AU713723B2 - Pipelaying vessel and a method of converting a maritime vessel to a pipelaying vessel - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventors: Address of Service: COFLEXIP STENA OFFSHORE LIMITED Robert George MARTIN and Philip Vaughn THOMAS SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 Invention Title: "PIPELAYING VESSEL AND A METHOD OF CONVERTING A MARITIME VESSEL TO A PIPELAYING VESSEL" Details of Original Application No. 17122/95 dated 20th February, 1995 The following statement is a full description of this invention, including the best method of performing it known to us:- "PIPELAYING VESSEL AND A METHOD OF CONVERTING .1 A MARITIME VESSEL TO A PIPELAYING VESSEL" 2 3 This invention relates to a pipelaying vessel, and more 4 specifically but not exclusively relates to a self- 5 propelled and dynamically-positioned reel pipelaying 6 ship in which a pipe-spooling reel and associated pipe 7 handling equipment are integrated into the structure of 8 the ship. In some embodiments of the pipelaying ship, 9 there is provision for the simultaneous laying of a plurality of pipes, or the simultaneous laying of one 11 or more pipes together with one or more cables.

12 13 In prior-art pipelaying vessels as employed in laying 14 offshore subsea pipelines for such uses as the gathering of oil and/or gas from offshore subsea wells, 16 as, for example, in the Gulf of Mexico, it has been 17 conventional to use one of two main methods to lay the 18 pipe. In the first, or "stovepiping", method, a 19 pipeline is fabricated on the deck of a lay barge by welding together individual lengths of pipe as the pipe 21 is paid out from the barge. Each length of pipe is 22 about 40 feet (12.19 metres) or 80 feet (24.38 metres) 23 long. Thus, the pay-out operation must be interrupted 24 periodically to permit new lengths of pipe to be welded 1 to the string. The stovepiping method requires that 2 skilled welders and their relatively bulky equipment 3 accompany the pipelaying barge crew during the entire 4 laying operation; all welding must be carried out on site and often under adverse weather conditions.

6 Further, the stovepiping method is relatively slow, 7 with experienced crews being able to lay only one or 8 two miles of pipe a day. This makes the entire 9 operation subject to weather conditions which can cause 0 substantial delays and make working conditions quite 11 harsh. (A modification of the stovepiping technique 12 known as the "J-lay" technique allows the laying of 13 pre-assembled pipestrings up to 240 feet (73.15 metres) 14 in length, but pipelaying is still discontinuous).

16 The other principal conventional method is the reel 17 pipelaying technique. In this method, a pipeline is 18 wound on the hub of a reel mounted on the deck of a lay 19 barge. Pipe is generally spooled onto the reel at a :i 20 shore base. There, short lengths of pipe can be welded 21 under protected and controlled conditions to form a 22 continuous pipeline which is spooled onto the reel.

23 The lay barge is then towed to an offshore pipelaying 24 location and the pipeline spooled off the reel between completion points. This method has a number of 26 advantages over the stovepiping method, among them, 27 speed (up to one mile per hour); lower operating costs 28 (eg smaller welding crews and less welding equipment 29 must be carried on the lay barge); and less weather dependency.

31 32 Historically, the technique of laying undersea 33 fluid-carrying pipelines had its rudimentary beginnings 34 in England in the 1940's in a War-time project known as "Operation Pluto". In the summer of 1944, 3-inch 1 nominal bore steel tubes, electrically flash-welded 2 together, were coiled around floating drums. One end 3 of the pipe was fixed to a terminal point; as the 4 floating drums were towed across the English Channel, the pipe was pulled off the drum. In this manner, 6 pipeline connections were made between the fuel supply 7 depots in England and distribution points on the 8 European continent to support the Allied invasion of 9 Europe. (See Blair, J S, "Operation Pluto: The Hamel Steel Pipelines", Transactions of the Institute of 11 Welding, February 1946).

12 The broad concept of reel pipelaying was also disclosed 14 in British Patent No. 601,103 wherein it was suggested that lengths of pipe can be joined together at the 16 manufacturing plant and coiled onto a drum, mounted on 17 a barge or ship; the loaded barge would then be moved 18 to the desired marine location and the pipe unwound S. 19 from the drum by fixing one end of the pipe and towing 20 the barge away from the fixed location.

21 22 While the concepts described in British Patent No.

601,103 and those actually used in Operation Pluto were 24 adequate for wartime purposes, no known further development work or commercial use of the technique of 26 laying pipe offshore from reels was carried out after 27 World War II. After a hiatus of about fifteen years, 28 research into the reel pipelaying technique was renewed 29 and was carried on by Gurtler, Herbert Co, Inc of New Orleans, Louisiana (USA); by 1961, Gurtler, Herbert had 31 sufficiently advanced the reel pipelaying technique to 32 make it a commercially acceptable and viable method of 33 laying pipe for the offshore petroleum industry, able 34 to compete with the traditional stovepiping technique.

The first known commercial pipelaying reel barge, 1 called the U-303, was built by Aquatic Contractors and 2 Engineers, Inc, a subsidiary of Gurtler, Herbert, in 3 1961. The U-303 utilised a large vertical-axis reel, 4 permanently mounted on a barge and having horizontally orientated flanges (generally referred to in the trade 6 as a "horizontal reel"). A combined straightener/level 7 winder was employed for spooling pipe onto the reel and 8 for straightening pipe as it was unspooled. The U-303 9 first laid pipe commercially in September 1961, in the 10 Gulf of Mexico off the coast of Louisiana and was used 11 successfully during the 1960's to lay several million 12 linear feet (hundreds of kilometres) of pipe of up to 6 13 inches (15.24 cm) diameter. The U-303 reel pipelaying 14 barge is described in US Patent No. 3,237,438 (Tesson) and US Patent No. 3,372,461 (Tesson).

16 *17 The successor to the U-303, currently in use in the 18 Gulf of Mexico and known in the trade as the 19 "Chickasaw", also utilises a large horizontal reel, 20 permanently mounted on the barge such that it is not 21 readily movable from one carrier vessel to another.

22 Various aspects of "Chickasaw" are described in the 23 following US Patents: 24 Sugasti, et al US Patent No. 3,630,461 26 Gibson US Patent No. 3,641,778 27 Mott et al US Patent No. 3,680,432 28 Key et al US Patent No. 3,712,100 29 Commercial reel pipelaying techniques require the use 31 of certain pipe handling equipment in addition to the 32 reel. Among such pipe handling equipment essential to 33 any commercial reel pipelaying system is a straightener 34 mechanism. This may take the form of a series of rollers or tracks, or any other arrangement which 1 imparts sufficient reverse bending force to the pipe to 2 remove residual curvature such that after unspooling, 3 the pipe will lay substantially straight on the sea 4 bottom. No such pipe-conditioning apparatus was used in "Operation Pluto" or contemplated in the British 6 Patent No. 601,103.

7 8 US Patents 3,982,402 and RE30486 (Lang et al) describe 9 an apparatus for laying pipe from a vertical reel in which the pipe conditioning apparatus is pivotable to 11 adjust the lift-off angle of the pipe relative to the 12 horizontal (eg the deck of a ship) as a function of the 13 water depth in which the pipe is being laid. This has 14 distinct commercial advantages, especially where the reel pipelaying system is incorporated into a 16 self-propelled ship capable of travelling to different 17 job sites, having different pipe size and/or lay depth 18 requirements.

19 20 An early concept for a reel pipelaying ship is 21 described in Goren, et al, "The Reel Pipelay Ship A 22 New Concept", Offshore Technology Conference 23 Proceedings, May 1975 (Paper No OTC 2400). This paper 24 (hereinafter the Goren, et al 1975 OTC Paper) described advantages and operating features of a proposed reel 26 pipelaying ship. However, the cost of construction of 27 a ship as described there was estimated to be of the 28 order of $100,000,000.

29 The research and development work for the ship 31 described in the Goren, et al paper was subsequently 32 materially revised in numerous major respects, and 33 substantial changes and improvements were made to 34 achieve the design of a substantially different reel pipelaying ship which is described in the following US 1 Patents:- 2 3 4 Springett, et al US Patent No. 4,230,421 Uyeda, et al US Patent No. 4,269,540 6 Yenzer, et al US Patent No. 4,297,054 7 Springett, et al US Patent No. 4,340,322 8 Uyeda, et al US Patent No. 4,345,855 9 10 The vessel described in these Patents was constructed 11 and is currently in use in various offshore oil fields, 12 being known in the offshore oil industry as the -13 "Apache" (now re-named the "Stena Apache"). This 14 vessel is a self-propelled dynamically-positioned reel pipelaying ship which has a specially constructed hull 16 comprising a reel support structure for rotatably 17 mounting a vertical reel for unspooling a rigid-walled 18 pipeline. Only a single pipeline was originally 19 handled by this ship, though the "Apache" was i 20 subsequently modified by the addition of an auxiliary 21 reel positioned forward of the main reel to enable the 22 laying of "piggyback" lines strapped to the main 23 pipeline. Other pipe handling equipment includes a 24 pipe bending radius controller; pipe straightening equipment; clamping assemblies; a stern pipe guide 26 assembly and a level wind assembly. A tensioning 27 assembly is also arranged on a support ramp assembly.

28 The pipe exit angle or the water entry angle is from 29 180 to about 60° since this is the range of angular movement of the support ramp assembly. The upper part 31 of this range of the pipe water entry angles is 32 sufficient to accommodate laying a single pipeline in 33 approximately 3,000 feet (915 metres) water depth. In 34 order to lay pipe at greater depths it is necessary to increase the pipe water entry angle.

1 The "Stena Apache" vessel is not equipped to lay 2 multiple lines since it has but a single main reel and 3 does not have adequate unused deck space to permit the 4 convenient placement of auxiliary reels. An early suggestion which was made during the vessel's 6 construction phase and mentioned in the above Patents, 7 was that portable reels could be placed on the "Apache" 8 deck to permit stern bundling of smaller lines with the 9 pipeline from the main reel. These smaller lines were not required to be passed through the pipe handling 11 equipment with the main reel pipeline according to the 12 suggestion and there were no operative disclosures as 0"13 to forming a juxtaposed plurality of operational lines 14 by contact with a laying device which is adapted to move all the lines at a common velocity. This stern 16 bundling suggestion was made in the OTC Paper No. 3069, 17 May 8-11, 1978.

18 "19 There are increasing requirements in the offshore 20 petroleum industry for laying single or multiple 21 operational lines in deep water at depths greater than 22 3,000 feet (915 metres) and in remote areas far from 23 supply bases. To be commercially viable a pipelaying 24 vessel should preferably also be capable of laying either single or multiple operational lines in shallow 26 waters of less than 2,000 feet (610 metres) up to 3,000 27 feet (915 metres) depth. The reel pipelaying vessel of 28 this invention (as defined below) represents a new and 29 different concept for meeting these needs.

31 It is also desirable that the stern deck space around 32 the pipelaying equipment be more easily and safely 33 accessible.

34 While it is technically feasible to design and build a 8 1 ship specifically to provide several or all of the 2 abovementioned desirable features, such a ship would be 3 relatively expensive. On the other hand, there are 4 many sea-going vessels that are currently surplus to requirements and hence available at relatively low cost 6 such that the cost of conversion to reel-lay capacity 7 is potentially more economical than new-build.

8 However, selection of a vessel to be modified, and the 9 actual modification procedures, require to be individually and collectively controlled in non-obvious 11 ways to avoid excessive costs and unsatisfactory 12 results.

13 S* 14 Certain aspects of the present invention will dl§o be shown to be applicable to new-build vessels, and/or to 16 retrofitting/upgrading an existing pipelaying vessel.

17 18 According to a first aspect of the present invention there is provided 19 a reel pipelaying vessel, said vessel being fitted 20 with a dynamic positioning system (DPS), said vessel 21 being provided with a reel-holding well at a location 22 amidships, said vessel being provided with reel- 23 mounting bearings on laterally opposite sides of said 24 well, said vessel being provided with ramp-mounting bearings at a sternwards location on said 26 vessel for the mounting of a pipe-launching ramp 27 thereon and further comprising a pipe-launching ramp 28 temporarily or permanently mounted on said ramp- 29 mounting bearings, wherein the mounting of said ramp is a rotational mounting whereby the elevation of the ramp 31 with respect to the vessel is variable and said vessel 32 further comprises ramp elevation control means for 33 controllably varying the elevation of the ramp, and 34 wherein the combination of said pipe-launching ramp and said ramp-mounting bearings is such that the underside P:\OPER\DH\48281-97.RS2 -11110/94 -9of said pipe-launching ramp is clear of underlying deck of the reel pipelaying vessel even at the lowest elevation of the ramp to an extent at least sufficient to constitute walk-under headroom, at least between said ramp-mounting bearings and such part or parts of the deck at which said ramp elevation control means is anchored.

Preferably also, said ramp-mounting bearings are arranged to dispose a horizontal pivot axis for the ramp substantially above said underlying deck whereby thus to provide at least the greater part of said clearance.

Preferably also, said ramp elevation control means comprises variable-length ramp support means anchored at or adjacent one end thereof upon fixed structure of the vessel and at or adjacent the other end of a variable length portion of the support to the ramp at a location thereon not adjacent said rotational mounting of said ramp.

15 Preferably also, said variable-length ramp support means comprises a pair of rack and pinion elevators located one on each side of said ramp and conjointly operable to vary the elevation of said ramp with respect to said vessel.

Preferably also, said pipe-launching ramp comprises a pipe radius control means for 20 imparting a substantially uniform radius of curvature to a length of pipe de-spooled from a reel mounted on said reel-mounting bearings in pipelaying operation of said vessel.

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C C 1 Preferably also, said pipe-launching ramp comprises level-wind means for 2 3 accommodating variations in the lateral positioning of a length of pipe spooled onto 4 a reel mounted on said reel-mounting bearings as a plurality of side-by-side turns, during spooling and de-spooling of said length of pipe.

6 7 Preferably, said level-wind means and said pipe radius 8 control means are mounted and controlled for conjoint 9 lateral movement.

11 Preferably also, said pipe radius control means is 12 mounted upon said level-wind means for carriage 13 thereby.

14 15 Preferably also, the vessel includes a pipe-spooling 16 reel having first and second lateral side portions each 17 comprising a central rotary bearing, a plurality of 9*9* 18 radial spokes extending outwardly from said central 19 rotary bearing and a main flange surface connecting at 9.

20 least the outer portions of said spokes, the reel 21 further including a hub surface connecting said lateral 9 22 side portions such that said reel, in radial crosso 9 23 section, has a portal frame configuration, there being 24 no central shaft connecting the rotary bearings of the respective side portions.

26 27 Preferably, the vessel further includes pipeline 28 clamping means located adjacent the aft end of a 29 pipeline launching ramp, said clamping means comprising at least a first clamp of generally cylindrical 31 configuration mounted on said ramp by clamp mounting 32 means, said first clamp comprising first and second 33 semi-cylindrical portions hinged together along their 34 lengths on a side of the clamp disposed below the pipeline path, and wherein said clamp mounting means i ~I L1-l_-i ~-j 1 has a load capacity greater than the load capacity of 2 said first clamp, whereby the clamp load capacity may 3 be increased up to the capacity of said clamp mounting 4 means by securing one or more additional clamps to the pipeline in abutment with the first clamp and upstream 6 therefrom in the direction of pipeline unspooling.

7 8 Preferably also, said clamp mounting means is adapted 9 to be retractable such that said first clamp may be 10 retracted to a position below the pipeline path when 11 not in use.

12 13 Embodiments of the invention will now be described by 14 way of example, with reference to the accompanying drawings wherein:- 16 17 Fig. 1 is a starboard elevation of a reel pipelaying 18 vessel in accordance with the present invention; 19 .20 Fig. 2 is a plan view of the vessel of Fig. 1; 21 22 Fig. 3 is a starboard elevation (to an enlarged scale) oom 23 of the stern area of the vessel of Fig. 1 with a 24 pipe-launching stern ramp to its lowest elevation; 26 Fig. 4 is a stern view corresponding to Fig. 3; 27 28 Fig. 5 is a view corresponding to Fig. 3 but with the 29 ramp at its highest elevation; 31 Fig. 6 is a stern view corresponding to Fig. 32 33 Fig. 7 is a starboard elevation of another form of reel 34 pipelaying vessel in accordance with the present invention; 12 1 Fig. 8 is a plan view of the main deck of the vessel of 2 Fig. 7, ie, with the vessel bridge and upper decks 3 removed; 4 Fig. 9 is a starboard elevation of a modified version 6 of the pipe-launching ramp and associated equipment 7 forming part of the vessel of Fig. 7; 8 9 Fig. 10 is a starboard elevation of ramp-mounting 10 bearings and a ramp elevation controller associated 11 with the ramp of Fig. 9; 12 13 Fig. 11 is a front elevation of the arrangement of 14 Fig. 16 Fig. 12 is a view from the starboard side of the 17 reeving arrangement of an abandonment and recovery 18 system (A&R system) associated with the ramp of Fig. 9, 19 shown with the ramp at its minimum elevation; 21 Fig. 13 is a view from above of the arrangement of eo, 22 Fig. 12, as seen from the direction of the arrow in 23 Fig. 12; 24 Fig. 14 is a cross-section of part of the arrangement 26 of Fig. 12, taken on the line A-A in Fig. 12; 27 28 Fig. 15 is a view corresponding to Fig. 12 but with the 29 ramp at its highest elevation; 31 Fig. 16 is a longitudinal section of a reel-clamping 32 chock for use with the present invention; 33 34 Fig. 17 is an outside end view of the arrangement of Fig. 16, as viewed in the direction of the arrow in 13 1 Fig. 16; 2 3 Fig. 18 is an inside end view of the arrangement of 4 Fig. 16, as viewed in the direction of the arrow in Fig. 16; 6 7 Fig. 19 is a plan view, to a much-reduced scale, of a 8 reel-clamping chock array applied to a reel; 9 Fig. 20 is a side view of a preferred embodiment of a 11 main reel for use with the vessel of Figs. 1 to 19; 12 *13 Fig. 21 is a sectional view on line A-A of Fig. 14 Fig. 22 is a sectional view on line B-B of Fig. 16 S* 17 Fig. 23 is a sectional view on line C-C of Fig. 18 19 Fig. 24 is a view similar to Fig. 23, showing a 20 modified chocking arrangement; 21 "*see 22 Figs. 25 and are schematic illustrations of 23 a preferred arrangement of a main pipeline clamp; and 24 Fig. 26 is a schematic illustration of a particularly 26 preferred arrangement of pipeline clamps.

27 28 Referring first to Figs. 1 and 2, these show 29 respectively starboard and plan views of a reel pipelaying vessel 100 which is similar in certain 31 respects to known forms of reel pipelaying vessels, for 32 example as disclosed in W093/06401 and W093/06402.

33 However, general and particular aspects of the vessel 34 100 are distinctively different from the prior art, as will be detailed below.

14 1 The vessel 100, to be known as the "Stena Apache Two", 2 is intended to be converted from the diving support 3 vessel (DSV) "Stena Wellservicer" (not separately 4 illustrated) by the method now to be described.

6 The method provides that the DSV will be transversely 7 divided immediately astern of the forward bridge and 8 accommodation section 102, and the sternwards section 9 104 separated from the forward section 102. A prefabricated hull section 106 will next be located 11 between the forward and sternwards sections 102 and 12 104, and the three sections then welded together to 13 form the basis of a vessel with an extended hull. Port 14 and starboard sponsons 108 and 110 are subsequently attached to the outside of the vessel hull from the 16 stern to about the middle of the forward section 102 so 17 as to increase the displacement of the resultant vessel 18 100, and hence increase the vessel's load-carrying i* 19 capacity. The sponsons 108 and 110 are also designed 20 and attached such as to increase the longitudinal 21 bending strength of the vessel 100.

22 22 23 The hull section 106 is formed with a reel-holding well 24 112. Bearing pedestals 114 and 116 are fabricated on port and starboard sides of the well 112 to form 26 reel-mounting bearings. A main pipe-carrying reel 118 27 is rotatably mounted in the bearings 114 and 116. A 28 main reel driving and braking system (not shown) is 29 installed in the well 112.

31 A large auxiliary reel 120 is installed immediately 32 forward of the main reel 118, in the redundant DSV dive 33 system garage in the after end of the forward section 34 102. The large auxiliary reel 120 is intended to carry cable(s) and/or auxiliary pipes.

i__ 1 A small auxiliary reel 122 is installed immediately aft 2 of the main reel 118, in the redundant DSV gas storage 3 area in the forward end of the sternwards section 104.

4 The small auxiliary reel 122 is intended to carry cable(s) and/or hose(s).

6 7 The stern of the vessel 100 is provided with 8 substantially elevated ramp mountings 124 and 126. A 9 ramp 128 in the form of a rectangular lattice has its 10 rear end 130 rotatably mounted on the upper ends 132 11 and 134 of the ramp mountings 124 and 126 (see Figs. 4 S. 12 and 6).

13 o:i" 14 The mountings 124 and 126 are not only shaped and dimensioned to support the ramp 128 on their upper ends 16 132 and 134 substantially above the vessel's main deck 17 136 such as to leave walk-through headroom under the 18 ramp 128, but also to locate their upper ends 132 and 19 134 clear of the stern of the vessel 100 such as to 20 enable pipe to be launched aft the ramp 128 at a 21 near-vertical angle (see Fig. 22 23 The forward end 138 of the ramp 128 is supported at a 24 controllably variable height above the deck 136 by means of a ramp elevation controller 140 comprising a 26 pair of rack and pinion elevators 142 and 144.

27 28 Referring to Figs. 9 and 10, each of the ramp elevators 29 142 and 144 comprises an elongate rack 146 with a row of teeth along both edges, the racks 146 each being 31 tiltably mounted on the deck 136 by means of a 32 respective hinge 148. The use of deck-fixed hinges 148 33 allows the necessary reinforcements of the deck 136 to 34 be limited to the two relatively small areas under the hinges 148, in contrast to the widespread deck 1 reinforcement required with prior art ramp elevators 2 (eg, the rail-mounted ramp elevators of W093/06401 and 3 W093/06402).

4 Each of the ramp elevators 142 and 144 further 6 comprises a power-driven pinion assembly 150 comprising 7 a pinion frame 152 mounting three pairs of pinions 154, 8 with one pinion of each pair engaging one of the rows 9 of teeth on either edge of the rack 146. Each of the pinions 154 is driven by a respective hydraulic motor 11 and reduction gear unit 156. The respective upper ends 12 of the two pinion assemblies 150 are pivotally coupled 13 to the forward end 138 of the ramp 128 by respective 14 pivot couplings 158. The pinion assemblies 150 are also mutually cross-linked by a transverse frame 159.

16 S• 17 Conjoint operation of the hydraulic drive units 156 18 causes the pinion assemblies 150 to crawl up/down the 0. 19 racks 146 hence to raise/lower the forward end 138 of ooo: 20 the ramp 128. Control of the drive units 156 is such 21 as to ensure (as far as possible) synchronous movement 0.0* 22 of the assemblies 150 and hence to avoid 23 movement-induced distortion of the ramp 128 (whose 24 structure is lighter and less rigid than the structures of the ramps described in W093/06401 and W093/06402).

26 Positive synchronisation of the movements of the two 27 pinion assemblies 150 can optionally be ensured by 28 cross-linking at least one pinion in one assembly 150 29 with the corresponding pinion in the opposite assembly 150 by means of a transverse drive shaft (not 31 illustrated) in addition to or as a substitute for use 32 of the transverse frame 159.

33 34 With the arrangement illustrated in the accompanying drawings, the ramp 128 can be rapidly adjusted to any 1 elevation in the range from 100 above horizontal 2 (Figs. 3 and 4) to 85° above horizontal (Figs. 5 and 3 The arrangement can be modified to suit other 4 desired ranges of ramp elevation.

6 The ramp 128 does not directly carry pipe being 7 de-spooled from the main reel 118, but carries the pipe 8 through the intermediary of a levelwind assembly 160 i 9 comprising an elongated frame 162 of rectangular 10 cross-section (see Fig. 14). The levelwind frame 162 11 is mounted for ramp-traversing movement by means of 12 rollers 164 (Fig. 9) running on the ramp crossbeams 13 forming the ramp ends 130 and 138. The ramp crossbeams 14 130 and 138 are also fitted with transverse racks 166 15 engaged by hydraulically-powered pinion/gearbox motor 16 units 167 for controllably displacing the levelwind 17 assembly 160 across the ramp 128 as necessary to ensure 18 correct spooling/de-spooling of pipe onto/off the main 19 reel 118 (ie, to ensure "level winding").

21 The levelwind assembly 160 further includes various 22 items of pipe-conditioning and pipe-handling equipment 23 which are mounted on the frame 162 for controlling 24 position, movement and shape of pipe passing through the levelwind assembly 160. Such equipment includes, 26 by way of non-limiting example, a curved main aligner 27 168 for imparting a controlled radius to pipe being 28 de-spooled from the main reel 118, pipeline 29 straightening and tensioning means comprising first, second, third and fourth caterpillar track assemblies 31 170, 171, 172, 173, the first, second and third of said 32 assemblies 170, 171, 172 together constituting a 33 "three-roll" pipe straightener, and the third and 34 fourth of said assemblies 172, 173 together constituting a pipe tensioner, at least one, and i _iI I_ _1_1 I; I 1 1 preferably a pair, of pipe clamps 174, and a roller 2 frame 176 for pipe guidance. The items 168-176 3 referred to above are known per se, and are described 4 in detail in the above-mentioned W093/06401 and W093/06402. Alternative types of straightener, 6 tensioner etc. may be substituted for those described 7 herein.

8 9 The levelwind assembly 160 may also include similar 10 equipment for handling auxiliary pipe(s) and/or 11 cable(s), for example an auxiliary aligner 178 and an 12 auxiliary straightener 180.

13 14 To facilitate procedures such as pipe inspection, pipe repairs, pipe jointing, attachment/removal of haulage 16 couplings to/from the pipe, and other tasks that have 17 to be performed on pipe in passage through the 18 levelwind assembly 160, the levelwind frame 162 is 19 fitted with a pair of work platforms 182 and 184 whose 20 inclinations on the frame 162 are selectively 21 adjustable to allow the platforms 182, 184 to be 22 levelled independently of the current inclination of 23 the ramp 128 while continuing to facilitate safe and 24 convenient access of personnel to the pipe in that region of the levelwind assembly 160. Access is 26 conveniently enabled by a ladder system and by a 27 man-riding lift, with a separate system on each side of 28 the levelwind assembly 160. The levelwind frame 162 29 may be shrouded or boxed-in to provide full weather protection.

31 32 Occasions may arise when it is necessary or desirable 33 to allow the end of a pipe to be let overboard in a 34 controlled manner, or to haul the end of pipe on-board in line with the normal path of continuous pipe. To ili-?-~-~C-iil-ir..I t_ 1 meet these requirements, the vessel 100 is rigged with 2 an "abandonment and recovery" system (A&R system) 186 3 which is essentially a winch system reeved partly 4 inside the vessel 100 and partly on the levelwind assembly 160. (The version of the A&R system 186 shown 6 in Fig. 9 differs slightly from that shown in Figs.

7 1-6, as do certain details of the levelwind system such 8 as the forward end of the frame 162).

9 As part of the A&R system 186, a winch 188 is located 11 inside the hull of the vessel 100, the winch 188 being 12 anchored on the redundant underdeck strongpoint S13 originally employed for mounting the DSV sterndeck 14 crane (removed). The A&R rope 190 runs from the winch 188 round a pulley 192 anchored between the ramp 16 mountings 124 and 126 up to a pulley or pulleys 194 17 anchored on the levelwind frame 162 and hence (when 18 deployed) down the centerline of the levelwind assembly 19 160 along the same path as that normally taken by pipe 20 being de-spooled from the main reel 118. When the A&R 21 system 186 is not required to be operative the pulley 22 or pulleys 194 is/are moved to the side of the 23 levelwind centerline to be clear of the pipe path (see 24 Fig. 14). The tail of the rope 190 on the non-load side of the winch 188 is carried round a pulley 196 and 26 onto a take-up drum 198 for tangle-free storage.

27 28 The location of the pulley 192 between the ramp 29 mountings 124 and 126 has at least two advantages, namely the closer the pulley 192 is to being coaxial 31 with the ramp bearings 132 and 134, the closer the A&R 32 system 186 is to being level luffing (ie, to not 33 pulling in or paying out as the ramp elevation 34 changes), and secondly, obstruction of the area of the deck 136 under the ramp 128 is minimised.

i -Ln 1 Between the main reel 118 and the large auxiliary reel 2 120 a combined pipe/cable bridge and personnel access 3 gangway 200 is cantilevered sternwards off the rear 4 wall of the forward vessel section 102 to pass partly over the main reel 118 at an elevation sufficient to 6 clear pipe being de-spooled from the reel 118 into the 7 levelwind assembly 160, whatever the current elevation 8 of the ramp 128. The upper side of the bridge/gangway 9 200 is fitted with lengthwise array of transverse axis rollers 202 to carry auxiliary pipe(s)/cable(s) being 11 de-spooled from the large auxiliary reel 120 onto the 12 ramp 128. A pedestrian-carrying gangway (not 13 illustrated) is mounted on the bridge/gangway 200 S14 alongside the rollers 202 to allow access from the upper deck of the forward section 102 to a location 16 close to and directly over the forward side of the hub 17 of the main reel 118. The bridge/gangway 200 is held 18 at the appropriate elevation by means of a strut 204, 19 which may be of a fixed length to hold the 20 bridge/gangway 200 at a corresponding fixed elevation; 21 alternatively, the strut 204 may be of a controllably 22 variable length to hold the bridge/gangway at a 23 selectively variable elevation.

24 Besides functioning as a combined bridge and gangway, 26 the structure 200 gives a measure of protection to the 27 forward section 102 and to the personnel therein, by 28 shielding the forward section 102 from the 29 uncontrollable and violent movement of the broken end of pipe should the pipe fracture between the reel 118 31 and the aligner 168, particularly if under considerable 32 tension (which may be as high as 200 Tonnes even when 33 operating within design limits).

34 The dynamic positioning system (DPS) of the original CI~I 1 DSV "Stena Wellservicer" is retained in the reel 2 pipelaying vessel "Stena Apache Two" ("100" in the 3 accompanying drawings). The DPS retained in the 4 converted vessel 100 comprises three variable-thrust 360 0 -steerable stern thrusters 206, and three 6 variable-thrust unsteerable transverse-tunnel bow 7 thrusters 208.

8 9 A crane 210 is mounted on the port rail of the vessel 10 100, aft of the main reel 128 and forward of the small 11 auxiliary reel 122. In-hull foundations of the crane 0* e 12 210 are partly in the original DSV and partly in the 13 conversion-added portside sponson 108.

14 A crane 212 is mounted on starboard rail of the vessel o; 16 100, at the furthest stern of the main deck 136 (Figs.

17 1-6 and As with the portside crane 210, the 18 in-hull foundations of the starboard crane 212 are 19 partly in the original DSV and partly in the 0'0000 20 conversion-added starboard sponson 110. In order to 21 avoid being unduly baulked by the levelwind assembly 22 160 at the maximum elevation of the ramp 128, it is 23 preferred to move the starboard crane further aft from 24 the position shown in Figs. 1-6 to the position shown in the modified vessel of Figs. 7 and 8, the starboard 26 sponson 110 and the overlying portion of the main deck 27 136 being correspondingly extended sternwards to 28 support the repositioned crane.

29 Apart from removal of the redundant dive systems, the 31 forward vessel section 102 retains all the essential 32 features of the forward section of the DSV; in addition 33 to the bow thrusters 208, these retained features 34 include the engine room (not visible), crew accommodation 214, forward bridge 216, stern bridge 218 22 1 (overlooking the main reel 118 and the pipe-launching 2 ramp 128), and helicopter landing deck 220.

3 4 Referring now to Figs. 16, 17 and 18, these show external and internal details of a reel-clamping chock 6 300.

7 8 The chock 300 comprises a cylindrical outer casing 302 9 which is welded to the main deck 136 through the 10 intermediary of a pair of saddle plates 304 and 11 longitudinal reinforcing webs 306. A longitudinally 12 slidable sleeve 308 is mounted within the outer casing 13 302 by anti-friction bushes 310 and 312. The reel end 14 of the sleeve 308 is fitted with a flanged plug 314 having an aluminium bronze pad 316 affixed to its outer 16 face.

17 18 Extension and retraction of the chock 300 is achieved 19 by a hydraulic cylinder 318 and piston 320 mounted 20 within the sleeve 308. (Hydraulic fluid connections are 21 omitted from Figs. 16-18 for clarity). The end of the 22 hydraulic cylinder 318 remote from the reel-contacting C C CC 23 end of the chock 300 is anchored to the casing 302 and 24 hence to the deck 136 by a cylinder eye 322 pinned between a pair of U-brackets 324 fixed to the end of 26 the casing 302 by fasteners 326.

27 28 The piston 320 is coupled to the reel-contacting end of 29 the chock by a piston eye 328 being pinned to a clevis fitting 330 secured to one end of a pushrod 332. The 31 other end of the pushrod 332 is secured to the inner 32 face of the plug 314.

33 34 The reel end of the sleeve 308 is externally screw-threaded with an Acme thread 334. An internally 1 threaded ring 336 is fitted on the sleeve thread 334 2 such that the ring 336 can be selectively positioned 3 along the outer end of the sleeve 308 by manually 4 turning the ring 336 around the sleeve 308. The periphery of the ring 336 is drilled with radial holes 6 338 to enable the ring 336 to be turned by a suitable 7 tool (not shown).

8 9 Fig. 16 shows the chock 300 fully extended such that 10 the pad 316 forcibly engages an annular contact surface 11 222 on the outside end face of the main reel 118.

12 Fig. 16 also shows the ring 336 screwed up against the 13 adjacent end of the sleeve 308 such that reel-clamping 14 forces continue to be applied to the reel 118 even if hydraulic pressure is removed from the cylinder and 16 piston 318 and 320, due to the mechanical locking of 17 the chock 300 provided by suitably turning the ring 336 18 on the sleeve thread 334.

19 Release of the reel-clamping chock 300 from the 21 fully-applied position shown in Fig. 16 is achieved by 22 unscrewing the ring 336 until it is clear of the sleeve 23 308, then applying reversed hydraulic pressure to the 24 cylinder 318 and piston 320 to pull the movable end of the chock 300 away from the main reel 118.

26 27 Hydraulic pressure is preferably applied in the 28 reel-clamping direction prior to and during unscrewing 29 of the ring 336 in order to relieve the ring 336 of loading which might otherwise hinder or prevent the 31 ring 336 being turned.

32 33 Fig. 19 is a plan view, to a much reduced scale, of a 34 preferred arrangement for sea fastening, ie, for clamping the main reel 118 against axial movement when

_IC

1 not spooling or de-spooling (eg, during transit to or 2 from a pipe-laying location, or when pipelaying is 3 suspended due to bad weather). An array of four chocks 4 300 (each as shown in Figs. 16-18) is secured to the main deck 136 around the lip of the reel-holding well 6 112. One pair of the chocks 300 is disposed to engage 7 the port side of the main reel 118, and the other pair 8 of chocks 300 is disposed to engage the starboard side 9 of the main reel 118. Within each of these pairs of i 10 chocks 300, one chock is located on one side of the 11 reel axis and the other chock is located on the other 12 side of the reel axis, as shown in Fig. 19. This S. 13 symmetrical array of reel-clamping chocks ensures 14 inherent equalisation of reel-clamping forces on the reel when the chocks are fed from a common hydraulic 16 supply, thus avoiding any tendency for the chocks to 17 induce skewing of the main reel 118.

18 19 Other arrangements of reel-clamping chocks are possible 20 within the scope of the invention, for example 21 different locations for the chocks and/or different •22 numbers of chocks.

*c i *23 24 Reel-clamping chocks may also be provided for the large auxiliary reel 120 and/or for the small auxiliary reel 26 122.

27 28 Figs. 20 to 23 show a preferred embodiment of the main 29 reel 400 of a reel pipelaying vessel such as that described herein. Fig. 20 shows a side view of the reel 31 400, whilst Figs 21 to 23 show sectional views on lines 32 A-A, B-B and C-C of Fig. 20 respectively.

33 34 The reel 400 is of a generally open construction to minimise its weight, and is formed largely from plate i tL..I1^ i I. l(j- I(--qY~II-IX~~~ 1 steel. A plurality of main spokes 402 extend radially 2 outwards from the centre of the reel 400 and have an I- 3 beam type configuration comprising a main planar member 4 404 and outer and inner planar flanges 406, 408. The outer ends of the spokes 402 are connected by flange 6 plating 410 which form the sides of the pipe-receiving 7 well 412 of the reel 400. The flange plating 410 is 8 strengthened by trapezoidal box-section stiffeners 414.

9 The outer and inner edges of the flange plating 410 are *oeo 10 further strengthened by knuckles 415, 416. The floor of 11 the well 412 is formed by hub plating 418, which is e" 12 braced by internal stiffeners 420. Intermediate partial 13 spokes 422 are located between each pair of main spokes

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14 402, extending across the width of the flange plating 15 410.

16 6.55 17 As seen in cross section in Fig. 21, the reel has a 18 "portal frame" configuration, without a main shaft 19 connecting the main rotary bearings 423. This configuration improves the fatigue performance of the 21 reel by removing the additional rigidity and associated 22 stresses caused by the presence of a continuous shaft 23 as in the original Apache vessel.

24 In this example, the reel 400 is adapted to be engaged 26 by sea-fastening chocks, as previously described above, 27 at portions 424 of two of the main spokes 402' on each 28 side of the reel 400. A bracing flange 426 extends 29 diagonally between a point adjacent the portion 424 of each of the spokes 402' and the adjacent intermediate 31 spoke 422. The portions 424 may be formed as anti- 32 friction pads similar to those of the chocks as 33 previously described. This arrangement allows the 34 chocks to be applied to the reel only when the reel is at a particular angular position. Accordingly, when the 1 chocks are to be applied, it may be necessary firstly 2 to rotate the reel 400 so as to align the portions 424 3 with the chocks.

4 Fig. 24 illustrates an alternative arrangement, whereby 6 the chocks may be applied to the reel at any position.

7 In this case a continuous, annular chock bearing 8 surface 428 extends around the reel, mounted on an 9 extension 430 of the hub plating 418. As is also illustrated schematically in Fig. 24, the contact shoe 11 432 of the chock may be enlarged in size, in comparison o 12 with the previously described embodiment of the chock, .13 presenting a greater contact surface area such that the 14 bearing surface 428 of the reel can be made generally lightweight in construction.

16 17 Figs. 25(a), and and Fig. 26 illustrate a 18 preferred arrangement of the pipe clamps 174 previously e "19 referred to. Figs. 3 and 9 show the use of first and second pipe clamps 174 located on the pipeline path 21 near the aft end of the levelwind frame 162. Firstly, o 22 it is preferred that the clamps 174 have a generally *23 cylindrical configuration as shown in Fig. 25, being 24 formed from first and second semi-cylindrical portions 450, 452 hinged together along their lengths at 454 26 below the pipeline path. Secondly, it is preferred that 27 the clamps be mounted so as to be retractable out of 28 the pipeline path when not in use (as shown in Fig.

29 Thirdly, it is preferred that one of the clamps (most preferably the uppermost clamp closest to the 31 tensioner 172,173) is removable. The maximum clamping 32 force provided by the two clamps is only likely to be 33 required in a minority of cases. Accordingly, it 34 desirable that the second clamp be removable to provide a greater work space when it is not required for a 1 particular operation. If the second clamp is removable, 2 then only a single retractable mounting need be 3 provided for the first clamp. The mounting will be 4 constructed to be capable of taking the total design load of both clamps, and the second clamp may simply be 6 attached to the pipe immediately above the first clamp.

7 This arrangement is schematically illustrated in Fig.

8 26, where the first clamp is designated 174a, the 9 second clamp is designated 174b, the mounting, partially hidden beneath the first clamp, is designated 11 440, and the pipeline 442 is being unspooled in the 12 direction of the arrow A, the load on the clamp 13 mounting 440 being in the direction of the arrows B.

0: 14 The clamps may be of the type having a rubber lining 16 and hydraulic packers as is known in the art. Fig.

17 25(c) shows the clamp extended and closed to engage the 18 pipeline, and Fig. 25(b) shows the clamp in an 19 intermediate position between the retracted/open 20 position of Fig. 25(a) and the extended/closed position *oo* 21 of Fig. 22 23 While preferred embodiments of the invention have been 24 described above, the invention is not restricted to these forms, and modifications and variations of these 26 embodiments can be adopted without departing from the 27 scope of the invention.

29 Throughout this specification and the claims which follow, unless the context requires 3o otherwise, the word "comprise", and variations such as "comprises" and 51 I "comprising", will be understood to imply the inclusion of a stated integer or step or 32. group of integers or steps but not the exclusion of any other integer or step or group 33 of integers or steps.

Claims (9)

1. A reel pipelaying vessel, said vessel being fitted with a dynamic positioning system (DPS), said vessel being provided with a reel-holding well at a location amidships, said vessel being provided with reel-mounting bearings on laterally opposite sides of said well, said vessel being provided with ramp-mounting bearings at a sternwards location on said vessel for the mounting of a pipe-launching ramp thereon and further comprising a pipe-launching ramp temporarily or permanently mounted on said ramp-mounting bearings, wherein the mounting of said ramp is a rotational mounting whereby the elevation of the ramp with respect to the vessel is variable and said vessel further comprises ramp elevation control means for controllably varying the elevation of the ramp, and wherein the combination of said pipe-launching ramp and said ramp-mounting bearings is such that the underside of said pipe- "launching ramp is clear of underlying deck of the reel pipelaying vessel even at the lowest elevation of the ramp to an extent at least sufficient to constitute walk-under headroom, at 15 least between said ramp-mounting bearings and such part or parts of the deck at which said ramp elevation control means is anchored. S

2. A reel pipelaying vessel as claimed in claim 1, wherein said ramp-mounting bearings are arranged to dispose a horizontal pivot axis for the ramp substantially above said S 20 underlying deck whereby thus to provide at least the greater part of said clearance.

3. A reel pipelaying vessel as claimed in claim 1 or claim 2, wherein said ramp elevation control means comprises variable-length ramp support means anchored at or adjacent one end thereof upon fixed structure of the vessel and at or adjacent the other end of a variable length portion of the support to the ramp at a location thereon not adjacent said rotational mounting of said ramp.

4. A reel pipelaying vessel as claimed in claim 3, wherein said variable-length ramp support means comprises a pair of rack and pinion elevators located one on each side of said and conjointly operable to vary the elevation of said ramp with respect to said vessel. i ji ^_11 I.-II P:\OPER\DH\48281-97.RS2 -11/10/99 -29- A reel pipelaying vessel as claimed in claim 3 or claim 4, wherein said pipe-launching ramp comprises a pipe radius control means for imparting a substantially uniform radius of curvature to a length of pipe de-spooled from a reel mounted on said reel-mounting bearings in pipelaying operation of said vessel.

6. A reel pipelaying vessel as claimed in claim 3, claim 4 or claim 5, wherein said pipe- launching ramp comprises level-wind means for accommodating variations in the lateral positioning of a length of pipe spooled onto a reel mounted on said reel-mounting bearings as a plurality of side-by-side turns, during spooling and de-spooling of said length of pipe.

7. A reel pipelaying vessel as claimed in claim 6 when dependent upon claim 5, wherein said level-wind means and said pipe radius control means are mounted and controlled for conjoint lateral movement. e 15 8. A reel pipelaying vessel as claimed in claim 7, wherein said pipe radius control means in mounted upon said level-wind means for carriage thereby.

9. A reel pipelaying vessel as claimed in any preceding claim, including a pipe-spooling C C reel having first and second lateral side portions each comprising a central rotary bearing, a plurality of radial spokes extending outwardly from said central rotary bearing and a main flange surface connecting at least the outer portions of said spokes, the reel further including a hub surface connecting said lateral side portions such that said reel, in radial cross-section, has a portal frame configuration, there being no central shaft connecting the rotary bearings of the respective side portions. A reel pipelaying vessel as claimed in any preceding claim, further including pipeline clamping means located adjacent the aft end of said pipeline launching ramp, said clamping means comprising at least a first clamp of generally cylindrical configuration mounted on said ramp by clamp mounting means, said first clamp comprising first and second semi-cylindrical I, 30 portions hinged together along their lengths on a side of the clamp disposed below the P:\OPER\DH\48281-97.RS2 11/10/99 pipeline path, and wherein said clamp mounting means has a load capacity greater than the load capacity of said first clamp, whereby the clamp load capacity may be increased up to the capacity of said clamp mounting means by securing one or more additional clamps to the pipeline in abutment with the first clamp and upstream therefrom in the direction of pipeline un-spooling.

11. A reel pipelaying vessel as claimed in claim 10, wherein said clamp mounting means is adapted to be retractable such that said first clamp may be retracted to a position below the pipeline path when not in use.

12. A reel pipelaying vessel, substantially as hereinbefore described with reference to the drawings. DATED this llth day of October, 1999 S* COFLEXIP STENA OFFSHORE LIMITED By DAVIES COLLISON CAVE Patent Attorneys for the applicant(s) C* 9C t 9