Marine pipe laying system, method and hoisting device

Abstract

The invention relates to marine pipe laying. For laying of an offshore pipeline, a system is used having a hoisting device. The hoisting device comprises a tower with a tower top side provided with cable pulleys. Furthermore the hoisting device has a traveling block which is displaceably attached to the tower. The traveling block comprises a first block and a second block, both provided with cable pulleys. The first block is provided with a clamp for holding a pipe section to be connected to the pipeline as well as for lowering the pipeline after the pipe section is connected to the pipeline. The hoisting device has a hoisting cable and a winch, the hoisting cable being guided over the cable pulleys on both the tower top side and the traveling block. The traveling block is moveable with respect to the tower by operation of the hoisting winch. The first block and the second block are adapted to be releasably coupled, in which coupled state they can travel along the tower as a unit and are able to support the weight of the pipeline. The second block can be locked to the tower, such that the first block can travel along the tower while the second block remains stationary with respect to the tower.

Description

The present invention relates to a marine pipe laying system for laying of an offshore pipeline, the system comprising:

a) a main supporting structure;

b) a pipe connecting station, wherein a pipe section is connected to an uppermost end of a previously launched pipeline;

c) a static clamp adapted for releasably securing the uppermost end of the previously launched pipeline, wherein the static clamp is adapted to support the weight of the previously launched pipeline;

d) a hoisting device comprising:

a tower with a tower top side provided with cable pulleys,

a traveling block which is displaceably attached to the tower and which is provided with cable pulleys and a traveling clamp for holding a pipe section to be connected to the pipeline as well as for lowering the pipeline after the pipe section is connected to the pipeline,

hoisting means comprising a hoisting cable and a winch, the hoisting cable being guided over the cable pulleys on both the tower top side and the traveling block, wherein the traveling block is moveable with respect to the tower by means of the hoisting means.

Such a system is known e.g. from U.S. Pat. No. 5,421,675. The traveling block has to be able to support the pipeline during launch of the pipeline, which in practice means that the traveling block has to be able to support a load of 1000 tons or more. To this end the traveling block and the tower top side have to be provided with enough cable pulleys to guide the hoisting cable in order to create enough cable parts extending between the traveling block and the tower top side, the load being distributed over the parts. However, the more cable parts extend between the traveling block and the tower top, the slower the block can be moved along the tower.

When laying a pipeline the application of a hoisting system with enough cable parts is necessary to support the load of the pipeline, but it has the drawback that when the load is released from the traveling block, the traveling block can only be moved upwards relatively slowly, which limits the length of pipe to be laid in one day.

The object of the invention is to provide an improved pipe laying system.

This object is achieved by a pipe laying system according to the preamble of claim 1, wherein the traveling block comprises a first block and a second block, both provided with cable pulleys, the traveling clamp being attached to the first block, wherein the first block and the second block are adapted to be releasably coupled, in which coupled state they can travel along the tower as a unit and are able to support the weight of the pipeline, and wherein the system comprises locking means for locking the second block to the tower, such that the first block can travel along the tower while the second block remains stationary with respect to the tower.

With this pipe laying system a pipe laying method according claim 8 can be performed, which method comprises the following steps:

• • i) holding the uppermost end of the pipeline and supporting it with the traveling clamp with the traveling block in an uppermost position on the tower,
  • ii) lowering the pipeline by lowering the coupled first block and second block by means of the hoisting means to a lowermost position on the tower,
  • iii) gripping the uppermost end of the pipeline with the static clamp,
  • iv) releasing the traveling clamp from the pipeline,
  • v) locking the second block to the tower by means of the locking means,
  • vi) hoisting the first block from the lowermost position to the uppermost position by means of the hoisting means,
  • vii) gripping the uppermost end of a pipe section to be connected to the pipeline with the traveling clamp,
  • viii) lowering the first block with the pipe section by means of the hoisting means such that the lowermost end of the pipe section can be gripped and lined up with the uppermost end of the pipeline at the pipe connecting station,
  • ix) releasing the traveling clamp from the pipe section,
  • x) unlock the second block from the tower,
  • xi) connecting the lowermost end of the pipe section to the uppermost end of the pipeline,
  • xii) hoist the second block to the uppermost position while the pipe section is connected to the pipeline,
  • xiii) couple the first block and second block,
  • xiv) grip the uppermost end of the pipe section with the traveling clamp,
  • xv) release the pipeline from the pipe connecting station and from the static clamp, while holding the uppermost end of the pipeline and supporting it with the traveling clamp with the traveling block in an uppermost position on the tower.

With the described system and method the first block with the traveling clamp and the second block can be moved upwards separately when the launched pipeline is supported by the static clamp. Since the second block remains locked with respect to the tower, the moving portion of the traveling block, i.e. the first block has less cable parts extending between it and the top side of the tower. This leads to a higher hoisting speed of the first block with respect to the case where the whole traveling block would be hoisted up as a unit. This results in that the traveling clamp is quicker available at the top side of the tower in order to grip a new pipe section to be connected to the pipeline hanging off the static clamp. The first block positions the lowermost end of the pipe section at the pipe connecting station, after which it is gripped by line up means that line up the pipe section with the uppermost end of the pipeline and the traveling clamp can be released. Simultaneous to the connecting operation the second block is unlocked from the tower and hoisted up. By the time the pipe section is connected to the pipeline, the second block is at the uppermost position and coupled to the first block, whereby the traveling block as a unit is ready for gripping the uppermost end of the pipeline and lowering it.

With the system according to the invention the first block with the traveling clamp can be available at the uppermost position within 17% of the time necessary for a non splittable traveling block to be available at the uppermost position. With the method and system according to the present invention valuable time is saved with respect to pipe laying methods according to the prior art which results in a significant decrease of costs.

Another aspect of the invention relates to a hoisting device according to claim 11, the hoisting device comprising:

a tower with a tower top side provided with cable pulleys,

a traveling block which is displaceably attached to the tower and which is provided with cable pulleys and holding means for holding a load,

hoisting means comprising a hoisting cable and a winch, the hoisting cable being guided over the cable pulleys on both the tower top side and the traveling block, wherein the traveling block is moveable with respect to the tower by means of the hoisting means. The traveling block comprises a first block and a second block, both provided with cable pulleys, the first block being provided with the holding means,

wherein the first block and the second block are adapted to be releasably coupled, in which coupled state of the first block and second block a higher load can be supported than in an unlocked state and in which coupled state of the first block and second block they can travel along the tower as a unit,

and wherein the second block is provided with locking means for locking it to a lower side of the tower, such that the first block can travel in an upward direction along the tower while the second block remains stationary with respect to the tower.

With such a hoisting device according to claim 11 a method comprising an operation cycle can be performed in which:

a first load is gripped by the traveling clamp with the traveling block consisting of the coupled first block and second block in an uppermost position on the tower;

the first load is lowered by lowering the coupled together first block and second block by means of the hoisting means to a lowermost position on the tower where the traveling clamp is releasde from the first load which is handed over to a load handling device;

wherein the second block is locked to the tower by means of the locking means, the first block alone is hoisted from the lowermost position to the uppermost position by means of the hoisting means, after which the first block is used for an intermediate operation after which the second block is unlocked from the tower and hoisted to the uppermost position where it is coupled to the first block.

The hoisting device is thus well adapted for performing a operation cycle wherein in an intermediate operation step only the first block has to be available at the top side of the tower for taking part in an intermediate operation which does not require the full load supporting capacity. The first block can thus be used to deliver an intermediate load to a load handling device. When the first block is released from the intermediate load and the intermediate load is being handled by the load handling device, the second block can return to the uppermost position. When the time period necessary to handle the intermediate load does not exceed the time necessary to hoist up the second block, the cycle time can be significantly reduced.

Such a hoisting device according to claim 11 can further advantageously be used in a method for connecting a first object and a second object at a connecting station. The method comprises the following steps:

• • i) holding the first object and supporting it with the traveling clamp with the traveling block in an uppermost position on the tower,
  • ii) lowering the first object by lowering the coupled first block and second block by means of the hoisting means to a lowermost position on the tower,
  • iii) gripping the first object with gripping means at the connecting station,
  • iv) releasing the traveling clamp from the first object,
  • v) locking the second block to the tower by means of the locking means,
  • vi) hoisting the first block from the lowermost position to the uppermost position by means of the hoisting means,
  • vii) gripping with the traveling clamp the second object,
  • viii) lowering the first block with the second object by means of the hoisting means such that the second object is delivered to the connecting station and gripped by its gripping means,
  • ix) releasing the traveling clamp from the second object,
  • x) unlock the second block from the tower,
  • xi) connecting the second object to the first object,
  • xii) hoist the second block to the uppermost position while connecting the second object to the first object,
  • xiii) couple the first block and second block,
  • xiv) grip the connected first and second object with the traveling clamp,
  • xv) release the connected first and second object from the connecting station, while holding them with the traveling clamp with the traveling block in an uppermost position on the tower.

The invention will be described in more detail in the following description of a preferred embodiment with reference to the accompanying drawing. In the drawing

FIG. 1 shows a schematic side elevational view of a pipe laying system, and

FIGS. 2-7 show a schematic front view of a pipe laying system illustrating the steps of a pipe laying method.

The embodied system relates to a vertical or near vertical pipeline laying technique, such as the J-lay technique, for a pipeline launched from a vessel in an essentially vertical orientation. The system provides an improved pipe laying system for vertical or near vertical marine pipelaying, particular in deep water.

The methods illustrated with reference to the FIGS. 1-7 relate to an efficient method for the vertical or near vertical laying of offshore pipelines.

The pipe laying system provides a-vessel which acts as a main supporting structure. In FIG. 1 and FIG. 2 a part of this vessel is shown and indicated by reference numeral 1. In the FIGS. 2-7 the vessel 1 is omitted for the reasons of clarity of the drawing.

On the vessel 1 is provided a hoisting device indicated by reference numeral 2. The hoisting device 2 comprises a tower 3 with a tower top side 3a. On the tower top side 3a are provided cable pulleys 4.

The hoisting device 2 further comprises a traveling block 5 which is displaceably attached to the tower 3. The traveling block 5 is provided with cable pulleys 6 and 7.

Also the hoisting device has hoisting means comprising a hoisting cable 8 and a winch 9. The hoisting cable 8 is guided over the cable pulleys 4 at the top side 3a of the tower 3 and the cable pulleys 6, 7 on the traveling block 5. By winding up and unwinding the cable 8 on and off the winch 9, the traveling block 5 is moveable with respect to the tower 3.

As can be seen best in FIG. 2 the traveling block 5 comprises a first block 51 and a second block 52. In the particular embodiment that is shown in the figures, the first block 51 is provided with two cable pulleys 6. The second block 52 is provided with four cable pulleys 7.

The first block 51 is provided with a traveling clamp 10 being attached to it. The traveling clamp 10 is adapted to grip the upper end of a single pipe section 20 or a pipeline 21 which will be described in more detail below.

The second block 52 has a substantially ring shaped body 52a with central opening 52b (see FIG. 3). The first block 51 has a body 51a with a diametrical dimension exceeding the diametrical dimension of the central opening 52b of the second block 52, such that the first block 52 cannot pass through the opening 52b of the second block 52. The second block 52 has a supporting surface 52c facing upwards and surrounding the central opening 52b for engagement with the first block 51 and for supporting it. The first block 51 and the second block 52 can be coupled together. In the coupled state, which is shown in FIG. 2, the first block 51 engages the supporting surface 52c. In the coupled state the first block 51 and second block 52 form a unit and are able to support together the weight of a load held by the traveling clamp 10. This load can be the load of a pipeline hanging off which can amount up to 1000 tons. The unit, or better the traveling block unit, formed by the coupled first block 51 and second block.52 can travel along the tower 3 by operation of the winch 9.

The structure of the traveling block 5 is such that the first block 51 and the second block 52 can be separated. Thereto the second block 52 can be locked to a lower part of the tower 3 by means of suitable locking means, preferably locking pins 13. The locking pins 13 can be arranged on the second block 52 such that they upon a suitable control signal move towards an extended position and extend into locking holes provided in the tower 3. It is also possible to provide the tower 3 with the pins 13, which upon a suitable control signal move towards an extended position and extend into locking holes provided in the second block 52.

Locking of components with locking pins and locking holes is a generally known locking mechanism. It is to be understood that in the above by locking means not only the preferred locking pins and locking holes are meant, but also any other suitable locking mechanism are meant like the ones mentioned here, such as e.g. bolt/nut combinations, cylinders, clamps etc.

When the second block 52 is locked to the tower 3, the first block 51 can travel along the tower 3 while the second block 52 remains stationary with respect to the tower 3.

The pipelaying system is furthermore provided with a pipe connecting station, more in particular a pipe welding station 14 for welding the lowermost end of a pipe section 20 to an uppermost end of a previously launched pipeline 21. In addition the pipe laying system has a line up tool 16 for linig up the lowermost end of a pipe section 20 with the uppermost end of the pipe line 21 such that they can be welded together in the welding station 14. Also, the pipelaying system has a static clamp 15, in the art also know as a hang off clamp for gripping an upper end of the pipeline 21 and which is adapted to support the load of the pipeline 21. These components will become more apparent in the following description of a pipe laying method.

In FIG. 2 is shown a first state wherein the first block 51 and second block 52 are coupled and the traveling clamp 10 is holding the uppermost end of the pipeline 21 and supporting the load of the launched pipeline 21. Then the static clamp 15 will grip the upper end of the pipeline 21 and take over the load of the pipeline 21, after which the traveling clamp 10 can be released from the pipeline 21.

Next, the second block 52 can be coupled to the tower 3 by means of the locking pins 13. As is illustrated in FIG. 3, this locked state of the second block 52 allows the first block 51 to be hoisted up by operating the winch 9 while the second block 52 is retained by the locking pins 13 at its lowermost position on the tower 3.

At the moment that the first block 51 has arrived at its uppermost position at the tower 3 a new pipe section 20 is delivered to the tower 3 by means of suitable pipe delivering means. This new pipe section 20 is then gripped at its upper end by means of the traveling clamp 10 as is shown in FIG. 4.

The pipe section 20 can be lowered over such a distance that it can be gripped by the line up tool 16, after which the traveling clamp 10 can be released from the pipe section 21. This state is shown in FIG. 5. Next the pipe section 20 can be lined up with the pipeline 21 hanging off the static clamp 15 before their respective ends are welded together in the welding station 14.

As is shown in FIG. 6, during the welding operation the locking pins 13 are released and the second block 52 is hoisted towards its uppermost position by operation of the winch 9. Preferably the system is designed such that hoisting the second block 52 to its uppermost position takes not more than the time necessary to weld the pipe section 20 and the pipeline 21 together. In such a way the intermediate time, during which the hoisting system is not necessary to carry a load, is used efficiently to join the first block 51 and second block 52.

In FIG. 7 is shown the state in which the second block 52 has arrived at its uppermost position on the tower 3 and is joined together with the first block. In this state the traveling clamp 10 grips the upper end of the pipeline 21. Because the unit 5 formed by the first block 51 and second block 52 is able to support the load of the pipeline 21, the static clamp 15 is released from the pipeline 21 and the pipeline 21 is lowered by operating the winch 9 until the state depicted in FIG. 2 is reached. This cycle is repeated to lay the pipeline 21.

In this example the first block 51 has two cable pulleys 6 and the second block 52 has four cable pulleys 7. As a result four cable parts 8a-8d extend between the top side 3a of the tower 3 and the first block 51, and eight cable parts 8e-8i extend between the top side 3a of the tower 3 and the second block 52 (see FIG. 3). This implies that in principle the first block 51 can be hoisted up in one third of the time that would be necessary if a non-splittable traveling block with twelve cable parts would be applied. This means that with the particular hoisting system shown in the figures the traveling clamp 10 is available at the top side 3a of the tower 3 much quicker for gripping a light load, i.e. a single pipe section 20. The intermediate time necessary to connect the pipe section 20 to the pipeline 21 is efficiently used to move the second block 52 upwards to bring the hoisting system to its full supporting capacity which is necessary to lower the pipeline 21.

With the present pipe laying system a considerable amount of time can be gained. This leads to a considerable reduction of the overall time of use of pipe laying equipment and thus in pipe laying costs.

It is to be understood that the invention is not limited to the particular embodiment illustrated in the figures. The invention can be performed and practiced in various ways. The invention can thus be applied with other pipe laying methods with a more inclined launch direction than the one illustrated in the above, even almost horizontal like S-lay. Also the application of the hoisting system is not limited to a pipe laying method, but could also be applied for other operations, e.g. offshore drilling.

In the embodiment of the pipe laying system shown in FIGS. 1-7 the first block 51 cannot pass through the central opening in the second block 52. A traveling block structure is however envisaged wherein the first block and second block can be coupled in another manner, e.g. by locking pins or the like, wherein the first block can pass the second block from above or below.

Claims

1. A marine pipe laying system for laying of an offshore pipeline, the system comprising: a) a main supporting structure; b) a pipe connecting station, wherein a pipe section is connected to an uppermost end of a previously launched pipeline; c) a static clamp adapted for releasably securing the uppermost end of the previously launched pipeline, wherein the static clamp is adapted to support the weight of the previously launched pipeline; d) a hoisting device comprising: a tower with a tower top side provided with cable pulleys, a traveling block which is displaceably attached to the tower and which is provided with cable pulleys and a traveling clamp for holding a pipe section to be connected to the pipeline as well as for lowering the pipeline after the pipe section is connected to the pipeline, hoisting means comprising a hoisting cable and a winch, the hoisting cable being guided over the cable pulleys on both the tower top side and the traveling block, wherein the traveling block is moveable with respect to the tower by means of the hoisting means, characterized in that the traveling block comprises a first block and a second block, both provided with cable pulleys, the traveling clamp being attached to the first block, wherein the first block and the second block are adapted to be releasably coupled, in which coupled state they can travel along the tower as a unit and are able to support the weight of the pipeline, and wherein the system comprises locking means for locking the second block to the tower, such that the first block can travel along the tower while the second block remains stationary with respect to the tower.

2. The system according to claim 1, wherein the locking means are adapted to lock the second block in a lowermost position at a lower side of the tower, such that the first block can travel in an upward direction towards an uppermost position along the tower while the second block remains stationary with respect to the tower.

3. The system according to claim 2, wherein the hoisting means are adapted in such a way that the travel time of the single second block from its lowermost position to its uppermost position on the tower is less or at most equal to the time to connect the pipe section to the pipeline.

4. The system according to any of the claims 1-3, wherein the locking means comprise one or more locking pins moveable between a locked position into a locking hole and an unlocked position.

5. The system according to claim 4, wherein the one or more locking pins are-arranged on the second block and the locking holes are arranged on the tower.

6. The system according to claim 4, wherein the one or more locking pins are arranged on the tower and the locking holes are arranged on the second block.

7. The system according to any of preceding claims, wherein the pipe connecting station comprises a welding station.

8. A method for laying of an offshore pipeline, wherein use is made of a system comprising: a) a main supporting structure; b) a pipe connecting station, wherein a pipe section is connected to an uppermost end of a previously launched pipeline; c) a static clamp adapted for releasably securing the uppermost end of the previously launched pipeline, wherein the static clamp is adapted to support the weight of the previously launched pipeline; d) a hoisting device comprising: a tower with a tower top side provided with cable pulleys, a traveling block which is displaceably attached to the tower and which is provided with cable pulleys and a traveling clamp for holding a pipe section to be connected to the pipeline as well as for lowering the pipeline after the pipe section is connected to the pipeline, hoisting means comprising a hoisting cable and a winch, the hoisting cable being guided over the cable pulleys on both the tower top side and the traveling block, wherein the traveling block is moveable with respect to the tower by means of the hoisting means, the traveling block comprising a first block and a second block, both provided with cable pulleys, the traveling clamp being attached to the first block, wherein the first block and the second block are adapted to be releasably coupled so as to travel along the tower as a unit, and wherein the system comprises locking means for locking the second block to the tower, such that the first block can travel along the tower while the second block remains stationary with respect to the tower, the method comprising the following steps: i) holding the uppermost end of the pipeline and supporting it with the traveling clamp with the traveling block in an uppermost position on the tower, ii) lowering the pipeline by lowering the coupled first block and second block by means of the hoisting means to a lowermost position on the tower, iii) gripping the uppermost end of the pipeline with the static clamp, iv) releasing the traveling clamp from the pipeline, v) locking the second block to the tower by means of the locking means, vi) hoisting the first block from the lowermost position to the uppermost position by means of the hoisting means, vii) gripping the uppermost end of a pipe section to be connected to the pipeline with the traveling clamp, viii) lowering the first block with the pipe section by means of the hoisting means such that the lowermost end of the pipe section can be gripped and lined up with the uppermost end of the pipeline at the pipe connecting station, ix) unlock the second block from the tower, x) connecting the lowermost end of the pipe section to the uppermost end of the pipeline, xi) hoist the second block to the uppermost position while the pipe section is connected to the pipeline, xii) couple the first block and second block, xiii) grip the uppermost end of the pipe section with the traveling clamp, xiv) release the pipeline from the pipe connecting station and from the static clamp, while holding the uppermost end of the pipeline and supporting it with the traveling clamp with the traveling block in an uppermost position on the tower.

9. The method according to claim 8, wherein the second block is moved from its lowermost position to its uppermost position on the tower and then connected to te first block within a time span that is equal or less than the time span for connecting the lowermost end of the pipe section to the uppermost end of the pipeline.

10. The method according to claim 8 or 9, wherein the traveling clamp is released from the pipe section after the pipe section is gripped at the pipe connecting station.

11. A hoisting device, preferably for a marine pipe laying system, comprising: a tower with a tower top side provided with cable pulleys, a traveling block which is displaceably attached to the tower and which is provided with cable pulleys and holding means for holding a load, hoisting means comprising a hoisting cable and a winch, the hoisting cable being guided over the cable pulleys on both the tower top side and the traveling block, wherein the traveling block is moveable with respect to the tower by means of the hoisting means, characterized in that the traveling block comprises a first block and a second block, both provided with cable pulleys, the first block being provided with the holding means, wherein the first block and the second block are adapted to be releasably coupled, in which coupled state of the first block and second block a higher load can be supported than in an unlocked state and in which coupled state of the first block and second block they can travel along the tower as a unit, and wherein the second block is provided with locking means for locking it to a lower side of the tower, such that the first block can travel in an upward direction along the tower while the second block remains stationary with respect to the tower.

12. A method for hoisting a load with a hoisting device according to claim 11, the method comprising an operation cycle in which: a first load is gripped by the traveling clamp with the traveling block consisting of the coupled first block and second block in an uppermost position on the tower; the first load is lowered by lowering the coupled together first block and second block by means of the hoisting means to a lowermost position on the tower where the traveling clamp is preferably released from the first load which is handed over to a load handling device; wherein the second block is locked to the tower by means of the locking means, the first block alone is hoisted from the lowermost position to the uppermost position by means of the hoisting means, after which the first block is used for an intermediate operation after which the second block is unlocked from the tower and hoisted to the uppermost position where it is coupled to the first block.

13. A method for connecting a first object and a second object at a connecting station wherein use is made of a device according to claim 11, the method comprising the following steps: i) holding the first object and supporting it with the traveling clamp with the traveling block in an uppermost position on the tower, ii) lowering the first object by lowering the coupled first block and second block by means of the hoisting means to a lowermost position on the tower, iii) gripping the first object with gripping means at the connecting station, iv) locking the second block to the tower by means of the locking means, v) hoisting the first block from the lowermost position to the uppermost position by means of the hoisting means, vi) gripping with the traveling clamp the second object, vii) lowering the first block with the second object by means of the hoisting means such that the second object is delivered to the connecting station and gripped by its gripping means, viii) releasing the traveling clamp from the second object, ix) unlock the second block from the tower, x) connecting the second object to the first object, xi) hoist the second block to the uppermost position while connecting the second object to the first object, xii) couple the first block and second block, xiii) grip the connected first and second object with the traveling clamp, xiv) release the connected first and second object from the connecting station, while holding them with the traveling clamp with the traveling block in an uppermost position on the tower.

14. The method according to claim 13, wherein the traveling clamp is released from the second object if after the second object has been gripped by the gripping means of the connecting station.