WO2001062582A2 - Offshore loading of hydrocarbons to a projecting arm of a vessel - Google Patents

Abstract

The invention relates to a means for offshore loading of hydrocarbons from a stationary loading station (1) to a dynamically positioned vessel (2) which during the loading is rotated according to the prevailing wave direction, in which the hydrocarbons are transported through at least two flexible loading pipes (61-65) suspended in separate arcs from the loading station (1) to intake couplings (71-75) arranged on a projecting arm (6) of the vessel (2), wherefrom the hydrocarbons are transported through pipes and swivels to a receiving plant (7) on the vessel (2). The arm (6) comprises an inner arm (3) with at least one inner arm pipe (31-33) which is connected to the receiving plant (7) on the vessel (2), and an outer arm (5) with at least one outer arm pipe (51-53) which is connected to at least one of the intake couplings (71-75). The inner arm (3) and the outer arm (5) are articulated (12) in a first vertical axis (10), and the inner arm pipes (31-33) are connected to the outer arm pipes (51-53) via at least one transfer swivel (81-83) arranged in the first vertical axis (10).

Description

Offshore loading of hydrocarbons to a projecting arm of a vessel

The invention relates to a means for offshore loading of hydrocarbons from a stationary loading station to a dynamically positioned vessel which during the loading is rotated according to the prevailing wave direction, in which the hydrocarbons are transported through at least two flexible loading pipes suspended in separate arcs from the loading station to intake couplings arranged on a projecting arm of the vessel

When producing hydrocarbons from reservoirs located underneath the sea floor, it is often desirable to load the hydrocarbons to a vessel for storage or transport ashore This loading can be done from a floating storage buoy, a fixed or floating storage tank, or from production equipment located on the sea floor The vessel may be a tanker, but it can also be another structure, e g a floating platform structure

The vessel can during the loading be kept essentially stationary by anchoring or dynamic positioning In dynamic positioning sensors all the time detect the position and movement of the vessel, and based on signals from the sensors, propellers which bring the vessel towards the desired position are controlled When loading to a dynamically positioned ship it is required that the ship is lying with the bow against the prevailing wave direction, possibly the prevailing wind direction To be able to load in all weather conditions, the ship must therefore be able to rotate 360° during the loading Some places with steady wind direction it is sufficient with a smaller rotation of the ship, e g 270° When loading to other types of vessels than ships there may be a similar need to rotate the vessel If the weather gets too bad, and the vessel's movement gets to big, the couplings between the loading pipes and the vessel are released, in order not to damage the loading pipes or the couplings In the loading one or more loading pipes which have to be flexible are used, since the vessel due to the motion of the sea never will be absolutely quiescent Due to requirements to strength, the loading pipes are still rather stiff, and must be treated with care If nothing is done to prevent it, said rotation of the vessel during a dynamic positioning will result in a twisting of the loading pipe or loading pipes, and, if there is more than one loading pipe, the loading pipes may contact each other and rub against each other and attack each other by lateral forces, which may result in a damage to the loading pipes

Loading of hydrocarbons can be done from a subsea buoy to a turret on the underside of a ship This is a technically good solution which may be used in waters with high sea, but it is expensive

The loading of hydrocarbons can also be done to an arm of a ship, which has a more reasonable cost than using a ship with a turret GB 2 168 939 describes loading of hydrocarbons from a piping system on the sea floor to a ship via a riser containing several pipes The riser extends from a foundation on the sea floor to a buoy which via a multiswivel can be connected to an arm of the ship The multiswivel includes several concentric annuh, which on the underside of the swivel are connected to its individual pipe, and on the upper side of the multiswivel are connected to pipes which transport the hydrocarbons to the ship The hydrocarbons in the different pipes can thereby be separately transported through the multiswivel, while at the same time the ship is allowed to rotate The above mentioned problem related to rubbing and lateral forces between the pipes due to mutual contact during a rotation of the vessel is thereby solved The multiswivel with several concentric annuh, is, however, a complicated and expensive device, and it is therefore desirable to solve the problem in a simpler and less expensive way

Norwegian patent application No 20000739 describes a method and a means for offshore loading of hydrocarbons from a stationary loading station to a dynamically positioned vessel which during the loading is rotated according to the prevailing wave direction, in which the hydrocarbons are transported through at least two flexible pipes suspended in separate arcs from the loading station to the vessel Each of the pipes are in their one end suspended from a swivel arranged in the loading station, and in their other end suspended from a swivel arranged in the vessel The rotation of the vessel according to the prevailing wave direction is carried out as a combination of a rotation of the vessel around its own axis and a movement along an arc around the loading station

The object of the invention is to provide a means to be used in offshore loading of hydrocarbons from a stationary loading station to a dynamically positioned vessel by means of loading pipes, in which the vessel during the loading is rotated according to the prevailing wave direction, which rotation shall not or only to a small extent cause twisting of the loading pipes or contact between the loading pipes

According to the invention the object is achieved with a means of the type which is mentioned in the introduction and which is characterised by the features of the claims The invention thus relates to a means for offshore loading of hydrocarbons from a stationary loading station to a dynamically positioned vessel which during the loading is rotated according to the prevailing wave direction, in which the hydrocarbons are transported through at least two flexible loading pipes suspended in separate arcs from the loading station to intake couplings arranged on a projecting arm of the vessel The loading station may be a floating buoy or subsea buoy or a subsea manifold which is connected to a piping system on the sea floor, or another fixed or floating structure, e g a loading arm of a storage buoy Preferably the loading pipes hang in catenaries, since this causes the smallest stress both to the loading pipes and the intake couplings, but this is no requirement for the invention

In a first aspect of the invention the arm comprises an inner arm with at least one inner arm pipe connected to a receiving plant on the vessel, and an outer arm with at least one outer arm pipe connected to at least one of the intake couplings The inner arm and the outer arm are articulated in a first vertical axis, and the inner arm pipes and outer arm pipes are interconnected via at least one transfer swivel arranged in the first vertical axis

In another aspect of the invention the arm in addition to the inner arm and the outer arm also comprises an intermediate arm with at least one intermediate arm pipe, arranged between the inner arm and the outer arm The inner arm and the intermediate arm are articulated in a first vertical axis, and the intermediate arm and the outer arm are articulated in a second vertical axis The inner arm pipes and the intermediate arm pipes are interconnected via at least one transfer swivel arranged in the first vertical axis, and the intermediate arm pipes and the outer arm pipes are interconnected via at least one transfer swivel arranged in the second vertical axis

When loading hydrocarbons the vessel with the inner arm can be rotated, while the outer arm is essentially stationary If the arm also comprises an intermediate arm, this can at initial rotation be essentially stationary, it can follow the rotation of the inner arm, or it can take an intermediate position When a large rotation of the vessel takes place, the intermediate arm will have to take an intermediate position between the rotated positions of the inner arm and the outer arm

When the outer arm is essentially stationary, the loading pipes which are connected to the outer arm are also essentially stationary, and there are no twisting of the loading pipes and no contact between the loading pipes

In the first aspect of the invention, in which the arm does not comprise any intermediate arm, it is not possible to rotate the vessel as much as 360° without rotating the outer arm In order to achieve a rotation of the vessel of 360° the outer arm may be rotated a little, which only causes a small twisting of the loading pipes In the second aspect of the invention, in which the arm also comprises the intermediate arm, the vessel can be rotated 360° without a rotation of the outer arm If it is desirable, it is however, also in this case possible to rotate the outer arm a little

Preferably the intake couplings comprises swivels which allow a rotation of the outer arm without transferring this rotation to the loading pipes Regardless of whether the intake couplings comprises swivels or not, the required rotation of the outer arm is so small that no contact between the loading pipes take place

Since the transfer swivels which connect the inner arm pipes, the outer arm pipes and possibly the intermediate arm pipes are arranged in the vertical axes which form joint axes for the inner arm, the outer arm and possibly the intermediate arm, the transfer swivels are rotated simultaneously with and just as much as the inner arm, the outer arm and possibly the intermediate arm Thereby no twisting or displacement of the inner arm pipes, the outer arm pipes and possibly the intermediate arm pipes take place during the rotation of the vessel The inner arm pipes, the outer arm pipes and possibly the intermediate arm pipes may comprise branchings or interconnections Preferably, however, each inner arm pipe is, possibly via a corresponding intermediate arm pipe, connected to a corresponding outer arm pipe via a transfer swivel arranged in the or each vertical axis, the inner arm pipes and the outer arm pipes are thereby connected in a one to one configuration The outer arm pipes, the inner arm pipes, and possibly the intermediate arm pipes thereby form continuous pipes from the outer arm to the inner arm, where from the pipes continue to the receiving plant

The relative rotation of the inner arm, the outer arm and possibly the intermediate arm can be carried out by actuators, which may be hydraulic cylinders The intake couplings and the outer arm pipes are preferably connected via an intake manifold, for branching off or combination of fluid flows between the loading pipes and the outer arm pipes In this way it is possible to use a different number of loading pipes and outer arm pipes, which may be relevant due to different content and different flow conditions in the pipes The invention will now be explained in more detail in connection with a description of specific embodiments, and with reference to the drawings, in which fig 1 illustrates a ship which is loading hydrocarbons from a loading station via an arm, fig 2 illustrates an embodiment of the arm in fig 1 in a larger scale, shown in a mid position, fig 3 illustrates the arm in fig 2 in a 90° position, fig 4 illustrates the arm in fig 2 in a 90° position, in which the loading pipes are slightly twisted, fig 5 illustrates another embodiment of the arm in fig 1 shown in a mid position, fig 6 illustrates the arm in fig 1 in a 90° position, fig 7 illustrates the arm in fig 5 in a 180° position

Fig 1 illustrates a vessel in the form of a ship 2 which is lying in the sea, and which is loading hydrocarbons in the form of oil from a stationary loading station 1 The loading station 1 is a subsea manifold which is connected to a piping system 15 on the sea floor, which in turn is connected to not illustrated oil producing wells in a hydrocarbon reservoir

Five flexible loading pipes 61-65 are suspended in separate arcs from the subsea manifold 1 to intake couplings 71 -75 arranged on the underside of an outwardly projecting arm 6 of the ship 2 The intake couplings 71 -75 is not illustrated in fig 1 , but is shown in fig 5 and 6

The separate arcs of loading pipes 61 -65 are between the subsea manifold 1 and the ship 2 arranged over a horizontal, cylindrical subsea buoy 16 which is connected to the sea floor by a mooring cable 9 The purpose of the subsea buoy 16 is to relieve the tension in the loading pipes 61 -65

The intake couplings 71 -75 are arranged in a coupling buoy 8 (see fig 5), which is attached to the arm 6 by not illustrated releasable couplings If the weather gets too bad, the loading pipes 61-65 have to be disconnected from the ship 2, in order not to be damaged by strains from the waves and movements of the ship The releasable couplings which keep the coupling buoy 8 secured to the arm 6 is then uncoupled, and the coupling buoy 8 with the loading pipes 61 -65 falls down in the sea, and remain suspended from the subsea buoy 16 The coupling buoy 8 comprises buoyant bodies, and will therefore seek to the surface, which makes it possible to find it when it again is desirable to connect it to the arm 6 During the loading the oil is transported from the wells, through the piping system 15 on the sea floor, through the loading pipes 61-65, the intake couplings 71-75 to pipes in the arm 6, which will be discussed in more detail in the following description of the invention From the arm 6 the oil is transported to a receiving plant 7 comprising process equipment and storage tanks in the ship 2 Thus, the loading takes place simultaneously with the production, but it should be understood that the invention is equally useable when loading from a storage buoy The arm 6 is in fig 1 illustrated in a side of the ship 2 It should, however, be understood that the invention, as it will be explained in the following, is not dependent upon the location of the arm 6, and that it could have been located e g in the bow of the ship It should further be understood that the invention is equally useable when loading gas, or for water injection or gas injection in the hydrocarbon reservoir The ship is kept essentially stationary by dynamic positioning, which means that sensors all the time detect the position and movements of the ship, and based on signals from the sensors, propellers which bring the ship towards the desired position are controlled When loading to a dynamically positioned ship it is required that the ship is lying with the bow against the prevailing wave direction, possibly the prevailing wind direction, and to be able to load during all weather conditions, the ship must therefore be able to rotate 360° during the loading

Fig 2 illustrates an embodiment of the arm in fig 1 in a larger scale The arm 6 comprises an inner arm 3 and an outer arm 5 which are formed by framework 17 comprising beams and bracing The inner arm 3 and the outer arm 5 are via joints 12 articulated in a first vertical axis 10, the outer arm 5 is thereby pivotal relative to the inner arm 3 and the ship 2 in the horizontal plane Fig 2 illustrates the arm 6 in a mid position, pointing perpendicularly out from the ship 2 When the ship 2 due to a change of the prevailing wave- or wind direction during the loading of oil is rotated away from the mid position, the outer arm 5 is kept essentially stationary, and the loading pipes 61 -65 are therefore also essentially stationary, while the inner arm 3 follows the ship

On the inner arm 3 there is arranged three inner arm pipes 31 -33, which on the ship 2 continue as receiving pipes 101 -103 which are connected to the receiving plant 7 for the hydrocarbons Correspondingly on the outer arm 5 there is arranged three outer arm pipes 5 1 -53 which via permanent couplings 21 -23, e g in the form of flanges, are connected to the intake couplings 71 -75, see fig 5 The arm 6 is schematically illustrated, and it should be understood that it may also comprise a gangway, handrail, pipe supports and other items which do not take part of the invention The inner arm pipes 31-33 are connected to the outer arm pipes 51 -53 via transfer swivels 81 -83 arranged in the first vertical axis 10 Since the transfer swivels 81 -83 are arranged in the first vertical axis 10 which form a joint axis for the relative rotation of the inner arm 3 and the outer arm 5, the transfer swivels 81 -83 are rotated simultaneously with and just as much as the relative rotation of the inner arm 3 and the outer arm 5 Thus, no twisting or displacements take place between the inner arm pipes 3 1 -33 and the outer arm pipes 5 1-53 during rotation of the ship 2

It is seen that every inner arm pipe 3 1 -33 is connected to a corresponding outer arm pipe 1 -53 via a corresponding transfer swivel 81-83 It is thereby formed continuous pipe connections from the permanent couplings 21-23, through the outer arm pipes 5 1 -53, through the transfer swivels 81 -83, the inner arm pipes 31 -33 and further on to the receiving pipes 101 -103 for transfer of oil from the loading pipes 61 -65 Fig 3 illustrates the arm 6 in a 90° position, l e a position in which the ship 2 with the inner arm 3 is rotated 90° relative to the outer arm 5 It is understood that the ship 2 with the inner arm 3 could have been rotated 90° in the opposite direction, the total possible rotation without any rotation of the outer arm 5 is thereby 180° Fig 4 illustrates the arm 6 in a 90° position, l e the same position as in fig 3, but both the ship 2, the inner arm 3 and the outer arm 5 are further rotated 90° Compared to the mid position, illustrated in fig 1 and 2, the ship is thereby rotated 180°, and by rotating the ship 2 between the position illustrated in fig 4 and a position in which the ship is rotated 180° in the opposite direction, it is thereby possible to rotate the ship 360° It is seen that the intake couplings 71 -75 (see fig 5) are arranged in a row, and that the loading pipes 61 -65 are rotated relative to each other, causing a plane which is formed by the arcs of the loading pipes to be somewhat twisted The loading pipes 61 -65 do, however, not contact each other If the intake couplings 71-75 are fixed (non-rotatable) connections, the rotation of the outer arm 5 will cause a twisting of the loading pipes 61 -65 The intake couplings

71 -75 may, however, comprise swivels, and in this case a rotation of the outer arm 5 will not cause a twisting of the loading pipes Whether a rotation of the loading pipes is acceptable or not will have to be evaluated in every single case, based on the length, flexibility and strength of the loading pipes The inner arm 3 and the outer arm 5 can be freely rotatable relative to each other, and the position of the outer arm 5 will then be determined by the loading pipes 61 -65 It is, however, preferred that the rotation of the inner arm 3 relative to the outer arm 5 is controlled by the same system which controls the dynamic positioning of the ship 2 This can be done by an actuator for relative rotation of the inner arm 3 relative to the outer arm 5 in the first vertical axis 10 Such an actuator can be formed by a gear πm which is permanently secured to the outer arm 5, with a centre in the first vertical axis 10, and a hydraulic motor which is permanently secured to the inner arm 3, and which via a cog wheel rotates the gear rim, causing a rotation of the outer arm 5 The hydraulic motor may in turn be controlled by the dynamic positioning system which, based on signals from a detector which e g via the same gear πm detects the rotational position of the outer arm, controls the supply of hydraulic oil to the motor

Fig 5 illustrates an embodiment of the arm 6 which comprises an inner arm 3 with three inner arm pipes 31 -33, which via receiving pipes 101 -103 are connected to a receiving plant 7 on the ship 2, an intermediate arm 4 with intermediate arm pipes 41-43, and an outer arm 5 with outer arm pipes 51-53 which via permanent couplings 21 -23 are connected to the intake couplings 71 -75 The inner arm 3 and the intermediate arm 4 are via joints 12 articulated in a first vertical axis 10, and the intermediate arm 4 and the outer arm 5 are via joints 13 articulated in a second vertical axis 1 1 The inner arm pipes 31 -33 are connected to the intermediate arm pipes 41-43 via transfer swivels 81 -83 arranged in the first vertical axis 10, and the intermediate arm pipes 41 -43 are connected to the outer arm pipes 51-53 via transfer swivels 91-93 arranged in the second vertical axis 1 1

What has been described about the arm 6 illustrated in fig 2-4 and its function also applies to the arm 6 illustrated in fig 5, with the same reference numerals, and this shall not be repeated It is understood that the arm 6 in fig 5 is in a mid position, in which it projects perpendicularly from the ship 2 It is further understood that what has been described with reference to fig 2-4 about the first vertical axis 10, the joints 12, the transfer swivels 81 -83 and their function equally applies to the second vertical axis 1 1 , the joints 13 and the transfer swivels 91-93, since the intermediate arm 4 forms an intermediate link between the inner arm 3 and the outer arm 5, and the intermediate arm pipes 41 -43 form intermediate pipes between the inner arm pipes 31 -33 and the outer arm pipes 51 -53 Correspondingly an actuator as described above may be used for a relative rotation of the inner arm 3 and the intermediate arm 4 in the first vertical axis 10, and a corresponding actuator may be used for a relative rotation of the intermediate arm 4 and the outer arm 5 in the second vertical axis 1 1

It is seen that every inner arm pipe 3 1 -33 is connected to a corresponding intermediate arm pipe 41-43 via a corresponding transfer swivel 81 -83 arranged in the first vertical axis 10, and that each intermediate arm pipe 41 -43 is connected to a corresponding outer arm pipe 51 -53 via corresponding transfer swivel 91 -93 arranged in the second vertical axis 1 1 It is thereby formed continuous pipe connections from the permanent couplings 21 -23 to the inner arm pipes 31-33

Fig 6 illustrates the arm in fig 5 in a 90° position, l e a position in which the ship 2 with the inner arm 3 is rotated 90° relative to the outer arm 5 It is seen that the rotation is carried out by a rotation of the joints 12 in the first vertical axis 10, while the joints 13 in the second vertical axis 1 1 has maintained the position which is shown in fig 5 The rotation could, however, have been carried out as a rotation of the joints 13 in the second vertical axis 1 1 only, or at a combination of a rotation of the joints 12 and 13 Fig 7 illustrates the arm in fig 5 in a 180° position, I e a position in which the ship 2 with the inner arm 3 is rotated 180° relative to the outer arm 5 It is seen that the rotation has been carried out by a rotation of both the joints 12 and 13 It is understood that the ship 2 with the inner arm 3 could have been rotated 1 80° in the opposite direction, the total possible rotation without rotating the outer arm 5 is thereby 360°

Fig 5 and 6 illustrate the intake couplings 71 -75 which are discussed above It is seen that the intake couplings 71 -75 and the loading pipes 61 -65 has a number of five, while the permanent couplings 21-23 and the outer arm pipes 51 -53 has a number of three The intake couplings 71-75 and the outer arm pipes 51-53 are connected via an intake manifold 14 in the outer arm 5, in which the three outer arm pipes are branched to the five loading pipes This may have economical/practical reasons, since it may be desirable to have a low number of swivels on the arm 6, while on the other hand, in order not to get too big resistance in the loading pipes, which may be very long, it is required to have a big number of loading pipes Further, the manifold enables a differentiated branching or combination of different types of fluid flows between the loading pipes 61 -65 and the outer arm pipes 51-53 An example of this is that the ship 2 simultaneously may carry out an oil loading, a gas injection and a water injection The three pipe connections on the arm is then used for different fluids, and in the manifold these pipe connections are branched off to three pipes for oil loading, one pipe for gas injection and one pipe for water injection

The invention has in the above been explained with reference to a preferred embodiment It should, however, be understood that variants of the invention are possible within the scope of the claims, e g associated with the location of the transfer swivels An example of such a variant is to locate the transfer swivels on the underside of the arm, with access to the transfer swivels via ladders from a gangway on the arm

Claims

PATENT CLAIMS

1 A means for offshore loading of hydrocarbons from a stationary loading station (1) to a dynamically positioned vessel (2) which during the loading is rotated according to the prevailing wave direction, in which the hydrocarbons are transported through at least two flexible loading pipes (61-65) suspended in separate arcs from the loading station (1 ) to intake couplings (71-75) arranged on a projecting arm (6) of the vessel (2), wherefrom the hydrocarbons are transported through pipes and swivels to a receiving plant (7) on the vessel (2), characterized in that the arm (6) comprises an inner arm (3) with at least one inner arm pipe (31 -33) which is connected to the receiving plant (7) on the vessel (2), and an outer arm (5) with at least one outer arm pipe (51 -53) which is connected to at least one of the intake couplings (71 -75), the inner arm (3) and the outer arm (5) are articulated (12) in a first vertical axis (10), and the inner arm pipes (31 -33) are connected to the outer arm pipes (51 -53) via at least one transfer swivel (81 -83) arranged in the first vertical axis (10)

2 A means according to claim 1, characterized in that each inner arm pipe (3 1 -33) is connected to a corresponding outer arm pipe (51 -53) via a transfer swivel (81 -83) arranged in the first vertical axis (10) 3 A means according to claim 1 or 2, characterized in comprising an actuator for relative rotation of the inner arm

(3) and the outer arm (5) in the first vertical axis ( 10)

4 A means for offshore loading of hydrocarbons from a stationary loading station ( 1 ) to a dynamically positioned vessel (2) which during the loading is rotated according to the prevailing wave direction, in which the hydrocarbons are transported through at least two flexible loading pipes (61 -65) suspended in separate arcs from the loading station (1) to intake couplings (71-75) arranged on a projecting arm (6) of the vessel (2), wherefrom the hydrocarbons are transported through pipes and swivels to a receiving plant (7) on the vessel (2), characterized in that the arm (6) comprises an inner arm (3) with at least one inner arm pipe (31 -33) which is connected to the receiving plant (7) on the vessel (2), an intermediate arm (4) with at least one intermediate arm pipe (41 -43), and an outer arm (5) with at least one outer arm pipe (51 -53) which is connected to at least one of the intake couplings (71 -75), the inner arm (3) and the intermediate arm (4) is articulated (12) in a first vertical axis ( 10), the intermediate arm (4) and the outer arm

(5) is articulated ( 13) in a second vertical axis ( 1 1 ), the inner arm pipes (3 1 -33) are connected to the intermediate arm pipes (41 -43) via at least one transfer swivel (81 -83) which is arranged in the first vertical axis (10), and the intermediate arm pipes (41-43) are connected to the outer arm pipes (51-53) via at least one transfer swivel (91 -93) arranged in the second vertical axis (1 1)

5 A means according to claim 4, characterized in that each inner arm pipe (31 -33) is connected to corresponding intermediate arm pipe (41 -43) via a transfer swivel (81 -83) arranged in the first vertical axis (10)

6 A means according to claim 4 or 5, characterized in that each intermediate arm pipe (41 -43) is connected to a corresponding outer arm pipe (5 1 -53) via a transfer swivel (91 -93) arranged in the second vertical axis (1 1)

7 A means according to one of the claims 4-6, characterized in comprising an actuator for relative rotation of the inner arm (3 ) and the intermediate arm (4) in the first vertical axis (10) 8 A means according to one of the claims 4-7, characterized in comprising an actuator for relative rotation of the intermediate arm (4) and the outer arm (5) in the second vertical axis (1 1)

9 A means according to one of the preceding claims, characterized in that the intake couplings (71 -75) are connected to the outer arm pipes (51 -53) via an intake manifold (14), for branching off or combining fluid flows between the loading pipes (61 -65) and the outer arm pipes (51 -53)

10 A means according to one of the preceding claims, characterized in that the intake couplings (71 -75) are arranged in a buoyant body (8)

1 1 A means according to claim 10, characterized in that the buoyant body (8) and the outer arm (5) are provided with corresponding releasable couplings

12 A means according to one of the preceding claims, characterized in that the intake couplings (71 -75) comprise swivels