GB2486014A

GB2486014A - A method and apparatus for removing a subsea concrete protection mattress from the sea floor

Info

Publication number: GB2486014A
Application number: GB201020395A
Authority: GB
Inventors: Ronald Wraith
Original assignee: UNDERWATER CUTTING SOLUTIONS Ltd
Current assignee: UNDERWATER CUTTING SOLUTIONS Ltd
Priority date: 2010-12-02
Filing date: 2010-12-02
Publication date: 2012-06-06
Anticipated expiration: 2030-12-02
Also published as: GB201020395D0; GB2486014B

Abstract

A method and apparatus 10 for removing a subsea concrete protection mattress from the seafloor are disclosed. The apparatus includes a vehicle body 18 to which is attached a mattress support 20 for lifting the mattress from the seafloor and then supporting it. The mattress support can pivot vertically to move over the asset 16 it is lifting the mattress from. It can also move horizontally by moving the vehicle body and/or sliding part of the vehicle body, to which the support is attached. The mattress support may comprise a conveyor means 22 such as a conveyor belt or a plurality of caterpillar tracks.

Description

A method and apparatus for removing a subsea concrete protection mattress from the seafloor The present invention relates to a method and apparatus for removing a subsea concrete protection mattress from the sea floor and relates particularly, but not exclusively, to a method and apparatus for removing concrete mattresses from the sea floor where the mattresses have become fatigued or damaged.

The use of a concrete mattress, to protect, for example, an oil pipeline lying on the sea floor, is well known. The mattresses are formed from a series of high strength concrete segments or blocks linked together with a network or mesh of high strength polypropylene, stainless steel or other ropes to form a continuous flexible concrete mat. The mattresses are produced in a variety of sizes for example with lengths of 6 or 9.4 metres, widths of 2.4 or 3 metres and thicknesses of 0.15 metres and 0.3 metres. The blocks are linked closely together and shaped so as to form a flexible mat that can shape itself around a pipeline with a high degree of flexibility in two planes.

The mattresses are installed by lowering them from a crane in a quick release installation frame from where they are lowered on to a subsea pipeline they are to protect.

The mattresses provide a high quality and low cost solution for protection and stabilisation of subsea pipelines and other structures.

Removal of the mattresses is performed by approximately reversing the installation method. A crane is used to lower a lifting frame to adjacent the mattress which is then attached to the mattress's lifting points located at the extremities of the mattress. This connection is performed by divers or by a remotely operated vehicle (ROV) . The crane then lifts the lifting frame together with the mattress which can then be pulled to the surface. However, if damage or fatigue has occurred to the network of ropes that connect the concrete segments, this removal method is ineffective and can be dangerous. The significant strain placed upon the network of ropes. by the weight of the concrete segments can cause them to fail resulting in the mattress coming apart. The concrete blocks then may damage the pipework or other structure that they were originally intended to protect. As a result, if it is suspected that the mattress is fatigued or damaged, the mattress must be dismantled a block at a time by divers who hand-lift the concrete sections into baskets that are recovered using a crane. Such a method is very expensive and time consuming. Furthermore, due to the weights and potential uneven terrain this dismantling can put divers at risk as well as risking damage to the pipeline or other asset that the mattress is designed to protect.

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Preferred embodiments of the present invention seek to overcome the above described disadvantages of the prior art.

According to an aspect of the present invention there is provided an apparatus for removing a subsea concrete protection mattress from the seafloor, the apparatus comprising: -a vehicle body; mattress support means for lifting a mattress from the seafloor and at least partially supporting said mattress once lifted, said mattress support means connected to said vehicle body; first support moving means for moving said mattress support means substantially horizontally under said mattress; and second support moving means for moving at least part of said mattress support means substantially vertically relative to the vehicle body.

By providing a vehicle with a mattress support means that is able to slide under a concrete mattress and means for moving the support horizontally under the mattress and vertically so as to lift the mattress over the asset, provides the advantage that a damaged or fatigued mattress can be lifted from its position with the apparatus of the present invention. In particular, because each line of concrete block segments is supported as the mattress support means moves horizontally, there is very little stress placed on the ropes connecting the blocks and as a result, the mattress can be lifted as a single piece.

In a preferred embodiment the mattress support means comprises conveyor means for conveying the mattress onto said apparatus.

By forming the mattress support means as a conveyor, the advantage is provided that the stresses applied to the mattress can be further reduced. For example, by carefully controlling the horizontal movement of the support means using the first support moving means together with controlling the conveyor as the support means moves forward so as to engage the next line of concrete blocks, the H previous line of concrete blocks can be moved out of the way. A skilled operator can therefore reduce the stresses placed on the mat thereby further decreasing the likelihood of damage.

In another preferred embodiment the conveyor means comprises at least one conveyor belt.

In a further preferred embodiment the conveyor means comprises a plurality of caterpillar tracks.

By using a plurality of caterpillar tracks for the conveyor, the advantage is provided that these simple mechanical parts, which are well tested for use in the subsea environment, can provide the conveyor means in a consistent and reliable manner.

In a preferred embodiment the first support moving means comprises vehicle moving means for moving said vehicle body relative to the seafloor.

If the apparatus is an ROV, using the existing vehicle moving means (for example tracked wheels) as part of the means for moying the mattress support provides the advantage that this feature of the apparatus is already present. Furthermore, it reduces the overall size of the vehicle.

In another preferred embodiment the vehicle moving means comprises a plurality of driven wheels.

In a further preferred embodiment the driven wheels run on at least one caterpillar track.

In a preferred embodiment the first support moving means comprises sliding means for sliding said mattress support means relative to said vehicle body.

By having a portion of the vehicles slide forward so that the support means can extend further forward provides the advantage that the reach of the apparatus can be extended without significantly increasing the size of the vehicle. If the vehicle were designed so that all of the horizontal movement of the support means as provided by the wheels of the vehicle, this would require a very large vehicle with a long reach which would in turn require significant counterbalancing weight at the rear. By using the wheels of the vehicle to move the support forward, until the wheels closely approach the pipeline, and then using a sliding mechanism to extend the mattress support further, the advantage is provided that a compact vehicle can be used to remove the mattress from the sea bed. The vehicle is therefore able to be not much longer than the mattress it is designed to carry.

In another preferred embodiment the second support moving means comprises pivoting means for lifting and lowering a distal end of said mattress support means relative to said vehicle body.

By allowing the support means to pivot relative to the vehicle body, the advantage is provided that the support means can move vertically so as to move over the pipeline from which the mattress is being removed.

In a preferred embodiment the pivoting means comprises at least one hydraulic ram for pivoting said mattress support means relative to said vehicle body.

The apparatus may further comprise digging means for digging out a trench in front of said an edge of said mattress to allow mattress support means to access the underside of said edge.

Digging out a small trench in front of the mattress allows easier access to the underside of the first row of mattress concrete blocks, thereby making it easier to commence the removal process.

According to another aspect of the present invention, there is provided a method of removing a subsea concrete protection mattress from the seafloor, comprising the steps of:-engaging mattress support means with an edge of a concrete mattress, the mattress support means for lifting a mattress from the seafloor and at least partially supporting said mattress once lifted and said mattress support means H ccnnected to a body of a vehicle; moving said mattress support means substantially P horizontally under said mattress; and moving at least part of said mattress support means substantially vertically relative to the vehicle body.

The method may further comprise moving said mattress along a conveyor means forming part of said mattress support means as said mattress support means moves horizontally under said mattress.

In a preferred embodiment the mattress support means moves horizontally by moving substantially all of said vehicle towards said mattress.

In another preferred embodiment the mattress support means moves horizontally by moving said mattress support means relative to said vehicle body.

In a further preferred embodiment the mattress support means moves vertically by pivoting said mattress support means relative to said vehicle body.

The method may further comprise digging out a trench in front of said edge of said mattress to allow mattress support means to access an underside of said edge.

Preferred embodiments of the present invention will now be described by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which: Figure 1 is a perspective view of an apparatus of the present invention; Figure 2 is a plan view of the apparatus of Figure 1; Figure 3 is rear view of the apparatus of Figure 1; and Figure 4, in parts (a) to (1), is a side view of the apparatus of Figure 1 in use.

Referring to Figures 1 to 3, an apparatus, in the form of unmanned ROV tool 10, is used to remove a subsea concrete protection mattress 12 from engagement with sea floor 14 and a pipeline 16, which is typically an oil pipeline. Such mattresses are also used to protect other subsea assets or structures and the tool 10 described herein is not limited to removal of mattresses from pipes.

The tool 10 has a vehicle body indicated generally at 18 to which is pivotally attached mattress support means 20 which are provided in the form of five conveyors or caterpillar tracks 22. Between the driven caterpillar tracks 22 are four supporting sections 24 which are formed from sections of PTFE. As an alternative to the supporting sections 24, nqn-driven conveyor belts could be provided. The caterpillar tracks are driven in a clockwise direction when viewed from the nearer side of the tool 10 as shown in Figure 1, and beyond the uppermost ends 26 of tracks 22 lies a large, and preferably grooved, supporting bed 28 that is also formed from, or coated with PTFE.

The tool 10 is provided with a pair of driven wheeled tracks 30 that allow the tool to move in a horizontal H direction along the sea bed. These tracks provide means for moving the mattress support means 20 in a horizontal direction. There is also provided a secondary means for moving the mattress support means 20 in a horizontal direction in the form of a hydraulically controlled sliding portion of the body, indicated generally at 32, that causes the caterpillar tracks 22 and other components that form the mat support means 20 together with the support bed 28 in a horizontal direction under the mattress.

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The mattress support means 20 is pivotally mounted to the sliding body portion 32 via pivots 34. The arm 36 that support the caterpillar tracks 22 of support means 20 can be raised and lowered by hydraulic rams 38. This allows the distal end 40 of mat support means 20 to be raised and lowered in a vertical direction. Also attached to the sliding body portion 32 is a frame 42.

Operation of the tool 10 will now be described with additional reference to Figures 4 (a) to (i) . A crane (not shown) is used to lower the tool 10 into position adjacent the section of mattress 12 that is to be removed. The tool 10 operates as a remotely operated vehicle (ROV) using cameras and lights to provide an operator with a view of the area in which the tool is working. Alternatively the tool 10 could be operated by a diver working adjacent the tool.

The driven tracks 30 are used to position the tool 10 close to mattress 12 so that the distal end 40 of caterpillar tracks 22 come into contact with the outermost edge of mattress 12. The caterpillar tracks 22 are driven in a clockwise direction, as seen in Figures 4(a) to (i), so as to slightly lift the first line 44 of blocks of mattress 12 onto the edge of the mattress support means 20 as shown in Figure 4 (a) . The caterpillar tracks 22 are then driven in a clockwise direction so as to lift the mattress 44 onto the mat support means 20. At the same H time, the driven tracks 30 move the whole tool 10 forward so that as little strain as possible is applied to the network of cables that hold the concrete blocks mattress 12 together. This operation requires very close control of the movement of the caterpillar tracks 22 and the driven tracks 30 by the operator.

Once the mattress 12 starts to lift up caterpillar tracks 22 it becomes partially disengaged from the sea bed with the weight being borne on the pipeline and the mat support means 20 with a few lines of blocks suspended above the sea bed there between, as shown in Figure 4 (b) . Although this causes some strain to be applied to the cables that hold the mattress together, the strain is significantly less than is experienced by lifting the whole mattress from its corners as seen in the prior art.

As seen in Figure 4(c), the hydraulic ram 38 retracts lifting arm 36 and causing distal end 40 of mattress support means 20 to lift above the sea bed. This occurs as the distal end 40 of mattress support means 20 comes close H *to the pipeline 16 as seen in Figure 4(c), The arm 36 continues to rise so as to clear pipeline 16 as shown in Figure 4 (d) . As can also be seen in Figure 4 (d), the forwardmost portion of driven tracks 30 is now close to pipeline 16 and is prevented from moving the mat support means 20 any further over pipeline 16. In order to prevent the mattress 12 from being dragged along the sea bed 14 towards pipeline 16, thereby introducing additional strain into the cables that hold the mattress together, it is desirable for the mat support means to continue to move over the pipeline 16. This is achieved, as shown in p Figure 4(e), by the sliding body portion 32 of the vehicle body 18 extending further forwards and reaching out over the pipeline 16. At the same time, the hydraulic rams 38 extend causing arms 36 to descend to adjacent sea bed thereby minimising the strain that is applied to the cables that form the mattress 12.

Eventually the mattress 12 is entirely supported on the tool 10, that is when the last line 46 of blocks are supported on the caterpillar tracks 22 and supporting sections 24 of mattress support means 20, as seen in Figure 4(f). Once the mattress 12 is entirely. on the tool 10, the hydraulic rams 38 retract so as to cause arms 36 to become horizontal thereby holding the mattress 12 horizontally on mattress support means 20 and support bed 28, as seen in Figure 4 (g) . The sliding body portion 32 is retracted using the hydraulic rams (not shown) to the position shown in Figure 4(h) and the tool 10 is able to drive away from the pipeline 16 using the driven tracks 30 as seen in Figure 4 (i) The removed mattress 12 is then taken to a holding basket that can contain several mattresses and the process is reversed so as to carefully place the mattress into the basket. A basket containing, typically five mattresses, can then be retrieved from the sea bed using a crane. The same crane can then be used to finally lift the tool 10 from the sea bed.

It will be appreciated by person skilled in the art that the above embodiments have been described by way of example only and not in any limitative sense, and that the various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

For example, the pivots 34 and hydraulic rams 38 could alternatively be replaced with a mechanism that lifts the whole of the mat support means 20 in a vertical direction not just the distal end 40. The caterpillar tracks 22 and supporting sections 24 can be replaced with a single conveyor belt that is sufficiently wide to support and carry the mattress 12.

Furthermore, a digging means could be provided at the distal end 40 in order to assist in getting slightly underneath the first line 44 of blocks of mattress 12.

This would be particularly important if, as used in another embodiment, the mattress support means is provided without the use of a conveyor and instead is a slab of material having a low coefficient of friction such as PTFE. In this instance, the mattress 12 is pushed up the mat support means 20 by simply driving the tool 10 forwards or sliding the sliding body portion 32 forwards as previously described. This non-conveying action is able to operate since the concrete blocks of the mat will press against each other and very little connection between them is required in order to prevent them from moving out of the plane of the mattress.

It is also the case that the sliding body portion 32 could be eliminated from the above design by making the vehicle sufficiently long so that the mattress support means 20 extends sufficiently far in front of the driven wheels in order that the support means can extend over the entire pipeline and to the end of the mattress 12.

Similarly, the driven tracks 30 could be eliminated by extending the operation of the sliding body portion 32. In this instance, the tool 10 would be located adjacent the pipeline and anchored into position and all of the movement of the mattress support means 20 undertaken by the hydraulic rams of the sliding body portion 32 causing the horizontal movement.

The above embodiment is described as operating using a hydraulic umbilical. However, it could equally operate using an electrical umbilical and replacing the hydraulic rams with other equivalent electrically operated devices.

Furthermore, the tool 10 can operate by a remote power source rather than an umbilical. It is also described as operating as an ROV but could instead be operated by a diver working in close proximity to the tool.

Claims

Claims 1. An apparatus for removing a subsea concrete protection mattress from the seafloor, the apparatus comprising:-a vehicle body; mattress support means for lifting a mattress from the seafloor and at least partially suppcrting said mattress once lifted, said mattress support means connected to said vehicle body; first support moving means for moving said mattress support means substantially horizontally under said mattress; and second support moving means for moving at least part of said mattress support means substantially vertically relative to the vehicle body.
2. An apparatus according to claim 1, wherein said mattress support means comprises conveyor means for conveying the mattress onto said apparatus.
3. An apparatus according to claim 2, wherein said conveyor means comprises at least one conveyor belt.
4. An apparatus according to claim 2, wherein said conveyor means comprises a plurality of caterpillar tracks.
5. An apparatus according to any one of the preceding claims, wherein said first support moving means comprises vehicle moving means for moving said vehicle body relative to the seafloor.
6. An apparatus according to claim 5, wherein said vehicle moving means comprises a plurality of driven wheels.
7. An apparatus according to claim 6, wherein said driven wheels run on at least one caterpillar track.
8. An apparatus according to any one of the preceding claims, wherein said first support moving means comprises sliding means for sliding said mattress support means relative to said vehicle body.
9. An apparatus according to any one of the preceding claims, wherein said second support moving means comprises pivoting means for lifting and lowering a distal end of said mattress support means relative to said vehicle body.
10. An apparatus according to claim 9, wherein said pivoting means comprises at least one hydraulic ram for pivoting said mattress support means relative to said vehicle body.
11. An apparatus according to any one of the preceding claims, further comprising digging means for digging out a trench in front of said an edge of said mattress to allow mattress support means to access the underside of said edge.
12. An apparatus for removing a subsea concrete protection mattress from the seafloor substantially as hereinbefore described with reference to the accompanying drawings.
13. A method of removing a subsea concrete protection mattress from the seafloor, comprising the steps of:-engaging mattress support means with an edge of a concrete mattress, the mattress support means for lifting a mattress from the seafloor and at least partially supporting said mattress once lifted and said mattress support means connected to a body of a vehicle; moving said mattress support means substantially horizontally under said mattress; and moving at least part of said mattress support means substantially vertically relative to the vehicle body.
14. A method according to claim 13, further comprising moving said mattress along a conveyor means forming part of said mattress support means as said mattress support means moves horizontally under said mattress.
15. A method according to claim 13 or 14, wherein said mattress support means moves horizontally by moving substantially all of said vehicle towards said mattress.
16. A method according to any one of claims 13 to 15, wherein said mattress support means moves horizontally by moving said mattress support means relative to said vehicle body.
17. A method according to any one of claims 13 to 16, wherein said mattress support means moves vertically by pivoting said mattress support means relative to said vehicle body.
18. A method according to any one of claims 13 to 17, further comprising digging out a trench in front of said edge of said mattress to allow mattress support means to access an underside of said edge.
19. A method of removing a subsea concrete protection mattress from the seafloor substantially as hereinbefore described with reference to the accompanying drawings.