WO2015112007A1

WO2015112007A1 - Manufacturing of a subsea pipeline and spooling said pipeline onto a reel of a pipelaying vessel at a spoolbase

Info

Publication number: WO2015112007A1
Application number: PCT/NL2015/050038
Authority: WO
Inventors: Joop Roodenburg
Original assignee: Itrec B.V.
Priority date: 2014-01-24
Filing date: 2015-01-22
Publication date: 2015-07-30
Also published as: NL2012137C2

Abstract

A method for manufacturing a subsea pipeline (1) and spooling said pipeline onto a reel (101, 102) or a carousel of a pipe laying vessel (100) at a spool base. The method comprises connecting pipes (2) end-to-end at a pipeline assembly station (10) to form a continuous pipeline stalk (1), said pipeline having an elastic limit. The continuous pipeline stalk is spooled directly from the pipe assembly station onto a floating intermediate pipeline storage device (20) that is adjacent the pipeline assembly station and the stalk is temporarily stored thereon. The pipeline stalk is later spooled from the floating intermediate temporary pipeline storage device onto the reel of the pipe laying vessel. The floating intermediate pipeline storage device is a carousel (30, 31) pipeline storage device which has an annular floating base that is assembled from multiple barges (25) which are interconnected in an annular array and having an above waterline carousel.

Description

MANUFACTURING OF A SUBSEA PIPELINE AND SPOOLING SAID PIPELINE ONTO A REEL OF A PIPELAYING VESSEL AT A SPOOLBASE

The present invention relates to the manufacturing of a subsea pipeline and spooling said pipeline onto a reel of a pipelaying vessel at a spoolbase. The pipeline spooled onto the reel of the pipelaying vessel is later installed at an installation site remote from the spoolbase by unspooling and then lowering the pipeline into the sea, e.g. to be installed on the seabed.

In case of a rigid pipeline it is common for the reel of the pipelaying vessel to have a diameter such that the rigid pipeline is subjected to plastic deformation due to the bending necessary to wind the rigid pipeline onto the reel. Therefore the pipelaying vessel is equipped with a straightener assembly which is adapted to straighten the pipeline after unspooling from the reel, which straightened pipeline is then lowered into the sea towards the seabed.

At various locations in the world, e.g. in the USA, Norway, Brazil, Angola, and the UK, so- called shore based spoolbases are present where long straight sections or stalks of rigid pipeline are manufactured by welding rigid pipes end-to-end. Known shore based spoolbases allow manufacturing of pipeline stalks having a length of e.g. 700, 1000, 1200, and 1500 meters. A pipelaying vessel is moored at the spoolbase and the stalks of pipeline are spooled onto the reel of the vessel, wherein the stalks are interconnected during the spooling process to make up a many kilometres long continuous pipeline that is spooled onto the reel.

Such a shore based spoolbase requires a long stretch of land. The associated costs, e.g. for the acquisition and preparation of the land, the obtaining of planning permissions, etc. are such that effectively only a limited number of shore based spoolbases exist nowadays.

In a present day offshore pipelaying project involving reel-lay installation of pipeline from a pipelaying vessel reel and using a common onshore spoolbase the actual pipelaying may form about 15% of the total project time. Transit time of the pipelaying vessel between the installation site and the spoolbase may be about 25% of total project time. The spooling of pipeline onto the pipeline vessel reel may be about 50% of total project time. The above example already indicates that the need exists to increase the efficiency of the spoolbase operation, in particular of the spooling process. As presently active and planned pipelaying jobs are quite remote from these shore based spoolbases, the transit time becomes a further issue which is nowadays countered by increasing propulsion power of the pipelaying vessel to sail faster which has drawbacks in view of vessel costs and operating costs.

One new development, which has become reality in recent years, is the use of

interchangeable reels on the pipelaying vessel, e.g. as disclosed in WO2011/105894. Herein the pipelaying vessel can remain at the pipelaying site whilst only one or more

interchangeable reels are shuttled between that site and the shore based spoolbase. This approach requires the presence of a heavy lift crane to lift the loaded reel onto the pipelaying vessel, e.g. the crane being arranged on the vessel itself, as the loaded reel may weigh well over 1000 metric tons, e.g. between 2500 and 3000 metric tons.

In the past, before the use of interchangeable reels became reality, several other approaches have been proposed but have largely remained theoretical.

For example in US7544013, on which the preamble of claim 1 is based, it is proposed to spool the continuous rigid pipeline directly from the pipe assembly station onto a floating intermediate pipeline storage device that is moored adjacent the pipeline assembly station and to store the pipeline temporarily thereon. The floating intermediate pipeline storage device has a barge on which a vertical reel is mounted having a horizontal axis and a diameter similar to the reel on-board the pipelaying vessel and it is proposed to subject the pipeline to plastic bending in order to spool it onto this intermediate reel. With the pipelaying vessel moored adjacent the intermediate pipeline storage device the pipeline is unspooled from the intermediate temporary reel and onto the on-board reel.

As discussed in US7544013 other prior art proposals envisage that the pipeline is spooled onto a floating, partly submerged horizontal reel or that the pipeline is provided with buoyancy members and then wound into a single spiral which floats at the water surface, which reel or spiral is then towed over sea to the pipelaying location. In these proposals the diameter of the spooled or wound pipeline is such that the pipeline is not subjected to plastic deformation which in practice requires diameters of 150 meters or more. Towing such a structure with the partly submerged pipeline out to sea to the pipeline installation site is regarded as impractical and associated with issues concerning the fatigue loads on the pipeline. Therefore these approaches have yet to see broad acceptance in the industry. The present invention aims to propose an alternative method and installation that is practically feasible and that is attractive financially, both with regard to efficiency of the process and total installed costs of the installation. The invention proposes a method according to the preamble of claim 1 , wherein the floating intermediate pipeline storage device is a floating carousel pipeline storage device which has an annular floating base that is assembled from multiple barges which are interconnected in an annular array, wherein the floating carousel pipeline storage device further comprises a horizontal pipeline storage carousel that is fixed on the interconnected barges and is adapted for above waterline storage of pipeline, said carousel comprising pipeline support members defining at least one of a circular outer perimeter and a circular inner perimeter of the carousel, wherein the method further comprises causing the annular floating base to revolve in a first direction and depositing the pipeline stalk arriving from the pipeline assembly station such that the pipeline stalk is stored in multiple windings in the carousel, which carousel revolves along with the annular floating base, and wherein the carousel has a diameter such that the bending of the pipeline stalk spooled in the carousel is within the elastic limit of the pipeline, wherein the method further comprises causing the annular floating base to revolve in a second direction opposite to the first direction and retrieving the pipeline stalk from the carousel, and wherein the method further comprises spooling the retrieved pipeline stalk onto the reel of the pipelaying vessel.

By means of arranging barges in an annular array it is practically feasible to fix on the barges an above waterline carousel having a diameter such that the spooled pipeline is within its elastic limit, e.g. with a carousel diameter of at least 150 meters given the normal minimal dimensions of subsea rigid pipeline.

It is envisaged that in practical embodiments a pipeline stalk spooled onto the carousel may have a length of at least 10.000 meter, e.g. of at least 20.000 meter, e.g. of at least 40.000 meters (for outer pipeline diameters ranging between 10 and 18 inch). This is many times longer than in prior art shore based spoolbases and allows to reduce the spooling time significantly, e.g. as fewer or even no interconnections are needed between pipeline stalks to make up the continuous pipeline to be spooled onto the pipelaying vessel reel.

The floating carousel pipeline storage device is preferably revolved in the second direction, during unspooling, at a speed of at least 25 meter/min, e.g. of about 30 meter/min. The structure with the annular array of barges allows such speeds without difficulty which is beneficial for the spooling time onto the vessel.

The pipeline assembly may, for example, be performed at a speed of about 4 - 8 meter/min. With a carousel circumferential length of about 900 meter, a complete revolution of the carousel may thus take about 2 hours during the spooling of the stalk onto the carousel.

As the carousel is above waterline the pipeline is not submerged during this temporary storage thereby avoiding issues like pipeline soiling and/or damage and also allowing for easy access by personnel during spooling and unspooling, inspection, and/or application of tie members to locally tie down the pipeline stalk when desired.

As the carousel is fixed on the barges it rotates along with the annular array of barges, which allows to dispense with any revolving chassis of the carousel relative to the barges which would be very complex in view of the diameter thereof.

It is envisaged that the barges are disconnected from one another for transportation thereof, e.g. for transportation on-board a heavy transport vessel, e.g. a semi-submersible heavy transport vessel, from one location to another.

Preferably the floating intermediate pipeline storage device is moored at a near-shore location, preferably in a sheltered basin, e.g. in a natural or man-made bay, a harbour, an estuary, a fjord, etc. so that the device is not subjected directly to the undampened sea swell. A breakwater may be installed to reduce sea swell, e.g. the breakwater comprising one or more caissons.

As the pipeline that is spooled in the carousel has the tendency to flex radially outward the carousel preferably at least comprises outer pipeline support members defining a circular outer perimeter of the carousel. In a practical embodiment the carousel also comprises inner pipeline support members defining a circular inner perimeter of the carousel. The pipeline is then stored in multiple windings between the inner and outer pipeline support members. In a practical embodiment the inner diameter of the pipeline spiral windings spooled in the carousel, e.g. limited by the circular inner perimeter of the carousel, is at least 150 meter, e.g. between 240 and 300 meter so as to avoid exceeding the elastic limit of rigid subsea pipeline.

In an embodiment multiple horizontal pipeline storage carousels are concentrically fixed on the interconnected barges, which e.g. allows to store a different diameter pipeline in each of the carousels and/or for example the helical winding of each individual pipeline in a single vertical layer. The spooling of pipelines into the different carousels may be done

simultaneously, but one can also envisage the sequential loading of the pipelines into the concentric carousels.

In an embodiment the pipeline assembly station may include parallel assembly lines and pipelines, e.g. of different diameter, can be manufactured simultaneously at said assembly lines. For example the multiple pipelines are manufactured in parallel and then spooled simultaneously in concentric carousels.

In an embodiment a pipeline stalk is spooled in a single spiral horizontal layer in the carousel, e.g. with multiple pipeline stalks being laid on top of one another (possibly with spacer members in between), each wound as a single spiral horizontal layer, e.g. the layer having a width between 4 and 15 meters. Preferably single layer spiral winding is performed from the outer perimeter of the carousel inwards.

In another embodiment a pipeline stalk is spooled in a multiple level spiral winding, so with the stalk having multiple spiral windings on top of another. This approach may involve that, e.g. in a layer wound from the inner perimeter to the outer perimeter, the pipeline stalk is secured in the carousel by ties (e.g. slings), e.g. to the adjacent inward pipeline winding, in order to restrain the pipeline from flexing outwards. In another embodiment a pipeline stalk is spooled in a single level helical winding, so with the windings of the stalk on top of one another. For example inner and outer pipeline support members are then vertically arranged with a spacing corresponding to the pipeline outer diameter. In an alternative helical windings of consecutive pipe stalks are arranged concentric starting with an outer winding of a first pipe stalk and an inner winding of a second pipe stalk supporting directly against a preceding outer winding of the first pipe stalk.

In another embodiment a pipeline stalk is spooled in a multiple level helical winding. In an embodiment use is made of barges having a monohull with parallel side walls, a bow, a stern, a bottom, and, preferably, a deck. Such barges are common as deck transportation barges and of a simple design allowing procurement at limited costs. In another embodiment use is made of barges having a monohull with parallel side walls, a bow, a stern, a bottom and an open topped hold, e.g. with a gangway along one or both sides of the hold. Such barges are common for transportation of bulk materials, e.g. coal, in the hold. They can be procured at limited cost. One can envisaged that the carousel is standing on the floor of the hold, or that the carousel comprises horizontal beams extending over the hold.

In another embodiment use is made of barges each having one or more submerged or submergible pontoons providing the majority of the buoyancy of the barge, and having columns erected from said one or more pontoons to intersect the design waterline and support thereon an above waterline deck of the barge, e.g. a deck box including said deck. It is envisaged that the carousel is fixed on the deck. Compared to common monohull barges this design allows to reduce the effect of sea swell on the stability of the floating base as the buoyant cross section intersecting the waterline is reduced, thereby reducing any sea swell induced loading on the spooled pipeline in the one or more carousels.

In a practical embodiment each barge is pre-fitted with a circle arc segment of the one or more horizontal pipeline storage carousels prior to interconnection of the barges into the annular array. For example the outer and/or inner pipeline support members are upright posts, e.g.

extending upward from the deck, e.g. mounted (e.g. removable), in post receiving holes mounted in the deck, or erected from a floor member, e.g. a horizontal beam, of the carousel.

For example a pipeline support member is pivotal, e.g. by means of a hinge at its lower end, between a non-active position and an erect operative position.

For example a pipeline support member is mobile between a non-active position and an operative position, preferably an actuator, e.g. a hydraulic cylinder, being provide for motion of the member between said positions. In an embodiment the carousel, or floor members of the carousel on which the pipeline stalk rests, is/are resiliently mounted on the barges, e.g. with elastic connectors, e.g. rubber blocks, allowing to absorb some relative motions of the carousel and the barges. In an embodiment the carousel, or floor members of the carousel on which the pipeline stalk rests, are mobile in vertical direction, e.g. resiliently mobile in vertical direction, e.g. on dampers or springs, allowing to absorb some vertical relative motions.

For example a carousel further comprises horizontal floor members, e.g. floor beams, to form a floor of the carousel on which the pipeline is resting.

In an embodiment a floor member, e.g. beam, is integrated with an inner post and an outer post to form an U- shaped member mounted on the deck of the barge, e.g. the U-shaped member being releasably secured on the deck. In an embodiment pipeline support posts may be secured to a floor beam at various positions, e.g. clamped, allowing to adjust the width of the carousel and/or to create multiple concentric carousels or vary the width thereof.

In an embodiment each of the barges has - seen in plan view - a bow and stern with an angled face to form a trapezium so that adjacent barges may be interconnected directly against one another.

In an alternative embodiment a bridge member, that is distinct from a barge, is arranged between adjacent barges and embodied to connect with each of said barges. For example the bridge member has - in plan view - a triangular contour with diverging sides to which a barge is connected. This will e.g. allow the barges to have a rectangular contour in plan view, which for example allows for simplicity of their design as well as for other use of the barge, e.g. as transport barge when the floating pipeline storage device is not (or no longer) needed. Preferably a bridge member spans the gap between barges, solely being supported by each of the barges. This allows, as is preferred, to embody a bridge member without a buoyancy hull portion.

In an embodiment a bridge member has a length that is significantly less than a barge, but in embodiments a bridge member may have a length that is about the same as a barge. In an embodiment the pipe-assembly station is mounted on a barge, the barge being equipped with a crane, e.g. allowing to lift pipes onto the barge. In an embodiment the crane of the pipe assembly station is used to lift the bridge members when installing the annular array of barges interconnected by bridge members.

In an embodiment one or more of the barges are provided with an active roll damping device to counter or reduce the roll of the barge, e.g. when parallel to the sea swell. For example a roll damping device comprises a solid roll damping ballast which is movable in the transverse direction of the barge. For example a sensor detects the rolling motion of the barge and/or the sea swell, and a drive and control system are provided and operated to cause and control the movements of the solid roll damping ballast in response to the detections of the sensor to provide roll stabilization. For example the active roll damping device comprises one or more of the features disclosed in WO2009/048322. In an embodiment one of more of the barges are provided with a ballast system comprising one or more ballast tanks allowing, e.g., to maintain a desired draft and/or to control inclination of the barge. For example the ballast system is used to compensate for the weight of the pipeline loaded into the one or more carousels, e.g. to maintain the barge draft within a predetermined range in view of stability of the floating base and its response to sea swell. A ballast system may also be used to compensate for load changes due to spooling and unspooling of pipeline that cause inclination of the barge, thereby e.g. allowing to keep the carousel level.

In an embodiment the one or more barges are provided with a ballast system that actively shifts ballast depending on whether the barge is primarily subjected to roll or to pitch during the revolution of the floating base.

In an embodiment the method involves placing a spiral winding of pipeline at the bottom of the carousel to serve as a floor of the carousel for the actual pipeline stalk or stalks that are later to be unspooled from the floating device. The bottom layer pipeline thus serves as a floor and is not to be installed in the sea. For example the bottom layer is made of scrap pipeline.

In an embodiment a damper device is arranged at the interconnection of barges to one another or to a bridge member, the damper device being embodied to absorb and dampen sea motion induced motions to the barges. For example the barges are connected via one or more cables and the one or more cables are connected to a tensioning arrangement including a damper, e.g. a gas buffer damper.

In an embodiment the system comprises a position monitoring device adapted and operated to monitor the position of one or more, preferably all, of the barges during spooling and unspooling. For example a monitoring like used by land surveyors is employed, e.g. a laser based and/or GPS based monitoring device is employed, to monitor the position of each barge. This monitoring may be used to check the proper operation of the floating device and may, for example, be used to monitor any misalignment of barges in the array, e.g. due to water currents or other uneven loading on the barges, or to monitor the speed of the barges.

In an embodiment the floating carousel pipeline storage device is guided with regard to its revolving motion by multiple base guides arranged at angularly spaced positions along the inside and/or outside of the annular floating base. For example such base guides each comprise a floating hull that is moored, e.g. by one or more piles driven into the seafloor, e.g. one or more spud piles. The base guide may include one or more rollers or wheels, e.g. rubber tires, engaging the hull of the barges, e.g. the side of the barges, and/or a dedicated guide member, e.g. circular, arranged on deck of the barges. In case barges with parallel sides are used it will be appreciated that the sides will then form a polygonal contour in plan view. One or more base guides engaging directly onto such polygonal contour preferably comprises a mobile carrier for the one or more barge hull side engaging members, e.g. mobile in radial direction, allowing the base guides to remain in contact as the floating base revolves during spooling and unspooling.

In an embodiment the floating carousel pipeline storage device is caused to revolve by at least one drive assembly, preferably the drive assembly comprising a drive motor that is not integrated in the barge. This allows the use of barges that have no motor of their own, which reduces the costs of the barges. In an alternative the barges could have a motor, e.g. in the form of an azimuthable thruster, possibly retractable in view of shipping the barges (stacked in desired) on-board a heavy transport vessel.

In an embodiment the drive assembly comprises a drive motor that is arranged on a drive base separate from the annular floating base.

In an embodiment the drive assembly is also embodied as a brake assembly allowing to retard the floating device. A separate brake assembly could also be provided if desired. In an embodiment the floating carousel pipeline storage device is caused to revolve by at least one drive assembly comprising a rack that is arranged on the array of barges and a motor driven pinion meshing with said rack. In an embodiment thereof each barge may be fitted with a semi-circular rack section so as to form a circular rack on the annular array of barges. Yet it is also envisaged that each barge is fitted with a straight rack section so that a polygonal rack is formed on the annular array of barges. This design may be simpler to implement on the barges and reduces the space required for the rack, e.g. allowing to place the rack on a deck along a side edge of the deck. It is noted that any rack structure does not need to be contiguous at the junction between barges as it is envisaged that the pinion drive may be released from the rack section on one barge and after passage of the gap to the next rack section be replaced into meshing engagement with the next rack section as the inertia of the floating device will assure that the revolving motion does not stop. The pinion drive can be mounted on a drive base that is pile mounted or moored adjacent the inner or outer contour of the annular floating base. The pinion drive can be mounted on a mobile carrier in order to keep the pinion in meshing engagement with the rack as the floating device revolves during spooling and unspooling. In another embodiment the drive assembly comprises one or more motor driven endless tracks, e.g. as in a pipelaying tensioner, engaging on a circular drive member arranged on the barges, e.g. a tubular drive member cooperating with two or three driven tracks mounted in a frame of the drive assembly. In another embodiment the drive assembly is embodied similar to a rack railway, wherein a motorized locomotive is placed on a circular track on the deck of the barges, e.g. with its wheel bogies on a circular rail track, and wherein a rack is provided, e.g. in between the rails of the rail track, and a motor driven pinion of the locomotive cooperates with the rack. It is envisaged that the rack may have gaps at the joints between the barges, with the pinion being released form the one track section and after passage of the gap being engaged with the next rack section. The locomotive may have wheels like trains that engage proper railway tracks, but it is also envisaged that the locomotive has wheels like a truck with the track resembling a road. The locomotive may be anchored to a drive base that is separate from the annular floating base, e.g. a moored barge and/or a pile foundation adjacent the annular array of barges. In an embodiment the annular floating base has radial guy wires leading from the annular array of barges to a centre of the floating base, e.g. to a central hub, e.g. a central hub revolving about a pile. In an embodiment a drive assembly is provided to rotate the central hub.

In an embodiment the system comprises a stationary inner spoke structure, e.g. with three radial spokes, e.g. formed by floating hulls, arranged at 120° angles, with the annular floating base revolving about said inner structure. In an embodiment the base guides and/or one or more drive assemblies of the system are arranged at the end of the spokes, e.g. the end of each spoke being moored by one or more piles, e.g. spud piles.

In an embodiment use is made of pipeline loader and unloader device which is adapted and operated to guide the pipeline close to the point of entry into or exit from the carousel of the floating carousel pipeline storage device. For example a pipeline loader and unloader device comprises a pipeline tensioner having one or more driven tracks, the tensioner being arranged on a mobile carrier allowing to position the tensioner relative to the carousel during loading and/or unloading. In an embodiment the pipeline loader and unloader device is arranged on a floating hull distinct from the annular floating base, which floating hull is moored, e.g. by one or more piles driven into the seafloor. In another embodiment the loader and unloader device comprises a tensioner that is suspended from a gantry that extends over the annular array of barges, e.g. with legs of the gantry being piled to the seafloor. In another embodiment the loader and unloader device comprises a mobile gantry that rides over the annular array of interconnected barges, e.g. like a container terminal straddle carrier.

It will be appreciated that the inventive method can be used to spool the pipeline from the floating carousel into an exchangeable reel of a pipelaying vessel, which reel is then transported on-board a transportation vessel to the actual pipelaying vessel. There the reel is hoisted or otherwise placed on-board the pipelaying vessel.

For example the annular base is composed of 12 directly interconnected barges each having a length of between 60 and 90 meter, e.g. about 75 meter, e.g. each of said barges having a trapezium contour in plan view. For example the annular base is composed of barges having a width between 15 and 15 meter. The invention will now be discussed with reference to the drawings. In the drawings:

Fig. 1 shows in plan view a system according to the invention,

Fig. 2 shows the floating carousel storage device of figure 1 in perspective view,

Fig. 3 shows a perspective view of the device of figure 2 with pipelines spooled in the carousels,

Fig. 4 shows in plan view the pipeline assembly station of figure 1 ,

Fig. 5 shows the spooling of pipeline onto the reel of a pipelaying vessel,

Fig. 6 shows the pipelaying vessel of figure 5,

Fig. 7 shows an example of a near shore location of a system according to the invention, Fig. 8 shows an example of a site comprising a system according to the invention,

Fig. 9 shows a portion of the system of figure 1 ,

Fig. 10 shows a portion of the system of figure 1 ,

Fig. 1 1 shows a portion of the system of figure 1 including the pipe loader and unloader device,

Figs. 12a, b show in side view and plan view the system of figure 11 including the pipe loader and unloader device,

Fig. 13 shows the components of the system of figure 1 being towed by tug boats, and Fig. 14 depicts an alternative barge 25' for the annular floating base. Figure 1 schematically shows in plan view a system for manufacturing a subsea pipeline 1 and spooling the pipeline onto a reel of a pipelaying vessel 50 (see figures 5, 6).

In general the system comprises a pipeline assembly station 10 which is adapted to form a pipeline stalk by connecting pipes 2 end-to-end. In practice the pipes 2 will be rigid pipes, most commonly steel pipes. As is known in the art the steel pipes can be provided with a coating either in the station or previously (as is preferred). The pipeline has an elastic limit above which the pipeline shows plastic deformation when the pipeline stalk is subjected to bending in view of spooling of the pipeline stalk. The pipes 2 supplied to the station can be double joints, e.g. two 40 foot pipes, that have been welded and coated at a remote location.

The pipeline assembly station 10, as is known in the art, may comprises one or more welding stations 11 (see e.g. fig 4) where the pipes 2 are welded end-to-end. Further a weld inspection station 12 may be provided and/or a coating station 13 to coat the welded connections. At the end of the pipeline assembly line a tensioner 14 is preferably arranged to maintain pipeline tension downstream of the tensioner 14. The pipeline assembly station 10 may comprise a winch (not shown) allowing to pull back - by means of a pullback cable - a pipeline stalk to the assembly station at the start of unspooling the stalk, e.g. allowing to connect one stalk to an already unloaded stalk in the station 10 in order to make up the continuous pipeline that is stored on the reel of the pipelaying vessel.

In this example the station 10 is arranged on a dedicated pipeline assembly station barge 15 but may also be part of an S-lay pipelaying vessel that is commonly equipped with a stinger (now removed) to guide the pipeline from the vessel into the sea.

The barge 15 is provided with a crane 16 allowing to load new pipes 2 from one or more pipe supply vessels 17, 18 onto the barge 15. As is preferred one or more such supply vessels 17, 18 may be moored alongside the barge 15 for transfer of the pipes. The barge 15 is equipped with one or more spud piles 19 that penetrate into the seafloor and so keep the barge 15 moored. Of course other mooring devices can be applied to moor the barge 15.

In an embodiment the pipeline assembly equipment is mounted mobile in the station 10 so as to be mobile in longitudinal direction of the pipeline, e.g. allowing to move with the pipeline during stopping of the manufacturing of the pipeline as the device 20 needs some time to come to a halt. In an alternative the station 10 is moored in a mobile manner allowing the station to move for the same purpose during stopping of the manufacturing of pipeline. The figure 1 further schematically shows a floating intermediate pipeline storage device 20 that is moored adjacent the pipeline assembly station 10 and that serves to temporarily store the pipeline stalk 1 thereon by spooling the pipeline stalk 1 directly from the pipe assembly station 10 onto the floating intermediate pipeline storage device 20. The floating intermediate pipeline storage device is embodied as a floating carousel pipeline storage device 20 which has an annular floating base that is assembled from multiple barges 25 which are interconnected in an annular array.

In this example, as preferred, each barge 25 has a deck 26 above waterline like a deck cargo barge. The floating carousel pipeline storage device 20 further comprises a horizontal pipeline storage carousel, here two concentric carousels 30, 31 , that is fixed on interconnected barges 25, here on top of the deck 26. Each carousel here comprises outer pipeline support members defining a circular outer perimeter of the carousel and inner pipeline support member defining a circular inner perimeter of the carousel.

As can be seen in figures 2 and 3 it is envisaged that multiple carousels 30, 31 are present in a concentric arrangement, so that here the pipeline support members 32 define the inner perimeter of carousel 30, the members 33 the outer perimeter of carousel 30 and the inner perimeter of carousel 31 , and the members 34 the outer perimeter of carousel 31.

When pipeline 1 is manufactured by use of station 10 it is envisaged that the moored annular floating base formed by barges 25 is made to revolve in a first direction P1 and that the pipeline 1 arriving from the pipeline assembly station 10 is stored in multiple levels of spiral windings in one of the carousels 30, 31. The carousels 30, 31 are mainly stationary structures fixed on the deck of the barges so that the carousels revolve along with the annular floating base.

The diameter of the carousels 30, 31 is such that the bending of the pipeline spooled in the carousel does not exceed the elastic limit of the pipeline. In the example of figure 1 the diameter of the median pipeline support members 33 is about 285 meters allowing to store in each carousel 30, 31 steel X60 quality pipelines (yield limit 413 N/mm2) with an outer diameter of 18 inch. Other pipeline diameters are of course also possible, e.g. from 6 inch, 10.27 inch, 12.75 inch, 14 inch, 16 inch, 18 inch outer diameter. For example about a 3 layer spiral winding of 18 inch pipeline can be stored in a carousel 30, 31.

In view of the desire to avoid plastic deformation of the pipeline due to the bending related to the spooling the diameter of inner diameter of the spooled pipeline is preferably at least 150 meters, and in practical terms preferably between 240 and 300 meters.

In the example shown the barges 25 have a monohull with parallel side walls 27, a bow, a stern, a bottom, and the cargo deck 26. As can be seen in figures 2, 3 each barge 25 is pre-fitted with a circle arc segment of the horizontal pipeline storage carousels 30, 31 prior to interconnection of the barges into the annular array. For example the outer and/or inner pipeline support members 32, 33, 34 are upright posts extending upward from the deck, e.g. mounted (e.g. removable), in post receiving holes mounted in the deck.

As shown here the carousel may further comprises horizontal floor beams 35 to form a floor of the carousel.

In an embodiment a floor beam 35 is integrated with an inner post and an outer post to form a U- shaped member mounted on the deck of the barge, e.g. the U-shaped member being releasably secured on the deck. As shown here a central post can also be provided to form two concentric carousels 30, 31.

As shown here (and visible in figure 13) each of the barges 26 has a bow and stern with an angled face to form a trapezium so that adjacent barges 26 are interconnected directly against one another when forming the annular array.

The system further comprises multiple base guides 40, 41 , 42 that are adapted to be arranged at angularly spaced positions along the inside of the annular floating base for guiding the floating carousel pipeline storage device with regard to its revolving motion about axis 43.

In the example shown here each base guide 40, 41 , 42 comprises a floating hull that is moored, here by one or more piles 45 driven into the seafloor.

In this example barges 46 form three radial spokes between a central piled member 47 and each of the base guides 40, 41 , 42, here three spokes art 120 degrees angles.

A possible embodiment of the base guides 40, 41 , 42 will be discussed later with reference to figure 10. The system further comprises a drive assembly 50 that is adapted to cause the floating carousel pipeline storage device 20 to revolve at a desired speed during spooling and unspooling of the pipeline into or from one or more of the carousels 30, 31. In an embodiment the drive assembly 50 is also embodied as a brake assembly allowing to retard the floating device 20. A separate brake assembly could also be provided if desired. The system further comprises a pipeline loader and unloader device 60 which is adapted to guide the pipeline stalk 1 close to the point of entry into or exit from the carousel 30, 31 of the floating carousel pipeline storage device 20. In this example the pipeline loader and unloader device is arranged on a floating hull distinct from the annular floating base, here the same floating hull as base guide 40.

Figure 1 further depicts an expansion curve station 70 between the pipeline assembly station 10 and the device 20. This station 70 allows for the pipeline 1 to have a range of curved trajectories which allows to compensate for any discrepancies between the speeds of the pipeline at either end of the station 70. Such a station 70 is known from shore based stations.

As each barge 25 has a deck 26 above waterline and as the carousels 30, 31 are fixed on deck 26 the stored pipeline remains above water and is thus easily accessible for personnel. As shown in figures 2, 3 it is envisaged that a circular road or footpath 26a is present along at least one of the inner or the outer perimeter of each carousel 30, 31 so as to allow for easy access of the pipeline by personnel. For example personnel can use bicycles, electric vehicles, or even ordinary road vehicles to drive around the perimeters of the carousels. Therefore it is preferred that each deck 26 extends at least 2 meters inward and/or outward of the inner and/or outer perimeter of the one or more carousels, or that such a width path is present between two concentric carousels.

The operational method for manufacturing and temporary storage of manufactured pipeline stalks involves causing the annular floating base to revolve in a first direction and depositing the pipeline arriving from the pipeline assembly station 10 such that the pipeline is stored in multiple levels of spiral windings in one of the carousels 30, 31 , which carousels revolve along with the annular floating base. As each carousel has a large diameter the bending of the pipeline spooled in the carousel does not exceed the elastic limit of the pipeline.

During this process any discrepancies between the manufacturing speed and the rotational speed of the device 20 are compensated by station 70. For example in case of stopping the manufacturing process the station absorbs the motion of the annular base until it comes to a standstill. Figure 5 depicts the process of unspooling the stored pipeline stalk 1 from the device 20, wherein the annular floating base is made to revolve in a second direction P2 opposite to the first direction PL Again, as preferred, the pipeline stalk 1 passes via the expansion curve station 70 and then onward to the pipelaying vessel 100.

As shown here, the pipelaying vessel 100 is moored in line with the pipeline assembly station 10, allowing to unspool the pipeline stalks form the carousels via the station 10 so that its pipeline assembly equipment can be employed for interconnection of pipeline stalks. In an embodiment the unspooled pipeline stalks pass through the same firing line as the one on which the pipeline stalks are manufactured so that the equipment need not be moved. In the example shown the station 10 has guide roller sets 29 supporting the pipeline as it passes from one end of the station 10 to the other end towards the vessel 100 parallel to such a firing line. It is envisaged that in such embodiment pipeline stalks may e.g. be interconnected by mechanical connectors not requiring welding.

If desired a pipeline stalk unspooled from one carousel 30 can be connected to pipeline stalk unspooled from the other carousel 31 using the equipment of the station 10, such as the welding station, the inspection station, and the coating station. This enhances such a procedure.

The vessel 100 may comprises on or more (here two) permanent pipeline reels 101 , 102 onboard onto with the pipeline 1 is spooled. If desired two pipeline stalks can be unspooled simultaneously from two concentric carousels 30, 31 and spooled simultaneously onto two on-board reels of the vessel 100.

The spooling of pipeline onto one of the permanent reels on-board the vessel 100 may involve the provision of a length of dummy pipe on such a reel, with the dummy pipe having mechanical connector at the end thereof allowing to couple with a mechanical connector fitted at the end of the pipeline spooled in a carousel 30, 31. The method then involves unspooling the dummy pipe from the reel until the connector is in the pipeline assembly station 10 and retrieving the pipeline from the carousel so as to couple the connectors. The same approach involving dummy pipe may be used to start the spooling of pipeline stalk onto a carousel 30, 31. Figure 7 depicts the proposal to moor the device 20, and if possible also the stations 10 and/or 70, in a sheltered basin so that at least the floating device 20 is sheltered from the undampened sea swell. Here a breakwater or jetty is provided to reduce the sea swell. Such a jetty may be a temporary structure, e.g. formed by submergible caissons or the like.

Figure 8 depicts an alternative site for the inventive system. Here the annular array of barges 25 is placed in an annular water filled channel 110 that may be purposely dug or dredged near the shoreline. This channel 1 10 may have a connection to the sea so as to allow for the barges 25 to sail into the channel, e.g. with this connection being closed (e.g. by a sheet pile wall or a mobile lock door arrangement) once the barges are in place to disconnect the channel from the sea (e.g. to avoid tidal motion).

Figure 8 also depicts to provide a shore based pipeline assembly station 10, e.g. aligned with a quay such that a pipelaying vessel 100 can be moored along said quay and is then aligned with the station 10. In another embodiment the station 10 is also floating, e.g. on a barge moored along a quay.

In figure 8 a pipeline loader and unloader device can be secured to the land, e.g. including a gantry spanning the channel 1 10.

Figure 9 depicts a possible embodiment of station 70, wherein a pipeline guide assembly comprises a transversely mobile cart 71 that is arranged on a rail base 72, e.g. with movable end stops 73, 74 defining the range of motion of the cart 71. The cart 71 has lateral guides 75, 76 between which the pipeline 1 passes.

The station 70 has multiple of such guide assembly behind one another in axial direction of the pipeline 1.

Figure 10 depicts a possible embodiment of a guide base 42. Herein it is envisaged that bogies having wheels 42a, b engage on a circular guide member on the barges 25 or directly onto the sides of the barges. As is preferred these wheels 42a, b are arranged above waterline.

Figure 11 , 12a, and 12b depict a possible embodiment of a loader and unloader device 60 which guides the pipeline 1 close to the point of entry into or exit from the carousel 30, 31 of the floating carousel pipeline storage device as well as the provision of a drive assembly 50 that is arranged on a drive base 40 separate from the annular floating base and serves to cause the floating carousel pipeline storage device to revolve. In an embodiment the floating carousel pipeline storage device is caused to revolve by at least one drive assembly comprising a rack 51 arranged on the array of barges 25 and a motor driven pinion 52 meshing with said rack. In an embodiment thereof each barge may be fitted with a semi-circular rack section so as to form a circular rack on the annular array of barges. Yet it is also envisaged that each barge is fitted with a straight rack section so that a polygonal rack is formed on the annular array of barges. The pinion drive then will be mounted on a mobile carrier to keep the pinion in meshing engagement with the rack as the floating carousel device revolves during spooling and unspooling. It is noted that any rack structure does not need to be contiguous at the junction between barges as it is envisaged that the pinion drive may be released from the rack section on one barge and after passage of the gap to the next rack section be replaced into meshing engagement with the next rack section as the inertia of the floating device will assure that the revolving motion does not stop. The pipeline loader and unloader device here comprises a pipeline tensioner 61 as known in the art which is mounted in mobile manner so as to position the tensioner in line with pipeline to be laid into or retrieved from the carousel. Here the tensioner is arranged in a motion frame 62 for up and down motion as well as motion in radial direction. Here the tensioner is suspended above the carousel by means of a cantilevered structure.

Figure 14 depicts an alternative barge 25' for the annular floating base having one or more submerged or submergible pontoons 25a providing the majority of the buoyancy of the barge 25, and having columns 25b erected from said one or more pontoons to intersect the design waterline and support thereon the above waterline deck 26' of the barge, here a deck box 25c including the deck.

In an embodiment the device 20 can be embodied to store 16000 metric tons of pipeline stalk(s) thereon, for example in two concentric carousels each storing 8000 metric tons.

Claims

C L A I M S

1. Method for manufacturing a subsea pipeline (1) and spooling said pipeline onto a reel (101 , 102) of a pipelaying vessel (100) at a spoolbase, wherein the method comprises: providing a spoolbase comprising a pipeline assembly station (10) and a floating

intermediate pipeline storage device (20) that is arranged adjacent the pipeline assembly station (10), connecting pipes (2) end-to-end at the pipeline assembly station (10) to form a pipeline stalk (1), said pipeline stalk having an elastic limit, spooling said pipeline stalk (1) directly from the pipe assembly station (10) onto the floating intermediate pipeline storage device (20) that is arranged adjacent the pipeline assembly station and temporarily storing the pipeline stalk thereon, spooling the pipeline stalk from the floating intermediate temporary pipeline storage device (20) onto the reel of the pipelaying vessel (100), possibly including interconnecting pipeline stalks during this spooling step, characterized in that the floating intermediate pipeline storage device (20) is a floating carousel pipeline storage device which has an annular floating base that is assembled from multiple barges (25) which are interconnected in an annular array, wherein the floating carousel pipeline storage device (20) further comprises a horizontal pipeline storage carousel (30,31) that is fixed on the interconnected barges and is adapted for above waterline storage of the pipeline stalk, said carousel comprising pipeline support members (32,33) defining at least one of a circular outer perimeter and a circular inner perimeter of the carousel, wherein the method further comprises causing the annular floating base (25) to revolve in a first direction (P1) and depositing the pipeline stalk (1) arriving from the pipeline assembly station in the carousel (30, 31) in multiple windings, which carousel revolves along with the annular floating base, and wherein the carousel has a diameter such that the bending of the pipeline stalk (1) spooled in the carousel is within the elastic limit of the pipeline, wherein the method further comprises causing the annular floating base (25) to revolve in a second direction (P2) opposite to the first direction and retrieving the pipeline stalk from the carousel (30,31), and wherein the method further comprises spooling the retrieved pipeline stalk (1) onto the reel (101 , 102) of the pipelaying vessel (100).

2. Method according to claim 1 , wherein the carousel comprises both outer perimeter pipeline support members defining a circular outer perimeter and inner pipeline support members (32,33) defining a circular inner perimeter of the carousel (30,31) and wherein the pipeline stalk is stored in multiple windings between the inner and outer pipeline support members.

3. Method according to claim 1 or 2, wherein the inner diameter of the pipeline windings spooled in the carousel (30, 31), e.g. limited by the circular inner perimeter of the carousel, is at least 150 meter, e.g. between 240 and 300 meter.

4. Method according to any of the preceding claims, wherein multiple horizontal pipeline storage carousels (30, 31) are concentrically fixed on the interconnected barges.

5. Method according to any of the preceding claims, wherein use is made of barges (25) having a monohull with parallel side walls, a bow, a stern, a bottom, and, preferably, a deck on which the carousel is fixed.

6. Method according to any of the preceding claims, wherein use is made of barges (25') each having one or more submerged or submergible pontoons (25a) providing the majority of the buoyancy of the barge, and having columns (25b) erected from said one or more pontoons to intersect the design waterline and support thereon an above waterline deck of the barge, e.g. a deck box (25c) including said deck (26), wherein the carousel is fixed on the deck.

7. Method according to any of the preceding claims, wherein each barge (25) is pre- fitted with a circle arc segment of the horizontal pipeline storage carousel (30, 31) prior to interconnection of the barges into the annular array.

8. Method according to any of the preceding claims, wherein each of the barges (25) has - seen in plan view - a bow and stern with an angled face to form a trapezium and wherein adjacent barges are interconnected directly to one another.

9. Method according to any of the preceding claims, wherein the floating carousel pipeline storage device is guided with regard to its revolving motion by multiple base guides (40, 41 , 42) arranged at angularly spaced positions along the inside and/or outside of the annular floating base, e.g. said base guides each comprising a floating hull that is moored, e.g. by one or more piles driven into the seafloor.

10. Method according to any of the preceding claims, wherein the floating carousel pipeline storage device is caused to revolve by at least one drive assembly (50) that is arranged on a drive base separate from the annular floating base.

1 1. Method according to any of the preceding claims, wherein the floating carousel pipeline storage device is caused to revolve by at least one drive assembly comprising a rack (51) arranged on the array of barges and a motor driven pinion (52) meshing with said rack.

12. Method according to any of the preceding claims, wherein use is made of pipeline loader and unloader device (60) which guides the pipeline close to the point of entry into or exit from the carousel of the floating carousel pipeline storage device (30, 31), e.g. said pipeline loader and unloader device being arranged on a floating hull distinct from the annular floating base, which floating hull is moored, e.g. by one or more piles driven into the seafloor.

13. System for manufacturing a subsea pipeline and spooling said pipeline onto a reel or a carousel of a pipelaying vessel at a spoolbase, wherein the system comprises: a pipeline assembly station (10) adapted to form a pipeline stalk (1) by connecting pipes (2) end-to-end, said pipeline having an elastic limit, a floating intermediate pipeline storage device (20) that is adapted to be arranged adjacent the pipeline assembly station and to temporarily store the pipeline stalk thereon by spooling said pipeline stalk directly from the pipe assembly station onto the floating intermediate pipeline storage device, characterized in that the floating intermediate pipeline storage device is a floating carousel pipeline storage device (20) which has an annular floating base that is assembled from multiple barges (25) which are interconnected in an annular array, wherein the floating carousel pipeline storage device further comprises a horizontal pipeline storage carousel (30,31) that is fixed on interconnected barges and adapted for above waterline storage of pipeline stalk, said carousel comprising pipeline support members (32,33) defining at least one of a circular outer perimeter and a circular inner perimeter of the carousel, wherein the annular floating base is adapted to revolve in a first direction (P1) and to deposit the pipeline stalk arriving from the pipeline assembly station (10) such that the pipeline stalk is stored in in the carousel (30, 31) in multiple windings, which carousel revolves along with the annular floating base, and wherein the carousel has a diameter such that the bending of the pipeline stalk spooled in the carousel is within the elastic limit of the pipeline.

14. System according to claim 13, wherein the carousel (30,31) comprises both outer perimeter pipeline support members defining a circular outer perimeter and inner pipeline support members (32,33) defining a circular inner perimeter of the carousel and wherein the pipeline stalk can be stored in multiple windings between the inner and outer pipeline support members.

15. System according to claim 13 or 14, wherein carousel (30,31) is embodied such that the inner diameter of the pipeline stalk windings spooled in the carousel, e.g. limited by the circular inner perimeter of the carousel, is at least 150 meter, e.g. between 240 and 300 meter.

16. System according to any of the preceding claims 13 - 15, wherein multiple horizontal pipeline storage carousels (30, 31) are concentrically fixed on the interconnected barges.

17. System according to any of the preceding claims 13 - 16, wherein the barges (25) have a monohull with parallel side walls, a bow, a stern, a bottom, and, preferably, a deck on which the carousel is fixed.

18. System according to any of the preceding claims 13 - 16, wherein the barges (25') have one or more submerged or submergible pontoons providing the majority of the buoyancy of the barge, and having columns erected from said one or more pontoons to intersect the design waterline and support thereon an above waterline deck of the barge, e.g. a deck box including said deck, whereon the carousel is fixed.

19. System according to any of the preceding claims 13 - 18, wherein each barge (25) is pre-fitted with a circle arc segment of the horizontal pipeline storage carousel prior to interconnection of the barges into the annular array.

20. System according to any of the preceding claims 13 - 19, wherein each of the barges (25) has - seen in plan view - a bow and stern with an angled face to form a trapezium.

21. System according to any of the preceding claims 13 - 20, wherein system further comprises multiple base guides (40, 41 , 42) that are adapted to be arranged at angularly spaced positions along the inside and/or outside of the annular floating base for guiding the floating carousel pipeline storage device with regard to its revolving motion e.g. said base guides each comprising a floating hull that is to be moored, e.g. by one or more piles driven into the seafloor.

22. System according to any of the preceding claims 13 - 20, wherein the system further comprises a drive assembly (50) that is adapted to cause the floating carousel pipeline storage device to revolve.

23. System according to any of the preceding claims 13 - 22, wherein the floating carousel pipeline storage device is caused to revolve by at least one drive assembly comprising a rack (51) arranged on the array of barges and a motor driven pinion (52) meshing with said rack, e.g. each barge being provided with a straight rack section to form a polygonal rack in plan view.

24. System according to any of the preceding claims 13 - 23, wherein the system further comprises a pipeline loader and unloader device (60) which is adapted to guide the pipeline stalk close to the point of entry into or exit from the carousel of the floating carousel pipeline storage device, e.g. said pipeline loader and unloader device being arranged on a floating hull distinct from the annular floating base, which floating hull is to be moored, e.g. by one or more piles driven into the seafloor.

25. A floating intermediate pipeline storage device (20) that is adapted to be arranged adjacent a pipeline assembly station and to temporarily store a pipeline stalk thereon by spooling said pipeline stalk directly from the pipe assembly station (10) onto the floating intermediate pipeline storage device, characterized in that the floating intermediate pipeline storage device is a carousel pipeline storage device (20) which has an annular floating base that is assembled from multiple barges (25) which are interconnected in an annular array, wherein the floating carousel pipeline storage device further comprises a horizontal pipeline storage carousel (30,31) that is fixed on the interconnected barges and adapted for above waterline storage of pipeline stalk, said carousel comprising pipeline support members (32,33) defining at least one of a circular outer perimeter and a circular inner perimeter of the carousel, wherein the annular floating base is adapted to revolve in a first direction (P1) and to deposit the pipeline stalk arriving from the pipeline assembly station such that the pipeline stalk is stored in multiple windings in the carousel (30, 31), which carousel revolves along with the annular floating base, and wherein the carousel has a diameter such that the bending of the pipeline stalk spooled in the carousel is within the elastic limit of the pipeline.