WO1984003869A1

WO1984003869A1 - Remotely-operable vehicles for use in the cleaning and inspection of marine contact surfaces

Info

Publication number: WO1984003869A1
Application number: PCT/GB1984/000119
Authority: WO
Inventors: John Cameron Robertson
Original assignee: John Cameron Robertson
Priority date: 1983-04-06
Filing date: 1984-04-05
Publication date: 1984-10-11

Abstract

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. According with the invention, the ROV has a frame (10) having means (18-21) for engaging the contact surface and at least one nozzle (25) mounted on the frame and directed away from the surface engaging means. The or each nozzle is provided with a supply of water under pressure via an umbilical hose from a source independent of the frame to issue from the or each nozzle to provide thrust which enables the vehicle to bear against the contact surface and progress therealong in sea or in air or through the air/sea interface of the zone. The vehicle can be steered by a pair of nozzles (25) which are differently vectorable fore and aft.

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 eitherin 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 adhere upwards or downward as the case may be, by buoyancy or gravity, with two of these for working on underwater surface areas of ships' hulls and like simple relatively shallow structures, and the third specifically for cleaning the walls and bottom of the machinecooling sea or lake water intake channels of nuclear or other electric power stations.

The smaller of the two aforementioned underwater surface area working ROVs can operate at depths of up to 100m (328 feet) and comprises a box-shaped body measuring approximately 61cm x 61cm x 36cm (24in. x 24in. x 14in.) which is enclosed and supported by a mushroom-shaped fibreglass fairing. Plastics spheres provide surface buoyancy, 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 underwater surface area working ROVs can operate at depths sufficient to accommodate the deepest draft ULCCs (Ultra Large Crude Carriers) and comprises a cylindrical platform of diameter 1.8m and depth 0.5m (6 feet and depth 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 underwater surface area working 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 35mm still camera, and a distance-travelled sensing unit. Navigation is by visual location on hull markings, with deadreckoning 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 1.78m long x 1.27m wide x 0.8m 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 hudraulic pressure and moves ahead of sideways, after finishing one section within a diameter of 110m, 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, algate and all other sticky obstacles is effected by a large, strong, revolving scouring brush.

Not one of the three known underwater surface area working 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, i.e. that state of the open sea corresponding to a wind of force 5 on the Beaufort scale.

In accordance with the present invention, a remotely-operable vehicle adapted to crawl on a marine contact surface and capable of operating into and through the splash zone up to at least sea state 5, is characterised by a frame having means for engaging the contact surface, at least one nozzle mounted on the frame and directed away from the surface engaging means, the or each nozzle being provided with a supply of water under pressure from a source independent of the frame to issue from the or each nozzle to provide thrust which enables the vehicle to bear against the contact surface and progress therealong in sea or in air or through the air/sea interface of the zone.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS. Fig. 1 is a side elevation of one embodiment of a vehicle according to the invention; Fig. 2 is a plan view of Fig. 1,

Fig. 3 is a side elevation of a second embodiment; and

Fig. 4 is a plan view of Fig. 3.

DETAILED DESCRIPTION OF THE INVENTION. A remotely-controlled vehicle or ROV in accordance with the invention is adapted to carry out cleaning and inspection work efficiently in the splash zone of oil production platforms and other marine structures and is designed to travel along the surface of the structure and to adhere firmly to said surface in all attitudes and during the transition from air to sea and back again up to at least sea state 5.

Referring now to the drawings, the frame of the ROV is made up of lengths 10 of 7.62cm (3") outside diameter aluminium alloy tubing of wall thickness .32cm (¾ " ) which is painted with epoxy resin.

The lengths 10 of 7.62cm {3") o/d aluminium tube of wall thickness .32cm (¾") and making up the frame comprise four of 81.28cm (32"), two of 61cm (24"), two of 20.32cm (8") and two of 5.08cm (2"), the lengths being welded at joints so that the tubes remain watertight.

Welded to the frame at appropriate positions are four aluminium plates 25 , 4cm x 7.62cm x .95cm (10" x 3" x h" ) thickness forming cheeks, hereinafter referred to and four aluminium plates 10.16cm x 7.62cm x .95cm (4n x 3" x ¾") thickness forming axle supports, also hereinafter referred to. The frame so made up weighs 12.09kgs (26.61bs.) in air and 9.38kgs (20.51bs) in water, i.e. it is buoyant.

The frame is 91.44cm (36") long and 60.96cm (24") wide with a 'deck' level when afloat 19.05cm (7.5") above the water surface, the highest point depending on the equipment fitted to the frame. In basic form the ROV would protrude a maximum of 40.64cm (16") from a surface along which it travels. At the front of the ROV are mounted, one at each end of a transverse rod 11 rotatably received in apertures therefor in two outer and two inner cheek members 12 and 13, respectively (only one of the latter being shown), projecting forwardly of the frame one adjacent each side of the latter, hydraulic arms 14, and 15 fast with the rod 11, one externally of each of the outer cheeks 13, and bridged at their frame-remote ends by a scraper blade 16 as shown, or by some other cleaning device such as a power brush. The arms 14 and 15 project 45.72cm (18") forwardly from the ROV when longitudinally aligned with the frame. The arms 14 and 15 are adapted to be raised and lowered or moved fore and aft relative to the frame by two symmetrically arranged hydraulic rams one of which is shown at 17.

The frame rides on a tricycle undercarriage consisting of two nylon rollers 18 and 19 of 15.24cm (6") width and 10.16cm (4") diameter set 30.48cm (12") apart at the front and two similar rollers 20 and 21 set together at the rear. The weight of the rollers in air is 5kgs (11.01bs.) and in water 0.5kgs (1.11bs.). The rollers 18 to 21 run on 2.54cm (1") diameter solid stainless steel axles 22 to 24 mounted in axle supports 30, and the wheelbase is 81.28cm (32"). The axles 22 and 23 are 17.78cm (7") long and the axle 24 is 63.5cm (25") long. Rubber bushes are provided around the axle mounts to reduce vibration and stainless steel securing split pins are provided at the ends of the axles. Adhesion of the ROV to a structural surface is effected by the reaction to two water jets ejected from stainless steel nozzles 25 and 26 which are set midway between the front and back of the frame and some 50.8cm (20") apart, and which act like firehose nozzles. The inside diameter of each of the nozzle outlets is

3.18cm (1.25"). In operation, seawater is supplied by a pump on a surface vessel through a 10.16cm (4") inside diameter firehose, which is the main part of the umbilical, via stainless steel piping 29 which divides and accelerates the water flow smoothly to the nozzles 25 and 26.

The rate of flow is some 4364.16 litres (960 imperial gallons) per minute with a pump pressure of 17.62kgs per cm² (250 pounds per square inch). This produces a total thrust force of 345.45kgs (7601bs). from the two jets. Each of the nozzles 25 and 26 is capable of being vectored independently from the control point through an arc from 48 degrees aft to 48 degrees forward thus to produce a thrust force fore or aft in addition to the adhesion force. The vectoring of the nozzles 25 and 26 is effected by water hydraulic jacks 27 and 28 controlled from the surface. This thrust force drives the ROV forwards or backwards as required. With both nozzles 25 and 26 in the fully aft position, for example, the adhesion force will be 2224. UN (5001bs.) and the forward thrust some 2491N (5601bs). With the two nozzles 25 and 26 vectored in anti-phase, one fully forward and the other fully aft, the adhesion force will be 2224.11N (5001bs) and the propulsive force will be nil, but there will be a turning moment on the ROV of some 637.24Nm (470 ft.1bs). This turning force, when moderately applied, steers the ROV. In normal manoeuvring the angle of vectoring will be small, amounting to 5 to 10 degrees, which will give a thrust of about 444.82N (1001bs). The control system is such that the rate of change of thrust available is some 222.41N (501bs), or thereabouts per second. The water is pumped continuously while the ROV is operating and the vectoring system enables the thrust to be varied sensitively as required while maintaining a minimum of 2224. UN (5001bs) adhesion force. The minimum thrust is about four times the weight of the ROV in air and about twelve times its weight in water.

There are four navigational/position instruments carried on board which report continuously to the control panel on the surface, these being:-

(1) A rolling axis indicator which is a pendulous weight fixed rigidly to a light axle which can turn freely about the longitudinal axis of the ROV. A potentiometer senses its position and transmits a proportionate voltage to an indicator (an appropriately calibrated voltmeter) on the control panel. This will show the position as an angle through 360 degrees about the axis.

(2) A looping axis indicator which is similar to the rolling axis indicator but is free to turn about the transverse axis of the ROV and thus to report the ROV's attitude in the looping plane.

(3) A distance run meter, which is an odometer driven by a small wheel spring loaded onto the surface. It enables the exact position of the ROV on, for example, a long and featureless pipe to be determined.

(4) A pressure depth indicator which is a standard item and will, whenever practicable, be interlinked with the tide gauge to give also a reading of the depth in relation to the platform datum.

An air powered tool will be used for power brushing. grinding etc., and will be of the type which has a motor integral with the tool chuck and which can take a wide variety of brushes, grinders and so forth. The tool will be carried in and manipulated by the front hydraulic arms 14 and 15. The necessary air line will be a permanent part of the umbilical cable. The ROV is provided with a brake in the form of a spike located on the longitudinal centre line of the vehicle adjacent the rear roller 20, 21 and which can be forced against the surface of the rear roller, the brake arm being indicated at 31. The brake will provide fine control of fore and aft movement of the ROV over some 6" as well as braking action.

The ROV is fitted with (1) two attitude indicators comprising heavy, short and rigid pendulums of MONEL 400 metal with axles, the pendulums being connected to potentiometers which in turn are electrically connected to the control point; (2) a depth gauge with electrical connection to the control point; (3) a distance-run meter comprising a rubber roller being on the right-hand front roller 18 and connected to an odometer; and (4) a colour T.V. camera 32 of length 30.48cm (12") and outside diameter lm.14cm. (45"), the cable connection to which is at right angles to the camera length and is 3.81cm (1.5") long and 3.81cm (1.5") outside diameter. The pedestal 33 for the camera is a 5.08cm (2") length of aluminium tubing of 5.08cm (2") outside diameter and .32cm (¾") wall thickness, a mount 34 of height 2.54cm (1") and outside diameter 5.08cm (2") and of high hysteresis rubber being provided to reduce shock.

The umbilical cable is made up of a 10.16cm (4") firehose of outside diameter 10.92cm (4.3") located at the inside and externally of and parallel to which are eight hydraulic lines, i.e. two for each double-acting jack 17, 28 and 29, an air hose of 1.27cm (0.5") inside diameter and 2.03cm (0.8") outside diameter, a T.V. cable of 2.03cm (0.8") outside diameter, and an electrical signal and power cable carrying the D.C. power supply and the potentiometer signals. The control station will have at its centre a T.V. monitor and control panel. The vehicle controls will be four levers similar to the track controls of a crawler tractor. The two centre ones will operate the jets through linked hydraulic jacks and will work in the natural sense i.e. forward movement of the lever for forward movement of the vehicle. Initially these would be manual but power assistance could be added if required. The brake lever will be on the left and the lever for the front arms on the right. The air-powered tool, if fitted, will be turned on and off by the air valve on the panel. It will be positioned by coordinated use of the front arms and the movement of the brake. Specialist equipment will, when fitted, be controlled via the appropriate specialist console. When the scraper blade 16 is replaced by a power wire brush, the latter is of length 30.48 cm (12") and outside diameter 7.62cm (3") with a brush head of 15.24cm (6") diameter and 3.81cm (1.5") wide, air being supplied thereto through the 1.27cm (0.5") inside diameter hose at about 8.46kgs/cm² (120 pounds per square inch).

The reference numeral 35 denotes swivel collars for the stainless steel piping 29.

In a second embodiment illustrated in Figs. 3 and 4, in which like parts are numbered corresponding to the first embodiment, a modified vehicle has a frame 10' of length lm and width 45cm. The frame carries a single centrally mounted water jet 25' vectorable fore and aft by a water hydraulic jack 27' and rides on a rectangular undercarriage consisting of two pairs of double wheels 40. Each pair of double wheels 40 is independently steerable by a linkage comprising a link 41, 42 extending from each double wheel and converging slightly to engage a cross link 43. One link 41 of each pair is connected to a link 44 which forms the piston of a steering jack 45; on actuation of a jack its link 44 causes rotation of one double wheel about a vertical steering axis 46 and the linkage 41, 44, 42 transmits movement to the other double wheel of the pair. Only one pair of wheels may be steered if desired, or both may be operated together to give the vehicle a crab-like sideways movement.

In this embodiment, the water jet 25' can be positioned for maximum thrust against the structure on which it is operating, or it can be vectored fore or aft to maintain the necessary thrust against the structure while causing also movement astern or ahead respectively.

Spaced forwardly of the forward end of the frame 10' is a plough in the form of a transverse steel blade 16' and mounted between the blade and frame is a lifter 50 (similar to a snow plough) to keep the detritus scraped from the sctructure from dripping under the vehicles wheels. The scraper blade is controlled by a water hydraulic jack (not shown) which can raise or lower the blade relative to the structure. The blade can be used as a brake, avoiding the need for a specific brake member.

The jacks controlling the steering vectoring and scraper blade are water-operated, single-acting jacks vented to ambient pressure and opposed in each case by a tension spring.

Position control will be by control at the surface of the pressure in the line of the appropriate jack. As visibility in the immediate vicinity of the vehicle will be very poor when growth is being 'ploughed' and as the water jet efflux will affect all of the centre line, a T.V. navigation camera (not shown) will be mounted on a high strut and offset forward and to the side of the frame centre.

The vehicle will have the facility to carry positionsensing equipment which will be interconnected to a video, display.

The ROv's shown diagrammatically and described can work on steel, concrete or other surfaces; however, the vehicle of the first embodiment with the tricycle undercarriage is more adaptable to use on pipes or columns of relatively small diameter whereas the vehicle of the second embodiment is more adaptable to use on large diameter or flat structures such as concrete structures and dams. They are capable of carrying out cleaning and inspection work in the splash zone of oil production platforms and other marine structures, the great majority of cleaning and inspection work being done in the splash zone. The operating envelope of the ROVs shown and described is from 10 feet above the water surface to 100 feet below the latter, with an umbilical of length 300 feet. Deployment may be either from the structure to be worked on or from a support vessel.

The ROV's shown and described will be able to undertake the following tasks:-

(1) Travel to any part of the structure within the splash zone and, in particular, gain access to the weld area of any node which requires inspection. (2) Report its position and attitude at any time with an accuracy of +/- 0.914m (1 foot) in relation to the X, Y and Z axes.

(3) Take colour video pictures of the structure.

(4) Remove mussels, kelp and like contamination cleanly and at a high rate by undercut scraping.

(5) Clean to bright metal by powered steel wire brush. The power brush is fitted as an alternative to the scraper.

(6) As options and by carrying the appropriate specialist equipment:-

(a) Take colour still pictures of high quality.

(b) Clean to bright metal by high pressure water jetting with or without the addition of sand or other abrasive. (c) Grind away metal as may be required using an air-powered grinder, (d) Take metal thickness measurements with the ability to position the gauge within a 1 inch radius of a specified and visible point. (e) Take cathodic potential readings and cathodic current density measurement, (f) Carry out Magnetic Particle Inspection

(M.P.I.) of welds to B.S. 6072. It will also have the ability to carry out MPI using a higher magnetic field and a greater ink concentration than specified in B.S.6072. In general the ROV's shown and described will carry only one major item of equipment, in addition to colour T.V. at any one time. Thus in inspecting a node, for example, the sequence would be:

1. Use scraper to remove surface contamination.

2. Return to surface, fit power brush or water jetting equipment and clean weld to bright metal.

3. Return to surface, fit TVP camera, U/V lamp and MPI kit then carry out MPI examination of weld.

With present techniques this will require to be done in darkness.

4. The various items of equipment will fit on the hydraulic arms of the ROV in a manner analagous to that used in fitting various implements to a farm tractor. Changeover of implements will be straightforward and rapid. The standard umbilical cable will carry all the necessary services except for the high pressure water line required for 'hydro-blasting'. If this is used for cleaning, the line will have to be clipped to the standard umbilical.

5. The ease and speed of deployment and re-deployment of the ROV will be enhanced if this is done from the structure itself rather than from an attendant vessel.

The ROV's shown and described will weigh some 90.91kgs (2001bs) in air and some 22.73kgs (501bs) when in water. Since the umbilical cable is very large by conventional standards - it will have a drag of 1.86kgs per metre (1.251bs per foot) length when perpendicular to a 1 knot current - special care will be needed to deploy it correctly. The control point for the ROV would preferably be on the structure being examined to eliminate umbilical heave due to relative motion between the control point and the structure.

The ROV's shown and described are adapted for cleaning and inspection of marine contact surfaces and are capable of operating into and through the splash zone up to at least sea state 5. The ROV's described can also traverse broken or difficult surfaces and can surmount obstacles, and have means of controlling and/ or measuring and reporting attitude and direction relative to the structure. They can gain access to the many tight and awkward corners of oil platform supporting structures.

For sophisticated inspection work when the force and jolting associated with 'mussel bashing' is not involved, a first-class T.V. camera and a still camera would be carried and a platform mounted on the frame would be sufficiently large to carry the largest of instruments used in such work. The platform would be capable of carrying a full range of sensors. Other modifications may be made; for example, the rollers 18 to 21 may be replaced by low friction skids; the single water jet 25' may be non-vectorable but set at an angle to give forward movement to the vehicle with a control valve to vary the thrust and alter the speed of the vehicle, reverse movement being done by pulling the vehicle mechanically.

Claims

CLAIMS .

1. A remotely operable vehicle adapted to crawl on a marine contact surface and capable of operating into and through the splash zone up to at least sea state 5, characterised in that the vehicle comprises a frame (10, 10') having means (18-21, 40) for engaging the contact surface, at least one nozzle (25, 25') mounted on the frame and directed away from the surface engaging means, the or each nozzle being provided with a supply of water under pressure from a source independent of the frame to issue from the or each nozzle to provide thrust which enables the vehicle to bear against the contact surface and progress therealong in sea or in air or through the air/sea interface of the zone.

2. A vehicle as claimed in claim 1, characterised in that a single fixed nozzle (25') is mounted on the frame.

3. A vehicle as claimed in claim 1, characterised in that a single nozzle (25') is mounted on the frame and is vectorable fore and aft.

4. A vehicle as claimed in any one of claims 1, 2, or 3 characterised in that the contact surface engaging means (40) is steerable.

5. A vehicle as claimed in any one of claims 1 to 4 characterised in that the contact surface engaging means comprises at least three wheels (40) at least two of which are a steerable pair.

6. A vehicle as claimed in claim 5 characterised in that two pairs of wheels (40) are provided.

7. A vehicle as claimed in claim 6, characterised in that each pair of wheels (40) is steerable independently of the other.

8. A vehicle as claimed in claim 1, in which two nozzles (25) are mounted on the frame and are vectorable differentially fore and aft.

9. A vehicle as claimed in any one of claims 1 to 8, characterised in that the or each nozzle is supplied with water through an umbilical hose via a pump on a surface vessel.