U.S. patent application number 16/311154 was filed with the patent office on 2019-10-24 for buoyancy element.
The applicant listed for this patent is Trelleborg Offshore UK Ltd. Invention is credited to Jonathan Lloyd Fox, Austin Harbison.
Application Number | 20190323298 16/311154 |
Document ID | / |
Family ID | 56891264 |
Filed Date | 2019-10-24 |
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United States Patent
Application |
20190323298 |
Kind Code |
A1 |
Harbison; Austin ; et
al. |
October 24, 2019 |
Buoyancy Element
Abstract
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.
Inventors: |
Harbison; Austin;
(Skelmersdale, GB) ; Fox; Jonathan Lloyd;
(Skelmersdale, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Trelleborg Offshore UK Ltd |
Skelmersdale, Lancashire |
|
GB |
|
|
Family ID: |
56891264 |
Appl. No.: |
16/311154 |
Filed: |
June 30, 2017 |
PCT Filed: |
June 30, 2017 |
PCT NO: |
PCT/GB2017/051924 |
371 Date: |
December 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 17/012
20130101 |
International
Class: |
E21B 17/01 20060101
E21B017/01 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2016 |
GB |
1611477.9 |
Claims
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.
2. The buoyancy module as claimed in claim 1 further comprising at
least one locating feature which projects into the passage to
engage in use with a clamp secured to the elongate member and
thereby locate the buoyancy module against axial movement with
respect to the elongate member.
3. The buoyancy module as claimed in claim 2, wherein the at least
one locating feature includes two locating features axially
separated from one another to abut opposite sides of the clamp, in
use.
4. The buoyancy module as claimed in claim 2, wherein the passage
is generally circular in section and the locating feature forms a
through-going opening in the passage of internal diameter smaller
than that of the passage.
5. The buoyancy module as claimed in claim 2, wherein the locating
feature is formed by a locating part sandwiched between axially
neighbouring buoyancy elements.
6. The buoyancy module as claimed in claim 5, wherein the locating
feature is formed by at least one plate sandwiched between axially
neighbouring buoyancy elements.
7. The buoyancy module as claimed in claim 6, wherein the plate is
captively received in a recess formed between the axially
neighbouring buoyancy elements and surrounding the passage.
8. The buoyancy module as claimed in claim 3, wherein the locating
feature is formed by at least one of the buoyancy elements.
9. The buoyancy module as claimed in claim 1, wherein the passage
is circular and has a substantially constant diameter along its
axial length.
10. The buoyancy module as claimed in claim 1, wherein five or more
buoyancy modules are stacked one upon another along the axial
direction.
11. The buoyancy module as claimed in claim 1, wherein three or
more buoyancy modules are stacked one upon another along the axial
direction.
12. The buoyancy module as claimed in claim 1, wherein buoyancy
elements have first and second faces directed along opposite axial
directions, through which axially neighbouring buoyancy elements
abut one another, the first and second faces being provided with
axial registration features and the axial registration features on
the first face of one buoyancy element being engageable with the
axial registration features on the second face of another buoyancy
element, so that through engagement of their respective axial
registration features, axially neighbouring buoyancy elements
register with one another and are thereby aligned with one
another.
13. The buoyancy module as claimed in claim 12, wherein the axial
registration features include complementary male and female
features.
14. The buoyancy module as claimed in claim 1, wherein laterally
juxtaposed buoyancy elements engage through lateral registration
features to align laterally juxtaposed buoyancy elements with one
another.
15. The buoyancy module as claimed in claim 1 further comprising at
least one axially extending fastener passes through stacked
buoyancy elements to prevent them from being separated from one
another along the axial direction.
16. The buoyancy module as claimed in claim 15, wherein the
fastener includes a threaded member.
17. The buoyancy module as claimed in claim 1, wherein each
buoyancy element has a male interlocking feature on a first side
and a female interlocking feature on a second side opposite to the
first, and in which the male engagement feature of one buoyancy
element interlocks with the female engagement feature of an axially
neighbouring buoyancy element, thereby locking the two buoyancy
elements together.
18. The buoyancy module as claimed in claim 17, wherein the male
engagement feature includes a boss and the female engagement
feature includes a recess for receiving the boss.
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.
20. (canceled)
21. The buoyancy element as claimed in claim 19, wherein the upper
and lower faces are provided with axial registration features and
the axial registration features on the upper face of one buoyancy
element are engageable with the axial registration features on the
lower face of another similarly formed buoyancy element, so that
through engagement of their respective axial registration features,
axially neighbouring buoyancy elements are able to register with
one another.
22. (canceled)
23. (canceled)
Description
[0001] The present invention relates to buoyancy for mounting on
elongate underwater members, for example risers, jumpers,
pipelines, cables and umbilicals.
[0002] 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.
[0003] A known form of buoyancy module for this purpose is commonly
referred to as a "distributed buoyancy module" and is depicted in
FIG. 1 of international patent application PCT/GB2013/051311,
published under number WO2013/171521 in the name of Trelleborg
Offshore U.K. Ltd. That drawing is reproduced here, with revised
reference numerals, as FIG. 1. The buoyancy module 10 comprises a
pair of buoyancy elements 12, 14 which are each semi-annular in
cross section and which, when assembled to one another, form a
through-going passage to receive and embrace a member such as a
riser 16. The buoyancy elements are moulded items. They can be
manufactured by first forming an exterior skin or shell by rotary
moulding (a technique which is well known to the skilled person and
will not be described herein). This shell forms the outer surface
of the buoyancy element but and can be formed from a tough plastics
material--polyethylene is used--but it does not have sufficient
rigidity to withstand hydrostatic pressure experienced by the
module in use. It is filled with a low density composite material
to give the module structural integrity. This material is commonly
syntactic foam--a mixture of settable plastics material with a low
density filler which can be in the form of microballoons--small
hollow glass spheres--and macrospheres--larger hollow bodies.
Syntactic foam can be strong and rigid enough to withstand what can
be very large hydrostatic pressures, but still low enough in
density to be buoyant. The buoyancy elements 12, 14 are assembled
to one another around the riser 16 to form the buoyancy module 10.
Straps 20 passed around the module keep the buoyancy elements 12,
14 together. The through-going passage is flared toward both its
ends as seen at 22 in FIG. 1, enabling it to accommodate curvature
of the riser 16. The buoyancy module 18 needs to be prevented from
moving along the riser and in this prior art example that function
is performed by a clamp 24 which embraces and grips the riser and
which is received in a pocket in the buoyancy module's
through-going passage, thereby engaging with the module and
preventing it from moving. Suitable clamps are known in the art and
examples are given in PCT/GB2013/051311. Multiple distributed
buoyancy modules may be used, singly or in groups, to provide a
specified buoyancy.
[0004] While the known type of distributed buoyancy module is
successful and widely used, certain challenges remain.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] The present invention is specified in the appended
claims.
[0010] Specific embodiments of the present invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0011] FIG. 1 represents a buoyancy module belonging to the prior
art, partly cut-away to reveal interior detail;
[0012] FIG. 2 represents parts of a first buoyancy module embodying
the present invention, some of the module's components being
omitted to reveal internal detail;
[0013] FIG. 3 represents parts of a second buoyancy module
embodying the present invention, some of the module's components
being omitted to reveal internal detail;
[0014] FIG. 4 is a partial section in an axial plane through the
second buoyancy module;
[0015] FIGS. 5a and 5b show certain details of FIG. 4 to an
enlarged scale;
[0016] FIG. 6 represents an individual buoyancy element used in the
second buoyancy module, part of which is cut-away to reveal its
internal structure;
[0017] FIGS. 7a and 7b represent the same buoyancy element viewed
from above and from beneath, respectively;
[0018] FIG. 8 is another representation of the second buoyancy
module;
[0019] FIGS. 9a, 9b and 9c each show a respective buoyancy element
used in the second buoyancy module;
[0020] FIG. 10 represents parts of a third buoyancy module
embodying the present invention, some of the module's components
being omitted to reveal internal detail;
[0021] FIG. 11 represents a buoyancy element used in the third
buoyancy module, partly in phantom;
[0022] FIG. 12 represents parts of a fourth buoyancy module
embodying the present invention, some of the module's components
being omitted to reveal internal detail;
[0023] FIG. 13 represents parts of a fifth buoyancy module
embodying the present invention, some of the module's components
being omitted to reveal internal detail;
[0024] FIG. 14 represents a further buoyancy element embodying the
present invention; and
[0025] FIGS. 15 and 16 represent a sixth buoyancy module embodying
the present invention, showing inter alia how the module can be
hoisted;
[0026] FIGS. 17 and 18 represent a seventh buoyancy module
embodying the present invention, in open and closed configurations
respectively;
[0027] FIG. 19 depicts to an enlarged scale a foot arrangement of
the seventh buoyancy module;
[0028] FIGS. 20 and 21 represent an eighth buoyancy module
embodying the present invention; and
[0029] FIG. 22 represents a ninth buoyancy module embodying the
present invention.
[0030] Principles underlying the present invention can be
appreciated from a study of FIG. 2 which represents a first
buoyancy module 100 embodying the present invention, in position
upon an elongate member 102 which may be a conduit, cable, pipe,
riser, jumper, pipeline, umbilical or other elongate member to be
deployed underwater and to be provided with buoyancy. The buoyancy
module 100 is assembled from a set of separately formed buoyancy
elements 104. Whereas the buoyancy elements making up the prior art
buoyancy module of FIG. 1 are bespoke, those of the present
invention are standardised in size and shape and able (a) to be
assembled into buoyancy modules of differing sizes and (b) to be
used on elongate members 102 having a range of diameters.
[0031] 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".
[0032] 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.
[0033] 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 FIG.
2 since those elements in the foreground have been omitted to
reveal the interior of the assembly.
[0034] 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 FIG. 2. Other
similar phrases such as "axially neighbouring" are to be
correspondingly construed. The term "lateral neighbours" refers to
a pair of buoyancy elements which are at the same level in the
stack of buoyancy elements. Again other similar phrases such as
"laterally neighbouring" are to be correspondingly construed. FIG.
15 shows a complete buoyancy module 700 and a laterally
neighbouring pair of buoyancy elements is designated 704a,
704b.
[0035] Looking again at FIG. 2, laterally neighbouring buoyancy
elements 104 together form a loop encircling the elongate member
102, so that the assembled buoyancy module 100 surrounds and is
captive upon the elongate member. In the present embodiment this
loop is formed by a pair of buoyancy elements 104, although it is
possible that in other embodiments a different number of elements
(e.g. three elements, each a 120 degree sector of a circle) may
make up the full circumference of the buoyancy module 100. Each
buoyancy element 104 has a pair of inner abutment faces 108 between
which is a recess 110. Inner abutment faces 108 of laterally
neighbouring buoyancy elements 104 abut one another, with their
recesses 110 aligned to form a through-going passage for the
elongate member 102. In the present embodiment the buoyancy
elements are semi-annular in plan, the recesses 110 being
semi-circular and the exterior of the assembled buoyancy module
being approximately circular in cross section. Other shapes could
however be used in other embodiments.
[0036] 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.
[0037] 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: [0038] a.
lateral registration features, which locate the buoyancy element
with respect to its lateral neighbour. In the FIG. 2 embodiment
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. [0039]
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.
[0040] 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 FIG. 1, where clearance was
provided mainly in the flared end regions of the passage. But
simple geometric calculations show this to be a small loss of
displacement volume, acceptable in typical applications.
[0041] 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 FIG.
2. Suitable clamps are known in the art. Details of some suitable
clamps are provided in prior art document PCT/GB2013/051311. The
clamp 118 is disposed within the passage 116 of the buoyancy module
100. Since the passage 116 is over-sized and of constant cross
section, some additional means needs to be provided for the clamp
118 to engage with the buoyancy module 100. In the present
embodiment, first and second locating plates 120, 122 are provided
on either side of the clamp 118. First locating plate 120 is
sandwiched between an axially neighbouring pair of buoyancy
elements 104 above the clamp 118. It has a through-going opening
124 which receives the elongate member 102. Some provision needs to
be made for the elongate member 102 to be introduced into the
opening 124. This may be achieved by forming the locating plate 120
in two halves (which in the present embodiment are semi-annular)
for assembly around the elongate member. The opening 124 is large
enough to receive the elongate member 102 but small enough to
ensure that the clamp 118 is unable to pass through. The second
locating plate 122 is similarly formed to the first but disposed
beneath the clamp 118. Together the two locating plates 120, 122
prevent movement of the buoyancy module 100 in either direction
along the elongate member 102. The diameter of the openings 124 in
the locating plates 120, 122 needs to be matched to some degree to
that of the riser, and the plates may need to be tailored to a
particular project in this respect, but this is a straightforward
process, e.g. involving machining the openings, and need not add
greatly to cost or delivery lead time.
[0042] The FIG. 2 embodiment uses only one type of buoyancy element
104 and can thus be manufactured using just one mould. The
embodiment depicted in FIGS. 3 to 9 is different in this
respect--it uses three different types of buoyancy element 204a,
204b and 204c--but as before the buoyancy elements are stacked to
form a buoyancy module 200 of a desired axial depth, and laterally
neighbouring buoyancy elements together encircle the elongate
member (which is not shown in these drawings), forming a passage
216 through which the elongate member passes. A clamp 218 is
secured upon the elongate member to axially locate the buoyancy
module 200, and FIG. 3 gives a little more detail of a suitable
clamp, seen to comprise multiple part-annular clamp shells 218a
surrounded by a clamping band 218b.
[0043] A first type of buoyancy element 204a is depicted on its own
in FIG. 9a. It is semi-annular in shape. It has plain inner
abutment faces 208 without any lateral registration features, and a
semi-circular cut-away or recess 210 to accommodate the elongate
member. Male axial registration features 230 (formed as upstanding
pips in the present example, although they may take other forms)
are provided on a top face 211a of the buoyancy element 204a to
register with complementary female axial registration features 232
on the bottom face 211b of an axially neighbouring buoyancy
element. The female axial registration features are formed as
shallow recesses in the present example, and are seen in FIGS. 5b,
6 and 7b. The male and female axial registration features 230, 232
locate one buoyancy element with respect to its axial neighbour in
the stack.
[0044] A second type of buoyancy element 204b is depicted on its
own in FIG. 9b and in FIGS. 7a and 7b and differs from the first
type only in that the radius of the semi-circular cut-away 210 is
smaller. The buoyancy elements of the second type 204b are disposed
on either side of the clamp 218 and their faces 211a, 211b (see
FIG. 3) abut the clamp and are unable to pass it, whereby these
buoyancy elements serve to axially locate the buoyancy module 200
with respect to the clamp 218.
[0045] A third type of buoyancy element 204c is depicted on its own
in FIG. 9c and differs from the first type in two respects:--
[0046] it comprises lateral registration features on its inner
abutment faces 208. These comprise a tongue 212 for receipt in a
recess 214. [0047] 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.
[0048] 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 FIG. 3) with
respect to its other half and, by virtue of the straps 231, to hold
the two halves together. More of this third type of buoyancy
element 204c could be incorporated in other assemblies.
[0049] The three different types of buoyancy element 204a, b, c may
be formed using a single basic mould with removable inserts
("change parts").
[0050] 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 FIG. 4 in particular).
[0051] 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. FIG. 3 depicts a single half shell. Respective
elongate threaded coupling members 244 are passed through each of
the coupling passages 238 to secure together the stacked buoyancy
elements 204a, b, c forming the half shell. In FIG. 5a, a washer
246 is seen to bear upon the top-most element in the stack and to
be retained by a nut 249 on the coupling member 244, and in FIG. 5b
a further washer 248 bears upon the bottom-most element in the
stack and is likewise retained by a nut on the coupling member
244.
[0052] 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.
[0053] The internal structure of the buoyancy elements 204a, b, c
can best be seen in FIG. 6. The buoyancy elements can be
manufactured by first forming an external plastics shell 250 which
forms the outer surface of the buoyancy element and has a small
wall thickness. This can be done by rotomoulding of plastics
material. Other moulding processes may be used. In the present
embodiment the shell 250 comprises polyethylene, although other
mouldable materials may be used. The shell 250 is then filled with
settable plastics material, which is syntactic foam in the present
embodiment and which forms a structural core for the buoyancy
element. The shell acts as mould for the core.
[0054] The through-going openings 234 are formed, as seen in FIGS.
4, 5 and 6, by opening walls 234a which are integral with the
remainder of the shell 250 and are formed during its
rotomoulding.
[0055] 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 FIG. 1. The large mouldings forming the prior art
buoyancy modules had to be filled with syntactic in multiple pours,
each being allowed to set before the next, to prevent them from
being destroyed by the heat that would be released upon curing were
they to be filled in one process. This problem is greatly
alleviated by the present invention due to the smaller depth of the
buoyancy modules, which can as a result be filled either in one
pour, or at least in a greatly reduced number of pours. This
reduces labour and especially reduces the time taken for
manufacture of each buoyancy element. It may also be unnecessary to
support the shell 250 in a jig during pouring of the core. If a jig
is required, it can be a standard item used for multiple orders, as
opposed to a bespoke or adaptable jig used in relation the prior
art modules of FIG. 1.
[0056] FIGS. 10 and 11 represent still a further buoyancy module
300 embodying the present invention. This uses buoyancy elements
304 of only a single type. That is, all the buoyancy elements 304
have the same shape and can be formed in the same mould. As before
the buoyancy elements 304 are stacked to form a buoyancy module 300
of a desired axial depth, and laterally neighbouring buoyancy
elements together encircle the elongate member 302, forming a
passage 316 through which the elongate member passes. A clamp 318
is secured upon the elongate member 302 to axially locate the
buoyancy module 300.
[0057] 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.
[0058] Like the embodiment depicted in FIGS. 3 to 9, the present
embodiment uses threaded, axially extending coupling members 344 to
secure the stacked buoyancy elements 304 to one another.
[0059] Like the embodiment depicted in FIG. 2, the present
embodiment has locating plates 320, 322 on either side of the clamp
318 to axially locate the buoyancy module 300, the locating plates
320, 322 being sandwiched between axially neighbouring buoyancy
elements 304. However in the present embodiment the locating plates
320, 322 are smaller in diameter than the buoyancy elements 304 and
are received in shallow annular recesses 352 formed in the lower
face of each buoyancy element 304.
[0060] FIG. 12 represents yet a further buoyancy module 400 which
differs from the embodiment depicted in FIGS. 10 and 11 in that the
threaded members 344 are dispensed with. Instead axially
neighbouring buoyancy elements 404 are shaped to interlock and so
couple to one another in a manner which prevents one from being
axially withdrawn from the other. This is achieved in the
illustrated example by providing each buoyancy element 404 with, on
one face, a semi-annular boss 460 with a radial undercut 462
running around its circumference, and on its other face with a
semi-annular recess 464 to with a radially inwardly directed
circumferential tongue 466 running around its circumference. In the
assembled buoyancy module 400 the boss 460 of one buoyancy element
404 is received in the recess 464 of its axial neighbour, and is
locked in that position by engagement of the tongue 466 in the
undercut 462. The top-most lateral pair of buoyancy elements, one
of which is designated 404a in the drawing and the other of which
is omitted, are secured to one another by strap 331. Note that this
may be sufficient in itself to prevent disassembly of the buoyancy
module 400. The top-most pair of buoyancy elements embraces the
second pair 404b below them and prevents them from being laterally
separated. The second pair 404b of buoyancy elements embraces the
third pair 404c below them and so prevents them from being
separated, and so on. In practice, bands at certain intervals may
be needed to provide a sufficiently robust assembly.
[0061] FIG. 13 represents yet a further buoyancy module 500
embodying the present invention. As before buoyancy elements 504
are stacked to form a buoyancy module 500 of a desired axial depth,
and laterally neighbouring buoyancy elements together encircle the
elongate member 502, forming a passage 516 through which elongate
member 502 passes. A clamp 518 is secured upon the elongate member
502 to axially locate the buoyancy module 500.
[0062] This embodiment uses two different types of buoyancy
element.
[0063] 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.
[0064] 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.
[0065] FIG. 14 represents a buoyancy element 604 according to still
another embodiment of the present invention, which exemplifies a
different manner in which the buoyancy elements 604 can be shaped
to interlock and so couple to their axial neighbours. Here, the
lower face of the buoyancy element 604 has a pair of elongate "T"
section slots 670 and its upper face carries a complementary pair
of "T" section upstands 672. The upstands 672 of one buoyancy
element 604 are to be slid into the slots 670 of its axial
neighbour, whereupon the engagement of the upstands with the slots
prevents one from being withdrawn from the other along the axial
direction.
[0066] 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.
[0067] FIGS. 15 and 16 show an entire buoyancy module 700 embodying
the present invention.
[0068] 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.
[0069] For handling purposes hooks eyes 780 may be screwed on to
the threaded members used to secure the stacked buoyancy elements
704 together.
[0070] FIGS. 17 to 19 show a further embodiment of the invention in
the form of a buoyancy module 800 in which buoyancy elements 804
form two half shells 801a, 801b, one hinged to the other. This
makes mounting of the module on the elongate member
straightforward. The buoyancy module 800 is initially open as
depicted in FIG. 17, enabling the elongate member to be introduced
to it. Turning one half shell relative to the other about the hinge
then closes it (FIG. 18). In the illustrated embodiment the
buoyancy elements 804 each have a pair of fingers 860, 862, one at
each end of the element. The fingers 860, 862 each have
through-going openings extending along the axial direction. Each
half shell 801a, 801b comprises a stack of buoyancy elements 804
coupled together by a respective elongate threaded coupling member
844a, 844b. To form the hinge, the fingers 860 of one half shell
801a are overlapped and interleaved with the fingers 862 of the
other half shell 801b, so that the fingers' through-going openings
are aligned to receive a further elongate threaded coupling member
844a, about which the half shells turn. When the buoyancy module
800 is closed as in FIG. 18, the fingers 862 of the first half
shell 801a overlap and are interleaved with the fingers 801b of the
second half shell 801b, and are secured to one another by passing
still a further threaded coupling member 844d through their aligned
openings, to lock the module in its closed configuration. The
straps used in other versions can be dispensed with. Note that
while the present embodiment used shaped fingers, an alternative
would be to angularly offset each buoyancy element 804 with respect
to its neighbours, enabling ends of each element of one half shell
to be interleaved with the ends of the elements of the other half
shell.
[0071] In the present embodiment the coupling members 844 terminate
in respective feet 866 (see FIG. 19) on which the buoyancy module
800 is able to stand prior to its deployment. Abrasion damage to
the module itself through contact e.g. with the deck of a ship may
thus be avoided.
[0072] FIGS. 20 and 21 depict still a further buoyancy module 900
embodying the present invention. In this example the axial
registration features comprise slots 960 on one face of buoyancy
elements 904 and tongues 962 on the opposite face, the tongues of
one buoyancy element being receivable in the slots of another.
[0073] FIG. 22 depicts still a further buoyancy module 1000
embodying the present invention. Whereas the modules described so
far rely on a separately formed clamp to resist movement of the
module along the elongate member on which it is mounted, buoyancy
module 1000 is formed in such a manner that it is able to locate
itself against such movement. It may be regarded as having an
integral clamp. For this purpose some of its buoyancy elements
1004a have recesses 1010a whose internal diameter is smaller than
that of the remaining buoyancy elements 1004b. These recesses 1010a
carry on their radially inwardly directed faces respective
resilient shoes 1060 through which seat in use upon the elongate
member. The shoes 1060 may comprise an elastomer. Rubber is
suitable. The shoes 1060 are somewhat elastically deformed when
seated on the elongate member, providing a clamping force. Due to
their resilience they are able to maintain this clamping force
despite factors such as creep which might otherwise enable the
integral clamp to loosen over time. To resist creep, the syntactic
foam of the clamp buoyancy elements 1004a may be a denser, stiffer
material than that of the remaining elements 1004b. Straps 1031 are
applied around the clamp buoyancy elements 1004a to apply the
required force directly to them to provide clamping. The drawing
shows a module having two pairs of clamp buoyancy elements 1004a,
but a different number may be used. This number may be one or
three.
[0074] 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.
[0075] 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.
* * * * *