Technical Field

The present invention relates to underwater pipeline anchoring apparatus.

Background

Traditionally, pipelines are not fixed when laid on the surface of the seabed as the cost of fixing is high, particularly in deep water locations, which maybe typically 500 to 2000m in depth. Also, fixing can itself lead to problems due to the power of currents in the water. Pipelines carrying hydrocarbons are often operated at high temperatures due to the temperature of the oil or gas coming out of the well. This results in thermal expansion of the pipeline, most significantly, in an axial direction. When the flow is shut down for any reason, the pipeline cools and contracts.

As a number of shut downs may occur over the operational life of a pipeline, the axial expansion and contraction can result in the pipeline ‘walking’ over the seabed. The consequence of this is that pipelines can break connections at their ends, or buckle laterally along their length. Both are undesirable and the usual solution to place a large single anchor at one end of the pipeline to prevent it walking. A more efficient solution is a number of small anchors which can be strategically placed along the pipeline.

In this specification, the relative positional terms above, below, etc are used in relation to a normal pipeline installation in which “below” means into or towards the seabed floor. “Axially directed” means in or along a direction which is aligned or parallel to the longitudinal axis of the pipeline. “Transversely directed” means in or along a direction which is transverse to the longitudinal axis of the pipeline.

In this specification, the word “substantially” is used to include the meaning of “exactly or for practical purposes, as will be understood by a skilled person in the technical field”. This includes some variation from “exactly” because of practical considerations. For example, in the technical field of this invention, “substantially horizontal” might include ±10° from the horizontal.

Statements of Invention

According to a first aspect of the present invention, there is provided underwater pipeline anchoring apparatus, the apparatus comprising: a fixing device for fixing the apparatus in an installed condition to an underwater pipeline, and an anchor member which, in the installed condition, extends outwardly downwardly from the pipeline into seabed material to resist movement of the pipeline relative to the seabed material, and wherein, in the installed condition, the anchor member is not fixed to the seabed material.

Possibly, the anchoring apparatus defines an aperture, which may include a pipeline receiving part, possibly in which, in the installed condition, the pipeline is located. Possibly, the aperture includes a slot part, which may be defined between the anchor members and may extend downwardly from the pipeline receiving part between the anchor members.

Possibly, the pipeline extends along a longitudinal axis. Possibly, the anchor member is arranged to resist movement of the pipeline along the longitudinal axis.

Possibly, the anchor member is substantially planar. Possibly, the anchor member plane extends substantially orthogonally to the longitudinal axis.

Possibly, the anchor member is plate-like in form. “Plate-like” means that the anchor member is in the form of a substantially flat, relatively thin, rigid sheet of material such as metal with a substantially even surface and a substantially uniform thickness.

Possibly, the apparatus includes a pair of the anchor members, each of which, in the installed condition, may extend laterally and downwardly outwardly from the pipeline, one member extending outwardly on each side of the longitudinal axis of the pipeline.

Possibly, the anchor members are substantially coplanar.

Possibly, in a plane that is normal to the longitudinal axis, the pipeline has a cross- sectional area. Possibly, in the normal plane, the or each anchor member has a cross-sectional area, which may be greater than the cross-sectional area of the pipeline and may be greater by a factor of at least four.

Possibly, the pipeline has a diameter. Possibly, each anchor member has a transverse dimension and a depth dimension. Possibly, the transverse dimension is greater than the pipeline diameter, and may be greater by a factor of at least 1.5 and more desirably at least three. b

Possibly, the depth dimension is greater than the pipeline diameter, and may be greater by a factor of at least two, and more desirably at least three.

Possibly, in the installed condition, each anchor member extends below the level of the pipeline by a penetration depth. Possibly, the penetration depth has a dimension of at least one pipeline diameter.

Possibly, in some embodiments, the depth dimension is greater than the transverse dimension. Possibly, in some embodiments, the transverse dimension is substantially the same as the depth dimension.

Possibly, the anchor members are substantially the same shape and size.

Possibly, the aperture extends axially. Possibly, the slot part has a width which is greater than the diameter of the pipeline, possibly to permit the pipeline to pass therealong.

Possibly, each anchor member extends only laterally outwardly and downwardly relative to the pipeline in the installed condition.

Possibly, each anchor member has a greater part (ie, greater than 50% by mass or by axially directed cross-sectional area) below the pipeline in the installed condition than alongside the pipeline or above the pipeline.

Possibly, each anchor member comprises an upper part and a lower part.

Possibly, the upper part extends outwardly laterally alongside (and possibly only outwardly laterally alongside and not above or below) the pipeline in the installed condition. Possibly, the lower part extends outwardly downwardly below (and possibly only outwardly and downwardly below, and not alongside or above) the pipeline in the installed condition.

Possibly, the lower part is located below the level of the pipeline in the installed condition. Possibly, in the normal plane, each of the upper and lower parts of the anchor members has a cross-sectional area, and the cross-sectional area of each lower part is greater than the cross-sectional area of each upper part.

Possibly, each of the upper part and the lower part include axially directed surfaces. Possibly, the surface area of the lower part surface is greater than the surface area of the upper part surface.

Possibly, each of the upper and lower parts of the anchor members has a depth, and the depth of each lower part is greater than the depth of each upper part. Possibly, the depth of each lower part is greater than the pipeline diameter.

Possibly, the apparatus includes a bracing/stability arrangement.

Possibly, the bracing/stability arrangement includes a yoke part, which extends between the anchor members.

Possibly, the bracing/stability arrangement includes a bracing member.

Possibly, the apparatus includes a support member, which supports the fixing device and the or each anchor member.

Possibly, in some embodiments, the bracing member is in the form of a strut which extends from the anchor member to the support member.

Possibly, in some embodiments, the bracing member is substantially planar Possibly, one bracing member is fixed to the or each anchor member and, in the installed condition, may extend downwardly, possibly substantially vertically downwardly. Possibly, the or each bracing member tapers downwardly.

Possibly, in some embodiments, the bracing/stability arrangement includes a lateral stability member, which may be substantially planar, one of which may be fixed to the or each respective anchor member and may extend axially outwardly from the respective anchor member. Possibly, in the installed condition, the or each lateral stability member extends downwardly, possibly substantially vertically downwardly, and may taper downwardly. Possibly, the or each bracing member comprises the or one lateral stability member.

Possibly, in some embodiments, the bracing/stability arrangement includes a vertical stability member, which may be substantially planar, one of which may be fixed to the or each respective anchor member and, in the installed condition, may extend axially outwardly from the anchor member, possibly substantially horizontally and may extend transversely across the respective anchor member.

Possibly, the fixing device is moveable between an open condition and a closed condition. Possibly, the fixing device comprises a clamp device, which may comprise a pair of clamp arms.

Possibly, the clamp device includes one or more pivot members around which the or each clamp arm pivots.

Possibly, the clamp device includes an actuator for moving the clamp arms between the open and the closed conditions. The actuator may comprise a screw mechanism or hydraulic ram.

Possibly, the fixing device includes a resilient arrangement to permit misalignment and/or movement. The resilient arrangement may comprise a spring or hydraulic ram which comprises a part of the actuator.

Possibly, the fixing device includes one or more upper contact members, which in the installed condition contact an upper surface of the pipeline.

Possibly, in some embodiments, the fixing device includes a pair of spaced upper contact members, and the clamp device may be located between the contact members.

Possibly, the clamp device contacts an under surface of the pipeline and in the installed condition may exert a clamping force to draw and hold the upper contact members, the pipeline and the clamp device together.

Possibly, the or each anchor member is located axially between the contact members, and may be located adjacent the clamp device.

Possibly, the support member extends axially and may support the contact members and/or the or each anchor member, and/or the clamp device. Possibly, the support member is circular in cross-section and may, in some embodiments, comprise the pivot member.

Possibly, the apparatus includes two pairs of anchor members, which are spaced apart along the support member.

Possibly, the apparatus includes two fixing devices, each of which may be associated with one of the pairs of anchor members.

Possibly, the support member is hollow and may define an interior in which ballast is receivable.

Possibly, the or each anchor member includes a pair of axially directed surfaces.

Possibly, the anchoring apparatus includes a release member which may locate against one of the axially directed surfaces of the/each anchor member.

Possibly, the release member is permeable and may comprise a membrane.

Possibly, the anchoring apparatus includes a plurality of release members. Possibly, one release member is located against each of the axially directed surfaces of the/each anchor member.

Possibly, the anchoring apparatus includes a hole formation device which may extend along an edge, possibly a lowermost edge in the installed condition, of the or each anchor member. Possibly, the hole formation device is relatively enlarged in width relative to the width of the anchor member. Possibly, the hole formation device includes a hole forming surface, which in an installed condition, may be a lowermost surface and may be a rounded surface. Possibly, the hole formation device is substantially rounded in cross-sectional shape and may be circular in cross-sectional shape.

Possibly, the anchoring apparatus includes a water supply arrangement to provide a water supply to a lowermost part of the or each anchor member. Possibly, the water supply arrangement provides the water supply at an elevated pressure relative to the sea pressure local to the lowermost part. Possibly, the hole formation device is hollow and defines an interior, and the water supply arrangement provides water to the interior. Possibly, the hole formation device defines water supply holes, which may be directed upwardly and through which, in use, water flows therethrough from the interior.

According to a second aspect of the present invention, there is provided a method of anchoring an underwater pipeline, the method including providing underwater pipeline anchoring apparatus, the apparatus comprising: a fixing device for fixing the apparatus in an installed condition to an underwater pipeline, and an anchor member which, in the installed condition, extends outwardly downwardly from the pipeline into seabed material to resist movement of the pipeline relative to the seabed material, and wherein, in the installed condition, the anchor member is not fixed to the seabed material.

Possibly, the apparatus includes any of the features shown or described in any of the preceding statements, following description or accompanying drawings. Possibly, the method includes any of the steps shown or described in any of the preceding statements, following description or accompanying drawings.

Figures

Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:-

Fig. 1 is a view on a first axially directed side of an underwater pipeline anchoring apparatus;

Fig. 2 is a view on a first transversely directed side of the anchoring apparatus;

Fig. 3 is a perspective view of the apparatus from below, on the first axially directed side and on the first transversely directed side;

Fig. 4 is a view on a second axially directed side of the anchoring apparatus, with an outline of a pipeline in dashed line for reference, and with part of an anchor member cross hatched to indicate an upper part of the anchor member;; Fig. 5 is a perspective view from above, on the first axially directed side and on a second transversely directed side, with the anchoring apparatus in the installed condition fitted to the pipeline;

Fig. 6 is a view on the second transversely directed side of the anchoring apparatus;

Fig. 7 is a cross-sectional view of a lowermost part of the apparatus, when fitted with the soil release and water supply arrangement;

Fig. 8 is a perspective view of a second anchoring apparatus;

Fig. 9 is an end view of the second anchoring apparatus; and

Figs. 10A and 10B are end views of the second anchoring apparatus located on a pipeline in, respectively, an unclamped condition and a clamped condition.

Description - First Embodiment

Figs. 1 to 6 show underwater pipeline anchoring apparatus 10, the apparatus 10 comprising a fixing device 12 for fixing the apparatus 10 in an installed condition to an underwater pipeline 14, and an anchor member 16 which, in the installed condition, extends outwardly downwardly from the pipeline 14 into seabed material S to resist movement of the pipeline 14 relative to the seabed material S and wherein, in the installed condition, the anchor member 16 is not fixed to the seabed material S.

The pipeline 14 extends along a longitudinal axis 20.

In one example, as shown in the Figures, the apparatus 10 includes a pair of the anchor members 16, each of which, in the installed condition, may extend laterally and downwardly outwardly from the pipeline 14, one anchor member 16 extending outwardly on each side of the longitudinal axis 20 of the pipeline 14.

The anchor members 16 are arranged to resist movement of the pipeline 14 along the longitudinal axis 20.

Each anchor member 16 is substantially planar. The anchor members 16 extend substantially orthogonally to the longitudinal axis 20 and are substantially coplanar.

Each anchor member 16 is plate-like in form. “Plate-like” means that the anchor member 16 is in the form of a substantially flat, relatively thin, rigid sheet of material with a substantially even surface and a substantially uniform thickness. The material could be a metal such as steel. In a normal plane, the pipeline 14 has a cross-sectional area. The normal plane is a plane that extends normally (ie at right angles, perpendicularly or orthogonally) to the longitudinal axis of the pipeline. In the normal plane, each anchor member 16 has a cross-sectional area, which is greater than the cross-sectional area of the pipeline 14 and could be greater by a factor of at least ten, possibly twenty and desirably forty.

Each anchor member 16 has a transverse dimension 22 and a depth dimension 24.

The transverse dimension 22 is greater than the pipeline diameter 26, and could be greater by a factor of at least 1.5 and more desirably, at least three.

The depth dimension 24 is greater than the pipeline diameter 26, and could be greater by a factor of at least two, and more desirably at least three.

The transverse dimension 22 is substantially the same as the depth dimension 24.

The anchor members 16 are substantially the same shape and size. In the installed condition, each anchor member 16 includes a pair of axially directed surfaces 78.

The anchoring apparatus 10 defines an aperture 28, which extends axially. The aperture 28 includes a pipeline receiving part 30, which in the installed condition receives the pipeline 14, and a slot part 32, which is defined between the anchor members 16. The slot part 32 has a width 34 which is greater than the diameter 26 of the pipeline 14, to permit the pipeline 14 to pass therealong. When being installed, this allows the apparatus 10 to be located from above over a pipeline 14 already in situ on the seabed S without requiring that a break is made in the pipeline or requiring installation of the apparatus when the pipeline is being laid.

The apparatus 10 includes a bracing/stability arrangement 36.

The bracing/stability arrangement 36 includes a yoke part 38, which extends between the anchor members 16. In one example, the yoke part 38 and the anchor members 16 could be formed integrally (ie, in one piece) and could be formed by machining/cutting one piece of plate material. In other examples the anchor members 16 and the yoke part 38 could be formed of separate pieces which are fabricated together eg by welding. The plate material could, for example, be a metal such as steel. The bracing/stability arrangement 36 includes bracing members 40, each of which is substantially planar. In the example shown, two bracing members 40 are fixed to each anchor member 16 and, in the installed condition, extend substantially vertically downwardly. Each bracing member 40 tapers (narrows) in axial dimension downwardly.

The bracing/stability arrangement 36 includes lateral stability members 42, which are substantially planar. In the example shown, two lateral stability members 42 are fixed to each respective anchor member 16. Each lateral stability member 42 extends axially outwardly from the respective anchor member 16. In the installed condition, each lateral stability member 42 extends substantially vertically downwardly, and tapers (narrows) in axial dimension downwardly.

In the example shown, each bracing member 40 comprises one of the lateral stability members 42.

The bracing/stability arrangement 36 includes vertical stability members 44, each of which are substantially planar. One vertical stability member 44 is fixed to each anchor member 16, and, in the installed condition, extends substantially horizontally axially outwardly from the anchor member 16 and transversely across the anchor member 16.

In the example shown, one vertical stability member 44 extends between upper parts of each of the bracing members 40/lateral stability members 42 of each respective anchor member 16, and an intermediate vertical stability member 44A extends between the neighbouring upper parts of the adjacent bracing members 40/lateral stability members 42 of the two anchor members 16, just above the aperture 28.

The fixing device 12 is moveable between an open condition and a closed condition. The fixing device 12 comprises a clamp device 46, which comprises a pair of clamp arms 48 and includes a pivot member 50 around which the clamp arms 48 pivot. The clamp device 46 includes an actuator 72 for moving the clamp arms 48 between the open and the closed conditions. In the example shown, the actuator 72 comprises a screw mechanism 52.

The fixing device 12 includes a pair of spaced upper contact members 54, which in the installed condition contact an upper surface of the pipeline 14. The clamp device 46 is located between the upper contact members 54. The anchor members are located axially between the upper contact members 54, adjacent the clamp device 46.

The apparatus 10 includes a support member 56, which extends axially and supports the upper contact members 54, the anchor member 16, and the clamp device 46.

In the example shown, the support member 56 is circular in cross-section and comprises the pivot member 50. The support member 56 has a longitudinal axis 76 which in the installed condition is aligned substantially in parallel with the pipeline longitudinal axis 20.

First Embodiment - In Use

Advantageously, the apparatus 10 can be installed to an existing pipeline in situ without requiring any break in the pipeline 14 as follows:

The apparatus 10 is lowered from above onto the pipeline 14 with the clamp arms 48 in the open condition. As the apparatus 10 is lowered, the pipeline 14 passes along the slot part 32 and is received in the pipeline receiving part 30.

As the apparatus 10 is lowered, the anchor members 16 sink into the seabed S by the self-weightself-weight of the apparatus 10. The seabed S usually comprises loose or soft material which becomes denser, firmer or stiffer with depth. The anchor members 16 will sink until sufficient resistance is reached to balance the self-weightself-weight of the apparatus 10 or it comes to rest on the pipeline 14.

Additional temporary weight can be provided to aid the installation process.

The bracing/stability arrangement 36 and in particular the vertical stability members 44, 44A increase the resistance of the seabed S to the sinking of the anchor members 16. The anchor members 16 will sink until the seabed S reaches the vertical stability members 44, 44A. The vertical stability members 44, 44A thus provide a stop or a limit to the sinking of the apparatus 10.

When the pipeline 14 is mostly within the aperture pipeline receiving part 30, the screw mechanism 52 can operated to move the clamp arms 48 from the open to the closed condition. As the clamp arms 48 move to the closed condition, the clamp arms 48 contact an under surface of the pipeline 14 and exert a clamping force to draw and hold the upper contact members 54, the pipeline 14 and the clamp arms 48 together. This can also aid in embedding the anchor members 16 in the seabed S as the action of embedding is now as a result of both the self- weightself-weight of the apparatus 10 and the inertia of the pipeline 14 which can act as a static point or base for pushing the anchor members 16 downwardly into the seabed S.

In the installed condition, with the clamp arms 48 in the closed condition, the anchoring apparatus 10 resists movement of the pipeline as follows.

The Applicant has realised that the primary source of movement of the pipeline 14 is as a result of thermal change causing expansion and contraction along the longitudinal axis 20. The expansion and contraction causes axial forces (labelled arrows F in Fig. 6) to be exerted on the pipeline 14. In the installed condition, as the pipeline 14 tries to move in response to the axial forces F, the seabed material S provides a resistive force (labelled arrows R in Fig. 6) which acts on the relatively large cross sectional area of the anchor members 16 to counter (at least partially) the axial forces F and thus reduce or eliminate seabed “walking” ie movement of the pipeline 14 on the seabed.

The apparatus 10 is particularly suitable for seabeds which comprise soft material (eg clay) which becomes firmer with depth. The arrangement of the anchor members 16 extending below the pipeline 14 and the planar plate-like form of the anchor members 16 permits the anchor members 16 to sink easily and deeply into the loose/soft material until denser/firmer material is reached. The Applicant has found that the depth of penetration is important, as reaching the firmer material helps to increase the resistive force R and therefore the ability of the apparatus 10 to resist the axial forces F and hence reduce or eliminate damage to the pipeline 14.

Functionally, the apparatus 10 is not designed to support the pipeline 14 vertically by grounding on hard seabed material such as rock. The anchor members 16 do not function as support legs. It is an advantage of the invention that the apparatus 10 is effective when not in contact with hard seabed material. This means that the apparatus 10 can be used in a wide variety of seabed types.

Fig. 4 shows an axially directed side view of the apparatus 10 with an outline of a pipeline 14 in dashed line. The pipeline 14 is located in the pipeline receiving part 30 of the aperture 28. Each of the anchor members 16 includes an upper part 104 (shaded with cross hatch lines in Fig. 4) and a lower part 106 (not shaded). The upper part 104 lies alongside the pipeline receiving part 30 and thus has a depth 108 that is approximately one pipeline diameter 26. The lower part 106 has a depth 102, and this is the potential depth of penetration of the respective anchor member 16 into the seabed material S below the level of the pipeline 14 in the installed condition.

In use, the apparatus 10 could be sized to fit a specific pipeline diameter. While the anchor members 16 could have different sizes for different seabed conditions (eg greater or lesser depth of loose material), the following can generally be said in respect of the invention:

• each anchor member 16 extends only laterally outwardly and downwardly and not upwardly relative to the pipeline 14 in the installed condition;

• each anchor member 16 has a greater part (ie, greaterthan 50% by mass or by axially directed cross-sectional area) below the pipeline 14 in the installed condition than alongside the pipeline or above the pipeline;

• each anchor member 16 comprises an upper part 104 and a lower part 106;

• the upper part 104 extends only outwardly laterally alongside (and not above or below) the pipeline 14 in the installed condition;

• the lower part 106 extends only outwardly downwardly below (and not alongside or above) the pipeline 14 in the installed condition;

• the lower part 106 is located below the level of the pipeline 14 in the installed condition;

• in the normal plane, the cross-sectional area of the lower part 106 is greater than the cross- sectional area of the upper part 104;

• each of the upper part 104 and the lower part 106 include axially directed surfaces 78U, 78L respectively;

• the surface area of the lower part surface 78L is greater than the surface area of the upper part surface 78U;

• the lower part depth 102 is greater than the upper part depth 108;

• the lower part depth 102 is greater than the pipeline diameter 26;

• in the installed condition, each anchor member 16 extends below the level of the pipeline 14 by a penetration depth 110. In one example, the penetration depth 110 has a dimension of at least one pipeline diameter 26. The penetration depth 110 is the same dimension as the lower part depth 102. The penetration depth 110 might not be the actual depth of penetration of the anchor members 16 into the seabed material S, but is the depth of anchor member 16 below the pipeline 14. Since, in each of the statements immediately above, in the installed condition the pipeline 14 is located in the pipeline receiving part 30 of the aperture 28, the term “pipeline” could be replaced by the term “pipeline receiving part”.

The Applicant has further realised that it is not necessary to fix the pipeline to the seabed and completely immobilise the pipeline and that in fact this might be a disadvantage as the pipeline can be more prone to damage if fully immobilised. It is advantageous, simpler and more economic to resist the longitudinal movement which is the major cause of damage to pipelines. The present invention thus provides an optimum in cost benefit since it is relatively simple to install and can be installed while the pipeline is in operation.

The lateral stability members 42 (which are of a relatively smaller area) resist lateral movement. This movement can be caused by ocean currents or buckling of the pipeline in a horizontal plane but is secondary as a cause of pipeline movement to the expansion and contraction movement and hence these members are of a relatively smaller area.

Removal of the anchoring apparatus 10 is a reversal of the process described above.

The anchoring apparatus 10 provides an anchoring solution which is scalable both in numbers and physical size to suit different situations.

The anchoring apparatus 10 facilitates installation as part of the pipelay and commissioning process, or at a suitable time during it’s operational life. This enables the system to be deployed in either a pre-emptive or reactive capacity.

The anchoring apparatus 10 provides the ability to be recovered at the end of the operational life of the pipeline. This will ease recovery of the pipeline, should that be a requirement.

Other Embodiments

Figs. 7 to 10 show other embodiments of the invention, many features of which are similar to those already described in relation to the embodiment of Figs 1 to 6. Therefore, for the sake of brevity, the following embodiments will only be described in so far as they differ from the embodiment already described. Where features are the same or similar, the same reference numerals have been used and the features will not be described again. Second Embodiment

Fig. 7 shows a detail of a lowermost part of an anchor member 216 of an anchoring apparatus 210. In the example shown, the apparatus 210 includes a plurality of release members 58, with one release member 58 located against each of the axially directed surfaces 78 of the anchor member 216.

Each release member 58 is permeable and comprises a membrane.

The release members 58 advantageously reduce soil resistance during installation and permit release of the seabed material from the sides of the anchor members 216 during movement. This has benefits to the axial response of the pipeline 14.

The Applicant has surprisingly found that while it is advantageous to resist movement of the pipeline 14, some movement should be permitted to prevent stress build up. In certain situations, the seabed material S on a rear face of the anchor members 16 relative to a forward movement can have a suction effect, substantially preventing or hindering the forward movement. The release members 58 permit separation of the rear face from the seabed material to permit an amount of movement.

The release members 58 could be provided to one or both of the axially directed surfaces 78 of the anchor member 216.

The anchoring apparatus 210 includes a hole formation device 60 which extends along a lowermost edge in the installed condition of the or each anchor member 216. The hole formation device 60 is relatively enlarged in width relative to the width of the anchor member 216. The hole formation device 60 includes a hole forming surface 64, which in an installed condition, is a lowermost surface and is a rounded surface. In the example shown, the hole formation device 60 is substantially circular in cross-sectional shape.

In one example, the width of the hole formation device 60 is larger than the width of the anchor member 216 by a factor of at least two and approximately three, but no more than four.

The relatively enlarged hole formation device 60 acts to push the seabed material outwards during installation and friction on the sides of the anchor member 216 during installation. The anchoring apparatus 210 includes a water supply arrangement 66 to provide a water supply to a lowermost part of the or each anchor member 216. The water supply arrangement 66 provides the water supply at an elevated pressure relative to the sea pressure local to the lowermost part.

In the example shown, the hole formation device 60 is hollow and defines an interior 68. The water supply arrangement 66 provides water to the interior 68. In one example the water supply arrangement 66 includes one or more bores 74 defined within the anchor member 216. In another example, the water supply arrangement 66 could include one or more pipes (not shown) external to the anchor member 216 to provide water to the lowermost part of the anchor member 216.

The hole formation device 60 defines water ejection holes 70, which in the example shown are directed upwardly and through which, in the installed condition, water flows therethrough from the interior 68.

The water supply at the lowermost part of the anchor member 216 aids installation by reducing friction by the seabed material on the sides of the anchor members 216.

The water supply could be provided on one or both sides of the anchor member 216.

Third Embodiment

Figs. 8 to 10 show a third embodiment, apparatus 310. In this embodiment, the apparatus 310 comprises a support member 56 which supports two spaced pairs of anchor members 16. The apparatus 310 comprises two fixing devices 12, with one fixing device 12 associated with each pair of anchor members 16.

The pipeline 14 has a diameter 26. Each anchor member 16 has a transverse dimension 22 and a depth dimension 24.

The transverse dimension 22 is greater than the pipeline diameter 26, and in this example is greater by a factor of approximately 1.5. The depth dimension 24 is greater than the pipeline diameter 26, and in this example is greater by a factor of approximately 2.4.

In this example, the depth dimension 24 is greater than the transverse dimension 22 by a factor of approximately 1 .6.

The shape of the anchor members 16 in terms of the ratio of the depth dimension to the transverse dimension could be varied to suit the seabed material, with a higher ratio being used for softer and/or deeper seabed materials.

In this example, each anchor member 16 has a cross-sectional area, which is greater than the cross-sectional area of the pipeline 14 and could be greater by a factor of approximately 4.5.

The size of the anchor members 16 in terms of the ratio of the cross-sectional area of each anchor member 16 to the cross-sectional area of the pipeline 14 could be varied to suit the seabed material, with a higher ratio being used for softer and/or deeper seabed materials.

The apparatus 310 includes a bracing/stability arrangement 36. The bracing/stability arrangement 36 includes a yoke part 38, which extends between the anchor members 16. The bracing/stability arrangement 36 includes bracing members 40, each of which is in the form of a strut which extends from an inward facing surface of the respective anchor member 16 to the support member 56.

Each fixing device 12 is moveable between an open condition and a closed condition. Each fixing device 12 comprises a clamp device 46, which comprises a pair of clamp arms 48. Each clamp arm 48 is associated with one of the anchor members 16 and comprises a pair of clamp arm members 48A which are located one on either side of the respective anchor member 16. Each clamp arm 48 is pivotally connected to the respective anchor member 16 by a pivot member 50. Each clamp arm member 48A includes an arm contact member 90 at one end. The arm contact members 90 of the clamp arm 48 are connected together by an arm pin 92 which extends through a guide slot 94 defined by the respective anchor member 16.

Each fixing device 12 includes an upper contact member 54 which extends downwardly from the support member 56. Each clamp device 46 includes an actuator 72 for moving the clamp arms 48 between the open and the closed conditions. In the example shown, the actuator 72 comprises a screw mechanism 52.

The actuator 72 includes a threaded connector 84 for connecting one of the clamp arms 48 to the screw mechanism 52 and a sliding connector 86 for connecting the other of the clamp arms 48 to the screw mechanism 52. The actuator 72 includes a pair of stops 88 which limit the sliding movement of the sliding connector 86 and a spring 96 which biases the sliding connector 86 to one of the stops 88 but permits a degree of resiliently biased movement of the sliding connector 86 between the stops 88.

The spring 96 provides a resilient arrangement 100 to permit misalignment and/or movement.

The actuator 72 includes a handle 80 for manually turning the screw mechanism 52.

The anchor members 16 are rounded or chamfered on their lower inner corners to provide guide surfaces 98 to help the location of the anchor members 16 on the pipeline 14.

Third Embodiment - In Use

The apparatus 310 is installed in a similar way to the previous embodiments. The apparatus 310 is lowered from above onto the pipeline 14 with the clamp arms 48 in the open condition. In this condition, the arm pins 92 are located at or towards an outer end of the guide slots 94 and the arm contact members 90 are clear of the slot part 32 of the aperture 28.

As the apparatus 310 is lowered, the anchor members 16 sink into the seabed S by the self-weight of the apparatus 310. In one example, the support member 56 could be hollow, defining an interior 82, in which ballast (not shown) could be located, to increase/vary the selfweight.

The apparatus 310 is lowered until the upper contact member 54 contacts the pipeline 14, as shown in Fig. 10A. Fig. 10A shows the anchoring apparatus 310 located on the pipeline 14 in an unclamped condition, in which the fixing devices 12 are in the open condition. The actuator 72 is then operated to move the fixing devices 12 to the closed condition as shown in Fig. 10B. The handle 80 is turned to move the threaded connector 84 away from the sliding connector 86, which moves the arm contact members 90 towards each other and inwardly and upwardly, to clamp the pipeline 14 against the upper contact member 54, with the arm pins 92 moving along the guide slots 94 to or towards an inner end of the guide slots 94.

In the closed condition, the spring 96 permits the clamp device 46 to apply a clamping force to the pipeline 14 while allowing a degree of movement. It also permits a degree of misalignment if, for example, the pipeline 14 is not straight.

Fig. 10B shows the anchoring apparatus 310 located on the pipeline 14 in a clamped condition, in which the fixing devices 12 are in the closed condition.

Advantageously, the Applicant has found that the arrangement of two pairs of anchor members 16 improves orientation and stability, in particular helping to ensure that the anchor members 16 penetrate the seabed material S perpendicularly.

In one example, the leverage exerted by the clamp arms 48 could achieve a force of several tonnes at each arm contact member 90. Such forces are typically available through the use of remotely operated vehicle (ROV) manipulators which are commonly used in subsea environments.

The arm contact members 90 could be shaped. For example, in clay soils, the arm contact members 90 could define grooves to allow any clay soils to be displaced. In sandy soils, a zip pump from an ROV may be required to clear a small amount of material where the arm contact members 90 will sit.

The compression in the spring 96 provides visual confirmation of the clamping force being exerted. This both ensures that the clamping load is well defined, and negates any problems with creep movement of the clamping system and pipeline coating or similar over time.

Other Modifications

Various other modifications could be made without departing from the scope of the invention. The apparatus and its various components could be of any suitable size and shape, and could be formed of any suitable material (within the scope of the specific definitions herein). In particular, the anchor members could be of different size and shape to that shown.

The anchor members 16 could include a rubbing strip (not shown) on their internal sides/edges to reduce friction/abrasion against the pipeline.

The self-weight of the apparatus could be altered by, for example, changing the thickness of the anchor members.

Any of the features or steps of any of the embodiments shown or described could be combined in any suitable way, within the scope of the overall disclosure of this document.

Final Remarks

There is thus provided anchoring apparatus with a number of advantages over conventional arrangements. The apparatus is relatively easy to fit without requiring a break to be made bin the pipeline. It does not require to be fitted at the same time as the pipeline is being installed but can be easily retrofitted after the pipeline has been laid on the seabed. It requires no maintenance to continue satisfactory operation. The apparatus resists in particular the movement caused by thermal expansion and contraction which causes pipeline walking and is an economical and effective solution to this problem.