Patent Description:
The present invention concerns a pipe-laying vessel including a pipe-laying tower extending upwardly from the vessel, for example a J-laying vessel, which includes a J-lay tower. The present invention also concerns a method of J-laying pipeline or other elongate product and/or also concerns a J-lay tower.

J-laying vessels are well known. Many known vessels (such as disclosed in <CIT>, <CIT>, <CIT> and <CIT>) have features such as tiltable towers, bulky item installation systems, a number of workstations along the tower, pipestring clamps with line-up capabilities and foldable towers (for stowage). <CIT> discloses a J-lay apparatus comprises a pipeline laying tower. A welding station on the tower welds consecutive segments / lengths of pipeline. The holders may be provided with relatively movable clamps. <CIT> and <CIT> disclose marine pipeline installation systems for laying an offshore pipeline and/or installing a subsea riser, the systems at least allowing to carry out the reel lay method. <CIT> discloses a marine pipelaying system comprising a vessel provided with a pipeline launch tower. The tower comprises pipe laying equipment defining a tower firing line, and is adapted for launching a pipeline along the firing line into the sea. The system furthermore comprises a hang off module supported in the lower part of the firing line for clamping and supporting the weight of previously launched pipeline as well as a stinger for guiding the launched pipeline. <CIT> discloses a pipe-laying vessel comprises: means for propelling the vessel during pipe-laying; means for assembling sections of pipe generally horizontally on the vessel to form longer lengths; a tower at the bow of the vessel, with respect to an intended direction of movement, pivotally mounted so that it can be angled forwards towards the top; means for raising a length of pipe from the deck to a position aligned with the tower; means for joining such a length of pipe to a pipeline being laid; tensioners (<NUM>) arranged to grip such a pipeline and to lower it into the water while maintaining a desired tension in the pipeline; one or more clamps arranged to grip the pipeline below the tensioners; and a lower ramp provided with rollers and arranged to guide the pipeline as it leaves the vessel.

However, none of these prior art vessels is capable of laying in J-lay configuration both rigid pipeline and a flexible conduit simultaneously with the flexible conduit being coupled to the rigid pipeline (in a manner referred to in the art as "piggy back" pipelaying). In addition, it is not readily possible to handle bulky items in situations where the angle of the tower (to the horizontal) is relatively low.

The present invention seeks to mitigate one or more of the above-mentioned problems.

The present invention provides, according to a first aspect, a pipe-laying vessel including a pipe-laying tower extending upwardly from the vessel, the vessel comprising at least three separate workstations spaced apart along the length of the tower. The tower may thus be configured to be able to lay in J-lay mode, and may thus be referred to as a J-lay tower. It will be appreciated that in cases where the tower is tiltable, it may also be possible for the tower to lay in other modes, such as S-lay.

A workstation, in the context of the different aspects of the invention, means a station at which the pipeline being formed can be processed in some way. It may be that one or more, or possibly all, of the workstations are manned when operational, or at least configured to allow personnel access. It may be that at least one of the workstations is configured for fully-automated processing of product (rigid or flexible pipe, for example) for at least some of the time when operational. At least one of the workstations may be configured for welding pipeline, for example joining sections of pipe. There may for example be a welding workstation which enables a pipestring above it to be welded to a pipestring below it, which, by then, may be regarded as the upper end of the pipeline. At least one of the workstations may be configured for performing coating operations. There may for example be a coating workstation which enables a pipestring joint or pipeline joint to be coated as it passes through the coating station. At least one of the workstations may be configured for performing inspecting/testing operations. At least one of the workstations may be configured for performing repairing and/or cutting operations. At least one of the workstations may be configured for connecting of a flexible conduit to the pipeline being laid. One or more of the workstations may be configured for performing two or more of the afore-mentioned processes. For example, a workstation may be configured to carry out non-destructive tests (NDT) on the pipestring or pipeline and, if necessary, repair or replace any defective welds, including for example cutting and re-welding (at least partially) defective welds.

Having three workstations enables each workstation to perform a different set of functions. For example, an uppermost workstation may be used for welding, NDT testing and repair (including for example cutting and then re-welding), a middle workstation may be used for coating and also for welding of bulky items, and a lowermost workstation may be used for connecting a flexible conduit to the pipeline being laid (for example in piggy-back configuration). In addition, these workstations may be used in parallel; for example one workstation can be used for coating and another can be used simultaneously for connecting a flexible conduit. This may reduce the time taken by the workstations as a whole and so speed up the laying process. The present invention has particular, but not exclusive, application in relation to the laying of rigid pipeline in J-lay configuration with flexible product piggy-backed onto the rigid pipeline.

The J-lay tower may be designed to be a relatively low height so as to take only double, rather than triple or quadruple, pipestring joints. Such double pipestring joints may have a length of between <NUM> and <NUM>, typically between <NUM> and <NUM>, for example <NUM>. This enables the tower to be lighter and shorter, and may enable smaller vessels to be fitted with a smaller lighter tower, which with the provision of three workstations, still offers a commercially viable laying speed. The centres of gravity of at least one pair of adjacent workstations may be separated by a distance of less than <NUM>, possibly less than <NUM>. The centres of gravity of the uppermost workstation and the lowermost workstation may be separated by a distance of less than <NUM>, possibly about <NUM> or less.

Preferably, the vessel includes a plurality of clamping assemblies for clamping a pipeline, the clamping assemblies being mounted along the length of the tower and wherein a lowermost workstation is mounted on the tower below a lowermost clamping assembly. This enables the lowermost workstation (which may be used for connecting a flexible conduit to the pipeline being laid, using saddles for example) to be below a final clamping assembly (for example, below a hang-off clamp). This means that any flexible conduit being connected to the rigid pipeline by the lowermost workstation is not clamped or secured by any of the clamping assemblies on the tower and so there is less chance of such clamping assemblies interfering with and/or damaging the flexible conduit (flexible conduit being more prone to clamping damage, by a friction clamp or tensioners, for example, than rigid pipeline). It may be that the tower is so arranged that rigid pipeline is laid along a first firing path and flexible conduit is laid along a second firing path, the first and second firing paths being offset from each other, for example for substantially the entire length of the paths upstream of the lowermost clamping assembly on the tower.

More preferably, the lowermost workstation is configured to attach a flexible conduit alongside the pipeline. In the context of the different aspects of the invention, the flexible conduit may be a flexible umbilical, flexible pipe, cables or any other kind of flexible product including bundles of flexible products. For example, it may be a heating cable, a power cable or a fibre optic cable. The flexible conduit may have a diameter of greater than <NUM>, possibly greater than <NUM>. The flexible conduit may have a diameter of less than <NUM>. The vessel and/or tower may be configured to be able to handle flexible conduit having any diameter within the range of <NUM> to <NUM>, and also possibly other sizes. Preferably, the lowermost clamping assembly is at or above deck level of the vessel. This provides more room for the lowermost workstation below the lowermost clamping assembly. In the context of the different aspects of the invention, the deck of the vessel refers to a lowermost, main deck level of the vessel.

Preferably, the lowermost clamping assembly comprises a hang-off clamp. The hang-off clamp may comprise a friction clamp. The hang-off clamp may comprise a collar clamp. The hang-off clamp may comprise both a friction clamp and a collar clamp. The lowermost clamping assembly may have a working capacity of at least <NUM> tonnes, possibly <NUM> tonnes or more.

Preferably, the vessel includes a plurality of clamping assemblies for clamping a pipeline, the clamping assemblies being mounted along the length of the tower and wherein an uppermost workstation is mounted on the tower above an uppermost clamping assembly. In the context of the different aspects of the invention, uppermost clamping assembly means the uppermost clamping assembly out of the clamping assemblies in or on the tower that have a controllable lateral position with respect to the tower. For example, this does not include an internal line up clamp on a winch or an abandonment/recovery apparatus on a sheave. However, it does include a travelling clamp assembly that moves up and down the tower at a controlled lateral position with respect to the tower. Further, the uppermost clamping assembly means the uppermost clamping assembly out of the clamping assemblies that have a capacity to clamp the pipeline. This does not include clamps simply arranged to clamp a pipestring, and not the whole pipeline being laid. This enables the uppermost workstation to be used for welding a pipestring to the pipeline above the first clamping assembly (i.e. above the clamping assembly clamping the pipeline). The term clamping is intended to cover holding or gripping of pipeline under tension. A pipeline may for example be clamped under tension without necessarily requiring physical contact between whatever apparatus forms the clamping assembly and the entire outer circumference around the pipe in the region of clamping. The term clamping assembly is not intended to cover rollers or other means for merely guiding the lateral position of the pipeline/product, without also holding the tension.

More preferably, the uppermost workstation is a welding station configured to weld a lower end of a pipestring to an upper end of the pipeline.

It may be that the uppermost clamping assembly comprises a pipeline tensioner arrangement. The uppermost clamping assembly may comprise a friction clamp. The uppermost clamping assembly may comprise a collar clamp. The uppermost clamping assembly may have a working capacity of at least <NUM> tonnes, possibly <NUM> tonnes or more.

Preferably, the vessel includes at least two clamping assemblies for clamping a pipeline, the at least two clamping assemblies being mounted along the length of the tower and wherein an intermediate workstation is mounted on the tower in between the two clamping assemblies. This enables the intermediate workstation to be used to coat the pipestring/pipeline and also to be used to weld bulky items to the pipeline.

More preferably, the intermediate workstation is a coating station configured to coat the pipeline.

The tower of the vessel may be configured as (or at least configurable as) a J-lay tower. The tower may be tiltable. The tower may be arranged to be tilted at any angle in the range of <NUM> degrees to <NUM> degrees to the horizontal. It may be that the tower is configured to perform laying of rigid pipeline at any angle in the range of <NUM> degrees to <NUM> degrees to the horizontal. It may be that the tower is arranged to be tilted at any angle in the range of <NUM> degrees to <NUM> degrees to the horizontal. It may be that the tower is additionally arranged to be tilted beyond the vertical, for example up to an angle of <NUM> degrees. In the case where the tower is tiltable it may be that at least one of, and preferably all of the workstations mounted on the tower, are also tiltable, for example so that the workstation can remain in the same orientation relative to the deck of the vessel irrespective of the tilt angle of the tower. The tower may be arranged in sections, there being an upper section (the upper section having a height more than <NUM>%, but less than <NUM>% of the full height of the tower above deck level, and preferably having a height greater than <NUM>% and preferably less than <NUM>% of the full height of the tower above deck level) that is configured to fold down so as to reduce the full height of the tower on deck. The upper section may be arranged to rotate relative to the rest of the tower by more than <NUM> degrees, possibly more than <NUM> degrees. The tower may have a modular construction, for example so that it may be broken down into multiple separate parts being relatively low in number and/or be readily assembled from such separate parts.

It may be that the tower comprises two (or more) sub-towers one of which folds down to lie substantially along the length of the other so as to form a compact configuration suitable for transit. There may be one or more demountable sub-towers. The tower may be associated with a stinger. The stinger may also be configured to be folded away or removed for transit.

According to a second aspect of the invention there is also provided a pipe-laying vessel including a pipe-laying tower extending upwardly from the vessel, the vessel comprising at least two clamping assemblies for clamping a pipeline, the clamping assemblies being mounted along the length of the tower, and at least one workstation mounted on the tower, wherein the workstation is mounted on the tower below a lowermost clamping assembly.

Having a workstation mounted below the lowermost clamp assembly enables the workstation (which may be used for connecting a flexible conduit to the pipeline being laid, using saddles for example) to be below a final clamping assembly (for example, below a hang-off clamp). This means that any flexible conduit being connected to the rigid pipeline by the lowermost workstation is, during operation, not clamped by any of the clamping assemblies on the tower and so is not damaged by them. A lowermost clamping assembly, in the context of the different aspects of the invention, may be "lowermost" in the sense that there is no other clamping assembly, as defined above, below the lowermost clamping assembly. In particular, there is no other clamping assembly, which is mounted at a position along the length of the tower that is lower than the "lowermost clamping assembly", and which is also provided for the purpose holding the full weight of the pipeline being laid.

Preferably, the lowermost clamping assembly is at or above deck level of the vessel. This provides more room for the workstation below the lowermost clamping assembly.

Preferably, the lowermost clamping assembly comprises a hang-off clamp, for example as described above in relation to the first aspect of the invention. Preferably, the workstation is configured to attach a flexible conduit alongside the pipeline. This enables the workstation to be below a final clamping assembly (for example, below a hang-off clamp).

Preferably, the vessel includes a plurality of clamping assemblies for clamping a pipeline, the clamping assemblies being mounted along the length of the tower and wherein an uppermost workstation is mounted on the tower above an uppermost clamping assembly. This enables the uppermost workstation to be used for welding a pipestring to the pipeline above the first clamping assembly (i.e. above the clamping assembly clamping the pipeline).

Preferably, the uppermost clamping assembly comprises a pipeline clamp or tensioner arrangement.

According to a third aspect of the invention there is also provided a method of J-laying pipeline from a vessel, the method including the steps of passing a rigid pipeline down a length of a J-lay tower on the vessel, and attaching a flexible conduit alongside the pipeline, wherein the J-lay tower includes a workstation at which the flexible conduit is attached to the rigid pipeline.

This enables the flexible conduit to be connected to the pipeline, for example by saddles, and laid simultaneously with the pipeline in J-laying (e.g. facilitating piggy-back pipelaying operations in J-lay mode).

The workstation at which the flexible conduit is attached to the rigid pipeline may be the lowermost workstation of the J-lay tower. Preferably, the vessel comprises a plurality of clamping assemblies, the clamping assemblies being mounted along the length of the tower such that there is a lowermost clamping assembly and wherein the workstation (i.e. the workstation at which the flexible conduit is attached to the rigid pipeline) is mounted on the tower below the lowermost clamping assembly.

Preferably, the lowermost clamping assembly is at or above deck level of the vessel. This provides more room for the workstation for connecting the flexible conduit, below the lowermost clamping assembly.

Preferably, the lowermost clamping assembly comprises a hang-off clamp, for example as described above in relation to the first aspect of the invention.

The uppermost clamping assembly may comprise a pipeline clamp, tensioner arrangement, or the like, for example as described above in relation to the first aspect of the invention.

More preferably, the intermediate workstation is a coating station configured to coat a joint of the pipeline.

According to a further aspect of the invention there is also provided a method of abandoning a product from a vessel, the product comprising a rigid pipeline with attached flexible conduit. Such a method comprises a step of passing the rigid pipeline along a first firing path, using a first apparatus. There is a step of passing the flexible conduit along a second, separate firing path, using a second, separate apparatus. The method further comprises a step of abandoning the rigid pipeline by breaking a direct connection between the rigid pipeline and the vessel, and retaining a direct connection of the vessel with the flexible conduit, such that the flexible conduit can continue to be passed along the second firing path whilst the rigid pipeline is abandoned.

This method, which can be used with J-laying or other modes of laying for example, enables the rigid pipeline to be abandoned, when required, whilst retaining a laying connection with the flexible conduit. This is achieved partly by the fact that the flexible conduit and rigid pipeline are laid through two separate firing paths. In addition, it is also possible because the flexible conduit is laid from a location lower than the abandonment apparatus, e.g. an abandonment/recovery winch system, used to abandon the rigid pipeline. The flexible conduit may be laid from a reel on the vessel. In certain embodiments, the vessel may be used to lay "rigid" pipeline from a reel, with such laying operations for example requiring pipe bending apparatus.

Advantageously, the step of abandoning the rigid pipeline includes using an abandonment/recovery winch system, separate from the first and second apparatus.

According to a further aspect of the invention there is also provided a method of recovering a previously abandoned product to a vessel, the product comprising a rigid pipeline with attached flexible conduit. The method comprises a step of paying-in the flexible conduit, while (a) the rigid pipeline remains disconnected directly from the vessel (b) there is retained a direct connection between the vessel and the flexible conduit, and (c) the rigid pipeline is attached to the flexible conduit. The method may also include a step of recovering a free end of the rigid pipeline onto the vessel, for example while still connected to the flexible conduit.

This method, which can be used in J-laying or other modes of operation, enables the rigid pipeline to be recovered, while maintaining the retained connection with the flexible conduit. This may, in certain embodiments of the invention, be achieved partly by arranging the flexible conduit and rigid pipeline to be laid through two separate firing paths. In addition, it may also be that the flexible conduit is laid from a location lower than the abandonment apparatus, e.g. an abandonment/recovery winch system, used to abandon the rigid pipeline.

Once recovered, the free end of the recovered rigid pipeline can be joined to a free end of a rigid pipeline product, such as a length of rigid pipestring for example. Pipelaying operations can then be recommenced.

According to a sixth aspect of the invention there is also provided a pipe-laying vessel including a pipe-laying tower extending upwardly from the vessel, wherein the tower is tillable and provided with an internal pipe clamp apparatus, the internal pipe clamp apparatus comprising an internal pipe clamp, a housing garage for the internal pipe clamp and a guide apparatus for guiding the internal pipe clamp from the garage to an end of a pipeline held by the tower.

The internal pipe clamp may be suspended by a line, such as a winch line, such that if the internal pipe clamp's orientation were not controlled or otherwise constrained by its garage, the guide apparatus or the pipe, it would tend to adopt a vertical orientation by virtue of gravity. Having the guide apparatus allows the internal pipe clamp to be guided from the garage to a pipeline end at a required orientation (aligned with the orientation of the pipeline end) so that it can be inserted into the pipeline end at that orientation. This aids with the insertion of the internal pipe clamp (as it is already held at the correct angle/orientation) and makes operation smoother.

It may be that the housing garage is arranged to tilt with the tower, so that the housing garage follows the tilting movement of the tower. It may be that the housing garage is mounted on the tower so as to move with the tower. It may be that the housing garage is mounted so that the tower may move independently of the housing garage.

It may be that the guide apparatus is arranged to tilt with the tower so that its orientation is substantially the same as the tower, and for example the pipeline held by the tower. It may be that the guide apparatus is mounted on the tower so as to move with the tower. It may be that the guide apparatus is mounted so as to be able to move independently of the tower. It may be that the guide apparatus is arranged to guide the internal pipe clamp at an orientation that depends on the orientation of the tiltable tower (e.g. it may be that the guide apparatus is arranged to guide the internal pipe clamp at an orientation that is the same as the orientation of the tiltable tower). This means that the internal pipe clamp is automatically held at the correct orientation for any given tower orientation.

The guide apparatus may comprise a trolley arranged to transport the internal pipe clamp apparatus between a stored position in the housing garage and a pipe-clamping position outside of the housing garage, preferably a position next to the end of the pipeline held by the tower. The trolley is preferably so configured that the orientation of the internal pipe clamp apparatus when in its pipe-clamping position corresponds to the orientation of the pipeline. The guide apparatus may comprise a rail for guiding the internal pipe clamp apparatus between a stored position and a pipe-clamping position. The rail is preferably so configured that the orientation of the internal pipe clamp apparatus when in its pipe-clamping position corresponds to the orientation of the pipeline. It may be that both such a trolley and such a rail are provided, with the internal pipe clamp apparatus being carried by a trolley that is guided by the rail. The internal pipe clamp apparatus is preferably releasably coupled to the trolley / rail.

The present invention also involves a tower, for example a J-lay tower, that is arranged for use in any of the aspects of the invention as described or claimed herein, possibly including any optional features described with reference thereto. The tower may be supplied separately from the vessel. The tower may be supplied as a kit of parts. The tower may comprise two, three or four sub-towers, which are arranged to be assembled together to form the full tower. The tower may comprise one or more workstations. It may be that one or more workstations are provided separately from the tower, but that the tower is configured to accommodate such workstations. The tower may include a main attachment point defined by load-bearing structure of the tower, the attachment point facilitating mounting of the tower to a vessel. There may be more than one main attachment point. The tower may include a tilting arm (or two or more such arms) so that the tower may be tilted relative to the vessel. The tilting arm may be rotatable connected to the vessel. The tilting arm may have a variable length. The tilting arm may comprise two or more telescopic parts that enable the arm to vary its length. The tilting arm may include a main attachment point defined by load-bearing structure that is arranged for attaching to the vessel. The tower may be provided with a stinger section.

Figure la shows a plan view, and <FIG> shows a side view, of a vessel <NUM> according to a first embodiment of the invention. Figures lb and <NUM> c show the stern and bow, respectively, of the vessel in plan view with certain parts shown in <FIG> a being omitted or made more schematic for the sake of clarity. The vessel has a main deck <NUM>. Various equipment is situated on the deck <NUM>, including a crane <NUM> on the portside of the vessel and a bulky item handling skid <NUM> (omitted from Fig lb) next to the crane <NUM> and in the region of the centreline of the vessel and towards the stern.

The vessel <NUM> is provided with a J-lay tower <NUM> at the stern of the vessel. The tower <NUM> is supported on the vessel by two supports <NUM>, <NUM>, one of either side of the tower. The tower <NUM> acts to lay rigid pipeline <NUM> along a first firing line <NUM>.

There is also provided flexible product handling equipment, designated generally by <NUM>, on the vessel deck <NUM>. This equipment <NUM> comprises a basket 141a and reel 141b for holding the flexible product <NUM>, a curvature controller <NUM> to provide a suitably large enough bend in the product when being taken off the basket/reel 141a/141b, and rollers <NUM> for supporting the flexible product and enabling it to smoothly be pulled out. The flexible product <NUM> is laid along a second firing line <NUM>.

There is also provided a pipestring stock <NUM> (shown schematically only in Figure lb) and a loading arm <NUM> for raising individual pipestrings <NUM> from the stock to a position parallel to the tower <NUM> and then to raise the pipestring up and in the tower.

Looking in more detail at the tower <NUM>, and with reference to <FIG> in particular, the tower has a top truss section <NUM> and a lower stinger <NUM>. Although not shown, both the truss section <NUM> and the stinger <NUM> can be folded back against a main central portion of the tower <NUM>, for transit. The truss section <NUM> is folded anti-clockwise (when looking at the vessel from the starboard side, as shown in <FIG>) to rest against the stern side of the tower <NUM>. The stinger is folded clockwise to rest against the stern side of the tower <NUM>. The tower <NUM> itself is tiltable about its connection at the stern of the vessel. It is tiltable from the <NUM> degrees angle shown, in <FIG>, to an angle of <NUM> degrees to the horizontal/vessel deck <NUM>, for the purposes of laying operations and further tiltable to an angle of <NUM> degrees to the horizontal/vessel deck <NUM> for the purpose of assisting transit. It is also tillable backwards from the position shown to an angle of <NUM> degrees. (An example of the tilting of the tower is shown and briefly described below with reference to <FIG>).

The tower <NUM> is designed to join together double pipestring joints at a time. In other words, each time a pipestring <NUM> is welded to a pipeline <NUM> being laid, the pipestring <NUM> is one of a double joint length (<NUM>). Therefore, the length of the truss section <NUM> corresponds to this height (as a minimum). In <FIG>, a pipestring <NUM> can be seen with its upper end 136a at the top of the truss section <NUM> and its lower end 136b at the bottom of the truss section.

At the top of the truss section is an internal line-up clamp winch <NUM> which is associated with a corresponding internal line-up clamp (not shown in <FIG>). Along the truss section <NUM> are three pipestring clamps <NUM>, labelled as upper clamp <NUM>, middle clamp <NUM> and lower clamp <NUM>. These clamps <NUM> clamp a pipestring <NUM> while it is welded to the pipeline <NUM>. The three pipestring clamps <NUM>, <NUM>, <NUM> are not required to hold the full tension of the pipeline and consequently have a relatively low load bearing capacity.

Where the truss section <NUM> joins to the main tower <NUM>, at the top of this main section of the tower, is an abandonment and recovery sheave <NUM>. The sheave has a first position <NUM> shown in <FIG> (and <FIG>, <FIG> and <FIG>) in which it is aft of the firing line <NUM> of the pipestring/pipeline. It also has a second position <NUM> which is shown in <FIG> and <FIG>, for example.

Slightly further down the tower <NUM>, is a first workstation, in the form of a welding station <NUM>. This is the station where the upper end 134a of the pipeline being laid is welded to the lower end 136b of the pipestring <NUM>. The welding station <NUM> has a first position <NUM> shown in <FIG> in which it is in the firing line <NUM> of the pipestring/pipeline. It also has a second position <NUM> which is shown in <FIG> for example.

Further down the tower <NUM> again, is a tensioner clamping arrangement <NUM>. The tensioners <NUM> are used to lay the pipeline <NUM> and are the main means provided on the tower for clamping the pipeline in position when being worked on at the workstations and are also the main means for paying out the rigid pipeline whilst withstanding the pipeline tension caused by the weight of the pipeline being held by the vessel. The tensioners <NUM> have a first position <NUM> shown in <FIG> in which they are in the firing line <NUM> of the pipestring/pipeline. They also have a second position <NUM> which is discussed in relation to <FIG> and <FIG>.

Again, going further down the tower <NUM> is a second workstation <NUM>. This second station is used for coating the pipeline <NUM>. It is also used to weld bulky items to the pipeline <NUM> as will be described in relation to <FIG>.

At slightly above deck level <NUM>, is a hang-off friction clamp <NUM>, which is moveable between an open, released and closed, clamping position. During normal laying operations the main tensioners perform the laying cycle without the need for the hang-off clamp <NUM>. The hang-off clamp <NUM> is used as a safety clamp to clamp the pipeline <NUM> when it is not being laid out, for example in case of emergency (e.g. in the case of there being a fault with the main tensioners) and also during special laying operations, for example when there is a need to manage the laying of bulky items.

Below the hang-off clamp <NUM>, but above the stinger <NUM>, is a third workstation <NUM>. This workstation is a flexible product attaching station <NUM> and is use to attach the flexible product <NUM> to the pipeline <NUM> at regular intervals.

As a first step in the laying process, a pipestring <NUM> is raised from the stock <NUM> by loading arm <NUM>, to a position parallel to the truss section <NUM> at the top of the tower <NUM>. Here is it clamped by the three pipestring clamps <NUM>, <NUM>, <NUM> and the loading arm <NUM> lowered back down the tower.

Internal line-up clamp is placed inside the upper end 136a of the pipestring and lowered on a winch to the lower end 136b of the pipestring <NUM>. The lower end 136b of the pipestring is then welded to the top 134a of the pipeline <NUM> in welding station <NUM>, after the ends 136b, 134a have been lined up by the internal line-up clamp. The internal line-up clamp and associated winch <NUM> for holding and managing individual pipestrings are not required to hold the full tension of the pipeline and consequently have a relatively low load bearing capacity.

Once the pipestring <NUM> has been joined to the pipeline <NUM>, the tensioners <NUM> are used to lay out the pipeline <NUM>, including the newly welded pipestring <NUM>. Once the upper end of the pipestring 136a (now the upper end of the pipeline 134a) reaches the welding station <NUM>, a new pipestring is raised by the loading arm, ready to repeat the process again.

During the whole process, the second work station <NUM> is used to coat the newly welded joints of the pipeline <NUM> as the pipeline <NUM> is laid out past the workstation <NUM>. Similarly, the third workstation <NUM> is used to attach flexible product to the pipeline <NUM> (using saddles every <NUM> metres, for example), as the pipeline <NUM> is laid out past the workstation <NUM>, so as to layout piggy-back product (i.e. the flexible product <NUM> piggybacking onto the rigid pipeline <NUM>).

If the pipeline <NUM> needs to be abandoned at any point, this is done using the abandonment and recovery winch <NUM>. Advantageously, when this is done, it is not necessary to also abandon the flexible product <NUM>, and the connection with the vessel <NUM> of the flexible product <NUM> can be maintained. When abandoning piggyback product from the vessel, the tension of the rigid pipeline is held either by the hang-off clamp or the main tensioner. An AIR head is then attached to the free-end of the pipeline (or an internal pipe holding apparatus, able to take the full weight of the pipeline, is inserted) so that the AIR winch line may be attached. Tension is then taken up by the AIR winch line (with appropriate AIR tensioning means provided on the J-lay tower or otherwise on the vessel). Any clamping function provided by the clamping assemblies (tensioners or hang-off clamp) in the tower is released, with full tension in the rigid pipeline then being held by the AIR equipment. The flexible pipeline piggybacking on the rigid pipeline is not cut. As the AIR winch line pays-out, so that the free end of the rigid pipeline is lowered from the vessel <NUM> towards the sea-bed, the flexible product is also paid-out (at the same rate) using the reel / basket 141b/141a. The path taken by the flexible product as it leaves the vessel is thus different from that taken by the rigid pipeline. Before the free end of the rigid pipeline leaves the vessel, there is a direct connection between the rigid pipeline below the vessel <NUM> and the rigid pipeline held by the tower <NUM> of the vessel. After, the rigid pipeline is released from the vessel and then lowered via the AIR winch <NUM>, that direct connection between pipeline and vessel no longer exists (and is effectively broken). There no longer exists a continuous length of rigid pipeline that extends from the vessel to the abandoned pipeline in the sea. However, a direct connection of the flexible conduit on the vessel <NUM> to the flexible conduit piggybacked on the rigid pipeline is retained during the abandonment process. The recovery of a piggyback pipeline product that has been previously abandoned as described above can be carried out effectively by performing the steps above in reverse. Thus, with the use of an AIR line (which may need to be attached as part of the recovery process, or may have remained attached since abandonment) the end of the rigid pipeline can be recovered back onto the vessel <NUM> and into the J-lay tower <NUM>. At the same time as rigid pipeline is being recovered, the reel / basket 141b/141a is operated to reel-in the flexible conduit which is still connected. Once the free end of the rigid pipeline has been fully recovered into the J-lay tower <NUM>, tension can be transferred from the AIR equipment to the tensioners <NUM> and welding of new pipe-strings recommenced.

It can be seen at the bottom of <FIG> that a bulky item string <NUM> has been inserted in the pipeline <NUM>. The bulky item string <NUM> comprises a pipestring <NUM> with a bulky item <NUM> on it. It has an upper end 125a and a lower end 125b. With reference to <FIG>, the process of laying the bulky item string <NUM> as part of the pipeline <NUM> will be described.

<FIG> shows a partial side view of the vessel during a first stage of a "bulky item" installation. Here, the bulky item string <NUM> is on the bulky item handling skid <NUM>. The bulky item string <NUM> is placed on the skid <NUM> by the crane <NUM>. The skid <NUM> is then slid towards the tower, from its position in <FIG> to the position shown in <FIG>. During this first stage, the welding station <NUM> is moved from its first position <NUM> to a second position <NUM>. In this second position <NUM>, the welding station <NUM> is moved aft of the firing line <NUM>. The pipeline <NUM> is being clamped by the hang-off clamp <NUM>.

<FIG> shows a partial side view of the vessel during a second stage of a "bulky item" installation. Here, the skid <NUM> has been rotated so that the bulky item string <NUM> is parallel to the tower <NUM>. In addition, the abandonment and recovery sheave <NUM> has been moved to its second position <NUM> on the firing line <NUM>. Also, the tensioners <NUM> have moved to their second position <NUM> aft of the firing line <NUM>.

<FIG> shows a partial side view of the vessel during a third stage of a "bulky item" installation. In this stage, the skid <NUM> had been used to adjust the position of the bulky item string <NUM>, ready for welding to the pipeline <NUM>. The welding is carried out in the second workstation (coating station) <NUM>. Then, internal pipe clamp apparatus is inserted in the upper end of the pipestring 125a and takes the full weight of the pipestring <NUM>. Further detail concerning this high-load capacity internal pipe clamp apparatus is provided with reference to <FIG> below. The bulky item handling skid <NUM> is then lowered back to its original position as it is no longer needed to clamp the bulky item string <NUM>.

<FIG> shows a partial side view of the vessel during a fourth stage of a "bulky item" installation. Here, the hang-off clamp <NUM> has been opened. At this point, the internal pipe clamp apparatus takes the entire weight of the pipeline <NUM> (including and via newly joined bulky item string <NUM>), via a line that is routed via the sheave <NUM>. The line is paid-out via the sheave <NUM> thus lowering the pipeline <NUM> down so that the bulky item <NUM> is located below the hang-off clamp <NUM> and the upper end of the bulky item string 125a is located adjacent the coating station <NUM>. At the same time, the flexible product <NUM> is unrolled from the basket/reel 141a/141b and attached in the normal manner so as to piggyback on the rigid product.

<FIG> shows a partial side view of the vessel during a fifth stage of a "bulky item" installation. Here, the hang-off clamp <NUM> has been closed around an upper region of the bulky item string <NUM>. The internal pipe clamp apparatus is then disconnected from the bulky item string <NUM> and the abandonment and recovery sheave <NUM> retracted.

<FIG> shows a partial side view of the vessel during a sixth stage of a "bulky item" installation. Here, the abandonment and recovery sheave <NUM> has been moved back to its first position <NUM>. In addition, the skid <NUM> has been loaded with a normal pipestring <NUM> using the crane <NUM>, and has then been rotated to be parallel to the tower <NUM>. The skid <NUM> is adjusted to line up the pipestring <NUM> with the upper end of the pipeline 134a (also the upper end of the bulky item string 125a). Welding of the new pipestring <NUM> and the pipeline <NUM> takes place in coating station <NUM>.

<FIG> shows a partial side view of the vessel during a seventh stage of a "bulky item" installation. Here, the welding station <NUM> is moved back to its first positon <NUM>. The tensioners <NUM> have also moved back to their first positon <NUM> and the bulky item skid <NUM> has been lowered. The normal laying process can then continue. <FIG> shows the bulky item <NUM> being lowered further It will be noted that the view shown in <FIG> corresponds broadly to that shown in <FIG>, but that <FIG> shows parts only of the vessel.

Above, mention is made of internal pipe clamp apparatus which is used to hold the full weight of the pipeline when managing a bulky item. <FIG> shows highly schematically the internal pipe clamp apparatus, which comprises an internal pipe lifting tool <NUM> suspended on a (detachable) line <NUM> (e.g. an AIR line) and is housed in the tower <NUM> in a garage <NUM>. <FIG> shows the tower arranged at a <NUM> degree to the horizontal configuration. The garage <NUM> is fixed to the tower, and is used to store the internal pipe lifting tool <NUM> when not in use. A guide apparatus comprising trolley <NUM> and guide rails <NUM> is also provided for guiding the lifting tool <NUM> from the garage <NUM> to the end of the rigid pipeline <NUM> in the tower. <FIG> shows the trolley <NUM> carrying the pipe lifting tool <NUM> from the garage towards the free end of the pipeline <NUM>. When the trolley is next to and aligned with the pipeline (as shown in <FIG>) the trolley <NUM> releases the pipe lifting tool <NUM>, so that the pipe lifting tool <NUM> is suspended and held by the line <NUM>. The line is lowered so that the pipe lifting tool <NUM> moves from within the trolley to the interior of the pipe (to a position like that shown in <FIG>), its passage being guided in part by the trolley and in part from the interior walls of the pipeline <NUM>. Once fully received within the pipeline, clamps of the pipe lifting tool <NUM> may operate to clamp the pipeline so that the weight of the pipeline can be transferred to the line <NUM>.

<FIG> shows the tower tilted at an angle of about <NUM> degrees to the horizontal. When the tower is so tilted the garage <NUM>, trolley <NUM> and guide rails <NUM> also tilt with the tower <NUM> to adopt the same relative angle. Whilst not shown in <FIG>, the workstations positioned along the length of the tower also rotate relative to the tower, in dependence on the tilting of the tower, so that the working floor/platform of each workstation is maintained level with the horizontal/vessel. <FIG> shows the trolley <NUM> carrying the pipe lifting tool <NUM> from the garage towards the free end of the pipeline <NUM>. When the trolley <NUM> is next to and aligned with the pipeline (as shown in <FIG>) the trolley <NUM> releases the pipe lifting tool <NUM>, so that the pipe lifting tool <NUM> is suspended and held by the line <NUM>. The line is lowered so that the pipe lifting tool <NUM> moves from within the trolley to the interior of the pipe (to a position like that shown in Figure 4O, its passage being guided in part by the trolley and in part from the interior walls of the pipeline <NUM>. Once fully received within the pipeline, clamps of the pipe lifting tool <NUM> may operate to clamp the pipeline so that the weight of the pipeline can be transferred to the line <NUM>. By controlling the orientation of the pipe lifting tool <NUM> in this manner, correct alignment with the end of the pipeline can be repeatedly and readily achieved at any angle of tilting of the J-lay tower.

As an alternative, the vessel may be provided with two chutes or reels / baskets for laying two different flexible products with the rigid pipeline. For example, there may be one chute (and associated firing line) on one side of the tower and a second chute (and associated firing line) on the other side of the tower.

As another alternative, the tensioners may be mounted on the tower such that there is a "dead-band" of movement of roughly between <NUM> to <NUM> metre or +- <NUM> tonnes. This allows for the pipeline to move up and down relative to the tower to allow for movement of the vessel. This puts less stress (tension) on the pipeline being laid. For this to work, it would be expected to have pipe joint processing apparatus (e.g. welding apparatus) clamped to the pipeline itself and so move with the pipeline and the site to be welded, rather than with the vessel.

Claim 1:
A pipe-laying vessel (<NUM>) including a pipe-laying tower (<NUM>) extending upwardly from the vessel, the vessel (<NUM>) comprising:
- at least two clamping assemblies (<NUM>, <NUM>) for clamping a pipeline, the clamping assemblies being mounted along the length of the tower, and
- at least three separate workstations (<NUM>, <NUM>, <NUM>) spaced apart along the length of the tower (<NUM>),
- at least one workstation (<NUM>) which is
• mounted on the tower below a lowermost clamping assembly (<NUM>), and
• a flexible product attaching station (<NUM>) for attaching a flexible conduit alongside the pipeline.