GB2026982A - Mobile hoists for positioning equipment carried thereby - Google Patents

Abstract

A mobile hoist for positioning equipment at selected locations on a structure, notably for positioning cleaning, inspection, repair or the like equipment on the submerged structures of offshore oil and gas platforms, comprises tensioned guide wires 11, 11A held between upper and lower carriages 9 and 14 which can be traversed horizontally in unison. Between the guide wires runs a hoisting carriage 13 to carry the equipment to the desired locations on the structure, the carriage 13 being driven by a cable 12 passing via pulleys supported by the carriage 9 to a winch drum 17. The wires 11, 11A are tensioned by further winch drums 16, 16A on the carriage 9. The lower carriage 14 runs on a clump block 6 which can be raised and lowered from the structure by wires 7 anchored to a further carriage 3. Carriage 3 is used to shift the clump block horizontally and also carries the track 8 upon which the upper carriage 9 runs. The hoisting carriage 13 has hydrodynamic thruster units 26 comprising ducted motor-driven propellers to move the carriage 13 through the water transverse to the plane of the cables 11, 11A, and has adjustable steadies 27 for engagement with an underwater structure. <IMAGE>

Description

SPECIFICATION Positioning apparatus The present invention relates to apparatus for positioning equipment at selected locations on a structure. Particularly, though not exclusively, the invention is concerned with apparatus for positioning cleaning, inspection, repair or like equipment at selected locations on structures of which significant proportions are disposed underwater-such as the supporting structures of offshore oil and gas platforms.

At present, cleaning, inspection and repair work on the submerged structures of offshore oil and gas platforms is usually performed by teams of divers with manually operated equipment. This is, at best, a relatively hazardous and inefficient pursuit. The divers are often limited to operating at ebb tides and in calm weather, and even so may be subject to dangerous water currents in the vicinity of the structure. The depth of operations can also be a limiting factor for divers. The invention accordingly seeks in particular to provide a means to enable cleaning, inspection, repair or like equipment to be positioned by remote control where required on the supporting structure of an offshore oil or gas platform, thereby eliminating the need to employ divers to perform this task.

According to the invention, apparatus for positioning equipment at selected locations on a structure comprises means for holding one or more guide wires in tension between an upper anchorage supported by the structure and a lower anchorage, means for horizontally traversing the wire(s), a vehicle for carrying the equipment adapted to be guided by said wire(s), and means for raising and lowering the thus guided vehicle. In this context the term "wire" is intended to embrace not only wires per se, but cables, ropes and any single or multi-stranded reelable, filamentary elements capable of sustaining the required tensile loads.

In a preferred embodiment the upper anchorage is to a first carriage moveable horizontally relative to the structure and the lower anchorage is to a second carriage moveable in parallel with the first. Preferably the second carriage is moveable along a track which can itself be raised and lowered from the structure, and the entire assembly of the vehicle, first and second carriages, and the track for the second carriage, may be borne by a third carriage located upon the structure so that the said assembly can be moved as a whole horizontally relative to the structure. Preferably the vehicle and said track are raised and lowered by means of further, lifting wires.

With a positioning apparatus as described above, the equipment-carrying vehicle can be traversed to any selected location lying generally within the plane defined by the range of horizontal movement of, and spacing between, the upper and lower guide wire anchorages. To impart a component of move ment to the vehicle in a direction perpendicularto such plane the vehicle may be provided with one or more hydrodynamic thruster units effective to urge the vehicle in a desired direction when submerged and/orthe vehicle may be provided with one or more extendable and retractable arms which can be engaged, eg magnetically, with the structure.

The positioning apparatus of the present invention is particularly adapted to operate in conjunction with the apparatus disclosed in our co-pending United Kingdom patent application number (Agents ref 7843) whereby complete cleaning, inspection, repair and the like operations can be carried out at selected locations on tubular structural members all by remote control.

The invention will now be more particularly described, by way of example, with reference to the accompanying schematic drawings, in which: Figure 1 is an isometricviewofa positioning apparatus in accordance with the invention, as provided on an offshore oil or gas platform; Figure 2 shows to an enlarged scale the vehicle used with the apparatus of Figure 1; and Figure 3 shows a typical installation of the positioning apparatus on an offshore oil or gas platform.

Referring to figure 1, the walkway of the lower deck 1 of an offshore oil or gas platform is fitted with a track 2 along which a carriage 3 can be traversed. Mounted to this carriage is an "A" frame lifting mechanism 4 and a winch system 5, 5A which can raise and place an elongate clump block 6 on the seabed at the base of the platform structure, by means of lifting wires 7, 7A. The clump block can be shifted horizontally relative to the platform by unlocking and traversing the carriage 3 along the track 2, and can be manoeuvred to a certain extent towards and away from the platform structure by altering the inclination of the "A" frame 4. For positioning in fast tidal conditions hydrodynamic thruster units may be required to be fitted to the clump block.

A track 8 is provided on the carriage 3 along which a shorter carriage 9 can be traversed by a position and rate control drive 19. Likewise a track 15 is provided on the clump block 6 along which a carriage can be traversed, in parallel with carriage 9, by a position and rate control drive 20. Attached to car riage 9 is a form of davit 10 supporting a series of pulleys by which a pair of parallel wires 11,1 1A are led from respective reeling drums 16, 16A on the carriage 9, around the edge of the deck 1, and down to the lower carriage 14. The wires 11, 11A act as guides for a vehicle 13 which can be raised or low ered by a third wire or cable 12 extending from a drum 17 on carriage 9 in parallel with the guide wires.The inclination of the davit 10 relative to car riage 9 can be altered, as also can the effective length of the lower limbs 10A of the davit, in order to manoeuvre the final pulleys 10B in the series towards and away from the platform structure. In this way the inclination of the operational length of the guide wires 11, 1 1A (ie the length which extends from the pulley 1 OB to the carriage 14) can be adjusted so that, for example, the guide wires can be made to follow a divergent structure such as is shown in figure 3.

Turning now to figure 2, this more clearly indicates the nature of the vehicle 13. The vehicle is provided with sheaves or bearing blocks 21 at each side by which it can run on the guide wires 11, 11A, and there may also be provision for locking the vehicle onto the guide wires if required. Mounted centrally to the vehicle is an extendable and rectractable arm 22 carrying at its end a docking mechanism 23 by which various pieces of cleaning, inspection, repair or the like equipment can be carried and fitted to/recovered from the platform structure.By way of example the vehicle is shown as carrying a piece of equipment which is fully described in ourco- pending United Kingdom Patent Application number (Agents ref 7843,) but which briefly comprises a split track 40 which can be clamped around a tubular structural member, and a carriage 41 which can traverse circumferentiaily around the track. In addition to its linear extension and retraction, the arm 22 can be rotated around its longitudinal axis and can swivel laterally to a certain extent by means of a central bearing 24, thereby imparting a considerable degree of manoeuvrability to the docking mechanism 23. A movable counterweight 25 is provided at the opposite end of the arm to the docking mechanism to keep the vehicle and its load in approximate balance throughout operations.

A pair of hydrodynamic thruster units 26 comprising ducted propellers are provided by which the vehicle can be driven towards or away from the submerged structure, and the propellers may be swivelled relative to the vehicle to provide a degree of cross flow tidal compensation. These thruster units can also be used to apply a holding force to the submerged structure through adjustable steadies 27.

The latter comprise extendable and retractable arms pivoted to the vehicle by bearings 28 and preferably carrying switchable electromagnetic pads 29 when operating in conjunction with steel structures. When engaged with the structure, the steadies can also be used to manoeuvre the vehicle towards or away from the structure by decreasing or increasing their effective lengths. The use of the steadies in this manner is particularly advantageous for operations above the waterline, when the thruster units 26 are ineffective.

Power supplies and control signals are transmitted to the vehicle 13 by means of an umbilical cable which is comprised in, or runs with, the lifting wire 12. The hub of drum 17 is provided with a slip ring mechanism 18 (Figure 1) by which the supplies can be permanently connected to the cable. A measuring wire 30 (Figure 2) may also be provided for determining the depth at which the vehicle is located at any time.

In use of the described positioning apparatus, the carriage 3 bearing the entire assembly of clump block 6, upper and lower carriages 9 and 14, and vehicle 13, is traversed to a position in which the point on the structure where work is to be carried out will lie within the lateral range of movement of the vehicle. With the carriage 3 locked in position, the clump block is lowered on the wires 7, 7A at the same time the guide wires 11, 1 1A being unreeled from the drums 16, 16A which latter keep the guide wires in the correct tension throughout operations.

The vehicle 13 can then be positioned as required.

As will be appreciated, lateral (y-axis) movement of the guidewires and vehicle is provided by the sync hronised traversal of the upper and lower carriages 9 and 14, while the vehicle can be raised and lowered on the guide wires (x-axis movement) by the lifting cable 12. The vehicle can also be moved to a certain extent perpendicularly to thex-y plane by means of the thruster units 26 and/or adjustable steadies 27. In addition, as previously indicated, the spacing of the pulleys 10B from the platform structure is open to some adjustment, as also is the spacing of the clump block from the structure.

Figure 3 shows a typical installation of the positioning apparatus on an offshore oil or gas platform.

With an essentially rectangular (or triangular) planform structure of the type indicated a respective carriage 3 and related equipment may be provided for each side of the deck 1, or a single assembly may be provided which can be hoisted onto tracks 2 provided along each side of the deck. Of course instead of employing a carriage-borne system as described the clump block 6 may be raised and lowered by fixed installations provided at each corner of the deck 1, the clump block extending the whole length of a side of the structure. However, by providing for lateral movement of the clump block by means of carriage 3 a shorter, and therefore lighter, block can be employed.

From the foregoing it will be understood howthe described apparatus is capable of positioning equipment at selected locations on an offshore oil or gas platform structure from the comparative safety of the deck of the platform, and without the necessity of employing divers. By way of example Figure 3 shows three-split-track units of the type described in our co-pending United Kindom patent application number (Agents ref 7843) fitted to the illustrated platform structure, unit 42 above the splash line, unit 43 in the splash line and unit 44 belowthe splash line, with a further unit 45 attached to the vehicle 13 and ready to be fitted to the structure. it is also of note that the entire positioning apparatus can be stored upon, and deployed from, the deck of the platform and does not depend on the provision of guides, supports or other fitments on the submerged structure itself.

Claims (13)

1. Apparatus for positioning equipment at selected locations on a structure comprising means for holding one or more guide wires in tension between an upper anchorage supported by the structure and a lower anchorage, means for horizontally traversing the wire(s), a vehicle for carrying the equipment adapted to be guided by said wire(s), and means for raising and lowering the thus guided veh icle.

2. Apparatus according to claim 1 wherein, in use, the upper anchorage is to a first carriage move able horizontally relative to the structure and the lower anchorage is to a second carriage moveable in parallel with the first.

3. Apparatus according to claim 2 wherein the second carriage is moveable along a track which can in use be raised and lowered from the structure.

4. Apparatus according to claims 2 and 3 wherein the assembly of the vehicle, first and second carriages, and the track for the second carriage, is borne by a third carriage located in use upon the structure so that the said assembly can be moved as a whole horizontally relative to the structure.

5. Apparatus according to claim 3 or claim 4 wherein, in use, said track is raised and lowered by means of lifting wires.

6. Apparatus according to any preceding claim wherein, in use, the vehicle is raised and lowered by means of a lifting wire.

7. Apparatus according to any preceding claim wherein the vehicle comprises means for imparting a component of movement to the vehicle in a direction perpendiculartothe plane defined by the range of horizontal movement of, and the spacing bet ween,the upper and lower guide wire anchorages.

8. Apparatus according to claim 7 wherein the vehicle comprises means for generating a hydrodynamicthrust when submerged, for imparting said component of movement to the vehicle.

9. Apparatus according to claim 7 wherein the vehicle comprises one or more extendable and retractable arms which can be engaged, in use, with the structure for imparting said component of movement to the vehicle.

10. Apparatus for positioning equipment at selected locations on a structure substantially as hereinbefore described with reference to the accompanying drawings.

11. A structure equipped with apparatus for positioning equipment at selected locations thereupon in accordance with any preceding claim.

12. A structure according to claim 11 of which a significant proportion is disposed under water.

13. A structure according to claim 12, being the supporting structure of an offshore oil or gas platform.