Connecting sections of split jacket structures

Abstract

A split jacket structure is installed offshore by lowering an upper jacket section onto a pre-installed lower jacket section, with coaxially-aligned legs of the respective jacket sections in mutual abutment about an interface. A grout pin positioned within tubular 5 walls of the abutting legs extends across the interface. Grippers disposed above and below the interface extend across an annulus between the pin and the tubular walls to effect engagement between the pin and the abutting legs. Grout is then injected into the annulus through the grout pin. The grippers are actuated and the grout is supplied to the pin from topside via lines that extend within the leg of the upper jacket section beside a lifting wire that suspends the pin and lowers the pin onto a stop formation in the lower jacket section. The stop formation aligns guide formations of the pin with centralising flanges in the abutting legs.

Description

[0001] Connecting sections of split jacket structures

[0002] This invention relates to jacket structures used as foundations to fix offshore installations, such as wind turbines or platforms, to the seabed. The invention relates particularly to split jackets comprising upper and lower sections, and to the challenges of connecting together those sections during installation offshore.

[0003] Jackets typically comprise a lattice frame of upright legs that are connected together by braces and nodes. Most jackets have three or four legs that converge upwardly in a frusto-pyramidal arrangement. However, some jackets have more legs; also, the legs can instead be in parallel or other relation.

[0004] Jackets are used widely to fix offshore installations relative to the seabed. Most commonly, such installations feature in the subsea oil and gas industry, such as hydrocarbon production platforms, and in the renewable energy industry, such as wind turbines and other components of an offshore wind farm. Jackets are being used increasingly for the latter application, particularly where there is a need to install bottom- fixed wind turbines in water that is too deep for conventional monopile foundations but too shallow to justify the higher cost of a floating wind turbine solution.

[0005] As bottom-fixed offshore wind moves into ever deeper waters, it becomes more challenging to design economically-viable foundation structures that can be fabricated, transported and installed successfully. For example, to date, the deepest jacket foundation for fixed offshore wind has been installed in a water depth of little more than 50m.

[0006] Installing a monolithic jacket in much deeper water would require an exceptionally large and expensive installation vessel such as a heavy-lift floating crane. Such vessels have only limited availability, especially to perform multiple lifts over the lengthy period required to construct an offshore wind farm comprising numerous turbines.

[0007] Consequently, it has been proposed to split a deep-water jacket foundation into upper and lower sections that can be installed in separate lifts and stacked in the water column using relatively small, readily-available installation vessels.

[0008] Connecting two or more parts of a subsea foundation and grouting the connections has long been proposed in the art. For example, legs of jackets are commonly connected to seabed foundations, such as piles, by grouting as exemplified in CN 113897967, CN 113356263 and US 5445476. In the case of US 4184790, inflatable packers are also included to create a seal against the pile and the jacket legs. GB 2548965 discloses a similar type of expandable gripping configuration to secure a jacket leg to a seafastening socket to allow the injection of cement or another curable substance. US 2023 / 313481 discloses an alternative apparatus to fix a jacket leg to a pile, comprising various grippers including hydraulic pistons to control the horizontality and verticality of the jacket leg within the pile.

[0009] In US 5445476, legs of a jack-up rig can be lowered onto and docked to a jacket base. The jacket base is fixed to the seabed by grouted piles and so is analogous to the lower section of a split jacket whereas the jack-up rig is analogous to the upper section of a split jacket. Feet of the jack-up rig land on upwardly-facing support interfaces of the jacket base. However, the resulting connection between the jack-up rig and the jacket base is merely temporary, being effected largely by gravity loads acting on the jack-up rig after its hull has been lifted clear of the water.

[0010] US 4854779 and EP 2769024 disclose split jackets in which legs of the upper section are aligned coaxially with and connected to corresponding legs of the lower section. The legs of the upper section therefore abut end-to-end with the legs of the lower section. Pins within the legs extend across the abutting joints between the upper and lower sections. The pins are then grouted in place to connect the upper and lower sections permanently.

[0011] Another proposal for effecting a grouted connection between upper and lower jacket sections is shown in Figure 1. Here, a split jacket 10 comprises upper and lower sections 12, 14 each comprising upwardly-convergent inclined legs 16 connected by braces 18. The upper and lower sections 12, 14 are joined by vertical stab-in connectors. Specifically, as shown in the circled detail, the legs 16 of the upper section 12 terminate in downwardly-extending spigots 20 that are received telescopically in upwardly-opening tubular sockets 22 atop the legs 16 of the lower section 14.

[0012] The spigots 20 and the sockets 22 must extend along a common vertical axis so that the stab-in connection can be effected by downward vertical movement of the upper section 12 onto the previously-installed lower section 14. This requires the conjoined legs 16 to have a vertically-extending kink 24 between their inclined major portions. Such kinks 24 are undesirable because they introduce a local moment and increase shear at the interface between the upper and lower sections 12, 14. This is onerous for the design of both the jacket 10 and the grouted connection.

[0013] Another drawback of vertical stab-in connectors is that they may require a double Y- joint arrangement between the legs 16 and the braces 18, which increases shear loads in the grouted connection in comparison with a more desirable K-joint. Handling the increased shear loads requires the spigots 20 and the sockets 22 to be lengthened to increase their overlap area.

[0014] In more remote prior art, US 4804018 discloses internal plugs that can be grouted in place to enable a tubular structure to be deballasted for refloating.

[0015] In principle, variations on a grouted connection are available as well as options to use mechanical or friction-based connections, including traditional connection methods such as bolting or swaging.

[0016] Despite these various prior art proposals, connecting together upper and lower jacket sections is a significant design and operational challenge when performed offshore with the interface between the sections disposed underwater. Among the challenges suffered by the prior art is how to hold the upper and lower jacket sections in fixed relation, when subjected to ocean dynamics, until all of the grouted joints are complete and the grout has cured.

[0017] To date, splitting a jacket structure and installing it in two separate deployment lifts has not yet been performed at scale on an offshore wind farm project. So, there is no field proven, fully certified solution in widespread use within the offshore wind sector at the time of writing. The need remains for a cost-effective, permanent connection system for a split jacket that uses field proven methods and minimises adverse effects on jacket design.

[0018] Against this background, the invention resides in a method of installing a split jacket offshore. The method comprises: lowering an upper jacket section onto a pre-installed lower jacket section; uniting coaxially-aligned legs of the respective jacket sections in mutual abutment about an interface; positioning a pin within tubular walls of the abutting legs, the pin extending across the interface; engaging the pin with the abutting legs by extending grippers across an annulus defined between the pin and the tubular walls, the grippers being disposed above and below the interface; and injecting grout into the annulus, that grout optionally embedding the grippers in the annulus. A grout seal can be extended across the annulus before injecting the grout.

[0019] The grippers and / or the grout seal may be extended from the pin toward the tubular walls and / or vice versa. Conveniently, the grippers can be extended with actuating energy supplied to the pin along an actuation line that extends within and along the leg of the upper jacket section. In that case, the actuating energy can be supplied to the actuation line from a power unit that is supported by a topside work platform of the upper jacket section. Subsequently, the power unit can be disconnected from the actuation line and removed from the work platform, optionally leaving behind the actuation line in the leg of the upper jacket section.

[0020] Elegantly, grout can be injected into the annulus via the pin, preferably from a bottom end of the pin. Grout can be supplied to the pin along a grout line that extends within and along the leg of the upper jacket section, for example from a grout spread that is supported by the topside work platform of the upper jacket section. Subsequently, the grout spread can be disconnected from the grout line and removed from the work platform, optionally also leaving behind the grout line in the leg of the upper jacket section.

[0021] The pin can be positioned by lowering the pin from within a leg of the upper jacket section until a lower portion of the pin is received within a leg of the lower jacket section. For example, the pin can be lowered onto a stop formation within the leg of the lower jacket section, which may conveniently align guide formations of the pin with centralising flanges within the respective legs of the upper and lower jacket sections. The stop formation can also be used to limit migration of the grout along the leg of the lower jacket section.

[0022] The pin can be suspended from a lifting wire that extends within and along the leg of the upper jacket section, whereby the pin can be lifted into that leg before the upper jacket section is lowered, preferably before the upper jacket section is transported to an installation site. An upper bearing flange, extending radially from the leg of the upper jacket section, can be lowered into a bucket atop the leg of the lower jacket section, the bucket comprising an upwardly-flared guide surrounding a lower bearing flange that extends radially from the leg of the lower jacket section. Lateral movement of the upper bearing flange can then be restrained within a side wall disposed between the guide and the lower bearing flange. The method may also, or instead, involve resisting lateral moment of the upper jacket section relative to the lower jacket section up an incline of the interface relative to a horizontal plane.

[0023] Correspondingly, the inventive concept embraces a split jacket structure that can be assembled in accordance with the method of the invention. The structure comprises: upper and lower jacket sections that have coaxially-aligned legs in mutual abutment about an interface; a pin positioned within tubular walls of the abutting legs, the pin extending across the interface; grippers disposed above and below the interface, the grippers being extensible across an annulus defined between the pin and the tubular walls to engage the pin with the abutting legs; and a grout path communicating with the annulus, which path preferably extends through the pin and may include at least one injection port at a bottom end of the pin. A grout seal may be extensible across the annulus. The structure may further include grout in the annulus, which grout can embed the grippers.

[0024] The grippers are suitably extensible from a body of the pin toward the tubular walls.

[0025] An actuation line extending within and along the leg of the upper jacket section can be configured to convey actuating energy to the grippers from a power unit disposed outside that leg. Similarly, a grout line extending within and along the leg of the upper jacket section can be configured to convey grout to the pin from a grout spread disposed outside that leg.

[0026] The pin may be deployable by being lowered from within a leg of the upper jacket section until a lower portion of the pin is received within a leg of the lower jacket section. The leg of the lower jacket section may contain a stop formation that is cooperable with the pin. In that case, centralising flanges within the respective legs of the upper and lower jacket sections can align with respective guide formations of the pin when the pin abuts the stop formation. The structure may comprise a bucket atop the leg of the lower jacket section, the bucket comprising an upwardly-flared guide at least partially surrounding a lower bearing flange extending radially from the leg of the lower jacket section. A side wall disposed between the guide and the lower bearing flange can at least partially surround the lower bearing flange.

[0027] The interface is preferably inclined relative to a horizontal plane. In that case, the upper and lower jacket sections may each comprise two or more legs whose interfaces are inclined upwardly and outwardly in mutual opposition.

[0028] The inventive concept also embraces a grout pin for grouting a joint between an upper jacket section and a lower jacket section of a split jacket structure. The grout pin comprises: an elongate body; circumferential arrays of grippers that are extensible radially from the body, the arrays being spaced apart longitudinally along the body; and a grout path extending through the body that may, for example, communicate with at least one injection port in an end of the body.

[0029] At least one circumferential seal may be extensible radially from the body. The grout pin may also comprise centralising guides that protrude radially and optionally also longitudinally from the body. A lifting point may be provided at an end of the body that is uppermost in use.

[0030] The proposed split connection solution of the invention employs pins that are preinstalled in the legs of an upper jacket section prior to load-out. Following installation of the upper jacket section onto a lower jacket section offshore, each pin is lowered down the conjoined jacket legs into a position straddling the joint or interface between them. The pin is then is grouted in place via grout lines that extend up the legs of the upper section to a topside work platform. Temporary restraint during the grout curing process is provided by inflatable grippers that extend radially from the pins to conform to the bore of the jacket legs.

[0031] The internal grouted pin arrangement of the invention minimises the negative impact on the design of a split jacket versus an equivalent standard monolithic jacket. The ability to maintain, virtually, a conventional jacket K-joint bracing arrangement at the interface between upper and lower jacket sections minimises critical shear loading of the grouted connection. This results in a smaller pin requirement than in an alternative vertical grouted stab-in design approach like that shown in Figure 1.

[0032] More generally, the arrangement of the invention minimises onerous effects on jacket design, primarily an increase in weight, and provides a solution with a high level of technology readiness that can be implemented immediately. In particular, the invention adapts existing field-proven techniques and technology to propose a simple design whose structural characteristics are easy to verify, hence providing a solution that would require only minimal testing to be approved by a developer or a certifying body.

[0033] Embodiments of the invention implement a method for assembling two sections of a subsea jacket, the method comprising: providing a first section of a subsea jacket, the first section comprising at least one internal stopper inside a leg; inserting a bottom section of a grout pin inside the leg comprising the stopper until it abuts on the stopper; inserting an upper section of the grout pin inside a leg of the second section of the subsea jacket to couple the two sections of the subsea jacket together; and injecting grout in the volume between the grout pin and the walls of the legs of the two subsea jackets sections.

[0034] The method may also comprise retaining the grout pin inside the leg of the second section of the subsea jacket while mounting the second section on the first section, and releasing the grout pin to lower it into the leg of the first section. The grout pin may, for example, be retained by a winch.

[0035] The grout pin may comprise inflatable seals to delimit the grout volume. The stopper may also comprise a seal.

[0036] The first section may comprise a guide, for example with the shape of a funnel or bucket, to align the legs of the second section with and on the legs of the first section. The guide may be coupled with a flange that effects connection between the legs of the sections.

[0037] Embodiments of the invention also provide a grouting pin to align and connect two sections of a subsea jacket, the grouting pin comprising: guiding devices; grippers; and at least one inflatable seal. The pin may also comprise a grout injection path. The guiding devices may comprise an upper guide and a lower guide, one at each end of the pin. The guiding devices may also comprises radial fins.

[0038] The grouting pin may further comprise external shear keys that can engage internal shear keys inside the tubular legs of the jacket sections.

[0039] In summary, a split jacket structure of the invention is installed offshore by lowering an upper jacket section onto a pre-installed lower jacket section, with coaxially-aligned legs of the respective jacket sections in mutual abutment about an interface. A grout pin positioned within tubular walls of the abutting legs extends across the interface.

[0040] Grippers disposed above and below the interface extend across an annulus between the pin and the tubular walls to effect engagement between the pin and the abutting legs. Grout is then injected into the annulus through the grout pin.

[0041] The grippers are actuated and the grout is supplied to the pin from topside via lines that extend within the leg of the upper jacket section beside a lifting wire that suspends the pin and lowers the pin onto a stop formation in the lower jacket section. The stop formation aligns guide formations of the pin with centralising flanges in the abutting legs.

[0042] To illustrate an example of the prior art, reference has already been made to Figure 1 of the drawings, which is a perspective view of a split jacket whose sections are joined by vertical stab connectors.

[0043] In order that the invention can be more readily understood, reference will now be made, by way of example, to the remainder of the accompanying drawings in which:

[0044] Figure 2 is a sectional side view of a split jacket of the invention comprising upper and lower sections;

[0045] Figure 3 is an enlarged sectional view of Detail III in Figure 2, showing a grout pin of the invention disposed between abutting legs of the jacket sections;

[0046] Figure 4 is a perspective view of the grout pin shown in Figure 3;

[0047] Figure 5 is a side view of the grout pin shown in Figure 4; Figure 6 is an enlarged side view of Detail VI in Figure 5;

[0048] Figure 7 is an enlarged side view of Detail VII in Figure 5;

[0049] Figure 8 is a sectional side view of a leg of an upper jacket section;

[0050] Figure 9 is an enlarged sectional view of Detail IX in Figure 8;

[0051] Figure 10 is an enlarged sectional view of Detail X in Figure 8;

[0052] Figure 11 is a sectional side view of a leg of a lower jacket section;

[0053] Figure 12 is an enlarged perspective view of an upper end of the leg shown in Figure 11 ;

[0054] Figure 13 is an enlarged sectional view of Detail XIII in Figure 11 ;

[0055] Figure 14 is a perspective view of an upper end of the lower jacket section;

[0056] Figures 15a and 15b are perspective views showing the grout pins being inserted into respective legs of the upper jacket section;

[0057] Figure 16 is an enlarged perspective view of a topside work platform at an upper end of the upper jacket section;

[0058] Figure 17 is a side view of the lower jacket section installed on the seabed;

[0059] Figure 18 is a side view of the upper jacket section being installed atop the previously installed lower jacket section;

[0060] Figure 19 is an enlarged sectional perspective view of a leg of the upper jacket section being guided, during installation, into coaxial alignment with a corresponding leg of the lower jacket section; Figure 20 is an enlarged perspective view corresponding to Figure 19 but showing the leg of the upper jacket section now abutting, and in coaxial alignment with, the corresponding leg of the lower jacket section;

[0061] Figure 21 is a sectional side view corresponding to Figure 20;

[0062] Figures 22a and 22b are sectional side views showing a grout pin within a leg of the upper jacket section being lowered into engagement with the conjoined leg of the lower jacket section;

[0063] Figure 23 corresponds to Figure 16 but shows the topside work platform supporting a grout spread for grouting and a hydraulic power unit for gripper extension;

[0064] Figure 24 is a perspective view of grippers of a grout pin engaging the surrounding tubular wall of a leg;

[0065] Figure 25 is a perspective view of a lower end of a grout pin;

[0066] Figure 26 corresponds to Figure 24 but shows grout injected into the annulus between the grout pin and the surrounding wall of the leg;

[0067] Figures 27a and 27b show the grout spread and hydraulic power unit of Figure 23 being recovered from the topside work platform to an installation vessel;

[0068] Figure 28 is a cut-away perspective view of an optional grout seal; and

[0069] Figure 29 is a sectional side view of a variant of the grout seal of Figure 28.

[0070] Referring next, then, to Figure 2 of the drawings, a split jacket 10 again comprises upper and lower sections 12, 14 each having upwardly-convergent tubular legs 16 or chord members connected by braces 18. Unlike the prior art proposal shown in Figure 1, however, the legs 16 of the upper and lower sections 12, 14 are in coaxial alignment with no vertical kink between them, hence avoiding a local moment and consequential shear loads at their mutually-abutting interface 26. In other words, there is a consistent batter angle at the interface 26 between the legs 16 of the upper and lower sections 12, 14.

[0071] In this instance, the jacket 10 is shown installed at an offshore location with the lower end of the lower section 14 fixed to the seabed 28 by conventional foundations 30 such as suction piles. The upper section 12 extends above the surface 32 and is surmounted by a work platform 34 that, conventionally, surrounds a tubular transition piece 36 for supporting the mast of a wind turbine (not shown).

[0072] The upper section 12 is lowered onto and connected to the pre-installed lower section 14. As the interface 26 between the upper and lower sections 12, 14 is in the water column beneath the surface 32, the connection between them must be effected underwater and preferably remotely from topside power, control and grout supply.

[0073] Figure 3, corresponding to Detail III of Figure 2, shows the abutting legs 16 of the upper and lower sections 12, 14 aligned on a common central longitudinal axis 38 that, in this example, is inclined to the vertical. The facing ends of the legs 16 terminate in bearing flange plates 40 that abut across the interface 26. In this example, the flange plates 40 lie in parallel planes that are orthogonal to the central axis 38.

[0074] The flange plate 40 of the upper section 12 is guided into coupling alignment with the flange plate 40 of the lower section 14 by a bucket formation comprising an upwardly- flared part-conical guide 42 that embraces the flange plate 40 atop the leg 16 of the lower section 14. As best appreciated in the enlarged views of Figures 11 and 12, a side wall 44 joins the guide 42 to the flange plate 40 of the lower section 14. The guide 42 could remain in place permanently after installation of the upper section 12 or could be in place only temporarily, being removed after installation of the upper section 12.

[0075] The abutting legs 16 of the upper and lower sections 12, 14 are joined together by a coaxial grout pin 46 that extends along the axis 38 within the common lumen or bore of the legs 16. The grout pin 46 is shown in isolation in Figure 4 and in more detail in Figures 5 to 7.

[0076] When deployed, the grout pin 46 straddles or bridges across the interface 26 between the upper and lower sections 12, 14. The grout pin 46 is spaced radially from the surrounding tubular wall of the conjoined legs 16 to leave a narrow gap in the form of an annulus between the grout pin 46 and that wall. Eventually, as will be explained, that annular gap receives grout injected through the grout pin 46.

[0077] Despite the annular gap, the grout pin 46 engages the respective legs 16 to hold them in fixed relation before grout is injected and cured. As will be explained, engagement between the grout pin 46 and the legs 16 is effected in various ways but principally by radial extension of integrated grippers 48 from the grout pin 46 and then by injection of grout into the annulus between the grout pin 46 and the surrounding tubular wall of the legs 16. When extended, the grippers 48 mainly resist tensile loads to ensure stability temporarily while the grout cures. Thereafter, the cured grout in the annulus completes a permanent connection between the legs 16 via the grout pin 46.

[0078] While the grout cures, lateral stability is also assured by frictional resistance arising from the dead weight of the upper section 12 acting on the abutting flange plates 40. Further, the angle of the flange plates 40, and hence of the interface 26, relative to the horizontal creates a ramp effect that provides additional resistance to lateral movement of the upper section 12 relative to the lower section 14. Further lateral resistance may be provided by the side wall 44 that joins the flared guide 42 to the flange plate 40 of the lower section 14, depending upon the lateral clearance between the side wall 44 and the outer edge of the flange plate 40 of the upper section 12.

[0079] Torsional loads in the legs 16 will be negligible in sea states that are anticipated during a grout curing period. Compressive loads are of course substantial but the arrangement of the legs 16 and abutting flange plates 40 provides a compressive load path from the upper section 12 to the lower section 14. This is analogous to how compressive loads are transferred along the legs of a conventional monolithic jacket.

[0080] By minimising shear and transferring compressive loads through the legs 16 of the jacket 10, the arrangement of the invention minimises loading on the grouted connection. This means that the grout pin 46 can be usefully shorter than the vertical stab-in spigot of the kinked jacket shown in Figure 1.

[0081] A further advantage of the arrangement shown in Figures 2 and 3 is that it minimises spacing around the interface 26 between joints that connect successive braces 18 to the legs 16. This allows a K-joint arrangement to be maintained, which also minimises shear loads on the grouted connection and so further minimises the length of the grout pin 46.

[0082] Turning next to Figures 4 to 7, these drawings show the grout pin 46 in detail. The grout pin 46 has a body 50 that is generally cylindrical, elongate and of uniform circular section along its length, hence being rotationally symmetrical about a central longitudinal axis 52. However, upper and lower guide formations 54 extend from the respective end portions of the body 50.

[0083] Each guide formation 54 comprises a main guide defined by plates 56 in a cruciform arrangement, extending parallel to and intersecting orthogonally on the central longitudinal axis of the body 50. The plates 56 extend longitudinally and radially beyond the ends and sides of the body. Thus, the sides of the plates 56 define longitudinally- extending guide fins that project radially from the sides of the body 50.

[0084] At an upper end, the grout pin 46 comprises a lift point 58 from which the grout pin 46 can be hung within a respective leg 16 of the jacket 10, as will be explained. Conveniently, as in this example, the lift point 58 comprises a shackle that is attached to one of the plates 56 of the upper guide formation 54.

[0085] Each guide formation 54 further comprises intermediate guide fins 60 that are disposed angularly between the plates 56 and also extend longitudinally. The guide fins of the plates 56 and the intermediate guide fins 60 have chamfered upper and lower edges that cooperate in a frusto-conical arrangement to form respective alignment surfaces.

[0086] Upper and lower arrays of the grippers 48 are disposed longitudinally inboard of the respective guide formations 54. The grippers 48 of each array are distributed angularly around the circumference of the grout pin 46. The grippers 48 can be extended radially beyond the width of the body 50, for example by inflation with hydraulic fluid or a gas.

[0087] An optional grout seal 62 is disposed longitudinally inboard of, hence beneath, the upper arrays of grippers 48 and encircles the body 50 of the grout pin 46. Like the grippers 48, the grout seal 62 can be extended radially beyond the width of the body 50, for example by inflation with hydraulic fluid or a gas. A major central portion of the grout pin 46 is encircled by upper and lower arrays of shear key formations 64 that project radially from the body 50 in the manner of parallel flanges, each being in a plane orthogonal to the central longitudinal axis 52.

[0088] Figures 8 to 10 show one of the legs 16 of the upper section 12 of the jacket 10 and an associated brace 18. The leg 16 contains female shear key formations 66 that are positioned to be in complementary interlocking opposition to the male shear key formations 64 of the grout pin 46, when the grout pin 46 is in its final deployed position bridging across the interface 26 between the legs 16 of the upper and lower sections 12, 14. The shear key formations 64, 66 then engage via an intermediate layer of grout that is injected into the annulus between them.

[0089] Above the shear key formations 66, the leg 16 of the upper section 12 contains an upper frusto-conical centralising flange 68 that lies in a plane orthogonal to the central longitudinal axis of the leg 16. As shown in detail in Figure 9 corresponding to Detail IX of Figure 8, the upper centralising flange 68 has an upper shoulder that is inclined upwardly and outwardly within the leg 16.

[0090] The aforementioned bearing flange 40 at the lower end of a leg 16 of the upper section 12 is shown in Figure 10 corresponding to Detail X of Figure 8. It will be noted that the brace 18 adjoins the leg 16 very close to the lower extremity of the leg 16. Indeed, in this example, a lower edge of the brace 18 intersects the leg 16 within the bearing flange 40. The closeness of the brace 18 to the lower extremity of the leg 16 helps to maintain a virtual K-joint bracing arrangement at the interface between the upper and lower sections 12, 14.

[0091] Figures 11 to 13 show a corresponding leg 16 of the lower section 14 of the jacket 10 and an associated brace 18, whereas Figure 14 shows three such legs 16 of the lower section 14 in a triangular formation, joined by their associated braces 18. Again, the closeness of the braces 18 to the upper extremities of the legs 16 helps to maintain a virtual K-joint bracing arrangement at the interface between the upper and lower sections 12, 14.

[0092] As before, each leg 16 of the lower section 14 contains female shear key formations 66 that are positioned to be in complementary opposition to the male shear key formations 64 of the grout pin 46, when the grout pin 46 is in its final position bridging across the interface between the legs 16 of the upper and lower sections 12, 14.

[0093] Beneath the shear key formations 66, each leg 16 of the lower section 14 contains a frusto-conical lower centralising flange 70 that lies in a plane orthogonal to the central longitudinal axis 38 of the leg 16. As shown in detail in Figure 13 corresponding to Detail XIII of Figure 11, the lower centralising flange 70 again has a shoulder that is inclined upwardly and outwardly within the leg 16.

[0094] Spaced longitudinally beneath the lower centralising flange 70, each leg 16 of the lower section 14 contains a stop plate 72 that also lies in a plane orthogonal to the central longitudinal axis 38 of the leg 16. In this example, the stop plate 72 extends as a continuous wall across the full internal width of the leg 16 to close off and seal the interior of the leg 16.

[0095] At its upper end, each leg 16 of the lower section 14 terminates in a bearing flange plate 40 that lies in a plane orthogonal to the central longitudinal axis 38 of the leg 16, hence being inclined to the horizontal. The flange plate 40 is partially surrounded by the aforementioned upwardly-flared guide 42, which is joined to the flange plate 40 via the part-circular side wall 44. One side of the guide 42, on a lower side of the inclined flange plate 40, is cut away to define a gap 74 where an outer edge of the flange plate 40 is exposed.

[0096] It will be apparent from the perspective view of Figure 14 that the flange plates 40 atop the legs 16 of the lower section 14 are inclined downwardly and inwardly with respect to a central upright axis of the lower section 14 and hence toward each other. Thus, when the upper section 12 is lowered onto the pre-installed lower section 14, the opposing inclinations of the abutting flange plates 40 of the legs 16 centralise and align the upper section 12 with the lower section 14, and thereafter resist lateral forces to maintain that alignment.

[0097] It will also be apparent from Figure 14 that the gaps 74 in the guides 42 atop the legs 16 face inwardly with respect to a central upright axis of the lower section 14 and hence toward each other. Thus, when lowering the upper section 12 onto the lower section 14, the flange plates 40 of the upper section 12 can enter the guides 42 through the gaps 74. The guides 42 thereby receive and, with further lowering, guide the flange plates 40 of the upper section 12 into abutting alignment with the flange plates 40 of the lower section 14. Thereafter, the guides 42 and the side walls 44 embrace the outward sides of the abutting flange plates 40 and so further resist lateral forces to maintain alignment of the upper section 12 with the lower section 14.

[0098] Having now described elements of the jacket 10 and the grout pin 46, an exemplary process of installing the jacket 10 will now be described with reference to Figures 15a to 27b.

[0099] Figures 15a and 15b show how the grout pins 46 are pre-installed or pre-loaded into the legs 16 of the jacket 10. The upper section 12 of the jacket 10 is shown with three grout pins 46, one for each leg 16, in coaxial relation with the respective legs 16. Figure 15a shows the grout pins 46 being lifted into the open bottom ends of the respective legs 16 whereas Figure 15b shows the grout pins 46 in a retracted position fully within the bores of the legs 16 before load-out of the upper section 12. For this purpose, the grout pins 46 are lifted, either simultaneously or in series, by a conventional topside crane or winch (not shown) acting on lifting wires 76 that extend along and within the legs 16 to suspend the grout pins 46.

[0100] As the grout pins 46 are lifted into the legs 16, the chamfered upper edges of the guide fins of the plates 56 and of the intermediate guide fins 60 shown in Figure 7 help the upper and lower guide formations 54 to slide through the upper and lower centralising flanges 68, 70 within the legs 16.

[0101] Figure 16 shows an upper end of the upper section 12 including the aforementioned topside work platform 34 and transition piece 36. Each lifting wire 76 emerges from the open top end of a respective leg 16 and terminates in a coupling 78 for attaching the lifting wire 76 to a crane or winch that retracts the grout pins 46. The coupling 78 also provides for connection to a crane or winch of an installation vessel for lowering or deploying the grout pins 46 offshore, as will be explained.

[0102] Figure 16 also shows that flexible lines 80, 82 extend to each grout pin 46 along and within the respective legs 16 of the upper section. The flexible lines 80, 82 accommodate longitudinal movement of the grout pins 46 relative to the legs 16 during retraction and deployment. Specifically, a grout line 80 is configured for injecting grout through the grout pin 46 whereas an actuation line 82 is configured for extending the aforementioned grippers 48 of the grout pin 46, for example hydraulically. Conveniently, the grout lines 80 and the actuation lines 82 are connected to the grout pins 46 before the grout pins 46 are retracted into the respective legs 16.

[0103] The lifting wires 76, the grout lines 80 and the actuation lines 82 can be hung off temporarily from any convenient attachment points on the work platform 34 after the grout pins 46 have been retracted into the legs 16. This secures the grout pins 46, the grout lines 80 and the actuation lines 82 and protects them within the legs 16 during transport and installation of the upper section 12.

[0104] Moving on to Figure 17, this shows the pre-installed lower section 14 fixed to the seabed 28 by foundations 30 at the lower end of each leg 16. The guides 42 at the upper ends of the legs 16 open upwardly, ready to receive the lower ends of the legs 16 of the upper section 12 when the upper section 12 is lowered beneath the surface 32 as shown in Figure 18. In this respect, Figure 19 shows one of the guides 42 guiding a flange plate 40 of the upper section 12 into abutting alignment with a complementary flange plate 40 of the lower section 14 to create the aforementioned interface 26 between the upper sections 12, 14 as shown in Figures 20 and 21.

[0105] The flange plate 40 of the upper section 12 is then constrained against lateral movement by the side wall 44 that joins the guide 42 to the flange plate 40 of the lower section 14, as best appreciated in Figure 21. As noted above, lateral stability is also assured by frictional resistance arising from the dead weight of the upper section 12 acting on the abutting flange plates 40 and by the inclination relative to the horizontal of the interface 26 defined by the abutting flange plates 40. Whilst the interface 26 between the flange plates 40 is orthogonal to the common central longitudinal axis of the abutting legs 16, the inclination of the interface 26 relative to the horizontal could be increased or steepened, if desired, if the interface 26 is instead at an acute angle to that axis.

[0106] Next, Figures 22a and 22b show deployment of a grout pin 46 from the temporarily retracted position within a leg 16 of the upper section 12, as shown in Figure 22a, to the permanently deployed position straddling the interface 26 between the upper and lower sections 12, 14, as shown in Figure 22b. For this purpose, a crane or winch of an installation vessel lowers the lifting wire 76 that suspends the grout pin 46 within the leg 16 of the upper section 12. This lowers the lower half of the grout pin 46 across the interface 26 and into the leg 16 of the lower section 14.

[0107] As the grout pin 46 is lowered, the upper and lower guide formations 54 of the grout pin 46 bear against the respective centralising flanges 68, 70 that are welded within the legs 16 of the upper and lower sections 12, 14. Specifically, the chamfered lower edges of the guide fins of the plates 56 and of the intermediate guide fins 60 shown in Figure 7 cooperate with and slide past the similarly-inclined downwardly-narrowing shoulders of the flanges 68, 70. Those interactions maintain concentric alignment between the body 50 of the grout pin 46 and the surrounding tubular wall of the legs 16 to meet minimum grout annulus requirements.

[0108] Eventually, the bottom end of the grout pin 46 defined by the longitudinally-protruding plates 56 of the lower guide formation 54 bears against the stop plate 72 within the leg 16 of the lower section 14 to limit downward movement of the grout pin 46. This ensures that the grout pin 46 is located at the correct elevation straddling the interface 26 between the upper and lower sections 12, 14, with the upper and lower arrays of grippers 48 respectively above and below the interface 26.

[0109] The guide fins of the plates 56 and the intermediate guide fins 60 of the upper and lower guide formations 54 are then in mutual radial opposition with the respective centralising flanges 68, 70. This ensures that the grout pin 46 and the surrounding tubular wall of the leg 16 are in coaxial relationship with a consistent and correct grouting annulus maintained between them. Moreover, the shear key formations 64, 66 of the grout pin 46 and of the legs 16 of the upper and lower sections 12, 14, as shown in Figures 5, 8 and 11, are also in mutual radial opposition.

[0110] Figures 22a and 22b show the grout line 80 and the actuation line 82 extending parallel to the lifting wire 76 up a leg 16 of the upper section 12. Once the grout pin has been deployed, the lifting wire 76 can be uncoupled from the crane or winch of the installation vessel and left in situ, hung off within the leg 16 of the upper section 12.

[0111] Like Figure 16, Figure 23 shows the upper end of the upper section 12 where the grout lines 80 and the actuation lines 82 emerge from the open top ends of the respective legs 16. The topside work platform 34 supports grout spreads 84 connected to the respective grout lines 80 and hydraulic power units 86 connected to the respective actuation lines 82. The grout spreads 84 and the hydraulic power units 86 may be deployed from the installation vessel to the work platform 34 and connected to the respective pre-installed lines 80, 82.

[0112] Figure 24 shows an array of the grippers 48 of a grout pin 46 in the annulus 88 between the body 50 of the grout pin 46 and the surrounding wall of the leg 16. The grippers 48 are shown inflated by hydraulic fluid pressurised by one of the hydraulic power units 86. For this purpose, all of the grippers 48 of the array are connected to a common hydraulic power unit 86 via a manifold 90 mounted on the body 50 of the grout pin 46. Inflation presses the grippers 48 radially outwardly from the body 50 as shown, into conforming clamping contact with the interior of the surrounding tubular leg 16. The upper and lower arrays of grippers 48 disposed on respective sides of the interface 26 between the upper and lower sections 12, 14 thereby provide temporary tensile axial capacity via the body 50 of the grout pin 46 during a period of grout curing. The grippers 48 can be actuated remotely if desired.

[0113] Similarly, the aforementioned upper grout seal 62 encircling the body 50 of the grout pin 48 can be inflated by hydraulic pressure from the associated hydraulic power unit 86. Again, inflation presses the grout seal 62 radially outwardly from the body 50 into conforming contact with the interior of the surrounding tubular leg 16. Once inflated, the grout seal 62 defines an upper limit for grout to fill the annulus 88 between the grout pin 46 and the surrounding wall of the leg 16.

[0114] Figure 25 shows that a grout injection path within the body 50 of the grout pin 46 terminates in grout injection ports 92 supplied from the associated grout spread 84. In this example, the grout injection ports 92 are disposed at a bottom end of the body 50 between the intersecting plates 56 of the lower guide formation 54.

[0115] Referring next to Figure 26, grout 94 injected through the ports 92 initially fills the cavity between the body 50 of the grout pin 46 and the stop plate 72 within the leg 16 of the lower section 14. The grout 94 confined by the stop plate 72 thereby embeds the lower guide formation 54. The grout 94 then flows upwardly into the annulus 88 between the body 50 of the grout pin 46 and the surrounding wall of the leg 16 to embed the body 50, the shear key formations 64, 66 and the arrays of grippers 48. The grout 94 continues to flow upwardly within the annulus 88 until the grout 94 rises above the interface 26 and is thereafter confined by the grout seal 62. The grout 94 thereby extends along the annulus 88 to the upper and lower sides of the interface 26. When cured, the grout 94 forms a permanent grouted connection between the grout pin 46 and the adjoining legs 16 of the upper and lower sections 12, 14.

[0116] In another option, a passive bi-directional grout seal could be employed instead of the inflatable grout seal 62. Alternatively, a grout seal could be omitted entirely from the grout pin 46, relying instead on simply pumping in a sufficient volume of grout to fill the required length of the annulus 88 extending above and below the interface 26.

[0117] In final steps of the process of installing the jacket 10, hydraulic pressure in the grippers 48 and the actuation lines 82 is released before the grout lines 80 and the actuation lines 82 are disconnected from the grout spreads 84 and the hydraulic power units 86 on the work platform 34. the grout lines 80 and the actuation lines 82 are left in place permanently within the legs 16 of the upper section, alongside the lifting wires 76 that were previously detached from the crane or winch of the installation vessel. Then, as shown in Figures 27a and 27b, the grout spreads 84 and the hydraulic power units 86 are recovered from the work platform 34 to the installation vessel 96, conveniently using a crane 98 of the vessel 96. The vessel 96 can then move off to the next target location at which the grout spreads 84 and the hydraulic power units 86 can be used again.

[0118] Many other variations are possible within the inventive concept. In one such variation shown in Figures 28 and 29, a grout seal 100 can be implemented within a leg 16 of the upper or lower section 12, 14 to extend radially inwardly, when inflated, into conforming contact with the body 50 of a grout pin 46.

[0119] Figure 29 shows an inflation port 102 that penetrates a tubular wall of a leg 16 of the lower section 14, communicating with the grout seal 100 within the leg 16. Figure 29 also shows the further option of a diaphragm 104 that spans the bore or lumen of that leg 16 to effect additional or supplementary sealing against migration of grout.

[0120] In principle, it would also, or instead, be possible to mount arrays of grippers 48 on the interior of the legs 16. Such grippers 48 could extend radially inwardly from the tubular walls of the legs 16 to bear against the body 50 of a grout pin 46 that has been deployed across the interface 26 between the adjoining legs 16. Grippers 48 and grout seals 62, 98 of the embodiments described above are extended or inflated hydraulically but they could instead be actuated pneumatically, electrically or mechanically.

Claims

Claims1. A method of installing a split jacket offshore, the method comprising: lowering an upper jacket section onto a pre-installed lower jacket section; uniting coaxially-aligned legs of the respective jacket sections in mutual abutment about an interface; positioning a pin within tubular walls of the abutting legs, the pin extending across the interface; engaging the pin with the abutting legs by extending grippers across an annulus defined between the pin and the tubular walls, the grippers being disposed above and below the interface; and injecting grout into the annulus.

2. The method of Claim 1 , comprising extending the grippers from the pin toward the tubular walls.

3. The method of Claim 2, comprising extending the grippers with actuating energy supplied to the pin along an actuation line that extends within and along the leg of the upper jacket section.

4. The method of Claim 3, comprising supplying the actuating energy to the actuation line from a power unit that is supported by a topside work platform of the upper jacket section.

5. The method of Claim 4, comprising subsequently disconnecting the power unit from the actuation line and removing the power unit from the work platform.

6. The method of Claim 5, comprising leaving the actuation line in the leg of the upper jacket section after removing the power unit.

7. The method of any preceding claim, comprising injecting the grout into the annulus via the pin.

8. The method of Claim 7, comprising injecting the grout into the annulus from a bottom end of the pin.

9. The method of Claim 7 or Claim 8, comprising supplying the grout to the pin along a grout line that extends within and along the leg of the upper jacket section.

10. The method of Claim 9, comprising supplying the grout to the grout line from a grout spread that is supported by a topside work platform of the upper jacket section.

11. The method of Claim 10, comprising subsequently disconnecting the grout spread from the grout line and removing the grout spread from the work platform.

12. The method of Claim 11, comprising leaving the grout line in the leg of the upper jacket section after removing the grout spread.

13. The method of any preceding claim, comprising embedding the grippers in the grout injected into the annulus.

14. The method of any preceding claim, further comprising extending a grout seal across the annulus before injecting the grout.

15. The method of any preceding claim, comprising positioning the pin by lowering the pin from within a leg of the upper jacket section until a lower portion of the pin is received within a leg of the lower jacket section.

16. The method of Claim 15, comprising lowering the pin onto a stop formation within the leg of the lower jacket section.

17. The method of Claim 16, comprising aligning guide formations of the pin with centralising flanges within the respective legs of the upper and lower jacket sections by lowering the pin onto the stop formation.

18. The method of Claim 16 or Claim 17, comprising using the stop formation to limit migration of the grout along the leg of the lower jacket section.

19. The method of any of Claims 15 to 18, further comprising lifting the pin into the leg of the upper jacket section before lowering the upper jacket section.

20. The method of any of Claims 15 to 19, comprising suspending the pin from a lifting wire that extends within and along the leg of the upper jacket section.

21. The method of any preceding claim, comprising lowering an upper bearing flange, extending radially from the leg of the upper jacket section, into a bucket atop the leg of the lower jacket section, the bucket comprising an upwardly-flared guide surrounding a lower bearing flange extending radially from the leg of the lower jacket section.

22. The method of Claim 21, comprising restraining lateral movement of the upper bearing flange within a side wall disposed between the guide and the lower bearing flange.

23. The method of any preceding claim, comprising resisting lateral moment of the upper jacket section relative to the lower jacket section up an incline of the interface relative to a horizontal plane.

24. A split jacket structure, comprising: upper and lower jacket sections that have coaxially-aligned legs in mutual abutment about an interface; a pin positioned within tubular walls of the abutting legs, the pin extending across the interface; grippers disposed above and below the interface, the grippers being extensible across an annulus defined between the pin and the tubular walls to engage the pin with the abutting legs; and a grout path communicating with the annulus.

25. The structure of Claim 24, wherein the grippers are extensible from the pin toward the tubular walls.

26. The structure of Claim 24, comprising an actuation line that extends within and along the leg of the upper jacket section and is configured to convey actuating energy to the grippers from a power unit disposed outside the leg of the upper jacket section.

27. The structure of any of Claims 24 to 26, wherein the grout path extends through the pin.

28. The structure of Claim 27, wherein the grout path communicates with the annulus through at least one injection port at a bottom end of the pin.

29. The structure of Claim 27 or Claim 28, comprising a grout line that extends within and along the leg of the upper jacket section and is configured to convey grout to the pin from a grout spread disposed outside the leg of the upper jacket section..

30. The structure of any of Claims 24 to 29, wherein grout in the annulus embeds the grippers.

31. The structure of any of Claims 24 to 30, further comprising a grout seal that is extensible across the annulus.

32. The structure of any of Claims 24 to 31, wherein the pin is deployable by being lowered from within a leg of the upper jacket section until a lower portion of the pin is received within a leg of the lower jacket section.

33. The structure of Claim 32, comprising a stop formation within the leg of the lower jacket section.

34. The structure of Claim 33, comprising centralising flanges within the respective legs of the upper and lower jacket sections, the flanges being aligned with respective guide formations of the pin when the pin abuts the stop formation.

35. The structure of any of Claims 24 to 34, comprising a bucket atop the leg of the lower jacket section, the bucket comprising an upwardly-flared guide at least partiallysurrounding a lower bearing flange extending radially from the leg of the lower jacket section.

36. The structure of Claim 35, comprising a side wall disposed between the guide and the lower bearing flange and at least partially surrounding the lower bearing flange.

37. The structure of any of Claims 24 to 36, wherein the interface is inclined relative to a horizontal plane.

38. The structure of Claim 37, wherein the upper and lower jacket sections each comprise two or more legs whose interfaces are inclined upwardly and outwardly in mutual opposition.

39. A grout pin for grouting a joint between an upper jacket section and a lower jacket section of a split jacket structure, the grout pin comprising: an elongate body; circumferential arrays of grippers that are extensible radially from the body, the arrays being spaced apart longitudinally along the body; and a grout path extending through the body.

40. The grout pin of Claim 39, further comprising at least one circumferential seal that is extensible radially from the body.

41. The grout pin of Claim 39 or Claim 40, further comprising centralising guides that protrude radially from the body.

42. The grout pin of Claim 41, wherein the centralising guides also protrude longitudinally from the body.

43. The grout pin of any of Claims 39 to 42, wherein the grout path communicates with at least one injection port in an end of the body.T144. The grout pin of any of Claims 39 to 43, further comprising a lifting point at an end of the body.

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