APPARATUS FOR OFFSHORE SWIVEL REPLACEMENT

Abstract: An apparatus for replacement of a swivel atop a first, operating foundation on a turret of a production ship or offshore platform, comprises a swivel lifting and moving means for taking a swivel off or replacing a swivel on the first operating foundation on the turret and a second storing foundation spaced from the turret. The apparatus also comprises storage means for supporting and moving at least one used and one spare swivel in connection with the second storing foundation and a guiding system on the first and second foundations and on the swivel for accurately positioning the swivel onto a desired foundation.

Description: Apparatus for offshore swivel replacement A swivel is a rotatable pipe joint typically used on production ships extracting oil and gas from submerged wells. It is mounted on a turret transferring the oil and gas from one or more risers to pipelines being connected to storage tanks, processing equipment or the like on the ship. Stacks of .swivels can be assembled within a turret structure. Conventional lifting equipment can mount and demount them. Small scale swivels are conventionally used in existing production ship installations. Many ships using these swivels are located in less turbulent waters or working in fields with less demands on ship availability. Because of their size, the swivels are easily handled at sea by conventional equipment., provided good weather. They cannot however efficiently handle production from planned large capacity installations. Prospective swivels with a characteristic weight of 50 to 100 tons and correspondingly cumbersome dimensions are being designed for these installations. Conventional equipment will not be able to quickly and efficiently replace the heavy swivels at sea. Many operators replace swivels at a shipyard, often during overhauling. The assumption is that swivel replacement is very dependent on external conditions. But onshore replacement stops production, or at least eliminates ship availability. Because of these inherent delays, some operators are now requiring SUBSTITUTE SHEET production ships to carry suitable lifting equipment to replace swivels. The best solution for heavy swivels is onboard disassembly and replacement, sending onshore only parts not reparable onboard. Further, disassembly should be done at a distance from the turret so that production is not impeded. This invention is concerned with how these large-scale swivels can be mounted and demounted with minimum production stoppage and with minimum impediment. A very high degree of availability is required from production ships. Therefore, the swivel has to be regularly, quickly and often promptly replaceable with minimal weather-dependence. To avoid production delay, the replacement has to occur at sea. Strong and versatile equipment is needed to lift and center large-scale swivels on a turret foundation. Conventional cranes, like trolley winches, give little or no lateral support during lifting. Normal manual steering with ropes is unsatisfactory in view of the pitching and rolling at sea. Swing, especially due to the ship's rolling and pitching, must be strictly controlled or avoided due to small clearances between sensitive parts in the swivel and the turret. An object of the present invention is to provide a lifting system making swivel positioning less weather-dependent and manpower intensive- Another object of the present invention is to provide an apparatus laterally supporting a swivel during lifting and positioning. Still another object of the present invention is to provide an apparatus laterally supporting a swivel with lightweight lateral supporting frames during the entire lifting operation. A further object of the invention is to provide equipment with a capacity for replacing a swivel on a turret in one operation. SUBSTITUTE SHEET The inventive apparatus comprises a combination of three main components: - a swivel lifting arrangement for taking a swivel off or replacing a swivel on a first, operating foundation on the turret, and a second storing foundation spaced from the turret, - a storage arrangement for supporting and moving at least one used and one spare swi in connection without the second storing foundation, - a guiding system on the fir-- and second foundations and on the swivel for accurately positioning the swivel onto one of the desired foundations. The invention is illustrated in the drawings in which - FIG. 1 is a longitudinal view of part of a ship with a swivel-equipped turret, with lifting and skid-equipped storage systems, and a downwardly extending frame providing lateral support. - FIG. 2 is a plan view showing the relationship of the trolley's movement to a sled pathway. - FIG. 3 is a side view of the preferred embodiment, showing the lifting and guiding means in operation. Close-up A-A shows how upper and lower arms connected to a jack can be independently laterally pushed by hydraulic cylinders. Fig. 3 shows how these arms engage the swivel. A close-up marked B-B shows an embodiment for wheels connecrJ ng the jack to the frame. Close-up C-C shews i centering or bolt-hole system to position the swi-- ~ 1 - FIG. 4 shows an alternative embodiment for the jack, fitting around and enclosing the frame and thereby functioning as a telescopic support. Close-up E-E is a cross section of a lower part of the telescopic guide SUBSTITUTE SHEET system. FIG.5 shows another alternative embodiment facilitating length adjustment for the upper and/or lower arms functioning as guiding mechanisms laterally pushing a swivel. The arms are mounted on a rotatable crankshaft for controlled vertical movement and for effective extension/retraction to facilitate fine adjustment of swivel positioning. FIG. 6 shows a side view of a further alternative embodiment in which the arms have an outward extension projecting from the jack which is itself laterally displaceable. Close-up D-D is a front view of the embodiment. FIG. 1 shows a turret 1 projecting upwardly through a well 2 located within the body of a ship 3. Ascending pipes 4 conduct the well stream into a choke or manifold chamber 5 of the turret- 1. The well stream is conducted further from the manifold 5 through a swivel 6 mounted on an operative foundation 9 at the top of the turret 1. Fig. 3 shows the swivel's structure. Each swivel 6 has a stationary part 31 mountable on a swivel foundation 9 mounted for example at the top of a turret 1, and a rotary part 32 so contrived so as to allow piping 7,10 extending between the swivel 6 and the ship 3 (not shown in FIG. 3) to turn freely in any horisontal direction so as to correspond to the rotation of the ship 3. FIG. 1 shows inlet pipes 16 at the lower edge of the swivel (or swivel stack) 6 coupled with connecting tubes or spool pieces 18 to the turret's piping system 35 at the lower edge or portion of the foundation 9. Outlet pipes 10 extending from the swivel's rotatable portion (numbered 32 in FIG. 3 but not numbered in FIG. SUBSTITUTE SHEET 1) are coupled to an externally directed piping system 7 arranged on a framework 8 longitudinally directed along and mounted on the ship's deck 16. Though preferably longitudinally directed, the framework 8 in accordance with the invention could also be only generally so directed or even transversely directed, particularly on a ship having a very substantial beam. An automatous (self-moving) trolley 13 is suspended in a longitudinally directed track 14 preferably mounted on the ship's centerline and along the lower edge of the framework 8. The trolley 13 has a rack and pinion operation in this embodiment. The trolley 13 is movable from the turret 1 to a first location at which the track 14 intersects with a sled track 12 arranged and directed athwartship (laterally across the ship) . A reserve swivel 11 is stored along or on the sled track 12 and more particularly on a swivel storing foundation 45 on a slidable support or sled 17. FIG. 2 is a top view showing the relationship of the sled track 12 to the trolley track 14. The longitudinally directed track 14 has two parallel rails 15 (shown in FIG. 3) upon which the trolley 13 moves along the length of the ship. FIG. 2 indicates a sled path or track 12 arranged athwartship. Two sleds/ slidable storage supports 17 are shown. Sleds are the preferred but not required embodiment. The reserve swivel 11 is normally stored on one of the sleds 17 at one side of the trolley track 14. The other sled 17 is usually kept unloaded so as to be immediately available to receive a demounted swivel. To facilitate its immediate availability, this other sled 17 is advantageously placed directly under track 14. Each sled 17 is independently displaceable along track 12 to move swivels 6,11 between the first location and a second location located to one side of the track 14. FIG. 3 shows the trolley 13 which lifts the swivel 6, with a support/guide frame 19 for controlling lateral swing or SUBSTITUTE SHEET oscillation of the swivel 6 during lifting. The trolley 13 is equipped with a main winch 26, preferably a synchronised double main winch 26, for lifting swivel 6 or 11. The trolley 13 also has a smaller winch 20 which lifts or lowers a lifting jack 21 at constant tension by means of wire 58 and hook 73. As shown in FIG. 3, the trolley 13 is mounted by wheels 36 onto the rails 15 of track 14. The support/guide frame 19 includes a framework 22 permanently mounted at and extending vertically downwardly from a lower edge of the trolley 13- The frame 19 further includes a lifting jack 21. The jack 21 is preferably steered by a set of two wheels 18, thereby providing lateral support for the jack 21 in an x & y plane while facilitating vertical movement in a z plane. The close-up marked B-B shows the preferred form of_ these wheels 18: respectively longitudinally and transversely directed wheels 48,49 running along rail system 23 to move and stabilize the jack 21. The rail system 23 is longitudinally mounted on the framework 22 to facilitate vertical movement of the jack 21. The rail system 23 is preferably mounted on the one side of the frame 22 facing the turret 1. The jack 21 is equipped with two pairs of mainly parallel holding arms 24 and 27. The upper arms 24 are advantageously connectable to the swivel 6 at a position (i.e. pivot 25) somewhat over the swivel's center of gravity. The arms 24 and 27 have hooks 38 and 39 at each of their respective free ends. Correspondingly, an upper diametrically spaced pivot pair 25 and a lower diametrically spaced pivot pair 29 are mounted on the swivel's rotating outer part 32. The hooks 38 of each upper arm 24 extend so as to engage the pivots 25. Similarly, the hooks 39 engage pivots 29- SUBSTITUTE SHEET As pictured in FIG. 3, the preferred embodiment for each upper arm 24 is that one end is connected in the vertical plane to jack 21, while the vertical position of hooks 38 is adjustable with a turnbuckle 37 on a rod (not numbered) connected to each respective arm 24. The preferred embodiment for each lower arm 27 is that extendable/retractable outer portions are provided via a screw-nut connection (or turnbuckle) 44. This increases or decreases the effect 's length of each lower arm 27. The benefit is that hook-up of ,:ha swivel 6,11 and the lower arms 27 is easier since the ~ , 27 can ' be longitudinally positioned relative to the upper -irms 24 after they are engaged. The upper arms 24 connect to the swivel 6,11 nearest its center of gravity and consequently bear the greatest lateral support load-; therefore preferably only the lower arms 27 are equipped with adjustable outer portions/turnbuckles 44. Hydraulic cylinders 34 operate the lower two arms 27. In the embodiment of FIG. 3, each hydraulic cylinder 34 is connected to a respective arm 27 by a rod (not numbered) , conveniently extending from hydraulic cylinder 34 at about a 45 degree angle relative to the jack 21. The cylinder 34 extends or retracts the rod thus lifting or lowering arm 27. It is important that the arms 27 can be lowered and positioned out of the way of the swivel 6,11 while its stationary part 31 is centered by other devices of the guiding system onto the foundation 9, 45. The upper arm pair 24 is operable by hydraulic cylinder 28 (see close-up A-A) , and is shown fixed to the jack 21. An upwardly extending rod (not numbered) , connected to a respective arm 24 and to the jack 21 and projecting conveniently at about 45 degrees from the jack 21, is equipped with a turnbuckle 37. Suitable actuating means can via the turnbuckle 37 raise or lower the outer part of the upper arms 24. The arm pairs 24 and 27 can be independently laterally pushed (in a vertical plane defined by raising or lowering the swivel) SUBSTITUTE SHEET respectively by the hydraulic cylinders 28 and 33 (see close-up marked A- in FIG. 3) . This facilitates adjustment of both the swivel's lateral position relative to the foundation 9,45 and lateral inclination during lifting and installation. The extent of lateral pushing is determined by the accuracy of trolley's positioning of the swivel 6 at the point of a hook-up operation (on the foundation 9 of the turret 1 or foundation 45 of the sled 17), and the radial play in the turret's bearing system (turret 1 having therefore a somewhat varying physical location relative to the deck of ship 3) . FIG. 3 shows diametrically spaced rings 40 projecting from a lowest portion of the swivel's stationary portion 31. Each ring 40 is penetratable by a projection consisting of a peg or lug 42 extending at least generally vertically from the foundation 9,45 and a conical funnel 43 mounted atop the lug 42. The two lugs 42 are spaced on opposite sides of the foundation 9,45 to thereby define a desired position for the swivel 6,11. The lugs 42 and rings 40 function as part of a guiding system to center the swivel's stationary part 31 relative to the foundation 9 and 45. Conceivably, the swivel could also be centered by use of complementarily interlocking guiding devices. FIG. 3 also shows in enlargement F-F, indicated by an arrow projecting from the cone 43, a preferred embodiment of the ring 40-lug 42 interlock. The ring 40 is connected by bar 58 to the swivel 6,11, " and has rounded or curved outer and interior surfaces forming a frustum 56 tapering evenly upwards to an upper edge defining a hole. A sleeve 57 is optionally mounted on this upper edge to provide better contact with lug 42 as it penetrates the hole. As the swivel 6,11 is lowered, the lug 42 is guided by the tapering interior surface through the hole defined by the upper edge of the ring 40. The lug 42 can advantageously be a frustum. Further fine adjustment of the swivel's position is provided for SUBSTITUTE SHEET by other devices withi "he guiding syste,., specifically a centering system 52 comprising bolts 53 at the underside of swivels 6, 11 and corresponding holes 55 at the top of foundations 9, 45. The bottom part 54 of each bolt 53 is shown in close-up C-C as a frustum and each hole 55 is complementarily tapered. The bolts 53 screw in to adjust the swivel position. The clearance between the upper part of the tapered holes 55 and the bottom part or frustum 54 (with the bolt 53 in its initial unscrewed position) corresponds to the clearances between the lug 42 and the rings 40. FIG. 3 also shows one of two lifting hooks 47 connected at one end to the trolley's main winch 26. The hooks 47 are parallel and horizontally spaced from each other to correspond to .the diameter of (or slightly more than) the swivel 6,11 at an upper swivel portion from which diametrically spaced lifting shanks 46 project. The invention operates to replace a swivel with the following general steps: - 1. trolley 13 lifts swivel 6 off foundation 9; - 2. trolley 13 is driven to the first location on sled track 12 where the demounted swivel 6 is mounted on foundation 45 on a sled 17 subsequently pushed to one side; - 3. reserve swivel 11 is pushed to the first location; - 4. reserve swivel 11 is lifted by trolley 13 over the center of the turret 1; - 5. the swivel 11 is lowered to fasten it to the foundation 9 at the top of turret 1; and - 6. the trolley 13 is stowed. In detail, the operation of the inventive apparatus involves: - dis-: ;;nectirr piping 18 and 10; - pos_ . ...oning . "Hey 13 , adjusting the arms 24 and 27 SUBSTITUTE SHEET relative to pivots 25, 29 of swivel 6; - demounting swivel 6 and lifting it from foundation 9; - hooking lifting hooks 47 to lifting shanks 46; - lowering jack 21 (50 in the alternative embodiment pictured in FIG. 4) such that upper hooks 38 are connectable to the swivel's upper pivots 25; - laterally positioning upper hooks 38 via hydraulic cylinders 28; - adjusting longitudinal positioning by driving the trolley 13 alongship in the longitudinal direction, and/or by adjusting turnbuckles 44 to extend or retract the lower arms 27; - lifting jack 21 to firmly connect upper hooks 38 and pivots 25; - lifting the lower arms 27 under the lower pivots 29 by activating respective hydraulic cylinders 34 and adjusting the lateral positioning of lower arms 27 via hydraulic cylinders 33. At this point in the procedure, deviating longitudinal positioning may cause the arms 24,27 to be either too far from or too close to the pivots 25,29 to safely lift the swivel 6,11. Lower arms 27 may be then adjusted lengthwise by extending them with the turnbuckles 44 and/or pushing the arms 27 out/in via e.g. an eccentric axle upon which arms 27 are mounted (FIG. 5) . The swivel 6 is then ready to be lifted away from the turret 1. The jack 21 is lifted at a constant tension or pull by the winch 20. This engages arms 24, 27 and respective pivots 25, 29 but the main winch 26 does the major portion of the lifting. Consequently, the frame 19 (51 as shown in FIG. 4) can be relatively lightweight and designed to support only lateral orces. SUBSTITUTE SHEET The trolley 13 is then driven from the turret 1 to the first location at the sled path 12. Before the swivel 6 is lowered, the stationary part 31 of the swivel 6 is turned so that the rings 40 are generally properly positioned to engage lugs 42 on the foundation 45 on sled 17. As it is lowered, the position or inclination of swivel 6 can be further laterally or longitudinally adjusted by activating the hydraulic cylinders 28,33 (displacing upper arms 24,27) and/or by moving the trolley 13. Lowering is suspended when the cones 43 (of lugs 42) and rings 40 engage or overlap the lower part 56 of the ring 40. The lower arms 27 are then disengaged to be out of the way. Swivel 6 is lowered further so that lugs 42 slide into respective rings 40 and thereby guide the swivel 6 into the correct position relative to the fastening arrangement (not shown) . The support 17 and its foundation 45 now holds the swivel 6. The support 17 is shoved to one side athwartship of the frame structure 8 to a second position at which the swivel 6 may be stored or disassembled. Preferably the disconnected swivel is stored on the other athwartship side of the sled track 12, reserve swivel 11 is slid on a support 17 to the first location for lifting. To mount the reserve swivel 11 on the turret 1, the foregoing procedure is reversed sequentially and operationally as to activities connected to raising and lowering. Before lifting, the reserve swivel's inner stationary portion 31, from which the rings 40 project, is turned e.g. by winches to an approximately correct direction relative to the lugs 42 on foundation 9. When suspended, the swivel's longitudinal and lateral position relative to the foundation 9 is adjusted by the SUBSTITUTE SHEET trolley 13 and the hydraulically operated cylinders 28 and 33 respectively. As the swivel 11 descends, lugs 42 and rings 40 and the centering system 52 (these being two steps) adapt the swivel's position appropriately relative to the foundation 9 and the piping system 7,10 and 18. Alternative embodiments: Telescopic support/guide frame FIG. 4 shows a lifting arrangement with an alternatively structured guiding frame 51 (compare to frame 19 shown in FIG. 3) . The jack 21, shown in FIG. 3 as essentially a two- dimensional structure, is a three-dimensional structure 50 in FIG. 4; the jack 50 fits around and encloses rectangular frame 22. Frame 50 is vertically displaceable along frame 22 by means' of wheels or bearing units 78, 79 (see enlargement E-E) . Frames 22 and 50 have correspondingly suitable rails. This improves support, particularly when the jack 50 is below framework 22. The three-dimensional jack 50 combined with the three dimensional wheel or bearing system as shown in enlargement E-E provides for a far better torsional or twisting strength when jack 50 is below fixed framework 22. This embodiment is advantageous where the foundation 9 and the foundation 45 are at different heights. The upper arms 24 can also be structured to be raised and lowered when not in use. This saves space. Horizontally and vertically displaceable jack FIG. 6 shows another alternative embodiment for the jack 21 or for the frame 50. The jack's main component is a frame 80 to which upper and lower arms 24,27 are fixed. The frame 80 itself is displaceable horizontally or laterally via bearings 83,84 by means of vertically spaced pusher rods 74,75 extending from jack 21, frame 50 (see FIG. 3) . These may be driven by hydraulic cylinders 81,82 replacing hydraulic cylinders 28,33. Bearings 83,84 provide for requisite vertical and longitudinal horizontal SUBSTITUTE SHEET load transfer, between hooks 38/39 and the jack 2l/frame 50. The advantage is that lateral movement is performed by a separate structure 80 (the frame) and the hooks 38,39 will be parallel and will align better with the pivots 25,29 independently of the relative inclination of the swivel 6,11 and the jack 21, frame 50. Another advantage is that the arms 24,27 need joints for rotation only and that the rods connected to these arms need to have joints permitting rotation only in one plane (longitudinally) . Adjustable length of upper and lower arms As illustrated in FIG. 5, each lower arm 27 and/or each upper arm 24 can be mounted on a respective independently hydraulically rotatable crankshaft 60. This permits adjustment of the arms 24,27 in a longitudinal plane both prior to and during lifting. As shown in FIG. 5, hooks 38, 39 on arms 24,27 are displaced by the hydraulic cylinders 34,72 connected to respective supports 76. The cylinders 34,72 act to control the height of the hooks 38,39. Hydraulic cylinders 64 connected to support 65 and rod 63 directly engage the crankshaft 60. Bearings 62 mounted on jack 21 facilitate crankshaft 60 rotation. As crankshaft 60 turns, the effective length of arms 24,27 changes. This embodiment gives each arm 24,27 a controlled longitudinally directed stroke of extension or retraction. A screw-cylinder rack system 66,67 moves the arms 27 laterally. The rack's 66 cylindrical shape lets the camshaft (at 61) be at any angle. The screw 67 is rotated by motor 68. The thrust bearing 69 converts rotation of the screw 67 into lateral movement of the cylindrical rack 66 independently of the camshaft (at 61) angle. The screw-cylinder racks 66,67 may be substituted by the hydraulic cylinders 28/33 in Fig. 3. The benefit of this embodiment is the capability to control the swivel's bottom relative to foundation 9,45 before setting in SUBSTITUTE SHEET place. This fine adjustment can be done by remote operation and without using the motor of the trolley 13. It is particularly advantageous to adjust the swivel's positioning by using the lower arms 27 since they are least strained by weight and since they may need adjustment after the upper arms 24 have been hooked up. An alternative arrangement for extending or retracting the length of the arms 24,27 may be performed by using servo operated cylinders in the arms 24 and 27 (instead of turnbuckles 44 in Fig. 3) . SUBSTITUTE SHEET

Claims: PATENT CLAIMS An apparatus for replacement of a swivel atop a first, operating foundation on a turret of a production ship or offshore platform, c h a r a c t e r i z e d b y swivel lifting and moving means for taking a swivel off or replacing a swivel on the first operating foundation on the turret and a second storing foundation spaced from the turret, storage means for supporting and moving at least one used and one spare swivel in connection with the second storing foundation, a guiding system oh the first and second foundations and on. the swivel for accurately positioning the swivel onto a desired foundation. Apparatus according to claim 1, c h a r a c t e r i z e d b y means connected to the swivel lifting means for laterally supporting and positioning the swivel during the lifting and mowing operation. Apparatus according to claim 1, c h a r a c t e r i z e d i n t h a t the storage means comprises a sled track (12) and two slidable skids or supports (17) . Apparatus according to claim 1, c h a r a c t e r i z e d i n t h a t the swivel lifting means comprise two parallel rails (15) forming a longitudinally directed track (14) mounted on a frame (8) , and an automatous trolley (13) suspended in and moveable along the track. SUBSTITUTE SHEET 5. Apparatus according to claim 4 , c h a r a c t e r i z e d i n t h a t the lifting means further comprises two longitudinally spaced winches (20,26) , a downwardly extending support frame (22) , and a jack (21) extending parallel to and vertically moveable along the support frame (22) and connected to one of the two winches so as to facilitate vertical movement of the jack in an area below the track. 6. Apparatus according to claim 5, c h a r a c t e r i z e d i n t h a t the jack (50) has a body fitting around and enclosing the frame (22) , and the frame has pairs of rails and wheels (78,79) on opposite sides to facilitate telescopic vertical movement of the jack. 7. Apparatus according to claim 5, c h a r a c t e r i z e d i n t h a t the guiding means comprises two pairs of vertically spaced, parallel holding arms (24,27), each arm being connected at one portion to the jack (21,50) and having another portion extending outwardly from the jack, and each arm having a hook (38,39) at the other outwardly extendingportion, and further comprising pivots (25,29) mounted on the swivel so as to be engageable with the hooks when the trolley is connected to the swivel. 8. Apparatus according to claim 7, c h a r a c t e r i z e d i n t h a t each lower arm is provided with turnbuckles (44) or hydraulic cylinders so as to facilitate increasing or decreasing an effective length of each arm. SUBSTITUTE SHEET 9. Apparatus according to claim 7, c h a r a c t e r i z e d i n t h a t each lower arm (27) is operatively connected to hydraulic cylinder (33) for lateral movement. 10. Apparatus according to claim 7, c h a r a c t e r i z e d i n t h a t each lower arm is mounted on a rotatable crankshaft (60) connected to the jack to thereby facilitate adjustment of length of the lower pair of arms (27) . 11. Apparatus according to claim 7, c h a r a c t e r i z e d i n t h a t each upper arm (24) is operatively connected to a hydraulic cylinder ;28) for lateral movement. 12. Apparatus according to claim 7, c h a r a c t e r i z e d i n t h a t each upper arm is mounted on a rotatable crankshaft (60) connected to the jack to thereby facilitate adjustment of length of the upper pair of arms. 13. Apparatus according to claim 7, c h a r a c t e r i z e d i n t h a t guiding means further comprises rods connected to the upper and lower arms (24,27) respectively the jack (21,50) which rods are provided with turnbuckles (37) and/or hydraulic cylinders (34) thereby elevating or lowering the upper and lower arms. 14. Apparatus according to claim 1, c h a r a c t e r i z e d i n t h a t means comprises a pair of diametrically spaced rings (40) projecting horizontally from a lower part of a stationary portion of the swivel and a pair of lugs (42) projecting upwardly from first and second foundations SUBSTITUTE SHEET (9,45) and spaced so as to facilitate entry of each lug into a respective one of the rings. 15. Apparatus according to claim 14 , c h a r a c t e r i z e d i n t h a t wherein each ring further comprises a frustum (56) and that the lugs have a conical top part (43) . 16. Apparatus according to claim 1, c h a r a c t e r i z e d i n t h a t guiding means comprises a plurality of centralizing bolts arranged on a bottom surface of the swivel and ' a plurality of holes complementarily arranged in an upper surface of each of the foundations. 17. Apparatus according to claim 7, c h a r a c t e r i z e d i n t h a t the arms (24,27) are mounted to a frame (80) which is laterally displaceable independantly at top and bottom by hydraulic cylinders 81,82. SUBSTITUTE SHEET

Inventors: ASKESTAD SIGMUND, ASKESTAD, SIGMUND
Applicants: NORSK HYDRO AS, NORSK HYDRO A.S
Application year: 1993
Main classification: B63B9
IPC codes: B63B21