GB2097749A - Marine loading arm - Google Patents

Abstract

In a marine loading arm of the kind having a riser 12, inboard arm 10 with counterbalance weight 16 and depending outboard arm 14, the counterbalancing parallelogram linkage including a connection member 36 which is positioned below the inboard arm 10 and provided with a counterbalance weight 32. <IMAGE>

Description

SPECIFICATION Marine loading arm The present invention relates to marine loading arms, which are used for transferring oil or other fluid from or to a marine tanker to a jetty alongside which the vessel is moored.

Such arms customarily have a rigid riser extending vertically from the jetty, pivotally connected to an inboard arm extending outwards from the jetty. An outboard arm pivotally connected to the outer end of the inboard arm hangs downwards and the end of the outboard arm is arranged to be connected to a pipe or conduit of the marine vessel. The arms and riser comprise rigid pipe for fluid flow, joined by swivels.

To enable free movement of the end of the outboard arm, to correspond to movement of the vessel due to tide, waves etc., it is customary that the loading arm is counterbalanced. The outboard arm pivots relative to the inboard arm. In consequence the couple on the inboard arm due to the outboard arm changes when the outboard arm moves, and the counterbalancing allows for this.

Several different arrangements are known for counterbalancing. One form, which has been commercially available for 10 years or so has a prolongation of the inboard arm past the riser and which carries a first weight at its end. An extension of the outboard arm extends above the inboard arm, and one end of a rigid connecting member pivotally connected to the end of the extension. The other end of the connecting member is connected to an intermediate point of a counterbalance arm extending upwards from the prolongation of the inboard arm. The upper end of the counterbalance arm carries a second weight.

The inboard arm, the extension of the outboard arm, the connecting member and counterbalance arm form a parallelogram arrangement above the inboard arm and the movement of the outboard arm relative to the inboard arm causes a movement of the second weight to counterbalance the changes in balance of the loading arm. Movement of the inboard arm relative to the riser is counterbalanced by the first weight.

According to the present invention there is provided a loading arm comprising an inboard arm pivotally connected to a riser; an outboard arm one end of which is pivotally connected to the inboard arm at one side of the riser; a first weight connected to a prolongation of the inboad arm at the other side of the riser; a counterbalance arm, an intermediate point of which is connected to the prolongation of the inboard arm, the counterbalance arm supporting a weight above the inboard arm and being connected to a connection member at a level below the inboard arm, the connection member extending parallel to the inboard arm, but at a lower level and being connected to an intermediate point on the outboard arm.

Such an arangement has the advantages that: a) since the outboard arm does not extend past the inboard arm, the so-called apex swivel between the inboard and outboard arms is easily accessible, for example, for replacement of the seal in the swivel; b) the load.on the apex swivel as the outboard arm moves relative to the inboard arm is reduced. This is because the forces applied to the joint due to the weight of the outboard arm and to the force applied by the connecting member are in opposite directions; and c) the structural weight at the outboard end of the inboard arm is reduced as the extension of the outboard arm is eliminated.

An embodiment of the present invention will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which: Figure 1 shows a side view of a loading arm; and Figure 2 shows an end view of the loading arm of Fig. 1, seen in the direction of arrow X in Fig. 1.

Referring first to Fig. 1 a loading arm has an inboard arm 10 connected to a riser 12.

One end of the inboard arm 10 is connected to an outboard arm 14 whilst the other end is prolonged at 1 5 past the riser to carry counterbalance weights 16. Usually, the riser 1 2 extends vertically from a dock or jetty and the outboard arm 14 hangs downwards from the inboard arm 10 to be connected to a marine vessel (e.g. a tanker) by head 18. Alternatively it is possible to mount the riser 1 2 on the vessel and connect the heat 1 8 to a pipe on the dock.

In customary manner the riser 1 2 is connected to the inboard arm 10 by a joint 20 which has two degrees of freedom, so that the inboard arm 10 can pivot about a vertical axis A-A (See Fig. 2) parallel to the riser 1 2 and about a horizontal axis B-B perpendicular to both the inboard arm 10 and the riser 12.

The outboard arm 1 4 and the inboard arm 10 are connected together by a joint 22 (the apex swivel) which has a single degree of freedom, so that the outboard arm 1 4 can pivot about a horizontal axis C (Fig. 1) perpendicular to both the outboard and inboard arms.

The head 1 8 is itself provided with three swivels 24, 26 and 28 which permit pivoting about three mutually perpendicular axes so that the end face 30 has in all six degrees of freedom relative to the riser 1 2 as is usual.

The weights 1 6 at the end of the prolongation of the inboard arm 10, counterbalance the weight of the outboard arm 1 4 and this counterbalance is maintained throughout any pivoting of the inboard arm relative to the riser 12.

However pivoting of the outboard arm 14 relative to the inboard arm 10 alters the balance of the system and it is necessary to provide a further weight 32, the movement of which is synchronised with the movement of the outboard arm 14. This permits the system to remain in balance throughout any move ment of the loading arm.

The weight 32 is supported on one end of a counterbalance arm 34, an intermediate point of which is pivoted on the prolongation 1 5 of the inboard arm 10 between the weight 1 6 and the joint 20. The other end of the coun terbalance arm 34 is pivotally connected to one end of a rigid connection member 36, the other end of which is pivotally connected to a collar 38 on the outboard arm 14.The in board arm 10 and the connection member 36 extend parallel to one another as do the outboard arm 14 and the arm 34 so that pivoting of the outboard arm 1 4 about the apex swivel 22 causes corresponding pivoting of the counterbalance arm 34 about the joint 40 by which it is attached to the inboard arm 1 2. In this way the movement of the outboard arm 14 about the apex swivel 22 can be counterbalanced by the weight 32, and hence the loading arm in fully counterbalanced.

As can be seen from Fig. 2 the counterba lance arm 34 is in the same vertical plane as the connection member 36, to which it is joined by means of a yoke 40. The collar 38 is cantilevered out from the connection mem ber 36, and lies on the opposite side to the inboard arm.

In this construction the inboard arm 10 is formed by the rigid pipe which carries fluid, -and the prolongation 1 5 is a length of pipe also. An alternative possibility, known for the prior arrangement mentioned above, and which could be used in this invention, is for the inboard arm to comprise both pipe and a supporting girder, and the girder be pro longed past the riser.

Claims (3)

1. A loading arm comprising an inboard arm pivotally connected to a riser; an out board arm with one end pivotally connected to the inboard arm at one side of the riser; a first weight connected to a prolongation of the inboard arm at the other side of the riser; a counterbalance arm, an intermediate point of which is connected to the prolongation of the inboard arm, the counterbalance arm support ing a weight above the inboard arm and being connected to a connection member at a level below the inboard arm, the connection mem ber extending parallel to the inboard arm, but at a lower level and being connected to an intermediate point on the outboard arm.

2. A loading arm according to claim 1 wherein the inboard arm between the riser and the outboard arm is formed by a pipe, and the prolongation of the inboard arm is also formed by a pipe.

3. A loading arm substantially as herein described with reference to the accompanying drawings.