CA2265711A1 - Device for detecting and locating leakage fluids in sealing systems - Google Patents

Abstract

The invention concerns a device for detecting and locating leakage fluids in sealing systems, said device being characterized by a single-layer flat structure (4) which comprises electrically conductive particles and/or fibres and is disposed all-over the exterior of a sealing region to be monitored. The flat structure comprises an area-specific electrical resistance which, when wetted with an electrically conductive fluid, decreases in the region of the wetting and, when wetted with an electrically non-conductive fluid, increases in the region of the wetting. The flat structure (4) is further provided with a plurality of measuring contacts (5, 6) which are connected via one or a plurality of bus transmission lines to a measuring and evaluating arrangement (9) by means of which the electrical resistance of the flat structure (4) and/or the potential distribution can be measured in relation to a counter electrode disposed on the interior of the sealing region to be monitored, and a variation in the local resistance distribution and/or potential distribution within the flat structure (4) can be determined.

Description

lCA 02265711 1999-03-10DEVICE FOR DETECTING AND LOCATING LEAKAGE FLUIDS INSEALING SYSTEMSThe present invention relates to a device for detectingand locating both electrically conductive and,electrically non-conductive leakage fluids in sealingsystems.DE 69014264 T2 describes a method for detecting leakagesin an insulation layer which for example is installedbelow a waste dump to protect the groundwater againstcontaminated leakage water from the waste dump. In this,a first and a second geotextile material are arranged,said geotextile materials being separated from each otherby a further insulation layer. Woven into the twogeotextile materials are electrically—conductive,essentially parallel—aligned threads, with the geotextilematerials being arranged in such a way that theconductive threads of the first geotextile material forman angle of preferably 90° with the conductive threads ofthe second geotextile material. This known process ischaracterised in that the conductive threads are combinedin pairs, with the spacing between the pairs beingfurther apart than the thread spacing in the pair. Inorder to detect a leakage, the electrical voltage and/orthe resistance between two conductive threads forming apair is determined. The location of the leakage can thusbe established by cross—position fixing.CA 02265711 1999-03-10This known method has the disadvantage in that detectionof a leakage is ensured only if the conductive threadsare woven into the geotextile materials with narrowspacing between said threads. For if the conductivethreads are spaced relatively wide apart, and if only asmall amount of liquid leaks from a defective position inthe insulation layer, then bridging of the conductivethreads by the liquid leaking out, and thus detection ofthe damage, is not ensured in every case. Since inaddition, it cannot be assumed that damage always onlyrelates to the inner insulation layer but, especiallywith damage occurring in the construction phase, veryoften also relates to the insulation layer between thetwo geotextile materials comprising the conductivethreads itself, under certain circumstances, leakageliquid can enter the ground without such damage beingdetected.If however the spacing of the parallel conductive threadsis selected so narrow as to really ensure detection of aleakage, then the number of measuring contacts which mustbe connected to the conductive threads is accordinglyhigh. However, this requires very considerable effortresulting in relatively high production costs of suchleakage detection and location systems.Furthermore it would be desirable if a device wereavailable which would enable the detection not only ofelectrically conductive leakage fluids such as forexample leakage water, but also electrically non-conduc-tive leakage fluids such as for example heating oil.CA 02265711 1999-03-10From EP 0372697 A2 a sensor for the detection of oilleaks is already known. However, the known sensor is notsuitable for the detection of leakage water or otheraqueous leakage fluids because it comprises a resistorsurrounded by an encasing made of a porous water-repellent resin, and is itself formed from a porous,water—repellent resin comprising electrically conductivecarbon particles, said carbon particles comprising awater—repellent layer.Furthermore, from US 5 191 785 a device for identifyingand locating a leakage of electrically conductive fluidsin the inner liner of a vessel having a laminated wallstructure is known. A graphite veil is mounted betweenthe interior layer of the vessel made from anelectrically non-conductive material and the outer shellof the vessel, said graphite veil comprising severalmeasuring electrodes. In addition, the device comprises amain electrode arranged within the vessel in such a waythat it is in permanent contact with the electricallyconductive fluid contained therein. To detect and locateany leakage in the interior layer of the vessel, avoltage difference is consecutively applied to variouselectrode pairs and measured against the main electrode,with a leakage in the electrically non-conductiveinterior layer of the vessel practically representing anintermediate measuring tap on a long resistor, formed bya section of the graphite veil located between a pair ofelectrodes. However, detection and location of a leakageof electrically non-conductive fluids is not possiblewith this known device.CA 02265711 1999-03-103aBased on this state of the art, it is the object of thepresent invention to provide a device of the typementioned in the introduction which ensures safedetection of leakages in sealing systems both in the caseof conductive and non—conductive leakage fluids, andwhich in addition can be produced economically.According to the invention, this object is met by adevice of the initially mentioned type characterised by asheetlike structure comprising electrically conductiveparticles and/or fibres, said structure being arrangedall over the exterior of a sealing area to be monitored,and comprising an area—specific electrical resistance;said resistance decreasing in the area of wetting whenwetted with an electrically conductive liquid, and saidresistance increasing in the area of wetting when wettedwith an electrically non—conductive liquid; with thesheetlike structure comprising an array of measuringcontacts which are connected to a measuring andevaluation device by way of one or several bustransmission lines; by means of which measuring andevaluation device the electrical resistance of thesheetlike structure can be measured and a change in thelocal resistance distribution within the sheet-like ‘structure can be determined.CA 02265711 1999-03-10With the device according to the invention, containers aswell as sealing systems can be reliably monitored forleakage of both electrically conducting and non-conducting fluids, with even small quantities of leakagebeing detectable. The number of measuring contactsrequired for this is comparatively small so that thedevice according to the invention is relativelyeconomical to realise. The use of the bus transmissionline or-lines also contributes to this. Furthermore, thedevice according to the invention makes it possible toexactly locate the place of damage, consequently therespective leakage can be repaired in a selective way andat justifiable cost. The number and spacing of themeasuring contacts are suitably to be selected in such away that the resistance distribution in the sheetlikestructure can be determined with a sufficient localresolution over its entire area. seal to be monitored, the device accordinginvention additionally makes it possib to monitor theinsulation resistance of the seal s well as to locatethe defective position by me of the potentialdistribution occurring in the sheetlike structure.Consequently, moist e in the sheetlike structure due tocondensation c be distinguished from moisture due todamage, locating any leakage is possible even whentheaeetlike structure is moist throughout, e.g. as aCA 02265711 1999-03-10The measuring and evaluation device can measure theelectrical resistance of the sheetlike structure eithercontinuously or at specified times. determine the resistance of the sheetl'The electrically conductive particles and/or fibres ofthe sheetlike structure preferably comprise metal and/orconductive carbon. The sheetlike structure, which ispreferably made on the basis of a nonwoven fibre fabricor a fine, grid—like net structure, is preferably made insuch a way that electrical conduction takes place betweenany points in the sheetlike structure, essentially viathe surface of the particles and/or fibres.According to a further advantageous embodiment, theoutside of the sheetlike structure is provided with aliquid—impermeable layer. This arrangement isparticularly advantageous if the sealing system to bemonitored is situated in the ground and one has to expectthat groundwater and/or surface water will impinge on thesheetlike structure thus possibly leading to a change inthe electrical resistance of the sheetlike structure.A further advantageous embodiment provides for at leastone counter electrode which is located wiehin—Ehe—sealingsyseem—er in the ground outside the sealing system. Inthis way if there is a liquid-impermeable layer on theéaséée—er outside of the sheetlike structure it can bedetected whether the layer is intact or damaged.CA 02265711 1999-03-10According to another advantageous embodiment of theinvention, the measuring contacts for coupling to thesheetlike structure comprise a contact surface made ofconductive foam material, preferably conductivepolyurethane foam. In this way a perfect coupling to thesheetlike structure is achieved, with said coupling beingeasy to produce. This applies in particular when usingpolyurethane foam material, which due to its high micro-deformability and at the same time superior conductivity,is able to contact the sheetlike structure with a lowtransition resistance between a metallic contact surfaceof the measuring contact and the sheetlike structure.A further preferred embodiment of the invention ischaracterised in that the measuring contacts are arrangedspread out on the sheetlike structure. In this way moreexact location of leakages can be achieved because, dueto the two—dimensional evaluation of the measuringresults, position fixing of the damage is not solelylimited to segments situated between the measuringcontacts arranged at the periphery of the sheetlikestructure, but with increased accuracy can also takeplace between the measuring contacts spread out on thesheetlike structure.For interrogating the measuring contacts, preferably ahybrid analog-digital bus system is provided whosedigital and analog lines are series—connected, withswitches at the measuring contacts being able to beactivated via the digital part of the bus, said switchesconnecting the analog signal and data lines to therespective measuring contact.CA 02265711 1999-03-10Below, the invention is illustrated in more detail bymeans of a drawing showing one embodiment. In the drawingFigure 1 is a diagrammatic illustration of a tank shownin a section view, wherein the tank comprises adevice according to the invention;Figure 2 is a top view of the tank and the deviceaccording to the invention of Figure 1;Figure 3 is a perspective view of a section of asheetlike structure of the device according tothe invention; are various views of a serial coupling element42°’Figurefor producing a measuring contact on thesheetlike structure.Figures 1 and 2 show a tank 1 in which a water-endangering liquid 2, such as e.g. heating oil or fuel,is stored. Reference 3 designates the lockable fillingaperture of the tank 1.All over the bottom and the sides of the tank 1, there isa sheetlike structure 4 which, preferably based on anonwoven fibre fabric, comprises electrically-conductiveparticles and/or fibres. The sheetlike structure 4 ismade in such a way that electrical conduction takes placebetween any points in the sheetlike structure 4,lCA 02265711 1999-03-10essentially across the surface of the particles orfibres. The specific resistance of the conductiveparticles or fibres and their mass per unit of area arematched in such a way that the sheetlike structure 4 hasan area—specific electrical resistance; said resistancedecreases in the area of wetting when wetted with anelectrically conductive liquid, and said resistanceincreases in the area of wetting when wetted with anelectrically non-conductive liquid.The sheetlike structure 4, at its upper edge surroundingthe tank, comprises an array of measuring contacts 5 to8, between which the electrical resistance of thesheetlike structure can be measured at any time by meansof an automatic measuring and evaluation device 9. Themeasuring contacts 5 to 8 are arranged in pairs, with theindividual pairs on the one hand forming parallelmeasuring taps and on the other hand intersectingmeasuring taps. The number and spacing of the measuringtaps is selected in such a way that the resistancedistribution for the entire area of the sheetlikestructure 4 can be determined with adequate localresolution.As an alternative to, or in addition to, the arrangementshown in the drawing, the measuring contacts can also bearranged spread out in a matrix-like arrangement, inspecified locations on the sheetlike structure +eee—PigT4+.The measuring contacts 5 to 8 shown in Figures 1 and 2are connected to the measuring and evaluation device 9via bus transmission lines 11 to 14. A hybrid analog-digital bus system is used which does not require ex-pensive analog~digital conversion at the measuring taps.1CA 02265711 1999-03-10Via the digital part of the bus, switches at themeasuring contacts are activated, said switchesconnecting the analog signal and data lines to themeasuring contact.The measuring and evaluation device comprises a displaydevice (not shown), for example in the form of a monitor,by way of which the location or the coordinates of anyleakage are displayed. Furthermore, the measuring andevaluation device 9 comprises a signal device (not shown)which signals any leakage by an acoustic and/or visualalarm signal. Moreover, the measuring and evaluationdevice 9 comprises a modem 15 for remote transfer of theacquired measuring data.If the resistance distribution of the sheetlike structure4 is known prior to filling the tank 1, i.e. withoutleakage fluid impinging on the sheetlike structure 4,then by comparing the resistance distribution measured ata later time with the first measured resistancedistribution, any occurrence of a leakage can be detectedby local increase or decrease of resistance values. Inthis way, any change of resistance values is at firstlimited to the area which is moistened by liquid, thus‘locating the leakage is possible.Since it cannot be ruled out that the leakage fluid willspread in the monitored area or below a seal to bemonitored, thus rendering exact position fixing no longerpossible, the number of measuring cycles of the measuringand evaluation device is set sufficiently high to ensurethat the resistance distribution is establishedimmediately after the first appearance of the leakagelCA 02265711 1999-03-10fluid, before the liquid has spread out over a largerarea .Figure 3 shows a diagrammatic marginal section of asheetlike structure 4 according to the invention. It canbe noted that the sheetlike structure 4 comprisingelectrically conductive particles and/or fibres, has atits margin a connection element 5 forming a measuringcontact. Furthermore, on its outside, the sheetlikestructure 4 comprises a liquid—impermeable layer 10, forexample a plastic layer.The application of the device according to the inventionis not solely limited to leakage monitoring of containersand sealing systems but is in particular also suitablefor monitoring pipelines carrying water—endangeringliquids. For this purpose, the sheetlike structure 44 shown in Figure 3 is produced in, or cut to, strip shapesor lengths of material.To produce an extensive sheetlike structure, severallengths of material can be adjoined, maintaining acertain overlap, for example 5 cm. To achieve goodcontact in the area of overlap it is advantageous if thesegment of the sheetlike structure overlapping on the topor outside, is placed with a longitudinal fold onto thelongitudinal margin of the segment below, and that alongthe margin of overlap, both segments are held together byadhesive tape. In this, the segments can be 2 m or 4 mwide.CA 02265711 1999-03-1011. 1 _ ' ; ': '....' - _ - ; ’- -.._;== ....- --device according to the invention is used for monito nga sealing membrane 16 of a flat roof for any leakage. Thesheetlike structure 4 which is preferably produ -d fromnonwoven fibre fabric is arranged below the s:-lingmembrane 16 to be monitored (shown partial v cut away)and on one side comprises an array of me. uring contacts17 in a matrix—like arrangement. The eetlike structure4 acts as an effective sensor surfao- over the entirearea. In order to detect any lea age, on top of the roofsealing membrane at least one counter electrode 18 isarranged. If the sealing me crane 16 is intact, then theresistance measured betwe= one of the measuring contacts17 and the counter ele rode 18 is very high. Bycontrast, if rain wa -r enters as a result of a leakage,the resistance of e sheetlike structure 4 is low in thearea of moisten‘ g. By sequential interrogation of theindividual m-;suring contacts 17, the leakage in the roofseal 16 cav quickly be located. Below the sheetlikestructur~ 4, a further seal 20 as well as at least onefurth= counter electrode 21 can be provided as anado'tional protection for the roof structure 19 below4 W 4Figures SA to $C show a lateral view (Fig. KA), a topview (Fig. $B) and a bottom view (Fig. %C) of a preferredembodiment of a measuring contact module 17 to bearranged on the sheetlike structure. The contact surfaceof the module 17 comprises a conductive polyurethane foammaterial. In this way a good contact between themeasuring points and the sheetlike structure is achieved.Both in the digital and in the analog lines of the bussystem the measuring positions are series—connected andtogether with the circuit electronics and a contact, _,_.._.....—._.._....a_CA 02265711 1999-03-10surface 22 are sealed in the module case 23 made of epoxyresin.

Claims (9)

Claims

1. A device for detecting and locating both electrically conductive and electrically non-conductive leakage fluids in sealing systems, c h a r a c t e r i s e d by a sheetlike structure (4) comprising electrically conductive particles and/or fibres, said structure being arranged all over the exterior of a sealing area to be monitored, and comprising an area-specific electrical resistance; said resistance decreasing in the area of wetting when wetted with an electrically conductive liquid, and said resistance increasing in the area of wetting when wetted with an electrically non-conductive liquid; with the sheetlike structure comprising an array of measuring contacts (5, 6, 7, 8; 17) which are connected to a measuring and evaluation device (9) by way of one or several bus transmission lines (11, 12, 13, 14); by means of which measuring and evaluation device the electrical resistance of the sheetlike structure (4) can be measured continuously or at predetermined times and a change of the local resistance distribution within the sheetlike structure (4) can be determined.

2. A device according to claim 1, characterised in that the sheetlike structure (4) comprises particles and/
or fibres made of metal and/or conductive carbon.

3. A device according to claim 1 or 2, characterised in that electrical conduction takes place between any points in the sheetlike structure (4), essentially via the surface of the particles and/or fibres.

4. A device according to one of the preceding claims, characterised in that on the outside the sheetlike structure (4) comprises a liquid-impermeable layer (10).

5. A device according to one of the preceding claims, characterised in that means are provided by which a constant measuring current can be sent across at least part of the sheetlike structure, so that the voltage distribution in the sheetlike structure (4) in which current flows, can be determined by means of the measuring contacts (5, 6, 7, 8; 17).

Claim 6:

6. A device according to one of the preceding claims, c h a r a c t e r i s e d in that furthermore at least one counter electrode is provided which is locatable outside the sealing area to be monitored;
with the potential distribution in relation to the counter electrode being measurable and a change in the potential distribution being determinable by the measuring and evaluation device (9).

7. A device according to one of the preceding claims, characterised in that each of the measuring contacts (5, 6, 7, 8; 17) comprises a contact surface made of conductive foam material for coupling to the sheetlike structure (4).

8. A device according to one of the preceding claims, characterised in that the measuring contacts (5, 6, 7, 8; 17) are arranged spread out, preferably in a matrix-like arrangement.

9. A device according to one of the preceding claims, characterised in that for interrogating the measuring contacts (5, 6, 7, 8; 17) a hybrid analog-digital bus system is provided whose digital and analog lines are series-connected, with switches at the measuring contacts being able to be activated via the digital part of the bus, said switches connecting the analogue signal and data lines to the respective measuring contact (5, 6, 7, 8; 17).