WO2026010508A1

WO2026010508A1 - Buckle mode trigger for coated pipelines

Info

Publication number: WO2026010508A1
Application number: PCT/NO2025/050123
Authority: WO
Inventors: Håvar ILSTAD; Erik Levold; Mario POLANCO LORIA; John Berntsen
Original assignee: Equinor Energy AS
Current assignee: Equinor Energy AS
Priority date: 2024-07-05
Filing date: 2025-07-01
Publication date: 2026-01-08
Anticipated expiration: 2027-01-05
Also published as: GB2642351A; GB202409770D0

Abstract

The present disclosure relates to a subsea pipeline buckling mode trigger system, the subsea pipeline buckling mode trigger system comprising a pipeline sub-section circumscribed by a coating, the coating defining an axially localised region of weakness that extends around at least part of the circumference of the pipeline sub-section, and associated methods of manufacture.

Description

Buckle Mode Trigger for Coated Pipelines

Technical Field

The present invention relates to systems for altering the buckle mode of a pipeline, particularly subsea pipelines with external coating, and associated methods of manufacture.

Background

When submerged in deep waters, subsea pipelines are exposed to high external pressures. Depending on the geometrical and material properties (such as but not limited to, the ovality, wall thickness, coating thickness and mechanical strength of the pipeline), such high external pressures may induce collapse of the pipeline. For example, a section of pipe with an ovality over 3% will be more susceptible to collapse due to high external pressures, compared to a pipeline with an ovality of 1% or less. While sections of pipe may not be designed and manufactured with a high ovality, accidental damage during installation or from excessive impacts from third parties during operation may cause the ovality of a section of pipe to increase.

If a section of pipe collapses due to external pressure forces, this can induce flattening of the entire pipeline, with the collapse propagating along the pipeline with a velocity in the range of 100 - 300 m/s. Flattening (or propagation buckling) of the pipeline will continue until the external pressure is reduced (for example when the pipe reaches shallower water), or when a sufficiently thick pipe, known as a buckle arrestor, is reached.

A known pipeline buckling arrestor comprises a pipe that has a wall thickness greater than that of the pipeline. One or more buckle arrestors may be included in a pipeline to ensure, in the event of pipeline collapse, that the collapse does not propagate too far along the pipeline. Inclusion of such buckling arrestors in a pipeline requires additional manufacturing time, logistics and expense though, which is undesirable.

Another solution to halt buckling propagation is a slip-on arrestor, which consists of stiff half-shells bolted on to the outside of the pipeline before it is submerged. However, installing these arrestors is costly due to increases in the overall pipeline installation time. As such arrestors also have significant weight, installing them on a vessel also poses a health, safety and environment (HSE) risk to personnel.

Under normal circumstances, if collapse of a subsea pipeline is to propagate it will do so in ‘dog-bone mode’. An example of a pipe 10 that has collapsed in ‘dog-bone’ mode 10’ is shown in Figure 1A.

Figure 1 B depicts an alternative collapse propagation mode of a pipe 10, known as ‘u- mode’ collapse propagation 10”. For u-mode collapse propagation 10” to occur, a pressure significantly greater is required than that required to induce dog-bone mode 10’ collapse propagation.

Other collapse propagation modes that occur at significantly higher pressures than dog bone mode, such as ‘pear mode’, can also be achieved. The variation in the propagation mode of collapse may be dependent upon a number of external factors, such as the pipeline being at least partially surrounded by tubing, rock or sediment, or defects in the pipe (such as damage or wall thickness variation).

Summary

A first aspect of the invention relates to a subsea pipeline buckling mode trigger system, the system comprising a pipeline sub-section circumscribed by a coating, the coating defining an axially localised region of weakness that extends around at least part of the circumference of the pipeline sub-section.

Such a localised region of weakness of the coating of a pipeline may be used to induce a change in the buckling propagation mode of a pipeline. In other words, the axially localised region of weakness may be used to ‘trigger’ a change of the buckling propagation mode of the subsea pipeline. For example, when external pressure causes buckling to propagate along a subsea pipeline (wherein the buckling propagation of the pipeline occurs in ‘dog-bone’ mode), the localised region of weakness defined by the coating of the pipeline may provide a trigger point to change the buckling propagation mode from a first buckling propagation mode to a second buckling propagation mode (e.g., from ‘dog-bone’ buckling propagation to ‘u-mode’ buckling propagation). When the mode of pipeline buckling propagation is changed, the pressure required to buckle the pipeline may be greatly increased. Therefore, propagation of pipeline buckling may be halted at or shortly after reaching the pipeline buckling mode trigger system of the present invention.

As outlined above, the external pressure required to induce ‘u-mode’ propagation buckling of a pipe may be in the range of three to four times greater than the external pressure required to induce ‘dog-bone’ buckling. Therefore, by including a trigger within the coating of the pipeline to ensure ‘u-mode’ buckling is the preferred mode of buckling propagation when exposed to high external pressure, a means of arresting propagation of pipeline buckling is provided which utilises the known buckling propagation modes of pipelines (and the pressure required to induce such failure modes), to help prevent total collapse of the pipeline in which it is incorporated.

Furthermore, the buckling mode trigger system of the present invention may also be less complex to manufacture and deploy than the known solutions currently used to arrest the propagation of pipeline buckling. For example, the buckling mode trigger system of the present invention may not require the same manufacturing time and expense of the known buckling arrestors that are simply a length of pipe with a wall thickness much greater than the pipeline in which they are incorporated.

The buckling mode trigger system of the present invention may also be less complex to deploy than traditional ‘slip-on’ buckling arrestors, as it can simply be included as subsection of a coated pipeline, without the need for additional components to be added to the pipeline prior to deployment (as with traditional ‘half-shell’ buckling arrestors). The buckle mode trigger system of the present invention can also be incorporated into the pipeline prior to transporting the pipeline to its offshore location/prior to the pipeline being wound on a reel.

The pipeline sub-section may comprise a length of steel pipe.

The coating of the buckling mode trigger system may comprise a thermal coating circumscribing the pipeline sub-section. A thermal coating may help minimise heat loss and maintain the product in the pipeline at as suitable temperature for transportation. The thermal coating may also help to prevent wax build up in the pipeline, with the pipeline being maintained at a suitable temperature to prevent wax deposits from forming. Thermal coatings may also offer corrosion resistance properties, protection the pipeline from corrosion which may be induced by the surrounding environment. One skilled in the art will also appreciate that alternative coatings (e.g. coatings not provided to help minimise heat loss from the product in the pipeline) may also provide corrosion resistance properties.

The coating may comprise a coating system. The coating system may comprise a plurality of layers. At least one of the plurality of layers may comprise or be formed of a material that is different from at least one of the other layers. At least one of the layers may be a bonding layer, bonding the coating to the pipe. At least one of the layers may be porous or comprise pores. This may allow water to pass through the porous layer. Alternatively, at least some of the pores may be at least partially filled, for example with glass. In certain examples, at least the pores may be filled with glass syntactic polypropylene (GsPP). Filling the pores may help to strengthen then coating, providing additional resistance from high subsea pressures. At least one of the layers may be non-porous. This may prevent water from passing through the non-porous layer.

It will be understood by one skilled in the art that at least one of the plurality of layers of the coating system may provide corrosion resistance properties, to protect the pipeline sub-section from corrosion.

In one example, the coating may comprise a multi-layered polypropylene coating (MLPP). In this example, the MLPP may comprise an innermost bonding layer, an intermediate layer of porous polypropylene and an outer layer of solid polypropylene. In this example, at least some of the pores may be at least partially filled, for example with glass. In certain examples, at least some of the pores may be at least partially filled with GsPP, providing a GsPP layer.

The axially localised region of weakness may comprise at least one channel defined by the coating. The at least one channel may extend around at least part of the circumference of the pipeline sub-section. The channel may extend axially along the pipeline sub-section. Therefore, the at least one channel defined in the coating may define a region of reduced thickness in the coating, providing the axially localised region of weakness. The at least one channel may extend partially through the coating. Alternatively, the at least one channel may extend fully through the coating. This may allow for the new pipeline buckling propagation mode to be defined/configured by the operator.

Advantageously, extending the at least one channel fully through the coating may also allow water to enter between the pipe and the coating circumscribing the pipe. Entry of water between the pipe and the coating may be used to provide increased pressure at specific points between the pipe and the coating, helping to reconfigure the pipeline to a new mode of buckling propagation. It is important to note that having water ingress close to the interface between the pipeline and the coating interface (e.g. in a channel which does not extend all the way through the coating) may also achieve the same effect.

The at least one channel may be formed by machining the coating once it has been applied to a pipe. Alternatively, the at least one channel may be formed using a mould during application of the coating to a pipe. It will be appreciated that the at least one channel may be formed by any means within the knowledge of the skilled person.

The at least one channel may have a uniform depth around the circumference of the pipeline buckling mode trigger system. The at least one channel may have a uniform width around the circumference of the pipeline buckling mode trigger system. Either of these characteristics may provide a consistent trigger mechanism to change the buckling propagation mode of the pipeline downstream of the pipeline buckling mode trigger system.

The coating may comprise at least one of a fusion bonded epoxy, coal tar epoxy, polypropylene, polyethylene; or any suitable polymer, composite or metallic material within the knowledge of the skilled person.

The at least one channel may be at least partially filled with a channel material. The channel material may comprise at least one of fusion bonded epoxy, coal tar epoxy, polypropylene, polyethylene, any suitable metallic material, or any suitable material known to the skilled person for this technical application. By filling the at least one channel with a channel material, this may still provide the pipeline with sufficient protection from damage in the subsea environment (e.g. from anchors, debris, etc.).

The channel material may comprise a different mechanical properties than the coating. For example the channel material may comprise a different stiffness, strength and/or energy dissipation properties than the coating material.

Either of the coating and channel material may also provide corrosion resistance properties. This may help to maintain the integrity of the pipeline buckling mode trigger system in a subsea environment.

The at least one channel may comprise a plurality of channels. This may provide a pipeline buckling propagation mode trigger system with multiple ‘triggers’ for allowing the pipeline to switch to an alternative mode of buckling propagation. For example, if buckling is propagating along a pipeline in ‘dog-bone’ mode, and the first region of weakness (i.e. the first circumferential channel) does not trigger the pipeline buckling to a new buckling propagation mode (e.g., ‘u-mode’), the second or subsequent channels may bring about the desired effect.

The plurality of channels may be parallel with one and other.

As outlined above, the coating of the buckling mode trigger system may comprise a bonding layer as a first layer of a coating comprising a plurality of layers. The bonding layer may at least partially circumscribe the pipeline sub-section between a second layer of coating and the pipeline sub-section. The bonding may partially circumscribe the pipeline sub-section, with the axially localised region of weakness being defined by or comprising the region with no bonding. Alternatively the bonding may fully circumscribe the pipeline sub-section and define a region of weakened bonding, with the region of localised weakness being defined or comprising the region of weak bonding.

In use, if flattening of the pipeline is induced (due to subsea pressure), flattening may propagate in a first propagation mode (e.g., ‘dog-bone’ mode) until it reaches the pipeline buckling propagation mode trigger system of the present invention. . When the flattening propagation reaches buckling propagation mode trigger system, the pipeline sub-section may separate from the coating at or after the region of no or weak bonding, allowing water to enter between the pipeline sub-section and the coating. Entry of water in these specified areas may cause increased pressure in specific/predefined regions around the circumference of the pipe. Use of increased pressure in specified areas around the circumference of the pipe may assist with reconfiguring the first buckling propagation mode (e.g., ‘dog-bone mode’) at the pipeline buckling mode trigger system to a second buckling propagation mode (e.g., ‘u-mode’); significantly raising the pipeline’s resistance to collapse propagation.

Any suitable means of bonding a coating to a pipeline understood by one skilled in the art may be used. Additionally, the region of weak or no bonding may also be determined by the surface finish of the pipe (e.g. the surface of the pipe may be smoothed in the required area of weak or no bonding), or the use of changing temperatures in the required region of weak or no bonding during application of the coating.

A second aspect of the invention relates to a pipeline comprising a pipeline buckling mode trigger system in accordance with the present disclosure, connected between two adjacent sections of coated pipeline.

A third aspect of the invention relates to a method of manufacturing a subsea pipeline buckling mode trigger system, the method comprising circumscribing a pipeline subsection with a coating; and, defining an axially localised region of weakness in the coating, wherein the axially localised region of weakness extends around at least part of the circumference of the pipeline sub-section.

The method may further comprise coating the pipeline sub-section with a thermal coating.

The method may further comprise coating the pipeline sub-section with a coating system, wherein the coating system comprises a plurality of layers. At least one of the plurality of layers may comprise or be formed of a material that is different from at least one of the other layers. At least one of the layers may be a bonding layer, bonding the coating to the pipe. At least one of the layers may be porous or comprise pores. This may allow water to pass through the porous layer. At least one of the layers may be non-porous.

The method may comprise defining a region of no bonding in the coating system of the coating of the present invention. The region of no bonding may be defined at or adjacent the axially localised region of weakness.

Alternatively, the method may comprise defining a region of weakened bonding in the coating system of the coating present invention. The region of weakened bonding may be defined at or adjacent the axially localised region of weakness.

The method may further comprise filling the at least one channel with a channel material.

The method may further comprise filling the at least one channel with a channel material that has a different mechanical properties than the coating. For example the channel material may comprise different stiffness, strength and/or energy dissipation properties than the coating material.

The method may further comprise defining a plurality of channels in the coating.

The method may further comprise defining a plurality of parallel channels in the coating.

Manufacture of a pipeline buckling mode trigger system in accordance with the third aspect may reduce manufacture time and expense in comparison with manufacture of known buckling arrestors. For example, manufacturing a pipeline buckling mod trigger system in this manner, may be significantly faster and less expensive than manufacture of a traditional ‘thick-walled’ pipeline buckling arrestor, given the significant amount of materials, manufacture and machine time used to produce such a buckling arrestor.

Manufacture of a pipeline buckling mode trigger system according to the third aspect also has reduced complexity (and is thus less time consuming and expensive) compared to manufacture of ‘half-shell’ buckling resistors, as described above. It will be appreciated any of the features defined with respect to any aspect of the disclosure may be used in combination with other aspects of the disclosure.

Brief Description of the Drawings

Figures 1A and 1B show initial and end states of different pipeline buckling propagation modes of subsea pipelines;

Figures 2A and 2B show plan views of different embodiments of the pipeline buckling mode trigger system according to the present invention;

Figures 2C and 2D shown examples of coating systems that may be used with the present invention;

Figures 2E and 2F shown plan view of different embodiments of the pipeline buckling mode trigger system according to the present invention;

Figures 3A and 3B show cross-sectional views of the embodiments of Figures 2A to 2F;

Figure 4A and 4B show cross-sectional views of further embodiments of the pipeline buckling mode trigger system of the present invention; and,

Figures 5A and 5B show plan views of further embodiments of the pipeline buckling mode trigger system of the present invention.

Detailed Description

Figure 2A shows the subsea pipeline buckling mode trigger system 100 of the present invention incorporated within a subsea pipeline 1000. The buckling mode trigger system 100 has been arranged in series between adjacent sections of pipe 105 to form the pipeline 1000, prior to being deployed on the seabed

The buckling mode trigger system 100 comprises a steel pipeline sub-section 120 circumscribed by a coating 140, with three channels 150 defined in the coating 140. Each of the channels 150 extends around the circumference of the buckling mode trigger system 100. In this example, the coating 140 is a coating system, formed of an innermost bonding layer 142 and one or more outer layers 144, 146. The coating system may be a system such as a MLPP coating, comprising an innermost bonding layer 142, an intermediate layer 144 of porous polypropylene and an outermost layer of non-porous polypropylene 146, as shown in the example of Figure 2C. In this example, the bonding layer 142 of the coating system circumscribes the pipeline sub-section 120.

As shown in the example of Figure 2D, one or more regions of weakened bonding 135 may be provided in the bonding layer 142. For example, one or more regions of weakened bonding 135 may be provided at or in the region of localised weakness 150, to assist with triggering the pipeline into a new mode of buckling propagation. In an alternative example, the bonding layer 142 of the coating system may partially circumscribe the pipeline sub-section 120 (i.e. there may be one or more regions 135 of the coating system that have no bonding). For example, there may be no bonding in or adjacent the axially localised region of weakness 150.

The region of weakened or no bonding 135 may extend partially along the circumference of the pipeline sub-section 120 between the pipeline sub-section 120 and the coating system 140. Alternatively, the region of weakened or no bonding 135 may extend around the entire circumference of the pipeline sub-section 120).

The region of weakened or no bonding 135 may extend as far along the interface 130 between the pipeline sub-section 120 and the coating system 140 as required by the user. For example, extension of the region of weakened or no bonding 135 along the interface 130 between the pipe 120 and the coating system 140 may be determined by predicted subsea pressures, and/or the pressure required to induce a required mode of buckling propagation of the pipeline. Additionally, more than one region of weak or no boding 135 may be provided at the interface 130 between the pipeline sub-section 120 and the coating system 140. Additional regions of weak or no bonding 135 may be provided at the interface 130 between the pipeline sub-section 120 and the coating system 140, dependent on the requirements to induce a new mode of buckling propagation of the pipeline.

In some embodiments, the region of weak or no bonding 135 between the pipeline subsection 120 and the coating system 140 of the buckling mode trigger system 100 may define the axially localised region of weakness of the pipeline buckling arrestor. In the example of Figure 2A, the axially localised region of weakness 150 is provided by the plurality of channels 150. While the channels 150 are provided with a rectangular profile, one skilled in the art will appreciate that these may be provided with any suitable any suitable shape profile (e.g. a triangular or square profile, depending on the required buckling characteristics required of the pipeline buckling mode trigger system 100).

Additionally, in this embodiment, the channels 150 are shown as fully extending through the coating 140 of the buckling mode trigger system 100, so that the inner pipeline sub-section 120 is exposed. In alternative examples. The depth of the channels 150 may be configured to provide the buckling mode trigger system 100 with required buckling characteristics. For example, the depth of the channels 150 may be configured so that ‘u-mode’ buckling of the buckling mode trigger system 100 occurs at a predetermined subsea pressure.

The channels 150 of the pipeline buckling arrestor 100 may be defined by any suitable means within the understanding of one skilled in the art. For example, the channels 150 may be machined into the coating 140 surface once it has been applied to the pipeline sub-section 120. Alternatively, the channels 150 may be moulded into the coating when it is applied to the pipe 120.

In use, pipeline flattening may propagate along the pipeline 1000 (induced by subsea pressure) in the direction of the arrow 115 shown. If this flattening/buckling is propagating in ‘dog-bone’ mode, when the pipeline flattening reaches the pipeline buckling mode trigger system 100, the localised region of weakness provided by the circumferential grooves 150 will trigger a change in the buckling/flattening of the pipeline 1000 into a new mode of buckling propagation (e.g., ‘u-mode’ buckling propagation). As this new mode of pipeline buckling propagation requires a far greater external pressure to be induced, the pipeline buckling propagation may be arrested shortly after reaching the pipeline buckling mode trigger system 100. This may limit the span of damage to the pipeline 1000, ultimately limiting any repairs to the pipeline 100 that are required in the event of collapse.

As outlined above, triggering of the pipeline 1000 into a new mode of buckling propagation buckling may be assisted by the use of one or more areas of weakened/no bonding between the pipeline sub-section 120 and the coating system 140 at or adjacent the region of localised weakness 150 of the pipeline buckling mode trigger system 100. Such regions of weakened/no bonding may allow water to be introduced between the coating 140 and the pipeline sub-section 120 during flatting/buckling of the pipeline 1000. Introduction of water between the pipeline sub-section 120 and the coating 140 of the buckling mode trigger system 150 in specified regions may provide an increase in pressure in specified regions between the pipeline sub-section 120 and the coating 140 of the buckling mode trigger system 150. Such an increase in pressure in specified regions may assist triggering a change in the first buckling propagation mode of the pipeline 1000 into a second buckling propagation mode.

The pipeline 1000 of the Figure 2A may be deployed from a reel on a vessel, with the pipeline buckling mode trigger system 100 prefabricated into the pipeline 1000 which is stored on a reel. Alternatively, the buckling arrestor 100 may be added to the pipeline 1000 as it is being deployed into the sea (for example, the buckling arrestor 100 may be welded to adjacent pipe sections 105 on a vessel, just prior to deployment).

Figure 2B shows an alternative pipeline buckling mode trigger system 100 to that of Figure 2A, wherein the buckling mode trigger system 200 comprises a region of localised weakness 250 that is formed by removal/absence of a single circumferential band of coating 240 from the pipeline buckling mode trigger system 100. As with the embodiment of the Figure 2A, one or more areas of weakened or no bonding may be provided in a coating system 240 at or adjacent the localised region of weakness 250 to assist with triggering the pipeline 2000 into a different failure/buckling mode (e.g., from ‘dog-bone’ mode collapse to ‘u-mode’ collapse), to assist with arresting propagation of pipeline buckling.

It will be appreciated that while Figures 2A and 2B show only one buckling mode trigger system 100, 200 being used in a pipeline 1000, 2000, a plurality of buckling mode trigger systems may be used in a pipeline, arranged at regular intervals to provide robust limitation of pipeline flattening propagation.

Figure 2E shows a variation of the embodiment of the invention shown in Figure 2A. Again, the pipeline buckling mode trigger system 100’ is shown as being incorporated in a pipeline 1000’ between two sections of coated pipe 105’. The pipeline buckling mode trigger system 150’ is of the same construction as that of Figure 2A, except in that the circumferential channels 150’ that form the region of localised weakness 150’ extend only partially around the circumference of the buckling mode trigger system 100’. As with the embodiment of Figure 2A, the coating 140’ may be a coating system of the same arrangement shown in Figure 2C, and may comprise regions of weak or no bonding at or adjacent the localised region of weakness 150’, to assist with triggering the pipeline into a new mode of buckling propagation in the event of pipeline 1000’ collapse.

Similarly, Figure 2F shows a variation of the embodiment of Figure 2B, with the only difference being that the localised region of weakness 250’ extends only partially around the circumference of the pipeline buckling mode trigger system 200’.

Figure 3A shows a cross-sectional view of the embodiments of the invention shown in Figures 2A and 2E, with the cross-section taken along central plane 110/110’. Figure 3A shows the pipeline sub-section 120/120’ of the buckling mode trigger system 100/100’ comprising a coating system 140/140’ (the same as that described in relation to Figure 2C), bonded to the pipe at the interface 130/130’. The coating system 140/140’ comprises three circumferential grooves formed therethrough, defining the region of localised weakness 150/150’.

While the localised region of weakness 150/150’ is formed by grooves which extend entirely through the coating 140/140’, and which have a rectangular profile, it will be appreciated that the localised region of weakness may comprise grooves that extend partially through the coating 104/140’ of the pipeline buckling mode trigger system 100/100’, or which have any other suitable profile (e.g. square, rounded, triangular, etc.). Therefore, localised region of weakness 150/150’ of the pipeline buckling mode trigger system 100/100’ may be configured dependent on the pressure required to trigger the pipeline 1000/1000’ into ‘u-mode’ buckling.

Figure 3A also shows regions of weakened or no bonding 135/135’ in the coating system 140/140’ at the interface between the pipeline sub-section 120/120’ and the coating system 140/140’, at/adjacent the localised region of weakness 150/150’ of the pipeline buckling mode trigger system 100/100’. Regions of weakened or no bonding 135/135’ may assist with inducing a new mode of pipeline bucking propagation of the pipeline 1000/1000’, as these regions may allow water between the coating 140/140’ and the pipe 120/120’, helping to increase the pressure at specified regions between the pipeline sub-section 120/120’ and the coating 140/140’, helping to trigger the pipeline into a second buckling propagation mode.

As outlined above, said regions of weakened or no bonding 135/135’ are optional with the buckling mode trigger system of the present disclosure.

Figure 3B shows a cross-sectional view of the embodiments of the invention shown in Figures 2B and 2F, with the cross-section taken along central plane 210/210’. This is largely similar to the embodiment of Figure 3A, except that the localised region of weakness 250/250’ is a single channel formed in the coating 240/240’ of the pipeline buckling mode trigger system 200/200’.

This embodiment may also include regions of weakened or no boding 235/235’ between the coating system 240/240’ (wherein the coating system is the same as that described in Figure 2C) and the pipeline sub-section 220/220’. These regions of weakened or no bonding 235/235’ are adjacent the localised region of weakness 250/250’.

Figures 4A and 4B show alternative embodiments of the present invention, wherein the coating 340, 440 comprises a coating system (as described above in relation to Figure 2C), and the region of localised weakness 350, 450 in each is at least partially filled with a channel material 355, 455. . The channel material 355, 455 is provided to ensure the pipe 320, 420 is still protected from the external environment (e.g. from anchor or debris damage) in the area of localised weakness, while still providing a buckling mode trigger system that is capable of changing the buckling propagation mode of the pipeline. This is achieved by the channel material 355, 455 having different mechanical properties than the than the coating system material 340, 440. For example, the channel material may provide different mechanical properties, such as different stiffness, strength and/or energy dissipation properties than the coating system 340, 440. The channel material 355, 455 may comprise any suitable material within the understanding of the skilled person. Figures 5A and 5B show further embodiments of the invention, wherein each pipeline buckling mode trigger system 600, 700 which comprises a coating 645, 745 that is different (e.g. comprises one or more different materials) than the coating of the rest of the pipeline 6000, 7000. Such a coating may be a coating system similar to that shown and described in Figure 2C. Such a coating may be used to cover a joint in the pipeline 6000, 7000, such as a weld between pipeline sub-sections. Therefore, the coating 645, 745 of the pipeline buckling mode trigger system 600, 700 in these example may be a field joint coating (FJC).

Referring firstly to Figure 5A, a pipeline buckling mode trigger system 600 according to the present invention is incorporated within a pipeline 6000, between two sections of pipe 605. The pipeline buckling arrestor 600 comprises a pipeline sub-section 620 circumscribed by a coating system 645. While not shown in this example, the outer diameter of the coating system 645 may be thicker than the outer diameter of the pipeline 6000 within which the buckling mode trigger system 600 is incorporated. In this example, the coating 645 is also formed of a coating system 645 that is different from the coating system of the rest pipeline 6000 (e.g., the coating system 645 comprises at least one material that is different from the rest of the pipeline coating, or the coating system 645 has different mechanical properties than the coating of the rest of the pipeline 6000), although this may not always be the case. The pipeline buckling mode trigger system 600 further includes two regions of localised weakness 650 in the form of circumferential channels in the coating, circumscribing the pipe 620.

The pipeline buckling mode trigger system 600 may further include one or more regions of weakened or no bonding between the coating system 645 and the pipe 620, to assist with triggering the pipeline into new mode of buckling propagation, as described above. The regions of weakened or no bonding may be at or adjacent the regions of localised weakness.

Figure 5B shows a pipeline buckling mode trigger system 700 that is largely the same as that of Figure 5A, with the exception of the configuration of the localised region of weakness 750. In this example, a single circumferential channel 750 has been formed in the coating system 745. While this example shows the channel extending fully through the coating system 745 to the pipe 720, the depth of the channel forming the localised region of weakness 750 may be varied dependent on the environmental factors, and/or the pressure at which a new mode of buckling propagation of the pipeline 7000 is triggered.

Claims

CLAIMS:

1. A subsea pipeline buckling mode trigger system, the system comprising a pipeline sub-section circumscribed by a coating, the coating defining an axially localised region of weakness that extends around at least part of the circumference of the pipeline sub-section.

2. The subsea buckling mode trigger system of claim 1, wherein the axially localised region of weakness of the coating is used to induce a change in the buckling propagation mode of the subsea pipeline.

3. The subsea pipeline buckling mode trigger system of claims 1 or 2, wherein the coating is a thermal coating.

4. The subsea pipeline buckling mode trigger system of any one of claims 1 3, wherein the coating comprises a coating system, the coating system comprising a plurality of layers.

5. The pipeline buckling mode trigger system of claim 4, wherein at least one of the plurality of layers is a bonding layer, configured to bond the coating system to the Pipe.

6. The subsea pipeline buckling mode trigger system of claim 5, wherein the bonding layer partially circumscribes the pipeline sub-section defining a region of no bonding, with the region of with no bonding being at or adjacent the region of localised weakness.

7. The subsea pipeline buckling mode trigger system of claim 5, wherein the bonding layer fully circumscribes the pipeline sub-section and defines a region of weakened bonding, with the region of weakened bonding being at or adjacent the region of localised weakness.

8. The subsea pipeline buckling mode trigger system of any preceding claim, wherein the region of localised weakness comprises at least one channel defined in the coating.

9. The subsea pipeline buckling mode trigger system of claim 8, wherein the or each channel extends partially through the coating.

10. The subsea pipeline buckling mode trigger system of claim 9, wherein the or each channel extends fully through the coating.

11. The subsea pipeline buckling mode trigger system of claims 8 to 10, wherein the or each channel has a uniform depth around the circumference of the pipe.

12. A subsea pipeline comprising, a pipeline buckling mode trigger system according to any one of claims 1 to 11 connected between two adjacent pipeline sections.

13. A method of manufacturing a subsea pipeline buckling mode trigger system, the method comprising circumscribing a pipeline sub-section with a coating; and, defining an axially localised region of weakness in the coating, wherein the axially localised region of weakness extends around at least part of the circumference of the pipeline sub-section.

14. The method of claim 13, further comprising coating the pipeline sub-section with a thermal coating.

15. The method of any one of claims 13 or 14, further comprising coating the pipeline sub-section with a coating system, wherein the coating system comprises a plurality of layers.

16. The method of claim 15, further comprising bonding the coating to the pipeline sub-section using bonding layer of the coating system.

17. The method of claim 16, further comprising defining a region of no bonding in the bonding layer of the coating system, wherein the region of no bonding is defined at or adjacent the axially localised region of weakness.

18. The method of claim 15, further comprising defining a region of weakened bonding in the bonding layer of the coating system, wherein the region of weakened bonding is defined at or adjacent the axially localised region of weakness.

19. The method of claims 13 to 18, further comprising defining at least one channel in the coating, wherein the at least one channel defines the axially localised region of weakness.