Download - Grouted vs Bolted Flange Connections 27102014-Libre

The Future For Monopile & Jacket Pile Connections – D eveloper &I nvestor Perspectives27 th October 2014 , PES/ Pagel I TW, Amsterdam

Dr. Chris Golightly GO-ELS Ltd.

Geotechnical & Engineering Geology Consultant

Summary Contents• History of Monopile [MP] Connections

• DNV J101 Code and Shear Keys

• Adoption of High Strength Grouts

• Monopile Vs Tripod/ Jacket Loading

Dr. C. R. Golightly GO-ELS Ltd. – The Future For Monopile & Jacket Pile Connections – Developer & Investor Perspectives 27th October 2014

• Monopile Vs Tripod/ Jacket Loading

• Billington I CE 2014 (Refs 1 & 2)

• RWE GYM Study 2011

• Conical Connections

• Trelleborg Spring Bearings (Ref. 11)

• Swaging & Slip Joints

• I ntegral and External Mating

• Quick Coupling; I ntegral MP & TP

• Fatigue Life; OWI -LAB BELWI ND (Refs. 3 & 4)

• Conclusions, References, Contact Details

History of Monopile Connections

The 1st UK Round 1 Blyth and Scroby Sands MP projects used bolted pre-fittedwelded flange connections, a technique subsequently rejected in favour of theperceived cheaper and quicker more efficient grouting technique.

Towards the end of 2009 many grouted connection joints, between large diametermonopiles [MP] and connecting tubular steel transition pieces [ TP] at the base ofoverlying support towers, were found to be failing.

For the majority of the 70% of UK offshore MPs which experienced grout cracking,settlements and failures. This was primarily due to the widespread absence of shearkeys (or weld beads) on straight MP and transition piece [ TP] surfaces.

Bending moments as a result of complex wind and wave loading is an importantBending moments as a result of complex wind and wave loading is an importantdesign consideration.

Axial connection capacity was found to be very significantly lower than previouslyassumed due to MP scale effect, a lack of manufacturing and installation tolerancesand abrasive wear due to the sliding of contact surfaces when subjected to largemoments.

Typical failure modes include disbonding, cracking, wear and compressive groutcrushing failure.

These failures have necessitated assessment and repairs which have not all beenfully reported publically. There have been a number of claims and arbitration cases.


History of Monopile Connections


DNV J101 Code and Shear Keys

The two projects where grouted connections have not (yet?) failed included shearkeys, which is common practice for oil and gas platforms for pile to sleeveconnections using the API RP2A Code. This is due to the designers having Oil & Gasindustry experience and staff

I t appears that many designers did not include shear keys because it was perceivedas a cheaper, quicker option. The DNV J101 (2007) offshore wind turbine designcode left it open to designers whether to use shear keys/weld beads or not. The useof annulus grouting allowed easier adjustment of the pile out-of-verticality usingjacking to level the turbine tower prior to grouting.

The use of “Plain Pipe” non shear keyed connections is now discontinued, notThe use of “Plain Pipe” non shear keyed connections is now discontinued, notrecommended and was essentially a systemic design error as a result of codephrasing omissions.

Some MP projects still adopt designs without shear keys, including a 1 to 3 degreeconical section which is presumed to be able to “catch” the TP as the groutedconnection ultimately settles and drops, allowing radial stresses to be regained. Thismight be regarded by some as “engineering for failure”.

Industry best practice and code guidelines are under review & DNV guidelines wererevised in 2011 (new Code to be issued in 2014, Refs 5, 6 & 7). There are still someanomalies in behaviour. Research is ongoing on scale & fatigue effects but thesituation is becoming clearer.


Adoption of High Strength Grouts

Tried and tested appropriate underwater grouts were originally used to cement pilesinto bedrock, amongst other applications. This technique was then adopted over 12years ago for offshore wind turbines, as a more efficient alternative to boltedflanges, which assisted in levelling towers to vertical.

Typically, britt le high and ultra high strength grouts used have UC strengths > 100MPa up to 200 MPa. In a geological context, this is a “Very Strong” rock which could“only be chipped by heavy hammer blows”, according to standard rock engineeringstrength descriptions. They exhibit high ratios of compressive to tensile strength.

I t is not difficult to envisage twin large diameter steel tubes sandwiching an annulusof such “rock” cracking & crushing, leading to progressive failure at the top and baseas piles are cyclically loaded by wind and waves over long periods. Patterns ofas piles are cyclically loaded by wind and waves over long periods. Patterns ofcracking measured are reputedly linked to predominant environmental loaddirections.

The MP grout failures may have been related to manufacturing, installation andpositioning tolerance uncertainties and out-of-roundness which in some cases haveled to MPs and TPs both being slightly out of shape, with the grouted annulusthicknesses therefore varying vertically. Little to nothing is published on this.

There have been question marks over the long term fatigue strength of HPC grouts,following work by Anders & Lohaus (2007) and Soerensen et al (2011).

There are suggestions in the work done now that a lower strength less britt le groutmay be more appropriate for use in some designs, should grout be adopted. Thereis a need to "bottom-out" the potential water ingress and cyclic fatigue problems.


Monopile Vs Tripod/ Jacket Loading

“Monopiles” with D/ t ratios often in excess of 100 are in reality “ thin-walled steelcaissons” rather than piles.

MP ability to transfer large moments is complex, but has become better understood.Design theories still have limitations & shortfalls. The use of conical TP sections[ “controlled engineering for failure”] is uncertain in the long term.

High dead weight oil & gas platforms have used API RP2A designed grouted leg-pileconnections for decades, but stresses are usually predominantly compressive. HoweverOWTs are low deadweight loaded, highly cyclic, with complex vertical & bending forcecoupling, with tensile stress zones in the grout.coupling, with tensile stress zones in the grout.

Dynamic load regimes experienced by the legs of tripods (Germany) and 4-leg jackets(mostly UK) are different to the predominant bending mode experienced by MPs.

Some tripod and jacket designs include “stopper plates”. (e.g. Borkum West 2) These“belt-and-braces” designs suggest a lack of confidence in the robustness under long termcyclic fatigue conditions over a 20+ year design life.

I t is uncertain whether or not tripods/ jacket grouted connections will experience fatiguedegradation in time, even with the provision of shear keys. There has been extensiveresearch especially at Leibnitz University Hannover (Refs. 10, 16, 17 & 18).


Monopile Vs Tripod/ Jacket Loading

For tripod/ jacket piles of smaller diameter up to ~ 2.5m, work mostly in Germany under the auspices of theGerman BSH committee has shown that with a different"push-pull" loading regime to monopiles, there is notheoretical reason why grout should not be used forthose connections, with shear keys, correctly designedand installed/constructed.

Two methods were used for German AV tripods:

1. Tripods lowered onto template pre-driven pilegroups [Borkum West 2] or:


groups [Borkum West 2] or:

2. Piles vibrated then conventionally driven throughthe sleeves of pre-placed tripods [Global Tech 1] ] .

Option (2) is preferable, since the tripod or jacket legsits inside the pile, as opposed to outside, whichrequires more complicated sealing and a different groutstress pattern.

This is similar to that used for the Ormonde I rish Seaproject appears preferable, where the jacket legs werestabbed inside a pre-installed seabed pile template,with a large annulus of lower strength grout used toallow for installation tolerances.

RWE Gwent-Y-Mor Study 2011

Julian Garnsey of RWE led a study published in 2011 assessing grouted connectionsfor the GYM monopiles (Ref. 8).

The project assessed eight generic concepts:

1) Grouted conical without shear keys; 2) Grouted cylinder with shear keys; 3) Bolted flange;

4) Bracket support; 5) Swaged Connection; 6) Integrated MP and TP; 7) Pinned Connection;

8) Clamped Connection

The bolted flange proved the most promising for further detailed investigation, butwas not selected because the change would have impacted on the project schedule.

Five concept variants emerged from this process as potential solutions;Five concept variants emerged from this process as potential solutions;

1) Grouted conical without shear keys and an axial bearing system

2) Grouted cylinder with shear keys and an axial bearing system

3) Bolted flange internal to the transition piece above high tide level

4) Conical grouted connection without shear keys and an axial bearing system

5) Conical grouted connection without shear keys.

Concluded best solution is shear keys in the middle third and a longer connectionplus necessary “back-up” elastomeric bearing support, allowing lower strength grout.This more robust connection with reduced contact pressures at the ends and a lessbrittle grout would reduce cracking around the shear keys and connection ends.Necessary to confirm zero water ingress does not adversely affecting the groutmatrix, which would lead to a simplified seal specification.


RWE Gwent-Y-Mor Study 2011

The methodology developed resulted in a numerical weighting for EIGHT criteria asfollows, with the subsequent ranking shown:


Conical Connections

A Joint Industry Project [ JIP] was carried out by DNV to investigate the structuralcapacity of these connections from autumn 2009 to January 2011 (Refs 5, 6 & 7).

Axial capacity was found to be more sensitive to diameter and surface/positioningtolerances than allowed for in existing design standards, so a design procedure withconical shaped connections was developed.

In January 2011 a further JIP on the capacity of cylindrical shaped groutedconnections with shear keys was initiated. Analytical design equations weredeveloped for the Ultimate and Fatigue Limit States. The recommended designmethodology was supported by laboratory tests.


Trelleborg Spring BearingsSeveral projects adopted or are adopting retro-fitted/new Trelleborg spring bearings (BELWIND[330] , Robin Rigg [360] , Sheringham Shoal [540] , Greater Gabbard 120] , Rhyl Flats [158] andGwent Y Mor [960] ). For a normal monopile foundation six bearings are required (see Ref. 11).

I f elastomeric bearings were not fitted during construction and slippage occurred later, they may beretrofitted by welding new brackets to the inside of the TP. The solution is used on installed windfarms where grout problems occur but also as a precaution.

At the start of construction, the bearings can be fitted so that they are unloaded and just resting atthe top of the MP. I f slippage occurs at a later stage, the bearings are gradually loaded to assist thegrout in supporting the weight of the TP and tower assembly.

A further function of the bearing is preloading to carry the static vertical load from the start with theaim of preserving the strength of the grout.aim of preserving the strength of the grout.

Long Term Measurement & Condition Monitoring is Essential


Swaging and Slip Joints

Many developers such as E.On for Amrumbank and Humber Gateway have revertedto bolted flanges, with some considering integral MP & TP, pile swaging, quickcoupling lock rings, internal/external mating, or slip joints as reliable long termsolutions. All require control on verticality, careful driving. Costly.

e.g. Beatrice project (DownVInD) pile swaging (Hydra-Lok® system) for jackets,which secures structures by expanding piles radially into surrounding sleeve insubstructure. Easily monitored and quicker, but more expensive.


I ntegral and External Mating


Quick Coupling; I ntegral MP & TP

http:/ / www.pes.eu.com/ assets/ misc_dec/ vanoordpdf-384857351196.pdf

Van Oord @ Luchterduinen andGemini:

“Next year in July we will start withpiling the first foundations. Thoseare quite innovative as it is acombined monopile and transitionpiece. We are piling on the flangeon which the wind turbine tower


on which the wind turbine towerwill be mounted. After piling thesecondary steel will be attached topre-mounted brackets. By doingthis we prevent a groutedconnection between the mono pileand transition piece. At the sametime this concept is cheaper than afoundation in two parts”.

Fatigue Life (Lohaus & Anders 2007; Soerensen et al , 2011)

Lohaus & Anders (Ref. 13)“The fatigue strength of UHPC in high-cycle fatigue seems to be lower compared to normalstrength concrete. Regarding UHPC in grouted Joints nearly bilinear load-deflection curves forspecimens with shear keys in uniaxial compression are shown, which represent two differentload-bearing mechanisms and a very ductile failure”

Soerensen et al (Ref 19)• BASF 140 MPa high performance grout, cementitious binder material containing microsilica and

other added minerals. Prepared at ultra-low water/ cement ratio using superplasticizingadmixture. Aggregate natural sand (0-4 mm). Strength after 28 days curing in water at 20o C.admixture. Aggregate natural sand (0-4 mm). Strength after 28 days curing in water at 20o C.

• In air grout fatigue life was comparable to that of ordinary concrete, but in water the groutexhibited drastically shorter fatigue life at stress levels in excess of 60% of the staticcompressive strength.

• In air, the frequency of the loading (0.35 Hz, 5 Hz, and 10 Hz) had no influence on the fatiguestrength, but in water the fatigue capacity was much lower at 0.35 Hz than at either 5 Hz or 10Hz. Reduction in fatigue life in water was particularly severe at the lowest frequency 0.35 Hz.

• Reduced fatigue capacity postulated due to water trapped during cyclic loading, exertinginternal pore pressures high enough to cause progressive crack formation (“micro-wedging”?).Effect more pronounced at low loading frequencies, with time available for water ingress andsubsequent pressure build-up during each load cycle.

• Fatigue life reduction in water was not observed at the lowest stress level investigated (45% ofthe static compressive strength).


Fatigue Life (Lohaus & Anders, Ref. 13; Soerensen e t al, Ref. 19)


Main Conclusions: Foundations

1. Initially the relatively new offshore industry has understandably used conservativemonopile, piled tripod (Germany) & 4-leg jacket (UK) solutions. CAPEX and investment isstill limited compared to other energy industries.

2. European Offshore Wind Industry has developed several alternative foundation solutions,steel / concrete, monopiles, “Alpha Ventus” piled tripods, BARD tripiles, triple & 4-legjackets, truss towers, concrete GBS, twisted jacket, guyed & A-frame monopiles, monopodsuction caisson, triple/quad suction caissons.

3. Industry needs to be more realistic about offshore turbine tilt criteria, based upon soundengineering analysis. Big impact on structure costs, influencing business cases.Development of tilt-tolerant DD turbines can reduce costs.Development of tilt-tolerant DD turbines can reduce costs.

4. For foundation costs to reduce [halved acc. US DoE] , innovative solutions needed,selected/ tailored to specific site conditions. Conservative risk averse attitudes in a relativelynew industry should change as experience is gained.

5. Main Foundation Risks: Grouted connections, piling noise mitigation, over-conservativelong, stiff, heavy pile design, pile tip buckling, internal & external corrosion, scourprotection and J-tubes, unplanned drilling/ re-driving, tilt and settlement.

6. The industry current push [Project PISA] to move to ~ 10 m dia., 1200 Tonne, 60 m +length monopiles in ~ 40 m WD may be questionable & should be challenged.


Main Conclusions: Grouted Connections

1. Discovery from late 2009 that > 70% of UK MPs failed, settled and cracked. This was asystemic design error over a long period.

2. Bolted flanges or other direct connections are possible. I f MP grouting is adopted use ofshear keys & robust grout seals is essential plus overlap length of at least 1.25 * D[Schaumann] . Indications from 2 major studies by Centrica/RES [Race Bank] and RWE[Gwent-Y-Mor] indicate that cost differential between bolted flanges and grout is minimal.

3. Developers are now (mid 2014) adopting:

none shear keyed conical [Anholt, London Array] ,

bolted flanges [Amrumbank, Humber Gateway] ,

retro-fitted bearings [Robin Rigg, Sheringham Shoal]retro-fitted bearings [Robin Rigg, Sheringham Shoal]

shear keyed with new elastomeric bearings [BELWIND] .

New single piece MP-TP [Achterduinen]

4. Full review of retro-fitted elastomeric bearings projects shows these should be robust andacceptable with condition monitoring and displacement measurement required for fulldesign life.

5. Questionable whether or not non shear keyed conical [ 1o-3o] sections and/or will remain“fully robust” for fatigue design lifetimes of 20+ years?

6. Questions regarding long term fatigue behaviour under high loading with water ingress?

7. Measurement, Monitoring and Mit igation for offshore structures is essential for long termdesign life O&M cost minimisation. The BELWIND project is state-of-the-art (Refs. 3 & 4)


References (1)1. Billington, C. (2012), “Failures of Large Diameter Grouted Connections in Monopile Supported Offshore Wind Farms and

implications for ISO 19902”, •OGP-BP Structural Reliability Conference 4 December 2012, p. 14.

http: / / info.ogp.org.uk/standards/1212London/Presentations/02-5bBillington.pdf

2. Billington, C. (2014), “Grouted Connections – What Can Be Learned From Previous R&D and the Monopile Failures to Helpthe Offshore Industry Design Reliable Connections?”. Offshore Engineering Society Presentation, Inst. Civil Engineers,London March 3rd 2014.

www.oes.org.uk/ recentmeetings.asp

www.ice.org.uk/ topics/energy/Recorded-lectures

3. Devriendt, C., Van Ingelgem, Y., De Sitter, G., De Wilde, D., Verlinden, K., Vanden Haute, C., Jan Jordaens, P. and Millis, S.(2013), “Foundation Monitoring Systems for Optimized O&M and Lifetime Assessment”, Proc. EWEA 2013, Ref. PO 0201,November 2013.

http: / /bruwind.eu/sites/default/ files/EWEAOffshore_2013_Poster_Christof_Devriendt.pdf

1.

http: / /bruwind.eu/sites/default/ files/EWEAOffshore_2013_Poster_Christof_Devriendt.pdf

4. De Sitter, G, Weijt jens, W., Van Ingelgem, Y., De Wilde, D., Verlinden, K., Millis, S., and Devriendt, C. (2014), “FoundationMonitoring Systems: Analysis of 2 Years of Monitoring at the North Sea”, Proc. EWEA 2014, Ref. PO 0266, March 2014.

http: / /proceedings.ewea.org/annual2014/conference/posters/PO_266_EWEApresentation2014.pdf

5. DNV. (2010). Summary Report from the JIP on the Capacity of Grouted Connections in Offshore Wind Turbine Structures.Norway: Det Norske Veritas.

6. DNV. (2011). Design of Offshore Wind Turbine Structures. Norway: DET NORSKE VERITAS AS, DNVOS-J101.

7. DNV. (2013). Certification of Grouted Connections for Offshore Wind Turbines. Norway: Det Norske Veritas, 04/12/2013.

8. Garnsey (2011), “The Future of Monopile Grouted Connections in Offshore Wind Farms – A Client’ s Perspective”, Proc.EWEA 2011, Amsterdam November 2011.

http: / /wiki-cleantech.com/wind-energy/ the-future-of-monopile-grouted-connections-a-clients-perspective

9. Golightly, C.R. (2014), “Tilt ing of Monopiles; Long, Heavy and Stiff; Pushed Beyond Their Limits”, Ground Engineering,January 2014, pp. 20 – 23.

www.nce.co.uk/Journals/2014/06/03/z/h/d/GE-January-2014-Tilt ing-of-monopiles-Golightly.pdf


References (2)10. Lochte-Holtgreven, S. (2013), “Zum Trag- und Ermüdungsverhalten Biegebeanspruchter Grouted Joints in Offshore-

Windenergieanlagen”, Schriftenreihe des Instituts für Stahlbau der Universität Hannover, Band 29, Univ. Hannover, Institutfür Stahlbau; 2013, VI I I ,247 S.

www.baufachinformation.de/buch/Zum-Trag-und-Ermüdungsverhalten-biegebeanspruchter-Grouted-Joints-in-Offshore-Windenergieanlagen/241371

11. LORC (2012), “Overcoming Problems With Crumbling Grout”, 31st October 2012.

www.lorc.dk/oceanwise-magazine/archive/2012-2/overcoming-problems-with-crumbling-grout

12. Lotsberg, I ., Serednicki, A., Oerlemans, R., Bertnes, H. and Lervik, A. (2013), “Capacity of Cylindrical Shaped GroutedConnections with Shear Keys in Offshore Structures”, The Structural Engineer, Vol. 91(Issue 1), January 2013, pp. 42 – 48.

www.istructe.org/ journal/ volumes/volume-91/ issues/ issue-1/articles/ research-capacity-of-cylindrical-shaped-grouted-co

13. Lohaus, A. and Anders, S. (2007), “High-cycle Fatigue of “Ultra-High Performance Concrete” and “Grouted Joints” for13. Lohaus, A. and Anders, S. (2007), “High-cycle Fatigue of “Ultra-High Performance Concrete” and “Grouted Joints” forOffshore Wind Energy Turbines”, Proc. Euromech Colloquium on Wind Energy, Springer-Verlag, 2007, pp. 309 – 312.

14. Lotsberg, I ., Serednicki, A., Oerlemans, R., Bertnes, H. and Lervik, A. (2012), “Design of Grouted Connections for MonopileOffshore Structures; Results from Two Joint Industry Projects”, General & Introductory Civil Engineering & Construction,John Wiley & Sons, DOI : 10.1002/stab.201201598.

15. Offshore WindBiz (2014), “Monopile Gripper Frame Fitted on Van Oord’ s Jack-Up”, 18th July 2014.

www.offshorewind.biz/2014/07/18/monopile-gripper-frame-fitted-on-van-oords-jack-up/

16. Schaumann, P.; Lochte-Holtgreven, S.; Bechtel, A. (2014), “Grouted Joints in Monopiles - Analyses and Discussion of EarlierDesign Approaches for Connections without Shear Keys: , Proc. Twenty-fourth (2014) International Ocean and PolarEngineering Conference, (ISOPE), Busan, Korea, June 15-20, 2014, pp. 47-54.

www.isope2014.org/docs/2014papers.pdf

17. Schaumann, P., Lochte-Holtgreven, S., Wilke, F. (2010), “Bending Tests on Grouted Joints for Monopile SupportStructures”, Proc. 10th German Wind Energy Conference DEWEK, 17th – 18th November 2010.


References (3)18. Schaumann, P., Wilke, F. and Lochte-Holtgreven, S.,. (2010), “Nonlinear Structural Dynamics of Offshore Wind Energy

Converters with Grouted Transition Piece”,

www.stahlbau.uni-hannover.de/170.html?&no_cache= 1&L= 1&tx_tkinstpersonen_pi1% 5BshowUid% 5D= 14&tx_tkinstpersonen_pi1% 5Bpublikationen% 5D= 1

19. Soerensen, E.V., Westhof, L.Yde,E., Serednicki, A. (2011), “Fatigue Life of High Performance Grout for Wind TurbineGrouted Connection in Wet or Dry Environment”, Proc. EWEA 2011, Amsterdam, November 2011, Ref. PO 178.

http: / / vbn.aau.dk/ files/58115513/Fatigue_Life_of_High_Performance_Grout_for_Wind_Turbine_Grouted_Connection_in_Wet_or_Dry_Environment.pdf

20. Van der Temple, J. (2011), “Slip Joint, Solving The Grout Problem” Proc. EWEA 2011, Amsterdam November 2011.

http: / /proceedings.ewea.org/offshore2011/programme/ info2.php?id2= 566&id= 104% 20&ordre= 1

21. Windpower Monthly (2010), “Offshore Monopile failure – A Solution May be In Sight”, 22nd June 2010.21. Windpower Monthly (2010), “Offshore Monopile failure – A Solution May be In Sight”, 22nd June 2010.

www.windpowermonthly.com/article/1011507/offshore-monopile-failure---solution-may-sight

22. Windpower Monthly (2010, “Be Prepared For New Technology Defects”, 1st November 2013.

www.windpoweroffshore.com/article/1217165/prepared-new-technology-defects

23. Wind Energy Update (2011), “Monopile Failures Put Grout in Doubt”, March 18 th 2011.

http: / / social.windenergyupdate.com/offshore/monopile-failures-put-grout-doubt

24. “Monopile Retrofits and Designs Going Forward: Room for Grout?”, April 11 th 2011.

http: / / social.windenergyupdate.com/offshore/monopile-retrofits-and-designs-going-forward-room-grout

25. Wind Energy Update (2012), “Monopile Worries Mount: Grouted Joint Doubts Linger”, April 10 th 2012.

http: / / social.windenergyupdate.com/ turbine-supply-chain/monopile-worries-mount-grouted-joint-doubts-linger

26. London High Court of Justice; Judgement Before: Mr. Justice Edwards-Stuart. Between : MT Højgaard a/s [Claimant] andE.ON Climate and Renewables UK Robin Rigg East and West Ltd. [Defendants] . November 2013. Queen’ s Bench Division;Technology and Construction Court. Neutral Citation Number: [2014] EWHC 1088 (TCC); Case No: HT-12-148.

www.bailii.org/ew/cases/EWHC/TCC/2014/1088.html


Contact Details

Dr. C.R. Golightly, BSc, MSc, PhD, MI CE, FGS .Geotechnical and Engineering Geology Consultant

Rue Marc Brison 10G, 1300 Limal, Belgium

Tel. + 32 10 41 95 25

Mobile: + 44 755 4612888

Email: [email protected]

skype: chrisgolightly

Linked In: linkedin.com/pub/5/4b5/469

Twitter: @CRGolightlyTwitter: @CRGolightlyAcademia.edu: https: / / independent.academia.edu/ChristopherGolightly

“You Pay for a Site Investigation - Whether Youdo One or Not” – Cole et al, 1991.

“ Ignore The Geology at Your Peril” – Prof. JohnBurland, Imperial College.
