Multi-cable subsea lifting system

Abstract

A multi-cable subsea lifting system including two or more load-cable lifting apparatus (2a, 2b); a load cable (4a, 4b) extending from each load-cable lifting apparatus (2a, 2b) to a subsea attachment point; a torque measuring device (22) associated with each load cable (4a, 4b); one or more subsea anti-cabling devices (20), each anti-cabling device (20) including a motor (24) connected to a respective load cable (4a, 4b); and a controller (30) in communication with each motor (24) and torque measuring device (22); wherein the controller (30) is configured to actuate each motor (24) to impart a rotational force to its respective load cable (4a, 4b) in response to measurements obtained from the torque measuring device (22) with the aim to limit cabling, remove cabling or control heading either automatically or from external control.

Claims

1. A multi-cable subsea lifting system comprising: two or more load-cable lifting apparatus; a load cable extending from each load-cable lifting apparatus to a subsea attachment point; a torque measuring device configured to detect a twisting of a load cable; one or more subsea anti-cabling devices, each anti-cabling device comprising a motor connected to a respective load cable; and a controller in communication with each motor and torque measuring device; wherein the controller is configured to actuate each motor to impart a rotational force to its respective load cable in response to measurements obtained from the torque measuring device.

2. A lifting system as claimed in claim 1, wherein each anti-cabling device comprises two or more load-cable terminations for connection with a load cable.

3. A lifting system as claimed in claim 2, wherein the load-cable terminations comprise a wedge socket, socket-resin connection or spelter socket.

4. A lifting system as claimed in claim 1, wherein at least one motor is directly connected to its respective load cable.

5. A lifting system as claimed in claim 4, wherein each motor is directly connected to its respective load cable.

6. A lifting system as claimed in claim 1, wherein each motor is indirectly connected to its respective load cable.

7. A lifting system as claimed claim 1, wherein at least one motor is battery operated and the lifting system comprises one or more batteries for powering each battery operated motor.

8. A lifting system as claimed in claim 1, wherein the lifting system comprises at least one measuring device configured to measure the tension and/or torque characteristics of each load cable, and a processor adapted to process said measured tension and/or torque characteristic.

9. A lifting system as claimed in claim 8, wherein the at least one measuring device comprises a load cell, accelerometer and/or gyroscope.

10. A lifting system as claimed in claim 9, wherein the controller is configured to actuate each motor to impart a rotational force to its respective load cable in response to measurement obtained from the accelerometer and/or gyroscope.

11. A lifting system as claimed in claim 1, wherein the anti-cabling device is self-controlled or automated.

12. A lifting system as claimed in claim 1, wherein the anti-cabling device is driven by direct control or wireless control.

13. A lifting system as claimed in claim 12, wherein the anti-cabling device is driven from a surface vessel, a remotely operated underwater vehicle or subsea communication device.

14. A method comprising: (i) providing the multi-cable subsea lifting system as claimed in claim 1; (ii) connecting the subsea anti-cabling device to the load cables at an attachment point; (iii) connecting the load to a connector on the base of the anti-cabling device; (iv) raising or lowering the load by extending or distending the load cables from the load-cable lifting apparatus; (v) actuating one or more motors to impart a rotational force to a respective load cable in response to measurements obtained from the respective torque measuring device.

15. A method as claimed in claim 14, wherein a load-balancing sheave is used to connect the load to a connector on the base of the anti-cabling device.

16. The lifting system as claimed in claim 1, wherein the one or more anti-cabling devices are positioned at the subsea attachment point, the subsea attachment point being configured to attach to a load to be lifted by the subsea lifting system.

17. The lifting system as claimed in claim 1, wherein the torque measuring device is positioned subsea.

18. The lifting system as claimed in claim 1, wherein the rotational force rotates its respective load cable with respect to a longitudinal axis of the load cable.

19. The lifting system as claimed in claim 1, wherein the rotational force rotates the load cable counter to the twisting of the load cable detected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention, and embodiments of the development of the present invention, will now be described by way of example only and with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic side view of a multi-cable subsea lifting system according to an embodiment of the present invention;

(3) FIG. 2 is a side view of a first embodiment of a subsea anti-cabling device for use in the lifting system of FIG. 1;

(4) FIG. 3 is a front view of the anti-cabling device of FIG. 2,

(5) FIG. 4 is an exploded view of some of the components of the anti-cabling device of FIG. 2;

(6) FIG. 5 is a schematic view of a second embodiment of an anti-cabling device in accordance with the invention depicting the connection of a load-bearing sheave to the base thereof;

(7) FIG. 6 is a schematic view of a development of the anti-cabling device of the present invention;

(8) FIGS. 7a and 7b are simplified side and top views inside the anti-cabling device of FIG. 6 showing a first gear train;

(9) FIGS. 8a and 8b are simplified side and top views inside another anti-cabling device according to this development of the present invention; and

(10) FIG. 9 is a perspective view of another anti-cabling device from FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS

(11) Referring to FIG. 1, a multi-cable subsea lifting system in accordance with the invention is shown. The lifting system comprises two load-cable lifting apparatus 2a, 2b, and two load cables 4a, 4b respectively extending from each load-lifting apparatus 2a, 2b to a subsea attachment point. The load-cable lifting apparatus 2a, 2b are located on a vessel 6, such as pipe laying service vessel or PLSV, on a sea 8.

(12) Each load-cable lifting apparatus 2a, 2b could be a winch or sheave, generally able to provide control for the movement of the respective load-cable 4a, 4b through the sea 8 to raise and lift a load 10.

(13) FIG. 1 also shows a seabed 12, which could be any distance below the surface of the sea 8, and towards which and optionally onto which it is desired to guide the load 10. However, the greater the subsea depth for location of the load 10, such as increasingly beyond 2000 or even 3000 meters, and the greater the actual load 10, such as being hundreds of tonnes, (increasingly up to or greater than 400 tonnes), then the greater is the desire to use multi-cable subsea lifting systems for obvious engineering reasons, compared with conventional single lifting cables or single cable lifting systems.

(14) The load cables 4a, 4b in FIG. 1 can be provided from one or more reels (not shown) to the load-cable lifting apparatus 2a, 2b in a manner known in the art. The nature, design and operation of the load-cable lifting apparatus 2a, 2b, and the nature, design, etc. of the load cables 4a, 4b, are not limiting in the present invention, and can be those conventionally used and operated.

(15) It will also be appreciated that FIG. 1 is a schematic drawing intended to show the present invention, and is not dimensionally accurate in relation to the relative sizes of the features shown. In particular, the distance between the load cables 4a, 4b could be any suitable distance, optionally based on or according to the load operation, the nature and number of the load cables etc., and possibly the load-lifting apparatus. For example, the distance between the load cables could be less than 1 m, 1 m, or greater than 1 m, such as 2 m, 3 m, 4 m, 5 m, or even more.

(16) With a distance between the load cables of less than 1 m, or possibly only a few meters, it can be appreciated that, as the extent of the parallel winch operation is greater with increasing depth operation, the potential for cabling increases, where the load cables could move relative to one another, in particular, come closer to one another and even result in rotational entanglement.

(17) Whilst this may seen more expectant for a two-cable subsea lifting system, the problem can occur also with multi-cable subsea lifting systems using more than two cables, especially where the lifting system may be divided into subsets or pairs of cables, each subset comprising closely spaced cables.

(18) Thus, the present invention extends to aiming to relatively maintain a defined divide or distance or space between any two load cables in a multi-cable subsea lifting system.

(19) Indeed, the present invention also extends to aiming to simultaneously relatively maintain the defined divide, distance or space between more than two cables, generally running in parallel operation, by extension of the subsea anti-cabling device imparting a rotational force to one or more of the load cables in response to and to counter the torque experienced by the load cable.

(20) FIG. 1 shows the load cables 4a, 4b extending to a subsea attachment point. FIG. 1 also shows a measuring device in the form of a tension/torsion load cell 14 able to provide tension and torsion information to a monitor or control (not shown) to identify the on-going tension and torsion of each load cable 4a, 4b to an operator.

(21) The system further comprises a subsea anti-cabling device 20 and a torque measuring device 22 associated with each load cable 4a, 4b.

(22) Referring to FIGS. 2 to 4, a first embodiment of a subsea anti-cabling device 20 for use in the lifting system in accordance with the invention is shown.

(23) The anti-cabling device 20 is connected to the load cables 4a, 4b at the attachment point and comprises two or more load-cable terminations 26 for connection with a respective load cable 4a, 4b.

(24) The load-cable terminations 26 may be in any suitable form for connecting the load cables 4a, 4b to the anti-cabling device 20. For example, the load-cable terminations 26 may comprise a wedge socket, socket-resin connection or spelter socket. In the embodiment shown, the load-cable terminations 26 are in the form of a spelter socket.

(25) In the embodiment shown, the anti-cabling device 20 comprises a symmetrical arrangement for each load cable 4a, 4b deployed in parallel.

(26) The anti-cabling device 20 comprises a motor 24 connected to a respective load-cable 4a, 4b. The motor 24 may be any suitable motor capable of imparting a rotational force to the respective load cable 4a, 4b. In the embodiment shown, the motor 24 is in the form of a stepper motor.

(27) Each stepper motor 24 is battery operated and the lifting system comprises one or more batteries 32 for powering the stepper motors 24. In the embodiment shown, each stepper motor 24 is powered by its own battery 32 which is housed within the anti-cabling device. While the motors 24 are shown as being battery operated, it would be understood that the motors may instead be electrically operated or operated by a different power source.

(28) Each motor 24 is directly connected to the load-cable termination 26, and hence the respective load cable 4a, 4b, via a shaft 28 (see FIG. 4). It would be understood that each or one of the motors 24 may be indirectly connected to a respective load cable 4a, 4b by suitable means.

(29) The torque measuring device 22 is in the form of a torque sensor which comprises a rotating disc encoder. The torque sensor 22 is mounted on the shaft 28 and a thrust bearing 42 is positioned between the torque sensor 22 and the load-cable termination 26.

(30) The system further comprises a controller 30 in communication with each motor 24 and torque sensor 22. The controller 30 is configured to actuate each motor 24 to impart a rotational force to its respective load cable 4a, 4b in response to measurements obtained from the torque sensor 22.

(31) A processor 34 is provided which is adapted to process the measured tension and torque characteristics of each load-cable 4a, 4b. The tension and torque characteristics of each load-cable 4a, 4b may be determined via the load cell 14 and/or at least one auxiliary measuring device configured to measure the tension and torque characteristics of each load-cable 4a, 4b. The auxiliary measuring device(s) may be in the form of a second load cell arrangement, accelerometer and or gyroscope.

(32) In the embodiment shown, the system comprises an auxiliary measuring device in the form of a gyroscope 36.

(33) The gyroscope 36 is configured to continuously feed heading and/or orientation data to the processor 34.

(34) The processor 34 is operably linked to the controller 30 and torque sensor 22, and the amount of rotational force imparted by the motor(s) will be determined by the controller 30 based on feedback/information received from the processor 34.

(35) The components of the anti-cabling device 20 associated with a load cable 4a, 4b, i.e. processors 34, controller 30, auxiliary measuring device etc., are in communication with the components associated with another load cable 4a, 4b. The connection between the components may be a wireless connection or a wired connection.

(36) The anti-cabling device 20 comprises a connector in the form of a pair of base plates 40 depending from the base thereof to facilitate the connection of the load 10 to the anti-cabling device 20.

(37) The lifting system may be configured such that the anti-cabling device 20 is self-controlled or automated by incorporating a software run by the processor 34 which determines the permitted tension and/or torsion tolerances experienced by the load cables 4a, 4b and when the controller 30 can activate/deactivate the motor(s).

(38) Alternatively or in addition, the anti-cabling device 20 may be driven by direct control or wireless control. In such an arrangement where the anti-cabling device 20 is driven by direct control or wireless control, the anti-cabling device 20 may be driven from a surface vessel, a remotely operated underwater vehicle or subsea communication device.

(39) In such an arrangement, information about the subsea lifting system can be provided to a control or monitor via one or more video links, such as from one or more ROVs (not shown), to assist with the activation of the anti-cabling device 20 in response to excessive torsion being experience by one or more of the load cables 4a, 4b. Data from the processor 34 will be transmitted to the control or monitor via a suitable link, for example a wireless link. The link is preferably a two way link such that any commands sent to the processor 34 from the control or monitor are sent through the same link.

(40) With increasing extension or depth of the load cables 4a, 4b, and possibly based on sea conditions both above the surface of the sea 8, (such as the heave of the vessel 6) and in the sea 8, the possible or expected locations or areas of the risk of cabling may be known or identifiable or otherwise predicable. Additionally or alternatively, monitoring of the status of the tension and/or torsion of the load cables 4a, 4b, through the load cell 14, auxiliary measuring devices, or one or more other monitors, including visual monitors from for example ROVs, can indicate locations or areas of risk of cabling during the operation of the lifting system.

(41) Thus, it is possible for the user or operator of the subsea lifting system to activate the anti-cabling device 20 when the onset of cabling is identified and monitor the effect of the anti-cabling device 20 in reducing the possibility of cabling occurring.

(42) Referring to FIG. 5, a second embodiment of a anti-cabling device 120 in accordance with the invention is shown. The reference numerals for similar features of the second embodiment to those of the first embodiment have been increased by 100 for convenience, while the same reference numerals have been used for identical features. For example, the load terminations which were indicated by the reference numeral 26 in the first embodiment are now indicated by the reference numeral 126.

(43) The embodiment differs from the previously describe embodiment in that rather than having the components of the anti-cabling device 120 associated with each load cable 4a, 4b housed in the same housing, the components are housed in separate housings. In the embodiment shown, the anti-cabling device 120 comprises two parts 121a, 121b, each part comprising the components associated with a respective load cable 4a, 4b.

(44) FIG. 5 also depicts a way of connecting the load 10 to the anti-cabling device 120.

(45) In the embodiment shown, the load 10 (not shown) is connected to the anti-cabling device 120 by way of a load-bearing sheave 150. The load-bearing sheave 150 has the advantage in that it mechanically ensures load balance is maintained between the two parts 121a, 121b of the anti-cabling device 120. Each part 121a, 121b of the anti-cabling device 120 being associated with a respect load cable 4a, 4b.

(46) Each part 121a, 121b of the anti-cabling device 120 comprises a connector having at least one base plate 140 depending from the base the anti-cabling device 120. The load-bearing sheave 150 is connected to the at least one base plate 140 by means of a wire rope 152 from which the load-bearing sheave 150 is suspended. The wire rope 152 comprises a diameter D that is greater than the diameter d of the load cables 4a, 4b. In this way, any torsion applied by the anti-cabling devices 120 will be passed onto the smaller diameter load cables 4a, 4b.

(47) The orientation and distance of the parts 121a, 121b of the anti-cabling device 120 relative to the load-balancing sheave 150 is determined by the auxiliary measuring device and communicated between the parts 121a, 121b. The depicted embodiment shows the communication in the form of a wireless communication.

(48) In order to raise or lower a subsea load 10 using the multi-cable subsea lifting system in accordance with the invention, a user or operator has to preform at least the steps of:

(49) (i) connecting the subsea anti-cabling device 20, 120 to the load cables 4a, 4b at the attachment point;

(50) (ii) connecting the load 10 to a connector 40, 140 on the base of the anti-cabling device 20, 120;

(51) (iii) raising or lowering the load 10 by extending or distending the load cables 4a, 4b from the load-cable lifting apparatus 2a, 2b;

(52) (iv) actuating one or more motors 24 to impart a rotational force to a respective load cable 4a, 4b in response to measurements obtained from the respective torque measuring device 22.

(53) FIG. 6 shows a development of the present invention to provide a multi-cable subsea lifting system comprising two load-cable lifting apparatus (not shown, but optionally the same or similar to those shown in FIG. 1); a load cable 204a, 204b extending from each load-cable lifting apparatus to a subsea load attachment point 208; and a subsea anti-cabling device 210.

(54) Parts of the subsea anti-cabling device 210 in FIG. 6 are shown in FIGS. 7a and 7b. It comprises a gear train 212 comprising gear wheels 214 labelled A and B attached to and symmetrically connected to each load cable 204a, 204b respectively, wherein the gear wheels 214 are inter-operably connected so that movement of one will provide or affect movement of the other. The load cables 204a, 204b and the gear wheels 214 can be connected by the same connection means as described previously for the connection between the load cables 4a, 4b and the motor 24, such as a load-cable terminations

(55) FIG. 7b in particular shows that following rotational motion of, for example, the load cable 204a, the inter-operability of the gear wheel A results in opposite rotational motion of the other gear wheel B, and thereby of the second load cable 204b, in an equal and opposite direction, assuming that the gear size or ratio, etc. of the gear wheels 214 is the same. Torsional balance is therefore achieved between the load cables 204a, 204b.

(56) FIGS. 8a and 8b show the internal working of an alternative arrangement in the subsea anti-cabling device 210, comprising a gear train 216 having two outer gear wheels labelled F and D attached to each of the load cables 204a, 204b respectively, and two intermediate gear wheels labelled E and C, able to rotate on their own axes 218, such that rotational movement of one outer gear wheel F (due to torque in load cable 204a) can still impart drive through the gear train 216 to the other outer gear wheel D to produce the same rotational effect as shown in FIG. 7b, without direct connection between the outer gear wheels F and D.

(57) FIG. 9 shows a further alternative subsea anti-cabling device 230 having four load cables 232, which may be based on two parallel load cables 232a derived from one lifting apparatus (not shown), and two parallel load cables 232b derived from a second lifting apparatus (not shown). Such a load cable lifting arrangement is known in the art. FIG. 9 shows developing a gear train based on inter-operability between either (i) each of the sets (x) of parallel cables 232a, 232b for each lifting apparatus, thereby using two gear trains and/or two anti-cabling devices, or (ii) by connection of two or more gear trains through an intermediate arrangement (y), such as that shown in FIGS. 8a and 8b, or (iii) the complete inter-operability of all the gear wheels connected to each of the loads cables 232. Each of these arrangements provides inter-cable rotational drive, which drive may be controlled by one or more controllers (not shown) either directly or indirectly connected to the load cables 232, and optionally based on the provision of one or more load cable rotation measurement devices (not shown) such as torque meters and the like.

(58) The development of the present invention as described in relation to FIGS. 6-9 provides the same benefits and advantages as described hereinbefore for the present invention, and again in particular for lifting apparatus involved at increased depth capacity for parallel winch operations. The development of the present invention provides use of an anti-cabling device which reduces the risk of cabling for parallel wire rope applications, in particular for lowering and recovery operations. The development may be self controlled (passive) or automated by use of a load cell, etc, with appropriate electronics capable of measuring, capturing, post-processing and/or responding to real time tension and torque characteristics of each load cable, either individually or cumulatively.

(59) The skilled man can understand the application of some or all of the embodiments described hereinabove in relation to the present invention apply equally to embodiments of the development of the present invention described, such that the development of the present invention uses some or all of the embodiments of the present invention, in the same or similar position, construction, arrangement, positioning etc., as described herein, and in the same or similar manner, in order to provide the same or similar benefit or effect. The present invention provides a subsea anti-cabling device able to be deployed in a multi-cable subsea lifting system to reduce the risk of cabling. In particular, the anti-cabling device can be positioned between the load cables and load to counter any torque experienced by the load cables. This increases the competitive advantage of the use of multi-cable lifting systems compared with single cable lifting systems, and thus their commercial applicability to use at increasing depth capacity for parallel winch operations. In particular, it can provide the user or operator with greater confidence of the use of multi-cable subsea lifting systems at greater depths, by aiming to reduce or even avoid completely one of a disadvantage associated with multi-cable subsea lifting systems.

(60) While a number of components of the lifting system have been shown incorporated in the anti-cabling device, it should be understood that they may be positioned at different locations within the lifting system.

(61) Furthermore, the controller may be configured to actuate each motor to impart a rotational force to its respective load cable in response to measurement obtained from the accelerometer and/or gyroscope or other heading instrumentation.

(62) While the multi-cable subsea lifting system has been described with two subsea anti-cabling devices, each connected to a load cable, it should be understood that it is not limited thereto. For example, the lifting system may comprise a single anti-cabling device or the lifting system may comprise a first anti-cabling device connected to the load cable as described above with a second anti-cabling device directly connected to another device such a spreader beam or balancing sheave etc.

(63) Various modifications and variations to the described embodiments of the invention will be apparent to those skilled in the art without departing from the scope of the invention as defined herein. Although the invention has been described in connection with specific preferred embodiments it should be understood that the invention as defined herein should not be unduly limited to such specific embodiments.