GB2103745A

GB2103745A - Underwater coupling unit

Info

Publication number: GB2103745A
Application number: GB08212412A
Authority: GB
Inventors: Konrad Wilke; Bernd Michaelsen; Joachim Groger; Heinz Knappich; Hans Sander; Ingo Sauer
Original assignee: Licentia Patent Verwaltungs GmbH
Current assignee: Licentia Patent Verwaltungs GmbH
Priority date: 1981-04-30
Filing date: 1982-04-29
Publication date: 1983-02-23
Also published as: DE3117203C2; NO821401L; GB2103745B; DE3117203A1

Abstract

An underwater coupling unit (9) enables a connection to be produced between a tanker (1) and an oil transfer unit (5) anchored on the seabed and connected with an oil conveying duct (6). For steering the coupling unit (9 into the transfer unit (5) during the lowering movement, a winch system (14 to 17) is provided on the tanker (1) and a water jet drive (21) in the coupling unit (9) is supplied with pressurised water through a hose duct (8) from the tanker (1) so as to permit a control of the coupling unit in six degrees of freedom. <IMAGE>

Description

SPECIFICATION Underwater coupling unit The invention relates to an underwater coupling unit for lowering into the sea from a watercraft to produce a connection between a riser attached to the coupling unit and an oil transfer unit anchored to the seabed and connected to a source of oil.

Several systems are already known for the transfer of oil from oil-conveying ducts into tankers which then bring the mineral oil to processing plants near the coast. These systems have been primarily disigned for mineral oil fields and production installations in fairly close proximity to the coast. Thus, for example, a system has been published in a house journal of Kongsberg Engineering A.S., Norway, under the title "A new Offshore Loading System directly from the seabed". According to this publication, a tanker is positioned dynamically over a bore hole and a flexible riser is unreeied from a storage drum and lowered to the seabed by a crane. The crane is equipped with means to compensate for the heaving movement of the ship during the lowering operation.The lower end of the riser is provided with control drives and a coupling equipment which make possible a connection with the underwater connecting parts of the oil conveying duct. Thereby, loading buoys or towers at the water surface can be avoided. A substantial disadvantage of this system arises from the riser being immersed in the water at the lee side of the ship and therefore being very highly stressed in the presence of strong wave motion.

Another system, published in the journal "Offshore", March 1980, pages 61 and 62, provides a tanker with a so-called moonpool, i.e. a cylindrical opening penetrating the rump of the ship in vertical direction, through which a flexible riser with a coupling unit is lowered into the water by a crane disposed over the deck opening. The tanker had previously been positioned dynamically above the bore hole. With the aid of transponders at the bore hole head and a television camera, the coupling unit of the riser is placed onto the bore hole head, latched and the hose connection is produced.

Finally, an oil take-over equipment is known from the DE-AS 29 21 890, in which a coupling element, which is positionable by means of hydrophones and controllable by means of propellor drives, is lowered from a tanker. This coupling element is steered to a transfer unit anchored at a certain depth of water and coupled mechanically to this. Thereafter, the hose connection is produced, whereupon the oil takeover can take place.

According to the present invention, there is now provided a coupling unit for lowering into the sea from a watercraft to produce a connection between a riser attached to the coupling unit and an oil transfer unit anchored to the seabed and connected to a source of oil, the coupling unit comprising control devices to enable it to be positioned relative to the oil transfer unit and being so provided with a water jet drive unit and means couplable to a winch on board the watercraft as to be movable in six degrees of freedom, wherein the drive unit is provided with means to receive water under pressure through a hose duct from the water-craft.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which Fig. 1 is a general illustration of a tanker above an oil transfer unit anchored on the seabed Fig. 2 shows a cross-section through the tanker and a more detailed side view of the oil transfer unit and Fig. 3 shows a partly sectioned side view of a coupling unit embodying the present invention.

Referring now to the drawings, Fig. 1 shows a tanker 1 after having been positioned dynamically above a loading location. For the sake of simplicity, the positioning means are illustrated as sound transmitter and hydrophone, which are designated by the reference numeral 3 on the seabed 2 and by 4 on the watercraft 1. A transfer unit 5 is anchored on the seabed 2 and connected with an oil conveying duct 6 coming from a production platform or from oil reservoir containers. A riser 8 with a coupling unit 9 has been lowered through a moonpool 7 from the tanker and brought to and firmly connected with the transfer unit 5 with the aid of measuring systems to be described still more closely. The oil take-over can take place in this relative position of ship 1 and transfer unit 5, the position being maintained by the dynamic positioning.When the loading operation is completed, the coupling between the parts 5 and 9 is detached and the riser again taken on board the tanker which can then leave the loading place.

It is evident from the cross-section shown in Fig. 2 that the moonpool 7 is arranged asymmetrically to the longitudinal axis of the tanker 1. The moonpool contains several guide tracks, of which two are indicated by the reference numerals 10 and 11 and in which a carriage 12 with rollers 1 3 or the like is guided. The carriage 12, which is locatable in the moonpool in a lower end position as illustrated and also in an upper end position, serves for the secure guidance of the coupling unit 9 in the moonpool during the raising and lowering operations. For this purpose, the carriage 1 2 has a receptacle matched in shape to the upper end of the coupling unit 9.

The coupling unit 9 is moved on board the ship by a lifting equipment which comprises a mast 14 with a jib 15, at which deflecting rollers 1 6 and 17 are borne. A further deflecting roller 1 8 is borne with a vertical bearing axis movable in direction of double arrow 19 for compensation of movement.

The riser 8 including an oil transfer hose is connected with the coupling unit 9, guided over the rollers 16, 17 and 18, reeled up on a not illustrated storage drum and connected by its end on board with the charging and discharging system of the tanker. A double arrow 20 indicates by its upper arrow point that the oil discharge or ballast pump during the lowering operation of the coupling unit 9 conveys pressurised water out of the ballast system of the tanker through the oil transfer hose in order to bring about changes in position through control jets 21 in the coupling unit 9.

In Fig. 2, the coupling unit 9 is illustrated during the lowering operation shortly before entry into the transfer unit 5 anchored on the seabed. With the aid of measuring and monitoring systems 22 and 23 on the coupling unit 9 and the transfer unit 5, the coupling unit is so controlled that it moves by its lower conical part 24 into the funnel-shaped opening formed by inlet surfaces 25 distributed over the circumference of the transfer unit 5. The coupling unit is then lowered until a lower pipe stub 26 thereof latches mechanically with a coupling part 27 of the transfer unit 5 and the oilconducting hose connection has thus been produced. Thereafter, a ball valve in the coupling unit 9 and a further valve in the transfer unit 5 are opened by remote control from the tanker.After production of the hose connection, the oil loading pump on the production unit is switched on and the loading operation can start. The oil take-over is indicated by the lower arrow point of the double arrow 20.

In Fig. 3, the coupling unit 9 with the oil transfer hose in riser 8 and the coupling part 27 of the oil transfer unit are illustrated in greater detail partly in section. The coupling unit housing has an upper part 28 of conical or frustoconical shape to facilitate the introduction into the moonpool carriage 1 2 and a lower part 24 of similar shape for introduction into the funnel formed by the inlet surfaces 25 of the oil transfer unit. These are indicated in dashed lines in the driven-in position.

A sleeve 29 with collars, from which an appropriate recess is provided in the carriage 12, serves to protect the riser 8 during its introduction into the moonpool carriage 12. The hose duct is replaced in the interior of the coupling unit 9 by pipe members 30 and 31 and an interposed threeway valve 32. A ring duct 33 is connected to the three-way valve 32. Several, for example four ejection nozzles at right angles one to the other, of which two 21 and 21' are illustrated in the drawing, are connected with the ring duct. To provide a possibility of control, each ejection nozzle 21 can be closed off by a respective control valve 34 each provided with a throttle flap 35 and connected at 36 with a hydraulic control duct.

A coupling mechanism 26, which comprises several curved levers 37, which are distributed over the circumference and are pivoted at 38, is mounted on the lower end of pipe member 31. A compression spring 40 is placed to act between a free end 39 of the lever 37 and the housing of the coupling. In the coupled-in state as illustrated, curved ends 41 of the levers 37 bear firmly against the underside of a flange 42 of the pipe stub 27 of the tranfer unit 5 and press the flange 42 of the pipe stub 27 and a flange, which is formed at the lower end of the pipe member 31 and disposed inside the coupling mechanism 26, firmly one against the other. A ball valve in the interior of the coupling housing is operable during the positioning operation to close off the lower end of the pipe member 31.

After simultaneous production of the mechanical connection and the oil-conducting hose connection, the three-way valve 32 is switched over to conveying and the ball valves in the coupling housing 26 and in the transfer unit are then opened. Thereafter, the mineral oil brought forward in the oil conveying duct 6 can be pumped into the tanker.

When the coupling unit 9 is to be separated from the transfer unit 5 after completion of the loading operation, it is most desirable to ensure no oil issues into the sea on detaching the connection. For this purpose, after closure of the blocking valve in the transfer unit 5, the scavenging of the separating location and the hose duct in the riser 8 is initiated by a scavenging valve arranged in the coupling unit 9. To enhance inflow of sea water, a suction pump on the tanker is switched through the charging manifold to the hose duct in the riser 8. After conclusion of the scavenging operation, a piston 43 is loaded hydraulically to act through a linkage and the springs 40 to undo the latching of the parts 41 and 42 so that the coupling unit after switching over of the three-way valve 32 can again be drawn on board by the crane 14 and 15.It will then move into the moonpool carriage 12 and be guided therewith up to the upper travel limit.

In order to be able to check over the coupling unit from time to time, the crane arm 15 can be moved into a higher position and the upper end abutments from the carriage be removed. Thereby, the carriage 12 with the coupling unit 9 can be drawn upwards out of the moonpool 7 and then be put down for movement on a working stage 44 (Fig. 2) covering over the moonpool 7.

A substantial advantage of a coupling unit constructed according to the preceding description is that a connection of the oil transfer hose with the coupling part at the oil transfer unit can be produced at greater wind strengths, say up to strength 9 on the Beaufort scale. The oil transfer hose, since it is lowered into the lower lying water in the interior of the ship, is no longer highly stressed by the swell and beat of the sea.

Finally, the so-called weather window, i.e. the range of tolerable weather conditions, is widened and the oil transport from the bore location to the processing plant is thereby made more economical.

Claims

1. A coupling unit for lowering into the sea from a watercraft to produce a connection between a riser attached to the coupling unit and an oil transfer unit anchored to the seabed and connected to a source of oil, the coupling unit comprising control devices to enable it to be positioned relative to the oil tranfer unit and being so provided with a water jet drive unit and means couplable to a winch on board the watercraft as to be movable in six degrees of freedom, wherein the drive unit is provided with means to receive water under pressure through a hose duct from the watercraft.

2. A coupling unit as claimed in claim 1 in combination with a watercraft provided with a pump for discharging oil or ballast and with means to so connect the pump as to apply pressure to water and to urge the water thus put under pressure through the riser towards the coupling unit.

3. A coupling unit as claimed in claim 1, wherein the water jet drive unit is provided with throttle flaps settable by remote control through control ducts included in the riser.

4. A coupling unit as claimed in claim 1 and comprising housing means having a conical or frustoconical shape at each of the upper and lower ends thereof.

5. A coupling unit as claimed in claim 1 and comprising a measuring system arranged to determine the position and attitude of the coupling unit relative to the oil transfer unit.

6. A coupling unit as claimed in claim 1 and comprising monitoring means and control means responsive thereto.

7. A coupling unit as claimed in claim 1 and comprising means for connecting the coupling unit mechanically with the oil transfer unit and a device for making a liquid-conducting connection between the source of oil and oil transfer duct means in the riser.

8. A coupling unit as claimed in claim 7, wherein said device is adapted to operate automatically.

9. A coupling unit as claimed in claim 7, wherein said device is adapted to be operated under remote control.

10. A coupling unit as claimed in any one of claims 7 to 9 and further adapted to produce a connection between the riser and a mobile o;l transfer unit.

11. A coupling unit as claimed in claim 1 in combination with a watercraft provided with a guide shaft therethrough to receive the riser and to guide the coupling unit, when received therein, in vertical motion through the watercraft.

12. A coupling unit as claimed in claim 11, wherein the watercraft is provided with a carriage guided in the guide shaft and provided with means to receive the coupling unit.

13. A coupling unit for lowering into the sea from a watercraft to produce a connection between a riser attached to the coupling unit and an oil transfer unit, the coupling unit being substantially as hereinbefore described with reference to and as illustrated by Figure 3 of the accompanying drawings.

14. A coupling unit as claimed in any one of claims 2 and 11 to 13, the coupling unit being substantially as hereinbefore described with reference to and as illustrated by Figures 1 to 3 of the accompanying drawings.