U.S. patent application number 10/363277 was filed with the patent office on 2004-01-22 for protection of underwater elongate members.
Invention is credited to Gibson, Robert.
Application Number | 20040013473 10/363277 |
Document ID | / |
Family ID | 26244921 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040013473 |
Kind Code |
A1 |
Gibson, Robert |
January 22, 2004 |
Protection of underwater elongate members
Abstract
An underwater cladding (10) for an elongate member such as a
pipe, has a substantially cylindrical outer surface with a
plurality of depressions (18) therein. The provision of depressions
in an otherwise cylindrical outer surface of a cladding interrupts
or reduces vortex induced vibrations and the absence of projections
facilitates use with conventional pipe-laying equipment.
Inventors: |
Gibson, Robert; (Bolton,
GB) |
Correspondence
Address: |
Stephen M De Klerk
Blakely Sokoloff Taylor & Zafman
12400 Wilshire Boulevard
Seventh Floor
Los Angeles
CA
90025
US
|
Family ID: |
26244921 |
Appl. No.: |
10/363277 |
Filed: |
August 6, 2003 |
PCT Filed: |
August 23, 2001 |
PCT NO: |
PCT/GB01/03792 |
Current U.S.
Class: |
405/211 ;
114/264; 405/216 |
Current CPC
Class: |
E21B 17/012 20130101;
F16L 1/123 20130101; E21B 17/01 20130101 |
Class at
Publication: |
405/211 ;
405/216; 114/264 |
International
Class: |
E02D 005/60; B63B
035/44 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2000 |
GB |
0021142.5 |
Feb 23, 2001 |
GB |
0104464.3 |
Claims
1. An elongate underwater vortex shedding cladding (10) for an
elongate member, comprising an outer surface having a plurality of
depressions (18) therein.
2. An underwater cladding as claimed in claim 1, wherein the
depressions (18) are arranged around the whole periphery or
circumference of the cladding (10).
3. An underwater cladding as claimed in claim 1 or claim 2,
comprising a plurality of depressions (18) having a generally
circular periphery.
4. An underwater cladding as claimed in claim 3, wherein the
diameter of the circular depressions is from 1 cm to 30 cm.
5. An underwater cladding as claimed in claim 4, wherein the
diameter of the circular depressions is from 10 cm to 20 cm.
6. An underwater cladding as claimed in any of the preceding
claims, comprising a plurality of depressions having an elliptical
periphery.
7. An underwater cladding as claimed in claim 6, wherein the length
of the major axis of the elliptical depressions is from 1 cm to 30
cm.
8. An underwater cladding as claimed in claim 7, wherein the length
of the major axis of the elliptical depressions is from 10 cm to 20
cm.
9. An underwater cladding as claimed in any of claims 6 to 8,
wherein the length of the minor axis of the elliptical depressions
is from 0.5 cm to 20 cm.
10. An underwater cladding as claimed in claim 9, wherein the
length of the minor axis of the elliptical depression is from 5 cm
to 15 cm.
11. An underwater cladding as claimed in any of the preceding
claims, comprising an external circular cross-section and wherein
the largest diameter of a depression is from 5% to 50% of the
external diameter of the cladding.
12. An underwater cladding as claimed in claim 11, wherein the
largest diameter of a depression is from 10% to 30% of the external
diameter of the cladding.
13. An underwater cladding as claimed in any of the preceding
claims, comprising a plurality of depressions having a smooth
depressed or recessed surface.
14. An underwater cladding as claimed in claim 13, comprising a
plurality of depressions which are smoothly concave or dished in
cross-section.
15. An underwater cladding as claimed in claim 13, comprising a
plurality of depressions having a planar base wall.
16. An underwater cladding as claimed in claim 15, wherein the
depressions further comprise a side wall inclined to the planar
base wall and extending to the periphery of the depression.
17. An underwater cladding as claimed in claim 16, wherein the side
wall extends perpendicularly to the planar base wall.
18. An underwater cladding as claimed in any of the preceding
claims, wherein the depressions are substantially identical.
19. An underwater cladding as claimed in any of the preceding
claims, wherein the depressions are randomly spaced over the
surface of the cladding.
20. An underwater cladding as claimed in any of claims 1 to 18,
wherein the depressions are regularly spaced over the surface of
the cladding.
21. An underwater cladding as claimed in claim 20, wherein the
depressions are arranged in a plurality of rows and/or columns.
22. An underwater cladding as claimed in claim 21, wherein the
depressions of the row or column are offset from those in an
adjacent row or column.
23. An underwater cladding as claimed in claim 20, wherein the
depressions are arranged in a plurality of waves.
24. An underwater cladding as claimed in claim 23, wherein adjacent
waves of depressions are in phase with one another.
25. An underwater cladding as claimed in claim 23, wherein adjacent
waves of depressions are out of phase with one another.
26. An underwater cladding as claimed in any of the preceding
claims, comprising positively buoyant material.
27. An underwater cladding as claimed in claim 26, wherein the
buoyant material comprises syntactic foam.
28. An underwater cladding as claimed in claim 26 or claim 27,
wherein the cladding comprises solely syntactic foam.
29. An underwater cladding as claimed in claim 26 or claim 27,
further comprising macrospheres.
30. An underwater cladding as claimed in any of the preceding
claims, comprising a plurality of preformed sections assembled on,
and secured to, the elongate member to be protected.
31. An underwater cladding as claimed in claim 30, wherein the
preformed sections comprise semi-tubular sections.
32. An underwater cladding as claimed in claim 30, wherein the
preformed sections comprise tubular sections.
33. An underwater cladding as claimed in claim 32, wherein the
tubular sections are split along their length.
34. An underwater cladding as claimed in claim 33, wherein the
split is longitudinal.
35. An underwater cladding as claimed in claim 33, wherein the
split is helical.
36. An underwater cladding as claimed in any of claims 1 to 29,
wherein the cladding is moulded directly onto the outer surface of
the elongate member to be protected.
37. An underwater cladding as claimed in any of the preceding
claims, wherein the depressions are moulded into the cladding.
38. An underwater cladding as claimed in any of claims 1 to 36,
wherein the depressions are cut, machined or otherwise formed into
the outer surface of the cladding after moulding the cladding.
39. An underwater cladding as claimed in any of the preceding
claims, wherein the cladding is profiled to receive objects other
than the elongate member being protected.
40. An underwater cladding as claimed in any of the preceding
claims, wherein the outer surface is substantially cylindrical.
Description
DESCRIPTION
[0001] The present invention relates to the protection of
underwater pipes, drill risers, cables or other elongate
members.
[0002] When water flows past an underwater pipe, drill riser, cable
or elongate member of circular cross section, vortices may be shed
alternately from each side. The effect of these vortices is to
induce fluctuating, across-flow forces on the structure. If the
natural frequency of the structure is close to the shedding
frequency of the vortex the member can be caused to vibrate with a
large oscillation amplitude.
[0003] Such oscillations not only cause the pipe, drill riser,
cable or member to bend more than is desirable, but can also induce
unwanted forces on a connector (either underwater or above water)
to which the pipe, drill riser, cable or the like is secured. In
extreme cases, the coupling between the pipe, drill riser, cable or
the like and the connector is damaged.
[0004] Also, if there are intermediate connections or joints (e.g.
welds), then similar problems can arise. One solution to the above
problem is found in our co-pending patent application published as
GB-A-2335248. The arrangement disclosed therein works extremely
well but in view of the fact that the cladding disclosed therein
comprises a series of helical strakes, problems can arise when a
clad pipe, drill riser, cable or other elongate member is fed
through conventional pipe-laying apparatus or a vessel moonpool.
Whilst it is possible to overcome such problems, there is a desire
to avoid such problems altogether.
[0005] In accordance with the present invention, an elongate
underwater vortex shedding cladding for an elongate member
comprises an outer surface having a plurality of depressions
therein.
[0006] It has been found that the formation of depressions in an
otherwise cylindrical outer surface of a cladding interrupts or
reduces vortex induced vibrations and in view of the fact that
there are no strakes or other projections extending outwardly from
the otherwise cylindrical outer surface, the aforementioned
problems which can be encountered with pipe-laying apparatus are
avoided.
[0007] The presence of the depressions has also been found to
reduce the drag of the elongate member in certain circumstances in
both a steady and a fluctuating current.
[0008] Preferably, the depressions are arranged around the whole
periphery or circumference of the cladding. Circumferential
coverage of the depressions ensures suppression of vortex induced
vibrations arising from omnidirectional flows.
[0009] In one embodiment, the depressions have a generally circular
periphery. In another embodiment, the depressions have an
elliptical periphery.
[0010] In some embodiments, the depressed or recessed surfaces of
the depressions can be smooth and it is convenient if each of the
depressions is smoothly concave or dished when viewed in
cross-section. However, in other, currently more preferred
embodiments the sides of the depressions are angular as this can
help to "trip" the vortices, moving from regular to irregular
shedding.
[0011] The size of the depressions may vary widely. For example,
for circular depressions the diameter may vary from 1 cm to 30 cm
and is preferably between 10 cm and 20 cm in diameter. For
elliptical depressions, the length of the major axis is preferably
between 1 cm and 30 cm with the width of the minor axis being
between approximately 0.5 cm and 20 cm. Preferably the length of
the major axis is from 10 cm to 20 cm and the length of the minor
axis is preferably from 5 cm to 15 cm.
[0012] Preferably, for cladding of circular cross-section, the
largest dimension of a depression (e.g. the diameter of a circular
depression or the length of the major axis of an elliptical
depression) is from 5% to 50% (and more preferably between 10% and
30%) of the external diameter of the cladding.
[0013] The depressions may be regularly spaced over the cylindrical
surface of the cladding or may be randomly spaced. Preferably, the
depressions are substantially identical.
[0014] If desired, the cladding may comprise positively buoyant
material. Syntactic foam (either with or without the inclusion of
macrospheres) would be particularly useful in this regard. The use
of positively buoyant material is particularly useful in the
context of drill risers. Thus, the cladding of the present
invention can comprise a buoyancy module for a drill riser. Such a
buoyancy module would offset much of the weight of the drill riser
whilst additionally providing protection against vortex induced
vibrations.
[0015] The cladding may comprise preformed sections which are
subsequently assembled on, and secured to, the elongate member to
be protected. For example, the preformed sections may comprise
semi-tubular sections. Alternatively, the preformed sections may
comprise tubular sections. If tubular sections are used, the
sections are preferably split along their length (e.g. a
longitudinal or helical split) to allow the sections to be located
at any point along the length of the elongate member to be
protected.
[0016] In either case, the depressions can be moulded into the
outer surface of the preformed sections. Alternatively, the
preformed sections may be moulded with a smooth outer surface and
the depressions may be cut or machined or otherwise formed into the
outer surface subsequently, either before or after the preformed
sections are assembled on the elongate member.
[0017] In another embodiment, the cladding may be moulded directly
onto the outer surface of the elongate member to be protected. The
depressions or recesses may be moulded into the outer surface of
the cladding as it is moulded. Alternatively, the cladding may be
moulded without the depressions, which may be cut, machined or
otherwise formed into the outer surface subsequently.
[0018] Preferably, the outer surface of the cladding is
substantially cylindrical.
[0019] By way of example only, specific embodiments of the present
invention will now be described, with reference to the accompanying
drawings, in which:
[0020] FIG. 1 is a perspective view of a first embodiment of
cladding in accordance with the present invention;
[0021] FIG. 2 is a side view of a second embodiment of pipe
cladding in accordance with the present invention;
[0022] FIG. 3 is across section of the pipe cladding of FIG. 2,
looking in the direction of arrows X-X in FIG. 2;
[0023] FIG. 4 is a side view of a third embodiment of cladding in
accordance with the present invention;
[0024] FIGS. 5a to 5d show examples of four possible orientations
of the recesses along the cladding length; and
[0025] FIG. 6 illustrates diagrammatically a typical cross-section
of a cladding moulding show the shapes and relative dispositions of
depressions.
[0026] Referring firstly to FIG. 1, a protective ducting 10 for a
pipe (not illustrated) comprises a tubular flexible, impervious,
polyurethane casing comprising a plurality of identical, preformed,
releasably engaged semi-tubular sections 12 which are arranged with
respect to one another to provide a cylindrical passage 14
therethrough which is dimensioned and shaped to receive the pipe.
The internal diameter of the protective ducting or cladding varies
with the diameter of the pipe to be clad. Thus, in the embodiment
illustrated in FIG. 1 the internal diameter is approximately 0.75
metres.
[0027] The required length of cladding is assembled by arranging
the appropriate number of preformed sections along the length of a
pipe. As illustrated schematically in FIG. 1, opposed semi-tubular
sections of the cladding are held together by means of metal bands
B passing around the outer surface of the assembled cladding.
[0028] It should also be noted that, in use, diametrically opposed
sections of the cladding may be "staggered" by approximately half
the length of the section to ensure that the vertical joints
between two longitudinal adjacent sections are not aligned with the
vertical joints between diametrically opposed longitudinally
adjacent sections. Moreover, each cladding section may be provided
with a reduced-diameter spigot portion at one end and an enlarged
diameter socket portion at the opposite end (as shown in
GB-A-2335248), whereby longitudinally adjacent sections are secured
to one another by fitting a reduced diameter end spigot portion of
one section into a complementarily-shaped enlarged inner diameter
end socket portion of the adjacent section.
[0029] The outer surface of the assembled cladding comprises a
smooth, generally cylindrical surface 16. However, it will be
observed that the cladding sections are provided with a plurality
of identical evenly-spaced depressions or recesses 18 in the outer
surface. In the embodiment illustrated in FIG. 1, the periphery of
the depressions is circular and the depressions are smoothly
concave or dished. In the embodiment illustrated, the diameter of
the depressions is approximately 15 cm and the maximum depth of the
depressions is approximately 3 cm. However, the diameter and depth
of the depressions may vary widely. Preferably the diameter of the
circular depressions is from 1 cm to 30 cm and more preferably from
10 cm to 20 cm, but it is not intended that the invention is
limited in any way to these preferred ranges.
[0030] In use, the cladding 10 is assembled on a pipe, drill riser,
cable or other elongate member and the clad elongate member is then
positioned underwater. The fact that the outer surface of the
cladding is devoid of projections greatly facilitates the laying of
the clad elongate member by conventional pipe laying equipment
which removes the requirement for modification of the pipe laying
equipment and improves the reliability of the laying operation.
[0031] The depressions or recesses 18 may be moulded into the outer
surface of the preformed semi-tubular sections 12. Alternatively,
the preformed sections may be moulded with a smooth exterior
surface (i.e. without the depressions or recesses 18) and the
depressions or recesses may be cut or machined into the outer
surface subsequently, either before or after the preformed sections
12 are assembled on the pipe, drill riser, cable or other elongate
member.
[0032] The embodiment illustrated in FIGS. 2 and 3 is very similar
to that of the first embodiment. However, it will be observed that
instead of being formed in two semi-tubular sections which are
subsequently clamped together, the cladding 10' comprises a
plurality of preformed, flexible, impervious, polyurethane tubular
cladding sections 20, each of which is provided with a single
longitudinally-extending slit 22 which passes along the length of
the cladding section, parallel to its longitudinal axis. In order
to fit the cladding section onto a pipe, cable or other elongate
member, the cladding section is opened at the slit 22 and
manipulated onto the elongate member to be protected. The cladding
member may then be held in the shut position by the use of metal
bands (not illustrated) identical to those used in the embodiment
of FIG. 1 or by any other suitable fixing means, such as two
semi-circular half shells, coupled together at their ends by
fastenings, such as bolts. As for the embodiment of FIG. 1,
opposite ends of the cladding section may be provided with a spigot
portion and a complementarily-shaped socket portion respectively to
assist in the connecting of longitudinally adjacent sections.
[0033] As for the first embodiment, the outer surface 24 of the
cladding section is generally smooth and cylindrical but is
provided with a plurality of identical, evenly-spaced elliptical
depressions or recesses 26. In the embodiment illustrated, the
major axis of each elliptical depression is aligned parallel with
the longitudinal axis of the cladding section, although this need
not be the case.
[0034] The dimensions of the depressions or recesses may vary
widely. However, in the illustrated embodiment the length of the
major axis is approximately 15 cm and the length of the minor axis
is approximately 7.5 cm. The depth of the depressions can also vary
widely but in the embodiment illustrated it is approximately 3 cm.
Preferably, the length of the major axis is from 1 cm to 30 cm, and
more preferably from 10 cm and 20 cm. Preferably, the length of the
minor axis is from 0.5 cm to 20 cm, and more preferably from 5 cm
to 15 cm.
[0035] The embodiment illustrated in FIG. 4 comprises a cladding
section 28 which is moulded directly onto the outer surface of a
pipe, drill riser, cable or other elongate member, rather than
being pre-formed and subsequently fitted as in the first and second
embodiments. As for the first two embodiments, the embodiment of
FIG. 4 comprises a generally cylindrical smooth outer surface 30
but in contrast to the first two embodiments, comprises a plurality
of randomly-spaced depressions or recesses 32, formed in the
cylindrical outer surface. The dimensions of the circular recesses
32 correspond to those for the first embodiment The depressions or
recesses 32 may be moulded into the outer surface as the cladding
section is moulded. Alternatively, the cladding may be moulded with
a smooth cylindrical exterior surface (i.e. without the depressions
or recesses 32) and the depressions or recesses may be cut or
machined into the outer surface subsequently.
[0036] FIGS. 5a-5d shows examples of possible orientations of the
depressions along the length of the cladding, FIG. 5a shows the
depressions in regular lines and columns, FIG. 5b shows lines and
columns which are offset, FIG. 5c shows the depressions arranged in
"waves" which are in phase in the various rows; and FIG. 5d shows
the depressions arranged in "waves" which are out of phase in the
various rows.
[0037] FIG. 6 is a partial section of a typical moulding showing
depressions which have sides which are substantially at right
angles with flat bases of the depressions. Purely by way of example
only, the dimensions a, b, c, d and r can be as follows in such a
moulding:
[0038] a=40 cms
[0039] b=40 cms
[0040] c=20 cms
[0041] d=25 cms
[0042] r=175 cms
[0043] In each of the embodiments, when the cladding is in position
underwater, the provision of the depressions or recesses in the
generally cylindrical outer surface of the cladding interrupts or
reduces vortex induced vibration. Moreover, in each case, because
the outer surface of the cladding is devoid of projections, the
clad pipe, or other elongate member, can be laid underwater using
conventional laying mechanisms which do not require
modification.
[0044] In the above embodiments, the material from which the
cladding is made need not be polyurethane but could, in fact, be
any material which is sufficiently flexible and impervious for the
intended use. For example, in the above embodiments it would be
possible to make the cladding from a syntactic foam, e.g. a mixture
of glass microspheres and a thermoset resin matrix (with or without
the inclusion of larger macrospheres). A cladding in accordance
with the present invention which is made from syntactic foam would
have increased buoyancy which can be desirable in some
circumstances. Indeed, the use of such a cladding is particularly
suitable as a buoyancy module for a drill riser. The use of
syntactic foam offsets much of the riser weight and the provision
of depressions in the outer surface of the cladding in accordance
with the present invention reduces or eliminates vortex induced
vibrations on the riser.
[0045] As indicated in FIG. 7, one embodiment of drill riser
buoyancy module in accordance with the present invention comprises
a plurality of identical, preformed, releasably engaged
semi-tubular sections 12' having an internal profile which, when
the sections are arranged with respect to one another, form an
aperture for receipt of the drill riser, auxiliary lines, riser
clamps and the like. The sections 12' are moulded from syntactic
foam made from a mixture of glass microspheres and a thermoset
resin matrix (either with or without the inclusion of
macrospheres). The required length of buoyancy modules is assembled
by arranging the preformed sections 12' along the length of the
drill riser. As indicated in FIG. 7, opposed semi-tubular sections
of the cladding are held together by means of metal bands B'
passing around the outer surface of the assembled cladding.
Alternatively, the buoyancy module halves may be bolted
together.
[0046] The outer surface of the assembled buoyancy module is
cylindrical, but as for the previous embodiments the cylindrical
surface is provided with depressions or recesses 18'. The number,
size, shape and pattern of the depressions or recesses 18' can, for
example, be as for the previous embodiments, but are not restricted
to those details. As for the previous embodiments, the depressions
or recesses 18' can be formed integrally with the moulded preformed
sections 12' or can be formed subsequently, either before or after
assembly on the drill riser.
[0047] The invention is not restricted to the details of the
foregoing embodiments. For example, the depressions as shown in
each of the four embodiments, could be used in each of the other
embodiments. Moreover, the number, shape, dimensions and pattern of
the depressions or recesses can vary widely from those
illustrated.
[0048] Preferably, for cladding of circular cross-section, the
largest dimension of a depression (e.g. the diameter of a circular
depression or the length of the major axis of an elliptical
depression) is from 5% to 50% (and more preferably between 10% and
30%) of the external diameter of the cladding.
[0049] The periphery of the depressions or recesses could be
polygonal or could be any other shape which interrupts or reduces
vortex induced vibrations. Moreover, the depressions or recesses
need not be smooth or dished and, for example, may comprise side
walls extending generally perpendicularly or at same angle or
angles to the cylindrical surface of the cladding and a flat or
curved (e.g. part-cylindrical, concentric with the cylindrical
surface of the cladding) base wall.
[0050] Furthermore, the material from which the cladding is made
may incorporate an anti-fouling agent which retards the build-up of
material in the depressions which might otherwise impair their
effectiveness at reducing vortex induced vibrations. An example of
a suitable anti-fouling agent is tributyl tin (TBT) which is
typically added to the material used to manufacture the cladding in
a concentration of 1-5%, more preferably 2-3%.
* * * * *