1. A buoyancy module for mounting on an elongate member to be deployed underwater, the buoyancy module comprising multiple buoyancy elements coupled to one another independently of the elongate member, wherein each buoyancy element has a recess and buoyancy elements are laterally juxtaposed with their recesses aligned with one another to encircle the elongate member in use, and wherein multiple buoyancy elements are stacked one upon another along a direction which is axial with respect to the elongate member in use, to form a buoyancy module of a predetermined axial depth, the recesses of the buoyancy modules together forming an axially extending passage through which the elongate member passes, in use.
The invention relates to a buoyancy module (100, 200, 300, 400, 500, 700) which comprises multiple buoyancy elements (104, 204, 304, 404, 504, 604, 704) coupled to one another. Each of the buoyancy elements has a recess (110, 210) and the buoyancy elements are laterally juxtaposed with their recesses aligned with one another to encircle the elongate member in use. Multiple buoyancy elements are stacked one upon another along a direction which is axial with respect to the elongate member in use, to form a buoyancy module of a predetermined axial depth. The recesses of the buoyancy modules together form an axially extending passage through which the elongate member passes.
- 1. A buoyancy module for mounting on an elongate member to be deployed underwater, the buoyancy module comprising multiple buoyancy elements coupled to one another independently of the elongate member, wherein each buoyancy element has a recess and buoyancy elements are laterally juxtaposed with their recesses aligned with one another to encircle the elongate member in use, and wherein multiple buoyancy elements are stacked one upon another along a direction which is axial with respect to the elongate member in use, to form a buoyancy module of a predetermined axial depth, the recesses of the buoyancy modules together forming an axially extending passage through which the elongate member passes, in use.
- 19. A buoyancy element for assembly into a buoyancy module which is for mounting on an elongate member to be deployed underwater and which has an axially extending passage to receive the elongate member, the buoyancy element having
abutment faces on either side of a recess so that a two or more of the buoyancy elements are able to be laterally juxtaposed around the elongate member to encircle it; upper and lower faces formed such that the upper face of one buoyancy element is abuttable with the lower face of an axially neighbouring element, to form a stack of buoyancy elements in which the recesses of the stacked buoyancy elements together form a through-passage for receiving the elongate member.
- View Dependent Claims (21)
- 20. (canceled)
- 22. (canceled)
- 23. (canceled)
The present invention relates to buoyancy for mounting on elongate underwater members, for example risers, jumpers, pipelines, cables and umbilicals.
Such buoyancy can serve a range of different purposes. In offshore extraction of oil and gas, tubular conduits extend from the wellhead to the surface platform. These conduits include the “risers”—flowlines through which the hydrocarbons are conducted to the surface. The risers are often provided with distributed buoyancy modules at chosen positions along their length to support them in a chosen configuration, such as the lazy S or steep S configurations which are well known to the skilled person. There are numerous other examples where the weight of an underwater conduit needs to be partially supported by submerged buoyancy attached to it.
A known form of buoyancy module for this purpose is commonly referred to as a “distributed buoyancy module” and is depicted in
While the known type of distributed buoyancy module is successful and widely used, certain challenges remain.
Known distributed buoyancy modules are typically bespoke items, designed and manufactured to meet the requirements of a particular project. The design constraints for a given project include the diameter of the elongate member on which the buoyancy is to be mounted, its tightest radius of curvature (which has a bearing on the degree of flare 22 of the through-going passage), the buoyant force that is required, the depth of deployment and so on. Based on these constraints a design process is carried out which includes mathematical analysis such as finite element analysis to ensure that the buoyancy module is capable of providing an adequate design lifetime (which can be decades long) in the hostile marine environment. The design process may involve successive refinements. Tooling is then made based on the bespoke design to form the exterior shell of the buoyancy elements and production begins. The process of design, tooling up and then manufacture involves a significant lead time which can be problematic for customers.
There are also certain challenges involved in the manufacture of large distributed buoyancy element of the known type. Typically syntactic foam is poured into the rotationally moulded shell, which thus acts as the mould for the syntactic core. But the shell of a large buoyancy element is insufficiently rigid to support itself and maintain its shape during this process, and so needs to be constrained in an external jig adapted to the shape of the particular buoyancy element under manufacture.
The syntactic foam typically comprises a thermosetting plastics material such as epoxy, whose setting reaction is exothermic. If the entire volume were poured and set in one process, excessive heat would be created. Instead the shells are filled by a small depth in one pour, and the layer thus created is allowed to set before the next pour. This repeated process of pouring and setting takes a protracted period of time.
The machinery needed to rotomould the shells for large conventional distributed buoyancy modules is not widely available, so that few rotomoulding companies are capable of doing this work.
The present invention is specified in the appended claims.
Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Principles underlying the present invention can be appreciated from a study of
Note that throughout the present description and claims, the term “buoyancy module” refers to an entire module which, in accordance with the present invention, is formed from multiple individually formed “buoyancy elements”.
The buoyancy elements 104 are formed in a manner which enables them to be stacked along the axial direction—that is, one is placed upon another to form a stack extending along the direction of the axis 106 of the elongate member 102. In the assembled buoyancy module 100 multiple buoyancy elements 104 are stacked and coupled to one another to form a module of a desired length. The number of layers in the stack thus determines the axial depth of the module and the volume of water it displaces, and thus the buoyant force it provides. In this way modules of a specified size (and in particular, volume) can be assembled from standardised buoyancy elements 104 without needing to design and manufacture bespoke mouldings to meet that specification.
Each buoyancy element 104 abuts at least two neighbouring buoyancy elements 104, and is coupled to them, in the loose sense that they form a common assembly and are directly or indirectly secured to one another. For example end buoyancy element 104a is coupled to an axially neighbouring buoyancy element 104b and to a laterally neighbouring buoyancy element, which is not seen in
The term “axial neighbours” is used herein to refer to a pair of buoyancy elements which form adjoining layers in the stack of buoyancy elements, such as 104a and 104b in
Looking again at
Each buoyancy element 104 has upper and lower axially directed faces 111, one facing in the opposite direction to the other. In the assembled buoyancy module 100 faces 111 of axially neighbouring buoyancy elements abut one another. The recess 110 extends from one face 111 to the other.
The buoyancy elements 104 are shaped to provide registration features to provide positive location of the buoyancy element 104 with respect to its neighbours. These are of two types:
- a. lateral registration features, which locate the buoyancy element with respect to its lateral neighbour. In the
FIG. 2embodiment these comprise a pip 112 and a recess 114 each formed on the inner abutment face 108. When a pair of laterally neighbouring buoyancy elements is assembled around the elongate member 106, the pip of one is received in the recess of the other and vice-versa.
- b. axial registration features, which locate the buoyancy element 104 with respect to its axial neighbours in the stack. These are omitted from
FIG. 2, which is somewhat simplified, but examples will be described below in relation to other embodiments.
- a. lateral registration features, which locate the buoyancy element with respect to its lateral neighbour. In the
The buoyancy elements 104 together form a passage 116 which is open-ended, extending from the exposed face 111 at one end of the buoyancy module 100 to a further exposed face at its other end. This passage 116 is in the present embodiment not flared, as in the prior art buoyancy module. Instead it is of constant diameter, and to accommodate flexure of the elongate member 102 it is oversized with respect to it. That is, the inner diameter of passage 116 is larger than the exterior diameter of the elongate member 102. This does result in some loss of module volume, as compared with the prior art buoyancy module 10 of
The buoyancy module 100 is located against movement along the elongate member 106 by means of a clamp 118 mounted on the elongate member. The clamp is depicted only schematically in
A first type of buoyancy element 204a is depicted on its own in
A second type of buoyancy element 204b is depicted on its own in
A third type of buoyancy element 204c is depicted on its own in
- it comprises lateral registration features on its inner abutment faces 208. These comprise a tongue 212 for receipt in a recess 214.
- it has a circumferentially extending recess 229 in its outer surface, to receive and locate a strap 231 which is secured around the buoyancy module 200 under tension.
In the illustrated example only two buoyancy elements of the third type 204c are provided and they serve to locate one half of the buoyancy module 200 (i.e. the components seen in
The three different types of buoyancy element 204a, b, c may be formed using a single basic mould with removable inserts (“change parts”).
All of the buoyancy elements 204a, b and c are provided with through-going openings 234 extending from one face 211 to the other. In the illustrated example these pass through the axial registration features 230, 232 and there are three of them in each buoyancy element 204a, b, c. In the assembled buoyancy module 200 they align to form through-going coupling passages 238 extending from one end face 211a of the buoyancy module to the other end face 211b (see
The buoyancy elements 204 are coupled to one another to form the buoyancy module 200. Prior to deployment, a pair of half shells is assembled.
Mounting the buoyancy module 200 to the elongate member involves assembling two half shells to one another around the elongate member. The aforementioned straps 231 secure the two half shells together.
The internal structure of the buoyancy elements 204a, b, c can best be seen in
The through-going openings 234 are formed, as seen in
Note that because the required depth of the entire buoyancy module 200 is made up from multiple buoyancy elements 204a, b, c which are stacked along the axial direction, the depth of individual buoyancy elements 204 in the present embodiment is much smaller than the depth of the prior art buoyancy modules 12, 14 depicted in
In this embodiment each of the buoyancy elements 304 is has a circumferentially extending recess 329 in its outer surface, able to receive and locate a strap 331 which secured around the buoyancy module 300 under tension to maintain its two halves together. Note that only two straps 331 are used in this embodiment, however.
Like the embodiment depicted in
Like the embodiment depicted in
This embodiment uses two different types of buoyancy element.
A first type 504a of buoyancy element has a circumferential recess 529 to receive and locate a strap 531, and also has male and female lateral registration features formed by a square upstand 512 and a square recess 514.
A second type 504b of buoyancy element serves to engage the clamp 518, and is in this embodiment a moulded, buoyant item which can have the shell-and-core structure described above.
There are numerous other ways in which the buoyancy elements can be coupled to one another. For example, the buoyancy elements forming one layer may be shaped to engage with the next in the manner of a part-turn lock. Alternatively elements of successive layers may be angularly offset so that the elements of one half form a set of fingers interleaved with matching fingers of the other half. By passing threaded coupling members axially through these interlocked fingers the two halves can be secured together without need of straps.
This differs from the above described embodiments with respect to the axial registration features, which in this embodiment comprise elongate skids 730 for receipt in slots 732. These perform a dual function. As well as locating one layer of buoyancy elements relative to its axial neighbour, the skids 730 on the lower surface of the module 700 provide the surfaces through which the module 700 rests upon the ground prior to its deployment. They can easily be incorporated in the moulded shells of the buoyancy elements 704 during its moulding and so add nothing to cost. And by keeping the remainder of the shell from contact with the ground which might abrade it, they make it possible to dispense with other protective measures such as the additional wooden skids currently used to protect the module during handling. The skids 730 can be sacrificial, in the sense that they can be abraded during handling and that this does not impair the module'"'"'s function once it is installed. The same dual function may be performed by other types of upstand upon the buoyancy elements'"'"' lower faces.
For handling purposes hooks eyes 780 may be screwed on to the threaded members used to secure the stacked buoyancy elements 704 together.
In the present embodiment the coupling members 844 terminate in respective feet 866 (see
The coupling members 244, 344, 844 used to couple together the buoyancy elements in a stack may take a variety of forms. They may comprise metal rod, e.g. of stainless steel. They may be flexible. They may be formed of a composite, such as a fibre reinforced composite.
The invention provide various advantages. It makes it possible to use one set of mouldings, which may be manufactured in advance of orders and kept in stock, to make buoyancy modules having a range of different volumes and suitable for use on elongate members having a range of different diameters. The lead time involved in the design and manufacture process described above can thus be avoided. The manufacture of the relatively shallow buoyancy elements of the present invention can be simpler in that fewer pouring processes are required to mould the structural core and jigging may not be necessary. The wall thickness of the shells used in the present embodiment can be relatively small due to the small size of the buoyancy elements, which can reduce rotomoulding time. There is a degree of variability in volume of the moulded buoyancy elements but in accordance with the invention this can be allowed for by matching—in a given buoyancy module—some elements which are over-sized with some that are under-sized, making it possible to closely match a design volume. The relatively small mouldings used in embodiments of the invention can be made in smaller rotomoulding machines, which are more widely available.