U.S. patent application number 14/006097 was filed with the patent office on 2014-01-09 for riser.
The applicant listed for this patent is Arne Austefjord, Geir Skaugen. Invention is credited to Arne Austefjord, Geir Skaugen.
Application Number | 20140008076 14/006097 |
Document ID | / |
Family ID | 45999875 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140008076 |
Kind Code |
A1 |
Skaugen; Geir ; et
al. |
January 9, 2014 |
RISER
Abstract
A riser and a method for reducing the risk of failure of a riser
system comprising a riser (100) arranged between an installation
and a subsea well the riser (100) having a bore (116) for conveying
fluids therebetween, the method comprising the step of providing at
least one vortex shedding member (111) in said bore (116) of said
riser (100) and flowing the fluid between the subsea well and the
installation.
Inventors: |
Skaugen; Geir; (Stavanger,
NO) ; Austefjord; Arne; (Sandnes, NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Skaugen; Geir
Austefjord; Arne |
Stavanger
Sandnes |
|
NO
NO |
|
|
Family ID: |
45999875 |
Appl. No.: |
14/006097 |
Filed: |
March 26, 2012 |
PCT Filed: |
March 26, 2012 |
PCT NO: |
PCT/GB12/50672 |
371 Date: |
September 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61467799 |
Mar 25, 2011 |
|
|
|
61490846 |
May 27, 2011 |
|
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Current U.S.
Class: |
166/367 |
Current CPC
Class: |
E21B 17/01 20130101;
F16L 11/083 20130101; F16L 55/027 20130101; E21B 17/015
20130101 |
Class at
Publication: |
166/367 |
International
Class: |
E21B 17/01 20060101
E21B017/01 |
Claims
1. A method for reducing the risk of failure of a riser system
comprising a riser arranged between an installation and a subsea
well, the riser having a bore for conveying fluids therebetween,
the method comprising: providing at least one vortex shedding
member in said bore of said riser; and flowing the fluids between
the subsea well and the installation.
2. The method in accordance with claim 1, further comprising
deploying said at least one vortex shedding member into the bore
while the riser remains installed on said subsea well.
3. The method in accordance with claim 2, wherein said at least one
vortex shedding member comprises a coil biased against an inner
surface of said riser.
4. The method in accordance with claim 3, wherein the deploying the
at least one vortex shedding member is carried out by unfurling the
coil in the bore.
5. The method in accordance with claim 3, wherein the deploying the
at least one vortex shedding member is carried out by unfurling the
coil in the bore with a constant pitch.
6. The method in accordance with claim 3, further comprising
dragging said coil through said bore to install the at least one
vortex member in said bore.
7. The method in accordance with claim 6, wherein the dragging said
coil through said bore is carried out using a coiled tubing
injector.
8. The method in accordance with claim 1, wherein the at least one
vortex shedding member comprises a tube filled with fluid, the
method further comprising monitoring the fluid in the tube to
assess integrity of the at least one vortex shedding member.
9. A riser, comprising: a hollow tubular body having an inner
surface defining a bore through which fluids may flow; and an
internal member arranged to follow a spiral path within the
bore.
10. The riser as claimed in claim 9, wherein the internal member
forms a continuous spiral.
11. The riser as claimed in claim 9, wherein the internal member is
biased against or fixed to an inner surface of the riser.
12. The riser as claimed in claim 9, wherein the internal member
comprises a tube.
13. The riser as claimed in claim 9, wherein said internal member
comprises a plurality of fins projecting from the inner surface of
the riser.
14. The riser as claimed in claim 9, further comprising an inner
liner having fins projecting from the inner liner into the bore of
the riser.
15. The riser as claimed in claim 14, wherein said inner liner is
formed from a coiled strip having said fins arranged thereon.
16. A method for installing a coiled internal member into a riser,
the method comprising: dragging said coiled internal member through
a bore on an end of a coiled tubing deployed along the riser with a
coiled tubing injector.
17. A riser, comprising: a hollow tubular body having an inner
surface defining a bore through which fluids may flow; and a vortex
shedding member along a substantial portion thereof.
Description
[0001] The present invention relates to a riser for conveying
fluids during production of hydrocarbons, and particularly, but not
exclusively, to flexible risers.
[0002] The present invention also provides a method for reducing
risk of failure of a riser system. The present invention also
relates to a method and apparatus for installing an coiled internal
member into a riser, preferably when the riser is installed in a
subsea wellbore system.
[0003] During production of hydrocarbons, one or more risers are
typically installed between a well in the seafloor and an
installation or floating vessel at or the near the sea surface. The
risers may be flexible to accommodate relative motions between the
installation or floating vessel and the well in the sea floor, such
motion may be induced by waves. The types of motions typically
encountered are heave and sway. Typically, but not always, a
wellhead is located on the sea floor and the riser extends from the
wellhead. Risers may comprise a hose, tubular, or series of
interconnected tubulars, used to convey fluids, such as liquids,
gases, and plasmas, between the wellhead and the surface
installation or floating vessel. One or more flow lines may then be
used to convey the fluids from the installation or floating vessel
to land, tanker ship, other storage vessel, processing plant or the
like. The flow line may be a few hundred metres long or may be
several kilometres long. The pressure of a gas in the riser may be
200 Bar.
[0004] During operation of a riser, fluid flows within the riser,
generally from the well to the installation or floating vessel.
Force is exerted by the fluid flowing through the riser on the
inner surface of the riser. Water pressure is exerted on the
outside of the riser. The inventors observed that in circumstances
where corrugations or other discontinuities are formed along the
inner surface of the riser, contact between the fluid and the
corrugations may induce vortex shedding, which in turn, may induce
vibration in the riser. Such discontinuities in the inner surface
of a riser are found in flexible risers, where the inner surface is
made up of a coil of wire or flat material, the discontinuities
occurring between adjacent flights of the coil, which allows for
flexing of the riser.
[0005] Vibration of the riser may necessitate a reduction in the
flow rate of fluid through the riser, which is commercially
undesirable and may be difficult to achieve. Over time, the
vibration may also cause fatigue damage in the riser and other
components of the riser system and shorten its service life. If the
frequency of the induced vibrations coincides with a resonant
frequency of the riser system, large amplitude vibrations are
induced in the riser system. This may induce failure of a component
of the riser system, such components are: a connection of the riser
between the wellhead and the riser; a connection between the riser
and a component at the top of the riser; or in the riser
itself.
[0006] The connection of the riser to the wellhead typically
comprises a bolted flange connection. The bolted flange connection
may comprise a rigid neck portion which is then joined to the
flexible riser.
[0007] The inventors observed that there is a risk of failure of a
riser system due to fatigue and particularly but not exclusively,
in the connection apparatus of the riser system. The inventors
observed that fatigue may be induced by pulsations in flow of gas
through a riser of the riser system. The inventors observed that
low frequency pulsation in the fluid may induce fatigue failure,
such as below 400 Hz. The inventors observed that the pulsations in
the fluid may be induced by vortex shedding, the vortex shedding
being induced by a rough bore.
[0008] In accordance with the present invention, there is provided
a method for reducing the risk of failure of a riser system
comprising a riser arranged between an installation and a subsea
well the riser having a bore for conveying fluids therebetween, the
method comprising the step of providing at least one vortex
shedding member in said bore of said riser and flowing the fluid
between the subsea well and the installation.
[0009] Advantageously, the installation is a drilling rig, FPSO,
submerged platform or other vessel. Preferably, the fluid is a gas,
such as natural gas or shale gas. For the avoidance of doubt, the
term subsea is used to mean under any kind of water, fresh,
brackish or salty. The bore may be discontinuous and rough, but may
be smooth. Preferably, the vortex shedding member lies along at
least a substantial portion (length) of the bore of the riser.
Fatigue may occur in a connection connecting the riser to the
subsea well or at a connection between the riser and a flowline.
Fatigue may also occur in the riser itself. Preferably, the riser
is flexible.
[0010] Advantageously, the method further comprises the step of
deploying said at least one vortex shedding member into the bore
whilst the riser remains installed on said subsea well. Preferably,
the at least one vortex shedding member comprises a coil biased
against an inner surface of said riser. Advantageously, the vortex
shedding member is injected through an opening in an injecting head
and expands to hold itself against said bore. Preferably, the step
of deploying the at least one vortex member is carried out by
unfurling the coil in the bore. Advantageously, the step of
deploying the at least one vortex member is carried out by
unfurling the coil in the bore with a constant pitch. Thus,
advantageously, leaving the vortex shedding member in the form of a
helix biased against the bore. Preferably, the VSM is deployed at a
constant rate. Preferably, the method further comprises the step of
dragging said coil through said bore to install the at least one
vortex member in said bore, wherein preferably, the dragging is
carried out from the top of the riser to the bottom.
[0011] Preferably, the step of dragging said coil through said bore
is carried out using a coiled tubing injector. Preferably, said
coiled tubing injector comprises a reel with coiled tubing thereon,
the method comprising the step of unreeling the coiled tubing to
drag the coil through the bore of the riser. Advantageously, the
injector comprises an advancing mechanism, such a caterpillar chain
drive, the method comprising the step of advancing the coiled
tubing down through the bore using the advancing mechanism.
Advantageously, an injector head is provided on a free end of the
coiled tubing. Preferably, the injector head comprises a gripper
for gripping the lower end of the coil. Advantageously, a
communication path and power supply are provided to activate the
gripper to release the lower end of the coil when the bottom of the
riser is reached, which may be the coupling, coupling the riser to
the subsea well. Preferably, the injector head is provided with at
least one camera, so that the operator can see the vortex shedding
member being deployed.
[0012] Advantageously, the vortex shedding member comprises a tube
filled with fluid, the method further comprising the step of
monitoring the fluid in the tube to assess the integrity of the
vortex shedding member. Preferably, the fluid in the tube is
pressurized and the pressure of the fluid therein monitored to
assess the integrity of the vortex shedding member.
[0013] The present invention also provides a riser comprising a
hollow tubular body having an inner surface defining a bore through
which fluids may flow, the riser further comprising an internal
member arranged to follow a spiral path within the bore.
[0014] Preferably, the internal member forms a continuous spiral.
Preferably, the spiral is a helix, having constant pitch.
Advantageously, the pitch is between one and twenty times the
diameter of the bore. Advantageously, between three and seven times
the diameter of the bore and most preferably five times the
diameter of the bore. Alternatively, the spiral may be
discontinuous, formed of discrete fins projecting from the bore
into the centre of the bore.
[0015] Advantageously, the internal member is biased against or
fixed to an inner surface of the riser. Preferably, the internal
member comprises a tube. Advantageously, the tube is between 4 mm
and 20 mm in diameter and preferably a coil of hydraulic tubing.
Preferably, the tube is between 6 mm and 12 mm in diameter.
Preferably, the internal member comprises wire. Preferably, the
internal member comprises a plurality of fins projecting from the
internal surface of the riser.
[0016] Advantageously, an inner liner is provided having fins
projecting into the bore (115) of the riser. Preferably to form a
continuous spiral, but may be non-continuous, having gaps
therebetween. Preferably, the inner liner is formed from a coiled
strip having said fins arranged thereon. Preferably, the fins are
arranged at an angle to the length of the strip.
[0017] The present invention also provides a method for installing
a coiled internal member into a riser, the method comprising the
step of dragging said coiled internal member through said bore on
the end of a coiled tubing deployed along the riser with a coiled
tubing injector.
[0018] The present invention also provides a riser comprising a
hollow tubular body having an inner surface defining a bore through
which fluids may flow, the riser further comprising a vortex
shedding member along a substantial portion thereof, preferably, of
the length.
[0019] Preferably, the riser comprises a plurality of sleeves,
wherein said inner liner forms one of said sleeves. Other
preferable and advantageous layers are set out in the description
with reference to FIGS. 3 and 4.
[0020] The present invention also provides a method of
manufacturing a flexible tubular, the method comprising: disposing
a plurality of spaced apart members along a face of a substantially
flat plate; bending the flat plate in a spiral fashion to form a
tubular body, the tubular body having an inner surface over which
the members are disposed and bounding a fluid flowbore; wherein
said bending aligns the members to form a helix along the inner
surface.
[0021] The present invention also provides a method for inhibiting
pulsations of a potentially damaging frequency in a fluid flowing
in a flexible riser using the above methods and apparatus.
[0022] The methods and apparatus may also be used in flow lines or
other tubulars for facilitating the conveying of fluids from a
wellbore.
[0023] For a better understanding of the present invention,
reference will now be made, by way of example, to the accompanying
drawings in which:
[0024] FIG. 1 is a schematic view of an offshore drilling platform
coupled to a subsea well by a riser system in accordance with the
invention;
[0025] FIG. 2 is a schematic view of a riser system coupled between
a Floating Production, Storage, and Offloading (FPSO) vessel and
the subsea well;
[0026] FIG. 3 is a perspective view, with layers cutaway, of a
prior art riser;
[0027] FIG. 4 is a perspective view, with layers cutaway of a riser
in accordance with the present invention with some hidden parts
shown in dashed line, the riser comprising an internal member;
[0028] FIG. 5A is a graph indicating flow pulsation against
amplitude;
[0029] FIG. 5B in a schematic diagram showing eddie currents
induced by a discontinuous inner surface of a riser;
[0030] FIG. 5C is a schematic diagram showing an internal member of
the riser shown in FIG. 4 before installation shown in a compressed
coil, an expanded coil and an unfurled coil;
[0031] FIG. 6A is a perspective view of an injector used in a
method of installing an internal member in accordance with the
present invention;
[0032] FIG. 6B is a perspective view of an injector head of the
injector shown in FIG. 6A;
[0033] FIG. 7 is a perspective view of a lining member being formed
into a liner for use in another embodiment of a riser in accordance
with the present invention;
[0034] FIG. 8A is enlarged view of the lining member shown in FIG.
7;
[0035] FIG. 8B is an axial cross-sectional view of the lining
member shown in FIG. 7;
[0036] FIG. 9 is an end view of a strip of the lining member shown
in FIG. 7; and
[0037] FIG. 10 is an end view of an alternative strip for use in
forming a lining member.
[0038] The following description is directed to exemplary
embodiments of a flexible riser having an internal contour system
preferably for mitigating vortex shedding during conveyance of a
fluid through the tubular. One skilled in the art will understand
that the following description has broad application, and that the
discussion is meant only to be exemplary of the described
embodiments, and not intended to suggest that the scope of the
disclosure, including the claims, is limited only to those
embodiments. The embodiments disclosed should not be interpreted,
or otherwise used, as limiting the scope of the disclosure,
including the claims. For example, in the exemplary embodiments
described below, the flexible tubular is a component of an offshore
riser system. However, the flexible tubular may also be utilized in
other types of systems where it is desirable to mitigate vortex
shedding.
[0039] Certain terms are used throughout the following description
and the claims to refer to particular features or components. As
one skilled in the art will appreciate, different persons may refer
to the same feature or component by different names. This document
does not intend to distinguish between components or features that
differ in name but not function. Moreover, the drawing figures are
not necessarily to scale. Certain features and components described
herein may be shown exaggerated in scale or in somewhat schematic
form, and some details of conventional elements may not be shown in
interest of clarity and conciseness.
[0040] In the following discussion and in the claims, the terms
"including" and "comprising" are used in an open-ended fashion, and
thus should be interpreted to mean "including, but not limited to .
. . ." Also, the term "couple" or "couples" is intended to mean
either an indirect or direct connection. Thus, if a first device
couples to a second device, the connection between the first device
and the second device may be through a direct connection, or
through an indirect connection via other intermediate devices and
connections.
[0041] Referring now to FIG. 1, there is shown a Small Water Plane
Area Twin Hull (SWATH) type drilling platform 1 floating at the sea
surface 11. The drilling platform 1 is coupled to a subsea well 7
located in the seafloor 9 by a riser system 5 in accordance with
the present invention. The riser system 5 has a riser 13 coupled to
a tensioning device 15. A riser extension 17, including a joint 19
and a manifold 21, is coupled between the tensioning device 15 and
the drilling platform 1. The riser 13 is coupled at its lower end
22 to a wellhead 23. A flanged coupling 24 is fitted to the end 22
of the riser 13 for connection to a flange fitting on top of the
wellhead. It will be appreciated that the wellhead 23 is optional
and that the coupling 24 could be connected directly to a template
and the wellhead fitted elsewhere, such as on the drilling platform
1. The riser system 5 may be used inter alia during an exploratory
phase, drilling phase, production phase, work-over phase and/or
re-injection phase.
[0042] Alternatively or latterly, preferably during a production
phase, as illustrated by FIG. 2, a riser system 5 may be installed
between a buoyant body 12 and the subsea well 7. The buoyant body
12 is arranged within 100 metres of the sea surface to enable easy
access thereto. A flowline or a continuation of the riser system 14
continues the flowpath of production fluids to a floating
production, storage, and offloading (FPSO) vessel 20 or other
storage vessel or the like. The production fluid is then
transported to point of use or for further processing on land. Such
transportation may be by tanker or by a subsea pipeline. In either
case, the riser system 5 enables fluid conveyance between the
subsea well 7 and a structure at the sea surface 11. As used
herein, the term "fluid" includes a liquid, a gas, a plasma, and a
mixture of any of one or more liquids, gases, and plasmas.
[0043] FIG. 3 shows a prior art flexible tubular 100 which forms
part of a riser system, such as the riser system 5 shown in FIGS. 1
and 2. The flexible tubular 100 comprises an inner sleeve 101,
known as a carcass which preferably inhibits collapse of a fluid
tight liner 103 and advantageously protects against abrasive
particles and/or pigging tools (not shown). The inner sleeve 101 is
constructed from an interlocking conduit 102, preferably made a
stainless steel strip. The interlocking conduit 102 has a
substantially flat portion and interlocking elements formed
integrally therewith on either side thereof such that upon coiling,
the interlocking elements interlock to form the inner sleeve 101.
The inner sleeve 101 thus has a rough discontinuous inner surface
115 defining a bore 116 through which fluids flow from the subsea
well 7 to the surface installation 1. The flexible tubular 100 also
comprises a fluid tight liner 103 made from an extruded polymer.
The flexible tubular 100 also comprises a first armour layer 104
made from a helically wound abutting C-shaped steel wires and/or
steel strips 108 to preferably provide resistance to radial loads,
such as water pressure. A pair of further armour layers 105 and
106, preferably comprising a helically wound rectangular steel wire
109, 110 which may be counterwound to provide additional resistance
to axial tensile loads. Anti-wear layers (not shown) may be
provided between each of the layers, sleeves and liners to provide
wear resistance therebetween. An outer sheath 107, advantageously
made from an extruded polymer, preferably shields the other layers
from the outer environment and provides mechanical protection. An
insulation layer (not shown) may be provided internal or external
to the outer sheath 107. Furthermore, a buoyancy jacket (not shown)
may be provided along at least a portion of the length of the
flexible tubular 100 to provide buoyancy.
[0044] The flexible tubular 100 may be sufficiently flexible to be
wound on to a reel. The reel may be 9.2 m in diameter. The internal
diameter of the flexible tubular is typically from 2.5'' to 16''
(50 mm to 410 mm).
[0045] The riser system 5 in accordance with the present invention
as shown in FIG. 4, comprises a flexible tubular 100 of the type
shown in FIG. 3 with the addition of an internal member 111. The
internal member 111 may be a solid wire, but is preferably a tube
112 having a substantially circular cross-section wound into a coil
and abutting the internal surface of the inner sleeve 101. The coil
preferably forms a helix having a pitch five times the internal
diameter of the flexible riser 100, although may be of an
alternative pitch, such as between one and ten times internal
diameter of the riser. The tube 112 is preferably between 6 mm and
12 mm in diameter, although may be for example of between 2 mm and
50 mm in diameter. The cross-sectional shape of the hydraulic tube
may be oval, square, triangular or other suitable shape. The tube
may be made from a metal, such as stainless and may be made from
steel, which may match the material of the inner liner. The tube
112 is advantageously hydraulic tubing. Hydraulic tubing is
commonly available with pressure ratings comparable to those need
for use as an internal member 111 of a riser system 5.
[0046] The tube 112 is preferably filled with a fluid, such as
hydraulic fluid and pressurized. The tube 112 may be suitably
capped at a distal end and a proximal end 114 connected to a
pressure gauge 113. The distal end is arranged at a bottom of the
riser 100 and the proximal end 114 is arranged at the top of the
riser 100. If the pressure gauge 113 sees a drop in pressure, a
user can assume that the integrity of the tube 112 has been
compromised. The internal member 111 can thus be removed from the
flexible riser 100 and replaced.
[0047] The internal member 111 is preferably continuous along the
length of the riser 100.
[0048] FIG. 5A shows a graph showing amplitude against flow
pulsation frequency. The inventors observed that the riser can
"sing" when subjected to certain frequencies. The inventors
observed that the flow of fluid, such as natural gas, through the
riser and over the discontinuous surface of the inner liner 101
formed by the interlocking conduit 102 induce vortices 120 (see
FIG. 5B) and audible frequencies. This range of frequencies is
shown in FIG. 5A. The inventors believe that it is the low
frequency range which may induce fatigue failure in a component of
the riser system. Furthermore, it is resonant frequencies which may
also induce rapid fatigue failure. Line 121 is a trace of frequency
against amplitude for a flexible riser, such as the riser shown in
FIG. 3. As can be seen from the graph in FIG. 5A, the line 121
shows that below 400 Hz there is a sharp increase in amplitude and
thus energy in the this low frequency range. Line 122 is a trace of
frequency against amplitude for a flexible riser with an internal
member 111, such as the riser shown in FIG. 4. As can be seen from
line 122, the amplitude and thus energy in the low frequency range
below about 350 Hz has been significantly reduced with the addition
of the internal member 111. The inventors believe the internal
member significantly changes the pressure pulsations and/or the
vortices induced by these pulsations.
[0049] The internal member 111 is produced in the form of an
expanded coil 130, as shown in FIG. 5C. When the internal member
111 is produced it lies at rest having a natural pitch shown as
expanded coil 130. The coil is axially compressed into a compressed
coil 131 for transport. The compressed coil 131 is then placed
above a mouth 133 of a flexible riser 100 and dragged down the
inner liner 101 until the internal member 111 is unfurled to form
an unfurled coil 134. The unfurled coil 134 preferably has a pitch
of approximately five times the internal diameter of the flexible
riser 100. The unfurled coil 134 preferably has a natural diameter
which is slightly larger than the internal diameter of the flexible
riser 100. The expanded coil 130 thus also has at rest is slightly
greater diameter than the internal diameter of the inner liner 101.
Thus the unfurled coil 134 biases itself under a radially outwardly
spring force pressing against the inner liner 101, inhibiting the
coil from falling down the riser 100. An internal shoulder (not
shown) in the coupling 24 will also inhibit the internal member 111
from falling down into the well 7 in the seafloor 9. The coil is
provided with a locking coil 135 at the distal end of the tube 112,
which includes a reverse bend 136 and a reverse directed coil 137.
The locking coil 135 inhibits the coil from being pulled upwardly
through the riser upon installation.
[0050] The internal member 111 can be installed into a riser 100
which is already installed on a well in the sea. A suitable
injector, such as the injector 200 shown in FIG. 6A is used. The
injector 200 comprises a frame 201 and a chain mechanism 202 for
pulling coiled tubing 204 (shown in dashed lines) from a reel (not
shown) through a slot 207 in the top of the frame 201 between two
chain drives 205, 206 through a slot 208 in a skid 209 and into the
riser 100.
[0051] A push rod in the form of coiled tubing 204 is provided with
a head 210 having a gripping mechanism 212 for gripping the distal
end of the tube 112 of the compressed coil 131. The distal end of
the tube 112 of the compressed coil 131 is pulled through the inner
liner 101 of the flexible riser 100. A wire frame 211 facilitates
unfurling of the compressed coil 131. Cameras 213 and 214 and
appropriate lighting are provided on the head 210 to provide a
visual inspection of the unfurling of the hydraulic tube 112. A
communication bus (not shown) which may be in the form of wires,
extends up through the coiled tubing 204. The communication bus
provides a data path to the surface for video footage from the
cameras 213 and 214 and a signal path for operating a latch 215 of
the gripping mechanism 212 to selectively grip and release the
distal end of the tube 112.
[0052] The coiled tubing is preferably of a large diameter,
preferably of 4'' (110 mm) diameter for use in large internal
diameter risers. This size coiled tubing is extremely rigid and
will deploy the coil without flexing, thus giving a consistent feed
out during unfurling of the coil in the flexible riser 100.
[0053] The internal member 111 may also be formed integrally with
the riser 100 as part of the riser's construction in a factory
environment. FIGS. 7 and 8 shows an inner liner 301 which may
replace or fit inside of inner liner 101 in the embodiment of FIG.
4. The inner liner 301 comprises a continuous strip of flat plates
305 bent, folded, moulded, drawn (such as through a die) or
otherwise formed into a spiral such as a helix to form a tubular
body 315. The tubular body 315 has an inner surface 320 defined by
a substantially constant diameter and bounding a flowbore 325
through which a fluid may be conveyed. The continuous strip of flat
plate 305 may be formed of discrete section of flat plate joined
end to end to form a continuous strip of flat plate.
[0054] The inner liner 301 further comprises a plurality of spaced
apart vortex shedding mitigation (VSM) members 330. The VSM members
330 are disposed along a face 335 of the continuous strip 305. The
VSM members 330 may be a series of discrete angled fins spaced
along the continuous strip 305, the spacing selected such that
after the continuous strip 305 is bent, folded, moulded or drawn to
form the tubular body 315, the VSM members 130 align to form a
spiral, preferably a helix 340 along the inner surface 320 of the
tubular body 315, as best viewed in FIG. 8. In the illustrated
embodiment, the spiral 340 formed by the VSM members 130 is
non-continuous, having spaces 345 between adjacent VSM members 330.
In alternative embodiments, the spacing of the VSM members 330
along the continuous strip 305 may be selected such that after the
continuous strip 305 is bent, folded, moulded or drawn to form the
tubular body 315, the VSM members 130 align to form a continuous
spiral, preferably a continuous helix along the inner surface 320
of the tubular body 315, having negligible space between adjacent
VSM members 330 or indeed overlapping. Further, the angular
orientation of the angled fins relative to the continuous strip 310
is selected such that after the continuous strip 305 is bent,
folded, moulded or drawn to form the tubular body 315, the spiral,
preferably helix 340 formed by the VSM members 330 along the inner
surface 320 of the tubular body 315 has a desired pitch P.
[0055] In preferred embodiments, each VSM member 330 is a
lengthwise discontinuity extending from the face 335 of the plate
310, as illustrated by FIG. 5. In some embodiments, the VSM member
330 may be a weld seam, which may project preferably at least 5 mm
from the inner surface 320 and advantageously be at least 2 mm
wide. Alternatively, the VSM member 130 may be joined to the face
335 by gluing, bonding, welding, folded, bent, pinched or other
equivalent methods known in the art. Further, the VSM member 330
may formed in the strip 305 through localized compression, or
pressing, of the strip 305. In such embodiments, the VSM members
330 as well as the spiral, preferably helix 340 formed by them
along the inner surface 320 of the inner liner 315 extends radially
inward from the inner surface 320 into the flowbore 345 of the
tubular body 315.
[0056] In alternative embodiments, the VSM members 330 may formed
in the strip 310 through localized compression, or pressing, of the
plate 110 such that each VSM member 330 becomes essentially a
depression, or recessed region, in the inner surface 320 of the
tubular body 315.
[0057] Regardless of their method of formation on the inner liner,
which may be a tubular body 315, the VSM members 330 form a spiral
such as a helix 340, or discrete sections aligned to pass through a
spiral path with optional gaps therebetween which preferably
disrupts and mitigates vortex shedding during conveyance of fluid
through the flexible riser 100.
[0058] While various embodiments have been shown and described,
modifications thereof can be made by one skilled in the art without
departing from the spirit and teachings herein. The embodiments
herein are exemplary only, and are not limiting. Many variations
and modifications of the apparatus disclosed herein are possible
and within the scope of the invention. Accordingly, the scope of
protection is not limited by the description set out above, but is
only limited by the claims which follow, that scope including all
equivalents of the subject matter of the claims.
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