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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

We have seen significant innovations 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. We have seen the offshore wind energy industry taking a step forward in design standards and regulations by developing bespoke design methods for the ever growing monopiles.

Sif is actively involved in the transition process of the offshore wind energy industry. This is reflected in our decision to acquire greater knowledge of design engineering which, in conjunction with our production expertise, ensures that Sif can fully and proactively contribute to progressive developments in this market. We believe that by providing earlier and more detailed input into our customers’ thinking in the design stage, we can more effectively contribute to further efficiency and cost reductions. We also believe that standardization of solutions to be applied at a detail level in foundation design can contribute to reducing LCOE (levelized cost of energy) targets.

Want to know more?
Richard Jongen
Richard Jongen
Commercial Manager Offshore Wind

Fabrication

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.

It is our knowledge of welding high-quality, high-strength steel alloys for harsh and cold environments requiring high Charpy values that sets Sif apart and underpins our track record. Despite the increasing time constraints, we never compromise and always deliver only the highest quality.

Sif services:

  • 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).
fabrication

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:

  • Over 73 years of experience in the industry.
  • 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

Diameter:
11 metres
Weight:
1,800 tonnes
Length:
105 metres
Wall thickness:
160 mm
Production rate:
4–5 per week

What we have seen is almost unbelievable. The size of the equipment, the technology used: really impressive.

Miguel Schaetzen, CEO Eneco Wind Belgium

Key data Sif production site

Sif productionsite
Production capacity

4-5

monopiles per week

Max load out capacity

10

tons/m2

Annual capacity

300,000

tons

Storage and Transshipment area

62

hectares

Deep sea quay

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 WTG (wind turbine generator), 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 starts 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 the general foundation 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:

  • Over 73 years of experience in the industry.
  • 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:

Diameter:
8.3 metres
Weight:
950 tonnes
Length:
32 metres
Wall thickness:
160 mm
Production rate:
4–5 per week

TP-less monopiles

In recent years we have seen the development of a new foundation concept being the TP-less solutions in which the WTG tower is connected directly to the monopile. Sif has already gathered several years of experience with this new concept during the execution of the Luchterduinen, Westermeerwind, Borssele 3+4 and the Hollandse Kust (Zuid) 1-2-3-4 projects. The technical specifications that Sif can cover in their production facilities are similar to the above-mentioned capabilities for monopiles. The difference being that in the case of a TP-less solution the top cans will be equipped with steel stubs and supports in order to accommodate flawless, smooth and rapid assembly of secondary steel after the monopiIe has been installed offshore.

Corrosion Protection

We have seen that requirements for protecting monopiles 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

Foundations at sea are exposed to a very aggressive 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). Both systems act as 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).

References

Hollandse Kust Zuid

In production
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Borssele 1-2

2020
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St. Brieuc

2020
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