Wall Thickness | Total Length | Approx. Weight |
|---|---|---|---|---|---|
| 8 MW | 10–25 m | Ø6.0 – 7.0 m | 60 – 90 mm | 60 – 75 m | 800 – 1,200 t |
| 10 MW | 15–30 m | Ø7.0 – 8.5 m | 80 – 110 mm | 65 – 85 m | 1,200 – 1,800 t |
| 12 MW | 20–35 m | Ø8.5 – 10.0 m | 100 – 140 mm | 75 – 95 m | 1,800 – 2,500 t |
| 15 MW+ | 25–40 m | Ø10.0 – 11.5 m+ | 120 – 210 mm | 85 – 110 m+ | 2,500 – 3,500 t+ |
Our offshore wind monopiles have reached international advanced levels in terms of large-scale and deep-water manufacturing capability,Under moderate water depths (typically 5–35 m).It is the most economical and commonly selected offshore wind mill foundation solution.
Recommended Steel Grades by Turbine Capacity
| Turbine Capacity | Primary Steel Grade (EN 10225) | Alternative Grades | Typical Application Notes |
|---|---|---|---|
| 8 MW | S355G10+M | S355ML | Adequate for moderate bending moments and fatigue loads |
| 10 MW | S420G2+M | S420ML / S355G10+M | Improved strength-to-weight ratio for larger rotors |
| 12 MW | S420G2+M / S460G2+M | S460ML | Used where fatigue and stiffness control governs design |
| 15 MW+ | S460G2+M | S460ML / NV 460 | Required for ultra-large monopiles and deep-water sites |
Notes:
- EN 10225 offshore grades are strongly preferred for primary load-bearing zones
- Higher-strength steel helps control wall thickness, fatigue life, and transport weight
- Mixed-grade designs are common (e.g. S460 for upper sections, S420/S355 for lower)
Manufacturing Process of Offshore Wind Monopile
Monopiles are typically designed as large-diameter steel pipe piles, with dimensions determined by turbine specifications and site geological conditions. For example, a monopile may reach a diameter of 7.3 m, a length of 84.6 m, and a weight of 974 tons.
The monoplie’s dimension is decided by turbine specifications and site geological conditions, its manufacturing process is divided into 2 steps: design and fabrication.
Monopile Design:
The monopile design must strictly comply with offshore wind and marine engineering standards. And shall consider the factors such as water depth, seabed geology, wind–wave–current loads, and turbine parameters are analyzed to evaluate structural strength, global stability, and fatigue life. After the evaluation, determine the optimal pile pipe diameter, wall thickness, steel grade, and corrosion protection method.
Fabrication Process:
- Steel Plate Rolling: marine-grade thick steel plates are rolled and formed into circle sections and conical shapes by a heavy-duty plate rolling machine. (The requirements for controlling roundness, ellipticity, and end perpendicularity are extremely high, and this is a critical step in ensuring subsequent welding and overall geometric accuracy.)
- Steel Plate Welding: Adopted with SAW and LSAW welding equipment, followed by longitudinal or circumferential submerged arc welding (SAW).
- LSAW Welding: Longitudinal seam welding of the steel plates is a submerged arc welding (SAW) process. Steel Plates are welded into tubular sections, Welding procedure qualification (WPS/PQR) must be completed before welding, and heat input and weld bead quality are strictly controlled to ensure the weld quality.
- Assembly and CSAW Welding: Multiple steel tubular sections are assembled and welded into a complete piece, to the designed length and connected into a longer monopile structure through circumferential submerged arc welding (CSAW). The requirements in this process are on controlling coaxiality, straightness, and internal weld quality.
Strict Quality Control: The manufacturing process of monopile has strict step-to-step quality control. Which includes plate cutting, rolling, welding, non-destructive testing, and corrosion protection treatment, ensuring long-term performance under high bending moments, cyclic loading, and harsh marine environments.
Optional Transition Piece and Ice Cone Protection
How are monopiles been transported? Monopiles can be delivered as single-piece or segmented structures; in most cases, they are delivered as a complete member for direct installation, depending on the transportation and installation requirements of your project.
- Monopile Without Transition Piece: The turbine tower is directly connected to the steel pile, simplifying the structure but requiring high installation accuracy.
- Monopile With Transition Piece: Uses a transition piece to accommodate different tower sizes and load conditions.
- Ice Cone Protection (Specific Applications): In regions prone to ice loads, monopiles may be equipped with ice-breaking cones to improve durability.
