OA10728A - Direct tendon to pile connection - Google Patents

Abstract

A foundation system is disclosed for securing the tendons of a TLP (8) to the ocean floor in which a plurality of piles are secured to the ocean floor (22) and a plurality of tendon receptacles (18) are secured to the piles (20) such that the load from tendons secured therein is transferred to the ocean floor through coaxially aligned load paths of tendon to tendon receptacle to pile to ocean floor. Other aspects of the present invention include an improved pile and a method of installing a TLP involving such a foundation system.

Description

1 010728

DIRECT TENDON ΤΟ PILE CONNECTION

The présent invention relates to deepwater platformfoundations. More particularly, it relates to a tension legplatform foundation anchored to the océan floor through a pluralityof piles.

As used herein, a "tension leg platform" or TLP refers to anybuoyant structure tethered to the océan floor through substantiallyvertical tendons tensioned to draw the buoyant structure below itsnormal floating draft. Various embodiments include a full scale TLPhaving full drilling facilities, a tension leg well platform("TLWP") having only a scaled down "completion" rig, a tension legwell jacket ("TLWJ") designed to accept well operations from anauxiliary vessel, or any other tendon deploying variation.

Tendons connect the buoyant hull to a foundation system at theocéan floor and are tensioned to draw the buoyant hull below itsnormal floating draft. The tendons transmit this static load to thefoundation System. Further, the tendons must transmit this staticload while subject to additional loads which hâve significantcyclical components driven by environmental forces of wind, wave andcurrent on the hull and tendons. The combined load is transmittedto the océan floor through the foundation system.

Some early designs for vertically moored platform conceptscontemplated using the same tubular members simultaneously for thetendons and for the risers through which drilling and productionoperations were to be conducted. However, this was found to beimpractical due to both operational constraints and the risks,difficulties, and expense of designing the tubular goods for theinternai pressure in these members as flowlines and the axial loadas moonng members .

The bottoms of the tendons are secured to a foundation systemat tendon receiving load connections cr tendon réceptacles. Intraditional practice, the foundation system is built around a 010728 - 2 - foundation template. The template is a framework whichpermanently interconnects the tendon réceptacles and thepile sleeves. Vertical (surface) access of tendons andpiles to tendon réceptacles and pile sleeves, respectively, is provided by a horizontal offset therebetween in their position on the template.

In the conventional practice, the foundation templateis placed and the piles are installed through the pilesleeves and set deeply into the sédiment at the océanfloor. The piles are then secured to the pile sleevesand the foundation template is ready to accept tendons.

The foundation template serves two purposes in such afoundation System. First, it provides spacing andmodular placement of the pile sleeves, the tendonréceptacles, and often a plurality of well guides.

Second, the template is a permanent fixture providingload bearing interconnection between piles anchored tothe océan floor and tendon réceptacles.

However, the tendon-to-receptacle, to-template (andover)-to pile sleeve, to-pile, to-ocean floor load pathof the conventional template based foundation System isan inefficient load transfer scheme. This also commits alarge quantity of Steel to the template and créâteshandling difficulties for transporting and deploying themassive template. Further, the latéral spacing betweenthe tendon réceptacles and the pile sleeves whichintroduces these inefficiencies also exacerbâtes thefatigue response of the template based foundation System. A plurality of smaller corner templates hâve beenused in designs which provide well guides outside of thetemplate as an alternative to a unitary template whichincludes well guides. This does reduce the materialrequirements, but does not alleviate the inefficienciesin load transfer discussed above. 3 010728 GB-A-2178101 and US-A-4907914 relate to TLP Systems.US-A-4540314 discloses a TLP foundation System accordingto the preamble of claim 1.

It is an object of the invention to provide animproved foundation System for securing a TLP hull to theocéan floor.

It is another object of the invention to provide animproved method of installing a TLP.

In accordance with the invention there is provided afoundation system for securing a TLP hull to the océanfloor, comprising a plurality of primary load bearingéléments, each load bearing element comprising a tendonconnected at its upper end to the TLP hull, a pilecomprising a tendon réceptacle receiving and securing thelower end of the tendon, and a pile member secured intothe océan floor and on its upper end being connected tothe tendon réceptacle, said tendon, tendon réceptacle,and pile member defining a coaxially aligned load pathfrom the TLP hull to the océan floor, the foundationsystem further comprising a guide template provided witha plurality of guide sleeves, each guide sleevesurrounding one of said piles, characterized in that theguide template includes spread members which providespacing between clusters of said sleeves.

In accordance with another aspect of the inventionthere is provided a method of installing a TLP, themethod comprising installing a plurality of piles intothe océan floor, providing tendon réceptacles on thepiles, and anchoring a plurality of tendons from the TLPto the océan floor through the tendon réceptacles suchthat the anchoring load paths from the TLP to the océanfloor are established in a plurality of vertical pathsextending in coaxial alignment from tendon-to-tendonreceptacle-to-pile, wherein installing a plurality ofpiles comprises placing a template on the océan floor and 5 010728 3a 10 placing piles in relative position to one another byinstalling the piles through sleeves provided on thetemplate, characterized in that the template is atemporary template including spread members which providespacing between clusters of said sleeves.

The invention will be more fully describedhereinafter with reference to the accompanying drawingsin which:

Figure IA is a side elevational view of a TLPdeploying one embodiment of a foundation System inaccordance with the présent invention;

Figure IB is a side elevational view of one of themembers of the foundation System of Figure IA;

MCS11/TH0219PC 4 019728

Figure 2A is a perspective view of installation of oneembodiment of the foundation system of the présent invention;

Figure 2B is a side elevational view of deployment of afoundation system in accordance with an alternate embodiment of theprésent invention;

Figure 3A is a partially cross-sectioned view of a pile havingan intégral tendon réceptacle in accordance with one embodiment ofthe présent invention;

Figure 3B is a partially cross-sectioned view of an alternateembodiment of a pile having a tendon réceptacle secured thereto;

Figure 3C is a partially cross-sectioned side view of a tendonréceptacle formed within a pile extension in accordance with analternate embodiment of the présent invention;

Figure 3D is a cross sectional view taken along line 3D-3D ofFigure 3C;

Figure 3E is a cross sectional view of an alternate connectionof a pile extension to a pile in accordance with an alternateembodiment of the présent invention;

Figure 4 is a partially cross sectionea view of a tendon aboutto engage a tendon réceptacle in accordance with one embodiment ofthe présent invention;

Figure 5 is a planar représentation of the guide surfacespresented annularly within the tendon réceptacle of Figure 4; and

Figure 6 is a partially cross-sectional view of anotherembodiment of the présent invention.

Figure IA generally illustrâtes a TLP 6 having buoyant bull 12ndmg on océan surface 14 and tethered m place about tendons 16secured to the foundation system 10 of the présent invention.Foundation system 10 mcludes tendon, réceptacles 18 mto which thebottom cf tendons 16 are secured and piles 20 which extend aeep mto·océan floor 22 .

Figure IB is a more detailed illustration of one of tendons 16latc'ned mto a tendon receiving load connection 12, here m the formof tendon réceptacle 18, providea on pile 20. In tnis embodiment,pile 20 combines an eior.gated cylindrical· member or pile member 28 010728 with an integrally formed tendon réceptacle 18. Elongated cylindrical member 28 extends deeply into sédiment 24 at océan floor22 to such a depth as which the skin friction between the sédimentand the exterior of the pile is competent to securely retain, withan adéquate margin of safety, the axial load of restraining buoyanthull 12 of TLP 8 in place and drawn below its natural buoyant draftthrough tendon 16. See Fig. IA.

Returning to Figure IB, foundation System 10 is shown to hâve aload path through the tendonto-tendon receptacle-to-pile which iscoaxial about axis 26 from the tendon to interaction with thesédiment at the océan floor. This alignment of tension réceptaclesand piles facilitâtes loading in tension without transmission as abending moment laterally over to a foundation template, and fromthere as a bending moment across a connection to a pile sleeve.

Figure 2A illustrâtes another embodiment of foundationsystem 10 on océan floor 22. In this embodiment, a light weight,temporary template 30 is deployed on the océan floor. This templatehas spread members 32 which provide spacing between clusters of pilesleeves 34. In this embodiment, temporary light weight template 30serves no continued structural purpose once piles 20 are spaced andit may be retrieved following pile installation.

Alternatively, the light weight template 30 may be left inplace to corrode under the natural exposure without worry or needfor cathodic protection. However, in yet another embodiment, sleevebracing 36 between piles in a cluster 38 may provide benefit asstructural members and pile sleeves 34 may be secured to piles 20such as by grouting or swaging operations. In this latterembodiment, the load path would still ordinarily be from the tendonto the tendon réceptacle, to the pile, coaxially. However,structurally interconnecting the piles withm each cluster providesassurance that the tendons of the cluster, e.g., at the corner of aTLP, distnbute the load in the event that the set of an individualpile to the océan floor shouid start to fail. Even so, spreadmembers 32 need serve only to secure spacing of the piles and that G 1 07 28 portion of the foundation template may be removed or sacrificed tocorrosion.

In this embodiment, fully assembled piles 20 are lowered intopile sleeves 34 one at a time, allowed to penetrate océan floor 22under their own weight to an initial set depth. A fluid driven pilehammer 40 then drives the pile into secure engagement with the océanfloor. In Figure 2A, pile 20A is illustrated being driven throughone of pile sleeves 34 by hydraulic pile hammer 40 actuated througha hydraulic line 42. Vertical blows to a load or drive surface atthe top of the pile drives the lower end of the pile deeper anddeeper into the sédiment. Underwater hammer 40 is removed after thepile has been driven to design depth. At this point, the pile willaccept a tension load, but the pile will continue to "set" over aperiod of time following installation during which period the loadbearing capacity of the pile increases as the sédiment compactsabout the pile.

It is common in the art to refer to driving piles "te refusai"at which point the skin friction and pénétration résistancediminishes the rate of pénétration. However, the "refusai” isdiminished pénétration, advance is not totally stopped, and itremains practical in many applications to design for horizontalalignment of the tops of piles 20. For instance, the tendonréceptacles 18 are formed integrallv with piles 20 in Figure 2A. Inthis embodiment it is preferred for tendon réceptacles 16 to bepresented m a single horizontal plane and this can be achievecthrough careful driving operations.

Figure 2B discloses an alternate method of freestandir.g pileinstallation in which no template is deployed, temporarily crotherwise. In this templateless practice of the présent invention,pile 203 is lowered on cable 40 from a crâne or draw Works on thesurface. The bottom of pile 20S reaches océan floor 22 to setdownand pénétrâtes the first interval of the sédiment, driven by theweight of the pile itself as alignment and position continue to becontrolied through the cable. Acoustic or other reference aids areused te secure position for tcuchdown. However, careful cable 7 710728 control remains very important for the advancing pile throughout theinitial interval such that the rate of feed does not exceed the rateof pénétration. The setdown and orientation thus controlled by rateof feed is the only guiding mechanism absent the benefit of atemplate secured pile sleeve.

The pile becomes self supporting after an initial interval andit is no longer necessary to maintain alignment of pile 20B withcable 40. The pile is then self guiding through the second intervalto "refusai" at the full depth of self pénétration. Cable 40 isreleased from its connection to the pile and a pile hammer is thendeployed in the same manner as for Figure 2A, discussed above, tocontinue driving pile 20B to a secure depth competent to restrainthe tendon loads. Pile deployment designs for a large scale TLP forselected seabed sédiments in the Gulf of Mexico were recentlycalculated based on a 84 inch diameter, 1.125 to 1.75 inch wallthickness pile and found to be self-supporting in 50-60 feet andself penetrating to 100-120 feet of a total 355 foot drive depth.

Figures 3A-3E illustrate a sampling of embodiments of theprésent invention. These are each illustrated with guide surfaces50 inside tendon réceptacles 18 suitable to cooperate with arotating lug tendon anchor assembly 52 (see Figure 4). However,those having ordinary skill in the art will appreciate that anynumber of hydraulic or mechanical latching mechanisms or otherconnection Systems may be used in the practice of the présentinvention.

Figure 3A illustrâtes an embodiment of pile 20 m which tendonréceptacle 18 is formed mtegraliy with eionqated cylindricai member26. Here the upper end of pile 20 mcludes a drive head 70, a icadring 72, a réceptacle body Ί 4 and a transition section 76. Thedrive head accepts an externally mounted underwater hammer andprésents anve surface 78 through which hammer blows are deliveredte drive the pile. It is preferred that the walls of drive head 70be thickened to protect agamst deformation during driving operations. Réceptacle body 74 is also strengthened with a thicker wall in this embodiment transmit the force of the hammer while 8 010728 protecting the dimensional intsgrity of guide surfaces 50 and protecting against métal fatigue. Transition section 76 reduces stress concentration in narrowing this wall thickness to that of elongated cylindrical member 28.

The embodiment illustrated in Figure 3B is configured to accept · an internally deployed underwater hammer. Funnel guide 80 willguide réception of the pile hammer for pile installation and later,the end of the tendon at a tendon anchor assembly. See Figure 5.

Returning to Figure 3B, drive surface 78 is provided in the form ofload shoulder 78B and is positioned below réceptacle body 74. Thisallows the direct force of the hammer blows to bypass the tendonload connection. In this illustration, transition section 76 oftendon réceptacle 18 bridges a significant différence in diametersbetween réceptacle body 74 and elongated cylindrical member or pilemember 28.

Figure 3C illustrâtes an embodiment in which piles are set bydrill and grout operations and tendon réceptacle 18 is provided as apile extension 18C. Pile and yrout operations use a jet assembly tostart a borehole, then use drilling operations to complété theinterval into which the pile is placed. Grout 81 is then injectedinto the annular space 82 between the pile and the borehole, e.g. bycirculating down the borehole and returning up the annulus.

Alternatively, the borehole may be filled with grout before the pileis inserted. The pile is secure after the grout sets. Those havingordinary skill in the art will appreciate that other bonding andsetting agents may be used in place of conventional grout.

In this illustration, pile extension 16C telescopicly engagesthe top of elongated cylindrical member 28, here pile member 2-8C.

This sleeve or overlapping annular région 84 is grouted to secure aconnection 85 of the pile extension 'to the elongated cylindricalmember. Further, the structural mtegrity of the connection isenhanced by usmg a plurality of interspaced rails 86 pro j ectmginto the grouted overlapping annular space 84. See Figure 3D.

Figure 3E illustrâtes another connection 85 of pile extension18C to pile member 28. In this example the top of the pile member 9 010728 is swaged out into one or more annular rings 88 presented on theinterior of the pile extension 18C. This swaging operation may beaccomplished by packing off the inside of pile member 28 adjacentthe annular rings and using hydraulic pressure denoted by arrow "p"or by mechanical swaging tools to cause the pile member to plasticlydeform into ring 88.

Alternatively, the pile extension may be configured forréception within pile member 28 and connected through analogousgrouting or swaging operations. Other methods for connecting a pileextension to a pile member either before or after the pile memberhas been installed are available to those having ordinary skill inthe art who are provided with the teachings of the présentdisclosure. These may also vary depending upon whether the pile isdriven or drilled and grouted.

The use of pile extensions also provides an opportunity forrehabilitating a pile having an integrally formed tendon réceptaclethat was damaged in installation. The damaged réceptacle may be eutoff, removed and replaced with a pile extension presenting a newtendon réceptacle.

Figures 4 and 5 illustrate one system for connecting the bottomof tendon 16 to a tendon réceptacle 18. Such a connection isdisclosed in detail in U.S. patent 4,943,188, the disclosure ofwhich is hereby fully incorporated and made a part hereof byreference. This type of connection uses guides 50 within tendonréceptacle 18 to guide the rotation of rotating lug anchorconnector 52.

In this embodiment, the lower extension of tendon 16 isprovided with a rotating lug anchor connector 52. The anchorconnector provides a plurality of spaced lugs 54 on a load ring 56.The load ring is allowed to rotate freely about retaining ring 58. Alimited degree of freedom for pivotai rotation is provided in theconnection between tendon 16 and tendon réceptacle 18 in theembodiment of Figure 4 by an elastomeric member 60 that connectsretaining ring 58 to a load shoulder 62 on the base of tendon 16. 10 010728

The latch sequence for connecting tendon 16 to the tendonréceptacle 18 begins with lowering rotating lug anchor connector 52into the tendon réceptacle. Actuating lugs 64 carried on the anchorconnector engage guides 50 within tendon réceptacle 18. Thisinitial stab-in causes a rotation of the rotating lug anchorconnector 52 such that lugs 54 on load ring 56 pass between lugs 66on load ring 72 within tendon réceptacle 18.

Figure 5 is an illustration of the path of one of actuationlugs 64 interacting with guides 50 in a figure that has been"flattened-out" to a planar view for simplification. The initialstab is illustrated by path 100. Pulling the tendon upward causesrotation of connector 52 as actuation lugs 64 travel a courseillustrated as path 102. This brings lugs 54 into alignment withlugs 66 and securely engages anchor connector 52 of the tendonwithin tendon réceptacle 18.

If necessary, this engagement may be released by a second dowr.and up stroke on tendon 16. This course is illustrated by paths 104and 106 which will rotate the lugs out of alignment and permitrelease of the tendon.

Figure 6 illustrâtes another embodiment which provides for arigid tendon anchor to tendon réceptacle engagement at tendon loadconnection 17. In this illustration, tendon 16 terminâtes in athreaded tendon anchor 17A which threadingly engages tendonréceptacle 18 in threaded région 17B below drive head 70 of pile 20.The necessary degree of freedom for rotation is accommodated byelastic flexure at stress joint 92 m pile 20. Alternative.y, rigidtendon load connection 17 might by provided by one or more rotatinglug rings on the bottom of a tendon without an elastomericflex-eiement.

Other modifications, changes and substitutions are mtended mthe foregomg disclosure and in some instances some features will beemployed without a corresponding use of other features.

Accordmgly, it is appropriate that the appended ciaims be ccnstruedbroadly and m a manner consistent with the spint and scope of theinvention herein.

Claims (9)

11 1 0 728 ΤΗ 0219 PCT C. L.A.I

1. A foundation System for securing a TLP hull to theocéan floor, comprising a plurality of primary loadbearing éléments, each load bearing element comprising atendon connected at its upper end to the TLP hull, a pilecomprising a tendon réceptacle receiving and securing thelower end of the tendon, and a pile member secured intothe océan floor and on its upper end being connected tothe tendon réceptacle, said tendon, tendon réceptacle,and pile member defining a coaxially aligned load pathfrom the TLP hull to the océan floor, the foundationSystem further comprising a guide template provided witha plurality of guide sleeves, each guide sleevesurrounding one of said piles, characterized in tnat theguide template includes spread members which providespacing between clusters of said sleeves.

2. The foundation System of claim 1 wherein the tendonréceptacle is formed integrally with the pile member.

3. The foundation System of claim 1 wherein the tendonréceptacle is attached to the pile member as a separateassembly.

4. The foundation system of any of daims 1-3 furthercomprising an angular rotation system adjacent theconnection of the lower end of the tendon to the tendonréceptacle.

5. The foundation system of claim 4, wherein the angularrotation system includes an elastomeric flex-joint withinthe connection of the tendon to the tendon réceptacle.

6. The foundation system in accordance with claim 4,wherein the connection of the tendon to the tendonréceptacle is rigid and angular rotation is provided by astress joint on the lower end of the tendon. c10728 - 12 -

7. A method of installing a TLP, the method comprisinginstalling a plurality of piles into the océan floor,providing tendon réceptacles on the piles, and anchoringa plurality of tendons from the TLP to the océan floor 5 through the tendon réceptacles such that the anchoring load paths from the TLP to the océan floor areestablished in a plurality of vertical paths extending incoaxial alignment from tendon-to-tendon réceptacle-to-pile, wherein installing a plurality of piles comprises 10 placing a template on the océan floor and placing piles in relative position to one another by installing thepiles through sleeves provided on the template,characterized in that the template is a temporarytemplate including spread members which provide spacing 15 between clusters of said sleeves.

8. The method of claim 7 further comprising retrievingthe temporary template after the piles are installed andbefore the tendons are anchored.

9. The method of claim 7 further comprising leaving the 20 temporary template in place without structurally interconnecting the piles to the pile sleeves. MCS11/TH0219PC