WO1984004733A1

WO1984004733A1 - Remotely-operable vehicles for use in the cleaning and inspection of marine contact surfaces

Info

Publication number: WO1984004733A1
Application number: PCT/GB1984/000165
Authority: WO
Inventors: John Cameron Robertson
Original assignee: John Cameron Robertson
Priority date: 1983-05-20
Filing date: 1984-05-16
Publication date: 1984-12-06
Also published as: GB2150512A; DK20485D0; DK20485A; GB8501492D0; NL8420121A; NO850229L

Abstract

An object of the invention is to provide a remotely-operable vehicle (ROV) which is capable of crawling along and adhering to the structure to be inspected and cleaned, both into and through the splash zone up to at least sea state 5, i.e. that state of the open sea corresponding to at least a wind of force 5 on the Beaufort scale. In accordance with the invention, the ROV has a frame (5, 30) adapted to be held fast during motion in relation to said surface by the alternate energization and de-energization of a plurality of electro-magnets (14, 15 - 38, 40), said electro-magnets being arranged such that at least one electro-magnet is movable in relation to at least one other electro-magnet in order to progress said frame in relation to said ferrous contact surface. The plurality of electro-magnets comprises in one embodiment, a series of electro-magnets (15) fixedly mounted on the periphery of the frame (5) and a cluster of electro-magnets (14) central of the frame and movable relative thereto. In another embodiment there are two transversely spaced slidable electro-magnets (38) and one fixed electro-magnet (40) arranged in triangular formation. Actuators (42) can slidably move one or both magnets (38) towards or away from the fixed magnet (40).

Description

REMOTELY-OPERABLE VEHICLES FOR USE IN THE CLEANING AND INSPECTION OF MARINE CONTACT SURFACES

BACKGROUND OF THE INVENTION

This invention relates to remotely-operable vehicles for use in the cleaning and inspection of marine contact surfaces. The invention is applicable to the cleaning and inspecting of offshore oil platforms and drilling rigs and more broadly to the cleaning and inspecting of, inter alia, the bottoms of ships, the interior faces of dams, sea water intake and outlet tunnels for power stations, and the faces of quays and wharfs.

The cleaning and inspection of oil platforms and like offshore structures is done to secure their structural integrity. Five factors may impair and could eventually imperil that integrity, namely bends, dents, corrosion, cracking and contamination. Of these five factors cleaning is directly effective against the fifth only. By removing heavy growth of mussels, etc., the excess weight and drag and the loss of fatigue life thereby resulting is cured. Cleaning is an essential preliminary to the effective detection of corrosion and the resultant thinning and of weld cracking. The detection of bends or dents may require cleaning but may only need the appropriate sensors. The cleaning and inspection of marine contact surfaces has hitherto been effected by divers, or by manned submersibles, or by remotely-operated vehicles, known as ROVs, which are free swimming but are connected to and controlled through an umbilical cable. All three procedures are expensive, and, where personnel are directly involved, the expense increases greatly either in deep water, i.e. in water of depth greater than fifty metres, or in the 'splash zone' i.e. the surface zone or zones of the structure projecting immediately above water level and subject to the vagaries of the body of water from which the structure projects. Elaborate saturation diving techniques are required in deep water, and even moderate sea states produce wave surge which makes a diver's work difficult and the risk of injury considerable in the splash zone. Increasing use has been made in recent times of ROVs for deep water and splash zone work but they also are beset with problems in the splash zone, such as the ever-present difficulty of positioning them accurately and steadily in relation to a fixed point on a structure and gaining access to the inner parts of a platform.

There are known ROV designs which are adapted in operation to adhere to and move along a surface under water. The majority of these are bottom crawlers, i.e. they are adapted to move over the sea bed, but three are structural surface crawlers, with two of these for working on under-water surface areas of ships' hulls and like simple relatively shallow structures, and the third specifically for cleaning the walls and bottom of the machine-cooling sea or lake water intake channels of nuclear or other electric power stations.

The smaller of the two aforementioned hull-crawling ROVs can operate at depths of up to 100 m (328 feet) and comprises a box-shaped body measuring approximately 61 cm x 61 cm x 36 cm (24 in. x 24 in. x 14 in) which is enclosed and supported by a mushroom-shaped fibreglass fairing. Plastics spheres provide surface buoyance, a free-flooding tank is blown free of water by compressed air to provide positive buoyancy to hold the ROV against the outer surface of the hull of the vessel which it is working, and propulsion along the hull surface is through two hydraulically-driven wheels. The larger of the two aforementioned hull-crawling ROVs can operate at depths sufficient to. accommodate the deepest draft ULCCs (Ultra Large Crude Carriers) and comprises a cylindrical platform of diameter 1.8 m and depth 0.5 m (6feet x 1.7 feet) integrated with the outer major surface of which is a fibreglass canopy of the external appearance of a rounded protuberance. The canopy has a styrofoam filling injected thereinto. The platform has a central aperture for an impeller, and is mounted on three traction wheels one of which provides for steering the ROV, power being supplied from a generator to a 15 hp submersible electric motor driving a duplex hydraulic pump one unit of which drives the impeller and the other unit of which powers the wheels and three wire cleaning brushes on the underside of the ROV, the diameter of the swath cleaned by the brushes being slightly less than the canopy diameter.

The instrumentation aboard the two aforementioned hull-crawling ROVs is, of course, dictated by the functions they are designed to undertake, and, in turn, strongly influences the dimensions of the ROVs. The smaller of the two has the task of inspecting the underwater area of ships' hulls, and has aboard two pan/tilt-mounted T.V. cameras, one for close viewing and one for distance viewing, a 35 mm still camera, and a distance-travelled sensing unit. Navigation is by visual location on hull markings, with dead-reckoning by measurement of the X-Y components of distance travelled. An acoustics positioning system may be used, if required. The support ship may be a barge or other small vessel on board of which are a control/display console and a Diesel generator. Operation and maintenance can be performed by one operative. The larger of the two, on the other hand, has the task of cleaning the underwater area of ships' hulls and is connected by a coaxial cable to a control console on the support craft which also carries a Diesel generator. The ROV advances, stops or reverses either by remote control from the console or by a local diver control, and can also be switched to automatic control to maintain a horizontal path on a vertical surface. The control console displays the depth and the attitude of the ROV and the distance travelled thereby. A variety of small surface craft may serve as the support craft. The number of operatives required depends on the scope of an operation to be performed but minimally one is required for console operation, one for coaxial cable tender control, one for diver tender (air support etc.), plus normal complement of crew to operate the surface craft.

The third of the aforementioned known ROV designs, i.e. that specifically for cleaning the walls and bottom of the machine-cooling sea or lake water intake channels of nuclear or other electric power stations, is 1.78 m long x 1.27 m wide x 0.8 m high and is made chiefly of reinforced plastics material and operated by one man through remote control and underwater television. This ROV is operated by hydraulic pressure and moves ahead or sideways, after finishing one section within a diameter of 110 m, the length of its hydraulic hose. The ROV sticks to the surface being cleaned by two reverse water jets from its impellers. The clearing of the walls and bottom of the channel of shellfish, algae and all other sticky obstacles is effected by a large, strong, revolving scouring brush.

Not one of the three known structural surface crawler ROVs specifically referred to above is capable of operating into and through the splash zone. SUMMARY OF THE INVENTION. The object of the present invention is to provide a ROV which is capable of crawling along and adhering to the structure to be inspected and cleaned, both into and through the splash zone up to at least sea state 5.

In accordance with the present invention, a remotely-operable vehicle adapted to crawl on a marine ferrous contact surface and capable of operating into and through the splash zone up to at least sea state 5, comprises a frame adapted to be held fast during motion in relation to said surface by the alternate energization and de-energization of a plurality of electro-magnets, said electro-magnets being arranged such that at least one electro-magnet is movable in relation to at least one other electro-magnet in order to progress said frame in relation to said ferrous contact surface.

In one embodiment, the plurality of electromagnets comprises two bilaterally-symmetrical series of similar electro-magnets which are shielded with magnetic shielding material, the electro-magnets of one said series being located at or adjacent the periphery of said frame and being fixed relative to said frame, and the electro-magnets of the other said series being clustered centrally of said frame and being movable as a cluster relative to said frame in either direction normal to said ferrous contact surface and also both fore and aft and to left and right when de-energized and withdrawn from said ferrous contact surface, whereby, for progression of said frame in relation to said ferrous contact surface, the de-energized electro-magnets of said clustered series are withdrawn as a unit from said ferrous contact surface and displaced on a unit relative to said frame in a desired direction prior to again being moved as a unit into contact with said ferrous contact surface and re-energized, the latter movement of the clustered series is continued with simultaneous withdrawal of said frame and the de-energized electromagnets of said peripheral series from said ferrous contact surface, said frame is moved relative to the clustered unit to restore the latter to its original centralized position relative to said frame, and said frame is moved towards said ferrous contact surface to restore contact with said ferrous contact surface of the electro-magnets of said peripheral series.

In a second embodiment the plurality of electromagnets comprises at least two electro-magnets transverselyspaced on the frame and adapted for sliding movement fore and aft thereof by means of actuators and at least one electro-magnet fixedly mounted on the frame, and longitudinally spaced from the slidable electro-magnets, whereby, for progression of the frame in relation to the ferrous contact surface, one electro-magnet at a time is de-energize to reduce but maintain its holding force on the contact surface and, by operating one or both actuators to both slidable electro-magnets for fore and after motion or one of the slidable electro-magnets for turning motion, the fixed electro-magnet can be drawn towards or pushed away from the slidable electro-magnets by reverse operation of the or each actuator.

Also, in accordance with the present invention, a free-swimming vehicle is adapted for crawling on a marine ferrous contact surface and has a capability of operating into and through the splash zone by the external attachment to the bottom thereof of a frame adapted to be held fast during motion in relation to said surface by the alternate energization and de-energization of a plurality of electromagnets, said electro-magnets being arranged such that at least one electro-magnet in movable in relation to at least one other electro-magnet in order to progress said frame in relation to said ferrous contact surface. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS. Fig. 1 is an isometric view looking on to the underside of a frame of one embodiment of the invention to be attached externally to the bottom of a freeswimming vehicle to adapt same for crawling on a marine ferrous surface; Fig. 2 is a plan view of a frame of a second embodiment,

Fig. 3 is a side elevation of Fig. 2; Fig. 4 is a schematic side elevation showing a freeswimming vehicle with a frame as shown in Fig. 1 or Figs 2 and 3 externally attached to the bottom of the vehicle, the view showing the vehicle at an intermediate stage of location thereof relative to a marine ferrous surface in an attitude to crawl along said surface in an upwards direction; Fig. 5 is another schematic side elevation of the vehicle of Fig. 4, but with the vehicle located in relation to said surface in an attitude to crawl therealong in an upwards direction and

Fig. 6 illustrates a ROV vehicle in use in conjunction with a mother ROV vessel.

DETAILED DESCRIPTION OF THE INVENTION. Referring now to Fig. 1, means for attachment to the underside of a free-swimming remotely-operable vehicle, to adapt the latter for crawling on a marine ferrous contact surface and capability of operating into and through the splash zone comprises a rigid rectangular frame 5 rounded at its corners and braced between its ends 6 and 7 by two spaced struts 8 and 9 parallel to one another and to the sides 10 and 11 of the frame 5 and spaced equidistantly from the sides of the frame. The longitudinal struts 8 and 9 are braced by two transverse struts 12 and 13 parallel to the ends 6 and 7 of the frame 5 and so located as to provide centrally within the frame a mean location for a cluster of four electro-magnets 14 spaced at the corners of a square. Four other electro-magnets 15 are located adjacent the junctions of the longitudinal struts 8 and 9 with the ends 6 and 7 of the frame 5. The eight electro-magnets are similar and in the mean position those of the central cluster are at the same spacing from the principal plane of the frame 5 as are those 15 at the ends of the longitudinal struts 8 and 9.. The central cluster of electro-magnets 14 is movable relative to the frame 5 in both directions normal to the principal plane of the frame so that the spacing thereof from said principal plane may be greater or less than that of the electro-magnets 15 at the ends of the longitudinal struts 8 and 9. The central cluster of electro-magnets 14 can also be moved in the directions of the arrows A and B through a distance of 2 feet towards each of the ends 6 and 7 of the frame 5 and also in the directions of the arrows C and D through a distance of about 9" towards each of the sides 10 and 11 of the frame 5. The movements of the central cluster of electro-magnets 14 are powered by remotely-controlled hydraulic jacks with an on-board hydraulic system driven by an electric motor, the control from the surface being by way of proportioning solenoids actuated through small electric cables which also carry the power for the hydraulic pump and the lamps as well as the T.V. and the instrument lines.

Referring now to Figs. 2 and 3 the attachment means in this second embodiment comprises a rigid, rectangular, tubular frame 30 braced between its ends 32 and 34 by a transverse strut 36, said frame 30 being provided with a plurality of electro-magnets arranged in a delta formation, two of said electro-magnets 38 being positioned substantially at the front portion of said frame 30 and being able to slide in fore and aft directions parallel to the principal plane of the frame 30, and said other electro-magnet 40 being rigidly attached to said strut 36 substantially at the rear of said frame 30.

The movement of the electro-magnets 38 is produced by hydraulic actuators 42 attached to said frame 30 by means of clamps 44. Alternatively the movement of the electro-magnets 38 may be produced by mechanical, electrical or pneumatic actuators.

The electro-magnets 38, 40 are typically cylindrical in form with concentric poles on a flat face.

The frame 30 is adapted to attach to and travel on curved as well as flat surfaces. and, in particular, to the surfaces of an offshore oil production platform. Three point suspension has been adopted to ensure that all the electro-magnets are firm on the surface irrespective of its curvature. Each electromagnet 38, 40 is attached to the frame 30 by means of a gimbal or pivot 46 which allows the magnets to rotate freely about an axis normal to the principal plane of the frame 30. The electro-magnets 38, 40 are also free to tilt about said axis at an angle of approximately 30° in any direction. Therefore, each electro-magnet 38, 40 can independently align itself such that a strong grip is achieved between each electro-magnet 38, 40 and the contact surface.

Movement over the contact surface and directional control are obtained by the two forward electromagnets 38 being able to slide fore and aft parallel to the close under the frame 30 as shown by the arrows in Figure 1. The electro-magnets 38 can slide either simultaneously or independently.

The single rear magnet 40 is rigidly attached to the frame 30 and is therefore subject to pivotal movement only. The dimensions 'track' and 'wheelbase' of the electro-magnets 38, 40 are variable both absolutely and relatively.

To achieve forward movement, the rear electromagnet 40 and the right-hand (RH) front electro-magnet are fully energized thereby fixing the vehicle to the contact surface.

The left-hand (LH) front electro-magnet is de-energized and slid fully forward by its actuator 42. The LH electro-magnet is then fully energized and the RH electro-magnet is de-energized and slid fully forward by its actuator 42. The RH and LH electro-magnets 38 are then simultaneously fully energized, the rear electro-magnet 48 is de-energized and both actuators 42 are fully retracted. This process moves the vehicle forward by a distance equal to the stroke A of the actuators 42.

To achieve motion in the opposite direction the above process is reversed. The same process gives motion axially or spirally along a tube or circumfertially around it. For movement over considerable distances an automatic control function (not shown) is provided with a manual over-ride for fine positioning,

The vehicle can operate upside down and can climb or descend vertically. When operating in such modes, the energized electro-magnets may, for example be set at 1.25 x the rated voltage with the de-energized or sliding electro-magnet set at 1 x the rated voltage to ensure and maintain vertical grip.

Starting from a stationary position with the actuators 42 retracted, a turn to the left is achieved as follows. The LH and the rear electro-magnets are energized and RH electro-magnet is de-energized. The RH electromagnet is then slid forward by no more than half its full stroke. The RH and LH electro-magnets 38 are then energized and the rear electro-magnet 40 is deenergized. The RH actuator is retracted which rotates the vehicle to the left by pivoting around the LH electromagnet. This process is repeated until the requisite degree of turn has been attained.

If the actuator movement is half of the full stroke the turn produced per-cycle will be about 14 degrees. Therefore 7 cycles will be needed to turn 90 degrees.

The actuator movement is restricted because the distance between the front electro-magnets 38 varies during the turn and the electro-magnets 38 consequently scuff sideways in relation to one another. This scuffing can be accommodated by the pivot 46 allowing the magnet face to roll. The use of a full stroke A for turning would result in excessive scuffing. Turns can be made to the left or right, in forward or reverse motion, on any flat or curved surface and in any attitude.

The frame 5, 30 is neutrally buoyant, i.e. buoyant in itself, and is dimensioned to fit externally on the underside of a free-swimming vehicle for which it is intended. This may be a self-propelled vehicle 20 as illustrated in Figs. 4 and 5 or a diver manoeuverable vehicle 50 as illustrated in Fig. 6.

Referring now to Figs. 4 and 5, the vehicle 20 has an underslung openwork three-dimensional construction 21 which is rectangular in all three dimensions and within which are housed accessories appropriate to the functioning of the instrumentation carried by the vehicle. The bottom of the construction 21 provides a rectangular border 22 with which the frame 5, 30 is compatible and to one end of which the forward end of the latter is connected for pivotable movement of the frame 5, 30 about said forward end through 90° away from the border 22 as indicated by the arrow E in Fig. 2. To bring the vehicle 20 into operative relationship with an upright marine ferrous surface such as indicated at 25 in Figs. 4 and 5, the vehicle 20, with the frame 5, 30 closed up to the border 22 and held in such position by a winch and locating lugs on the border 22, is directed to swim up close to the surface 25 in an attitude square to said surface, i.e. with the principal plane of the frame 5, 30 horizontal and normal to the surface 25. The locating lugs are released and the winch is then operated to swing the frame 5, 30 through 90° away from the border 22 about the forward end of the latter (see Fig. 2) and bring the magnets 14/15, 38/40 up to said surface 25. The magnets are then energized so that the frame 5, 30 is held fast to the surface 25 and next the winch is operated to swing the vehicle 20 through 90° down on to the frame with engagement of the locating lugs (see Fig. 5) .

The arrangement described enables the vehicle 20, when in operative relationship to the marine ferrous contact surface 25, to move forwards or backwards in steps of 2 feet as the electro-magnets 14 and 15 or 38 and 40 are alternately energized and de-energized and the jacks appropriately actuated. Similarly, the vehicle 20 can move sideways at 90° to the left or the right. The latter property is especially useful when working progressively around a node where several pipes of a marine structure join. The electro-magnets 14/15, 38/40 are each of 250 Kg holding power and each weighs 5 Kg and draws 20 watts. On board the vehicle are a robust solidstate T.V. camera complete with lamps and able to look forwards or backwards for navigation, two indicators giving the attitude of the vehicle in the looping and rolling planes, a pressure depth gauge and a speedometer cum distance run meter. A mechanical linkage to one set of electro-magnets 14 or 40 actuates two pointers in the T.V. camera's field of vision such that the two pointers aiming together denotes a forward setting, the two pointers aiming apart denotes a reverse setting, the two pointers aiming to left or right denotes a turn in that direction, and the two pointers when vertical denote stop.

The umbilical cable from the remote control point to the vehicle is comparatively light and small and would be deployed from a conventional cable drum. The vehicle is capable of returning from its work site by reversing along the umbilical cable so as to minimise the risk of creating a loop in the cable which may then snag over some projection on the structure.

The electro-magnets and the T.V. cameras and other sensors on board the vehicle are shielded with magnetic shielding material, preferably Mumetal or other material of high magnetic permeability.

Referring finally to Fig. 6, the ROV 50 in this embodiment is a work module normally transported by a mother vessel 51 which takes it to or adjacent to the work area. At the work area, either the mother vessel locates the ROV 50 on the structure to be worked then releases it and stands off, or the ROV 50 is manoeuvered by a diver onto the structure.

The ROV 50 is designed to be as dimensionally small as practical so that it can work in areas of the structure that would be too confined or restricted to a larger-sized ROV.

Hence the ROV 50 may comprise the frame 5, 30 carrying the equipment necessary for its purpose such as magnetic particle inspection (MPI) or non-destructive testing (NDT) of the structure over which is crawls.

In the illustration of Fig. 6, the mother vessel 51 and ROV work module 50 are remotely controlled via umbilicals 52, 53 respectively from a surface vessel 54 which carries control panels 55, 56 for the mother vessel 51 and module 50 respectively and an auxiliary instrumentation control panel 57. The surface vessel also carries a crane 58 and winch 59 to deploy a hoist 60 in which the mother vessel and its attached module can be garaged for passage between the surface vessel and a selected. depth at which the mother vessel and module can leave to head for the work area or return after completion.

The frame 5, 30 may also carry at the front thereof a scraper blade some 50 cm wide, the blade being of spring steel or of plastics material and being capable of conforming to various curvatures. The scraper blade is carried on two arms which can be raised or lowered independently by hydraulic jacks relative to the principal plane of the frame. Gross mussel, kelp or like contamination can be cleared cleanly and at high rates by this scraper blade arrangement. The arms can also be used to jack the vehicle up so that it can climb on to a surface at 90° to the surface erstwhile being dealt with or surmount an obstacle up to 12" proud of the latter surface. A rotating brush system is also carried on the arms and is powered by an electric motor. This rotating brush system is intended for cleaning the marine ferrous contact surface to bright metal prior to inspection thereof. When the frame 5 is used as a vehicle in its own right it is capable of operating into and through the splash zone up to at least sea state 5. When fitted to a vehicle, such as the vehicle 20, however, it can operate in the upper splash zone up to sea state 2 or 3 only.

Claims

1. A remotely-operable vehicle adapted to crawl on a marine ferrous contact surface and capable of operating into and through the splash zone up to at least sea state 5, comprising a frame (5, 30) adapted to be held fast during motion in relation to said surface by the alternate energization and de-energization of a plurality of electro-magnets (14, 15 - 38, 40), said electro-magnets being arranged such that at least one electro-magnet is movable in relation to at least one other electro-magnet in order to progress said frame in relation to said ferrous contact surface.

2. A vehicle as claimed in claim 1, characterised in that said plurality of electro-magnets (14, 15) comprises two bilaterally-symmetrical series of similar electromagnets which are shielded with magnetic shielding material, the electro-magnets ( 15 ) of one said series being located at or adjacent the periphery of said frame (5) and being fixed relative to said frame, and the electro-magnets (14) of the other said series being clustered centrally of said frame and being movable as a cluster relative to said frame in either direction normal to said ferrous contact surface and also both fore and aft and to left and right when deenergized and withdrawn from said ferrous contact surface, whereby for progression of said frame (5) in relation to said ferrous contact surface, the de-energized electromagnets (14) of said clustered series are withdrawn as a unit from said ferrous contact surface and displaced on a unit relative to said frame in a desired direction prior to again being moved as a unit into contact with said ferrous contact surface and re-energized, the latter movement of the clustered series is continued with simultaneous withdrawal of said frame and the de-energized electromagnets (15) of said peripheral series from said ferrous contact surface, said frame is moved relative to the clustered unit to restore the latter to its original centralized position relative to said frame, and said frame is moved towards said ferrous contact surface to restore contact with said ferrous contact surface of the electro-magnets of said peripheral series.

3. A vehicle as claimed in claim 1, characterised in that said plurality of electro-magnets (38, 40) comprises at least two electro-magnets (38) transversely spaced on the frame (30) and adapted for sliding movement fore and aft thereof by means of actuators (42) and at least one electro-magnet (40) fixedly mounted on the frame (30) and longitudinally spaced from the slidable electro-magnets

(38), whereby for progression of the frame in relation to the ferrous contact surface, one electro-magnet at a time is de-energized to reduce but maintain its holding force on the contact surface and, by operating one or both actuators (42) to both slidable electro-magnets (38) for fore and after motion or one of the slidable electro-magnets for turning motion, the fixed electro-magnet (40) can be drawn towards or pushed away from the slidable electromagnets (38) by reverse operation of the or each actuator

(42).

4. A free-swimming vehicle adapted for crawling on a marine ferrous contact surface and having a capability of operating into and through the splash zone characterised by the external attachment to the bottom thereof of a frame (5, 30) adapted to be held fast during motion in relation to said surface by the alternate energization and de-energization of a plurality of electro-magnets (14, 15 - 38, 40) said electro-magnets being arranged such that at least one electro-magnet is movable in relation to at least one other electro-magnet in order to progress said frame in relation to said ferrous contact surface.