U.S. patent application number 09/779661 was filed with the patent office on 2002-08-15 for partial stroke testing system.
Invention is credited to Albuaijan, Tareq Nasser.
Application Number | 20020108436 09/779661 |
Document ID | / |
Family ID | 25117114 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020108436 |
Kind Code |
A1 |
Albuaijan, Tareq Nasser |
August 15, 2002 |
PARTIAL STROKE TESTING SYSTEM
Abstract
A partial stroke testing system for online testing of emergency
shut-off valve, said system is designed for implementation on an
emergency shut-off valve with a main solenoid with manual reset,
main solenoid valve, quick exhaust valve and a pneumatic actuator
connected to a source of pressurized air supply for opening and
closing the said emergency shut-off valve and the said shut-off
valve normally movable between a fully open and fully closed
position. The system also include control means programmed into the
plant emergency shutdown system controller for initiating
electrical signal for initiating a test and for enhancing the bleed
rate from the said pneumatic actuator in the event of a emergency
trip signal. Test means for testing the said emergency shut-off
valve without fully closing the emergency shut-off valve in
response to signal from the said control means is included in the
system. The said test means, controlled by the said control means,
include a second solenoid and a second solenoid valve for bleeding
off pressurized air to thereby move the said emergency shut-off
valve from full opened position to partially closed position. Means
for limiting the movement of said emergency shut-off valve to a
partially closed position because of the bleeding of pressurized
air is included in the system. The system also includes an
isolation valve for isolating the said test means for maintenance
purpose.
Inventors: |
Albuaijan, Tareq Nasser;
(Khaldiya, KW) |
Correspondence
Address: |
DOUGHERTY & TROXELL
SUITE 1404
5205 LEESBURG PIKE
FALLS CHURCH
VA
22041
US
|
Family ID: |
25117114 |
Appl. No.: |
09/779661 |
Filed: |
February 9, 2001 |
Current U.S.
Class: |
73/168 ;
73/865.9 |
Current CPC
Class: |
F16K 37/0083
20130101 |
Class at
Publication: |
73/168 ;
73/865.9 |
International
Class: |
G01M 019/00; G01N
019/00 |
Claims
What is claimed is:
1. A partial stroke testing system for online testing of emergency
shut-off valve, said system implemented on an emergency shut-off
valve normally movable between fully open and fully closed
position, control means for initiating an electrical signal for
initiating a test, a source of pressurized gas and means including
a main solenoid, a main solenoid valve quick exhaust valve and a
pneumatic actuator for opening and closing the said shut off valve,
test means for testing the said emergency shut-off valve, test
means for testing the said emergency shut-off valve without fully
closing the emergency shut-off valve in response to a signal from
the said control means, said test means including a second
solenoid, a second solenoid valve for bleeding off pressurized gas
to thereby move said emergency shut-off valve from full opened
position to partially closed position, means for limiting the
movement of said emergency shut-off valve to a partially closed
position as a result of the bleeding off of pressurized gas and
means for detecting actual movement of said emergency shut-off
valve.
2. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 1, which includes a second
solenoid valve (PITT solenoid valve) for bleeding of pressurized
air to thereby close said emergency valve to partial limit.
3. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 2, which includes an isolation
valve between said second solenoid valve said pneumatic actuator
for isolating the said second solenoid valve from the rest of the
system.
4. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 1, which includes control
sequence programmed into the plant emergency shutdown system
controller which acts as control means for initiating partial
stroke test on said shut-off valve.
5. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 1, in which the means for
detecting the movement of the said emergency shut-of valve is a
limit switch.
6. A partial stroke testing system for online testing of emergency
shut-off valve which includes a partial stroke limit switch to
indicate the partial valve closure during the test of an emergency
shut off valve.
7. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 2, which bleeds pressurized gas
from the shut-off valve actuator during partial stroke checking of
emergency shut-off valve.
8. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 4, in which backup means for
terminating the partial stroke test is the timer programmed in to
the plant emergency shutdown system controller.
9. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 2, which bleeds pressurized air
from the system during emergency closure (trip) of the said
emergency shut-off valve to enhance the bleed rate and act as a
backup to the main solenoid valve and quick exhaust valve in the
event of unsafe failure of the said main solenoid valve and quick
exhaust valve.
10. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 2, which includes means of
monitoring the full stroke travel time of said emergency shut-off
valve in the event of emergency closure of the said emergency
shut-off valve as a result of a trip signal from the plant
emergency shutdown system controller.
11. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 2, which includes means
preventing inadvertent manual opening of the said emergency
shut-off valve, subsequent emergency closure of the said emergency
shut-off valve as a result of a trip signal from the plant
emergency shutdown system controller and prior to reset of trip
signal in the plant emergency shutdown system controller.
12. A partial stroke testing system for online testing of emergency
shut-off valve according to claim 2, which includes means for
initiating partial stroke test manually or at programmed intervals
from a computer interfaced to plant emergency shutdown system
controller and to generate printed report of test results.
13. A partial stroke testing system for testing of emergency
shut-off valve according to claim 2, which can be implemented as a
portable and self contained test apparatus for conducting partial
stroke test on shut-off valves controlled by non-programmable
shutdown system.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a partial stroke testing system
and more particularly to a partial stroke testing system for the
online testing of an emergency shut-off valve.
BACKGROUND FOR THE INVENTION
[0002] In the oil, gas, petroleum and power industries, various
conditions may occur that necessitate immediate shut down or
tripping of the operations, process or plant In those industries, a
majority of the final control element of shutdown systems are
implemented with fast acting shut-off valves. In such industries, a
majority of the shut-off valves remains open while the process is
in a safe and controlled state. Such valves are closed only upon a
plant trip rising from an out of control process or during a normal
maintenance outage.
[0003] In practice, the testing of emergency shut-off valve is
normally done during shut down of the process. However, there is
tendency for such valves to stick or freeze due to corrosion or
other reasons, which lead to an unsafe condition. This problem is
exacerbated by economic conditions which have lead to a reduction
in the frequency of shutdowns. For example, in some operations, a
process may run continuously for one or more years without shutting
down the process for maintenance.
[0004] State of the art emergency shutdown systems, which control
the shut-off valves, have a number of features to detect plant or
process failures and typically include redundancies for added
reliability. However, such systems may not provide for the testing
of shut-off valves itself other than stroking the valve. The
problem is that full stroking or completely closing the valve
causes an undesirable disruption in the process.
[0005] Recognizing that the emergency shut-off valve can be stroked
partially as a safeguard against frozen or stuck valve has lead to
a need for a simple, secure and reliable system for testing such
valves without adversely effecting production. This approach will
also improve the safety of the operation.
[0006] It is now believed that a partial stroke testing system in
accordance with the present invention will provide a low cost,
simple and reliable test for emergency shutdown valves in the oil,
gas, petrochemical and power industries. Such tests will not
adversely interrupt a process and will minimize or almost eliminate
the risk of a "frozen" emergency shutoff valve in the event of an
out of control process. The system in accordance with the present
invention is cost effective and has been designed to utilize a
shut-off valve with fast acting piston actuator. The system is also
applicable to slow acting valves.
[0007] In addition, the partial stroke testing system in accordance
with the present invention will not interfere with a plant trip,
i.e. a full shut down due to an emergency condition. Furthermore,
if a partial stroke test is being conducted at the time of a plant
trip, the partial stroke test will contribute to a more rapid
closing of the emergency shut-off valve. Thus, the partial stroking
design acts as a backup to the main trip mechanism. Accordingly,
such systems should reduce the cost of insurance or risk coverage.
In essence, the system partially closes the emergency shut-off
valve to a predetermined position to test and confirm its ability
to function and to ensure its availability on demand in the event
of a plant emergency.
BRIEF SUMMARY OF THE INVENTION
[0008] In essence, the present invention contemplates a partial
stroke testing system or apparatus for the online testing of
emergency shut-off valves. Such systems are particularly applicable
in the oil, gas and petrochemical industries. The system is
designed for implementation on an emergency shut-off valve, which
is normally movable between a fully opened and a fully closed
position. As contemplated by the preferred embodiment of the
invention, the emergency shut-off valves will be in its fully
opened position during operation of a process and will rapidly
close to shut down the process in the event of an emergency. The
system is designed for interfacing to the plant emergency shutdown
system controller for generating electrical signals for initiating
the test and to a source of pressurized gas such as compressed air
for driving the system. The essential control components of an
emergency shut-off valve are the main trip solenoid valve with
manual reset, quick exhaust valve and the pneumatic actuator. On a
trip signal, the solenoid valve de-energizes signaling the quick
exhaust valve to vent the actuator and close the shut-off valve.
The invention provides a test means for testing the emergency
shut-off valve without fully closing the emergency shut-off valve
in response to a signal from the plant emergency shutdown system
controller. The test means includes a second solenoid valve for
bleeding off compressed air to thereby move the emergency shut-off
valve from a fully opened position to a partially closed position.
Means such as closed limit switch which may be operable on the
basis of the movement of the shut-off valve is provided. Means such
as a timer set to a predetermined time limit to terminate the
shut-off valve test in the event of the limit switch failure is
also provided. In addition, means for initiating cyclical or
periodical testing and reporting of test results of the partial
stroking of the emergency shut-off valve is provided.
[0009] The invention will now be described in connection with the
accompanying drawings.
DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is schematic illustration of a partial stroke testing
system in accordance with a preferred embodiment of the
invention;
[0011] FIG. 2 is a flow chart, which illustrates the operation of a
partial stroke testing system software, residing in the plant
emergency shutdown system controller, in accordance with the
present invention and
[0012] FIG. 3 is a flow chart, which illustrates the operation of
the software, residing in the plant emergency shutdown system
controller, controlling the partial stroking means in the event of
an emergency trip signal from the plant emergency shutdown system
controller in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
[0013] It is well known in the oil, gas and petrochemical
industries that emergency shut-off valves are susceptible to a
build-up of frictional forces which if undetected can cause failure
of the emergency shut-off valve during an out of control process.
It is for this reason, that the various regulatory agencies
concerned with the safety of such operations, mandate periodic
shut-off valve testing and inspection in order to ascertain
shut-off valve availability.
[0014] As disclosed herein, a partial stroke test system tests an
emergency shut-off valve on-line, i.e. without shutting down the
process, for free movement over a small portion of its full stroke.
Therefore, tests can be performed at frequent intervals. By so
doing, there is a high probability of ensuring the emergency
shut-off valve's operability, which reduce the likelihood of
failure of an emergency shut-off valve during extended runs.
[0015] In the oil, gas and petrochemical industries, emergency
shut-off valves generally remain open while the process is in a
safe and controlled state. These valves close only upon a plant
trip, which arises from an out of control process. The emergency
shut-off valve typically includes a pneumatic cylinder which drives
an emergency shut-off valve into a fully closed position within
about one second.
[0016] A partial stroke testing system 10, incorporated in a
shut-off valve for use in the oil, gas, petrochemical and power
industries is illustrated schematically in FIG. 1. Such system is
incorporated in an emergency shut-off valve 20 which remains in an
open position during normal process conditions. Compressed air from
a source 22 is used for maintaining the valve 20 in an open
position. The compressed air maintains the valve 20 in an open
position by driving a spring biased piston actuator 24. The
compressed air is connected with the spring biased actuator 24
through a main solenoid valve 26 and a quick exhaust valve 28. The
source 22 of compressed air is connected to the main solenoid valve
26, quick exhaust valve 28 and actuator 24 by tubing 23, 25 and
27.
[0017] In the event of plant trip i.e. an out of control process, a
signal as for example from plant emergency shutdown system
controller 30 actuates a solenoid 32 which closes the main solenoid
valve 26 with respect to the pressurized air from the source 22 and
allow the air from tubing 25 to exhaust through an exhaust port
26A. The release of pressure against the quick exhaust valve 28
opens an exhaust port 28A allowing the actuator 24 to bleed through
tubing 27, quick exhaust valve 28 and exhaust port 28A and close
the shut-off valve 20 and thereby shut down the process or
plant.
[0018] The partial stroke testing portion of the system 10 includes
a second solenoid 40 and second solenoid valve 42. That portion
also includes an isolation valve 44. The second solenoid valve 42
is operatively connected to the actuator 24 through tubing 47,
isolation valve 44, tubing 43 and "T" connection 45 through tubing
27.
[0019] For a partial stroke test, a signal from the plant emergency
shutdown system controller 30 energizes the second solenoid 40
which opens the second solenoid valve 42 to bleed off compressed
air so that the spring biased actuator 24 partially closes the shut
down valve 20. This partial closing is limited by partial stroke
limit switch 52, which sends a signal to plant emergency shutdown
system controller 30 in a conventional manner. The plant emergency
shutdown system controller 30 de-energizes the solenoid 40 to
thereby close the second solenoid valve 42 and the shut-off valve
returns to fully open state. By limiting the movement of the shut
down valve 20 by time or stroke, there is no interruption of the
process. Nevertheless open limit switch 53 and partial stroke limit
switch 52 provide signals to the plant emergency shutdown system
controller 30 that the valve actually moved which indicate it is
not frozen or stuck. Suitable sensing means such as a linear
variable transducer can also be used to check that the valve 20 has
in fact been displaced in response to the signal from the plant
emergency shutdown system controller 30. If the linear variable
transducer indicate that a preselected degree of deflection has
occurred, the valve tested has been shown to be free to move.
[0020] However, if the sensing means indicate that the deflection
has not occurred, signal is sent to the plant emergency shutdown
system controller 30 indicative of the fact. Suitable alarm is to
be provided to indicate that the valve is stuck and to initiate
corrective action.
[0021] The magnitude of the displacement may be any suitable degree
to positively indicate that the valve movement is possible, but
must not be of such magnitude as to disrupt the process or the
plant operation and will ordinarily be accomplished in few seconds
or less.
[0022] The plant emergency shutdown system controller 30 may be
interfaced to a computer 54 to initiate periodic partial stroking
of the shut-off valve 20. The computer 54 is also used to record
the results of each test, which may be printed out on a printer 56.
The isolation valve 44 isolates the second solenoid valve 42 from
the shut-off valve system for maintenance without affecting the
operation of the shut-off valve.
[0023] The manual latch facility 37 in the main solenoid valve
allows the operators to manually open the shut-off valve, after
field verification, subsequent a trip and reset of the trip
signal.
[0024] The control sequence, for conducting the partial stroke test
of shut-off valve, programmed into the plant emergency shutdown
system controller 30 (FIG. 1) is illustrated in FIG. 2. The Partial
Instrument Trip Testing (PITT) or partial stroking of the shut-off
valve is initiated by the plant emergency shutdown system
controller 30 (FIG. 1) by initiating the execution of the program
sequence illustrated in FIG. 2. Starting at step 60 the plant
emergency shutdown system controller 30 (FIG. 1) energizes power
supply to the solenoid 40 (FIG. 1) of the solenoid valve 42 (FIG.
1) and start an internal timer as indicated in step 61. On
energisation of the solenoid 40 (in FIG. 1), the solenoid valve 42
(FIG. 1) opens and bleed the actuator air supply causing the
actuator 24 (in FIG. 1) to move the shut-off valve 20 (FIG. 1)
towards the closed position.
[0025] The shut-off valve movement to partial limit is checked in
step 64. If the shut-off valve 20 (FIG. 1) has reached the partial
limit, the program sequence proceeds to step 66 to de-energise the
solenoid 40 (in FIG. 1) to close the solenoid valve 42 (FIG. 1) and
to stop the timer. The actuator 24 (FIG. 1) on closure of the
solenoid valve 42 (in FIG. 1) gets full air supply and drive the
shut-off valve 20 (in FIG. 1) to fully open position. The program
sequence then proceeds to step 68 to set the status of the test as
pass and to step 70 for generating test report and archiving of
test data. After generating the test report and archiving the test
data, (valve Tag. No, test status and test duration), the test
control sequence is terminated at step 72 and divert to other
applications in the plant emergency shutdown system controller 30
(FIG. 1).
[0026] In the event that the shut-off valve has not closed to its
partial limit in step 64 and the test timer (PITT timer) has not
timed out as in step 71, the control sequence returns to step 62
and loop through steps 64 and 71 until either the valve reaches the
partial limit or the PITT timer time out.
[0027] In the event that the shut-off valve has not closed to its
partial limit in step 64 and the test timer (PITT timer) has timed
out as in step 71, the control sequence goes to step 73 to
de-energise the solenoid 40 (FIG. 1) to close the solenoid valve 42
(FIG. 1). The actuator 24 (FIG. 1) on closure of the solenoid valve
42 (FIG. 1) gets full air supply and drive the shut-off valve 20
(FIG. 1) to fully open position. The program sequence then proceeds
to step 75 to set the status of the test as fail and to step 70 for
generating test report and archiving of test data. After generating
the test reports and archiving the test data, (valve Tag. No, test
status and test duration), the test control sequence is terminated
at step 72 and divert to other applications in the plant emergency
shutdown system controller 30 (FIG. 1).
[0028] A bleed enhancement scheme in accordance with the embodiment
of the invention is illustrated in FIG. 3. The bleed enhancement is
achieved by implementing the control scheme as indicated in FIG. 3
in the plant emergency shutdown system controller 30 (FIG. 1) as an
application program routine. The program is initiated in the event
of an emergency trip signal at step 80. On an emergency trip, plant
emergency shutdown system controller 30 (FIG. 1) issues a trip
signal to de-energise the main solenoid valve 26 (FIG. 1), energise
the PITT solenoid valve 42 (FIG. 1) and starts a valve stroke timer
as in step 81. The PITT solenoid valve 42 (FIG. 1) will remain
energised and the valve stroke timer continue to run as indicated
in step 82 until the shut-off valve is fully closed as in step 83.
Up on full closure of the shut of valve the timer is stopped as in
step 84. The plant emergency shutdown system controller 30 (FIG. 1)
will then generate a full stroke report and archive the valve
stroke time data as in step 85. Upon completion of the report
generation and data archiving task the control sequence is
terminated at step 86 and divert to other applications in the plant
emergency shutdown system controller 30 (FIG. 1).
[0029] The PITT solenoid valve 42 (FIG. 1) will remain energised
until the trip is reset. The additional bleed introduced by the
solenoid valve 42 (FIG. 1) will enhance the shutdown performance of
the shut-off valve.
[0030] A partial stroke testing system for on line testing of
emergency shut off valves can also implemented as a portable self
contained test apparatus for conducting partial stroke test on shut
off valves which are controlled by non-programmable shutdown
system.
[0031] While the invention has been described in connection with
its preferred embodiments, it should be recognized that changes and
modifications may be made therein without departing from the scope
of the applied claim.
* * * * *