CA1286523C - Apparatus and method for determining rate of leakage of liquid from and into tanks - Google Patents
Apparatus and method for determining rate of leakage of liquid from and into tanksInfo
- Publication number
- CA1286523C CA1286523C CA000535868A CA535868A CA1286523C CA 1286523 C CA1286523 C CA 1286523C CA 000535868 A CA000535868 A CA 000535868A CA 535868 A CA535868 A CA 535868A CA 1286523 C CA1286523 C CA 1286523C
- Authority
- CA
- Canada
- Prior art keywords
- liquid
- storage tank
- tank
- delta
- hydrostatic pressure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
- G01M3/32—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators
- G01M3/3236—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers
- G01M3/3245—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers using a level monitoring device
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M3/00—Investigating fluid-tightness of structures
- G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
- G01M3/26—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors
- G01M3/32—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators
- G01M3/3236—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers
- G01M3/3263—Investigating fluid-tightness of structures by using fluid or vacuum by measuring rate of loss or gain of fluid, e.g. by pressure-responsive devices, by flow detectors for containers, e.g. radiators by monitoring the interior space of the containers using a differential pressure detector
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
Abstract
ABSTRACT
Apparatus and method for measuring leakage of liquid into or from a storage tank such as a buried gasoline tank. The storage tank should have rigid walls. A reference tank is immersed into liquid stored in the storage tank and is filled to the same height and with the same liquid as contained in the storage tank, and having sealed and rigid thermal energy conducting walls at least where it is in contact with the liquid, but having vapor space above the liquid in the reference tank vented to the vapor space in the storage tank. The cross-sectional area of the reference tank is desirably (but not necessarily) proportional to the cross-sectional area of the storage tank at least wherever it is in contact with liquid. The material of the reference and storage tanks should have similar temperature coefficients of linear expansion. A sensing structure is located at approximately the same levels within the storage tank and within the reference tank for sensing differential hydrostatic pressure between liquids in the two tanks. The volume of any liquid lost from or gained by the storage tank over a period of time is determined from an algorithm.
Apparatus and method for measuring leakage of liquid into or from a storage tank such as a buried gasoline tank. The storage tank should have rigid walls. A reference tank is immersed into liquid stored in the storage tank and is filled to the same height and with the same liquid as contained in the storage tank, and having sealed and rigid thermal energy conducting walls at least where it is in contact with the liquid, but having vapor space above the liquid in the reference tank vented to the vapor space in the storage tank. The cross-sectional area of the reference tank is desirably (but not necessarily) proportional to the cross-sectional area of the storage tank at least wherever it is in contact with liquid. The material of the reference and storage tanks should have similar temperature coefficients of linear expansion. A sensing structure is located at approximately the same levels within the storage tank and within the reference tank for sensing differential hydrostatic pressure between liquids in the two tanks. The volume of any liquid lost from or gained by the storage tank over a period of time is determined from an algorithm.
Description
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01 This invention relates to apparatus and 02 to a method for determining the rate of leakage of 03 liquid out of or into a storage tank, and i5 04 particularly useful with petroleum storage tanks.
05 For economic as well as environmental 06 hazard reasons it has become increasingly important to 07 determine whether liquid is leaking from storage 08 tanks. ~or exa~ple, the accurate measurement of the 09 amount of gasoline stored in gasoline storage tanks at automobile service stations can help determine the ll value of any lost gasoline and also can determine 12 whether gasoline is leaking and thus possibly 13 polluting ground water. It is also important to 14 determine whether surEace or ground water is leaking into such storage tanks, in order to ensure that the 16 stored liquid su~h as gasoline is not becoming 17 polluted.
18 It is common to measure the amount of 19 gasoline stored in a tank by measuring the volume of liquid in the tank at two times separated typically by 21 sev~ral hours. The amount of leakage is determined by 22 subtracting one measurement value from the other.
23 However inaccuracies in the result are 24 introduced by changes in temperature which change the volume of stored liquid and also change the volume of 26 the tank during the interval between the two 27 measurements, and also by imperfections in the 28 measuring instrumentation. Further the leakage 29 determination is subject to the inaccuracies in the dlfference between two large, nearly equal quantities, 31 each beinc~ determined under the inaccurate conditions 32 noted above.
33 The present invention is a structure and 34 method for avoiding the aforenoted problems and has been shown to be capable of accurately detec-ting very 36 small amounts of leakage in relatively large tanks.
37 Instead of attempting to measure the total 38 - l -: .
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01 volume oE liquid at two different times within the 02 tank, it has been found that the measurement problem 03 is greatly simpliEied if the level of liquid in ~he 04 tank suspected of leaking is compared to the level of 05 liquid in a reference tank having a particular 06 structure. In general the reference tank should be 07 made of the same material as the main tank suspected 08 of leakage and should be filled to the same level as 09 the main tank and with an identical liquid. rrhe reference tank is subjected to the identical 11 temperature influences as the main tank under study.
12 The liquid level in the reference tank will as a 13 result always be at the level that the main tank would 14 be if there is no leakage. The re~erence tank need not be identical in size to the tank under study, but 16 can instead be a scale model. The desired conditions 17 regarding identical fluid and identical temperature 18 can be satisfied by inserting the reference tank 1~ inside the tank under study. A measurement o~ the difference in liquid levels between the two tanks 21 after some time has elapsed will be indicative of the 22 rate of leakage.
23 More particularly a preferred embodiment 24 of the invention for measuring leakage of liquid into or from a storage tank is comprised of a liquid 26 containing storage tank having rigid walls, and a 27 reference tank immersed into liquid stored in the 28 storage tank and filled with the same liquid as 29 contained in the storage tank, and having sealed and rigid thermal energy conducting walls at least whe~e 31 it is in contact with the liquid, but having vapor 32 space above the liquid in the reEerence tank vented to 33 the vapor space in the storage tank. rrhe 34 cross-sectional area of the reference tank is desirably (but not necessarily) proportional to the 36 cross~sectional area of the storage tank at least 37 wherever it is in contact with liquid. A sensing ., ~ .. : .. ::. ~ . :~ . . .. .
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I structure is located at approximately the same levels 2 within the storage tank and within the reference tank 3 for sensing differential hydrostatic pressure between 4 liquids in the two tanks. The material of the S reference and storage tanks should have similar 6 temperature coef~icients of linear expansion. The 7 reference tank should be filled to the same height as 8 the liquid in the ~torage stank. The volume of any 9 liquid lost from or gained by the storage tank ( V) over a period of time (~T) is determined from the 11 expression 13 ~V = -pxg where ~P is the ssnsed change in differential in 16 hydrostatic pressure between the storage 17 and refer~nce tanks over the time period 18 ~T, 19 A is the cross-sectional area at the level of the liquid surface of the storiny 21 tank, 22 p is the density of the li~uid in the tank, 23 and 24 g is the gravitational constant.
2S Another embodiment of the invention is a 26 method for determining leakage of liquid from or into 27 a rigid walled storage tank comprising detecting 2~ hydrostatic pressure at a level within the liquid 29 within the storage tank, detecting hydrostatic pressure, at about the same level, of liquid contained 31 within a rigid walled reference tank, which reference 32 tank has thermal energy conducting ~ealed walls, and 33 which is immersed within the liquid of the storage 34 tank and is filled to the same level as the storage tank with the same liquid, and has the vapor space 36 above its liquid vented to the vapor space above the 37 liquid in the storage tank, and determining the volume 38 of liquid leakage from the change in detected . ,:
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2 diPferential hydrostatic pressure between the storage 3 tank and the reference tank over a time interval.
4 Another embodiment of the invention is S apparatus for measuring leakage of liquid from a 6 liquid storage tank having rigid liquid containing 7 walls which comprise a reference tank for immersion 8 into the storage tank r the reference tank being rigid 9 walled wherever it is in contact with liquid, and having thermal energy conducting walls, sealed within 11 the liquid of the storage tank, and being fabricated 12 of material whereby the reference and storage tank 13 have similar temperature coefficients of linear 14 expansion, apparatus for Eilling the reference tank lS with the same liquid and to the same height as the 16 liquid in the storage tank, apparatus for sensing the 17 change in differential hydrostatic pressure of the 18 liquid at about the same level within the storage and 19 re~erence tanks, and apparatus for determining the volume of liquid lost from the storage tank from any 21 sensed change in differential hydrostatic pressure.
22 A better understanding of the invention will 23 be obtained by reference to the detailed description 24 below, in conjunction with the accompanying drawings, in which:
26 Figure 1 i5 a cross-sectional schematic in 27 the vertical plane illustrating the invention, and 28 Figure 2 is a detail illustrating the 29 preferred embodiment of a pressure gauge.
Turning to the figures, a liquid storage tank 31 1 is shown which contains a liquid 2. A reference 32 tank 3 i5 inserted into the storage tank. The 33 reference tank 3 is filled to the same level w.ith 34 liquid 2 as the liquid storage tank 1. This may be conveniently done by fitting a valve 4 into a wall of 36 the reference tank 3, preferably near the bottom of 37 the reference tank. The valve 4 may be operated by 38 remote control in a well known manner, to fill the 39 - 3a --' : .- : .
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01 reference tank 3 from the storage tank 1, then close.
02 Pressure sensors 5 are located at about 03 the same level, one near the botto~ of the storage 04 tank and one near the bottom of the reference tank, 05 whereby the liquid pressure at the level of the 06 pressure sensor within the reference tank may be 07 determined and the liquid pressure about the same 08 depth within the storage tank may be separatel~
09 determined (or their differential). In the preferred embodiment only one pressure sensor 5' is used, 11 connected between the two tanks, as shown in Figure 2.
12 The reference tank should be made of 13 material which conducts thermal energy easily, in 14 order that -the temp0rature of the liquid in the storage tank should be conducted to the liquid 16 contained in the reference tank, and their 17 temperatures should remain the same. Furthermore, the 18 material of the reference tank should be such that its 19 temperature coefficient of linear expansion is similar to that of the storage tank. The cross-sectional area 21 of the reference tank is preferably, but optionally 22 proportional at every height which is in contact with 23 the liquid to that of the storage tank.
24 The reference tank should be sealed 25 wherever it is in contact with the liquid. However 26 the vapor spaced above the reference tank should be 27 ve~ted to vapor space above the liquid in the storage 28 tank. The vapor spaced above both can be open to the 29 atmosphere, and may be vented to the atmosphere via a 30 pre~tsure relief valve.
31 It is preferred, but it is not necessary, 32 that should khe outer tank have straight vertical 33 walls, so should the inner tank. If the outer tank 3~ has walls which are bowed outwardly, 60 preferabl~
should the inner tank. For measurement of leakage 36 from petroleum storage tanks having a cylindrical.
37 cross-section and a vertical axis, the above may be : . .:
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~ ~65~."3 01 accomplished by fabricating a tube having a sealed 02 bottom (with the ancillary filler valve if desired as 03 described above), the tube being made out of the same 04 material (e.g. steel) as the storage tank. The 05 reference tank can then be inserted into the liquid of 06 the storage tank through its open filler hole at the 07 top of the storage tank. The filler valve may then be 0~ closed by mechanical or solenoid means in a manner 09 known in the art. However the storage tank often will be cylindrical with a horizontal axis, and in this 11 case the reference tank can be a cylindrical tube 12 having a vertical axis.
13 A frame carrying pressure sensors may be 14 used to lower pressure sensors one on each side of -the outer wall of the reference tank into the liquid to 1~ the bottom of the tanks. One pressure sensor thus 17 determines the liquid pressure within the reference 18 tank and the other pressure sensor determines the 19 liquid pressure at about the same height within the storage tank. However it is preferred that a single 21 pressure sensor 5' should be connected through the 22 wall of the reference tank in order to sense the 23 differential pressure between the liquid in the 24 reference tank and in the storage tank.
Because the reference tank is in very 26 intimate thermal contact with ~he liquid in the 27 storage ~ank, the temperature of the liquid in the two 28 tanks will be very nearly identical. Small changes in 29 the temperature of the liquid in the outer tank will be transmitted to the reference tank and the liquid 31 therein. Similarly changes in temperature of the 32 storage tank will be transmitted by the liquid to the 33 reEerence tank and the liquid contained therein.
34 Temperature changes causing thermal expansion or contraction of the liquid and/or the tanks has been 36 found to cause the liquid level in both tanks to rise 37 and fall in almost exactly the same manner. A
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01 differential measurement of the hydrostatic pressures 02 at a convenient level below the liquid sur~ace of each 03 tank would show no changes over the time period T
04 unless liquid was leaking into or out of the storage 05 tank.
06 The volume of any liquid lost from or 07 gained ~y the storage tank (aV) over a period of -time 08 aT is determined by apparatus processing the algorithm a V = ~PxA
~xg 11 where aP is a signal representing the sensed change 12 in differential hydrosta-tic pressure between 13 the storage and reference tanks during the 14 lapsed time ~T, A is a signal representing the cross-sectional 16 area at the level of the liquid surface of 17 the storage tank, 18 ~is a signal representing the density of the 19 liquid in the tank, and g is a signal representing the gravitational 21 constant.
22 The density o~ the liquid in the tanks may 23 be estimated to sufficient accuracy for most 24 applications, or may be determined by other means which is not part of the present invention.
26 The algorithm noted above may be processed 27 by applying signals representing the sensed pressure 28 differential generated by the pressure sensors 5 or 29 pressure sensor 5' to the input of a microcomputer or other processor, which preferably has a display 7 31 associated with it. The display may be located at a 32 remote operator position, and may be Eor example, a 33 cathode ray or other instantaneous display, or may be 34 a printer, and may include signal storage mean~ Eor storing output signals from the microcomputer for 36 later absolute or comparative display. The pressure 37 signals could be transmitted to the microcomputer or . . .
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01 other signal processing apparatus located at a remote 02 location.
03 The pressure sensors 5 or 5' can be 04 sensors which translate liquid pressure to electrical 05 signals, which can be transmitted directly to an 06 interface (not shown) connected to microcomputer 6.
07 Preferably however the pressure readings may 08 accurately be obtained by use of bubble tubes as 09 described in Canadian patent 1,201,532 which issued March 4th, 1986, in conjunction with bubble plates 11 described in Canadian patent application 500,905, 12 Eiled January 31st, 1986.
13 The chanye in volume ~V can be converted 14 to a leakage rate over time ~at) by processing the algorithm dV/~t. This will provide an indication of 16 the severity of the leak. This algorithm may also be 17 processed by microcomputer 6 or by other means 18 provided to operate it.
19 It should be noted that if the leak rate need not be known to a high degree of accuracy, it is 21 not necessary to know ~P, A,f, g or at -to a very high 22 degree of accuracy; yet the existence o~ a leak 23 becomes evident very clearly using the present 24 invention. This distinguishes from systems which involve measuring the total volume in the storage tank 26 over a period of time in which the exact volume must 27 be known to a high degree of accuracy.
28 It is important in this invention that the 29 pressure sensors should be sensitive enough to indicate a small change in pressure. ~Iowever they 31 need not be very linear, nor very accurate.
32 Since typical tank materials, e.~. steel, 33 do not change dimensions very much ~ith temperat~re, 3~ some difference in rela~ive temperature of the two tanks can be tolerated, with benefits of the present 36 invention still being obtained. For cylindrical steel 37 tanks having a vertical axis as shown in the figure, .
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01 it has been found that differences in relative 02 temperature of up to + 0.4C. can be tolerated and the 03 apparatus still resolve leakage to within one part in 04 lOo,ooo.
05 Because the volume of most liquids has 06 been found to vary rather strongly with temperature, 07 it is important that the liquid within the two tanks 08 should be subjected to the same temperature changes.
09 The intimate contact between the liquids in the reference tank and storage tank ensures that this will 11 be the case.
12 The two pressure sensing points, one in 13 each tank, do not have to be exactly at the same 14 level. A difference would result in an initial value of di~ferential pressure which is not ~ero. The 16 pressure change a P to be used in the fundamental 17 algorithm would be the amount by which the 18 differential pressure changes over the duration o~ the 19 test.
Difference in height of the two pressure 21 sensing points will make the operation somewhat ~ore 22 sensitive to temperature a-ffects, but this has been 23 determined as not being critically so. For example in 2~ a typical underground storage tank a height di~ferential of 1 millimeter would cause the observed 26 leak rate to be in error by about 1% for every degree 27 Celcius that the temperature of the liquid changed 28 during the course o~ ~he test. This has been ~ound to 29 ~e a neyligible error for most purposes.
The present invention has been found to be 31 highly useul to service station operators and in 32 other petroleum storage facilities. It is of course 33 not limited thereto, and can be used for such 34 applications as water storage tanks, milk storage tanks, heavy oil storage tanks, liquid chemical 36 storage tanks, etc.
37 The entire structure is also highly 3~ - 8 -. .
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01 adaptible to remote control sensing. Signals from the 02 pressure sensors can be transmitted via a network to a 03 cen-tral computer which receives similar signals from a 04 large number of facilities, providing constant 05 monitoring of leakage by a central control computer, 06 for display to management personnel.
07 The reference tank with differential 08 pressure gauge can be made portable and used as needed 09 in connection with different storage tanks.
A person skilled in the ar-t understanding 11 the present invention may now conceive of variations 12 or other embodiments using the concepts descr;.bed 13 herein. All are considered to be within the sphere 14 and scope of the invention as defined in the claims appended hereto.
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01 This invention relates to apparatus and 02 to a method for determining the rate of leakage of 03 liquid out of or into a storage tank, and i5 04 particularly useful with petroleum storage tanks.
05 For economic as well as environmental 06 hazard reasons it has become increasingly important to 07 determine whether liquid is leaking from storage 08 tanks. ~or exa~ple, the accurate measurement of the 09 amount of gasoline stored in gasoline storage tanks at automobile service stations can help determine the ll value of any lost gasoline and also can determine 12 whether gasoline is leaking and thus possibly 13 polluting ground water. It is also important to 14 determine whether surEace or ground water is leaking into such storage tanks, in order to ensure that the 16 stored liquid su~h as gasoline is not becoming 17 polluted.
18 It is common to measure the amount of 19 gasoline stored in a tank by measuring the volume of liquid in the tank at two times separated typically by 21 sev~ral hours. The amount of leakage is determined by 22 subtracting one measurement value from the other.
23 However inaccuracies in the result are 24 introduced by changes in temperature which change the volume of stored liquid and also change the volume of 26 the tank during the interval between the two 27 measurements, and also by imperfections in the 28 measuring instrumentation. Further the leakage 29 determination is subject to the inaccuracies in the dlfference between two large, nearly equal quantities, 31 each beinc~ determined under the inaccurate conditions 32 noted above.
33 The present invention is a structure and 34 method for avoiding the aforenoted problems and has been shown to be capable of accurately detec-ting very 36 small amounts of leakage in relatively large tanks.
37 Instead of attempting to measure the total 38 - l -: .
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01 volume oE liquid at two different times within the 02 tank, it has been found that the measurement problem 03 is greatly simpliEied if the level of liquid in ~he 04 tank suspected of leaking is compared to the level of 05 liquid in a reference tank having a particular 06 structure. In general the reference tank should be 07 made of the same material as the main tank suspected 08 of leakage and should be filled to the same level as 09 the main tank and with an identical liquid. rrhe reference tank is subjected to the identical 11 temperature influences as the main tank under study.
12 The liquid level in the reference tank will as a 13 result always be at the level that the main tank would 14 be if there is no leakage. The re~erence tank need not be identical in size to the tank under study, but 16 can instead be a scale model. The desired conditions 17 regarding identical fluid and identical temperature 18 can be satisfied by inserting the reference tank 1~ inside the tank under study. A measurement o~ the difference in liquid levels between the two tanks 21 after some time has elapsed will be indicative of the 22 rate of leakage.
23 More particularly a preferred embodiment 24 of the invention for measuring leakage of liquid into or from a storage tank is comprised of a liquid 26 containing storage tank having rigid walls, and a 27 reference tank immersed into liquid stored in the 28 storage tank and filled with the same liquid as 29 contained in the storage tank, and having sealed and rigid thermal energy conducting walls at least whe~e 31 it is in contact with the liquid, but having vapor 32 space above the liquid in the reEerence tank vented to 33 the vapor space in the storage tank. rrhe 34 cross-sectional area of the reference tank is desirably (but not necessarily) proportional to the 36 cross~sectional area of the storage tank at least 37 wherever it is in contact with liquid. A sensing ., ~ .. : .. ::. ~ . :~ . . .. .
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I structure is located at approximately the same levels 2 within the storage tank and within the reference tank 3 for sensing differential hydrostatic pressure between 4 liquids in the two tanks. The material of the S reference and storage tanks should have similar 6 temperature coef~icients of linear expansion. The 7 reference tank should be filled to the same height as 8 the liquid in the ~torage stank. The volume of any 9 liquid lost from or gained by the storage tank ( V) over a period of time (~T) is determined from the 11 expression 13 ~V = -pxg where ~P is the ssnsed change in differential in 16 hydrostatic pressure between the storage 17 and refer~nce tanks over the time period 18 ~T, 19 A is the cross-sectional area at the level of the liquid surface of the storiny 21 tank, 22 p is the density of the li~uid in the tank, 23 and 24 g is the gravitational constant.
2S Another embodiment of the invention is a 26 method for determining leakage of liquid from or into 27 a rigid walled storage tank comprising detecting 2~ hydrostatic pressure at a level within the liquid 29 within the storage tank, detecting hydrostatic pressure, at about the same level, of liquid contained 31 within a rigid walled reference tank, which reference 32 tank has thermal energy conducting ~ealed walls, and 33 which is immersed within the liquid of the storage 34 tank and is filled to the same level as the storage tank with the same liquid, and has the vapor space 36 above its liquid vented to the vapor space above the 37 liquid in the storage tank, and determining the volume 38 of liquid leakage from the change in detected . ,:
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2 diPferential hydrostatic pressure between the storage 3 tank and the reference tank over a time interval.
4 Another embodiment of the invention is S apparatus for measuring leakage of liquid from a 6 liquid storage tank having rigid liquid containing 7 walls which comprise a reference tank for immersion 8 into the storage tank r the reference tank being rigid 9 walled wherever it is in contact with liquid, and having thermal energy conducting walls, sealed within 11 the liquid of the storage tank, and being fabricated 12 of material whereby the reference and storage tank 13 have similar temperature coefficients of linear 14 expansion, apparatus for Eilling the reference tank lS with the same liquid and to the same height as the 16 liquid in the storage tank, apparatus for sensing the 17 change in differential hydrostatic pressure of the 18 liquid at about the same level within the storage and 19 re~erence tanks, and apparatus for determining the volume of liquid lost from the storage tank from any 21 sensed change in differential hydrostatic pressure.
22 A better understanding of the invention will 23 be obtained by reference to the detailed description 24 below, in conjunction with the accompanying drawings, in which:
26 Figure 1 i5 a cross-sectional schematic in 27 the vertical plane illustrating the invention, and 28 Figure 2 is a detail illustrating the 29 preferred embodiment of a pressure gauge.
Turning to the figures, a liquid storage tank 31 1 is shown which contains a liquid 2. A reference 32 tank 3 i5 inserted into the storage tank. The 33 reference tank 3 is filled to the same level w.ith 34 liquid 2 as the liquid storage tank 1. This may be conveniently done by fitting a valve 4 into a wall of 36 the reference tank 3, preferably near the bottom of 37 the reference tank. The valve 4 may be operated by 38 remote control in a well known manner, to fill the 39 - 3a --' : .- : .
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01 reference tank 3 from the storage tank 1, then close.
02 Pressure sensors 5 are located at about 03 the same level, one near the botto~ of the storage 04 tank and one near the bottom of the reference tank, 05 whereby the liquid pressure at the level of the 06 pressure sensor within the reference tank may be 07 determined and the liquid pressure about the same 08 depth within the storage tank may be separatel~
09 determined (or their differential). In the preferred embodiment only one pressure sensor 5' is used, 11 connected between the two tanks, as shown in Figure 2.
12 The reference tank should be made of 13 material which conducts thermal energy easily, in 14 order that -the temp0rature of the liquid in the storage tank should be conducted to the liquid 16 contained in the reference tank, and their 17 temperatures should remain the same. Furthermore, the 18 material of the reference tank should be such that its 19 temperature coefficient of linear expansion is similar to that of the storage tank. The cross-sectional area 21 of the reference tank is preferably, but optionally 22 proportional at every height which is in contact with 23 the liquid to that of the storage tank.
24 The reference tank should be sealed 25 wherever it is in contact with the liquid. However 26 the vapor spaced above the reference tank should be 27 ve~ted to vapor space above the liquid in the storage 28 tank. The vapor spaced above both can be open to the 29 atmosphere, and may be vented to the atmosphere via a 30 pre~tsure relief valve.
31 It is preferred, but it is not necessary, 32 that should khe outer tank have straight vertical 33 walls, so should the inner tank. If the outer tank 3~ has walls which are bowed outwardly, 60 preferabl~
should the inner tank. For measurement of leakage 36 from petroleum storage tanks having a cylindrical.
37 cross-section and a vertical axis, the above may be : . .:
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~ ~65~."3 01 accomplished by fabricating a tube having a sealed 02 bottom (with the ancillary filler valve if desired as 03 described above), the tube being made out of the same 04 material (e.g. steel) as the storage tank. The 05 reference tank can then be inserted into the liquid of 06 the storage tank through its open filler hole at the 07 top of the storage tank. The filler valve may then be 0~ closed by mechanical or solenoid means in a manner 09 known in the art. However the storage tank often will be cylindrical with a horizontal axis, and in this 11 case the reference tank can be a cylindrical tube 12 having a vertical axis.
13 A frame carrying pressure sensors may be 14 used to lower pressure sensors one on each side of -the outer wall of the reference tank into the liquid to 1~ the bottom of the tanks. One pressure sensor thus 17 determines the liquid pressure within the reference 18 tank and the other pressure sensor determines the 19 liquid pressure at about the same height within the storage tank. However it is preferred that a single 21 pressure sensor 5' should be connected through the 22 wall of the reference tank in order to sense the 23 differential pressure between the liquid in the 24 reference tank and in the storage tank.
Because the reference tank is in very 26 intimate thermal contact with ~he liquid in the 27 storage ~ank, the temperature of the liquid in the two 28 tanks will be very nearly identical. Small changes in 29 the temperature of the liquid in the outer tank will be transmitted to the reference tank and the liquid 31 therein. Similarly changes in temperature of the 32 storage tank will be transmitted by the liquid to the 33 reEerence tank and the liquid contained therein.
34 Temperature changes causing thermal expansion or contraction of the liquid and/or the tanks has been 36 found to cause the liquid level in both tanks to rise 37 and fall in almost exactly the same manner. A
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01 differential measurement of the hydrostatic pressures 02 at a convenient level below the liquid sur~ace of each 03 tank would show no changes over the time period T
04 unless liquid was leaking into or out of the storage 05 tank.
06 The volume of any liquid lost from or 07 gained ~y the storage tank (aV) over a period of -time 08 aT is determined by apparatus processing the algorithm a V = ~PxA
~xg 11 where aP is a signal representing the sensed change 12 in differential hydrosta-tic pressure between 13 the storage and reference tanks during the 14 lapsed time ~T, A is a signal representing the cross-sectional 16 area at the level of the liquid surface of 17 the storage tank, 18 ~is a signal representing the density of the 19 liquid in the tank, and g is a signal representing the gravitational 21 constant.
22 The density o~ the liquid in the tanks may 23 be estimated to sufficient accuracy for most 24 applications, or may be determined by other means which is not part of the present invention.
26 The algorithm noted above may be processed 27 by applying signals representing the sensed pressure 28 differential generated by the pressure sensors 5 or 29 pressure sensor 5' to the input of a microcomputer or other processor, which preferably has a display 7 31 associated with it. The display may be located at a 32 remote operator position, and may be Eor example, a 33 cathode ray or other instantaneous display, or may be 34 a printer, and may include signal storage mean~ Eor storing output signals from the microcomputer for 36 later absolute or comparative display. The pressure 37 signals could be transmitted to the microcomputer or . . .
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01 other signal processing apparatus located at a remote 02 location.
03 The pressure sensors 5 or 5' can be 04 sensors which translate liquid pressure to electrical 05 signals, which can be transmitted directly to an 06 interface (not shown) connected to microcomputer 6.
07 Preferably however the pressure readings may 08 accurately be obtained by use of bubble tubes as 09 described in Canadian patent 1,201,532 which issued March 4th, 1986, in conjunction with bubble plates 11 described in Canadian patent application 500,905, 12 Eiled January 31st, 1986.
13 The chanye in volume ~V can be converted 14 to a leakage rate over time ~at) by processing the algorithm dV/~t. This will provide an indication of 16 the severity of the leak. This algorithm may also be 17 processed by microcomputer 6 or by other means 18 provided to operate it.
19 It should be noted that if the leak rate need not be known to a high degree of accuracy, it is 21 not necessary to know ~P, A,f, g or at -to a very high 22 degree of accuracy; yet the existence o~ a leak 23 becomes evident very clearly using the present 24 invention. This distinguishes from systems which involve measuring the total volume in the storage tank 26 over a period of time in which the exact volume must 27 be known to a high degree of accuracy.
28 It is important in this invention that the 29 pressure sensors should be sensitive enough to indicate a small change in pressure. ~Iowever they 31 need not be very linear, nor very accurate.
32 Since typical tank materials, e.~. steel, 33 do not change dimensions very much ~ith temperat~re, 3~ some difference in rela~ive temperature of the two tanks can be tolerated, with benefits of the present 36 invention still being obtained. For cylindrical steel 37 tanks having a vertical axis as shown in the figure, .
:, , ' ', ' . ,, ' ', :
~r3~iS~
01 it has been found that differences in relative 02 temperature of up to + 0.4C. can be tolerated and the 03 apparatus still resolve leakage to within one part in 04 lOo,ooo.
05 Because the volume of most liquids has 06 been found to vary rather strongly with temperature, 07 it is important that the liquid within the two tanks 08 should be subjected to the same temperature changes.
09 The intimate contact between the liquids in the reference tank and storage tank ensures that this will 11 be the case.
12 The two pressure sensing points, one in 13 each tank, do not have to be exactly at the same 14 level. A difference would result in an initial value of di~ferential pressure which is not ~ero. The 16 pressure change a P to be used in the fundamental 17 algorithm would be the amount by which the 18 differential pressure changes over the duration o~ the 19 test.
Difference in height of the two pressure 21 sensing points will make the operation somewhat ~ore 22 sensitive to temperature a-ffects, but this has been 23 determined as not being critically so. For example in 2~ a typical underground storage tank a height di~ferential of 1 millimeter would cause the observed 26 leak rate to be in error by about 1% for every degree 27 Celcius that the temperature of the liquid changed 28 during the course o~ ~he test. This has been ~ound to 29 ~e a neyligible error for most purposes.
The present invention has been found to be 31 highly useul to service station operators and in 32 other petroleum storage facilities. It is of course 33 not limited thereto, and can be used for such 34 applications as water storage tanks, milk storage tanks, heavy oil storage tanks, liquid chemical 36 storage tanks, etc.
37 The entire structure is also highly 3~ - 8 -. .
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01 adaptible to remote control sensing. Signals from the 02 pressure sensors can be transmitted via a network to a 03 cen-tral computer which receives similar signals from a 04 large number of facilities, providing constant 05 monitoring of leakage by a central control computer, 06 for display to management personnel.
07 The reference tank with differential 08 pressure gauge can be made portable and used as needed 09 in connection with different storage tanks.
A person skilled in the ar-t understanding 11 the present invention may now conceive of variations 12 or other embodiments using the concepts descr;.bed 13 herein. All are considered to be within the sphere 14 and scope of the invention as defined in the claims appended hereto.
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Claims (25)
1. Apparatus for measuring leakage of liquid from a liquid storage tank having rigid liquid containing walls comprising:
(a) a reference tank for immersion into the storage tank, the reference tank being rigid walled wherever it is in contact with liquid, and having thermal energy conducting walls, sealed within the liquid of the storage tank, and being fabricated of material whereby the reference and storage tank have similar temperature coefficients of linear expansion, (b) means for filling the reference tank with the same liquid and to the same height as the liquid in the storage tank, (c) means for sensing the change in differential hydrostatic pressure of the liquid at about the same level within the storage and reference tanks, whereby the volume of any liquid lost from or gained by the storage tank (.DELTA.V) during a time interval .DELTA.T may be determined by operating the algorithm .DELTA.V= where .DELTA.P is a signal representing the sensed change in differential hydrostatic pressure between the storage and reference tanks during the time interval .DELTA.T, A is a signal representing the cross-sectional area at the level of the liquid surface of the storage tank, ? is a signal representing the density of the liquid in the tank, and g is a signal representing the gravitational constant.
(a) a reference tank for immersion into the storage tank, the reference tank being rigid walled wherever it is in contact with liquid, and having thermal energy conducting walls, sealed within the liquid of the storage tank, and being fabricated of material whereby the reference and storage tank have similar temperature coefficients of linear expansion, (b) means for filling the reference tank with the same liquid and to the same height as the liquid in the storage tank, (c) means for sensing the change in differential hydrostatic pressure of the liquid at about the same level within the storage and reference tanks, whereby the volume of any liquid lost from or gained by the storage tank (.DELTA.V) during a time interval .DELTA.T may be determined by operating the algorithm .DELTA.V= where .DELTA.P is a signal representing the sensed change in differential hydrostatic pressure between the storage and reference tanks during the time interval .DELTA.T, A is a signal representing the cross-sectional area at the level of the liquid surface of the storage tank, ? is a signal representing the density of the liquid in the tank, and g is a signal representing the gravitational constant.
2. Apparatus as defined in claim 1 in which the space above the reference tank is vented to the space above the storage tank.
3. Apparatus as defined in claim 2 including computing apparatus for receiving signals from said sensing means corresponding to said pressures and providing an output display and/or signal representative of the volume of said liquid lost or gained by storing digital data signals representative of said cross-sectional area, said density of the liquid, and said gravitational constant, and operating a computer program implementing said algorithm.
4. Apparatus as defined in claim 3 in which said computing apparatus includes means for controlling said sensing means and thereby receiving signals representative of said pressure at predetermined intervals over time and providing said output display and/or signals at predetermined intervals.
5. Apparatus as defined in claim 4 in which said computing apparatus includes means for providing an output display and/or signals representative of the liquid leak rate by operating a computer program operating an algorithm where .DELTA.t is a signal representing the elapsed time during which the change in differential hydrostatic pressure .DELTA.P was sensed.
6. Apparatus as defined in claim 2 in which said same level at which the pressures are sensed is adjacent the bottom of both tanks.
7. Apparatus for measuring leakage of liquid into or from a storage tank comprising:
(a) a liquid containing storage tank having rigid walls, (b) a reference tank having similar coefficient of thermal expansion as the storage tank immersed into liquid stored in the storage tank, filled with the same liquid as contained in the storage tank, and having sealed and rigid heat conducting walls at least where it is in contact with the liquid, the cross-sectional area of the reference tank being proportional to the cross-sectional area of the storage tank at least wherever it is in contact with liquid, the vapor space above the liquid in the reference tank being vented to the vapor space above the liquid in the storage tank, (c) means at the same level within the liquid in the storage tank and within the liquid in the reference tank for sensing change in differential hydrostatic pressure of the liquid over a time interval .DELTA.T, whereby the volume of any liquid lost from or gained by the storage tank (.DELTA.V) during the time interval .DELTA.T may be determined from the algorithm .DELTA.V= where .DELTA.P is the sensed change in differential hydrostatic pressure between the storage and reference tanks during the time interval .DELTA.T, A is the cross-sectional area at the level of the liquid surface of the storage tank, ? is the density of the liquid in the tank, and g is the gravitational constant.
(a) a liquid containing storage tank having rigid walls, (b) a reference tank having similar coefficient of thermal expansion as the storage tank immersed into liquid stored in the storage tank, filled with the same liquid as contained in the storage tank, and having sealed and rigid heat conducting walls at least where it is in contact with the liquid, the cross-sectional area of the reference tank being proportional to the cross-sectional area of the storage tank at least wherever it is in contact with liquid, the vapor space above the liquid in the reference tank being vented to the vapor space above the liquid in the storage tank, (c) means at the same level within the liquid in the storage tank and within the liquid in the reference tank for sensing change in differential hydrostatic pressure of the liquid over a time interval .DELTA.T, whereby the volume of any liquid lost from or gained by the storage tank (.DELTA.V) during the time interval .DELTA.T may be determined from the algorithm .DELTA.V= where .DELTA.P is the sensed change in differential hydrostatic pressure between the storage and reference tanks during the time interval .DELTA.T, A is the cross-sectional area at the level of the liquid surface of the storage tank, ? is the density of the liquid in the tank, and g is the gravitational constant.
8. Apparatus as in claim 7 including a valve in a wall of the reference tank located at a level for controllably introducing liquid from the storage tank into the reference tank prior to sensing said pressures.
9. Apparatus as defined in claim 7 in which the storage tank is a cylinder having a vertical axis and the reference tank is a cylindrical tube having a sealed bottom extending from the top to the bottom of the storage tank.
10. Apparatus as defined in claim 9 in which the storage tank contains a filler hole at a top surface and in which the reference tube extends downwardly from the filler hole.
11. Apparatus as defined in claim 9 including computing apparatus for receiving signals from said sensing means corresponding to said pressure and providing an output display and/or signals representative of the volume of said liquid lost or gained, by storing data signals representative of said cross-sectional area, said density of the liquid, and said gravitational constant, and operating a computer program processing said algorithm.
12. A method for determining leakage of liquid from or into a rigid walled storage tank comprising detecting hydrostatic pressure at a level within the liquid within the storage tank, detecting hydrostatic pressure ? at about the same level, of liquid contained within a rigid walled reference tank, which reference tank has thermal energy conducting sealed walls, and which is immersed within the liquid of the storage tank and is filled to the same level as the storage tank with the same liquid, and has the vapor space above its liquid vented to the vapor space above the liquid in the storage tank, and providing a liquid volume leakage signal .DELTA.V representing leakage over a time interval .DELTA.T by operating a computer program to process the algorithm .DELTA.V= where .DELTA.P is the change in detected differential hydrostatic pressure between the storage tank and the reference tank during a time interval .DELTA.T, A is the cross-sectional area of the storage tank at the level of the liquid surface, ? is the density of the liquid in the tank, and g is the gravitational constant.
13. A method as defined in claim 12 including the step of providing a leakage rate signal by operating said computer program to process the algorithm where .DELTA.t is the time interval over which the pressure change .DELTA.P is determined.
14. Apparatus for measuring leakage of liquid from a liquid storage tank having rigid liquid containing walls comprising:
(a) a reference tank for immersion into the storage tank, the reference tank being rigid walled wherever it is in contact with liquid, having cross-sectional area proportional at every height in contact with the liquid to that of the storage tank, and thermal energy conducting walls, sealed within the liquid of the storage tank, and being fabricated of material whereby the reference and storage tank have similar temperature coefficients of linear expansion, (b) means for filling the reference tank with the same liquid and to the same height as the liquid in the storage tank, (c) means for venting the vapor space above the liquid of the reference tank, (d) means for sensing the change in differential hydrostatic pressure of the liquid at about the same level within the storage and reference tanks, whereby the volume of any liquid lost from or gained by the storage tank (.DELTA.V) during a time interval .DELTA.T may be determined by operating the algorithm .DELTA.V= where .DELTA.P is a signal representing the sensed change in differential hydrostatic pressure between the storage and reference tanks during the time interval.DELTA.T, A is a signal representing the cross-sectional area at the level of the liquid surface of the storage tank, ? is a signal representing the density of the liquid in the tank, and g is a signal representing the gravitational constant.
(a) a reference tank for immersion into the storage tank, the reference tank being rigid walled wherever it is in contact with liquid, having cross-sectional area proportional at every height in contact with the liquid to that of the storage tank, and thermal energy conducting walls, sealed within the liquid of the storage tank, and being fabricated of material whereby the reference and storage tank have similar temperature coefficients of linear expansion, (b) means for filling the reference tank with the same liquid and to the same height as the liquid in the storage tank, (c) means for venting the vapor space above the liquid of the reference tank, (d) means for sensing the change in differential hydrostatic pressure of the liquid at about the same level within the storage and reference tanks, whereby the volume of any liquid lost from or gained by the storage tank (.DELTA.V) during a time interval .DELTA.T may be determined by operating the algorithm .DELTA.V= where .DELTA.P is a signal representing the sensed change in differential hydrostatic pressure between the storage and reference tanks during the time interval.DELTA.T, A is a signal representing the cross-sectional area at the level of the liquid surface of the storage tank, ? is a signal representing the density of the liquid in the tank, and g is a signal representing the gravitational constant.
15. Apparatus as defined in claim 1, 2, 7 or 14 in which the storage tank and reference tank are open to atmospheric pressure.
16. Apparatus as defined in claim 1, 2 or 3 in which the storage tank is a cylinder having a horizontal axis and the reference tank is a cylindrical tube having a sealed bottom extending from the top to the bottom of the storage tank.
17. Apparatus as defined in claim 1, 2 or 3 in which the storage tank is a cylinder having a horizontal axis and the reference tank is a cylindrical tube having a sealed bottom extending from the top to the bottom of the storage tank, and in which the storage tank contains a filler hole at a top surface and in which the reference tube extends downwardly from the filler hole.
18. Apparatus as defined in claim 1, 2 or 3 in which the storage tank is a cylinder having a horizontal axis and the reference tank is a cylindrical tube having a sealed bottom extending from the top to the bottom of the storage tank, and further including computing apparatus for receiving signals from said sensing means corresponding to said pressure and providing an output display and/or signals representative of the volume of said liquid lost or gained, by storing data signals representative of said cross-sectional area, said density of the liquid, and said gravitational constant, and operating a computer program processing said algorithm.
19. Apparatus as defined in claim 1, 2, 7 or 14 in which the storage tank and reference tank are vented to the atmosphere via a pressure relief valve.
20. A method for determining leakage of liquid from or into a rigid walled storage tank comprising detecting hydrostatic pressure at a level within the liquid within the storage tank, detecting hydrostatic pressure, at about the same level, of liquid contained within a rigid walled reference tank, which reference tank has thermal energy conducting sealed walls and which is immersed within the liquid of the storage tank and is filled to the same level as the storage tank with the same liquid, and has the vapor space above its liquid vented to the vapor space above the liquid in the storage tank, and has cross-sectional area proportional to the cross-sectional area of the storage tank at every level wherever it is in contact with liquid, and providing a liquid volume leakage signal .DELTA.V
representing leakage over a time interval .DELTA.T by operating a computer program to process the algorithm .DELTA.V= where .DELTA.P is the change in detected differential hydrostatic pressure between the storage tank and the reference tank during a time interval .DELTA.T, A is the cross-sectional area of the storage tank at the level of the liquid surface, ? is the density of the liquid in the tank, and g is the gravitational constant.
representing leakage over a time interval .DELTA.T by operating a computer program to process the algorithm .DELTA.V= where .DELTA.P is the change in detected differential hydrostatic pressure between the storage tank and the reference tank during a time interval .DELTA.T, A is the cross-sectional area of the storage tank at the level of the liquid surface, ? is the density of the liquid in the tank, and g is the gravitational constant.
21. A method for determining leakage of liquid from or into a rigid walled storage tank which is open to the atmosphere comprising detecting hydrostatic pressure at a level within the liquid within the storage tank, detecting hydrostatic pressure, at about the same level, of liquid contained within a rigid walled reference tank, which reference tank has thermal energy conducting sealed walls, which is open to the atmosphere and which is immersed within the liquid of the storage tank and is filled to the same level as the storage tank with the same liquid, and providing a liquid volume leakage signal .DELTA.v representing leakage over a time interval .DELTA.T by operating a computer program to process the algorithm .DELTA.V = where .DELTA.P is the change in detected differential hydrostatic pressure between the storage tank and the reference tank during a time interval .DELTA.T, A is the cross-sectional area of the storage tank at the level of the liquid surface, ? is the density of the liquid in the tank, and g is the gravitational constant.
22. A method for determining leakage of liquid from or into a rigid walled storage tank which is open to the atmosphere comprising detecting hydrostatic pressure at a level within liquid within the storage tank, detecting hydrostatic pressure, at about the same level, of liquid contained within a rigid walled reference tank, which reference tank has thermal energy conducting sealed walls, which is open to the atmosphere. and which is immersed within the liquid of the storage tank and is filled to the same level as the storage tank with the same liquid, and has cross-sectional area proportional to the cross-sectional area of the storage tank at every level wherever it is in contact with liquid, and providing a liquid volume leakage signal .DELTA.V
representing leakage over a time interval .DELTA.T by operating a computer program to process the algorithm .DELTA.V= where .DELTA.P is the change in detected differential hydrostatic pressure between the storage tank and the reference tank during a time interval .DELTA.T, A is the cross-sectional area of the storage tank at the level of the liquid surface, ? is the density of the liquid in the tank, and g is the gravitational constant.
representing leakage over a time interval .DELTA.T by operating a computer program to process the algorithm .DELTA.V= where .DELTA.P is the change in detected differential hydrostatic pressure between the storage tank and the reference tank during a time interval .DELTA.T, A is the cross-sectional area of the storage tank at the level of the liquid surface, ? is the density of the liquid in the tank, and g is the gravitational constant.
23. A method as defined in claim 20, 21 or 22 including the step of providing a leakage rate signal by operating said computer program to process the algorithm where .DELTA.t is the time interval over which the pressure change .DELTA.P is determined.
24. Apparatus for measuring leakage of liquid from a liquid storage tank having rigid liquid containing walls comprising:
(a) a reference tank for immersion into the storage tank, the reference tank being rigid walled wherever it is in contact with liquid, and having thermal energy conducting walls, sealed within the liquid of the storage tank, and being fabricated of material whereby the reference and storage tank have similar temperature coefficients of linear expansion, (b) means for filling the reference tank with the same liquid and to the same height as the liquid in the storage tank, (c) means for sensing the change in differential hydrostatic pressure of the liquid at about the same level within the storage and reference tanks, and (d) means for determing the volume of liquid lost from the storage tank from any sensed change in differential hydrostatic pressure.
(a) a reference tank for immersion into the storage tank, the reference tank being rigid walled wherever it is in contact with liquid, and having thermal energy conducting walls, sealed within the liquid of the storage tank, and being fabricated of material whereby the reference and storage tank have similar temperature coefficients of linear expansion, (b) means for filling the reference tank with the same liquid and to the same height as the liquid in the storage tank, (c) means for sensing the change in differential hydrostatic pressure of the liquid at about the same level within the storage and reference tanks, and (d) means for determing the volume of liquid lost from the storage tank from any sensed change in differential hydrostatic pressure.
25. A method for determining leakage of liquid from or into a rigid walled storage tank comprising detecting hydrostatic pressure at a level within the liquid within the storage tank, detecting hydrostatic pressure at about the same level, of liquid contained within a rigid walled reference tank, which reference tank has thermal energy conducting sealed walls, and which is immersed within the liquid of the storage tank and is filled to the same level as the storage tank with the same liquid, and has the vapor space above its liquid vented to the vapor space above the liquid in the storage tank, and determining the volume of liquid leakage from the change in detected differential hydrostatic pressure between the storage tank and the reference tank over a time interval.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000535868A CA1286523C (en) | 1987-04-29 | 1987-04-29 | Apparatus and method for determining rate of leakage of liquid from and into tanks |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000535868A CA1286523C (en) | 1987-04-29 | 1987-04-29 | Apparatus and method for determining rate of leakage of liquid from and into tanks |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1286523C true CA1286523C (en) | 1991-07-23 |
Family
ID=4135532
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000535868A Expired - Fee Related CA1286523C (en) | 1987-04-29 | 1987-04-29 | Apparatus and method for determining rate of leakage of liquid from and into tanks |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1286523C (en) |
-
1987
- 1987-04-29 CA CA000535868A patent/CA1286523C/en not_active Expired - Fee Related
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