WO2007027087A1

WO2007027087A1 - Method and device for providing a protrusion on a pipeline

Info

Publication number: WO2007027087A1
Application number: PCT/NL2006/000438
Authority: WO
Inventors: Cornelis Van Zandwijk; Caspar Huub Berends; Jan Van Egmond
Original assignee: Heerema Marine Contractors Nederland B. V.
Priority date: 2005-09-01
Filing date: 2006-08-30
Publication date: 2007-03-08

Abstract

The present invention relates to a pipeline laying vessel, a method for laying pipelines and a pipeline. In the invention protrusion devices, also known as Vortex Induced Vibration strakes, are provided on the pipeline by an installing device during the laying of the pipeline by the pipeline laying vessel.

Description

Method and device for providing a protrusion on a pipeline

FIELD OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

The present invention relates to an apparatus and method for providing a protrusion, such as a Vortex Induced Vibration strake, on a pipeline.

Pipelines are widely applied in the off-shore industry. Often, a pipeline is laid which rests on a seabed over a certain distance and rises from the seabed at a certain point, generally known as the touch-down point. The pipeline then extends upwards toward a structure at the water level, such as a vessel or a platform. This section of the pipeline is generally indicated as a riser.

On a riser, forces are exerted by the water, such as forces from a current in the water. Water flowing past the pipeline can induce vortices, which are located in the wake of the pipeline. These vortices first occur and subsequently move away from the pipeline in the direction of flow.

These vortices can create dynamic loads on the pipeline, in particular dynamic loads in a direction transversal to the main longitudinal axis of the pipeline, in particular transversal to the direction of the water flow. The dynamic forces occur in particular during the movement of the vortex away from the pipeline.

These dynamic loads may cause the pipe to move, in particular in a swaying or vibrating manner. In the field of the art, this movement is generally indicated as Vortex Induced Vibration (VIV) .

Vortex induced Vibrations may affect the pipeline adversely. The adverse affects may for instance be an increased fatigue damage, which leads to loss of lifetime of a riser.

It is possible that the dynamic loads from the vortices may be exerted on the pipeline in a certain frequency. This frequency is dependent on a number of factors relating to the pipeline and the flow of water. When the frequency is substantially the same as a natural frequency of the pipeline, the vibrations in the pipeline may become very strong, affecting the pipeline adversely even stronger. In particular when the vortices occur over a large portion of the length of the riser at a same time, this may lead to strong vibrations .

Therefore, in the field of the art, protrusions are generally provided on the riser in a helix shaped arrangement, which protrusions prevent the vortices from occurring over large lengths of the riser at a same instant. These protrusions are generally- referred to as VIV strakes . Generally, a VIV strake comprises an organ, in particular a fin-like organ, which projects from the pipeline .

The protrusions accomplish that the vortices occur over short lengths of the pipeline at the same instant, which leads to dynamic loads on the pipeline which are exerted on the pipeline over only a relatively short length of the pipeline. The directions of the respective dynamic loads thus vary along the length of the pipeline. In this way, the dynamic loads may substantially neutralize one another, and a riser can be provided which is substantially free of vibrations in water currents .

Typically, when a pipeline is installed from an oil well to a floating production facility, a certain length of pipeline rests on the seabed (for instance 8 km) and a certain length of pipeline extends upwards from the seabed to the floating production facility (for instance 2 km) .

A pipeline may be laid in several different modes. A J-lay mode, an S-lay mode and a reeling mode, in which pipelines are spooled off a reel, are known in the field of the art. In all these modes of laying pipelines, the pipeline or sections thereof are handled by devices disposed along a lay path. These devices may involve clamps, welding stations, inspection stations, tensioners, etc.

A pipeline including a protrusion generally has a substantially larger cross-sectional area than a pipeline without a protrusion. In general, the protrusions may hinder the passing of the pipeline along the lay path on board the vessel, in particular in the gripping area of supporting rollers, clamps and tensioners.

In the field of the art, the VIV strakes are generally mounted to the pipe in a manual process in the form of 1 to 1.5m long flat plate plastic elements on which the protrusions are preinstalled. The plate sections are pre-shaped to a circular form, having a cut line at one side such that the element can be opened, arranged around the pipe and closed. Once closed, steel straps are tied around the element to keep it closed and secure it to the pipeline. The protrusions are shaped such that the protrusions of the successive elements form a continuous helix around the pipe.

When a pipeline is laid in S-lay mode, the protrusions are generally mounted to the pipe in the zone which has passed through the tensioner. The protrusions are mounted in non-critical time in the time intervals, during which the pipeline is constructed in the work stations. In the S-lay mode, it is generally accepted that the protrusions still have to pass over the pipelay stinger, which may cause damage to the protrusions.

When a pipeline is laid in a J-lay mode, the protrusions are often in part provided on a pipe section before the pipe section is positioned in an abutting position with the free end of the pipeline. The protrusions are preinstalled in all zones which are not later gripped by supporting rollers, clamps or tensioners. Depending on the design of the J-lay equipment, the protrusions may be preinstalled on the pipe section over 80% of the length of the pipe section (which length can be 75 meters) . The remaining 20% of the length of the pipe section is preferably kept free of protrusions during the welding operation and during a substantial portion of the subsequent moving downwards of the pipe section, because supporting rollers, clamps and tensioners require a certain length of pipe section which is free of protrusions.

It is often desirable to also provide the protrusions to the pipe section over the remaining 20% of the length thereof (for instance a length of fifteen meters) . The remaining protrusions are usually provided on the pipe section after it has passed all supporting rollers, clamps and tensioners situated near the lay path.

This installation of the remaining protrusions must usually be performed in one work station at the end of the laying process, i.e. just before the pipeline leaves the pipeline laying vessel, and preferably after the section of pipeline to which the protrusion is to be connected has passed all the devices which may interfere with the protrusions, which installation takes a substantial period of critical time. Typically, a protrusion has a length of 1 to 1.5 meter, when viewed in the direction of the main longitudinal axis of the pipeline. Typically, the connecting of a protrusion to a pipe section costs about 1.5 minutes. The total time period necessary to cover the remaining length of pipeline with protrusions may thus typically be 15 minutes to one half hour.

In the pipeline laying industry, time is precious and therefore the manual provision of protrusions in a single work station is very disadvantageous . A method to reduce the installation time of protrusions is desirable.

Alternatively, the remaining length of pipeline is not provided with protrusions at all in a J-lay mode. This is disadvantageous because it may cause Vortex Induced Vibrations in the pipeline.

A pipeline may also be laid by spooling the pipeline from a reel. With this method, in current practice, the protrusions generally cannot be preinstalled, because it is technically problematic to wind a pipeline having protrusions onto a reel. The unwinding or spooling of the pipeline from the reel causes similar problems as with laying pipelines in J-lay, because the protrusions interfere with supporting rollers, clamps and tensioners disposed along the lay path during the moving of the pipeline along the lay path.

Therefore, the protrusions preferably are to be connected to the pipeline at the end of the laying process, i.e. just before the pipeline leaves the pipeline laying vessel, and preferably after the section of pipeline to which the protrusion is to be connected has passed all the devices which may interfere with the protrusions.

Currently, in the reeling of pipelines, the protrusions are also installed manually, which is very time consuming and hence, expensive. In particular during reeling, as the protrusions can not be mounted in non-critical time as in S-lay, or partly preinstalled as in J-lay, there is a need to install protrusions faster.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and device for quickly providing at least one helix shaped protrusion on a pipeline on board a pipeline laying vessel.

It is another object of the present invention to provide a method and device for providing at least one helix shaped protrusion on a pipeline on board a pipeline laying vessel in a cost-effective and technically reliable way.

At least one of the above objects is reached in a pipeline laying vessel having a lay path along which a pipeline is to be laid, the pipeline laying vessel comprising an installation device configured for providing a protrusion device on at least part of the pipeline .

The invention also relates to a method for laying a pipeline having at least one protrusion installed thereupon, the method comprising the steps of:

(a) providing a pipeline laying vessel having an installation device configured for installing at least one protrusion device on the pipeline at an installing location near the lay path;

(b) laying the pipeline from the pipeline laying vessel;

(c) providing a protrusion device on the pipeline by the installation device.

The invention also relates to a protrusion device and to a pipeline or pipe section for use in the method. The invention further relates to a pipeline provided with protrusions. The invention also relates to a method for pre-assembling a pipeline which is to be laid.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure Ia shows a schematic side view of a pipeline laying vessel according to the invention;

Figure Ib shows a cross-sectional side view of a protrusion device;

Figure Ic shows a cross-sectional top view of a deformed protrusion device in a target position;

Figure 2a shows a schematic side view of a pipeline laying vessel according to another embodiment of the invention; Figure 2b shows a cross-sectional side view of a protrusion device in a target position;

Figure 2c shows a cross-sectional top view of a deformed protrusion device;

Figure 2d shows a side view of a protrusion device in its original form;

Figure 2d shows a cross-sectional side view of a protrusion device in its original form;

Figure 2f shows a side view of a protrusion device in its target position around the pipeline;

Figure 2g shows a cross-sectional side view of a protrusion device in its target position around the pipeline;

Figure 2f shows a top view of a protrusion device in its target position around the pipeline;

Figure 3a shows a diagrammatic axonometric view of an extrusion device for forming a protrusion;

Figure 3b shows a cross-sectional top view of a pipeline provided with extruded protrusions;

Figure 4a shows a diagrammatic axonometric view of a molding device for forming a protrusion;

Figure 4b shows a cross-sectional top view of a pipeline provided with molded protrusions;

Figure 5a shows a diagrammatic top view of an installation device for installing protrusion segments on a pipeline;

Figure 5b shows a cross-sectional side view of an installation device for installing protrusion segments on a pipeline;

Figure 6a shows a cross-sectional view of a pipeline having recesses and protrusions capable of being fitted in the recesses;

Figure 6b shows a cross-sectional view of a pipeline having protrusions fitted in the recesses;

Figures 6c and 6d show enlarged cross-sectional top views of a recess and a protrusion fitted therein;

Figure 7 shows a cross-sectional view of a pipeline having protrusions foldable against the outer surface of the pipeline.

Figure Ia shows a pipeline laying vessel 1 comprising a tower 2 positioned along a lay path 4. A moving friction clamp 11 is provided along the lay path 4 and a fixed friction clamp 13 is also provided directly at an installing location 16. A pipeline reel 6 is provided from which a pipeline 8 can be spooled during the laying thereof. An installing device 7 comprising a protrusion device reel 10 is provided on board the vessel, on the deck 15 (also indicated as Landing Support Structure (LSS)) of the pipeline laying vessel. A protrusion device 12 in the form of a VIV strake is wound on the protrusion device reel 10.

A deforming organ in the form of a chute 14 is provided at the installing location 16 for deforming the protrusion device 12 in order to arrange it substantially around the pipeline 8.

In operation, the pipeline 8 passes down the tower 4 in the direction of arrow 17. At the same time, the protrusion device 12 is spooled from the protrusion device reel 10 in the direction of arrow 19 and moved towards the installing location 16. The protrusion device 12 is deformed by the chute 14 so that it is provided around the pipeline 8, for instance by wrapping or folding.

A protrusion device closing device 26 is provided, which is configured to close the protrusion device 12 and fix it to the pipeline 8 with straps.

The embodiment of the installing device 7 shown in Figure Ia may also be applied in a J-Iay or S-lay mode.

Figures Ib and Ic show the protrusion device 12, which comprises an elongate body 18 and different protrusions 20a, 20b and 20c projecting from the elongate body 18. In Fig. Ib, the protrusion device is shown in its original form, wherein the elongate body 18 is substantially flat, in particular a flat plate. In Fig. Ic, the elongate body 18 is shown in its deformed form, in which it substantially surrounds the pipeline 8. The elongate body has the form of a C-shape.

The protrusions 20a, 20b, 20c project from one side of the elongate body 18 which forms a substrate for the protrusions 20a, 20b, 20c. The protrusions 20a, 20b, 20c may be provided on the elongate body in different configurations.

As shown in Figs 2d, 2e, 2f and 2g, protrusions sections 20al, 20bl, 20cl, 20a2, 20b2, 20c2, etc. may have a ridge-like form extending laterally substantially across the width of the elongate body 18 substantially from a first rim 45 to a second, opposite rim 47. The protrusions sections 20al, 20bl, 20cl, 20a2, 20b2, 20c2, etc. may in particular extend under an angle α to a main longitudinal axis 25 of the elongate body 18, which angle α may for instance be 30 degrees. Other angles are also possible. An end 41 of a protrusion section 20al may end at the first rim 45 at or near an end 43 of another protrusion section 20a2.

When the elongate body is deformed around the pipeline 8, the end 41 of protrusion section 20al meets the end 43 of protrusion section 20a2. Protrusions sections 20al, 20bl, 20cl, 20a2, 20b2, 20c2, etc. thus may form three helically formed protrusions 20a, 20b, 20c spiraling around the pipeline. The helical protrusions 20a, 20b, 20c may be arranged about the pipeline in an intertwined manner .

It is also possible to provide the protrusions 20a, 20b, 20c in a different configuration than a helical form, as long as the radial direction in which they protrude from the pipeline varies along the length of the pipeline. Protrusions 20a, 20b, 20c which are randomly scattered over the surface of the elongate body 18 may for instance also be applied.

It is also possible to provide different patterns of protrusions 20a, 20b, 20c on the elongate body 18, such as a zigzag pattern or an oscillating pattern.

As shown in Fig. 2g, a closure line 27 is formed by the protrusion device 12 where the rims 45, 47 of the elongate body 18 meet one another.

Turning to Figs. 2a, 2b and 2c, an embodiment of the invention is shown, wherein an assembly line 22 is disposed on the pipeline laying vessel 1. The assembly line 22 defines a pre-assembly path 23 extending towards the installing location 16.

In operation, protrusion device segments 24 of the protrusion device 12 are assembled into an elongate protrusion device, which moves toward the assembling location 16. The protrusion device 12 is deformed and fastened to the pipeline in a similar way as in the embodiment of Fig. Ia. The protrusion device 12 forms a continuous strip.

Turning to Figs. 3a and 3b, an extrusion device 26 is shown, comprising a reservoir 28 filled with liquid polyethylene (PE) 29. Other materials suitable for extrusion are also possible. An extrusion opening 30 is provided comprising two protrusion opening parts 32. The extrusion opening 30 surrounds the pipeline 8.

In operation, the pipeline 8 moves in the direction of arrow 34. At the same time, the extrusion opening 30 is rotated about the pipeline 8. The polyethylene 29 is extruded through the extrusion opening 30, thereby forming a coating 35 covering the exterior surface of pipeline 8. Protrusions 20a, 20b, 20c are formed by the protrusion opening parts 32, which protrusions 20a, 20b and 20c are integrated with the coating 35.

The protrusion opening parts 32 rotate about the pipeline 8 in the direction of arrow 36 during the moving of the pipeline 8 in the direction of arrow 34. This causes the protrusions 20a, 20b and 20c to be formed as a helix around the pipeline 8. Other forms of the protrusions 20a, 20b and 20c are also possible. If the protrusion opening parts 32 have a fixed position for a predetermined period of time, after which the fixed position is changed to another fixed position, protrusions 20a, 20b and 20c can be formed having staggered positions along the pipeline 8.

Turning to Figs 4a and 4b, an embodiment is shown wherein the exterior surface of the pipeline 8 is covered with a layer of moldable material 38. This layer may have been provided previously, for instance on land. A molding device 40 is provided which surrounds the pipeline 8. The molding device 40 comprises an extrusion opening 42 having protrusion opening parts 44.

In operation, the molding device 40 provides heat to the moldable material 38, thereby increasing the moldability of the moldable material 38. Subsequently, the moldable material 38 is deformed by the extrusion opening 42. A coating 46 is thus provided on the exterior surface of the pipeline 8, the coating 46 having protrusions 20a, 20b, 20c integrally connected thereto. After the moulding, the coating 46 may be cooled in order to fix (or ^λfreeze' ) the form of the protrusions 20a, 20b, 20c.

The extrusion opening 42 may rotate in the direction of arrow 48 in the same way as the extrusion opening 30 of Fig.3a, providing the same results. Turning to Figs. 5a and 5b, an embodiment of the invention is shown comprising a winding device 49 comprising three positioning devices 50a, 50b, 50c are provided at different radial positions around the pipeline 8. The positioning devices 50a, 50b, 50c can position three respective strips 52a, 52b, 52c of material near the pipeline 8, which strips may be spooled from respective reels 51a, 51b, 51c in the positioning devices 50a, 50b, 50c. The strips have a width which is larger than the diameter of the pipeline 8. Initially, the strips are flat.

The positioning devices 50a, 50b, 50c comprise respective roller organs 54a, 54b, 54c.

The roller organs 54a, 54b, 54c have a diameter 58 which is relatively small in a central section 55 of the roller organs 54a, 54b, 54c, and which diameter 58 gradually and smoothly increases in the direction of the ends 57a, 57b of the roller organs. Near the ends 57a, 57b of the rollers, the diameter 58 smoothly decreases again.

In operation, the pipeline 8 is moved in the direction 34. At the same time, the strips 52a, 52b, 52c are reeled from the respective reels. The roller organs 56a, 56b, 56c press and deform the strips 52a, 52b, 52c against the pipeline 8, such that the strips substantially take on the form of ^• the roller organs 54a, 54b, 54c. Each strip 52a, 52b, 52c has two opposite rims 59a, 59b which extend beyond the pipeline. One rim 59a of each strip 52a, 52b, 52c meets a rim 59b of another strip, in such a way that the strips 52a, 52b, 52c substantially enclose the pipeline 8. The respective rims 59a are connected to rims 59b by connection means 60, such as bolts or caps. The rims 59a, 59b of the strips 52a, 52b, 52c thus form three protrusions 20a, 20b, 20c projecting outwardly from the pipeline 8.

The positioning devices 50a, 50b, 50c may be configured for rotation about the pipeline 8, for instance on at least one rotary device 62, which is configured to rotate about the pipeline 8. The positioning devices 50a, 50b, 50c may also each be provided on a separate, independently movable rotary device 62a, 62b, 62c (not shown) . In operation, the positioning devices 50a, 50b, 50c rotate about the pipeline 8 in direction 64, thereby providing the protrusions 20a, 20b, 20c in a helical form about the pipeline 8.

Turning to Figs 6a, 6b, 6c and 6d, an embodiment of the invention is shown wherein recesses 66a, 66b, 66c are provided in the exterior surface 72 of the pipeline 8. ^' The recesses 66a, 66b, 66c may be provided in the exterior surface 72 of a metal pipeline 8, but it is also possible that the pipeline 8 is covered with a layer 70 of synthetic material in which the recesses are provided.

The recesses 66a, 66b, 66c may have various forms. They may be elongate such as a groove, or may have a non-elongate form such as a circular, square or triangular form. The recesses may be provided on land, prior to the loading of the pipeline of pipe sections on board the pipeline laying vessel 1. The recesses may also be provided on board the pipeline laying vessel 1.

In operation, protrusion devices 68a, 68b and 68c (also indicated by 68) are inserted in the respective recesses 66a, 66b, 66c. The protrusion devices 68a, 68b and 68c may be clicked in the recesses 66a, 66b, 66c in the direction of arrows 74a, 74b, 74c.

The recesses 66a, 66b, 66c have openings which may be constricted relative to the size of the cavities 78 of the recesses 66a, 66b, 66c. The protrusion devices may have a constriction 80 at one end 82 thereof. The ends 82 may be formed as a sphere, a swallow-tail or have a different form.

It is possible that prior to or during the insertion of the protrusion devices 68, the openings 76 of the recesses are bent open by deforming the material near the openings 76 in order to provide access to the end 82 of the protrusion device 68.

The coating material 70 may for instance be a synthetic material. A known material which is suitable for this purpose is Glass Syntactic Polyurethane (GSPU) . Other materials are also possible. GSPU has the advantageous characteristic that it is a coherent and flexible material with equal properties in all directions, in which it is easy to manufacture the recesses 66a, 66b and 6βc.

The protrusion devices 68a, 68b, 68c may have various sizes and shapes. It is possible that a single elongated protrusion element 68 is inserted into at least one recess, for instance in a helical form about the pipeline. It is also possible that a plurality of protrusion devices 68a, 68b, 68b are provided on the pipeline 8, wherein many different configurations are conceivable. A staggered configuration is possible, or an alternating configuration of discrete protrusion elements 68a, 68b, 68c.

Turning to Fig. 7, an embodiment of the invention is shown, wherein a protrusion device 84 is provided on a pipeline 8, the protrusion device 84 covering the exterior surface 72 of the pipeline 8. Protrusions 86a, 86b, 86c are provided on the protrusion device which protrusions 86a, 86b, 86c can adopt an installing position 88 and a target position 90. In the installing position 88, the protrμsions are folded substantially against the pipeline 8, such that they only slightly protrude outwardly from the pipeline 8. In the target position 90, the protrusions fully protrude outwardly from the pipeline 8.

Connection organs 92 may be provided in order to keep the protrusions fixed in their installing position 88.

In operation, the connection organs 92 are removed or cut after the pipeline 8 has passed the installation devices along the lay path, such as the aligner, the straightener or supporting rollers, clamps 11, 13 or tensioner. The protrusions 86a, 86b, 86c may veer from the installing position 88 back to their target positions due to the stress in the material, or may be moved to their target positions 90 by a straightener organ (not show) . This embodiment is especially suitable for pipe reeling, but may also be applied in S- lay or J-lay.

It will be obvious to a person skilled in the art that numerous changes in the details and the arrangement of the parts may be varied over considerable range without departing from the spirit of the invention and the scope of the claims.

Claims

1. A pipeline laying vessel (1) having a lay path (4) along which a pipeline (8) is to be laid, the pipeline laying vessel comprising an installation device (7) configured for providing a protrusion device (12, 68a, 68b, 68c) on at least part of the pipeline.

2. The pipeline laying vessel of claim 1, wherein the installation device comprises a protrusion device path extending from a protrusion device source (10) towards an installing location (16) , and wherein the installation device is configured to move a protrusion device from the protrusion device .source location along the protrusion device path toward the pipeline, in order to provide the protrusion device on the pipeline.

3. The pipeline laying vessel of claim 1, wherein the installation device comprises a wrapping device (14) configured for wrapping the protrusion device around the pipeline.

4. The pipeline laying vessel of claim 3, wherein the wrapping device comprises a wrapping organ configured to deform a protrusion device comprising an elongated body (18) of material, thereby substantially wrapping the elongated body of material around the pipeline, the elongated body of material having at least one protrusion (20a, 20b, 20c) provided on it.

5. The pipeline laying vessel of claim 1, wherein the installation device comprises a protrusion device reel on which a protrusion device comprising an elongated body of material, and configured for spooling the protrusion device from the reel in order for the protrusion device to be provided on the pipeline, in particular substantially in a lengthwise direction of the pipeline.

6. The pipeline laying vessel of claim 1, wherein the installation device comprises a protrusion device pre-assembly device (22) configured for pre-assembling a protrusion device (12) .

7. The pipeline laying vessel of claim 1, wherein the installation device (7) comprises an extrusion device (26) configured for extruding a material (28) for forming a protrusion device (12) which is to be connected to the pipeline.

8. The pipeline laying vessel of claim 7, wherein the extrusion device (26) is configured for providing a synthetic material (35) on the pipeline, wherein the at least one protrusion (2OA, 2OB, 20C) projects from the synthetic material.

9. The pipeline laying vessel of claim 7, wherein at least a part (32) of an outflow opening (30) of the extrusion device is configured to rotate about the lay path during the passing of the pipeline, to provide at least one protrusion protruding from the pipeline 8 at a varying radial angle (α) along the length of the pipeline.

10. The pipeline laying vessel of claim 1, wherein the installation device comprises a molding device (40) provided substantially around the lay path and configured for molding a material (38) which covers at least a part of the outer surface (74) of the pipeline during the passing of the pipeline for forming at least one protrusion on the pipeline, in particular in a helical form around the pipeline.

11. The pipeline laying vessel of claim 1, the installation device comprising a winding device (49) configured to wind a protrusion device comprising an elongated body (59a, 59b, 59c) of material around the pipeline, in particular in a helical form.

12. The pipeline laying vessel of claim 1, wherein the installation device comprises at least a first positioning device (50a) and a second positioning device (50b) provided at the installing location at different radial positions relative to the lay path, the first positioning device configured to position a first segment (52a) of a protrusion device near the pipeline, and the second positioning device configured to position a second segment (52b) of a protrusion device near the pipeline, in such a manner that the at least first and second segments can be interconnected and form at least one protrusion on the pipeline 8.

13. The pipeline laying vessel of claim 12, wherein the at least two positioning devices are configured to substantially position at least a respective first (52a) and second (52b) elongate body of material at the pipeline (8) in such a manner that opposite rims (59a, 59b) of the at least first and second elongated bodies of material are positioned near one another in order to be connected to one another, the rims forming protrusions (20a, 20b) .

14. The pipeline laying vessel of claim 12, wherein the at least two positioning devices are provided on at least one rotary device configured for rotation around the lay path.

15. The pipeline laying vessel of claim 1, wherein the installation device (7) is configured to insert an end (82) of a protrusion device (68a, 68b, 68c) into a recess (66a, 66b, 66c) provided in the exterior surface (72) of the pipeline, the end (82) configured for mating with the recess in order to be substantially fixed to the pipeline.

16. The pipeline laying vessel of claim 15, wherein the installation device is configured to insert a part of an elongate body of material in the recess of the pipeline in order for the elongate body of material to extend along a substantial length of the pipeline and protrude outwardly from the pipeline.

17. A method for laying a pipeline having at least one protrusion installed thereupon, the method comprising the steps of:

(a) providing a pipeline laying vessel (1) having an installation device (7) configured for installing at least one protrusion device (12, 68a, 68b, 68c) on the pipeline at an installing location (16) near the lay path

(4);

(b) laying the pipeline from the pipeline laying vessel;

(c) providing a protrusion device on the pipeline by the installation device.

18. The method of claim 17, comprising providing at least one protrusion which is oriented at a varying radial angle (α) along the length of the pipeline.

19. The method of claim 17, wherein the protrusion device comprises an elongate body of material having at least one protrusion projecting from the elongate body, and wherein the elongate body of material is provided on the pipeline. .

20. The method of claim 19, comprising moving the elongate body along a protrusion device path (23) toward the installing location (16) , and wherein the elongate body is provided on the pipeline as the pipeline passes the installing location.

21. The method of claim 17, comprising wrapping the elongate body substantially around the pipeline.

22. The method of claim 17, comprising winding the elongate body around the pipeline, in particular in a helical form.

23. The method of claim 17, comprising spooling the elongate body off a reel (10) positioned at the protrusion device source.

24. The method of claim 17, comprising pre-assembling the protrusion device prior to it being provided on the pipeline.

25. The method of claim 17, comprising forming at least a part of the at least one protrusion device by an extruding device, in particular as the pipeline passes the installing location.

26. The method of claim 25, comprising providing a layer of material substantially around the pipeline and providing at least one protrusion projecting from said layer of material.

27. The method of claim 25, comprising moving a protrusion outflow opening of the extrusion device relative to the pipeline during the laying thereof,

28. The method of claim 27, comprising rotating the protrusion outflow opening about the pipeline, for forming a helical protrusion.

29. The method of claim 17, wherein at least one protrusion is formed by molding a material which has previously been provided on a substantial part of the outer surface of the pipeline.

30. The method of claim 17, comprising:

(cl) arranging at least one substantially flexible body of material against the pipeline;

(c2) deforming at least a part of the body substantially around the pipeline, in such a way that at least one part of the body forms a protrusion projecting from the pipeline; and

(c3) fixing the position of the at least one flexible body relative to the pipeline.

31. The method of claim 17, comprising:

(cl) providing at least a first body of material at a first side against the pipeline and a second body of material at a second side against the pipeline,

(c2) deforming the first and second bodies such that a first end of the first body is positioned near a first end of the second body, and a second end of the first body is positioned near a second end of the second body, thereby forming at least one protrusion; and

(c3) connecting the respective first ends to one another and connecting the respective second ends to on another.

32. The method of claim 31, wherein the respective first ends form a first protrusion and the respective second ends form a second protrusion.

33. The method of claim 31, comprising winding the at least first and second elongate body helically around the pipeline.

34. The method of claim 17, comprising connecting at least one protrusion device to a recess in the outer surface of the pipeline.

35. The method of claim 34, comprising providing the recess in the outer surface of the pipeline.

36. The method of claim 34, comprising: providing a synthetic material on the pipeline, in particular covering a substantial part of the outer surface of the pipeline, and providing the recess in the synthetic material.

37. The method of claim 34, comprising providing the recess in the form of an elongate channel.

38. The method of claim 34, wherein at least a part of a material near the recess is at least temporarily deformed in order to form a substantially fixed connection between the protrusion device and the pipeline.

39. The method of claim 17, further comprising the steps of: p) pre-assembling the pipeline comprising at least one protrusion device, the protrusion device having an installation position and a target position, wherein the protrusion device projects from the pipeline substantially further in the target position than in the installation position, and q) moving the protrusion device relative to the pipeline from the installation position to the target position.

40. A protrusion device for use in the method according to any of claims 17-39.

41. The protrusion device of claim 40, comprising an elongate body (18) having at least one protrusion (20a, 20b, 20c) protruding from the body.

42. The protrusion device of claim 41, wherein the elongate body is deformable.

43. The protrusion device of claim 41, wherein the protrusion device comprises a plurality of protrusions (20a, 20b, 20c) extending from the elongate body.

44. The protrusion device of claim 43, wherein the elongate body has a main longitudinal axis, and wherein at least a part of the protrusions have different axial position and lateral positions on the elongate body.

45. The protrusion device of claim 41, wherein ridges are provided on the elongate body.

46. The protrusion device of claim 45, wherein at least a number of ridges extend in a ridge direction which is oriented at an inclination to a main longitudinal axis of the elongate body.

47. The protrusion device of claim 41, wherein the elongate body comprises a series of interconnected elements which are movable relative to one another in order to enable the deforming of the elongate body.

48. The protrusion device of claim 40, comprising an end (82) which is configured to be inserted into a recess (66) in an outer surface (72) of a pipeline, the end being configured to form a secure connection with the recess when inserted into the recess, in particular configured to form a swallow-tail connection with the recess .

49. A pipeline for use in the method of claim 17.

50. The pipeline according of claim 49, having at least one recess in the exterior surface thereof for inserting a protrusion device therein.

51. The pipeline of claim 49, comprising a metal inner pipeline substantially covered on the outer surface by a substantially synthetic material (70) , the substantially synthetic material having at least one recess for insertion of a protrusion device therein.

52. The pipeline of claim 49 or 50, wherein at least a part of the material near the recess is deformable, and wherein the recess has a predetermined form such that the recess can form a substantially secure connection with a protrusion device inserted in the recess.

53. The pipeline of any of claims 50-52, wherein the at least one recess is elongate.

54. The pipeline of claim 50, wherein the at least one recess has a helical form, spiraling around the pipeline along the length thereof.

55. The pipeline of claim 50, wherein the at least one recess has a form suitable for forming a substantially secure connection with a protrusion device inserted therein, in particular a ^λswallow- tail connection' .

56. The pipeline of claim 50, wherein the recess has an opening (76) which is constricted relative to a size of a cavity (78) behind the opening.

57. The pipeline of any of claims 49 or 56, wherein a plurality of recesses are provided in the outer surface of the pipeline, wherein at least a part of the recesses have different axial and radial positions on the pipeline.

58. Assembly of a pipeline and at least one protrusion device manufactured by the method of claim 17.

59. Method for pre-assembling a pipeline which is to be laid by the pipeline laying vessel of claim 1, the method comprising: a) providing a material (70) , in particular a synthetic material, substantially covering the outer surface of the pipeline; and b) forming at least one recess in the material.

60. Method for pre-assembling a pipeline which is to be laid with the pipeline laying vessel of claim 1, the method comprising: a) arranging a material, in particular a deformable material, substantially covering the outer surface of the pipeline.

61. A pipe section for use in the method of claim 17, in particular for laying a pipeline by each time connecting a pipe section to an end of a pipeline suspended from the pipeline laying vessel .