Note: Descriptions are shown in the official language in which they were submitted.
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PRESSURE RELIEF VALVE AND METHOD FOR SUBSEA
COMPONENTS
Background of Disclosure
Field of the Disclosure
100011 Embodiments of the present disclosure relate to a pressure relief
system for
subsea vessels. More particularly, embodiments of the present disclosure
relate to a
relief valve for subsea vessels.
Background Art
[0002] As subsea oil production is taken to greater depths, equipment and
processes
must be adapted to operate in this harsh environment. A major obstacle in the
progress of oil production in deep water is the extremely high pressures
experienced
at these depths. Accordingly, pressure vessels that maintain an inside
pressure of one
atmosphere are often used to protect eguipment at these depths.
[0003] Pressure vessels used subsea to maintain and simulate an ambient
pressure
similar to what is experienced at the surface are often called "one atmosphere
chambers." A conunon use in the oil industry for such chainbers may be to
protect
pressure sensitive components subsea. In the event that a pressure charnber
leaks
slowly while subsea, and then is withdrawn back to surface relatively rapidly,
it may
contain hyperbaric pressure, or pressure higher than noranal atmospheric
pressure.
With depths reaching close to 10,000 ft, this pressure may become extremely
large
(about 0.47 psi per foot of depth), even as high as 5000 psi. A large pressure
buildup
inside the subsea chamber may be capable of releasing large amounts of energy
when
retrieved and brought to the surface. As such, a relief system may be
implemented to
reduce the pressure inside the chamber to an acceptable and safe level as it
is retrieved
to the surface.
[0004] Pressure relief valves are commonly provided in various systems to
limit the
maximum pressure to less then a predefined threshold level. For example, a
pressure
relief valve may be provided at the outlet of a pump so that the supply line
may not be
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pressurized to an excessive level. Should the pressure threshold level be
exceeded, the
relief valve opens, thereby creating a path to a reservoir, or tank. Another
pressure
relief valve may be provided at the workport of a control valve assembly to
which a
hydraulic actuator, such as a piston and cylinder combination, is connected.
This
arrangement may protect against shock loading or inertial overloading from the
load
acting on the piston and cylinder. If that load results in an excessively high
pressure
within the hydraulic lines attached to the cylinder, the workport pressure
relief valve
is designed to open to relieve pressure to the system tank. The workport
relief valve
may remain open until the load condition no longer exists and pressure within
the
hydraulic line decreases below a threshold pressure.
[0005] One type of relief valve includes a movable element biased against a
valve
seat by a spring to maintain the valve in a closed state. When pressure acting
on the
valve element exceeds the force of the spring, the valve element moves away
from the
seat, thereby opening the pressure relief valve. In this type of valve, the
valve opens
as soon as the spring force is exceeded and closes immediately upon the
pressure
dropping below the spring force.
[0006] However, in some applications, it may be desirable for the valve not to
open
immediately when the pressure threshold is exceeded, but rather to delay
opening
until the excessive pressure exists for a given amount of time. Thus, such a
pressure
relief valve may be less affected by occasional short duration pressure events
which
exceed the threshold level. Nevertheless, when the pressure exceeds the
threshold
setting for longer than a specified amount of time, the valve opens to relieve
that
pressure before damage to the hydraulic system can occur. Similarly, it is
also
desirable in certain situations to delay the valve closing to ensure that the
pressure
remains below the threshold. This may prevent a momentary pressure decrease
from
closing the valve in a situation where pressure relief may still be required.
[0007] Numerous relief valves have been disclosed in the prior art. U.S.
Patent No.
6,957,660, assigned to Holder, discloses a pressure relief valve having a
valve
element that is biased by a spring into a closed position. A pressure being
controlled,
or regulated, is applied to the valve element to counter the force of the
spring. When
the pressure applied to the valve element exceeds the force of the spring the
pressure
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relief opens. When the pressure applied to the valve element falls below the
force of
the spring, the valve closes.
[0008] Further, U.S. Patent No. 3,945,395, assigned to Reinicke, et. al,
discloses a
vent and relief valve for a tank containing pressurized fluid characterized in
that
coaxial vent and relief valve members have inter-engaged seats to close the
vent
outlet of the valve. Vent and relief valve further comprises an actuating
means
associated therewith to disengage said seats to open communication between the
interior of the tank and the vent outlet of the valve as during filling of the
tank. The
relief valve member is actuated by fluid pressure in the tank exceeding a
predetermined value to move said relief valve member to disengage said seats
and
thereby again establish communication between the interior of the tank and the
vent
outlet of the valve thus to vent excess fluid pressure.
[00091 The American Petroleum Institute mandates certain standards which apply
to
the equipment used in subsea operations. The American Petroleum Institute,
commonly referred to as API, is the main U.S. trade association for the oil
and natural
gas industry. API is an American National Standards Institute ("ANSI")
accredited
standards developing organization, operating with approved standards
development
procedures and undergoing regular audits of its processes. API produces
standards,
recommended practices, specifications, codes and technical publications,
reports and
studies that cover each segment of the industry. API standards promote the use
of
safe, interchangeable equipment and operations through the use of proven,
sound
engineering practices.
[0010] API specification 16D discusses standards for electrical and electronic
chambers, a vessel on which a relief valve may be used. "All electrical and
electronic
chambers shall be double sealed at all areas exposed to seawater or
hydrostatic
pressure and should have a provision for a test port. These test ports shall
be plugged
and sealed when not in use for testing". (API 16D). As such, a relief valve
having a
double seal between the interior volume of a vessel and an exterior subsea
environment, as well as a test port, would be well received in industry.
Furthermore,
the ability to test both a front and backside of the seals as in a factory
acceptance test
would be highly desirable.
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Summary of Invention
[0011] In one aspect of the present disclosure, a relief valve for a pressure
vessel
includes a housing having an inner bore extending between an inlet and an
outlet, a
piston located within the inner bore, and a spring disposed about the piston
and
configured to bias the piston into a closed position. Furthermore, the relief
valve
includes a test port in communication with the inner bore, a removable test
plug
sealingly disposed within the test port, and a first seal and a second seal
disposed
within the inner bore on either side of the test port. Preferably, the first
and second
seals configured to engage the piston and hydraulically isolate the inlet from
the outlet
when the piston is in the closed position.
[0012] In another aspect of the present disclosure, a relief valve for a
pressure vessel
includes a housing comprising an inlet and an outlet, a piston located within
the
housing, the piston biased into a closed position by a spring, and a first
seal and a
second seal configured to hydraulically isolate the inlet from the outlet when
the
piston is in the closed position. Preferably, the piston configured to move
out the
closed position when a force exerted on the piston by fluids of the pressure
vessel
exceeds a force of the spring.
[0013] In another aspect of the present disclosure, a method to test a relief
valve
includes applying a test pressure to a backside of a first and a second seal
through a
test port of the relief valve.
[0014] Other aspects and advantages of the disclosure will be apparent from
the
following description and the appended claims.
Brief Description of Drawings
[0015] Figure l is a relief valve in a closed position in accordance with
embodiments
of the present disclosure.
[0016] Figure 2 is a relief valve in an open, or vent, position in accordance
with
embodiments of the present disclosure.
[0017] Figure 3 is a relief valve in a test position in accordance with
embodiments of
the present disclosure.
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[00181 Figure 4 is a relief valve in a closed position in accordance with
embodiments
of the present disclosure.
[0019] Figure 5 is a relief valve in a vent position in accordance with
embodiments of
the present disclosure.
Detailed Description
[0020] Embodiments disclosed herein relate to a relief valve for a subsea
pressure
vessel. More particularly, the present embodiments disclose an apparatus and
method
for a relief valve for a subsea pressure vessel.
[0021J Referring to Figure 1, a section view of a relief valve 100 is shown in
accordance with embodiments of the present disclosure. Relief valve 100
includes a
housing 102 having an inner bore 104 which allows communication between an
inlet
106 and an outlet 108. Relief valve 100 further comprises a piston 110
disposed in
inner bore 104, a spring 112 disposed in inner bore 104 and acting upon piston
110,
and a first seal 114 and a second seal 116, both of which are
circumferentially
disposed on and configured to dynamically seal on piston 110.
[0022] Relief valve 100 also includes a test port 118 in communication with
inner
bore 104, and a test plug 120 removeably and sealably disposed in test port
118.
Alternatively test port 118 and test plug 120 may be replaced with a test
valve without
departing from the present disclosure. Test plug 120 is described as being
removeably disposed in test port 118, therefore, it should be understood that
engagement in test port 118 could be accomplished by means such as threading,
welding, brazing, epoxy, and any other fastening method known to one of
ordinary
skill in the art. Further, sealably refers to any method know to one of
ordinary skill in
the art, including, but not limited to, elastomeric seals, rubber seals, metal-
to-metal
seals, etc. As shown in Figure 1, relief valve 100 is in a "closed" position,
wherein
spring 112 is uncompressed and piston 110 is in sealed engagement with first
seal 114
and second seal 116. Thus, as shown, relief valve 100 prevents communication
of a
pressure between inlet 106 and outlet 108.
[0023] Referring now to Figure 2, relief valve 100 is shown in a "vent"
position in
accordance with embodiments of the present disclosure. The vent position is
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described as when spring 112 is compressed and piston 110 is axially displaced
within
inner bore 104 and out of sealed engagement with first seal 114 and second
seal 116.
Pressure inside a vessel is constantly applied through an inlet onto an area
of an end
face 122 of piston 110. As the pressure inside the vessel increases and
reaches a
predetermined level, the force applied to end face 122 of piston 110 becomes
greater
than a force of spring 112 thereby causing axial displacement of piston 110.
As it is
displaced, piston 110 breaks contact with first seal 114 and second seal 116,
allowing
pressure to escape or "vent" through outlet 108. It should be noted that
pressure may
be unable to escape through relief valve 100 until piston 110 is out of
sealable
engagement with both first seal 114 and second seal 116.
100241 As pressure gradually decreases to acceptable levels within the vessel,
the
preset spring force of spring 112 is able to overcome the applied force from
the
vessel, and piston 110 is displaced back into sealable engagement with second
seal
116 at which point pressure is unable to vent. Piston 110 continues to be
displaced
and sealably engage first seal 114, at which point spring 112 is substantially
uncompressed and relief valve is once again in a closed position. Persons
having
ordinary skill in the art will recognize that the spring force acting upon the
piston may
be provided by any means known in the art including, but not limited to, metal
coiled
springs, Belleville washers, elastomeric springs, etc.
[0025] Referring now to Figure 3, relief valve 100 is shown in a "test"
position in
accordance with embodiments of the present disclosure. The test position is
described
as when the test plug (120 of Figure 1& 2) is removed from test port 118 and
pressure is able to be applied to "backside" surfaces of first seal 114 and
second seal
116. Backside 130 of first seal 114 is the face of the seal facing away from
inlet 106,
while backside 132 of second seal 116 is the face of the seal facing away
outlet 108.
Thus, backside 130 of first seal 114 and backside 132 of second seal 116 face
each
other.
[0026] Referring still to Figure 3, piston 110 maintains contact with both
first seal
114 and second seal 116 during a factory acceptance test (FAT). Test plug (not
shown) has been removed from test port 118 to allow access to "backsides" of
first
seal 114 and second seal 116 for pressure testing and a test pressure is
applied through
test port 118 and into inner bore 104. The test pressure may be a working
pressure of
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the valve to simulate working conditions, or any other appropriate pressure
know to
one of ordinary skill in the art. First seal 114 and second seal 116 may be
simultaneously tested to ensure proper sealing for seals between piston 110
and inner
bore 104. Upon completion of the FAT procedure, pressurization of inner bore
104
and test port 118 is discontinued and test plug (not shown) is reinstalled in
test port
1 I8. Persons having ordinary skill in the art will recognize that the test
plug may be
replaced with a test valve, etc. without departing from embodiments disclosed.
[0027] Referring now to Figure 4, a section view of a relief valve 200 is
shown in
accordance with enbodiments of the present disclosure. Relief valve 200
comprises a
housing 202 having an inner bore 204 which allows communication between an
inlet
206 and an outlet 208. Relief valve 200 further comprises a piston 210
disposed
within inner bore 204, a spring 212 disposed within inner bore, a first seal
214 and a
second seal 216 in sealing engagement with piston 210, and a test port 218
with a test
plug 220 removeably and sealably disposed within. Furthermore, piston 210
coi-nprises leak ports 222, which may include circumferential grooves, axial
grooves,
drilled holes or any other configuration known to one of ordinary skill in the
art.
Relief valve 200 is shown in a closed position, described as when piston 210
is
sealably engaged with first seal 214 and second seal 216 thereby disallowing
communication of pressure between inlet 206 and outlet 208.
[0028] Referring now to Figure 5, a section view of relief valve 200 is shown
in
accordance with embodiments of the present disclosure. Relief valve 200 is
shown in
a vent position, in which piston 210 has been displaced out of sealable
engagement
with first seal 214 by pressure inside of a chamber. Pressure inside the
chamber enter
inlet 206 is applied on an area of an end face 224 of piston 210. When the
pressure
inside the charnber reaches a certain level, it overcomes a preset force
applied to
piston 210 by spring 212, and begins to compress spring 212 and move piston
210 out
of sealable engagement with first seal 214. Also, a portion of the leak ports
222 is
displaced past second seal 216, thereby allowing full communication of
pressure
between inlet 206 and outlet 208.
[0029] As the pressure applied on the area of end face 224 decreases to a
level below
the preset force of spring 212, piston 210 is moved back into sealable
engagement
with first seal 214, and leak ports 222 are moved back into the closed
position so as to
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disallow fiu-ther communication of pressure through inner bore 204. Persons
having
ordinary skill in the art will recognize that the spring force acting upon the
piston may
be provided by any means known in the art, including, but not limited to,
metal coiled
springs, Belleville washers, elastomeric springs, etc.
[0030] Further, relief valve 200 may be configured in such a way as to test a
backside
of both seals. Referring again to Figure 4, test plug 220 may be removed and a
test
pressure applied through test port 218 and into inner bore 204. A test
pressure is
applied to backsides of both first seal 214 and second seal 216 with piston
210 in a
closed position. Upon coxnpletion of testing, pressure is discontinued and
test plug
220 is disposed within test port 218. Those having ordinary skill in the art
should
recognize that the test plug may be replaced with a test valve, etc. without
departing
from embodiments disclosed.
[0031] Furthermore, alternate embodiments of the present disclosure include a
relief
valve comprising seals, wherein at least one of the seals may be a metal-to-
metal seal.
In selected embodiments, the metal-to-metal seal may be the first or primary
seal,
while the second seal may be an elastomeric seal. Alternatively, the metal-to-
metal
seal may be the second seal, while the first seal is an elastomeric seal.
Alternatively
still, both the first and second seals may be metal-to-metal seals. However,
it should
be understood that embodiments using metal-to-metal seals may require a spring
having a larger spring force because of the high contact stresses that may be
needed to
create a metal-to-metal seal. Further, alternate embodiments of the present
disclosure
may include a first seal area that is larger than the second seal area.
Because of the
larger first seal area, the valve may be able to relieve, or vent, at lower
pressures.
[0032] Einbodiments of the present disclosure advantageously allow for a
backside
seal test of both seals. Reciprocating motion, as is present between the
piston and the
two seals adds a extra dimension to the sealing problem. Friction, and its
associated
wear, join a list of factors that must be contended with including
temperature, fluid
compatibility, and pressure. The seals used for sealing a reciprocating member
must
meet static and dynamic sealing requirements at their contact areas with the
stationary
mennber, which is the inner bore, and also seal effectively at their contact
areas on the
reciprocating member, in this case the piston. To ensure reliability of a
seal, it may be
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desirable and advantageous to be able to test both sides of a seal from
opposite
directions.
[0033] Further, embodiments of the present disclosure preferably conform to
API
standard 16D, which requires a "double seal" between an inner chamber of a
pressure
vessel and an outer subsea environment. Since the relief valve provides
communication between the two, a double seal is a desirable feature. According
to
API Specification 16D, chambers shall be double sealed at all areas exposed to
seawater or hydrostatic pressure. Furthermore, a test port may be used, and
when
present should be plugged and sealed when not in use for testing. The double
seal
configuration of relief valve is a built-in redundancy that may be appreciated
by one
of ordinary skill in the art.
[0034] While the invention has been described with respect to a limited number
of
embodiments, those skilled in the art, having benefit of this disclosure, will
appreciate
that other embodiments can be devised which do not depart from the scope of
the
invention as disclosed herein. Accordingly, the scope of the invention should
be
limited only by the attached claims.
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