NL1041049A

NL1041049A - Quadrant handling system.

Info

Publication number: NL1041049A
Application number: NL1041049A
Authority: NL
Inventors: Koch Kasper
Original assignee: Kci The Eng B V
Priority date: 2014-11-17
Filing date: 2014-11-17
Publication date: 2016-07-28
Also published as: NL1041049B1

Description

Quadrant handling system

The invention concerns a device for handling a so called quadrant for the installation of subsea cables, in particular during the procedure for making cable connections.

If the ends of two cables lying on the seabed are to be connected, the two ends are lifted up and pulled over a so called chute at the stem of an installation vessel onto the working deck. One cable is pulled to a so called tensioner, which is capable of clamping the cable and holding it in position. The other cable pulled around a so called quadrant, which is a half circular shaped frame which supports the cable such that the bending radius is restricted. From the quadrant the cable is pulled in the direction of the second cable end where equipment is installed to make the cable connection. After the connection is made the cable forms a loop running over the quadrant. A wire is attached to the quadrant which is then lifted up by a crane or an A-frame after which the wire is paid out to lay down the quadrant with the cable loop on the seabed.

During the lay down procedure, when the quadrant is in the water, wave loads can cause uncontrolled movements of the quadrant and the cable. Therefore the lay down procedure is sensitive to wave conditions. The maximum wave height allowing the lay down procedure is limited to about 3 meters. This wave height is further referred to as HI. The connection procedure typically takes between 24 hours and 48 hours. If the wave height increases and nearly reaches the limiting height (HI) before the connection is completed, an abandonment procedure is to be started whereby the incomplete connection is disconnected and the two cables are lowered to the seabed.

As a result of vessel motions and wave loads on the cables during the connection procedure fatigue damage to the cable gradually increases. It is therefore an advantage to minimize the duration of the connection procedure. Also the chances of an unwanted abandonment procedure are reduced if the duration of the connection procedure is short.

The handling of the quadrant by a crane or by an A-frame has several disadvantages, which will be described in the following. The inclination angle of the quadrant when it supports the cable loop and is lifted from deck by a crane should be such that the cable is guided in a straight line towards the chute. If this inclination angle is different, the cable will bend and could be damaged. A first disadvantage of handling the quadrant by a crane is that the inclination angle is difficult to control.

Another disadvantage of handling the quadrant by a crane is that the vessel motions induce uncontrolled swinging motions of the quadrant when it is lifted from deck. Uncontrolled swinging motions are unfavorable as they can result in overbending and overstressing the cable and impose risks of collision with nearby structures resulting in structural damage and safety risks for personnel. This also means that the quadrant handling procedure is limited to a maximum wave height, further referred to as H2. If the wave height increases and could exceed the maximum height (H2) of quadrant handling before the connection can be completed, the abandonment procedure is to be started, whereby the incomplete connection is disconnected and the cables are lowered to the seabed. This is unfavorable because of the time delay and the additional fatigue damage to the cable, as described in the previous. If the wave height has already exceeded the maximum height (H2) of quadrant lifting from deck, and the maximum wave height (HI) for quadrant lowering to for abandonment, the execution of the cable connection procedure is to be postponed until the moment that the wave height has reduced to an acceptable value below HI and H2. The fatigue damage to the cable increases during this period, which is unfavorable as described in the previous.

The objective of the invention is to mitigate the above disadvantages by a system which can control motions of the quadrant at all times. This is achieved by connecting the quadrant to a mechanism which can rotate and translate the quadrant from a horizontal position on deck to a vertical position over board at the required clearance from the chute, allowing the quadrant to be lowered by a winch to the seabed. The mechanism is designed such that the position and inclination of the quadrant is tangential to the chute, such that the cable is not overstressed by bending. Further this mechanism is referred to as Quadrant Handling System (QHS).

Further explanation of the invention will be given by means of figures below, which will give a practical embodiment of the invention, but may not be considered in a limiting sense, wherein:

Figure 1 shows an isometric view of a cable installation vessel and a commonly used deck arrangement for connecting two cables, which are pulled on deck from the seabed.

Figure 2 shows a side view of an installation vessel equipped with a QHS (8) according to the invention, where the quadrant (3) is moved over the main deck to the stem of the vessel and is fixed to the quadrant handling frame (8) by a pin (9).

Figure 3 shows a side view of an installation vessel equipped with a QHS (8) according to the invention, where the quadrant (3) with the cable (2) is lifted and rotated by hydraulic cylinders (10).

Figure 4 shows a side view of an installation vessel equipped with a QHS (8) according to the invention, where the quadrant (3) with the cable (2) has reached the position that is required for lowering the quadrant, and the fixing pine (9) can be removed before lowering.

Figure 5 shows a side view of an installation vessel equipped with a QHS (8) according to the invention, where the quadrant (3) with the cable (2) is lowered by paying out the cable (7) by a winch (6).

Figure 6 shows an isometric view of the QHS.

The cables (2) in figure 1 are pulled up from the seabed by a winch after connecting steel hoisting wires to the cable ends. The connection is usually made by so called Chinese fingers. A quadrant (3) is laying horizontally on the deck of the vessel (1), and consists of a half circular guide frame for the cable, which is used to control the smallest allowable bending radius of the cable. One cable is pulled around the quadrant (3) such that the two cables are in line and the connection can be made. In the conventional operation the quadrant with the cable is lifted from deck by the crane (5) and is moved to the stem of the vessel where it is lowered in the water. At the moment the quadrant is lifted from deck, the alignment of the quadrant with the cable is not fully controlled, which can result in unwanted bending and overstressing of the cable. Once the quadrant is lifted it is suspended from the crane hoisting wire and it can start swinging due to vessel motions. Swinging can result in overstressing of the cable and also result in collisions with other structures.

The configuration presented in Figure 2 shows the quadrant handling frame (8) according to the invention installed on the deck of the vessel (1) near the stem. The initial position of the quadrant (3) and the cable (2) is shown in dotted lines. The quadrant is connected to a winch (6), which can pay out the wire such that the quadrant can move backward due to the pulling tension in the cable. In the end position in figure 2 the quadrant is on top of the QHS (8) and can be fixed to the QHS by inserting a pin (9).

Figure 3 shows that the QHS with the quadrant handler is pushed up by hydraulic cylinders (10). During this rotation the winch (6) is paying out the wire (7) running over a sheave (11) under a low tension to avoid the wire becoming slack. The mechanism of the QHS is designed such that the wire and the quadrant are always in line.

In Figure 4 the position of the QHS is reached where the frame can be lowered to the seabed. Before lowering the wire (7) is tensioned to release the load from the pin (9), which can then be removed.

In Figure 5 the quadrant with the cable is finally lowered by paying out the wire (7).

Figure 6 shows the assembly of the QHS in more detail. The mechanism is formed by a lower frame (12), and upper frame (13) and two beams (16,17). A sheave is installed at the top of the upper frame which guides a wire between the quadrant (3, not shown in Fig. 6) and the winch (6, not shown in Fig. 6) on deck. The lower frame (12) and the upper frame (13) are connected by two hinges (14,15) and the two beams are connected to the upper frame by two hinges (28,29). At the bottom the lower frame is connected to the foundation on the vessel (1) by two hinges (24, 25). The two beams are also connected to the foundation of the vessel by hinges (26,27). Two hydraulic cylinders (18,19) are installed which can move the mechanism.

Claims

A structure for controlled placement of a cable and a supporting frame for the purpose of restricting the bending radius of the cable from a ship and dropping it overboard to the seabed, characterized in that all degrees of freedom of movement of three movements and three rotations of the cable supporting frame and of the cable can be checked at any time by means of a driven movable mechanism.

A structure according to claim 1, wherein the support frame can be temporarily attached to the mechanism by means of at least one pin connection.

A structure according to the preceding claims, wherein the mechanism consists of a bottom frame that is rotatably mounted at the bottom to a fixed foundation and a top frame that is rotatably mounted to the top of the bottom frame, and two beams that are rotatably mounted to the top of the upper frame and on the foundation, such that a mechanism is created that can move by means of hydraulic cylinders.

A structure according to the preceding claims, wherein the lowering of the cable and the supporting frame is done by means of at least one cable which is connected over a disk in the upper frame to a winch on the deck of the ship.