HANGING-OFF ELONGATE ELEMENTS DURING OFFSHORE OPERATIONS

A hang-off system comprises support blocks that are movable toward a launch axis for engagement with an elongate element such as a flexible pipeline being laid from a vessel into water. Each support block comprises an array of plates that together define an engagement face of the support block and are movable relative to each other to conform a contour of the engagement face to a contour of the element.

This invention relates to suspending an elongate element from a surface vessel during an offshore operation, for example when constructing underwater installations in the subsea oil and gas industry or in the marine renewable energy industry. An example of such an element is a subsea pipeline, a cable or an umbilical that hangs as a catenary from a surface vessel toward the seabed during installation. In the art of offshore operations, supporting such an element may be referred to as ‘hanging off’ or ‘holding back’, depending upon the phase of the installation operation.

As explained in WO 2017/139861 to the Applicant, flexible elongate elements such as flexible pipelines are most commonly laid underwater by an installation vessel that firstly spools the element onto a reel or carousel. During installation offshore, the element is unspooled from the reel or carousel and is then overboarded into the sea to hang from the vessel as a catenary. Rigid pipelines can also be laid by this reel-lay technique if the pipeline is straightened after unspooling to reverse plastic deformation imparted to the pipeline by spooling. In this respect, the invention is primarily concerned with flexible elements such as flexible pipelines but in a broad sense, the principles of the invention can also be used with rigid pipelines launched into the sea along an upright launch axis.

Between unspooling and overboarding, the elongate element passes over structures that guide the element, such as a tower, a chute or a ramp, and through various items of equipment that may contribute to hold-back tension, such as aligners, straighteners or tensioners. The inclination of a tower, chute or ramp may be adjustable, for example on a vessel fitted with a tilting lay tower whose inclination may depart from the vertical.

Frictional hold-back devices such as tensioners or friction clamps can be used to support the suspended weight of an elongate element. Examples of such devices may be found in WO 2018/147735, WO 2020/075126, WO 2018/073453, GB 2591771, GB 1352983 and US 2009/229424. However, the reliance of such devices upon friction means that there is nothing else to hold the element if it starts to slip through the device, for example because the outer surface of the element has a poor surface finish or is wet or oily. Also, hold-back devices have to be moved away from the launch axis of the element to allow laterally-protruding equipment that is wider than the remainder of the element, such as accessories or modules, to be attached to the element and to allow such equipment to bypass the hold-back device in the launch direction.

Installation of elongate elements on the seabed in deep water requires the installation vessel to have sufficient hang-off capacity to support the weight of the long catenary that is suspended in the water column between the vessel and the seabed. Usually, hang-off systems are used to keep the upper end of the element supported at deck level for connection to equipment such as in-line modules before deployment and also for connection between ends of pipeline sections during an installation campaign. In those situations, the element has to be suspended temporarily without moving in the launch direction.

It is conventional for a laterally protruding hang-off feature of an elongate element to be engaged mechanically with a hang-off plate or bushing on the pipelaying vessel. The element may hang from such a hang-off structure through a moonpool of the vessel or over the side or stern of the vessel. The laterally protruding hang-off feature that abuts a shoulder of the hang-off bushing may be a flanged collar or another item of equipment that is wider than the remainder of the element, such as an accessory or a module attached to the element. This provides a steady and reliable mechanical connection between the element and the laying equipment of the vessel.

For example, a hang-off collar may be a metallic part of the elongate element that defines a radially-projecting flange or ring. Examples are a forged radially-projecting ring that is incorporated into the element, or forgings comprising such rings that are attached to an end of the element or incorporated at intervals along the element. Other specific examples of equipment that has a greater diameter than the remainder of the element are a connector, an end fitting or an armour pot.

An example of a conventional hang-off system of the prior art is shown inFIG.1of the accompanying drawings. An elongate element10that is exemplified here as a flexible pipeline extends along a generally vertical launch axis as it passes through the hang-off system12. The hang-off system12comprises a tubular support structure14whose inner opening flares downwardly to accommodate bending of the elongate element10.

The elongate element10carries an armour pot16as an example of a laterally-protruding hang-off feature. The element10further comprises a vertebrae bend restrictor18extending from the armour pot16.

The open top of the tubular support structure14is closed by a hang-off bushing20that is assembled in two halves around the elongate element10and so has a central hole22to accommodate the element10.

A simple hang-off bushing20like that shown inFIG.1can only accommodate one diameter of elongate element10: in other words, a hang-off bushing20cannot be purpose-designed as a universal hang-off insert for all such elements10. Consequently, it is conventional to use one of a selection of split hang-off inserts24as an adaptor between a specific element10and a hang-off bushing20. The inner edge region of the hang-off bushing20around the central hole22serves as a shoulder upon which the hang-off insert24rests.

The hang-off insert24is made of semi-circular or half-moon parts machined from steel, whose internal curvature matches the external curvature of a particular elongate element10. The two parts of the hang-off insert24are bolted together around the element10to lie between the element10and the hang-off bushing20. The armour pot16sits on the hang-off insert24. This transfers the weight of the element10to the hang-off bushing20through the hang-off insert24.

As noted above, the armour pot16is just an example of a hang-off feature protruding laterally from the elongate element10. Such a feature may be provided by any other equipment that has a greater diameter than the remainder of the element10, or by a flanged collar protruding radially from the element10.

An installation vessel may have to cater for elongate elements10of many different diameters during routine operations. Each diameter of element10requires a different hang-off insert24. Consequently, around fifty different hang-off inserts24may be required per vessel. This involves a high cost of design and fabrication and requires a large area of deck space on the vessel to store multiple hang-off inserts24onboard. Alternatively, there is a risk of expensive downtime to fabricate or obtain a specific hang-off insert24if such an insert is not kept onboard.

To mitigate these drawbacks of conventional prior art, WO 2017/139861 discloses a hang-off insert in the form of a circular loop that comprises circumferentially-spaced support segments. Collectively, the segments define a substantially planar support face of the insert and have respective radially inner faces that define an inner radius of the loop. The radially inner faces of the support segments can be positioned at various radial positions to determine the inner radius of the loop and hence to adapt the circumference of the loop to suit different diameters of elongate subsea elements.

With the hang-off insert supported by a hang-off structure of the vessel, a laterally-protruding hang-off feature of the elongate element extending through the loop may be rested on the support face to transfer suspended weight loads through the insert to the hang-off structure.

FIG.2illustrates a hang-off system26comprising a hang-off insert28as taught by WO 2017/139861, in place of the rigid split hang-off insert24of the prior art as shown inFIG.1. Otherwise, the hang-off system26ofFIG.2is similar to the hang-off system12ofFIG.1, so like numerals are used for like features.

The hang-off insert28is tightened around and encircles an elongate element10, again exemplified here as a flexible pipeline of circular cross-section that extends along a generally vertical launch axis as it passes through the hang-off system26.

As in the hang-off system12shown inFIG.1, the hang-off system26shown inFIG.2comprises a tubular support structure14whose open top may be closed by a hang-off bushing20that is assembled in two halves around the elongate element10. The hang-off bushing20has a central hole22to accommodate the elongate element10.

The inner edge region of the hang-off bushing20around the central hole22serves as a shoulder upon which the hang-off insert28rests. In use of the invention, a laterally-protruding hang-off feature of the elongate element10such as an armour pot16as shown inFIG.1(which has been omitted fromFIG.2for clarity) rests in turn on the hang-off insert28to transfer loads of the elongate element10through the hang-off insert28to the hang-off bushing20.

Against this background, the invention resides in a hang-off system comprising at least one support block that is movable forwardly toward a launch axis for engagement with an elongate element being laid from a vessel into water. The or each support block comprises an array of plates that together define an engagement face of the support block and are movable relative to each other to conform a contour of the engagement face to a contour of the element. Each plate comprises mutually parallel upright side faces joined by an upper face that is narrower than either of the side faces of that plate and the upper faces of the plates together define an upper face of the support block.

Each plate may comprise a lower face that is parallel to the upper face, the lower faces of the plates together defining a lower face of the support block.

The side faces of each plate may also be joined by a front face, the front faces of the plates together defining the engagement face of the support block. The engagement face of the support block may be inclined forwardly and upwardly toward an upper leading edge of the block.

The front face of each plate may be shaped to define a facet that is angled acutely relative to a plane of a side face. The facets of one subset of the plates may be in mirror relation to the facets of another subset of the plates, such that the facets of both of those subsets face toward the launch axis. The subsets may be separated by an upright plane that bisects the support block and that contains the launch axis.

The plates can be moved relative to each other in respective upright planes, which planes may be mutually parallel and parallel to a plane containing the launch axis.

A housing may constrain the plates against movement transverse to the forward direction. For example, the housing may comprise side walls disposed on respective sides of the support block that constrain lateral movement of the plates. The housing may further comprise a top wall disposed above the support block that constrains upward movement of the plate. The housing may define an aperture through which the support block can be advanced forwardly from the housing.

Actuators may act on the block portions to drive forward movement of the block portions. It is also possible for the block portions to be biased forwardly, for example by springs.

Conveniently, the support block can be mounted on a jaw of a hang-off bushing, for example via a housing fixed to that jaw. The support block may be movable relative to the jaw of the hang-off bushing. For example, the support block may be movable forwardly or be pivotable about horizontal and/or vertical axes relative to the jaw of the hang-off bushing.

The inventive concept embraces a lay system or a vessel comprising the hang-off system of the invention. The inventive concept also extends to a corresponding method of hanging-off an elongate element being laid from a vessel into water. The method comprises advancing first and second portions of a support block into contact with the element beneath an outwardly-projecting formation of the element wherein the first and second portions are advanced in parallel planes; effecting relative displacement between those portions to conform a contour of the support block to an abutting contour of the elongate element; and hanging-off the element from the portions of the support block in contact with an underside of the outwardly-projecting formation.

Relative displacement between the portions of the support block may take place after bringing the first portion into contact with the element. For example, the first portion of the support block may be advanced into contact with the element and then, with the first portion stationary relative to the element, the second portion of the support block may be advanced into contact with the element. Alternatively, relative displacement between the portions of the support block may take place before bringing either portion into contact with the element. In either case, relative displacement may involve advancing a leading edge of the second portion beyond a leading edge of the first portion.

The portions of the support block are preferably advanced in directions parallel to an upright plane containing a launch axis of the element. The portions of the support block are preferably constrained against transverse movement and/or upward movement.

Movement of the portions of the support block may be driven individually. The portions of the support block may be biased toward the element, in which case relative movement between the portions may be effected against that bias.

The support block may be moved with and/or relative to a supporting jaw of a hang-off bushing, for example by translational movement or pivotal movement of the support block about horizontal and/or vertical axes relative to the supporting jaw.

Whilst the adaptable hang-off insert of WO 2017/139861 has significant advantages over the multiple hang-off inserts required by conventional prior art, the inventors have now addressed the problem of adapting a hang-off-system from a different perspective. Specifically, they have explored a fresh approach in which the hang-off structure itself can adapt to suit elongate elements of different diameters, without necessarily requiring an adaptable insert.

The invention contemplates that a hang-off structure such as a hang-off bushing can comprise a series or set of plates assembled in parallel to form a supporting block. Each plate can move independently of other plates of the set to change the shape of the block, particularly the shape or curvature of a face or an upper edge of the block that abuts an elongate element to be supported by the block. This adapts a leading end or edge of the set to complement the external diameter or shape of the element, which may include a fitting on the element such as an end fitting of a flexible pipeline.

Like WO 2017/139861, the invention solves the problem of providing a supporting interface between a hang-off structure and pipelines or other elongate elements, or their fittings, that are not standardised and so may have various shapes and diameters.

The invention provides a versatile alternative to hang-off inserts of the prior art. The solution of the invention can comply with a wide range of diameters of elongate elements that may be suspended from a hang-off structure and ensures a reliable mechanical interface between equipment of the element and the hang-off structure.

The invention improves safety because it requires no work to be performed under a suspended load. The invention also generates a considerable cost saving. By reducing the setup time for each hang-off operation by 25% to 30%, the invention could, on aggregate, save hundreds of thousands of US dollars of operational cost per vessel, per year. There is also a saving in the cost of fabricating bespoke hang-off inserts as sometimes required in the conventional prior art. Unlike the hang-off inserts of the prior art, apparatus of the invention can be assembled and disassembled, if ever necessary, without impacting the critical path of a laying operation. Also, preliminary results suggest that in comparison with a prior art solution, the invention could reduce loads on key components by 70% to 90%.

Embodiments of the invention provide a device for supporting a formation on a pipeline or other elongate element, such as a head or a termination of a flexible pipeline, during installation from a vertical or tiltable lay system, the device comprising at least two partial support boxes, each box comprising a plurality of vertical plates, each plate being able to slide horizontally to adjust the position of the top of the plate to the shape and diameter of the formation on the pipeline.

The plates may be biased or forced in the direction of the pipeline, for example by a hydraulic circuit, by jacks or by springs. The plates can also be tilted slightly in a vertical plane.

Each box may comprise four or five walls and one open side through which the plates can slide. The number of plates in a box may be determined by filling in the width of the open side with the sum of the thicknesses of the plates. The plates may be fully packed in the box.

The plates need not necessarily all have identical thickness. For example, outer or outermost plates may be thicker than inner or innermost plates, or vice versa.

The boxes may be mounted on mountings such as gimbals, pivots or rubber pads that are arranged to accommodate any misalignment of the flexible pipeline with the normal launch direction.

Embodiments of the invention also implement a method for supporting a formation of a flexible pipeline during installation from a vertical or tiltable lay system. The method comprises: providing boxes containing a plurality of vertical support plates; guiding the support plates around the trajectory of the flexible pipeline; adjusting the transverse positions of the plates by sliding them inside or relative to the respective boxes until the plates are in contact with the flexible pipeline or a bottom part of the formation; and then abutting the bottom of the formation with the top of the plates.

Thus, in embodiments of the invention, a hang-off system comprises support blocks that are movable toward a launch axis for engagement with an elongate element, such as a flexible pipeline, being laid from a vessel into water. Each support block comprises an array of plates or other block portions that together define an engagement face of the support block, adapted to engage the element. The plates are movable relative to each other to bring a contour of the engagement face into conformity with a contour of the element. Each plate comprises upright side faces joined by an upper face that is narrower than either of the side faces of that plate and the upper faces of the plates together define an upper face of the support block.

Referring firstly toFIGS.3to10of the drawings, support blocks30of the invention are held in respective housings32mounted on respective jaw sections of a hang-off bushing20. The support blocks30are therefore in mutual opposition around an elongate element10supported by the hang-off bushing20, the element10in this example being a flexible pipeline34surrounded by an end fitting36.

The pipeline34is coaxial with an upright launch axis38that is nominally vertical but may depart from the vertical, for example when laying a pipeline34from a tiltable lay tower of a vessel. In that case, the hang-off bushing20could, correspondingly, depart from a horizontal plane to remain orthogonal to the launch axis38.

In the arrangement shown, there are two support blocks30equiangularly spaced around the launch axis38, hence at an angle of 180° relative to each other. In other arrangements, there could be more support blocks30, for example three or four support blocks30at angles of 120° or 90° to neighbouring support blocks30around the launch axis38.

When advanced telescopically from within its housing32in a forward direction, that being a radially inward direction toward the launch axis38, an end of each block30protrudes from its housing32in cantilever fashion and overhangs a central hole22in the bushing20. A front face40of the protruding end of the block30engages with the pipeline34, thus being an engagement face of the block30. Specifically, an upper leading edge42of the front face40engages under a radially protruding flange44of the end fitting36.

In a retracted or rest configuration, each block30is approximately cuboidal, comprising a planar upper face46, a planar lower face48parallel to the upper face46, and planar side faces50parallel to each other and orthogonal to the upper and lower faces46,48. The upper and lower faces46,48are both nominally horizontal to match the plane of the hang-off bushing20. The block30is of squat or shallow proportions, with the upper and lower faces46,48being substantially larger than the side faces50. In this example, however, the block30departs from a cuboidal shape in that its front face40is not orthogonal to the other faces46,48,50. Instead, the front face40is inclined forwardly in an upward direction from the lower face48to the upper face46. Thus, the upper face46of the block30is longer or deeper from front to back than the lower face48. The resulting chamfered profile of the front face40better transfers loads from the end fitting36to the hang-off bushing20. Also, as will be described later, the front face40of the block30is contoured and hence non-planar.

By virtue of the invention, the shape or contour of the block30and particularly its front face40reconfigures or adapts to match, complement or conform to the external shape or contour of the end fitting36, especially the radius of curvature of the end fitting36. Thus, the front face40adopts a female or concave contour in response to encountering the male or convex contour of the end fitting36when the block30is moved toward the launch axis38. To enable reconfiguration in this way, each block30is divided into block portions that can move relative to each other. Specifically, each block30comprises an array of planar support elements being rigid leaves or plates52, suitably made of steel. Each plate52can move relative to neighbouring plates52of the array in directions parallel to the upper, lower and side faces50of the block30, hence forwardly and rearwardly.

The plates52are arranged in a horizontal stack, lying in upright, nominally vertical planes that are parallel to each other and to the forward direction in which the block30advances from the housing32toward the launch axis38. The planes of the plates52are also substantially parallel to an upright plane54containing the launch axis38as shown inFIGS.7and8. The plates52are all substantially identical to each other although, as will be explained, subsets of the plates52may have contoured front faces56that are oppositely handed or mirrored to suit the shape of the pipeline34on opposite sides of the plane54containing the launch axis38.

FIGS.9and10show that like the block30, each plate52is approximately cuboidal, comprising a planar upper face58, a planar lower face60parallel to the upper face58, and planar side faces62parallel to each other and orthogonal to the upper and lower faces58,60. The planes of the side faces62correspond to the planes of the plates52. The front face56of each plate52is inclined forwardly in an upward direction to lend the aforementioned chamfered profile to the block30.

The upper and lower faces58,60of the plates52all lie in respective nominally horizontal common planes so that, collectively, the upper and lower faces58,60of the plates52together define the upper and lower faces46,48of the block30. The side faces62of the plates52correspond to the side faces50of the block30; indeed, the outermost plates52of the array define the side faces50of the block30. In this instance, however, the plates52are thin in a lateral direction orthogonal to the side faces50, in that their upper and lower faces58,60are much smaller than the side faces62. In this example, the side faces62of neighbouring plates52abut with sliding contact between them.

The block30is a close sliding fit in the housing32, substantially filling the width and height of an aperture64of the housing32defined by a top wall66and side walls68of the housing32, and in this case also by the hang-off bushing20that defines a base of the housing32. Specifically, the housing32comprises upright side walls68outboard of, and in close sliding contact with, the outermost plates52of the array. Between them, the side walls68of the housing32thereby hold the plates52together in close sliding contact, so that the individual plates52are supported by neighbouring plates52of the block30and will not collapse, tilt or buckle under compressive loads applied by the suspended weight of the pipeline34. Those loads are shared by the plates52in contact with the underside of the flange44of the fitting36and are transferred through the block30from the upper face46to the lower face48of the block30and from there to the hang-off bushing20.

On an inner face, the side walls68correspond in height to the plates52. The side walls68are joined by a top wall66, shown in shadow inFIGS.3,4and7and in dashed lines inFIG.6, that is parallel to the hang-off bushing20and therefore to the upper face46of the block30. The plates52are a sliding fit between the hang-off bushing20and the underside of the top wall66. Thus, there is a sliding fit between the upper face46of the block30and the underside of the top wall66and an additional sliding fit between the lower face48of the block30and the upper surface of the hang-off bushing20. These small sliding clearances prevent the block30or the plates52pivoting about a lateral axis under the downward weight load applied by the pipeline34.

In this example, the housing32is closed by an optional back wall70that is orthogonal to the side walls68, the top wall66and the hang-off bushing20. The back wall70stiffens the housing32and leaves space on its forward side for plates52of the block30to retract into the housing32but does not interact directly with the plates52. In other examples to be described with reference to later drawings, the housing32has a bottom wall72between the side walls68, independent of the hang-off bushing20. In those examples, the plates52are a sliding fit between the underside of the top wall66and the upper side of the bottom wall72. Thus, there is a sliding fit between the lower face48of the block30and the upper side of the bottom wall72.

FIGS.7and8show the ability of the block30to adapt to the circular-section shape of the fitting36, and to adapt to fittings36of different diameters. In particular,FIG.7shows the front face40of the block30shaped to complement a relatively wide fitting36whereasFIG.8shows the front face40of the block30shaped to complement a relative narrow fitting36. These drawings show the central position of the upright plane54that bisects the block30and that extends in the forward direction to contain the launch axis38shown in the preceding drawings. Plates52of the block30are retracted into the housing32to an extent determined by the curvature of the fitting36, with plates52closer to the plane54therefore being retracted more than plates52further from the plane54. The outermost plates52inFIG.7lie outside the radius of the fitting36and so are fully extended in the forward direction, although they would be retracted to some extent if the fitting36was any wider. Conversely, where the fitting36is relatively narrow as shown inFIG.8, more of the outer plates52are fully extended.

FIGS.9and10show one of the plates52in isolation. The forward and upward inclination of the front face40is plainly apparent, as is the cuboidal relation of the other faces58,60,62. These drawings also show that the upper end of the front face40comprises a forward extension74of the upper face46defining the upper leading edge76of the plate52. In three dimensions, the forward extension74is prism-shaped, comprising a facet78and a stress-reducing chamfer80in respective nominally vertical planes that are orthogonal to the upper face46. The facet78and the chamfer80meet at an upright edge82that is also orthogonal to the upper face46and that intersects the upper face46at the leading edge76.

The angle of the facet78relative to the plane of the side face50reflects the curvature of the fitting36on opposite sides of the central plane shown inFIGS.7and8. Thus, the plates52of the block30are arranged in two subsets divided by the central upright plane54, with the facets78of one subset in mirrored relation to the facets78of the other subset. Specifically, the facets78of both subsets face inwardly, facing approximately toward the launch axis38in parallel directions that will intersect the circumference of a fitting36wide enough to encounter their plates52.

As best appreciated in the plan views ofFIGS.11band12b, the oppositely angled facets78on opposite sides of the central upright plane54approximate to, or at least approach, tangential relationship with the circumference of the fitting36. This increases the area of contact between the forward extensions74of the plates52and the underside of the flange44, helpfully reducing stress when the block30bears the weight load of the pipeline34suspended from the fitting36. The large number of plates52and the slimness of the plates52also helps to follow the curvature of the fitting36more closely and to maximise the area of load-supporting contact.

FIGS.11aand11bshow that the plates52could be driven forwardly from the housing32and into engagement with the fitting36by individual actuators84acting on the back of each plate52. In that case, the housing32can remain stationary while the plates52and hence the block30advance relative to the housing32.

In an alternative approach shown inFIGS.12aand12b, the plates52are biased forwardly by respective springs86. The springs86could of course take forms other than the coils springs shown schematically here. When the housing32carrying the extended plates52is moved forwardly, the plates52encountering the fitting36retract into the housing32to an extent determined by the curvature of the fitting36. The springs86compress as the associated plates52retract.

It will be apparent fromFIGS.11a,11b,12aand12bthat the block30is firstly advanced forwardly until the leading edge42of the front face40comes into contact with the fitting36, with contact initially being between the innermost plates52and the circumference of the fitting36closest to the central plane54. The block30then begins to conform to the shape of the fitting36as the innermost plates52remain stationary while plates52outboard of them continue to advance forwardly with continued forward movement of the remainder of the block30. Moving outwardly from the central plane54, the plates52successively contact the circumference of the fitting36and therefore cannot advance further as the plates52outboard of them continue to advance forwardly. The result is that the leading edge42of the front face40has a stepped concavity corresponding to the convexity of the fitting36. Eventually, any outermost plates52that do not intersect the circumference of the fitting36stop in alignment with a line that intersects the launch axis38.

The housings32can be moved forwardly in accordance withFIGS.12aand12bin various ways. For example,FIG.13shows the housings32fixed to respective jaws of the hang-off-bushing20to be moved forwardly as the jaws are brought together. Alternatively, the housings32can be moved relative to the jaws of the hang-off bushing20, for example on rails88mounted on the respective jaws and extending in the forward direction as shown inFIG.14.FIGS.13and14also show a bottom wall72of the housing32that is distinct from the hang-off-bushing20as mentioned previously.

As noted previously, the preceding embodiments contemplate that the plates52of the block30may be identical apart from mirroring the facets78of their forward extensions74. However, this is not necessarily the case. In this respect,FIG.15shows a simplified variant in which the block30has fewer plates52, and facets78that vary in angle relative to the side faces50in accordance with the lateral distance from the central upright plane54. Specifically, the facets78of the outer plates52are at a smaller or more acute angle to the side faces50than the facets78of the inner plates52. Thus, the inclination of the plates52more closely matches the curvature of the fitting36and maximises the area of load-bearing contact with the flange44, even though there are fewer plates52in the block30.

FIG.16shows another variant in which plates52of the block30vary in accordance with lateral distance from the central upright plane54. In this instance, outer plates52are thicker than inner plates52in a lateral direction, transverse to the forward direction. Thus, the outer plates52have greater resistance to deformation, such as twisting, under downward weight loads and so are better able to support the thinner inner plates52closer to the central plane54when the block30is advanced forwardly from the housing32.

If the plates52are strong enough, an alternative arrangement may be possible in which the outer plates52are thinner than the inner plates52, the better to follow the curvature of the fitting36away from the central plane54. It would of course be possible to combine the approaches ofFIGS.15and16by varying the angle of the facets78relative to the side faces50and by varying the thicknesses of the plates52in accordance with the distance from the central plane54.

Moving on toFIG.17, this shows a variant in which the housing32is not fixed rigidly but can instead pivot relative to the hang-off bushing20. For example, the housing32can be mounted to the hang-off bushing20via elastomeric mounts90, gimbals or other pivot arrangements. Pivotal movement of the housing32may thereby be permitted about horizontal and/or vertical axes. This allows the housing32to realign to reorient the block30when compensating for slight misalignment between the launch axis38and the hang-off system. Movement of the housing32relative to the hang-off bushing20can be passive in response to the block30encountering the fitting36or can be active, in the sense of being driven by actuators to compensate for misalignment between the launch axis38and the hang-off system.

Turning finally toFIG.18, this shows that the plates52need not necessarily only move in horizontal directions orthogonal to the launch axis38. Here, the housings32and the plates52are tilted downwardly toward the launch axis38, for example to use gravity to assist deployment of the plates52from the housings32.

The plates52may also tilt, or be driven to tilt, in vertical planes to compensate for slight tilting of the supported part or poor planarity of the interface. For example, blocks30or plates52on one side of the launch axis38could be tilted slightly downwardly and blocks30or plates52on an opposite side of the launch axis38could be tilted slightly upwardly, potentially with matching inclination to the horizontal. Another approach to this issue would be to lower a block30and/or to raise a block30relative to other blocks30to compensate for a slightly misaligned pipeline.

Many other variations are possible within the inventive concept. For example, the plates52need not be in sliding contact with each other and/or with the housing32and could be supported for movement in another way, for example on individual rails or individual bearings. Indeed, the housing32may not be necessary if the plates52are supported in a different way, for example with individual supports. Also, the plates52need not necessarily be parallel and could, for example, converge on the launch axis38in plan view while remaining in substantially vertical planes.

With individual control of the positions of the plates52or other portions of a support block30, it would be possible to configure the contour of the front face40to suit a particular fitting36before bringing the support block30into contact with the fitting36. Such control could, for example, be achieved by selective operation of individual actuators84.