GB2210838A - Subsea working arrangement including submersible vehicle docking arrangement and garage - Google Patents

Abstract

The docking arrangement 134 (Fig. 5) carried by a submersible 8 enables docking with a spaced pair of guide posts 71, 72 of a subsea structure. A pair 24 of outwardly acting bracing jaws 17', 20 and a pair 25 of inwardly acting clasping jaws 16, 19' are all hydraulically reciprocable so as to releasably engage and clamp the pair of structure posts. The four spaced jaw contact points help absorb linear and rotational reaction forces between the submersible and the structure and use of posts which exist on a majority of structures for installation purposes permits a variety of docking positions without special docking points. The docked vehicle may be accurately manoeuvred along the posts, by means of further hydraulics 26 altering displacement between the jaw pairs when one pair at a time is unclamped, and manoeuvred transversley to the posts by unclamping the individual jaws of each pair acting on the posts in the direction of desired movement. The working arrangement includes also a transit garage (Figs. 1 and 7 not shown) having similar posts for containing the submersible docked with the posts, and the garage may include a storage area accessed between posts to which a submersible can dock. <IMAGE>

Description

SUBSEA WORKING ARRANGEMENT INCLUDING SUBMERSIBLE VEHICLE DOCKING ARRANGEMENT AND GARAGE This invention relates to subsea working with submersible vehicles and in particular to docking such vehicles with respect to sub sea structures to facilitate working thereon by the vehicle.

Submersible vehicles are frequently employed to perform inspection, maintenance and repair tasks on subsea structures, such as well-head trees, which may be at depths or in other conditions which preclude attention by divers. Such vehicles may be manned or remotely piloted, the latter being fitted with television cameras by which a view of the work scene is provided for an operator on a surface vessel, and have a tool manipulating arm or hand controlled, usually hydraulically, by the pilot.

Amongst the problems encountered with the use of such a vehicle are the acquisition of, and maintenance of, a working position with respect to a workpiece due to the effects on the vehicle of sea currents and to changes in buoyancy and reaction forces between the vehicle and the workpiece.

Maintenance of alignment between the vehicle and workpiece is often maintained by attaching the vehicle to the workpiece by some docking mechanism and to ensure that relatively large reaction forces which may be encountered when loads are transferred to and from the vehicle or when the vehicle drives a tool against the workpiece do not damage the equipment such mechanisms have usually employed specially fabricated locating and docking points at each major worksite on the equipment to absorb the forces.

Where such equipment is as complex as a tree the number of docking points required to reach all potential worksites may be large, with consequentially expensive modification to the tree, whilst providing little positional flexibility to the vehicle in effecting docking or after docking, and doing little to alleviate the difficulties of remotely piloting such a vehicle, which may be carrying awkward or heavy loads or tools to the docking points.

As an alternative to the provision of expensively and accurately disposed docking points it is known for simple workpiece structures to use suction devices or hydraulic grabbers to fix the position of one point of the vehicle with respect to the workpiece and 'piloting' it until its orientation in the water is observed to be the desired positional relationship with respect to the workpiece. Hydraulic grabbers can present a high risk of damage to the workpiece whilst offering little or no help with alignment whilst suction devices, a traditional mechanism for docking submersible vehicles to surfaces, are not suited to workpieces like valve trees where most available surfaces have a high degree of curvature and also have weight penalties associated with water pumps to maintain adequate gripping force.

Positioning of a submersible vehicle in relation to a workpiece is further complicated by the need to provide control signals and services from the surface vessel to the vehicle by way of an umbilical, the length of which for operation at depth may be of such a weight and provide such a drag as to seriously impede movement and manoeuvring of the vehicle.

To avoid time wastage by returning the vehicle to the surface vessel each time a new tool or load is required it is known to lower a store of such tools and loads with the vehicle and between which and the workpiece it commutes. It is also known to provide as part of the underwater working arrangement a cage or garage for the vehicle in which it can be contained for transit to or from the surface and to which it can be connected by a relatively short and light duty tether umbilical, facilitating manoeuvrability of the submerged vehicle whilst decoupled from a long heavy duty umbilical and lifting cable by which the garage is connected to the surface vessel.

Although provision of such a garage for the submersible vehicle mitigates certain problems it introduces others relating to locating the vehicle safely in the garage whilst it is in transit.

It has been proposed to hold a submersible in such a garage while being raised or lowered by gripping the vehicle by hydraulically actuated plates, pressurised cushions or bars acting against the top or sides of the vehicle or by tensioning or otherwise fastening the tether umbilical.

It is believed, however, that such proposals risk damage to the vehicle from pressure applied to it by such plates, cushions or bars as does restraining by the tether umbilical risk damage to that or the vehicle. Furthermore such arrangements are heavily dependent upon the dimensions of the vehicle and any attachment to the basic vehicle, such as a sled by which tools or loads are carried, may be precluded from change or require extensive modifications to the garaging system.

It is an object of the present invention to provide a subsea docking arrangement for a submersible vehicle which, by utilising virtually universal constructional features of subsea structures, mitigates the disadvantages of known submersible vehicle docking arrangements and a further object to provide a subsea working arrangement including a subsea vehicle with such a docking arrangement and a garage for it which mitigates disadvantages or known garage arrangements in subsea working arrangements.

According to a first aspect of the present invention a sub sea docking arrangement for releasably attaching a submersible vehicle to a subsea structure having a pair of substantially coplanar and parallel posts comprises, carried by the vehicle, two pairs of retractable jaws, each pair disposed when the vehicle is in a docking relationship with the structure to enclose a respective one of the posts and define a post pair of jaws, and control means responsive to control signals to reversibly exert forces on at least a corresponding one of the jaws of each post pair to move the jaws of each pair together to effect a grip on the associated post.

According to a second aspect of the present invention a subsea working arrangement, to facilitate work on a subsea structure having a pair of substantially coplanar and parallel posts by a submissible vehicle, comprises a subsea docking arrangement as defined in the preceding paragraph and a subsea garage structure, into whi,ch the vehicle can manoeuvre, constructed with at least one pair of substantially parallel posts, separated by a distance within the operating range of the docking arrangement jaws and arranged as a docking point for a vehicle. contained within the garage.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a subsea working arrangement including component parts thereof according to the present invention in relation to a subsea structure and illustrating their interrelationships, particularly a remotely operated submersible vehicle (ROV) carrying a docking arrangement and a garage for the vehicle, Figure 2 is a schematic perspective view of the ROV of Figure 1 carrying a first and basic form of docking arrangement according to the invention by means of a tool sled attached to the ROV and disposed in docking relationship with structural posts of the subsea structure, Figure 3 is a perspective view similar to Figure 2 showing an alternative form of docking arrangement, Figure 4 is a perspective view similar to Figure 2 showing yet another form of docking arrangement, Figure 5 is a perspective view of an ROV similarly disposed to that of Figure 2 and carrying a further and preferred form of docking arrangement permitting controlled movement of the docked ROV along and transversely to the structure posts to which it is docked, Figure 6 is a schematic diagram of the hydraulic.

circuit and transducers of the docking arrangement control means, Figure 7 illustrates the ROV of Figure. 5 disposed within, and docked with, the garage of Figure 1, and Figure 8 illustrates the ROV of Figure 1 docked externally of the garage with a tool storage section.

Referring to Figure 1 a subsea structure 1 comprises a satellite well comprising a pre-fabricated well-head tree 2 contained within a protective housing structure 3 lowered into position onto a prepared base, structure 4 on the sea bed 5 to cap the well and feed well products into flow line 6 connected to a central collection point. The base structure 4, in accordance with usual practice, is formed with upstanding corner posts (not shown) and the prefabricated tree housing structure is provided with a framework comprising correspondingly disposed hollow guide posts 7 which locate over the base corner posts upon lowering of the structure onto its base.

The e guide posts and framework are of substantial construction to protect the tree during installation or removal and to offer some protection from collision damage when in situ.

The dimensions and disposition of such guide posts are fixed by convention, normally being located at an industry standard 6 feet (1.829 metres) radius from the well head centre and running vertically for the full height of the tree. For a square structure this results in an industry standard spacing between adjacent posts of 8.5 feet (2.69 metres). Although no special precautions are taken to work to high tolerances in positioning the posts in structure manufacture their disposition for guiding the structure onto the carrier posts of the prepared bed results in them being substantially parallel and, therefore, for any pair of posts, substantially coplanar.

It will be seen from the Figure that a typical sub sea structure such as a well 1 has, when approached from any of the four sides, four pairs of substantially coplanar or parallel posts which are not part of the delicate well-head tree structure and which have the strength to be used in docking a submersible vehicle and in accordance with the present invention use is made of such posts in pairs.

A submersible vehicle 8 is remotely operated from a surface vessel 9, the remotely operated vehicle (ROV). 8 receiving control signals and electrical power by way of a light duty tether umbilical from a garage structure 10 and a heavy duty umbilical and lifting cable 11 between the garage and the surface vessel. The ROV includes an electrically driven compressor of hydraulic fluid to provide such fluid at one or more pressures for control and effecting movement of various movable devices such as arms pr grips or the like for carrying and positioning parts of workpieces or tools and for operating and applying forces to such tools.There are usually two pressure levels defined for submersible vehicles giving a so-called primary or high pressure circuit at approximately 3000 pounds per square inch ( 200 bar) and a so called secondary or moderate pressure circuit at about 1000 pounds per square inch ( 70 bar). The ROV also includes television camera means (not shown) by which the surface operator can observe the position of the ROV with respect to any underwater structure and the progress of work undertaken by said movable devices and any tools they carry. A tool sled 12 attached to the ROV enables tools or replacement parts to be transferred between the well head structure 1 and a store in, or near, the garage.

The subsea working arrangement thus far described, insofar as the structure of the garage is not defined, is known per se and forms the starting point of the present invention.

In accordance with the present invention the ROV, or more particularly the tool sled 12 attached thereto, carries a docking arrangement 13 shown more clearly in Figures 2 to 5 which illustrate various embodiments thereof with the ROV 8 in docking disposition with respect to a pair of the posts 71 72 of the structure 1.

Referring firstly to Figure 2, a basic and first form of docking arrangement 131 comprises two pairs 14, 15 of retractable jaws. The pair 14 comprises jaws 16 and 17 which are disposed with respect to the sled 12 and ROV 8 so as to enclose one of the vertically extending posts 7 of the subsea structure. The jaw 17 is fixed with respect to the sled but the jaw 16 is reciprocable by fluid operated piston and cylinder arrangement 18 in a direction orthogonally to the longitudinal axis of the post 71 to effect separation, or retraction, and closure of the jaw pair.

Control means, described more fully hereinafter, includes the piston and cylinder arrangement 18 and valve means indicated generally at 27 to govern supply of the fluid pressure generated within the ROV and is responsive to control signals from the surface vessel to ,exert, by fluid pressure in the cylinder, a force on the jaw 16 closing it with respect to the jaw 17 and exerting a gripping or clamping force onto the post 71 between them. Preferably the control means operates with hydraulic fluid at two pressure levels, utilising the aforementioned existing standard high and moderate pressure levels available in the ROV, the moderate pressure being used to move the jaw into engagement with the post and retracting it therefrom and the higher pressure being used to exert the clamping force.Removal of the high pressure releases the clamping force, reversal of the fluid pressure retracts the jaw 16 and permits the ROV and docking arrangement to leave the post and maintenance of enagement pressure only permits the vehicle to manoeuvre relative to (along) the post without drifting away from it. The pair 14 of jaws 16 and 17 associated with the one post 71 may conveniently be called a post pair of jaws as may be the corresponding pair 15 associated with the other post The The post pair 15 comprises a fixed jaw 19, spaced from the fixed jaw 17 by a distance equal to the industry standard separation between posts for a particular type of structure with which it is to dock, and a retractable jaw 20 reciprocable by a piston and cylinder arrangement 21 forming part of the control means.

The retractability of the jaws is sufficient for the ROV to be manoeuvred into an approximate docking disposition with respect to the subsea structure with the posts 71 and 72 located between the retracted jaws which are ' thereafter closed by the control means until first engaging, and then clamped to the posts. The ROV is thereby held stationary with respect to the subsea structure to a part of the structure which is not susceptible to damage and furthermore any reaction forces or torques generated by operations performed on the subsea structure by normal working operations by the ROV are readily and safely absorbed into the structure by way of the posts.

Also any change in buoyancy of the ROV caused by transferring a weighty body to or from the structure does not result in a position change of the vehicle with respect to the structure, any displacement forces being absorbed into the structure through the docking arrangement until the ROV buoyancy is trimmed to accommodate the change or until the clamping force of docking is released.

As indicated hereinbefore one of the difficulties in working with a ROV is the accurate positioning of the vehicle with respect to a workpiece and which fixed docking points fail to solve for all but a limited number of positions. It will be appreciated that with the ROV 8 docked by means of the arrangement 131 with respect to the posts 71 and 72 the grip between the jaws and the posts may be relaxed into mere engagement with the posts and permit sliding movement of the ROV along the posts to assume a desired position with respect to the subsea structure.

Such position adjustment as is available from the arrangement of Figure 2 is in one direction only, that is, along the longitudinal axes of the posts 71 and 72 and the accuracy with which any position can be assumed is dependent upon the degree of control over vehicle motion (by whatever propulsion means it employs) and/or the ability to re-clamp the jaws quickly when the desired position is reached. A commonly desired small change in position or slow continuous movement, that is, 'inching' of ROV, is difficult to achieve.

It will also be appreciated that the ability of the docking arrangement 131 to engage both posts of any structure and apply clamping pressures uniformly to them is, with one fixed jaw to each pair, dependent upon the accuracy with which the posts in the structure are separated in relation to the nominal industry standard separation and, inherent within this, their parallelism, and may be considered as placing undue reliance upon the accuracy which has hitherto required no tighter tolerances than to permit the posts to guide and locate the structure on its prepared bed.

However if such equivalence of separation between posts and fixed jaws is assured the docking arrangement 131 may be used to effect.

The arrangement 131 does show the basic principles of the invention and also demonstrates a useful construction option in that the cylinder 18 which provides for linear reciprocation and clamping of jaw 16 may also conveniently be mounted inboard of the jaw as shown by dotted lines at 18'.

Referring now to Figure 3 this shows a modified form 132 of the docking arrangement 131 of Figure 2, the difference being that in each of the post pairs of jaws, both jaws are reciprocable with respect to the sled and ROV to effect opening and closing of the jaws. Considering post pair 14', corresponding to the pair 14 of Figure 2, one jaw 16 (as in Figure 2) is reciprocated by piston and cylinder arrangement 18' and the other jaw 17' is reciprocated along the same directional axis by piston and cylinder arrangement 22. Post pair 15', has one jaw 20 (as in Figure 2) reciprocated by piston and cylinder arrangement 21 and other jaw 19' reciprocated along the same directional axis by piston and cylinder arrangement 23.

The jaws are thus able to accommodate variations in the separation of structure posts from the nominal provided that such jaws when separated can dispose themselves around the respective posts. All of the jaws are individually movable with respect to the ROV and transversely to the longitudinal axes of posts 71 and 72 to close into engagement with the posts by moderate hydraulic ]ressure and by increased pressure are caused to exert uniform clamping forces into the posts.

Furthermore, the control means can, by simultaneously energising each of the piston and cylinder arrangements appropriately, cause all of the jaws to be moved in the same direction with respect to the vehicle without retracting from engagement with the posts and thereby move the docked vehicle transversely to the longitudinal axes of the posts 71 and 72 along the reciprocation axis of the jaws. To move the vehicle to the right of the Figure, for example, the control means may operate by relaxing the clamping force on jaws 16 and 20 acting in the direction of desired movement to the lower engagement pressure while maintaining clamping pressure on jaws 17' and 19', the difference in forces exerted by each jaw of each pair drawing the ROV to the right of the Figure.

It will be appreciated that the positional control exertable over the piston and cylinder arrangements may be made very precise whereby after the vehicle has docked by clamping the jaws to the posts its position or motion transversely to the post axes may be considered separately from and subsequent to the initial docking, thereby alleviating strain on the operator in the performance of these tasks. The ROV can still, of course, be piloted along the axes of the posts by unclamping both post pairs of jaws to their engagement states.

Figure 4 shows a further alternative in which the further modified docking arrangement shown generally at 133 has similarities to that 132 shown in Figure 3 (with parts numbered similarly) having two retractable jaws to each post pair. The arrangement differs in that the jaws of each post pair are displaced with respect to each other along the longitudinal axis of the associated post when in a docking disposition, oppositely acting jaws of the two pairs being displaced in like directions with respect to the other jaws of the pairs so as to counter rotational reaction torques between the vehicle and structure when the displaced jaws are clamped to the posts. That is, the jaws 17' and 20, each of which acts outwardly against an inward, or proximate, face of the respective post are displaced from the jaws 16 and 19' which act inwardly against outward, or distal faces, of the respective posts.

Preferably, but not essentially, the displacements for each post pair are equal in magnitude so as to cancel out completely any such rotational torque due to the displacement of the jaws of either post pair.

In the arrangement 133 of Fig. 4 the reciprocable jaws 17' and 19', may be replaced by the jaws 17 and 19 of the arrangement 131 (Figure 2) and be fixed with respect to the ROV and sled although the difficulties of post separation accuracy discussed with respect to that embodiment have to be considered.

With the jaws of each post pair 14' (14) and 15' (15) displaced as shown in Figure, 4 it becomes more convenient to consider the oppositely acting jaws at each displaced axial position as a functional pair and to couple them thus in the control means.

The jaws 17' (17) and 20 which are operationally disposed between the posts 71 and 72 and act against inward, or proximate, faces thereof in a direction to force the posts apart are considered as a bracing pair 24 whereas the jaws 16 and 19' (19) which act on the distal, or outward, faces of the posts in a direction to draw the posts together are considered as a clasping pair 25.

The docking arrangement 133 may still be operated as arrangement 132 to displace the docked vehicle transversely to the axes of the structure posts by removing clamping pressure from correspondingly directed jaws of the clasping and bracing pair, say 18' and 20 to move the vehicle to the right of the Figure.

The vehicle may also be moved along the posts by unclamping all of the jaws, that is, removing clamping pressure but retaining post engagement, and piloting the vehicle along the post axes and with respect to which it is guided by the sliding engagement between jaws and posts.

Displacement of the jaws in this direction along the axes of the posts reduces any tendency for such sliding motion along the posts to suffer binding due to slight rotation of the vehicle as might happen with the arrangements 131 and 132.

Referring now to Figure 5, this shows at 134 a further modification to the docking arrangement 133 of Figure 4 wherein one, shown as the clasping, pair of jaws is operationally displaceable with respect to the other, bracing, pair in a direction transversely to the direction of clamping movement of 'the jaws to permit accurate displacement or repositioning of the docked vehicle along the posts by the control means. To effect such displacement the control means includes further piston and cylinder arrangements 26 operated in the same manner as those which move the jaws.The control means, by valve means contained at 27 and to be described hereinafter, couples the pistgn and cylinder arrangement to the source of high hydraulic pressure and enables a docked vehicle to be moved with respect to the structure posts along their longitudinal axes in a sequence of operations. The sequence, involving control of the jaws, comprises unclamping one of the jaw pairs, say the clasping pair 25, to a post engaging disposition and holding the vehicle docked with the structure by means of bracing pair of jaws 24 only, followed by extending or retracting the piston and'cylinder arrangements 26 to effect a change in displacement between the clasping and bracing pairs of jaws and then re-clamping the clasping pair of jaws are re-clamped onto the posts and full docking contact restored.

The previously undisturbed bracing pair of jaws are then unclamped to a post-engaging disposition, whereby the vehicle is held docked with the structure by means of the clasping pair of jaws only, the previous extension or retraction of the piston and cylinder arrangements 26 is then reversed, either fully or partially, which moves the ROV a precisely controllable distance along the axes of the posts 71 or 72 and finally, the bracing pair of jaws is re-clamped to the posts and the ROV docked in a precisely defined position with respect to the structure.

Clearly the motion may also be effected by firstly unclamping the bracing pair and displacing them and the ROV with respect to the clasping pair and structure before unclamping the clamping pair and restoring, or partially restoring, the displacement from the bracing pair. A movement of the vehicle with respect to the structure which is within the extension range of piston and cylinder arrangements 26 may be effected by just the unclamping of the bracing pair and movement of the vehicle without unclamping and repositioning of the clasping pair of jaws.

It will be appreciated also that the bracing pair of jaws may just as readily be made displacable with respect to the sled instead of, or in addition to, the clasping pair.

The displaceable jaw pair may be provided with a datum position at one extreme of ,the movement of the piston and cylinder at which it locates mechanically with respect to the sled framework to prevent significant lateral operational forces being transmitted by the cylinders 26. In such a case the sequence of movements for moving the ROV along the posts should always end with restoration of the clasping jaws to the datum displacement position.

The docking arrangement 134 is of course able to perform postdocking movement transversely to the post axes in the same manner as the arrangement 133 for all displacements of the jaw pairs.

The docking arrangement according to the present invention may thus have several embodiments as described, including those which permit assumption of accurately and infinitely variable docked positions with respect to the structure by displacing the vehicle with respect to the structure clamping jaws of the docking arrangement by the forces of the control means. Furthermore, in the case of positioning transversely to the longitudinal axes of the posts the control means may, if desired, be constructed to define positional relationship between the ROV and structure with initial docking by disposing the retracted jaws assymetrically with respect to the ROV.

The control means comprises in addition to the piston and cylinder arrangements shown in Figures 2 to 5 other hydraulic circuit elements such as control valves generally housed at 27. These hydraulic elements include a plurality of electrically operated solenoid valves responsive to command control signals from the surface operator to connect the cylinders to a source or sources of pressurised fluid developed in the ROV or to vent them as appropriate in different configurations to enable a particular jaw function to be performed.

Figure 6 is an electrohydraulic circuit diagram of the control means as carried by the ROV at 27 and distributed as the piston and cylinder arrangements already described.

A high pressure (say 200 bar) hydraulic supply line 28, conveniently connected to the, high pressure vehicle supply and generated within the vehicle in known manner for use thereby, and a return line 29 are connected to a pressure reducing valve 30 between them to feed a moderate pressure (say 70 bar) supply line 31. Alternatively the supply line 31 may be connected to a secondary or auxilliary supply 'line existing in the ROV at similar moderate pressure. The terms 'high' and 'moderate' are used within the context of hydraulic pressures normally available within submersible vehicles wherein a pressure of the order of 200 bars is considered high and of the order of 70 bars considered moderate. Conventional electrically energised solenoid valves S1-S7 are connected between the supply lines 28 and 31 and the cylinders already described.The circuit also includes flow dividers D1-D3.

The solenoid valves S1 to S7 are 3-position 4-port valves in which supply and function ports are blocked or dead-ended (as shown), connected straight through, or crossed over, depending upon the energisation of the solenoid by the control signal. For convenience the valves assume the shown dead-ended position when the solenoid is unenergised. Valve S1 has a supply port connected to the high pressure supply line 28, a return port to return line 29 and two function ports connected to the cylinder means 26. Valves S2 and S3 each have a supply port connected to the moderate pressure supply line 31 and return ports connected to return line 29. The two function ports of valve S2 are connected respectively to a supply/return port of each of solenoid valves S4 and S5 and to flow divider D2.Similarly, the two function ports of valve S3 are connected respectively to a supply/rettn port of each of solenoid valves S6 and S7 and to flow divider D3. The solenoid valves S4 to S7 are shown as similar 4-port devices although only one function port is used in each, these being connected to the cylinders 18', 23, 24 and 21 respectively which operate the jaws and to individual pressure accumulators A4 to A7. The other supply ports of each of the valves S4 to S7 are connected to the high pressure supply line 28. The flow dividers D2 and D3 respectively provide equal fluid flow to the cylinder pair 18' and 23 o,f the clasping pair of jaws and to the cylinder pair 21 and 24 of the bracing pair of jaws.

The piston and cylinder arrangements 26 are operable as a pair by the solenoid valve S1 which operates to displace the clasping pair of jaws in relation to the bracing pair, by raising them or lowering them, or to lock them in position at any displacement and the solenoid valve S1 may be considered as the 'displacement' valve. Solenoid valves S2 and S3 control extension and retraction of the jaw pairs to and from engagement positions with the posts and may be considered as 'engagement' valves whereas valves S4 to S7 control clamping of the jaws to the posts and may be considered as 'clamping' valves.

To summarise the control operations outlined above, with clamping solenoid valves S4 to S7 energised to a straight-through position (to the left in the Figure) corresponding energisation of solenoid valve S2 moves the retracted or open clasping pair of jaws 25 into non-clamping engagement with the posts 71 and 72 under the moderate fluid pressure in line 31, and solenoid valve S3 similarly positions the bracing pair of jaws 24.

When the jaws are disposed in their post-engaging positions the clamping solenoid valves S4-S7 are energised to the cross-over position (to the right in the Figure) to connect the high pressure supply line 28 directly to the cylinders to increase the pressure on the individual jaws and effect positive clamping between the jaws and the structure posts. The accumulators A to A7 are also charged to the supply line high pressure. The solenoid valves S2 and S3 are returned to a dead-head or isolating position (as shown in the Figure) to isolate the flow dividers D2 and D3 from the return line 29 and thereafter, solenoid valves S4 to S7 are de-energised to isolate the cylinders from the supply line and lock the jaws in position under pressure maintained by the accumulators.Such isolation of the cylinders of each jaw pair prevents any transverse creeping of the vehicle due to unequal forces exerted within the cylinders of the pair as a result of dimensional or other differences.

Movement of the docked vehicle transversely to the post axes may of course be effected intentionally by operating the jaws of pairs 24 and 25 independently. With the solenoid valves S2 and S3 energised to the straight through position as aforesaid and valves S4 to S7 energised to the cross over position to maintain jaw clamping pressure, energisation of solenoid valves S4 and S7 to the straight through position reduces the high pressure clamping forces exerted to the right (of the Figure) by jaws 16 and 20 to the moderate pressure positioning forces provided by positioning solenoid valves S2 and S3 whereas the high pressure clamping forces exerted to the left by jaws 19' and 17' are undiminished and the docking arrangement and ROV traverses to the right with respect to the posts 71 and 72.The clamping solenoid valves S4 and S7 may be energised to the cross-over configuration at any time to halt the movement.

Corresponding changes to the configurations of clamping solenoid valves S5 and S6 causes the docking arrangement to move transversely to the posts in the opposite direction, that is, to the left of the Figure.

To move along the post from a docked position, for example in the sequence described hereinbefore, the control means establishes clamping pressures through each of the solenoid valves S4 to S7 in their cross-over configurations.

The clamping solenoid valves S4 and S5 are energised to the straight-through configuration like the positioning solenoid valve S2 to maintain the post-engaging disposition of the clasping jaws. The displacement solenoid valve S1 is operated to supply fluid to cylinder 26 and displace the jaw pair 25 with respect to jaw pair 24 before restoring the fluid lock to hold the new displacement.

The clamping solenoid valves S4 and S5 are then re-configured to restore high pressure clamping on the posts.

Next, the clamping solenoid valves S6 and S7 are re-configured to unclamp the bracing pair of jaws whilst their positional engagement with the posts is maintained by positioning solenoid valve S3. The displacement solenoid valve S1 is then operated in the opposite sense causing the displacement between the clasping pair and bracing pair of jaws to be restored to, or towards, its initial value, thereby moving the ROV along the posts to which the clasping pair of jaws are clamped. When the ROV is correctly positioned with respect to the structure the displacement solenoid valve S1 is returned to its dead-head fluid-lock state and clamping solenoid valves S6 and S7 re-configured to clamp the bracing pair of jaws to the posts and restore the full clamping of the docked vehicle.The solenoid valves S2 to S7 may then be de-energised and returned to the dead-head position.

To undock the vehicle the clamping solenoid valves S4 to S7 are energised to the straight-throught configuration and the positioning solenoid valves energised into the third cross-over position (to the right of the Figure) to force the jaws apart by the moderate pressure.

Other configurations of control means, valves and interconnections may be devised to produce the described or other modes of jaw operation and displacement.

The docking arrangement of the present invention is operable to dock with a structure having posts which are substantially coplanar and parallel.

The arrangements in all of the embodiments may cope with posts which are not strictly coplanar by forming the jaws 16-20, shown with recessed faces each conforming to a post section to contain and extend partly around the periphery thereof, with essentially planar or shallowly concave faces extending forward of the sled 18 to make tangential contact with the disparate contact points on non-coplanar posts at different distances from the sled.

The extent to which the posts may depart from parallelism, that is, converge or diverge, or both, along the length of the structure without inhibiting operation is dependent upon the embodiment of docking arrangement.

Thus as any departure from parallelism is accompanied by a change in the separation, of the posts, the embodiment 131 of Figure 2 and any other incorporating fixed jaws requires a high degree of parallelism if the docking is to be effected at any point along the posts.

The embodiments 132 to 134, wherein all jaws are movable to tolerate variations in post separation from structure to structure, also permit such variations within a single structure due to variations from parallel of the posts.

Docking is unaffected by different separations between jaws, which is accommodated by the equalisation of the engagement forces before final clamping forces are exerted, and in movement of the vehicle along the posts, changes to the engagement forces on moving jaws by the converging or diverging posts acting as cams on the sliding jaws are overcome or redistributed within the hydraulic system.

The degree of convergence between posts must however be limited so as to obviate the possibility of a reverse cam action where the effective engagement or clamping forces act through each of the displaced jaw pairs of 133 and 134.

Where the posts converge from one end of the structure to the other there is no problem as any component of clamping force acting along the posts is oppositely directed for clasping and bracing pair and effectively neutralised. However, if the posts are bowed to the extent that one pair of jaws acts on locally converging posts whereas the other jaw acts on locally diverging posts then all along-post componets of clamping force act in the same direction and the vehicle is prevented from moving itself along the posts only by the friction between the clamped jaws and the posts.

In the arrangement 135, wherein to move the vehicle along the posts the arrangement is at times docked by means of one pair of jaws only, then local. convergence between the posts at the points of engagement by either pair of jaws may also, if the along-post component of clamping force exceeds friction, cause additional movement of the ostensibly docked jaw pair.

Clearly the extent to which such departure from parallelism is tolerable is a function of the frictional engagement between any particular jaw and post and is seen as a purely practical limitation to be taken into consideration in setting constructional design details.

In accordance with the present invention the subsea working arrangement of Figure 1 comprises not only the docking arrangement 13 described in detail above in individual embodiments 131 to 134 but also a garage 10 constructed in conjunction with the operation of the docking arrangement carried by the vehicle whereby that docking arrangement is employed to retain the vehicle within the garage for raising or lowering by 'docking' the vehicle to the structure of the garage.

Referring to Figure 7 the garage 10 is shown in greater detail and comprise an open structure having at least one pair of vertically extending parallel posts 351 352 spaced, with the substantially same universal spacing as, and preferably dimensioned as, those posts 7 of the subsea well-head tree structure.

The pair of structural posts 351' 352 may be separated from other structural members, conveniently similar posts, by greater than the dimensions of the ROV with the tool sled and docking mechanism attached, to permit it to enter the garage and engage the posts 351 and 352 in a docking operation, or the ROV and tool sled may be made narrower than the spacing between the post pair 351 and 352 and the range of linear movement of the jaws made sufficient for them to be drawn towards the vehicle to permit its passage between the posts before extending them for docking.

Additionally, or alternatively, provided all jaws are movable the range of rectilinear movement of the jaws may be made sufficient to facilitate docking with posts which are of different separation to those of any other subsea structure with which the vehicle docks.

The above described docking arrangement concerns the attachment of the vehicle to any subsea structure having appropriately spaced posts and upon which the vehicle performs some work. It will be appreciated that the structure is not limited to some fixed and, complex structure such as the well-head 1 but may be a simple container adapted to be lowered from and raised to the surface, such as the garage 10, or a carrier of tools or supplies which are to be transferred to or from the vehicle or tool sled.

The advantages for docking the vehicle with respect to such a structure to effect such transfer are readily appreciated upon consideration of the accurate positioning of the vehicle with respect to the structure provided by the docking arrangement as well as providing an opportunity to trim the buoyancy and stability of the vehicle as a result of the transfer of loads while the vehicle is firmly and strongly held in position by the structure.

Instead of providing a subsea structure which is solely such a tool and/or supplies store the garage 10 may be dimensioned to include a storage volume 36 thereof to fulfil such a function of carrying tools and/or supply loads for use on a structure by the vehicle. The access to the storage volume 36, shown in Figures 7 and 8 is by way of a pair of parallel support posts, 353, 354 to which the vehicle working outside the structure can dock. The docking posts of the garage structure or additional posts, such as 355 may be provided intermediate the vehicle parking and storage regions with which the vehicle can dock and transfer material between the sled and the storage region or indeed be transported to or from a work site in the garage while carrying a load whose dimensions includes both the tool sled and storage region.

Although the submersible vehicle 10 has been described in the form of a remotely operated vehicle and one which depends upon a garage as a point to tether a light duty umbilical, it will be appreciated that such a vehicle may be supplied with electrical and, if desired, hydraulic power by other means, making it independent of such a garage, and/or may be manned, the facilities for making small and accurate positioning movements with respect to any structure after docking therewith being equally valuable as for an ROV.

Further, the docking arrangement as described above is advantageously constructed on, a tool sled arrangement 12, the most common reason for docking to a structure being to transfer loads between sled and structure or tools between sled and ROV for working on the structure. The docking arrangement is thereby implemented by modification of the essentially simple structure of the sled rather than the complex vehicle and, by making the sled detachable from the vehicle, the vehicle is able to function fully in any other role not requiring docking without hinderance by an unused docking arrangement and be employed with a variety of different sled designs (with or without docking arrangements) depending upon the type of work to be undertaken. However, the docking arrangement could of course be built for direct attachment, either permanent or temporary, to the vehicle rather than a removable sled 12.

Whereas the docking arrangement described hereinbefore has been shown as comprising hydraulic control means for operating the jaws and applying clamping forces therethrough it will be appreciated that other common control media may be used, such as electrical power effecting jaw movement and clamping forces by electrical motors or other actuators.

Claims (17)

Claims:

1. A subsea docking arra,ngement for releasably attaching a submersible vehicle to a sub sea structure having a pair of substantially coplanar and parallel posts, the arrangement carried by the vehicle comprising two pairs of retractable jaws, each pair disposed when the vehicle is in a docking relationship with the structure to enclose a respective one of the posts and define a post pair of jaws, and control means responsive to control signals to reversibly exert forces on at least a corresponding one of the jaws of each post pair to move the jaws of each pair together to effect a grip on the associated post.

2. A subsea docking arrangement as claimed in claim 1 in which all of the-jaws are individually reciprocable with respect to the vehicle and transversely to the post axes in the docking relationship to effect engagement with, and clamping against, the posts and the control means is operable to move the vehicle, docked to a subsea structure, transversely to the axes of the posts thereof by causing each of the clamped jaws to move with respect to the vehicle simultaneously and in the same direction.

3. A subsea docking arrangement as claimed in claim 2 in which the control means is operable to reduce clamping against the posts by the. jaws acting in the direction of desired vehicle movement whilst retaining clamping by the jaws acting against direction of desired vehicle movement, displacement of said clamping jaws with respect to the vehicle causing displacement of the vehicle with respect to the structure.

4. A sub sea docking arrangement as claimed in claim 3 in which the jaws acting in the direction of desired vehicle movement are maintained in non-clamping engagement with the posts by the control means.

5. A subsea docking arrangement as claimed in any one of claims 1 to 4 in which the jaws of each post pair are displaced with respect to each other along the longitudinal axis of the associated post, oppositely acting jaws of the two pairs being displaced in like directions with respect to the other jaws of the pairs so as to counter rotational reaction torques between the vehicle and subsea structure.

6. A subsea docking arrangement as claimed in claim 5 in which the displacements betweqn the jaws of each pair along the longitudinal axes of the associated posts are substantially equal in magnitude.

7. A subsea docking arrangement as claimed in claim 5 or claim 6 in which the control means is operable to vary the magnitude of displacement aldng the post axis between the jaws of each post pair.

8. A subsea docking arrangement as claimed in any one of claims 5 to 7 in which the relatively displaced jaws of each post pair are coupled by the control means, for positioning in relation to the posts, to the relatively displaced jaws of the other post pair at each position along the posts axes, defining by such coupling a bracing pair of jaws disposed between the posts and operable to act against the proximate faces of the posts in a direction to force the posts apart and a clasping pair of jaws operable to act on the distal faces of the posts in a direction to draw the posts together.

9. A subsea docking arrangement as claimed in claim 8 when dependent on claim 7 in which the control means is operable to move a docked vehicle with respect to the structure posts thereof along their longitudinal axes, being arranged to sequentially unclamp one of the clasping or bracing jaw pairs, effect a change in displacement along the post axes between the jaw pairs, re-clamp said one released jaw pair on the posts, unclamp the other jaw pair, restore at least part of the displacement along the post axes between the jaw pairs and re-clamp said other jaw pair on the posts.

10. A subsea docking arrangement as claimed in any one of the preceding claims in which the control means includes transducer means for each jaw movable with respect to the vehicle comprising a rectilinear piston and cylinder arrangement responsive to the pressure of fluid within the cylinder to effect reciprocation in a rectilinear sense with respect to the vehicle.

11. A subsea docking arrangement as claimed in claim 10 in which the control means comprises sources of moderate and high hydraulic pressure, positioning valve means operabe to connect the source of moderate hydra,ulic pressure to the piston and cylinder arrangements to position the jaws with respect to the posts into and out of engagement therewith and clamping valve means operable with the jaws positioned in engagement with the posts to connect the source of high hydraulic pressure to the cylinder arrangements to clamp the jaws against the posts.

12. A sub sea docking arrangement as claimed in any one of the preceding claims in which the jaws and control means are mounted on a sled removably attached to a conventional submersible remotely operated vehicle.

13. A subsea docking arrangement for releasably attaching a submersible vehicle to a subsea structure having a pair of substantially coplanar and parallel posts, the arrangement being substantially as herein described with reference to, and as shown in any one of Figures 2 to 4 or Figures 5 and 6 of the accompanying drawings.

14. A subsea working arrangement to facilitate work on a subsea structure having a pair of substantially coplanar and parallel posts by a submersible vehicle, said arrangement comprising a subsea docking arrangement as claimed in any one of the preceding claims and a subsea garage structure, into which the vehicle can manoeuvre, constructed with at least one pair of substantially parallel posts separated by a distance within the operating range of the docking arrangement jaws and arranged as a docking point for a vehicle contained within the garage.

15. A sub sea working arrangement as claimed in claim 14 in which the garage structure is provided with a load storage region and at least one further pair of posts to facilitate docking of the vehicle to the outside of the garage whilst transferring loads between the vehicle and the storage region.

16. A subsea working arrangement, to facilitate work on a sub sea structure having a pair of substantially coplanar and parallel posts by a submersible vehicle, comprising a subsea docking arrangement and garage structure for the vehicle substantially as herein described with reference to the accompanying drawings.

17. A method of moving a submersible vehicle, including a docking arrangement as claimed in claim 8 docked with a pair of substantially coplanar and parallel posts of a subsea structure, along the longitudinal axes of the posts comprises the steps of unclamping one of the clasping or bracing jaw pairs, effecting a change in displacement along the post axes between the jaw pairs, re-clamping said one released jaw pair on the posts, unclamping the other jaw pair, restoring at least part of the displacement along the post axes between the jaw pairs and re-clamping said other jaw pair on the posts.