WO2013012318A1

WO2013012318A1 - A load spreader, marine load raising and lowering system and a method for raising and lowering a load from a vessel

Info

Publication number: WO2013012318A1
Application number: PCT/NL2012/000053
Authority: WO
Inventors: Joop Roodenburg; Terence Willem August Vehmeijer
Original assignee: Itrec BV
Current assignee: Huisman Equipment BV
Priority date: 2011-07-18
Filing date: 2012-07-17
Publication date: 2013-01-24
Anticipated expiration: 2014-01-18
Also published as: NL2007131C2

Abstract

The invention relates to a load spreader comprising: - two cable connectors, wherein each cable connector is configured to connect a respective suspension cable to the spreader; - a load connector configured to connect a load to the spreader; and - a passive actuator system configured to move the two cable connectors between a first and second position, wherein, in use, the horizontal distance between the two cable connectors is larger in the second position than in the first position, and wherein the passive actuator system is operable by water pressure, such that the spreader automatically moves the two cable connectors towards the second position when the spreader is lowered into a water body and moves the two cable connectors towards the first position when the spreader is raised. The invention further relates to a marine load raising and lowering system comprising such a load spreader and a method for raising and lowering a load into a body of water.

Description

P30715PC00/MVE

A load spreader, marine load raising and lowering system and a method for raising and lowering a load from a vessel

The invention relates to a load spreader, to a marine load raising and lowering system for use on a vessel including such a load spreader, and to a method for raising and lowering a load from a vessel. A marine load raising and lowering system is well-known, for example on vessels used for laying pipelines. The system is then used in particular to abandon and recover a pipeline, which system and method are respectively referred to as an A&R system and an A&R method. During pipelaying it is sometimes necessary to abandon a pipeline and recover it later. For example, a pipeline might need to be abandoned due to weather conditions or alternatively for the vessel to be loaded with pipeline, e.g. on a reel. Conventionally, such A&R method is carried out by connecting an A&R head to the end of the laid pipeline;

connecting a suspension cable to this head; transferring pipeline tension from a pipeline tensioning arrangement on the vessel that is used during pipelaying to a winch via the suspension cable; and laying the pipeline and the head on the bottom of the sea by controlled lowering of the suspension cable via driving means of the winch.

A marine load raising and lowering system may also be used to place other components on the bottom of the sea, e.g. a canister, manifold or any other kind of object. US 7,182,550 discloses an A&R system and method using a single winch, suspension cable and associated driving means for lowering and raising the laid pipeline. The use of this system in deep water, e.g. several hundred metres or even more than one kilometre causes several problems. The suspension cable associated with the winch must have a very high tensile strength to support a heavy load. This requirement leads to a heavy suspension cable with the result that the weight of the suspension cable itself becomes a further factor. Thus an even higher load capacity of the winch will be required.

One way to solve the abovementioned issue is to use more than one suspension cable. An example of this solution is shown in international publication WO 2009/002142 of the applicant. Two suspension cable portions are used and interconnected at the lower ends via a rotatable sheave arrangement that ensures that the tension in both suspension cable portion is equal.

A disadvantage of the system according to WO 2009/002142 is that especially for deep water purposes the load connector may rotate/twist about a vertical oriented axis, thereby entangling the two suspension cable portions.

It is therefore an object of the invention to provide a marine load raising and lowering system in which the chance of entanglement of the two suspension cable portions is reduced.

This object is achieved by providing a load spreader comprising:

- two cable connectors, wherein each cable connector is configured to connect a respective suspension cable to the spreader;

- a load connector configured to connect a load to the spreader; and

- a passive actuator system configured to move the two cable connectors between a first and second position,

wherein, in use, the horizontal distance between the two cable connectors is larger in the second position than in the first position,

and wherein the passive actuator system is operable by water pressure, such that the spreader automatically moves the two cable connectors towards the second position when the spreader is lowered into a water body and moves the two cable connectors towards the first position when the spreader is raised.

An advantage of using this spreader is that by increasing the distance between the two cable connectors when the spreader is lowered into the water body, the chance of entanglement of the suspension cables connected to the two cable connectors is reduced and possibly prevented at all depending on the distance between the two cable connectors in the second position and the depth to which the load spreader is lowered. Another advantage is that by using a passive actuator system that is operable by water pressure, no active components and complex control have to be used in order to obtain the same result. Using active components would require the use of umbilical lines to the load spreader which is a disadvantage especially for deepwater purposes.

In an embodiment, the load spreader comprises a foldable mechanism to which the two cable connectors are mounted, said foldable mechanism having a collapsed state associated with the first position of the two cable connectors and an unfolded state associated with the second position of the two cable connectors, and wherein the passive actuator system is configured to move the two cable connectors between the first and second position by folding or unfolding of the foldable mechanism. An advantage of the foldable mechanism may be that the space occupied by the load spreader in the collapsed state is much smaller than in the unfolded state so that above water, the spreader is easy to handle, may pass openings that can not be passed in the unfolded state and can be stored using minimal space. Preferably, the foldable mechanism is a bar linkage with at least four bars that are pivotable relative to each other by respective hinges.

In an embodiment, the passive actuator system comprises a drive cylinder having:

• a cylinder sleeve with a cylinder bottom and cylinder head arranged set axially apart from each other;

• a piston/piston rod assembly which can move axially back and forth, with a piston rod which protrudes outwards through an associated bore in the cylinder head and with a piston which is securely attached to one end of the piston rod and which is displaceable over an axial stroke between the cylinder bottom and the cylinder head; and

• a fluid seal on the piston for providing a seal with an inner surface of the

cylinder sleeve, so that the piston delimits in the drive cylinder between the piston and the cylinder head a variable head-side chamber and further delimits between the piston and the cylinder bottom a variable bottom-side chamber;

wherein the head-side chamber or the bottom-side chamber is filled with a compressible first medium that exerts a pressure on the piston that urges the piston/piston rod assembly towards a position associated with the first position of the two cable connectors, and wherein the pressure in the other one of the head-side chamber or the bottom-side chamber that urges the piston/piston rod assembly towards a position associated with the second position of the two cable connectors is determined by water pressure.

The water pressure may be directly applied to the piston, such that the other one of the head-side chamber or the bottom-side chamber is filled with water when the spreader submerges to exert a pressure on the piston that urges the piston/piston rod assembly towards a position associated with the second position of the two cable connectors. Alternatively, the water pressure may be indirectly applied, for instance using an

embodiment wherein the other one of the head-side chamber or the bottom-side chamber is in fluid communication with a bellow filled with a second medium, and wherein the bellow is collapsible so that the surrounding water pressure can be transmitted via the bellow and the second medium to the piston to urge the piston/piston rod assembly towards a position associated with the second position of the two cable connectors.

In an embodiment, the passive actuator system comprises a buoyant member to provide a buoyancy force to the spreader when the spreader is lowered into the water body to move the cable connectors towards the second position.

In an embodiment, the passive actuator comprises both a buoyant member and a drive cylinder as described above. The buoyant member then provides a buoyancy force that is able to move the cable connectors partially towards the second position and the drive cylinder provides a further force depending on the depth to which the spreader is lowered to move the cable connectors further towards the second position.

In an embodiment, the passive actuator system is configured as a bi-stable actuator system in which both the first and second position of the cable connectors correspond to a stable position of the actuator position, but wherein the actuator system jumps from the first position to the second position when a certain predetermined first depth is reached during lowering and jumps from the second position to the first position when a predetermined second depth is reached during raising of the spreader. The first and second depth may be the same, but this is not necessary and the actuator system may have a hysteresis-like behavior.

The invention also relates to a marine load raising and lowering system for use on a vessel, preferably a vessel for laying an offshore pipeline, which system comprises:

i. a first winch comprising first driving means for raising or lowering a first suspension cable from the first winch;

ii. a second winch comprising second driving means for raising or

lowering a second suspension cable from the second winch;

iii. operating means connected to the first and second driving means of respectively the first and second winch for synchronising the driving means so as to perform synchronous raising or lowering of the first and second suspension cable; and iv. a load spreader according to one or more of the preceding claims, wherein the first and second suspension cable are connected with a terminal end thereof to a respective cable connector of the load spreader,

and wherein the system further comprises a tension equalizing mechanism adapted to equalize the tension in the first and second suspension cables.

The invention further relates to a method for raising and lowering a load from a vessel using a load connector that is suspended by two suspension cables, said method comprising the following steps:

b) connecting a load to the load connector;

c) lowering the suspension cables;

d) increasing the horizontal distance between the two suspension cables while the suspension cables are lowered;

e) raising the suspension cables;

f) decreasing the horizontal distance between the two suspension cables while the suspension cables are raised.

In an embodiment, the steps d) and f) are performed automatically as a result of changing water pressure.

In an embodiment, the horizontal distance between the two suspension cables is increased and decreased at the location where the two suspension cables are directly or indirectly connected to the load connector. In an embodiment, use is made of a load spreader according to the invention.

The invention will now be described with reference to the accompanying drawings in which like parts are indicated by like reference numerals, and in which:

Fig. 1 depicts a schematic view of a load spreader according to an embodiment of the invention;

Fig. 2 depicts the load spreader of Fig. 1 in another position;

Fig. 3 depicts a drive cylinder suitable for a passive actuator system of a load spreader according to the invention;

Fig. 4 depicts a load spreader according to another embodiment of the invention in collapsed state;

Fig. 5 depicts the load spreader of Fig. 4 in an unfolded state; Fig. 6A-6G depict in a simplified way the unfolding process of the load spreader of Fig. 4 and 5 from the position as shown in Fig. 4 to the position as shown in Fig. 5;

Fig. 7 depicts schematically a marine load raising and lowering system according to an embodiment of the invention;

Fig. 8 and 9 depict schematically a load spreader according to a further embodiment of the invention.

Figs. 1 and 2 schematically depict a load spreader CS according to an embodiment of the invention. The load spreader CS comprises a load connector LC to connect a load LO to the spreader CS, in this case via a cable CA, and two cable connectors CC to respectively connect a first suspension cable SC1 and a second suspension cable SC2 to the load spreader CS.

The load spreader CS is further equipped with a passive actuator system, here indicated by arrow PAS, to move the cable connectors CC between a first position as shown in Fig. 1 to a second position as shown in Fig. 2. As can be seen by comparing the two figures, the horizontal distance between the two cable connectors CC is larger in the second position (see Fig. 2) than in the first position (see Fig. 1 ). As a result of that the distance between the first suspension cable SC1 and the second suspension cable SC2 increases when moving from the first position towards the second position, thereby reducing the chance of entanglement, i.e. twisting, of the two suspension cables SC1 , SC2.

The passive actuator system PAS is configured to be operable by water pressure, such that when the spreader is submerged under water and lowered, the increased water pressure moves the cable connectors automatically towards the second position so that with increased suspension cable length, the distance between the two suspension cables is increased as well. When the spreader is raised again, the opposite occurs, such that the decreased water pressure automatically results in movement of the cable connectors towards the first position until the spreader resurfaces.

In Figs. 1 and 2, the cable connectors CC are moveable along a beam BE which is configured to guide said movement, wherein the load connector LC is fixed to that beam BE.

The passive actuator system PAS may comprise a drive cylinder directly arranged between the two cable connectors CC. Alternatively, the passive actuator system may comprise a drive cylinder per cable connector, wherein each drive cylinder is arranged between the respective cable connector and the beam BE. An example of a suitable drive cylinder DC that is operable by water pressure is depicted in Fig. 3 in cross-sectional view. The drive cylinder DC of Fig. 3 comprises a cylinder sleeve 100 with a cylinder bottom 101 and a cylinder head 103 arranged axially apart from each other.

Inside the cylinder sleeve 100, a piston/piston rod assembly is provided which can move axially back and forth, wherein the piston/piston rod assembly includes a piston rod 105 which protrudes outwards through an associated bore BO in the cylinder head 103 and with a piston 107 which is securely attached to one end of the piston rod 105 and which is displaceable over an axial stroke between the cylinder bottom 101 and the cylinder head 103.

A fluid seal 109 is provided on the piston 107 for providing a seal with an inner surface of the cylinder sleeve 100, so that the piston 107 delimits in the drive cylinder DC between the piston 107 and the cylinder head 103 a variable head-side chamber 111 and further delimits between the piston 107 and the cylinder bottom 101 a variable bottom-side chamber 113.

In the embodiment of Fig. 3, the head-side chamber 1 11 is a closed chamber filled with a compressible medium. Alternatively, the head-side chamber 11 may be in fluid

communication with an external chamber, wherein both chambers are filled with a compressible medium. The pressure exerted on the piston 107 by the compressible medium urges the piston towards the cylinder bottom 107. To be suitable for a load spreader according to the invention, this should correspond to movement of the cable connectors towards the first position.

In the embodiment of Fig. 3, the bottom-side chamber 113 is in fluid communication with the surroundings via openings 115 in the cylinder bottom 101. When the drive cylinder, i.e. the load spreader, submerges under water, water is able to fill the bottom-side chamber 113 via the openings 115 (see arrows A1 ), so that the water pressure surrounding the drive cylinder can be applied to the piston 107 which urges the piston to move towards the cylinder head 103. This should correspond to movement of the cable connectors towards the second position. In another embodiment, the bottom-side chamber is filled with compressible medium and the head-side chamber is filled with water, so that consequently movement of the piston towards the cylinder head corresponds to movement towards the first position and movement of the piston towards the cylinder bottom corresponds to movement towards the second position.

In yet another embodiment, the pressure inside the bottom-side chamber is induced by water pressure, but not directly. For example, the bottom-side chamber may be in fluid communication with a bellow instead of the surrounding, wherein the bellow and the bottom- side chamber are filled with a second medium. The bellow is collapsible so that it is able to transmit the water pressure exerted on the bellow to the piston via the second medium in the bellow and the bottom-side chamber. When the operation of the drive cylinder is reversed as described in the previous paragraph, it will be apparent that the same principle of the bellow can be applied, but that this now relates to the head-side chamber.

The drive cylinder is further provided with hinge connections HC to connect the drive cylinder to a cable connector and/or a beam BE as described with reference to Figs. 1 and 2.

Fig. 4 and 5 depict a load spreader CS according to another embodiment of the invention. The load spreader CS comprises two cable connectors CC to connect the load spreader respectively to a first suspension cable SC1 and a second suspension cable SC2.

The load spreader CS further comprises a load connector LC to which a load can be connected. The load connector LC and the cable connectors CC are hingably connected to a bar linkage via respectively hinges H1 , H2, and H3. The bar linkage includes a load bar LB to which the load connector is attached, and four bars B1 -B4 which together with the load bar LB form a five-bar linkage. The bars B1 and B2 are hingably mounted to the load bar LB via respectively hinges H4 and H5. Bar B3 is hingably connected to bar B1 via hinge H6 and hingably connected to bar B4 via hinge H7. Bar B4 in turn is hingeably connected to bar B2 via hinge H8. The five bar linkage forms a foldable mechanism having a collapsed state as shown in Fig. 4 which is associated with a first position of the cable connectors CC. In the first position, the horizontal distance between the cable connectors is small such that the distance between the first and second suspension cables is small. The foldable mechanism also has an unfolded state as shown in Fig. 5 which is associated with a second position of the cable connectors CC. In the second position, the horizontal distance between the cable

connectors is larger than in the first position, preferably the distance in the second position is maximal. As a result, the distance between the first and second suspension cables in the second position is larger than in the first position, thereby reducing the risk of entanglement of the first and second suspension cables when lowering a load into a water body.

The load spreader comprises a passive actuator system including four drive cylinders DC. Two of the drive cylinders DC are arranged between bar B1 and bar B3. The other two drive cylinders DC are arranged between bar B2 and bar B4. As a result, the drive cylinders are able to actuate the five bar linkage to move between the collapsed state of Fig. 4 and the unfolded state of Fig. 5 as will be explained with reference to the Figs. 6A-6G. Fig. 6A depicts the load spreader of Figs. 4 and 5 in a simplified way. For example, the suspension cables, load connector and drive cylinders are omitted to clearly depict the five bar linkage. Fig. 6A depicts the five bar linkage in the collapsed state of Fig. 4. In this state, the drive cylinders are fully retracted and the bars B1-B4 are substantially parallel to each other, such that the width W of the five bar linkage is minimal. This state is also associated with the absence of any load to the load connector.

When the five bar linkage is unfolded, the bars B1 and B2 are pivoted sideways thereby increasing the distance between the hinges H2 and H3 to which the cable connectors are connected. This is shown in Figs. 6B - 6G. The sideways movement of the bars B1 and B2 continues until the bars B3 and B4 reach a substantially horizontal orientation corresponding to the maximum distance between the hinges H2 and H3 as shown in Fig. 6G.

The drive cylinders of the load spreader are in this embodiment of the type of Fig. 3. The head-side chamber of each drive cylinder is filled with a compressible first medium under pressure that exerts a pressure on the piston urging the piston rod to retract inside the cylinder sleeve. In the absence of any significant counter pressure in the bottom-side chamber or loads, the drive cylinder will be in the retracted position as shown in Fig. 4 and corresponding to the state of Fig. 6A. When a significant load is connected to the load connector, this may result in an initial unfolding of the five bar linkage as the load is providing a force to the drive cylinders that pulls the piston rod out of the cylinder sleeve until the pressure in the head-side chamber has risen to such an extent that it is able to withstand the gravitational force of the load. By connecting the load to the load connector, the spreader may unfold for instance towards one of the positions as depicted in Figs. 6B-6D depending on the size of the load. When the spreader including load is lowered into the water, the pressure in the bottom-side chamber will automatically rise depending on the depth to which the spreader is lowered. This water pressure in the drive cylinders will urge the piston to move towards the cylinder head and thus to further unfold the mechanism, e.g. towards a position as depicted in one of the Figs. 6D-6F. When a depth, i.e. a water pressure, has been reached in which the drive cylinder is fully extended, the position of Fig. 6G is reached and no further movement is possible upon further lowering the spreader.

When the spreader is raised, the opposite movement will occur. An advantage of a spreader according to this embodiment is that when the spreader is in the collapsed state, the width W is small and the spreader is able to pass small openings compared to the size of an opening required if the spreader has to pass in the unfolded state.

Fig. 7 schematically depicts a marine load raising and lowering system 1 for use on a vessel, preferably a vessel for laying an offshore pipeline, which system comprises a first winch 2 with first driving means 3 for raising and lowering a first suspension cable SC1 from the first winch 2, and a second winch 5 with second driving means 6 for raising and lowering a second suspension cable SC2 from the second winch 5. The first and second driving means 3, 6 can be synchronized by operating means 8 connected to the first and second driving means so as to perform synchronous raising and lowering of the first and second

suspension cable. The operating means are in this embodiment electronic operating means.

The first and second suspension cable SC1 , SC2 will in practice be very long, but represented here short for reasons of clarity. The first and second driving means are electronically and/or mechanically connected to the respective first and second winch 2,5. The driving means may include any type of motor. The first suspension cable SC1 is suspended via a sheave 9 from the first winch 2. Similarly the second suspension cable SC2 is suspended via a sheave 10'from the second winch 5.

The first and second suspension cable SC1 , SC2 are connected to a load spreader CS according to the invention with a respective terminal end 4c, 7c of the first and second suspension cable SC1 , SC2. The load spreader CS comprises a load connector which is or can be coupled to a load 12. The load spreader is able to vary the distance between the terminal ends 4c, 7c of the first and second suspension cable thereby enabling a large distance when the load is lowered into a water body to minimize or prevent entanglement of the first and second suspension cable. The load spreader may be of one of the types as shown with reference to the Figs. 1-6G. Between the load spreader and the sheaves 9, 10, a first tension equalizing mechanism 13 is provided through which the first and second suspension cable SC1 , SC2 pass. The first tension equalizing mechanism is not shown in detail in Fig. 1 , but ensures that the load is suspended by both the first and second suspension cable and no overload in one of the suspension cables occurs due to e.g. non-synchronous lowering or raising of the cables.

Fig. 8 and 9 depict a load spreader CS according to another embodiment of the invention, wherein said load spreader includes a four bar linkage with four bars B1-B4. The four bar linkage forms a foldable mechanism having a collapsed state as shown in Fig. 8 and an unfolded state as shown in Fig. 9. The four bars are linked together via respective hinges H10-H13. Not shown, but a load connector is provided at hinge H10 and two cable connectors are provided at hinges H11 and H13 respectively to connect a first and second suspension cable SC1 , SC2 to the spreader. The load spreader further comprises a passive actuator system comprising springs SP that urge the mechanism towards its collapsed state and a buoyant member BM that urges the mechanism towards its unfolded state when the spreader including buoyant member are lowered into the water. The operation of the load spreader is similar to the one described in relationship to Figs. 4-6G.

Claims

C L A I M S

1. A load spreader comprising:

- a load connector configured to connect a load to the spreader; and

2. The load spreader according to claim 1 , comprising a foldable mechanism to

which the two cable connectors are mounted, said foldable mechanism having a collapsed state associated with the first position of the two cable connectors and an unfolded state associated with the second position of the two cable

connectors, and wherein the passive actuator system is configured to move the two cable connectors between the first and second position by folding or unfolding the foldable mechanism.

3. The load spreader according to claim 2, wherein the foldable mechanism is a bar linkage with at least four bars that are pivotable relative to each other by respective hinges.

4. The load spreader according to claim 1 , wherein the passive actuator system

comprises a drive cylinder having:

wherein the head-side chamber or the bottom-side chamber is filled with a compressible first medium that exerts a pressure on the piston that urges the piston/piston rod assembly towards a position associated with the first position of the two cable connectors, and wherein the pressure in the other one of the head- side chamber or the bottom-side chamber that urges the piston/piston rod assembly towards a position associated with the second position of the two cable connectors is determined by water pressure.

5. The load spreader according to claim 4, wherein the other one of the head-side chamber or the bottom-side chamber is filled with water when the spreader submerges to exert a pressure on the piston that urges the piston/piston rod assembly towards a position associated with the second position of the two cable connectors.

6. The load spreader according to claim 4, wherein the other one of the head-side chamber or the bottom-side chamber is in fluid communication with a bellow filled with a second medium, and wherein the bellow is collapsible so that the surrounding water pressure can be transmitted via the bellow and the second medium to the piston to urge the piston/piston rod assembly towards a position associated with the second position of the two cable connectors.

7. The load spreader according to claim 1 , wherein the passive actuator system comprises a buoyant member to provide a buoyancy force to the spreader when the spreader is lowered into the water body to move the cable connectors towards the second position.

8. A marine load raising and lowering system for use on a vessel, preferably a

vessel for laying an offshore pipeline, which system comprises:

ii. a second winch comprising second driving means for raising or

lowering a second suspension cable from the second winch;

iii. operating means connected to the first and second driving means of respectively the first and second winch for synchronising the driving means so as to perform synchronous raising or lowering of the first and second suspension cable; and

iv. a load spreader according to one or more of the preceding claims, wherein the first and second suspension cable are connected with a terminal end thereof to a respective cable connector of the load spreader, and wherein the system further comprises a tension equalizing mechanism adapted to equalize the tension in the first and second suspension cables. A method for raising and lowering a load from a vessel using a load connector that is suspended by two suspension cables, said method comprising the following steps:

a) connecting a load to the load connector;

b) lowering the suspension cables;

c) increasing the horizontal distance between the two suspension cables while the suspension cables are lowered;

d) raising the suspension cables;

e) decreasing the horizontal distance between the two suspension cables while the suspension cables are raised.

The method according to claim 9, wherein the steps c) and e) are performed automatically as a result of changing water pressure.

The method according to claim 9, wherein the horizontal distance between the two suspension cables is increased and decreased at a location where the two suspension cables are directly or indirectly connected to the load connector. The method according to claim 9, wherein use is made of a load spreader according to one or more of the claims 1-7.