EP0157864B1

EP0157864B1 - Heave compensation for a pipeline hoisting system

Info

Publication number: EP0157864B1
Application number: EP84903767A
Authority: EP
Inventors: Peter Eric De Lang
Original assignee: Gusto Engineering BV
Current assignee: Gusto Engineering BV
Priority date: 1983-10-07
Filing date: 1984-10-08
Publication date: 1987-01-07
Also published as: NO852310L; DE3461944D1; FI852295A0; FI852295L; WO1985001775A1; NL8303451A; EP0157864A1

Abstract

An apparatus for carrying out operations at a point deep under water comprises a floating device (1) having a suspension system (2) with hoisting means for lowering and raising a line of pipes (3). The hoisting means is combined with a passive and an active swell compensation. To be able to carry out the movements which are necessary for carrying out the operations in conjunction with the swell compensation, especially when a very great weight is suspended from the suspension system and there is no support by the ground to take part of the weight, according to the invention, the derrick (2) of the suspension system has a number of vertical guide tracks (12, 13, 14) disposed at intervals from each other, on which is guided a horizontal yoke (15) which is positioned between the guide tracks and can be moved up and down vertically in the guides by means of driven pinions which engage with a number of pulling elements (17, 18) bearing the load of the yoke and from which the latter is suspended. The hydraulic system of the hydraulic motors (19, 20, 21, 22) contains both the passive and the active part of the swell compensation. There is the possibility of giving vertical movements to the yoke on which the swell compensation is superposed.

Description

The invention relates to an apparatus for carrying out operations at a point deep under water, such as carrying out dredging operations on a seabed, consisting of a floating apparatus having on it a suspension system with hoisting devices for lowering and raising a line of pipes, said devices being combined with a passive and an active swell compensation of the type in which the active part controls the spring action of the passive part.
Such an apparatus is known, for example, from Dutch Patent Application 7,413,233, which has been laid open for inspection. This known apparatus is in particular a floating drilling station, in which the drill line suspended from the suspension system is linked with a passive swell compensator, to which is added an active compensation part to permit changing of the force which acts upwards on the drill line with the intervention of the compensation system, through which adjustment to the swell result and to the weight of the line is possible. In a drilling apparatus, part of the weight of the line is taken by the ground and produces the vertical downward force necessary for drilling.
In floating drilling apparatuses the derrick is also provided with hoisting devices in the form of a tackle, by means of which the drill line can be lowered and raised, and by means of which pipe sections can be added to or removed from the drill line.
The object of the invention is to produce an apparatus with which it is possible to carry out the movements which are necessary for carrying out the operations in conjunction with the swell com= pensation, and with which it is in particular possible to carry out operations where a very great weight is suspended from the suspension system, and to which another separate movement which is independent of the ground can be given, in other words, where there is no support by the ground to take part of the weight.
This object is achieved according to the invention in the first place by the derrick of the suspension system having a number of vertical guide tracks disposed at intervals from each other, and on which a horizontal yoke positioned between the guide tracks is guided, said yoke being movable up and down vertically in the guides by means of pinions which are driven by hydraulic motors and engage with a number of pulling elements bearing the load of the yoke and from which the latter is suspended, and the hydraulic system of the hydraulic motors contains both the passive and the active part of the swell compensation, while there is also the possibility of giving the yoke vertical movements on which the swell compensation is superposed. The yoke guided on vertical guide tracks can easily be designed in such a way, in conjunction with a corresponding design of the parts of the derrick, that heavy loads can be carried. This yoke is movable vertically by hydraulic drives, consisting of gearboxes with hydraulic motors, which engage with pulling elements, and these hydraulic motors handle both the vertical movements which the yoke has to make to carry out the operations within the derrick and also at the same time the passive and active swell compensation.
The invention is intended in particular for an apparatus with which dredging operations can be carried out at great depth from a floating apparatus, in which case the line of pipes carries at its lower end a sucking and forcing dredging pump unit, to which the line of pipes connects as a delivery pipe. Suspended from the line in this case is an itself heavy dredging apparatus, which represents a great weight, in particular when it is filled with dredgings.
It is conceivable here to have dredging circumstances, for example for the dredging of very thick layers of mud, where this heavy line with dredging apparatus has to be given a particular movement in the vertical direction, because the layer to be dredged makes a partially vertical dredging movement desirable. This movement can, for example, be a sawtooth-type movement.
With the suspension according to the invention with the hydraulic motors engaging with the pulling elements, it is now possible also to give the line, and thus the dredging apparatus, a vertical dredging movement on which the swell compensation is superposed. All movements can thus be controlled from one hydraulic system.
It is pointed out that Dutch Patent Application 7,201,218, which has been laid open for inspection, already discloses a floating apparatus provided with an active and passive swell compensation in the hoisting device, which has a hoisting cable, at the lower end of which a vertically operating and vertically moving dredging apparatus is suspended. In this case, however, the main idea was to create a swell compensation relative to a dredging apparatus, which itself stands still in relation to the seabed or is hauled up by means of the hoisting cable in order to be lowered at another point, and in which the delivery pipe does not run upwards to the floating apparatus.
The pulling elements can consist of chains which run over the pinions supported in the derrick and linked with the hydraulic motors. The pulling elements can, however, also consist of gear racks which are suspended in the derrick, in which case the hydraulic motors with the pinions engaging with the gear racks are supported in the yoke.
It is preferable to have a design in which the derrick has four guide tracks, in which case the yoke rests on the guide tracks near the corners of a yoke which is essentially rectangular when viewed from the top.
An efficient design is obtained if the guide tracks are made up of pipes, which can, of course, form part of the construction of the derrick. Where chains are used, they can be connected to counterweights which together compensate for at least the weight of the yoke. Compensation for the load suspended therefrom is certainly not desired in full, because in the absence of the load the counterweights then constitute an unwieldy top load for the floating apparatus.
These counterweights can be conducted in the guide pipes, and in them it is simple to install devices for lubricating the chains. For instance, the pipes can be filled with oil, or oil can drip on the chains.
As an additional measure to prevent the yoke from twisting or tilting sideways in the guides, the free lower ends of the chains can be connected via deflection wheels to the lower side of the yoke, for example by means of lighter chains or cables which help to hold the yoke in the correct position.
It is preferable to have an embodiment in which the yoke is suspended at each corner from at least two chains, each running over an individual sprocket chain wheel with its own hydraulic motor with gearbox, and in which the free ends of each set of chains are attached to one or more counterweights. The quality and number of chains must be such that a system which can be realistically produced results.
It is preferable for three chains to be used for each corner, with three sprocket chain wheels with their hydraulic motors. If one of the chains breaks, sufficient chains remain to allow the system to continue to operate safely, and the counterweights continue to work fully.
According to the invention, the hydraulic system of each hydraulic motor can also consist of a main circuit with main pump and main hydraulic motor, a first auxiliary circuit with auxiliary pump which can produce a greater quantity of fluid per unit of time than is the case with the main pump and, via connection of the auxiliary circuit to the main circuit, can feed it to the main hydraulic motor, and also of a second auxiliary circuit with auxiliary pump and auxiliary hydraulic motor, the outgoing shaft of the latter engaging with the same pinion drive mechanism as the main hydraulic motor. The main circuit here serves to produce the movements which are necessary for the operations to be carried out, such as dredging, being movements which can consist of vertical movements necessary for obtaining the required production with the aid of the dredging apparatus on or in the layer to be worked. This main circuit also serves to give passive compensation, to which end this main circuit is linked in a known manner to storage batteries which act as springs.
The first auxiliary system makes it possible to supply fluid to the main motor temporarily in much large quantities. This means that the yoke can be moved at greater speeds than is the case with the main circuit. These greater speeds are important when building up or taking apart the line of pipes.
The second auxiliary system is for the active swell compensation. By using this second system to make the auxiliary motor perform a particular desired torque, one can eliminate entirely the friction losses in the whole apparatus, friction losses which occur, for instance, in the guide tracks for the yoke, in the bearings of pinion and driving mechanism etc. The passive swell compensation is then no longer hampered by friction losses, for the latter are eliminated by the active swell compensation produced by the second auxiliary circuit. Since the friction losses will generally have a constant value, this second auxiliary circuit can generally also operate with constant pressure.
The swell is an up and down movement, which thus changes direction all the time. The working direction of the second auxiliary circuit has to be adjusted to this each time. In order to ensure rapid action of the second auxiliary circuit, and thus in fact to have the active swell compensation available right from the start, the second auxiliary circuit can have a control device for the size of the torque and the direction of rotation of the auxiliary motors, said control device being connected to an acceleration meter which measures the acceleration of the swell.
It is necessary for the yoke to move correctly in the guides, i.e. remaining vertical on the guide tracks and generally moving horizontally. Deviations from this desired position lead to tilting sideways, increasing the friction and possibly jamming.
This can be achieved in various ways, for instance mechanically by linking together the pinions by means of shafts and gear wheels.
It is preferable according to the invention for the pinions to be connected to tachometers and for the data of the tachometers in a control device to control the auxiliary motors in such a way that the yoke remains horizontal. The auxiliary motors of the active swell compensation are therefore, according to the invention, also used for holding the yoke horizontal. By this measure, it is also possible to make the construction lighter, in particular as regards the guide elements for the yoke.
It is important that buckling of the long line of pipes should be avoided. This buckling could occur when the lower end of the line of pipes meets resistance in the vertical direction. Provision can be made for it by fitting a telescopic part in the lower end, so that the lower end of the line of pipes can slide in. This can, however, also be achieved according to the invention by having the pinions connected to devices which measure the torque, and of which the measurement values act upon the regulation of the main motors in such a way that the pressure in the line of pipes remains essentially constant. The main motors then immediately raise the line of pipes further if during the dredging movements inadmissible resistance with danger of buckling arises for the line of pipes. This impact need not be hard, but can consist of gradually increasing friction resistance, or friction resistance which becomes too great.
The hydraulic system can also be designed in such a way that all pumps are placed on the driving shaft of the same drive motor, in which case the main pump of the main circuit is a variable pump, the auxiliary pump of the auxiliary circuit can be a pump which delivers a constant quantity per unit of time, and which can be short-circuited via a governor slide valve or can give feed to the main circuit in the one or the other direction. The pump of the second auxiliary circuit is also a pump with variable output and working direction.
Finally, there can also be a pump which is also driven by the motor and which supplies a feed cirucit.
The invention will now be explained in greater detail with reference to the drawings.

Fig. 1 is a schematic illustration of a possible use of the apparatus according to the invention.
Fig. 2 is a front view of an embodiment of the apparatus.
Fig. 3 is a side view of the apparatus of Fig. 2.
Fig. 4 shows on a larger scale an embodiment of the upper part of the apparatus according to the invention.
Fig. 5 is a schematic illustration of a variant with parallel guide.
Fig. 6 is a schematic illustration of a variant of the suspension system.
Fig. 7 shows a hydraulic diagram.
Fig. 8 shows a block diagram to illustrate the functioning.

Fig. 1 shows a floating apparatus 1 with derrick 2, from which floating apparatus is suspended a line 3 made up of lengths of pipe which at a great depth, say, over 2000 metres, is provided with a suction head 4 and a sucking and forcing pump 5. At 6 there can be thrusting elements by means of which the whole line can be shifted from a vertical position to a slanting position, as shown. The suction head 4 here is in a layer 7 to be worked. Above this layer there is a thicker layer 8 with a specific weight of, for example, 1.2, lying between that of the seawater and that of the layer to be worked.
The top end of the line 3 extends into the derrick 2 of the floating apparatus 1.
As shown in Figs. 2 and 3, this floating apparatus consists of a pontoon on which the derrick 2 is positioned. Under the derrick, the pontoon is provided with a throughgoing opening or moon- pool for allowing through, say, a line of pipes.
The derrick 2 stands on a bridge 10, and this derrick consists of two main lattice parts 2a and 2b, which are connected to each other at the top end by a head 11.
The derrick hasfour guide tracks, of which Fig. 2 shows tracks 12 and 14 and Fig. 3 shows tracks 12 and 13.
Between these guide tracks there is a yoke 15 which is conducted on the guide tracks, for example with wheels 16. These guide tracks are in the form of pipes which are of sufficiently great internal diameter and form part of the lattice construction of the derrick parts 2a and 2b.
The yoke 15 is suspended near each corner from several chains 17, 18.
Located on top of the cap 11 of the derrick are several hydraulic motors 19,20,21 and 22, one for each chain. The hydraulic drives consist of a gearbox with two hydraulic motors and one brake.
In the embodiment shown, two chains are fitted at each corner of the yoke, so that a total of eight hydraulic motors is found on top of the cap 11, each of them provided with a pinion over which runs a chain whose free end runs into the pipes 12, 13, 14 and is fastened there to the counterweight 23 indicated by the broken lines.
The line of pipes 3 is suspended from the yoke 15.
The apparatus is also provided with elements which are not shown in detail and which are known per se, by means of which a pipe section can be placed in or removed from the line, and with which the line of pipes can be held fast temporarily if the connection with the yoke is broken.
At 24, there are cylinders of the storage battery of the apparatus for swell compensation.
Fig. 4 shows the upper part of an embodiment of the apparatus according to the invention, in which the derrick is again made up of a lattice with pipes 25, 26 which make up the guide tracks, and in which the yoke 27 is suspended near each corner from three chains 28,29 and 30, each running over pinions 31, 32 and 33.
The free ends of these chains, i.e. the parts which run out over the pinions down to a guide 34, are linked to one and the same counterweight 35. The apparatus therefore has four counterweights which together compensate for the weight of the yoke.
The chains can be chains of the "Gallse" chain type, with or without rollers.
Fig. 5 shows schematically that each chain, like chain 36, is connected at its free end to a pulling element or chain 36' ;which is connected by means of deflection wheels 37, 38 to the lower end of the yoke 27 at a point situated at a distance from the place where the yoke 27 is suspended from the chain 36. The yoke can in this way be held better in the correct horizontal position between the guides.
Fig. 6 shows a totally different embodiment in which a number of toothed rods 40, 41 are suspended in the derrick 39. The yoke 44 conducted between the guides such as 42 and 43 carries hydraulic motors with a number of pinions 45, 46 which engage on either side with the toothed strips 41, 40.
Fig. 7 shows the hydraulic diagram.
The hydraulic system shown in Fig. 7 consists of a main circuit with a variable main motor (sic) 47, which via the line 48, 49 drives the main motor 50 whose outgoing shaft acts upon the pinion drive mechanism, which in the general sense is indicated by 52. This main circuit also has the return line 53, 54 to pumnp 47. If the pump is operating in the opposite direction, the flow runs via the pipes 53, 54, 49 and 48. Reference figure 55 indicates a high-pressure storage battery with control device 56, while 57 indicates a low-pressure storage battery with control device 58. Both of them take care of the passive swell compensation, the high-pressure storage battery mainly taking care of the swell compensation, and the low-pressure storage battery dealing with the necessary oil infeed during the compensation.
The main pump 47 is driven by a motor 59, which also drives the auxiliary motor 60 of an auxiliary circuit consisting of the outgoing line 61 and the return line 62, and a slide 63. This slide 63 short-circuits the pump 60 in the position shown. When the connection shown in the righthand section of the slide is made by shifting it to the left, the pressure fluid is fed via the line 64 to the line 48 and thus to the main motor 50. In the other position of the slide 63, this infeed goes to the line 54.
If both pumps 47 and 60 deliver fluid to the main motor 50, the latter can operate faster, so that the yoke can be moved faster. This is important, for example in order to move the empty yoke to its initial position during putting together or taking apart of a line of pipes.
The motor 59 also drives an auxiliary pump 65, of which the output is also variable or reversible, and which can deliver fluid to an auxiliary motor 66, whose outgoing shaft 67 is also connected with the pinion drive mechanism 52. The pump 65 feeds the fluid via the line 68 to the motor 66 and back via the line 69 or vice versa. This circuit 68, 69 with pump 65 and motor 66 forms the second auxiliary circuit.
Fig. 7, of course, shows only the circuit for one pinion drive, and at 70, 71 and 72 connections are therefore indicated with ring lines for comparable circuits.
The motor 59 via a gearbox 73 also drives a pump 74 of a supply circuit which consists of a tank 75 from which the pump sucks up fluid via the line 76.
This feed pump 74 can via line 77, 78, control device 79 and line 80 supply fluid to the main circuit, and the excess returns to the tank 75 via the line 82 and the conditioning device 83. Via the line 84, control device 85 and lines 86 and 87, fluid is supplied to the second auxiliary circuit, with the excess returned via the line 88 and conditioning device 89 to the tank 75. The pump 74 can also supply fluid via the line 90 and the non-return valve 91 to the first auxiliary circuit, which is connected via the line 92 and an overload valve 93 to the tank 75.
The operation will now be explained further with reference to Fig. 8, which is a block diagram intended for the apparatus shown in Figs. 2 and 3, where the derrick is provided at each corner with two chains, and thus two pinions with accompanying drive mechanisms and hydraulic motors. The main motors are indicated by 50.1, 50.2 etc. to 50.8, and the auxiliary motors by 66.1, 66.2 to 66.8.
The control system should have the following functions:

1. Dredging in the form of an up and down sawtooth movement;
2. Swell compensation;
3. Synchronisation of the drives to hold the yoke horizontal;
4. Keeping the pressure constant in the line of pipes and
5. Moving the yoke up and down during making up or taking apart of the line of pipes.

The dredging process takes place from a control room or control device 100 from which the main motors 50.1 to 50.8 are controlled either manually or automatically according to a particular programme. Reference figures 101 to 108 indicate measurement devices which measure the torque which occurs at the pinion drive mechanism. The data of these measurement devices are important for holding constant the pressure in the line of pipes, and thus go via the control device 100 to the main motors.
They also serve as safety devices, for they deliver a signal when there is underloading or overloading of the chains, if too great resistances occur, or if a chain breaks.
For the active shell compensation, the auxiliary motors 66.1 to 66.8, which are driven by a control device 109, are dependent on the measurements of an acceleration meter 110.
For synchronisation of the movements to hold the yoke horizontal, tachometers such as 111, 113, 115 and 117 are fitted at the pinion shafts and via a control device 118 also drive the auxiliary motors 66.1 to 66.8. The readings of the tachometers 111 to 117 can also be used as a value in the control of the main motors, as indicated by the broken line 120.
Instead of the tachometers for controlling the synchronisation, one can also use clinometers on the yoke or flow meters in the lines of the hydraulic motors.
Instead of the torque meters 101 to 108, one can also use sensors which measure the ground resistance or measure the load on the yoke.

Claims

1. Apparatus for carrying out operations at a point deep under water, such as carrying out dredging operations on a seabed, consisting of a floating apparatus (1) having on it a suspension system with hoisting devices for lowering and raising a line of pipes (3), said devices being combined with a passive and an active swell compensation of the type in which the active part controls the spring action of the passive part, characterised in that the derrick (2) of the suspension system has a number of vertical guide tracks (12-14) disposed at intervals from each other, on which is guided a horizontal yoke (15) which is positioned between the guide tracks and can be moved up and down vertically in the guides by means of driven pinions which engage with a number of pulling elements (17, 18) bearing the load of the yoke (15) and from which the latter is suspended, and the hydraulic system of the hydraulic motors contains both the passive and the active part of the swell compensation, and also the possibility of giving vertical movements to the yoke, on which the swell compensation is superposed.

2. Apparatus according to Claim 1, characterised in that the line of pipes has on its lower end a sucking and forcing pump unit, to which the line of pipes connects as a delivery pipe.

3. Apparatus according to Claim 1 or Claim 2, characterised in that the pulling elements consist of chains which run over into the pinions supported in the derrick and linked with hydraulic motors.

4. Apparatus according to Claim 1 or Claim 2, characterised in that the pulling elements are toothed rods which are suspended in the derrick, and the hydraulic motors are supported in the yoke with the pinions engaging with the toothed rods.

5. Apparatus according to one or more of the preceding claims, characterised in that the derrick has four guide tracks.

6. Apparatus according to one or more of the preceding claims, characterised in that the guide tracks consists of pipes.

7. Apparatus according to Claims 3, 5 or 6, characterised in that the chains have counterweights which together compensate for at least the weight of the yoke.

8. Apparatus according to Claim 6 or 7, characterised in that the counterweights are guided in the pipes.

9. Apparatus according to Claim 3 and one or more of Claims 5 to 8, characterised in that the free lower ends of the chains are linked via deflection wheels with the lower end of the yoke.

10. Apparatus according to Claim 8, characterised in that the pipes are provided with means for lubricating the chains.

11. Apparatus according to Claim 3, 5, 6, 7, 8 or 10, characterised in that the yoke at each corner is suspended on at least two chains, each running over an individual sprocket chain wheel with its gearbox with hydraulic motor, and the free ends of each set of chains are attached to one or more counterweights.

12. Apparatus according to one or more of the preceding Claims 1 to 11, characterised in that the hydraulic system of each hydraulic motor consists of a main circuit with main pump and main hydraulic motor, a first auxiliary circuit with auxiliary pump which can supply a greater quantity of fluid per unit of time than the main pump and can feed it, via connection of the auxiliary circuit to the main circuit, to the main hydraulic motor, and also consists of a second auxiliary circuit with auxiliary pump and auxiliary hydraulic motor whose outgoing shaft engages with the same pinion drive mechanism as the main hydraulic motor.

13. Apparatus according to Claim 12, characterised in that all pumps are connected to the same driving motor shaft.

14. Apparatus according to Claim 12 or Claim 13, characterised in that the second auxiliary circuit has a control device to control the size of the torque and the direction of rotation of the auxiliary motors, said control device being linked to an acceleration meter which measures the acceleration of the swell.

15. Apparatus according to Claim 12, 13 or 14, characterised in that the pinions are linked with tachometers, and the data of the tachometers in a control device controls the auxiliary motors in such a way that the yoke remains horizontal.

16. Apparatus according to Claim 12, 13, 14 or 15, characterised in that the pinions are connected with devices which measure the torque, and of which the measurement values act in such a way upon the control of the main motors that the pressure in the line of pipes remains essentially constant.