Note: Descriptions are shown in the official language in which they were submitted.
CA 02714125 2014-11-05
METHOD OF TESTING FOR LEAKS IN A CONTAINED SYSTEM
TECHNICAL FIELD
[0001] This document relates to methods of testing for leaks in a
contained system.
BACKGROUND
[0002] Leak detection systems incorporate the injection of tracer fluid
into a tank and
the use of sensors outside the tank to detect for the presence of leaked
tracer. Most detection
systems require that operating fluid be first removed entirely from the tank,
resulting in
downtime and cost to the tank operator. Some detection systems are able to
work while
operating fluid is present and the tank is in operation, for example the
systems disclosed in
US patent nos. 5,767,390, and 4,709,577. However, such systems usually require
a mixing
device for dispersing tracer gas uniformly throughout the fluid and have
lengthy response
times.
[0003] Leak detection systems may incorporate permanent cable sensors
along a
length of a pipeline or underground tank that allow fluid diffusion along the
length of the
cable for detection of leaks.
SUMMARY
[0004] A method of testing for leaks in a contained system, the method
comprising:
pressurizing an interior of the contained system, wherein the interior
contains system gas and
system liquid at an operating pressure, the system liquid and the interior
defining a
headspace of system gas above the system liquid, wherein pressurizing the
interior includes
introducing gas comprising tracer gas directly into the headspace, in which
the tracer gas is
soluble in the system liquid, to at least 0.5 pounds per square inch above the
operating
pressure to disperse the tracer gas throughout the system liquid; and sensing
for the presence
of the tracer gas using one or more sensors located outside the contained
system to detect
tracer gas that has escaped the contained system and traveled from the
contained system to
the one or more sensors.
CA 02714125 2014-11-05
[0005] In further embodiments, pressurizing further comprises flushing the
system
gas out of the interior during introduction of the gas into the interior. The
gas may comprise
carrier gas. The carrier gas may be inert. The tracer gas may be present in
the gas at a
concentration of up to 10% by volume of the gas.
[0006] In further embodiments, the method is carried out while the
contained system
is in operation. The interior may be pressurized to at least 1 pound per
square inch above the
operating pressure. The interior may be pressurized to at most 5 or 15 pounds
per square inch
above the operating pressure.
[0007] In further embodiments, the contained system comprises one or more
of a
pipeline, a tank, or a liner. The contained system may be underground.
Pressurizing may
further comprise continuously introducing the gas into the interior throughout
sensing for the
presence of the tracer gas. The one or more sensors may comprise an array of
riser wells.
BRIEF DESCRIPTION OF THE FIGURES
[0008] Embodiments will now be described with reference to the figures, in
which
like reference characters denote like elements, by way of example, and in
which:
[0009] Fig. 1 is a side elevation view of a contained system that is being
tested for
leaks.
[0010] Fig. 2 is schematic of a tracer gas mixing system.
[0011] Fig. 3 is a side elevation view of different types of contained
systems that the
method may be used on.
[0012] Fig. 4 is a flow diagram of a method of testing for leaks in a
contained
system.
[0013] Fig. 5 is a side elevation view of a leak detection apparatus.
[0014] Fig. 6 is a front elevation view of a plurality of tubes dispersed
about the front
exterior of a contained system.
[0015] Fig. 7 is a side elevation view of a sampling inlet end of a tube.
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[0016] Fig. 8 is a flow diagram of a method of testing for leaks in a
contained system
with an interior containing a unique fluid species.
DETAILED DESCRIPTION
[0017] Immaterial modifications may be made to the embodiments described
here
without departing from what is covered by the claims. The figures are not
drawn to scale,
and other components not mentioned may be present in order to allow the
disclosed methods
to be carried out.
[0018] Changing legislation, evolving technologies, environmental
awareness, and
aging infrastructure have all challenged companies to assess exposure to the
potentially
damaging environmental, public relations, and financial, risks caused by
undetected leaks in
petroleum storage facilities and associated piping. Thus, integrity testing of
for example
underground storage tank (UST) and above-ground storage tanks (AST) has become
a
lucrative market. Various systems and methods for leak testing of storage
tanks and
pipelines, often used for petroleum crude or refined-product storage and
transport, have been
introduced to meet this need. One method to detect leaks in these vessels and
pipelines
involves adding a specialty compound or mixture (called a "tracer") to the
product being
stored or moved that is both soluble in the product and not ordinarily present
in the product
or in the environment. Subsequent detection of this tracer compound or mixture
outside the
vessel or pipeline system can demonstrate that the tracer mixture has escaped
the system,
thereby indicating the system has developed a leak.
[0019] A typical tracer release detection application involves blending a
tracer such
as sulfur hexafluoride (SF6) (a nontoxic, inert gas) with petroleum-related
products in a
pipeline or storage tank. Halogenated nonpolar compounds, halogenated
methanes,
halogenated ethanes, halogenated propanes and propenes, halogenated butanes,
cyclobutanes
and butenes have also been used as tracers to test fuel storage and pipeline
systems. Tracer
compounds have also been used to locate the underground presence and/or
movement of
water, soil gases, petroleum, or natural gas. Tracers have also been used to
help define the
presence and continuity of geologic faults and permeable formations. In each
case, the
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specialty compound or mixture, soluble in the phase or medium of interest and
not ordinarily
present in the environment, is introduced at a particular location. Successful
sampling for the
tracer at points removed from the original release point then indicates
"communication" with
or "continuity" to the original release point.
[0020] Conventional tracer release detection methods to detect fuel leaks
involve
analyzing soil vapors drawn from sampling wells surrounding the fuel storage
system for
evidence of the tracer escaping the storage system. Typically, companies using
tracer-related
test methods locate sampling wells in the soil adjacent to fuel storage
equipment. A
background sample is usually taken prior to introducing the tracer compound
into the fuel
storage system to provide a baseline for the soil surrounding the storage tank
prior to the
actual tracer-related test.
[0021] After installing sampling wells and taking background tracer
measurements, a
technician will typically introduce one or more tracer chemicals in either gas
or liquid phase
into the fuel storage system. A predetermined mass of tracer(s) is inserted
into the fuel
storage system through a tubing line inserted into the storage tank, which is
usually
connected to a fritted diffuser for mixing. An alternative tracer introduction
system can
involve placing an enclosed gaspermeable membrane containing a given mass of
tracer(s)
into the storage tank and having the tracer release through the membrane over
a period of
time. If a storage system has a leak, the tracer may escape the storage system
with the fuel.
[0022] After a predetermined time period has elapsed, a technician may use
a
vacuum pump attached either to the top of the sampling well, or to tubing
placed into the
well, to draw soil vapors through the bottom end of the sampling well into a
sample
container. Typically, some portion of the soil vapor sample in the container
is injected into a
gas chromatograph equipped with an electron capture detector (ECD) to analyze
the vapor
sample for the presence of the tracer. These test samples are then compared to
the
background samples to determine if a product leak exists.
[0023] Referring to Fig. 1, a contained system 10, such as a tank 12 below
a ground
level 14, is illustrated as having an interior 16. Interior 16 may contain
system liquid 18 and
system gas, for example in headspace 20, at an operating pressure. Tank 12 may
be for
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example a gasoline storage tank at a petroleum service station, and may be
connected
through a line 21 to a gas pump 19 above ground level 14. Referring to Fig. 3,
the contained
system 10 may comprise one or more of a pipeline 58 or liner 60, in addition
to the tank 12
illustrated in Fig. 1. Referring to Fig. 1, the system liquid 18 and system
gas refer to fluids
that are present in the system 10 before the method is carried out.
[0024] Referring to Fig. 4, a method of testing for leaks in a contained
system is
illustrated. The various stages of the method will now be described with
reference to figures
other than Fig. 4. As indicated, prior to the method being carried out, system
10 is at an
operating pressure. The operating pressure may be at or above atmospheric
pressure, and
may be a normal operating pressure of the system 10 for example during
operation.
[0025] Referring to Fig. 1, in a stage 100 the interior 16 of the
contained system 10 is
pressurized, by introduction of gas comprising tracer gas into the interior
16, to at least 0.5
pounds per square inch above the operating pressure to disperse the tracer gas
above a
threshold concentration throughout the system liquid 18. A threshold
concentration is a
concentration above which the tracer gas is sufficiently dispersed to be
detectable by sensors
placed outside the vessel. The threshold concentration may vary depending on
the number
and sensitivity of sensors 26 used in the method. Stage 100 may be carried out
on tank 12 by
connecting a tracer gas source 22 to a line 24 into tank 12. Line 24 may be an
injection line
for storage fluids, for example. If a substantial leak is located above the
system liquid 18,
pressurization to the desired level may not be possible or required. In a
stage 102, the
presence of the tracer gas is sensed using one or more sensors 26 located
outside the
contained system 10.
[0026] Pressurizing may comprise flushing the system gas out of the
interior 16
during introduction of the gas into the interior 16. For example, a vent 28
may be used to
flush out the system gas as the tracer is introduced via input line 24. By
controlling the
output flow of system gas through vent 28, the desired pressurization of
system 10 may be
maintained during flushing. For example, a controllable restrictor 29
connected to vent 28
may be used to adjust the size of the outlet (not shown) for system gas to
flow through. The
gas flushed out through vent 28 may be collected, for example to prevent
flushed gas
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containing tracer gas from interfering with sensor 26 operation. Flushing
allows the
headspace 20 volume of system gas to be replaced with the introduced gas
comprising tracer
gas at the desired pressure. This allows a relatively large amount of tracer
gas to be
introduced even if injected at a low concentration in inert carrier gas, and
also ensures that
system gases such as oxygen that may negatively react with the tracer gas are
expelled from
the system 10.
[0027] The interior 16 may be pressurized to at least one pound per square
inch
above the operating pressure, and may be further pressurized in some
embodiments to five or
fifteen pounds per square inch above the operating pressure depending on for
example the
expected integrity of the vessel being tested. The increase in pressure
increases the solubility
of the tracer gas in the system liquid, thereby forcing the tracer gas like a
plunger throughout
the system liquid in a more efficient and quick manner than conventional leak
detection
systems. This effect is analogous to the increased dissolution of nitrogen in
a diver's blood
as the diver moves to lower depths underwater. As a result of the increased
pressure, no
mixing devices such as fritted diffusers are required to achieve fast and
effective tracer gas
dispersal throughout the system liquid.
[0028] The level of pressure increase may be selected by consideration of
various
factors. In determining the maximum pressure to apply, the pressure increase
should be
limited to a level below the burst pressure of the vessel. In general, burst
pressure is more
relevant to above-ground systems than underground systems because the pressure
of backfill
surrounding underground systems increases the resistance of the system to
bursting. For
above-ground systems, pressure may be applied incrementally, for example in 03
psi
increments through a multi-step regulation process, in order to reduce the
risk of bursting. In
addition, in some embodiments a maximum of a five psi increase may be adopted
to avoid a
potential garden-hose situation where a large volume of system liquid is
continually and
uncontrollably propelled out of the system by a large backing pressure.
Determining the
minimum pressure increase to apply depends on consideration of pressures
outside the
system that may oppose leakage of system liquid. Thus, for an underground tank
located
below the water table, the pressure applied should be sufficient to ensure
that fluid in the
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system is able to overcome the hydrostatic pressure of the groundwater at the
base of the
tank in order to allow tank fluids to leak out of the tank for detection of
dissolved tracer(s).
For above ground tanks, the pressure need only increase above the atmospheric
pressure. For
double-walled vessels, the minimum pressure increase required may be even less
because the
interstitial space may be under vacuum. Moreover, the amount of system liquid
in the vessel
may be considered in determining how much pressure increase to apply. Greater
volumes of
system liquid generally require greater pressures to adequately disperse the
tracer gas in a
given amount of time. Although pressurization has been used on empty tanks in
the past, the
Applicant believes that pressurization was not used in the fashion disclosed
herein on
systems 10 containing system liquid 18 because it would have been thought that
such a large
increase in pressure could result in tank rupture or an uncontrollable leakage
of system liquid
from the system. However, the benefits observed with the disclosed method have
been found
to outweigh such risks.
[0029] The methods disclosed herein allow the gas to be introduced into
headspace
20 of system gas defined by the system liquid 18 and the interior 16 above the
system liquid
18. In some embodiments, however, the gas may be introduced directly into the
system
liquid 18, for example using tracer gas source 56 and line 57. Source 56 may
be located
remotely, for example several kilometers away from system 10. In the field,
the systems
disclosed herein can achieve sufficient tracer gas dispersal in the system
liquid in several
minutes, even when performing the method on large tanks such as 40000 L
underground
storage tanks. Dispersal refers to the achievement of tracer gas concentration
that is at least
at a predetermined threshold concentration throughout the system liquid at
which point
accurate sensing may begin. Time to dispersal depends on various factors,
including the
height of system liquid 18, the size of headspace 20 and the pressurization of
the system 10.
[0030] Referring to Fig. 2, as indicated above, the gas introduced into
the interior 16
may comprise carrier gas, for example inert gas like nitrogen or argon. Argon
may be
desirable because gas chromatography is able to detect argon. The =Tier gas
may be located
in a carrier gas storage unit 48, while the tracer is present in a tracer
storage unit 50.
Respective regulators 52 and 54 may be controlled, for example using
controller 36, to
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combine tracer and carrier gas in the desired concentration prior to
introduction into system
10. Using carrier gas allows a reduction, in the introduced gas, of the
concentration of tracer
gas, which is generally expensive and may be explosive at higher
concentrations when in the
presence of oxygen. In one embodiment the tracer gas is present in the gas at
a concentration
of up to 10 % by volume of the introduced gas. In another embodiment tracer
gas is present
in the gas at up to 5% by volume of the gas. Pressurizing in stage 100 may
further comprise
maintaining the pressure in the interior 16 at least 0.5 pounds per square
inch above the
operating pressure during the sensing stage 102, for example if the gas is
introduced
continuously into the interior 16 throughout the sensing stage 102.
[0031] Referring to Fig. 1, because the method is designed to operate
while the
system liquid 18 is in the contained system 10, the method may be carried out
while the
contained system 10 is in operation. Thus, a pipeline operator or tank
operator may have his
or her contained system 10 checked for leaks with zero downtime and no lost
profits. In
addition, tracer gas can be rapidly flushed from the system using carrier or
other gas upon
completion of the method. Thus, tracer gas need not be always present in
fluids stored in the
contained system 10.
[0032] Referring to Fig. 1, once sufficient dispersal is reached, any
fluids 30 that leak
from the contained system 10 through a leak 32 will have a sufficient
concentration of tracer
gas for detection by the one or more sensors 26. Dotted lines are used in Fig.
1 to indicate the
travel of tracer gas through the soil after exiting system 10 with leaked
fluids 30. The sensing
stage 102 may further comprise collecting fluids and then analyzing the fluids
for the
presence of tracer gas. Analysis may be carried out on site, for example by
performing the
analysis in a control vehicle (not shown) or within the sensor 26 itself, or
remotely, for
example by transporting samples collected by sensors 26 to a remote facility.
Initially, the
sensing stage 102 may simply be looking for the presence of any tracer gas
irrespective of
the exit location from the system 10. Thus, carpet probes (not shown) or other
relatively
imprecise sensory systems may be used. If tracer gas is detected, then a more
precise
detection may be carried out to pinpoint the location of leak 32. For example,
an array of
riser wells 34 may be positioned at sufficient distances around tank 12 using
water pic
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installation for example. Riser wells 34 may allow sensors 26 to locate the
leak 32 to within
several centimeters. After the leak 32 location is confirmed, targeted
excavation may proceed
to uncover and repair the leak 32, if the system 10 is underground. If the
system is above
ground, the leak 32 may simply be repaired. Other detection systems such as IR
imaging
may be used to confirm the presence of the leak.
[0033] Test duration may be taken from tables of pre-calculated saturation
times for
the ullage and product portion of the system being tested. If using the array
of riser wells 34
sampling method, test times may be <1 minute. If samples are taken directly
off the surface
of the cover material different test duration may be encountered and may be <5
minutes but
dependant on cover material. The soil vapor samples may be collected using a
vacuum pump
to draw the soil vapor through the array of riser wells 34. The soil vapor may
then be sent to
a test vehicle (not shown) via hoses attached to each riser well 34. If sent
to the test vehicle
the vapor may pass through a collection manifold and then travel to an
expansion chamber
where an aliquot sample is analyzed for the tracers used as test agents.
Because the tracers
have different properties, the mixture holds the test agents against a
verifying agent(s) in the
same mixture. At the same time as the test is in progress the pressure is
monitored and if
there is no flow of the tracer in a closed system for a certain period of time
such as two
hours, the system is declared tight. With this method the detection of or non
detection of one
more tracers determines a pass or fail of the system.
[0034] In one embodiment, the method is at least partially orchestrated
using a
controller 36 such as a programmable logic controller. Referring to Fig. 1,
controller 36 may
be connected to one or more of tracer gas source 22, which may comprise tracer
storage unit
50 and carrier gas storage unit 48 as shown in Fig. 2, through control line
40. Other control
lines such as lines 38, 42, 46, and 44 may connect to various other components
of the system
as desired. In one embodiment, controller 36 may be connected to carry out the
method
remotely, for example at various times and dates according to a regular
schedule. For
example, controller 36 may be located in a shed adjacent system 10, and may
automatically
begin the method as instructed by a remote user or a computer program.
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[0035] One or more tracer gases can be used in the method, for example one
to eight
tracers. Tracer gases act as quantifiable tagging agents, and may have
different solubilities in
the system liquid. In one embodiment at least two tracers are injected, one
water soluble, and
one oil soluble.
[0036] The disclosed methods provide numerous advantages. For example, the
methods enable operators of system 10 to quickly produce documentation to
confirm that a
tank is in compliance, reduce the manpower costs required to prove tank
compliance and
help prevent lost revenue from regulatory enforcement. In addition, the
methods may be
completed without having to shut in, clean out, or adjust product levels in
most tanks and
associated lines. The system remains in normal service with no downtime, and
with no lost
revenue. Data from the test results may be used to accurately locate the leak.
Previous leaks
or spills have no bearing on the testing. Moreover, the methods provide
precision leak
detection for underground and aboveground tanks and associated piping. Tanks
on skids or
elevated off the ground can also be tested, for example using an ETM testing
method.
Complex manifolded tank systems may also be tested. Examples of applications
where the
disclosed methods are useful include upstream systems such as storage tanks,
both above
ground and below ground, midstream systems such as plants and processing
facilities,
pipelines of any diameter and length, covering a wide range of product, and
downstream
systems such as service stations, cardlocks, industrial sites, and field
storage facilities. The
methods may be nonintrusive and can be conducted without isolating the tank or
lines. As
well, a testing system for carrying out the method can be installed on most
existing storage
systems and can easily and inexpensively be included in new construction. A
scheduled
testing program can easily interface with normal facility operations.
[0037] Example tracers that may be used include Methanes including: (1)
chlorobromodifluoromethane; (2) trifluoroiodomethane; (3)
trifluorobromomethane; (4)
dibromodifluoromethane; (5) dichlorodifluoromethane; and (6)
tetrafluoromethane;
B, Ethanes including: (1) dichlorotetrafluoroethane; (2)
chloropentafluorethane; (3)
hexafluoroethane; (4) trichlorotrifluoroethane; (5) bromopentafluoroethane;
(6)
dibromotetrafluoroethane; and (7) tetrachlorodifluoroethane; C. Others
including: (1)
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sulferhexafluoride; (2) perfluorodecalin; and (3) perfluoro 1,3
dimethylcyclohexane. In
addition, hydrogen, helium, R134A, and others as disclosed herein and
elsewhere may be used.
[0038] Referring to Fig. 5, a leak detection apparatus 70 for a contained
system 10
having an interior 16 is illustrated. Leak detection apparatus 70 comprises a
plurality of tubes
72 and one or more sensors 26. Each of the plurality of tubes 72 has a
sampling inlet 74 and
a sensing outlet 76. In addition, each tube 72 is fluid impermeable between
the sampling
inlet 74 and the sensor outlet 76. The sampling inlets 74 are positioned at
different
predetermined locations about an exterior 78 of the contained system 10. Thus,
the sampling
inlets 74 may be positioned at spacings, such as regular intervals, at varying
heights and
horizontal separations around the system 10 (Figs. 5 and 6). Columns and rows
of inlets 74
may be used. Arranging the inlets 74 in these manners allow the establishment
of a leak
detection perimeter around the system 10 that is capable of being used to
ascertain the
location of a leak (not shown) in the system 10 to within a precision that is
on the order of
the spacing between sampling inlets 74 and the capabilities of the sensory
system 26. The
sampling inlets 74 may be positioned substantially around the system 10,
although the
minimum requirement is that at least two sampling inlets 74 be provided at
different
locations.
[0039] Referring to Fig. 7, the tubes 72 may terminate in the sampling
inlets 74 such
that sampling inlets 74 form an end of each tube 72. The sampling inlet 74 may
be formed by
cutting the tube 72 to length. The sampling inlets 74 may comprise a screen
86. The screen
86 may be any device that is capable of restricting the entry of solids into
tube 72. Screen 86
may also restrict liquid entry into tube 72, for example if screen 86 is a gas
permeable frit.
As shown in the illustration, an embodiment of screen 86 incorporates a plug
88 with axial
passages 90 bored to allow fluid communication into tube 72.
[0040] Referring to Fig. 5, apparatus 70 may comprise one or more sensors
26
connected to the sensing outlets 76 of the plurality of tubes 72. The one or
more sensors 26
may be adapted to detect the presence of a unique fluid species, such as a
tracer, tracer gas,
or system liquid, indicative of a leak (not shown) in the contained system 10.
Each sensor
outlet 76 may be connected to a separate and distinct sensor 26, or all sensor
outlets 76 may
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be connected to the same sensor 26 for example through a manifold (not shown).
A pump 84
may be provided for applying suction to the plurality of tubes 72 to draw
fluids in through
the sampling inlets 74. Pump 84 may be present as part of the sensor 26
system, or may be
provided as a distinct component. In the embodiment shown in Fig. 5, pump 84
applies
suction to sensor outlets 76 through line 77 to sensor 26.
[0041] Referring to Figs. 5 and 6, at least a portion of the plurality of
tubes 72 may
be arranged together as a bundle 80. The bundle 80 may be contained at least
partially within
a containment tube 82. Initially, the tubes 72 may be entirely contained
within the
containment tube 82, for protecting tubes 72 during transport to and from a
point of sale. To
install the apparatus 70 the containment tube 82 may simply be cut at the
desired point along
the length of the tube 82, and sample inlets 74 positioned as desired. Tube 80
may also be
positioned along a top of the system 10, for example as shown. Tubes 72 can
then be draped
along and down the sides of the tank and terminated for example by cutting at
pre-
determined coordinates calculated for example based on the dimensions of
system 10 and the
precision of detection required at each sampling inlet 74. Tube 80 protects
tubes 72 from
damage after and during installation. Other forms of bundling may be used such
as plural ties
spaced at intervals. Sampling inlets 74 may be positioned for example using
brackets 92
(Fig. 6) connected to exterior 78. Other means of positioning sampling inlets
74 may be used
however, such as by welding to exterior 78. Further methods include
backfilling up to a
predetermined vertical height along system 10, positioning a row of sampling
inlets 74 about
a horizontal perimeter, and backfilling overtop of inlets 74. Plural
horizontal rows of inlets
74 may be arranged in such a manner. It should be understood that sampling
inlets 74 need
not be positioned directly upon exterior 78, and instead sampling inlets 74
may be spaced
from exterior 78. However, the closer sampling inlets 74 are to exterior 78,
and the smaller
the separation between adjacent sampling inlets 74, generally the higher the
precision in leak
detection possible with apparatus 10. In general, sampling inlets 74 should be
installed in
close proximity to the walls of the tank.
[0042] Various arrangements are possible, with the only requirement being
that upon
installation a user is able to somehow associate sensory data from sensor 26
with the location
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of each sampling inlet 74 about the exterior 78 of system 10. This may require
making an
association between each sampling inlet 74 and corresponding sensor outlet 76.
For this
purpose, tubes 72 may be color-coded or marked such as with numbering in some
fashion to
allow a user to make the required association. Sampling inlets 74 may also
contain
electronics for transmitting location signals that may be detected and used to
record 3D
positioning. Such information may then be used to accurately plot a 3D model
of the location
of each sampling inlet 74 about a contained system 10. System 10 may be above
or below
ground.
[0043] In some embodiments, a controller 36 may be used. For example the
sensors
26 may be adapted to produce an output signal, and controller 36 may be
connected for
example through line 46 to receive as input the output signal from the one or
more sensors
26. Controller 36 may be further connected to operate a tracer introduction
system, such as
the introduction systems disclosed elsewhere in this document. Controller 36
may also be
connected to other components in the apparatus 70, such as pump 84 through
line 91.
[0044] Referring to Fig. 8, a method of testing for leaks in a contained
system 10
with an interior 16 containing a unique fluid species such as tracer is
illustrated. The method
stages will now be described with reference to the other figures. In a stage
104, fluids are
drawn into respective sampling inlets 74 of a plurality of tubes 72 (Fig. 5).
The sampling
inlets 74 are positioned at different predetermined locations about an
exterior 78 of the
contained system 10. In a stage 106, the presence of the unique fluid species
is sensed for
using one or more sensors 26 connected to respective sensor outlets 76 of the
plurality of
tubes 72. Each of the plurality of tubes 72 are fluid impermeable between the
sampling inlet
74 and the sensor outlet 76. As mentioned, the unique fluid species may be
tracer gas. The
method may further comprise introducing tracer gas into the interior 16, for
example using
the methods disclosed elsewhere in this document.
[0045] The methods disclosed herein may further comprise determining the
location
of a leak (not shown) in the contained system 10 based upon signals from the
one or more
sensors 26. Thus, controller 36 in Fig. 5 may receive sensory data from sensor
26 and may
perform an association between each particular fluid sample analyzed and the
corresponding
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location on exterior 78. By analyzing the intensity and presence of signals
indicative of the
presence of a tracer or unique fluid species, the location of the leak can be
mapped out and
inferred. A leak may cause detection at more than one sampling inlet 74, so
detection
intensities at different points may need to be compared to determine the most
likely
candidate for location of the leak.
[0046] The embodiments described above and illustrated in Figs. 5-8 may be
used for
new installations. These embodiments may eliminate a need to bore holes in the
tank cover
material after construction is completed. In addition, after installation,
controller 36 and
sensor 26 may be conveniently located above ground a sufficient distance away,
for example
in an accessible terminal box (not shown).
[0047] In the claims, the word "comprising" is used in its inclusive sense
and does
not exclude other elements being present. The indefinite article "a" before a
claim feature
does not exclude more than one of the feature being present. Each one of the
individual
features described here may be used in one or more embodiments and is not, by
virtue only
of being described here, to be construed as essential to all embodiments as
defined by the
claims.
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