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Raised Flange ConnectionWinddays 2016 - Innovations at Eneco Luchterduinen

Wybren de Vries

Foundations Package Manager

16 June 2016

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Eneco Luchterduinen

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• Located 23km off the Dutch coast

of Noordwijk

• Area 25.5km²

• Water depth of 18-24

• Average annual wind speed of

9.3 m/s at 80.8m

• Installed capacity of 129MW

• 43 Vestas 3MW V112 turbines

• Expected production of more than

4,000 full load hours (FLH)

• Landfall at Noordwijk

• Grid access point at Tennet

150kV station 8km inshoreInnovations:

• 2 foundations without scour protection

• All 43 foundations with raised flange connection

• Innovative metocean buoy

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Introducing an innovation

• Risk reduction

– No grout connection – No certification risk

• Cost reduction

– Reduction of grout overlap -> less steel

– Reduction of grout curing time -> faster installation

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Raised flange connection

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The Raised Flange Connection concept

1. No grout connection, no TP: single

foundation element

2. Tower bolted directly onto monopile

3. Pile driving on monopile flange

4. Large pile driving forces: secondary

steel installed separately offshore

5. No J-tubes: internal free-hanging

cable

6. Corrosion protection: ICCP anodes

integrated in boatlanding

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Boatlanding

Airtight platform

External platform

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Parties involved

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• Supply Wind turbine, • Design tower & flange

connection• WT load calculations• Design foundations

Certification:• Foundation primary steel,• Secondary steel • Loads• Tower• Flange connection

EPCI:Design, supply installation• WTG Foundations• Cables• OHVS

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Design requirements

• Flange:

– Must withstand pile driving– Avoid impact with hammer– Adequate corrosion protection

• Monopile

– Install within 0.5° of vertical– Provide corrosion protection when ICCP inactive– Include attachments for secondary steel mounting

• Secondary Steel

– Minimise number of lifts– Easy offshore installation– Cable hang-offs on internal airtight platform– Incorporation of ICCP in access arrangement

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Design of flange connection

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• Foundation flange design

adapted for pile driving

• Flat driving surface

• Downward inclined flange

• Larger thickness

• Acceptance on basis of FE

analysis

• Verification of stresses in

tower wall and bolts

• Better understanding of

load levels and paths

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Secondary steel details: Main Platform

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Secondary steel details: Boatlanding

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ICCP anodes

Stabbing pins below waterline

Bolted connection above waterline

Resting platformssupported on boatlanding

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Secondary steel: Airtight platform

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Design - Challenges

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Design of stubs & attachments:

• Stiffeners to resist driving

accelerations

• Long curved weld extensions

• FE analysis to determine SCFs

FE analysis of Flange Design:

• Pile driving on driving face (40mm)

• Waviness of flange included

• FE analysis to determine Stresses

and SCFs

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Installation – Mock up/ Pre-assembly

• Full scale trial fit in Hoboken

• Lot of attention for details during design and construction

• Improvements to vessel during installation

• Small damages to coating and a few to steel structures

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Installation - Sequence

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Transport on Aeolus

Pile upending Lifting pile into position over gripper

Lifting hammer onto pile

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Installation - Sequence

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Pile driving, with gripper engaged

Lifting boatlandinginto position

Disengaging gripper

Foundation inspection

Flange measurement

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Installation - Results

• Second MP out of vertical, exceeding tolerance; wedge adapter flange installed

• Cycle times showed strong learning curve

• New vessel with few teething problems

• Gripper worked very well

• Average inclination < 0.1 degree

• No damage to flanges

• No Lost Time Incidents

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Monitoring

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• Aim: determine bolt tension variations and tower wall strains

• Strain gauges on 8 bolts

• Strains gauges on tower wall above flange

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Conclusion

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Questions?