U.S. patent application number 11/718705 was filed with the patent office on 2009-05-21 for hydraulic rams.
Invention is credited to Anthony Stephen Bamford.
Application Number | 20090127482 11/718705 |
Document ID | / |
Family ID | 35539617 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090127482 |
Kind Code |
A1 |
Bamford; Anthony Stephen |
May 21, 2009 |
HYDRAULIC RAMS
Abstract
There is disclosed an actuator for delivering a supplementary
force to the piston of a shear ram in a blowout preventer (BOP),
and a corresponding BOP. In one embodiment, a supplementary force
actuator (12) is disclosed for use on a hydraulic ram (10), the
actuator comprising an actuator body (30) connected to the
hydraulic ram; first and second chambers (38, 36) located in the
body, the chambers isolated from each other by an actuator piston
(46); a rod (42) connected to an operating piston (24) of the
hydraulic ram, passing through the first chamber and the actuator
piston, and extending into at least a portion of the second
chamber; wherein the actuator piston is releasably engageable to
the rod by gripping means (48); and wherein the hydraulic ram is
operated by a force from movement of the operating piston and by a
supplementary force from movement of the actuator piston.
Inventors: |
Bamford; Anthony Stephen;
(Montrose, GB) |
Correspondence
Address: |
OSHA LIANG L.L.P.
TWO HOUSTON CENTER, 909 FANNIN, SUITE 3500
HOUSTON
TX
77010
US
|
Family ID: |
35539617 |
Appl. No.: |
11/718705 |
Filed: |
November 4, 2005 |
PCT Filed: |
November 4, 2005 |
PCT NO: |
PCT/GB2005/004272 |
371 Date: |
January 13, 2009 |
Current U.S.
Class: |
251/1.3 ;
251/1.1; 251/58 |
Current CPC
Class: |
E21B 33/063
20130101 |
Class at
Publication: |
251/1.3 ;
251/1.1; 251/58 |
International
Class: |
E21B 33/06 20060101
E21B033/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 2004 |
GB |
0424401.8 |
Jun 25, 2005 |
GB |
0512995.2 |
Claims
1. A supplementary force actuator for use on a hydraulic ram, the
actuator comprising; a) an actuator body connected to the body to a
hydraulic ram; b) first and second chambers located in the body,
the chambers isolated from each other by an actuator piston; c) a
rod adapted to be connected to an operating piston of the hydraulic
ram, pass through the first chamber and the actuator piston, and
extend into at least a portion of the second chamber; d) the
actuator piston being releasably engageable to the rod by a
gripping device; and e) wherein the hydraulic ram is operated by a
force from movement of the operating piston and by a supplementary
force from movement of the actuator piston.
2. A supplementary force actuator as claimed in claim 1 wherein the
actuator includes a release mechanism to operate the actuator
piston.
3. A supplementary force actuator as claimed in claim 1 wherein a
separation element is located between the hydraulic ram and the
body.
4. A supplementary force actuator as claimed in claim 3 wherein one
or more seals are arranged on the separation element to act upon
the rod and prevent the release of hydraulic fluid from the body
into a hydraulic chamber of the hydraulic ram.
5. A supplementary force actuator as claimed in claim 1 wherein the
actuator includes an energy storage device arranged to provide a
force to act upon the actuator piston.
6. A supplementary force actuator as claimed in claim 5 wherein the
energy storage device comprises a mechanical means.
7. A supplementary force actuator as claimed in claim 6 wherein the
mechanical means comprises one or more springs held in
compression.
8. A supplementary force actuator as claimed in claim 6 wherein the
mechanical means comprises a plurality of Bellville springs.
9. A supplementary force actuator as claimed in claim 5 wherein the
energy storage device comprises is a hydraulic means.
10. A supplementary force actuator as claimed in claim 9 wherein
the hydraulic means comprises hydraulic fluid held under
pressure.
11. A supplementary force actuator as claimed in claim 1 wherein
the actuator includes a resetting device configured to move the
actuator piston back to its original operating position.
12. A supplementary force actuator as claimed in claim 11 wherein
the actuator includes a ram setting device to move the operating
piston back to its original position.
13. A supplementary force actuator as claimed in claim 1, wherein
the gripping device comprises a ball gripping device.
14. A supplementary force actuator as claimed in claim 13, wherein
the ball gripping device comprises a plurality of balls mounted in
a ball mounting element having a plurality of apertures, each
aperture associated with a corresponding ball.
15. A supplementary force actuator as claimed in claim 14, wherein
the actuator piston is adapted to urge the balls into engagement
with the rod, to grip the rod.
16. A supplementary force actuator as claimed in claim 13, wherein
the ball gripping device is adapted to grip the rod during movement
of the actuator piston in a first direction and to release the rod
during movement in a second, opposite direction.
17. A supplementary force actuator as claimed in claim 14, wherein
the ball gripping device comprises a ball release mechanism for
permitting relative movement between the ball mounting element and
the actuator piston.
18. A supplementary force actuator as claimed in claim 17, wherein
the ball release mechanism comprises a shoulder adapted to abut the
ball mounting element, to exert a force on the ball mounting
element to disengage the balls from the rod during movement of the
actuator piston in the second direction.
19. A supplementary force actuator as claimed in claim 18, wherein
the ball mounting element comprises a flange and at least one
spring provided between the flange and the actuator piston.
20. A method of operating a hydraulic ram comprising: a) releasing
a first piston to act on a ram; b) using the movement of the first
piston to trigger a release mechanism; and c) releasing a second
piston on operation of the release mechanism, to act upon the
ram.
21. A method of operating a hydraulic ram as claimed in claim 20
wherein the method includes the step of pressurising hydraulic
fluid behind the first piston which is then used to operate the
first piston.
22. A method of operating a hydraulic ram as claimed in claim 20
wherein the method includes: releasably engaging the second piston
to the first piston, so that the second piston is stationary when
the first piston operates and the second piston also moves the
first piston upon operation of the second piston.
23. A method of operating a hydraulic ram as claimed in claim 20
wherein the release mechanism is triggered at or near the end of
the stroke of the first piston.
24. A method of operating a hydraulic ram as claimed in claim 20
wherein the method includes: resetting the hydraulic ram by moving
the first and second pistons back to their original operating
positions.
25. A blow out preventer for use in oil well drilling, the blow out
preventer comprising: a pair of opposing hydraulic rams, each ram
having a shear blade on a leading face; and at least one
supplementary force actuator as claimed in claim 1 located on at
least one of the hydraulic rams.
26. A blow out preventer as claimed in claim 25 wherein a
supplementary force actuator is arranged on each of the hydraulic
rams.
Description
[0001] The present invention relates to hydraulic rams and in
particular, though not exclusively, to an actuator for delivering a
supplementary force to the piston of a shear ram in a blowout
preventer.
[0002] There are a number of applications where hydraulic rams are
used. Each ram typically includes a piston which is driven forward
by a hydraulic force. In oil well drilling, hydraulic rams are
located in blowout preventers. In an emergency procedure when a
well is required to be shut in to prevent a blow-out whilst
drilling, two opposing rams are brought together to seal the well
bore. These rams are typically referred to as shear rams as they
include a shear blade on the front face of the piston used to sever
drill pipe or casing in the wellbore.
[0003] When the shear rams are actuated by a hydraulic force, the
opposing shear blades are brought together to interact, with the
blades being driven by the hydraulic pistons. The shear blades
first crush and then shear the drill string, casing or other
tubular in the well. As wells are drilled to greater depths the
tubulars are of increasing diameter, wall thickness and increased
steel grades. Consequently shearing the tubular in the well
requires more hydraulic force. This calls for a larger actuator
piston, hence larger operating fluid volumes and higher closure
pressures.
[0004] For shear rams deployed onshore or on fixed offshore
installations, the increasing size is inconvenient but can be
accommodated. For shear rams that are deployed subsea, the volume
of hydraulic fluid that must be stored under pressure in fluid/gas
accumulators increases exponentially with water depth. The volume
and weight of these accumulators makes the subsea blowout preventer
or shut off system much heavier and therefore more difficult to
deploy.
[0005] It is amongst the objects of embodiments of the present
invention to provide a supplementary force actuator for use on a
hydraulic ram to increase the applied force without substantially
increasing the volume of hydraulic fluid required.
[0006] It is also amongst the objects of embodiments of the present
invention to provide a two stage method of operating a hydraulic
ram.
[0007] It is also amongst the objects of at least one embodiment of
the present invention to provide a blowout preventer having a two
stage actuator mechanism for improved shearing of drill pipe,
casing or other tubular.
[0008] According to a first aspect of the present invention, there
is provided a supplementary force actuator for use on a hydraulic
ram, the actuator comprising:
an actuator body including fixation means to connect the body to a
hydraulic ram; first and second chambers located in the body, the
chambers isolated from each other by an actuator piston; a rod
adapted to be connected to an operating piston of the hydraulic
ram, pass through the first chamber and the actuator piston, and
extend into at least a portion of the second chamber; the actuator
piston being releasably engageable to the rod by gripping means;
and wherein the hydraulic ram is operated by a force from movement
of the operating piston and by a supplementary force from movement
of the actuator piston.
[0009] Thus once the normal operating piston has moved the ram to
crush an object, the actuator piston can be released to provide a
supplementary force on the ram.
[0010] Preferably the actuator includes a release mechanism to
operate the actuator piston. In this way the actuator piston can be
released at or near the end of the stroke of the operating piston
and thereby provide the supplementary force where it is most
required.
[0011] Preferably a separation element is located between the
hydraulic ram and the body. More preferably one or more seals are
arranged on the separation element to act upon the rod and prevent
the release of hydraulic fluid from the body into a hydraulic fluid
chamber of the hydraulic ram.
[0012] Preferably the actuator includes energy storage means
arranged to provide a force to act upon the actuator piston.
[0013] In a first embodiment the energy storage means is a
mechanical means. Preferably the mechanical means is one or more
springs held in compression. Advantageously the mechanical means is
a plurality of Bellville springs as are known in the art.
[0014] In a second embodiment the energy storage means is a
hydraulic means. Preferably the hydraulic means is hydraulic fluid
held under pressure.
[0015] Preferably also the actuator includes resetting means to
move the actuator piston back to its original operating position.
Preferably also the actuator includes ram setting means to move the
operating piston back to its original position. In this way the
hydraulic ram may be reset.
[0016] Preferably, the gripping means comprises a ball-gripping
device and may comprise a device of the type disclosed in U.S. Pat.
No. 2,062,628 (Yannetta) or U.S. Pat. No. 2,182,797, the
disclosures of which are incorporated herein by way of
reference.
[0017] The ball gripping device may comprise a plurality of balls
mounted in a ball mounting element, which may be a ball cage or
sleeve, having a plurality of apertures, each aperture associated
with a corresponding ball. The actuator, in particular, the
actuator piston may be adapted to urge the balls into engagement
with the rod, to grip the rod. This may facilitate application of
the supplementary force.
[0018] The actuator piston may define one or more cam surface or
ramp for urging one or more of the balls radially into engagement
with the rod.
[0019] The ball gripping device may be adapted to grip the rod
during movement of the actuator piston in a first direction and to
release the rod during movement in a second, opposite direction. To
facilitate this, the device may comprise a ball release mechanism
for permitting relative movement between the ball mounting element
and the actuator piston. The ball release mechanism may comprise a
shoulder or the like which, during return movement of the actuator
piston, may be adapted to abut the ball mounting element, to exert
a force on the ball element to disengage the balls from the rod.
The ball mounting element may comprise a flange or spring plate,
and at least one spring may be provided between the flange and the
actuator piston. The spring may facilitate operation of the
actuator and may prevent the actuator piston from impacting other
components of the actuator following disengagement of the balls
from the rod. Following release, the rod may move independently of
the actuator piston back to a start position.
[0020] According to a second aspect of the present invention there
is provided a method of operating a hydraulic ram comprising the
steps; [0021] (a) releasing a first piston to act on a ram; [0022]
(b) using the movement of the first piston to trigger a release
mechanism; [0023] (c) releasing a second piston on operation of the
release mechanism, to act upon the ram.
[0024] Preferably the method includes the step of
compressing/pressurizing hydraulic fluid behind the first piston
which is then used to operate the first piston. Preferably the
method includes the step of releasably engaging the second piston
to the first piston, so that the second piston is stationary when
the first piston operates and the second piston also moves the
first piston upon operation of the second piston.
[0025] Advantageously the release mechanism is triggered at or near
the end of the stroke of the first piston.
[0026] Preferably the method includes the step of resetting the
hydraulic ram by moving the first and second pistons back to their
original operating positions.
[0027] Further features of the method are defined in relation to
the first aspect of the invention.
[0028] According to a third aspect of the present invention there
is provided a blow out preventer for use in oil well drilling, the
blow out preventer comprising:
a pair of opposing hydraulic rams, each ram having a shear blade on
a leading face; at least one supplementary force actuator according
to the first aspect located on at least one of the hydraulic
rams.
[0029] Preferably a supplementary force actuator is arranged on
each of the hydraulic rams. In this way the rams will initially
crush the tubular by action of the operating piston and then the
tubular is sheared by operation of the actuator piston.
[0030] Preferably the energy storage means is a hydraulic energy
store. In this way the blow out preventer can be kept within the
dimensions of 5.7 m.times.5.7 m for deployment through a moon
pool.
[0031] Embodiments of the present invention will now be described,
by way of example only, with reference to the following drawings in
which:
[0032] FIG. 1 is a schematic cross-sectional view of a hydraulic
ram including a supplementary force actuator according to a first
embodiment of the present invention, shown in a first operating
position;
[0033] FIG. 2 is an illustration of the release mechanism of the
supplementary force actuator of FIG. 1;
[0034] FIG. 3 is a schematic cross-sectional view of the hydraulic
ram including a supplementary force actuator of FIG. 1, shown in a
second operating position;
[0035] FIG. 4 is a schematic cross-sectional view of the hydraulic
ram including a supplementary force actuator of FIG. 1, shown in a
third operating position;
[0036] FIG. 5 is a schematic cross-sectional view of a hydraulic
ram including a supplementary force actuator according to a second
embodiment of the present invention;
[0037] FIG. 6 is a schematic cross-sectional view of a hydraulic
ram including a supplementary force actuator according to a third
embodiment of the present invention; and
[0038] FIGS. 7 and 8 are schematic cross-sectional views of part of
a supplementary force actuator according to a further embodiment of
the present invention, shown in second and third operating
positions, respectively.
[0039] Reference is initially made to FIG. 1 of the drawings which
shows a hydraulic ram, generally indicated by reference numeral 10,
upon which is mounted a supplementary force actuator 12, according
to a first embodiment of the present invention.
[0040] The hydraulic ram 10 is part of a blow out preventer 14.
Blow out preventer 14 comprises a body 16 having an axial bore 18
therethrough and at least one transverse port 20 accessing the bore
18. Mounted at the transverse port 20 is the hydraulic ram 10. The
ram 10 comprises cylindrical shaft 22 having a piston 24 at a first
end and a shear blade 26 mounted on an opposing end. The piston is
operated by the pressurisation of hydraulic fluid behind the piston
24, in a ram chamber 36.
[0041] As is conventional, a drill pipe or tubular 28 is located
through the bore 18. In the event of a blow out, the piston 24 is
actuated to force the shaft 22 towards the bore 18. Typically two
opposing hydraulic rams 10 are mounted across the bore so that the
shear blades 26 interact. The shear blades first crush and then
shear the tubular 28. The shear blades are arranged such that when
they meet, the bore 18 is sealed and blow out is prevented.
[0042] The supplementary force actuator 12 is connected to an
existing hydraulic ram 10. In this way the actuator 12 may be
retrofitted to existing ram systems. An end cap can be removed from
the existing ram and the body 30 is then located at this position
32. Body 30 is fixed to the ram, being secured by bolts 34 or other
accepted fixation means. A separation plate 40 isolates the ram
chamber 36 from the inside of the body 30.
[0043] Body 30 comprises first and second chambers, 38,37
respectively. In this embodiment these chambers 37,38 have a
greater diameter than chamber 36. The chambers are divided by a
piston 46.
[0044] The piston 24 of the conventional ram 10 is fitted with an
additional connecting rod 42 that extend through seals 44 on the
separation plate 40. Said seals 44 contain the full hydraulic
pressure that is applied to close the ram 10.
[0045] The connecting rod 42 travels through the first chamber 38
and through the centre of the piston 46. Mounted within the piston
46 is a gripping device 48. In the illustrated embodiment, the
gripping device 48 is a ball gripping device of the type described
in U.S. Pat. No. 2,062,628, incorporated herein by reference. The
ball-gripping device 48 is described hereinafter with reference to
FIGS. 5 and 6. Essentially the device 48 selectively grips the rod
42 such that the piston 46 and rod 42 move together. It will be
understood that gripping devices of various different types may be
utilised.
[0046] Mounted behind the piston 46 in the second chamber 37 are a
stack of Bellville springs 50. These springs 50 can store enormous
amounts of energy but the applied force drops off rapidly over a
few centimetres of travel.
[0047] Chamber 38 is arranged to provide only a small distance of
possible travel for the piston 46. The purpose of the piston 46 is
to compress and retain the Bellville springs 50 arranged in radial
fashion around the connecting rod 42. Pressure applied to chamber
38 acting on piston 46 compresses the Bellville springs 50.
[0048] The load in the compressed Bellville springs 50 is retained
by a rotating "half pin" 52. This is constructed of high tensile
steel capable of supporting or retaining very high loads in excess
of 100 metric tons. The movement of the rotating "half pin" is
effected by means of a linkage, lever arm or circular plate 54 as
illustrated in FIG. 2. FIG. 2 is a schematic diagram of a release
mechanism, generally indicated by reference numeral 56. The choice
of linkage depends on the provision made for safety of personnel in
the release of the stored energy. A circular plate 54 as
illustrated in FIG. 2 has obvious safety advantages.
[0049] A spring loaded linkage arm 58 rotates the "half pin" 52
once the piston 46 has compressed Bellville springs 50. The load is
supported on the flattened section of the rotating "half pin" 52 as
indicated by the arrow in FIG. 2. The linkage arm 58 is attached to
an adjustable collar 60 fixed to the connecting rod 42 so that when
it has moved by a pre-adjusted length, the spring operates the
rotation of the circular plate 54 and hence the rotating "half
pin".
[0050] By changing the position of the adjustable collar 60, the
operator can set at what point in the shear ram closure, the
Bellville Springs 50 will discharge their load. This feature would
be useful where the properties of steel and other materials to be
sheared are changed. Also affecting the optimum discharge point
would be the geometry of the pipe or pipes to be sheared. For
example pipe in pipe shearing may require an earlier discharge
point than single pipe configurations.
[0051] In use, the chambers 36,38 are filled with hydraulic fluid
so as to move the pistons 24,46 away from the bore 18. As piston 24
moves it retracts the shear blade 26 of the ram 10. The linkage arm
58 also moves rotating the plate 54 as described above. The piston
46 moves independently of the rod 42 to compress the Bellville
springs 50 under the force of the hydraulic fluid supplied to the
chambers 36,38. This operating position is as illustrated in FIG. 1
and the ram 10 and actuator 12 can remain fixed in this position
until movement of the ram is required.
[0052] The operation of the shear ram is illustrated in FIG. 3. The
operator functions the controls of the hydraulic piston 24 and
shaft 22 as would occur on a conventional ram 10. By supplying
hydraulic fluid between a rear face of the piston 24 and plate 40,
the piston 24 is urged forward to advance the shaft 22, so that the
shear blades 26 start to crush the pipe 28 to be sheared. At a
critical point in the travel of the connecting rod 42, the linkage
arm 58 causes the circular plate 54 and "half pin" 42 to rotate and
release the stored energy in the Bellville springs 50. This is be
cause the "half pin" cutaway section is flush with the circular
section of the actuator wall. On release of the stored energy, the
piston 46 moves towards the bore 18. As the piston 46 moves, the
gripping device 48 forces balls against the rod 42 and the rod 42
is thus forced towards the bore 18 also. This movement of the rod
42 is passed onto the shaft 22 and the blades 26 are forced further
into the bore 18. Thus, the mechanical force from the springs 50 is
added to the hydraulic force generated on closure, providing a
massive shearing force proportional to the piston area, hydraulic
pressure applied and length and configuration of the Bellville
springs 50.
[0053] FIG. 4 shows the configuration when the force of the
Bellville Springs 50 has been expended. A second ram, referenced
10a, is illustrated to show that the blades 26,26a interact to seal
the bore 18. To re-set the system, a control system directs
hydraulic fluid to chamber 36 on the front face of piston 24. This
immediately starts to compress the Bellville springs 50. When the
piston 46 with the attached female ball-gripping device 48 makes
contact with actuator sleeve 62, the compression of the Bellville
springs 50 is complete.
[0054] At this point the spring loaded "half pin" 52 rotates to
retain the stored energy. Further movement of the connecting rod 42
causes the female ball-gripping device 48 to contact the
actuator-sleeve 62. This depresses a ball-cage within the
ball-gripping device 48 and allows the connecting rod 42 to
continue its travel until the piston 46 has fully stroked back. The
actuator sleeve 62 may need to be hydraulically activated to
release the ball-cage within the ball-gripping device 48 to ensure
immediate contact to the connecting rod 42. Fluid ports 64,66 in
chambers 37,38 can be used to apply fluid pressure or vent fluid on
either side of the piston 46.
[0055] It will be appreciated by those skilled in the art that the
Bellville springs 50 could be replaced by an ordinary coil spring
to provide an alternative embodiment. Other types of ball gripping
devices may be employed, such as those of the type disclosed in
U.S. Pat. No. 2,182,797 to Dillon, the disclosure of which is
incorporated herein by way of reference. Further embodiments could
use alternative mechanical gripping devices instead of the
ball-gripper system 48, for example, based on tapered slips. Other
spring retaining mechanisms could be used based for example on the
ball-gripper mechanisms.
[0056] The automated mechanical linkage of the release mechanism 56
could be changed in subsequent embodiments, for example instead of
a conventional spring a small closed hydraulic piston could be
used.
[0057] Another embodiment would be to use a proximity switch or
some electronic method of pre-determining the point at which the
stored mechanical energy in the Bellville spring 58 is discharged.
In this case the release mechanism 56 would be operated by
solenoid.
[0058] Yet another embodiment would provide for a release mechanism
based on a pre-set value of hydraulic pressure. Once this hydraulic
pressure threshold is reached communication to the release
mechanism 56 could be via a pilot hydraulic line, a solenoid or
even a pneumatic line in the event the mechanism is deployed at
atmospheric pressure.
[0059] Reference is now made to FIG. 5 of the drawings which
illustrates a hydraulic ram, generally indicated by reference
numeral 110, including a supplementary force actuator 112 according
to a second embodiment of the present invention. Like parts to
those of FIGS. 1 to 4 have been given the same reference numeral
with the addition of 100.
[0060] The actuator 12 in the first embodiment had a design length
of 1.761 metres. When incorporated into a subsea blow out preventer
(BOP) stack, the overall design length was 7.61 metres. As the BOP
stack must be lowered through a moon pool for sub sea deployment,
this size is unacceptable as many moon-pools have dimensions of 6.5
metres by 6.5 metres. The length of the actuator can be reduced by
re-designing the Bellville springs 50. So instead of a single
stack, there are multiple stacks, typically four in number arranged
radially around the rod 42. However for some BOP's the diameter of
the resulting actuator 12 impinged on the space of the next ram
which was located in series down the well bore.
[0061] Even with the redesign, the overall length of the actuator
12 is 1.18 metres which results in a BOP stack with an overall
design length of 5.966 metres, just outside the limit set by
certain oil companies of 5.7 metres.
[0062] The second embodiment seeks to achieve the same objectives
i.e. to reduce the volume of accumulator bottles required for
shearing pipe, especially in deepwater, whilst maintaining or
enhancing the available stored shearing force, but with a reduced
overall length.
[0063] The ram 110 of FIG. 5, has the same arrangement as the ram
10 of FIGS. 1 to 4. The actuator 112 is similar except that the
first chamber 138 is narrower than the second chamber 137 so that
the body 130 increases in diameter at one end, typically into an
18'' cylinder. The actuator piston 146 is located in the second
chamber 137. The piston 146 is connected directly to the
ball-gripping device 148, which is of the type described U.S. Pat.
No. 2,062,628.
[0064] The ball gripping device 148 comprises a surface of tapered
sections forming cam surfaces or ramps 139 in each of which a ball
141 can travel on the tapered edge. A ball mounting element in the
form of a ball cage 143 is biased, via springs for example, to
constrain the balls 141 within the tapered sections 139. The balls
141 thus travel in the tapers 139, constrained by the ball cage
143. When the balls 141 travel down the tapers 139 they grip the
rod 142. To retract them, the ball cage 143 is moved so that the
balls can retract into pockets within the tapered sections 141. In
the first embodiment it is contact between the cage 143 and the
actuator sleeve 62 which causes movement of the cage 143 to retract
the balls 141.
[0065] The purpose of the actuator piston 146 is to apply a second
stage force, once the primary piston 124 has had fluid pressure
applied to it and has moved sufficiently to deform and crush the
pipe in the well-bore 18.
[0066] The release of the actuator piston 146 is controlled and
actuated by means of a pressure signal from the hydraulic fluid
applied to the primary piston 124 or from a position
indicator/sensor measuring the desired length of stroke.
[0067] At the appropriate pressure value or position of the stroke
sensor, the inlet valve 164 is opened to a separate accumulator
bank containing operating fluid, whose pressure is normally stored
at 200 bar. Movement of the piston 146 causes the ball-gripping
device 148 to engage the rod 142 and apply the full force of the
pressure applied over the cross sectional area of the actuator
piston 146. At the same time full operating pressure is applied to
the piston 124 in the first chamber 136. The shear blades 126 will
thus engage and shear the tubular 128, sealing the bore 118 and
shutting in the well.
[0068] The small volume of fluid required to operate the actuator
piston 146 in chamber 137 means that accumulator pressure will not
fall as rapidly as would be the case with a larger volume piston.
Furthermore an electric pump operating from a subsea reservoir may
be used to ensure maximum applied pressure to the inlet 164 at all
times.
[0069] After delivering the combined force applied to the piston
124 and actuator piston 146, the well may be opened by applying a
small pressure at port 170 in the second chamber 138. The seal 172
causes the ball-gripper device 148 to move to the right and allows
the balls to be retracted and hence the well may be opened by
applying pressure to the front face of piston 124.
[0070] The length of stroke of the actuator piston 146 is small,
generally about 50 mm, which is enough to apply maximum force at
the point it is needed to sever the pipe 128 in the well-bore 118.
It is expected that the actuator piston 146 and the chamber 141 it
occupies will be typically about 270 mm in length and the
ball-gripping device 148 about 250 mm in length. The total length
of the actuator 112 should be about 520 mm in length.
[0071] For very deepwater where the accumulator volumes required
are very large an alternate approach to the controls of the system
can be implemented. This is illustrated in FIG. 6. Like parts to
those of FIG. 5 have been given the same reference numeral.
[0072] In this embodiment an accumulator 174 of a given volume is
filled with nitrogen and kept as close as possible to atmospheric
pressure. The accumulator 174 is connected to the inlet 166 by a
valve 176. The accumulator lines and valve 176 will be rated for a
collapse pressure of at least 300 bar. When the required threshold
pressure or position is reached to operate the actuator piston 146,
the valve 176 is opened. This allows the fluid on the return side
of the actuator piston 146 to vent to the accumulator 174.
[0073] In water depths below 1850 metres the seawater pressure
alone may be sufficient to drive the actuator piston 146 to the
left and shear the pipe 128. In water depths less than this,
accumulator pressure may be required at inlet 166 to shear the pipe
128.
[0074] Turning now to FIG. 7, there is shown a schematic
cross-sectional view of part of a supplementary force actuator
according to a further embodiment of the present invention, the
actuator indicated generally by reference numeral 212. Like
components of the actuator 212 with the actuator 12 of FIGS. 1 to
4, and with the actuator 112 of FIGS. 5 and 6 share the same
reference numerals incremented by 200 and 100, respectively.
[0075] The actuator 212 is essentially of similar structure to the
actuator 112, and is for use with a ram such as the ram 110.
Accordingly, only the substantial differences between the actuator
212 and the actuator 112 of FIG. 5 will be described herein in
detail.
[0076] In FIG. 7, the actuator 212 is shown in a second operating
position similar to that of the actuator 12 shown in FIG. 3. In
this position, an actuator piston 246 is retracted. The actuator
212 includes a ball gripping device 248 of similar structure and
operation to the device 148 of FIG. 5, except that the device 248
additionally includes a release mechanism 78 which facilitates
release of balls 141 from engagement with a rod 242. The release
mechanism 78 comprises a flange or spring plate 80 provided on a
ball cage 243 and a number of springs 82 provided between the
flange 80 and a shoulder 84 on the actuating piston 246. The
release mechanism 78 additionally includes a shoulder 86 formed on
or in a body housing the actuator piston 246.
[0077] The actuator 212 is operated in a similar fashion to the
actuator 112, and is shown in FIG. 8 following movement of the
actuator piston 246 towards a bore of a blow out preventer such as
the BOP 14 shown in FIG. 1. As with the actuator 112, this movement
causes the balls 141 to be urged radially inwardly to grip the rod
242. When the actuator 212 is returned to the start position, to
open the BOP bore, the actuator piston 246, carrying the rod 242,
is moved back towards the position of FIG. 7.
[0078] During this movement, the ball cage flange 80 comes into
contact with the shoulder 86 before the actuator piston 246 has
fully returned to its start position.
[0079] Accordingly, continued movement of the actuator piston 246
towards the FIG. 7 position causes the balls 141 to disengage the
rod 242, through abutment between the ball cage flange 80 and the
shoulder 86, as the balls 141 are them permitted to move radially
outwardly and along the surfaces 239. Further movement of the
actuator piston 246 closes the distance between the piston shoulder
84 and the flange 80, compressing the springs 82. In this fashion,
the springs 82 prevent the actuator piston 246 from impacting other
components of the actuator 212 following release of the balls 141,
such as a base 88 on which the shoulder 86 is provided.
[0080] The principal advantage of the present invention is that it
provides a supplementary force actuator for use with a hydraulic
ram to augment the force supplied by the hydraulic ram without
requiring large volumes of hydraulic fluids.
[0081] A further advantage of the present invention is that it
provides a supplementary force actuator for use with a hydraulic
ram in a two stage application of force to shear an object such as
a pipe. An initial force is delivered by the standard hydraulic ram
and a secondary force is discharged at a preset point on the stroke
to more or less double the applied force.
[0082] A yet further advantage of the present invention is that it
provides a supplementary force actuator for use with a hydraulic
ram wherein the preset point where the supplementary force is
discharged is adjustable to optimise the pipe severance load at the
point of hydraulic stroke where the discharged mechanical force is
most effective.
[0083] It will be appreciated by those skilled in the art that
various modifications may be made to the invention herein described
without departing from the scope thereof. For example, multiple
chambers may be arranged transversely to the bore to provide
stepped increases in actuator force. As described herein, any
release mechanism may be chosen to set and release the actuator
piston.
[0084] Alternative gripper mechanisms may also be incorporated.
* * * * *