U.S. patent application number 11/507865 was filed with the patent office on 2006-12-14 for riser tensioner with shrouded rods.
This patent application is currently assigned to VETCO GRAY INC.. Invention is credited to Fife B. Ellis, Charles E. Jennings, Jeffery K. McCarty, Joseph W. Pallini.
Application Number | 20060280560 11/507865 |
Document ID | / |
Family ID | 38566653 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060280560 |
Kind Code |
A1 |
Ellis; Fife B. ; et
al. |
December 14, 2006 |
Riser tensioner with shrouded rods
Abstract
A surface assembly that communicates with subsea structures and
includes a working deck on a floating structure. The working deck
has an aperture extending axially therethrough. A riser extends
from a subsea location to the working deck and through the
aperture. The surface assembly includes a frame extending
circumferentially around the riser so that the frame moves axially
with the riser. The assembly also includes a tensioner assembly
connected between the working deck and the frame. The tensioner
assembly includes a piston slidably carried in a piston chamber, a
piston rod extending from the piston and away from the piston
chamber, and a shroud enclosing the piston rod. The shroud has a
plurality of segments with at least one of the shroud segments
being movable in unison with the piston rod.
Inventors: |
Ellis; Fife B.; (Houston,
TX) ; Pallini; Joseph W.; (Tomball, TX) ;
McCarty; Jeffery K.; (Houston, TX) ; Jennings;
Charles E.; (Tomball, TX) |
Correspondence
Address: |
BRACEWELL & GIULIANI LLP
P.O. BOX 61389
HOUSTON
TX
77208-1389
US
|
Assignee: |
VETCO GRAY INC.
|
Family ID: |
38566653 |
Appl. No.: |
11/507865 |
Filed: |
August 22, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11020857 |
Dec 23, 2004 |
|
|
|
11507865 |
Aug 22, 2006 |
|
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60534831 |
Jan 7, 2004 |
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Current U.S.
Class: |
405/223.1 |
Current CPC
Class: |
E21B 19/002 20130101;
E21B 19/006 20130101 |
Class at
Publication: |
405/223.1 |
International
Class: |
E02D 5/34 20060101
E02D005/34 |
Claims
1. A surface assembly for subsea wells, comprising a working deck
on a floating structure, the working deck having an aperture
extending axially therethrough; a riser extending from a subsea
location to the working deck and through the aperture; a frame
extending circumferentially around the riser, the frame being
connected to the riser so that the frame moves axially with the
riser; and a tensioner assembly connected between the working deck
and the frame comprising a piston slidably carried in a piston
chamber, a piston rod extending from the piston and away from the
piston chamber, and a shroud enclosing the piston rod, the shroud
having a plurality of telescoping segments with at least one of the
shroud segments being movable in unison with the piston rod.
2. The surface assembly of claim 1, wherein the plurality of
segments comprises an inner shroud segment being stationary
relative to the piston rod.
3. The surface assembly of claim 1, wherein the plurality of
segments comprises an inner shroud segment and an outer shroud
segment, the outer shroud segment telescoping over the inner shroud
segment when the tensioner assembly is in a contracted
position.
4. The surface assembly of claim 1, wherein the plurality of
segments comprises an inner shroud segment and an outer shroud
segment, a substantial portion of the inner shroud segment is
uncovered when the tensioner assembly is in an extended
position.
5. The surface assembly of claim 1, wherein the plurality of
segments comprises an outer shroud segment and an inner shroud
segment that is fixedly connected to an end portion of the piston
chamber that receives the piston rod.
6. The surface assembly of claim 1, wherein the plurality of
segments comprises an inner shroud segment and an outer shroud
segment that is fixedly connected to an end portion of the piston
chamber that receives the piston rod.
7. The surface assembly of claim 1, wherein the plurality of
segments comprises an inner shroud segment, an intermediate shroud
segment, and an outer shroud segment, the intermediate shroud
segment telescoping over the inner shroud segment when the
tensioner assembly is in a contracted position, and the outer
shroud segment telescoping over the intermediate and inner shroud
segments when the tensioner assembly is in a contracted
position.
8. The surface assembly of claim 1, wherein the piston chamber is
sealed from the shroud.
9. The surface assembly of claim 1, wherein the interior surface of
the shroud is substantially at atmospheric pressure.
10. A surface assembly for subsea wells, comprising: a working deck
on a floating structure, the working deck having an aperture
extending axially therethrough; a riser extending from a subsea
location to the working deck and through the aperture; a frame
extending circumferentially around the riser, the frame being
connected to the riser so that the frame moves axially with the
riser; and a tensioner assembly connected between the working deck
and the frame, the tensioner assembly having a contracted position
and an extended position, the tensioner assembly comprising a
piston slidably carried in a piston chamber, a piston rod extending
from the piston chamber, and a shroud surrounding at least part of
the piston rod while in the contracted and extended positions, the
piston chamber containing a pressurized fluid on an end of the
piston opposite from the piston rod, the shroud having a plurality
of shroud segments with at least one of the shroud segments being
movable in unison with the piston rod and at least one of the
shroud segments being fixedly connected to an end portion of the
piston chamber that receives the piston rod.
11. The surface assembly of claim 10, wherein the plurality of
shroud segments comprise an inner shroud segment and an outer
shroud segment, and the outer shroud segment telescoping over the
inner shroud segment in the contracted position.
12. The surface assembly of claim 10, wherein the plurality of
shroud segments comprise an inner shroud segment and an outer
shroud segment; and the piston chamber being positioned above the
piston rod and the outer shroud segment is the at least one of the
shroud segments being fixedly connected to an end portion of the
piston chamber that receives the piston rod.
13. The surface assembly of claim 10, wherein the plurality of
shroud segments comprise an inner shroud segment and an outer
shroud segment; and the piston chamber being positioned below the
piston rod and the inner shroud segment is the at least one of the
shroud segments being fixedly connected to an end portion of the
piston chamber that receives the piston rod.
14. The surface assembly of claim 10, wherein the plurality of
shroud segments comprise an inner shroud segment and an outer
shroud segment; and the piston chamber being positioned above the
piston rod; the outer shroud segment is the at least one of the
shroud segments being fixedly connected to an end portion of the
piston chamber that receives the piston rod; and the inner shroud
segment is the at least one of the shroud segments being movable in
unison with the piston rod.
15. The surface assembly of claim 10, wherein the plurality of
shroud segments comprise an inner shroud segment and an outer
shroud segment; and the piston chamber being positioned below the
piston rod; the inner shroud segment is the at least one of the
shroud segments being fixedly connected to an end portion of the
piston chamber that receives the piston rod; and the outer shroud
segment is the at least one of the shroud segments being movable in
unison with the piston rod.
16. The surface assembly of claim 10, wherein: the plurality of
segments comprises an inner shroud segment, an intermediate shroud
segment, and an outer shroud segment, the intermediate shroud
segment telescoping over the inner shroud segment when the
tensioner assembly is in a contracted position, and the outer
shroud segment telescoping over the intermediate and inner shroud
segments when the tensioner assembly is in a contracted position;
and the at least one of the shroud segments being movable in unison
with the piston rod is one of either the inner shroud segment and
the outer shroud segment.
17. A riser tensioner assembly for maintaining tension in a riser
extending from a subsea well through an aperture in a working deck
of a floating structure, comprising: a piston slidably carried in a
piston chamber; a piston rod extending from the piston chamber, the
piston rod and piston being movable between a contracted position
and an extended position of the tensioner assembly; and a shroud
surrounding at least part of the piston rod while in the contracted
and extended positions, the shroud having a plurality of shroud
segments with at least one of the shroud segments being movable in
unison with the piston rod and at least one of the shroud segments
being fixedly connected to an end portion of the piston chamber
that receives the piston rod
18. The riser tensioner assembly of claim 17, wherein the plurality
of shroud segments comprises an inner shroud segment and an outer
shroud segment; the inner shroud segment having a flange end
connected to either the piston chamber or the piston rod and a
telescoping end having an outer lip, and the outer shroud having a
flange end connected to the other of the piston chamber or the
piston rod and a telescoping end having an inner lip; and when the
tensioner assembly is in the extended position: the outer lip of
the inner shroud engaging another shroud segment telescoping over
the inner shroud and the inner lip of the outer shroud engaging
another shroud segment telescoping within the outer shroud.
19. The riser tensioner assembly of claim 18, wherein the plurality
of shroud segments further comprises an intermediate shroud
segment, the intermediate shroud segment telescoping over the inner
shroud segment when the tensioner assembly is in a contracted
position, and the outer shroud segment telescoping over the
intermediate and inner shroud segments when the tensioner assembly
is in a contracted position.
20. The riser tensioner assembly of claim 19, wherein each
intermediate shroud segment has an extension end and a contraction
end, the extension end having an outer lip and the contraction end
having an inner lip; and when the tensioner assembly is in the
extended position: the outer lip of the intermediate shroud segment
engages an interior lip of either another intermediate shroud
segment or the outer shroud segment, and the inner lip of the
intermediate shroud segment engages an outer lip of either another
intermediate shroud segment or the inner shroud segment.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates in general to hydro/pneumatic
tensioners for applying tension to a riser supported from a
floating platform.
[0003] 2. Background of the Invention
[0004] An offshore facility includes a riser extending to a subsea
facility such as a subsea well or subsea manifold located at the
sea floor. Offshore facilities that float, such as a tension leg
platform, move up and down and horizontally relative to the subsea
well with the oscillations of the waves and currents. It is often
desirous to maintain a desired tension on the riser during these
oscillating movements. Tensioners are often utilized in order to
react to the movements of offshore facilities moving with the wave
oscillations and currents.
[0005] Previous tensioner assemblies, like those on tension leg
platforms, include a plurality of piston assemblies suspended from
a deck that connect to a tension ring surrounding the riser. One
type relied upon gas positioned in a chamber surrounding the piston
rod to create tension. These piston assemblies are pull-type piston
assemblies because they react when the piston is being pulled
through the piston chamber and the fluid surrounding the piston rod
is compressed. These assemblies require large piston assemblies to
accommodate the necessary fluid for creating tension in reaction to
the movements of the platform.
[0006] Other previous tensioner assemblies include ram style or
push-type piston assemblies that have the reactive fluid on the
side of the piston opposite from the piston rod. Ram style piston
assemblies react when the piston is being pushed through the piston
chamber. This arrangement allows for smaller piston assemblies
because there is no piston rod in the chamber containing the fluid.
Moreover, in previous assemblies, the piston rod extends downward
to the piston housed with the piston chamber. Therefore, drippings
and debris from above often fall onto the piston rods which can
damage the seals of the piston assembly. Failure and less reactive
tensioning can occur when the seals are damaged.
[0007] In other ram style or push-type piston assemblies, the
piston rod extends upward to the piston housed with the piston
chamber. In these assemblies, drippings and debris fall from above
onto the rods. Such an arrangement typically required expensive
coatings to be applied to the outer surface of the piston rods that
were exposed to the elements.
SUMMARY OF THE INVENTION
[0008] A surface assembly that communicates with subsea structures
includes a working deck on a floating structure. The working deck
has an aperture extending axially therethrough. A riser extends
from a subsea location to the working deck. The riser extends
through the aperture. The surface assembly includes a frame
extending circumferentially around the riser. The frame is
connected to the riser so that the frame moves axially with the
riser. The assembly also includes a tensioner assembly connected
between the working deck and the frame. The tensioner assembly
comprises a piston, a piston chamber, a sealing portion between the
piston and the piston chamber, a piston rod extending from the
piston and away from the piston chamber, and a shroud enclosing the
piston rod and at least the sealing portion of the piston
assembly.
[0009] In another configuration, the sealing portion is between the
piston and an interior surface of the shroud. A piston chamber is
defined by the sealing portion, the piston, and the shroud. The
tensioner assembly can also include a cylinder. The sealing portion
can then be located between the piston and the cylinder. The piston
chamber is then defined by the sealing portion, the piston, and the
cylinder. The shroud typically has a closed upper end, and an open
lower end that exposes a portion of its interior surface to
atmospheric pressure.
[0010] In yet another configuration, a surface assembly for subsea
wells includes a working deck on a floating structure. The working
deck has an aperture extending axially therethrough. A riser
extends from a subsea location to the working deck and through the
aperture. A frame extends circumferentially around the riser. The
frame is connected to the riser so that the frame moves axially
with the riser. A tensioner assembly is connected between the
working deck and the frame. The tensioner assembly includes a
piston slidably carried in a piston chamber, a piston rod extending
from the piston and away from the piston chamber, and a shroud
enclosing the piston rod. The shroud has a plurality of segments
with at least one of the shroud segments being movable in unison
with the piston rod.
[0011] The plurality of segments can include an inner shroud
segment being stationary relative to the piston rod. The plurality
of segments can have an inner shroud segment and an outer shroud
segment, with the outer shroud segment telescoping over the inner
shroud segment when the tensioner assembly is in a contracted
position. A substantial portion of the inner shroud segment can be
uncovered when the tensioner assembly is in an extended position.
Either the outer shroud segment or the inner shroud segment that is
fixedly connected to an end portion of the piston chamber that
receives the piston rod.
[0012] The plurality of segments can also include an intermediate
shroud segment. The intermediate shroud segment telescoping over
the inner shroud segment when the tensioner assembly is in a
contracted position, and the outer shroud segment telescoping over
the intermediate and inner shroud segments when the tensioner
assembly is in a contracted position.
[0013] In another configuration a riser tensioner assembly for
maintaining tension in a riser extending from a subsea well through
an aperture in a working deck of a floating structure includes a
piston slidably carried in a piston chamber. A piston rod extends
from the piston chamber. The piston rod and piston are movable
between a contracted position and an extended position of the
tensioner assembly. A shroud surrounds at least part of the piston
rod while in the contracted and extended positions. The shroud has
a plurality of shroud segments with at least one of the shroud
segments being movable in unison with the piston rod and at least
one of the shroud segments being fixedly connected to an end
portion of the piston chamber that receives the piston rod.
[0014] In the tensioner assembly, the plurality of shroud segments
can include an inner shroud segment and an outer shroud segment.
The inner shroud segment can have a flange end connected to either
the piston chamber or the piston rod and a telescoping end having
an outer lip. The outer shroud can also have a flange end connected
to the other of the piston chamber or the piston rod and a
telescoping end having an inner lip. When the tensioner assembly is
in the extended position, the outer lip of the inner shroud
engaging another shroud segment telescoping over the inner shroud
and the inner lip of the outer shroud engaging another shroud
segment telescoping within the outer shroud.
[0015] The plurality of shroud segments can also include an
intermediate shroud segment. The intermediate shroud segment
telescopes over the inner shroud segment when the tensioner
assembly is in a contracted position. The outer shroud segment
telescopes over the intermediate and inner shroud segments when the
tensioner assembly is in a contracted position.
[0016] Each intermediate shroud segment can have an extension end
and a contraction end. The extension end has an outer lip and the
contraction end has an inner lip. When the tensioner assembly is in
the extended position the outer lip of the intermediate shroud
segment engages an interior lip of either another intermediate
shroud segment or the outer shroud segment, and the inner lip of
the intermediate shroud segment engages an outer lip of either
another intermediate shroud segment or the inner shroud
segment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic side view of a riser tensioner
constructed in accordance with this invention and shown in an
extended position.
[0018] FIG. 2 is a schematic side view of the riser tensioner in
FIG. 1, shown in a contracted position.
[0019] FIG. 3 is a schematic side view of an alternate embodiment
of a riser tensioner in accordance with this invention and shown in
an extended position.
[0020] FIG. 4 is a schematic side view of an alternate embodiment
of a riser tensioner in accordance with this invention and shown in
an extended position.
[0021] FIG. 5 is a schematic side view of an alternate embodiment
of a riser tensioner in accordance with this invention and shown in
an extended position.
[0022] FIG. 6 is a schematic side view of an alternate embodiment
of a riser tensioner in accordance with this invention and shown in
a partially an extended position.
[0023] FIG. 7 is a schematic side view of another alternate
embodiment of a riser tensioner in accordance with this invention
and shown in an extended position.
[0024] FIG. 8 is a schematic side view of the riser tensioner in
FIG. 7, shown in a contracted position.
[0025] FIG. 9 is a schematic side view of another alternate
embodiment of a riser tensioner in accordance with this invention
and shown in an extended position.
[0026] FIG. 10 is a schematic side view of another alternate
embodiment of a riser tensioner in accordance with this invention
and shown in an extended position.
[0027] FIG. 11 is a schematic side view of the riser tensioner in
FIG. 10, shown in a contracted position.
[0028] FIG. 12 is an exploded view of a cylinder assembly in the
riser tensioner shown in FIGS. 7-9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] Referring to FIGS. 1 and 2, a floating platform deck 11 is
schematically shown. Deck 11 may, for example, be a deck of a
barge, a tension leg platform, a spar or other types. However, the
arrangement of FIG. 1 is particularly suited for a spar. Deck 11
has an opening 13 through which a riser 15 extends.
[0030] Riser 15 is connected on its lower end to a subsea well. In
this embodiment, riser 15 is a production riser. Typically, a
production tree (not shown) is mounted to the upper end of riser
15. Well fluids flow from the subsea wellhead of production riser
15 to the tree. Typically, the floating platform will support a
number of risers 15.
[0031] A tensioner assembly comprising a plurality of
hydro/pneumatic cylinder assemblies 17 supplies tension to each
riser 15 as deck 11 moves upward and downward. Two cylinder
assemblies 17 are shown in FIG. 1, but preferably, at least two
more cylinder assemblies 17 will provide tension to each riser 15.
Each cylinder assembly 17 includes a cylinder 19 and a piston 21
that strokes within cylinder 19. Piston 21 has a rod 23 that
protrudes from one end of cylinder 19. In this embodiment, rod 23
is located on the upper end of cylinder 19 above deck 11. A closed
system of pressurized gas over fluid is utilized to provide force.
The pressurized fluid and gas may be internal or external to the
cylinder. Both internal and external sources may be used together.
An external pressurized fluid and gas source or accumulator 24 is
shown. If desired, fluid under atmospheric or low pressure may be
placed in the annular space surrounding rod 23 above piston 21 to
serve as lubricant for piston 21. The lubricant may lead to a
reservoir for maintaining a constant supply as piston 21 strokes up
and down.
[0032] In the preferred embodiment, a plurality of seals 22
surround the circumference of piston 21. In the embodiment shown in
FIGS. 1 and 2 seals 22 engage an interior surface of cylinder 19. A
piston chamber is defined by piston 21, seals 22 and cylinder 19.
In the embodiment shown in FIGS. 1 and 2, a plurality of seals 26
also extend from cylinder 19 to sealingly engage rod 23.
[0033] Cylinder 19 is connected on its lower end to a brace 27 by a
pin 25. In the preferred embodiment, pin 25 is spherical so as to
allow pivotal rotation not only in the plane containing the
drawing, but also in a Z-plane perpendicular to the plane
containing the drawing. Brace 27 in this embodiment is secured to
deck 11, and the lower ends of cylinders 19 are located
approximately at the same level as deck 11.
[0034] Each cylinder assembly 17 inclines relative to riser 15 and
deck 11 in the embodiment shown in FIG. 1 and 2. The upper ends of
rods 23 are closer to riser 15 than the lower ends of cylinders 19.
Rods 23 are secured by spherical pins 29 to a top frame 31. Top
frame 31 is mounted to a tension ring 33 that is clamped or
otherwise secured to riser 15 for movement therewith. The radial
distance from the axis of riser 15 to upper pins 29 is less than
the radial distance from the riser axis to lower pins 25. The angle
of each cylinder assembly 17 relative to the riser 15 will change
as rods 23 stroke from a retracted position as shown in FIG. 2 to
an extended position shown in FIG. 1. In FIG. 2, a wave or tidal
variation has caused deck 11 to rise relative to riser 15, causing
cylinder assembly 17 to retract. In FIG. 1, deck 11 has moved
downward from that shown in FIG. 2 due to wave movement or tidal
action. The pressurized gas over fluid (FIG. 1) maintains pressure
on the lower side of piston 21 to cause cylinder assemblies 17 to
extend.
[0035] A shroud 35 encloses the exposed portion of rod 23 of each
cylinder assembly 17. Shroud 35 is a cylindrical member having a
closed upper end 37 and an open lower end 39. Each rod 23 extends
through a hole in closed end 37 that is preferably sealed to
prevent corrosive fluids from contacting rod 23. Shroud 35 protects
rod 23 and seals 26 from any debris falling onto cylinder
assemblies 17 from above. The length of shroud 35 is selected so
that lower end 39 will be close to the lower ends of cylinders 19
while cylinder assembly 17 is fully retracted as shown in FIG. 2.
When fully extended, as shown in FIG. 3, lower end 39 of each
shroud 35 is spaced below the upper end of cylinder 19. The
interior of shroud 35 is at low or atmospheric pressure.
[0036] Sets of guide rollers 41 are employed to engage riser 15 and
maintain riser 15 generally centralized in opening 13 but allow for
angular offset of the riser relative to the platform. Although only
two guide rollers 41 are shown, preferably more would be employed
for each riser 15. Each guide roller 15 is mounted to an arm 43
that is fixed in length in the preferred embodiment. Arm 43 has an
outer end that is secured by a pin 45 to a lug 47. Lug 47 mounts to
deck 11 in this embodiment. Pivot pins 45 allow rods 43 to be
pivoted and rotated away from deck opening 13 for other operations,
such as when a larger diameter drilling riser is employed in a
preliminary operation. In this embodiment, arms 43 are spaced above
deck 11 only a short distance, thus provide centralizing to riser
15 at opening 13.
[0037] An upper deck 51 is located below tensioning ring 33 and
above deck 11 in this embodiment. Mounting guide rollers to deck 51
reduces any moment arm on guide rollers 41 due to the failure of a
cylinder assembly 17. Preventing angular movements are desirable
during many workover and intervention operations. Preferably, pivot
pins 45 allow rods 43 to be pivoted and rotated so that rollers 41
connected to upper deck 51 may be disengaged and pivoted away from
riser 15. This may be desirable during operations where angular
movements are allowable, or when a larger diameter drilling riser
is employed.
[0038] The embodiment of FIG. 3 is the same as the embodiment of
FIGS. 1 and 2 except for placement of guide rollers 41 and upper
deck 51. Consequently, the same numerals will be used except for
the different structure. In this embodiment, upper deck 51 is
mounted above tension ring 33 and a considerable distance above
deck 11. Arms 43 for guide rollers 41 are mounted to upper deck 51.
An advantage of the embodiment of FIG. 3 occurs if one of the
cylinder assemblies 17 loses pressure. A loss in pressure causes a
bending moment arm to be applied to riser 15, which is resisted by
guide rollers 41. Because of the placement above tension ring 33,
the force applied by the moment arm is reduced over that which
would exist if rollers 41 were placed as in FIGS. 1 and 2.
[0039] The embodiment shown in FIG. 4 includes the use of a sleeve
or conductor 53. Conductor 53 is mounted to top frame 31 and
extends concentrically around riser 15. Conductor 53 extends
downward a distance that is at least equal to the total stroke of
cylinder assemblies 17. Guide rollers 41 engage conductor 53 rather
than directly engaging riser 15. Conductor 53 provides wear
protection to riser 15 due to contact with rollers 41.
[0040] Referring to the embodiment shown in FIG. 5, cylinder
assemblies 17 are inverted in this alternative embodiment. Piston
21 sealingly engages the interior surface of cylinder 19 which
contains pressurized gas as in the previously discussed
embodiments. Cylinder 19 has an open lower end for receiving piston
21, but it does not sealingly engage rod 23 in this embodiment.
Accordingly, the lower end of piston 21, below seals 22 is open to
atmospheric pressure. Any fluid or debris dripping onto cylinder
assembly 17 from above lands on cylinder 19, which protects the
sealing region between seals 22 and the interior surface of
cylinder 19. There is no separate surrounding rods 23 in this
embodiment.
[0041] Referring to another alternative embodiment shown in FIG. 6,
cylinder assemblies 17 and tension ring 33 are located below deck
11. Cylinder assemblies 17 extend downward at an angle so that the
lower ends of cylinder assemblies 17 are radially inward and below
the upper ends of cylinder assemblies 17. Shroud 35 continues to
protect rod 23 from any debris falling onto cylinder assemblies 17
from above. This embodiment is particularly useful for replacing
tensioner assemblies on existing structures, like existing tension
leg platforms, wherein the tension ring is located below the deck.
In this embodiment, gas over fluid pressure acts on the annular
space between rod 23 and housing 19 to pull housing 19 upward.
[0042] In operation of the embodiments in FIGS. 1-5, tension ring
33 is mounted to riser 15, and guide rollers 41 are mounted in
engagement with riser 15 or conductor 53 (FIG. 3). Gas pressure in
cylinder 19 exerts a desired upward force on riser 15 to maintain a
desired tension in riser 15. As deck 11 moves upward relative to
riser 15, cylinder assemblies 17 retract. As deck 11 moves downward
relative to riser 15, cylinder assemblies 17 extend.
[0043] In each of the embodiments, seals 22 are protected from
drippings and debris from above while in both the contracted and
retracted positions. Moreover, in the embodiments shown in FIGS.
1-4, and 6, shroud 35 also protects rod 23 and seals 26, in
addition to the sealing region located between piston 21 and the
interior surface of cylinder 19.
[0044] In the alternative embodiment of cylinder assembly 17' shown
in FIGS. 7-11, shroud 35 is replaced with a shroud 35' having
telescoping shroud portions 35a', 35b', 35c'. Similarly, piston and
piston rod 22,23, and cylinder 19 from the embodiments shown in
FIGS. 1-6 are replaced with piston 22', piston rod 23', and
cylinder 19'. FIGS. 7 and 8 are similar to the embodiment shown in
FIGS. 1 and 2, with upper deck 51 being positioned below engagement
ring 31. FIG. 7 illustrates the alternative embodiment in an
extended position, while FIG. 8 illustrates the alternative
embodiment in a contracted position. Likewise, FIG. 9 is similar to
the embodiment shown in FIG. 3 such that upper deck 51 is
positioned above engagement ring. Finally, FIGS. 10-11 are similar
to the embodiment shown FIG. 5, with cylinder 19' being disposed
above piston rod 23' and shroud 35'. FIGS. 10 and 11 illustrate
this alternative embodiment in both an extended and a contracted
position. The alternative embodiments illustrated in FIGS. 7-11
also show cylinder assemblies 17' extending substantially vertical
rather than extending at an angle radially inward from lower deck
11 to upper deck 51.
[0045] Referring to FIGS. 7-12, shroud 35' includes a plurality of
tubular, telescoping shroud portions or segments 35a', 35b', and
35c'. In the preferred embodiment, outer shroud segment 35a' has an
inner diameter larger enough to receive intermediate shroud segment
35b' and shroud segment 35c'. Intermediate shroud segment 35b'
preferably has an inner diameter large enough to receive inner or
small shroud segment 35c'. Outer or large shroud segment 35a' is
preferably positioned above intermediate and small shroud segments
35b', 35c' so that shroud 35' shields piston rod 23' from drippings
from above when shroud 35' is both extended and contracted, whether
cylinder is positioned below shroud 35' (FIGS. 7-9) or below shroud
35' (FIGS. 10-11).
[0046] As is perhaps shown best in FIG. 12, shroud segments
35a',35b',35c' include upper and lower lips 61, 63 for engaging
each other when moving from the contracted position to the extended
position. Lower lips 63 are preferably formed on an interior
surface of the respective shroud segments for engaging an outer
surface of another shroud segment disposed therein. Lower lips 63
are typically formed on a contraction end--or the end in the
direction of movement of the shrouds during contraction--of each
shroud segment. Upper lips 61 are preferably formed on an outer
surface of the respective shroud segments for engaging an inner
surface of another shroud. Typically, upper lips 61 are formed on
an extension end--or the end in the direction of movement of the
shrouds during extension--of each shroud segment. As will be
appreciated by those skilled in the art, upper and lower lips 61,
63 engage each other when shroud 35' is in its extended position
and help to define the overall length of shroud 35' when
extended.
[0047] In the preferred embodiment, each intermediate segment 35b'
includes both upper and lower lips 61b, 63b because each
intermediate shroud segment receives a shroud segment, and is
received by a larger shroud segment. In the preferred embodiment,
large shroud segment 31 a' includes only lower lip 63a, but has a
flange 62 at its upper end for connecting to a piston rod connector
flange 67 located on a piston rod connector 65 (FIGS. 7-9), or a
flange located at the upper end portion of cylinder 19' (FIGS.
10-11). In the preferred embodiment, small shroud segment 35c' only
includes upper lip 63c. However, small shroud segment 35c' also
includes a flange 64 at its lower end for connecting to a flange
located at the upper end portion of cylinder 19' (FIGS. 7-9) or to
piston rod connector flange 67 (FIGS. 10-11).
[0048] In the embodiments shown in FIGS. 7-12, piston rod 23' is at
least one shroud length longer than piston rod 23 in the previous
embodiments because no shroud segment telescope over cylinder 19'.
As will be readily appreciated by those skilled in the art, in the
embodiment shown in FIGS. 7-9, small shroud segment 35c' could be
adapted to telescope over an outer surface of cylinder 19', for
example with a lower lip 63 rather than a flange 64, so that piston
rod 23' could have substantially the same length as piston rod
23.
[0049] In each of the alternative embodiments illustrated in FIGS.
7-12, seals 22 are protected from drippings and debris from above
while in both the contracted and retracted positions. Moreover, in
each of the embodiments shown in FIGS. 7-12, shroud 35' also
protects rod 23' and seals 26, in addition to the sealing region
located between piston 21' and the interior surface of cylinder 19.
Protecting the outer surface of piston rod 23' allows for a less
expensive manufacture of piston rod 23' because a protective layer
will not be necessary.
[0050] While the invention has been shown in only three of its
forms, it should be apparent to those skilled in the art that it is
not so limited but is susceptible to various changes without
departing from the scope of the invention. For example, the number
of intermediate shrouds 35b' can be increased or decreased, even
such that large shroud 35a' registers with small shroud 35b'.
Furthermore, the telescoping shroud segments could also be utilized
with the tensioner assemblies having the piston rod extending
radially inward from the working deck to the tension ring.
* * * * *