Grouted vs Bolted Flange Connections 27102014-Libre

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Grouted Vs bolted flange connections, paper.

Transcript of Grouted vs Bolted Flange Connections 27102014-Libre

  • The Future For Monopile & Jacket Pile Connections Developer &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-fitted

    welded 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 important

    Bending 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.

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

  • History of Monopile Connections

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

  • DNV J101 Code and Shear Keys The two projects where grouted connections have not (yet?) failed included shear

    keys, 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, not

    The 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.

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

  • Adoption of High Strength Grouts Tried and tested appropriate underwater grouts were originally used to cement piles

    into 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 couldonly 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 of

    as 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.

    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

    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) Thesebelt-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).

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

  • Monopile Vs Tripod/ Jacket LoadingFor 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 pile

    groups [Borkum West 2] or:

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

    groups [Borkum West 2] or:2. Piles vibrated then conventionally driven through

    the 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 connections

    for 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 sol