Monopiles & Transition Pieces
There are several types of foundations for offshore wind energy projects. The type that is used depends on a number of factors, including water depth and the soil composition of the seabed. Monopiles are the most commonly used foundations for offshore wind turbines since they offer the best value for money. They can be used in water depths of up to 50–60 metres.
Design engineering
A number of important innovations have taken place in recent years. Technologies such as slip-joint connections and narrow-gap welding can contribute to making offshore wind energy more sustainable and have the potential to make the industry more efficient, more affordable and safer. The offshore wind industry took a big step with the development of standards for offshore wind by developing bespoke design methods for the ever growing monopiles.
Sif is actively involved in the transition process of the offshore wind energy industry. For that reason, Sif is gaining more design engineering knowledge with the acquisition of KCI The Engineers. KCI's expertise will be combined with our manufacturing expertise, enabling us to proactively contribute to further developments within the offshore wind market. We can now think more in-depth together with our clients earlier in the design phase, enabling us to offer more efficient and cost-effective solutions. We are striving for more standardization of foundation solutions to contribute to the reduction of the Levelized Cost of Energy (LCOE).
Fabrication
There are different types of foundations for offshore wind farms. The type of foundation depends on several factors, such as water depth and seabed composition. Monopiles are the most commonly used foundation for offshore wind turbines: they are considered the best value for money, and they are used at water depths of 50 up to 60 meters.
However, monopiles are not yet the preferred choice for very rocky soil conditions. In such situations, jackets or gravity-based foundations are good alternatives. Suction buckets and floating foundations are being used on an experimental basis. Our technical know-how enables us to efficiently and effectively communicate with our technical clients.
Our technical know-how enables us to communicate efficiently and effectively with our customers. We have broad knowledge of welding high-quality, super-strong steel alloys for severe and cold conditions, which require high Charpy values. This is our defining strength which confirms our excellent track record. We never compromise but consistently deliver only the best quality despite increasing time pressure.
What we are proud of
- Almost 75 years of experience in rolling and welding.
- Sif’s proprietary welding machines design.
- Multiwire multihead SAW (submerges arc welding) processes, optimized underhand positions: ‘one machine operator replacing more than a 100 hand welders’.
- Optimizations in weld preparation (semi-narrow-gap, start–stop blocks).
- In-house qualification of all welders.
- Large number of roller beds for welding automation.
- Long-lasting craftsmanship in plate rolling.
- Highest rollable wall thicknesses by cold rolling (5,000 tonnes rolling machine).
Monopiles
Compared to other options, monopile foundations are popular due to their low manufacturing costs, low transport and installation costs, and low risk profile due to their flawless track record. More than 80% of the wind turbines currently installed in the North Sea are based on monopile foundations.
Sif has over 20 years of experience in the manufacturing of monopiles. Sif has constantly invested in manufacturing capabilities in order to follow the technical developments in the monopile foundations industry. In fact, Sif is regularly one step ahead of the market, creating new possibilities for the use of monopiles as the preferred foundations solutions for future projects.
The above has led to the following range of services and capabilities that Sif can offer in relation to monopile foundations.
Sif services:
- In-house engineering and knowledge.
- Fabrication of the primary steel components.
- Engagement of the secondary steel supplier.
- Marshalling and long-term storage at the Sif Maasvlakte 2 Marine Terminal.
- Load-out at the Sif Maasvlakte 2 Marine Terminal.
- Interface management.
Sif capabilities
What we have seen is almost unbelievable. The size of the equipment, the technology used: really impressive.
Key data Sif production site
4-5
monopiles per week
10
tons/m2
300,000
tons
62
hectares
600 15.6
meters length
meter draught
Ro-Ro quay
Transition pieces
The transition piece (TP) is a tubular structure made out of high-grade offshore steel. The TP is the second part of a wind turbine generator (WTG), which is directly connected to the monopile foundation and the WTG tower. The most common connection of a TP is with flanges or a grouted connection. The production process begins with rolling the steel plates; after that, the rolled steel plates are welded together. In order to weld steel plates of this size together, Sif uses highly automated welding systems.
As a contractor, Sif provides the primary steel components for the TP. For the secondary steel package, coating and final completion of the TP structure, Sif has excellent collaborative relationships with industry-respected partners and subcontractors.
Sif services:
- In-house engineering and knowledge.
- Fabrication of the primary steel components.
- Procurement of the secondary steel supplier.
- Marshalling and long-term storage at the Sif Maasvlakte 2 Marine Terminal.
- Load-out at the Sif Maasvlakte 2 Marine Terminal.
- Interface management.
Sif capabilities transition pieces:
Corrosion Protection
Increasing requirements for the protection of our products against corrosion are becoming substantially more stringent. Higher-quality, more complex coating systems and larger surfaces that have to be coated both inside and outside have become the standard. Sif has built two additional coating halls in 2019 to meet the increased demands for coating quality and the extended surface area for the protection of monopiles when installed at sea. We now have six large coating halls at our Maasvlakte 2 facility, all with state of the art environmental controls and surface treatment plant and equipment
At sea, foundations are exposed to an extremely violent environment. This environment is classified according to ISO 12944-2 as the CX/lm4 zone (offshore class, extreme corrosivity). This means that we need to take a number of corrosion protection measures to achieve the minimum service life of 25 years or more.
These include thermal metal sprayed coatings (TSZA, thermally sprayed zinc aluminium, or TSA, thermally sprayed aluminium) and very strong organic two-component coatings (epoxy). These form a barrier against water and oxygen to impede rust formation and metallic systems provide additional galvanic (electrochemical) protection.
There’s an incredible number of different coating systems, and every system has its advantages and disadvantages. That’s why we usually use a combination. Some parts are applied manually (the hard-to-reach parts), and other parts are applied automatically; some parts have epoxy applied (multiple coating layers), and the most critical parts are coated with aluminium or zinc (metallizing).
