METHOD AND APPARATUS FOR DETECTING LEAKS AND OTHER DEFECTS ON SEWERS AND THE LIKE CHANNELS

Abstract: A method for detecting leaks and other defects on inspection of underground sewers and the like channels, wherein a movable detecting and inspection unit (3) communicating with an above ground localized central unit (12) is moved along the sewer (3) and scanning the inside of the sewer with the aid of an IR scanning unit or the like temperature. The novelty lies in the steps of adapting the scanning device to register and sense temperatures deviating from the prevailing temperature of the inside of the sewer or the like caused by ground or surface water flowing or leaking in, adapting said scanning device to convey to the central unit (12), which includes display and recording means, signals indicating sensed temperatures; adapting a metering device connected to the scanning unit to simultaneously send information on distance moved and processing the signals and information received in the central unit to give a thermal picture and location indication.

Description: METHOD AND APPARATUS FOR DETECTING LEAKS AND OTHER DEFECTS ON SEWERS AND THE LIKE CHANNELS This invention relates to a method for detecting leaks and other defects on inspection of underground sewers and the like channels, wherein a movable detecting and inspection unit communicating with an above ground localized central unit is moved along the sewer and upon travelling along such, by scanning the inside of the sewer with the aid of an IR scanning unit or the like tempera¬ ture registering device. In all countries the sewage systems comprise diffe- rent parts of various age and quality. A disquietingly large part of the system is in strong need of repair. It is not to exaggerate to say, that many towns today are facing a "maintenance bomb". Damages like cracks, roots growing into the sewers and displaced joints are causing leakage. The greatest problem, however, is not water leaking out from the sewage system, but irrelevant water leaking into it, e.g. ordinary ground water. This type of irrele¬ vant water in the sewage system can today make up some 50% of the total water flow, with the following consequences: waste water treatment plants and sewers must be over- dimensioned - increased operation and treatment costs increased costs due to the need for earlier investment in new treatment plants lower treatment effect in existing treatment plants overloaded sewage systems damage to the environment as the amount of disposed waste increases - flooded basements It is very clear that the above mentioned factors strongly influence the cost for waste water treatment. To repair the whole sewage system is not realistic, which has boosted the efforts to find inspection methods on which the plans for repair can be based, which gives priority to the worst leakages. A number of inspection and detection methods are today in commercial use, like manual measurement of the water flow at different spots, level registration, acou¬ stical doppler measurement, dilution measurement by means of tracer elements and TV inspection inside the sewers. By using these methods it can be confirmed that there is irrelevant water in the sewers. The common shortcoming in hitherto known methods is, however, that they only indicate that there is a leakage somewhere in a part of a sewer but they do not give any clue to the exact loca- tion of most of the leakages. Major leakages and damages have to be taken care of. The municipality budget cannot, however, carry the cost for repair and renovation to the necessary extent. The main aim with inside for example TV inspection is therefore to form a basis for giving priority to certain parts of the network and to select the appropriate repair methods. The above described difficulty to give an indication of the exact situation of the leakages has given as a result that the whole sewer between two manholes is repaired, i.e. 100 m (330 ft) is repaired instead of the damaged parts only. Insufficient test and inspection methods have, thus, resulted in unnecessarily expensive repair techniques. The new method for detecting where water, ground water or surface water leaks into a sewer includes the use of an IR scanning device, a so called THERMOVISION camera. It has earlier in U.S. Patent No. 3 771 350 been suggested to use an IR scanning device for detection of leaks at pressurized pipe lines and it is said that fluid under pressure leaking out from a pipe line causes a change of temperature. This latter statement is neither founded on any facts nor supported by any test reports or the like and must, accordingly, be regarded as wishful thinking unsupported by reality. The present invention is based on the proven fact that the temperature inside a sewer, due to the tempera- ture of the waste water flowing therethrough differs from and normally is considerably higher than the temperature of the surroundings and, thus that the temperature of any ground or surface water leaking into said sewer is lower than the inside temperature of the sewer. This fact has been utilized to create the method and an apparatus for the same accordning to this invention. The new method includes the following steps: adapting the scanning device to register and sense temperatures deviating from the prevailing temperature of the inside of the sewer or the like and being caused by ground or surface water flowing or leaking in, the prevailing tempe¬ rature of the sewer being determined by the waste water flowing therethrough; further adapting said scanning de¬ vice to convey to the central unit, which includes dis- play and recording means, signals indicating sensed tem¬ peratures and location of areas having such temperatures; adapting a metering device connected to the scanning unit to simultaneously send to such central unit information on distance moved and processing the signals received in the central unit to give a thermal picture and location indication. The sewer is inspected from the inside by means of a modified Thermovision ®782. The inspection is carried out in a fairly simple way. The Thermovision ®scanner is encapsulated into a water¬ tight protective cover and is mounted on a sleigh. The sleigh is pulled by a wire through the sewer between two manholes. The scanner is connected with the display unit over a long cable. This technique is wellknown and is used in the same way for TV inspection of sewers. The information from the thermal camera is taped on to a Video Tape Recorder together with date, number of the inspected sewer and the distance. Thus registered data are checked continuously during the field work and are evaluated later. As a basis for giving the correct priorities to various repair measures to be taken, a re¬ port is made, which comprises a video tape and an evalua¬ tion protocol where the kind of damage and the extent of the leakage and its exact location are stated. The measurement capacity per equipment is approxi¬ mately 400 m (1300 ft) per working day. The equipment can inspect sewers of a smallest dimension of 225 mm (9 inch) . The invention will be further described below with reference to the accompanying drawings. On the drawings Figure 1 is a highly schematic view, partly in section illustrating the inspection method and apparatus, Figure 2 is a diagram illustrating the build up of the electronic system, Figures 3, 4, 5 and 6 are examples of thermographic pictures and Figures 3a, 4a, 5a and 6a are schematic dia¬ grams explaining the thermographic pictures of Figs. 3 - 6. With reference to Fig. 1 a sewer with waste water is designated 1 and manhole wells are designated 2. An IR scanning device 3 is mounted inside a waterproof protecting shell 4 with a window 5 and carried by a sledge 6. A pulling wire 7 coupled to a winch 8 is attached to the sledge and a communication cable 9 rolled off and on' a reel 10 with a metering device 11, fig. 2, connects the scanning unit 3 with a cetral unit 12 hosed inside a van 13. The physical environment inside sewers is, for ob¬ vious reasons, hostile to the thermographic equipment, which has, thus, to be encapsulated. This is carried out by enclosing it into the watertight sleigh, with special leakproof connectors 14, e.g. of so called military type and a rugged protective lens. The cable, which is dragged through the sewer must also be of a waterproof quality. The surrounding temperature in the sewer ranges from 8 to 12°C (46-54°F). The thermal resolution of Thermovision ® at this am¬ bient temperature is far better than the 1°C (2°F) resolu- tion required by the application. The protection of the front lens of Thermovision has to be a window 5, which is coated for the actual wavelengths 2-6 mikrons. An uncoated sapphire window would give a strong radiation loss because of very misadapted transmission properties and high reflexions as a consequence. The chosen window has a low transmission loss, is not harmed by the damp environment and has a coating which withstands fre¬ quent cleaning. The fitting of the window is, however, made in such a way, that it may be exchanged quite easily. The application needs a wide-angle lens of 40° field of view, because of the small dimensions of the better part of the sewers, the smallest of which are 225 mm in diameter. This lens has a large depth of focus, which makes it possible to sharply see very close objects as well as more remote objects, i.e. a few meters away. As it is of greatest importance to know the exact location of a found leak, there is a distance meter hooked up to the Thermovision display unit, which displays the distance at the bottom end of the screen. The accuracy of the distance is a tenth of a meter (4 inches). A code designation of the sewer being measured and a size code can also be written onto the screen besides the distance, for example 850818 364 3 68.3, meaning August 18, 1985, sewer No. 364, size ø 300 mm and at 68,3 m from the opening of the sewer. The measurement is recorded onto video tape together with the distance information. The evaluation gives as result a written protocol with reference to the distance indications, with comments and with a tape. On Figure 2, the part to the left the double dash- dotted line indicates the scanner unit 3 inside the sewer and the part to the right of same dash-dotted line the so called central unit designated 12 in Fig. 1. The scanner 3 is enclosed by the water and moist proof shell 4 and the cable 9 is connected to the said unit by a connector 14. Inside the van 13 is found the cable reel 10 with its metering device 11 adapted to count the length of cable reeled off (or on). The cable 9 is via a connector box 15 connected to a display unit 16 in turn via a two way cable connection 17 connected to a video tape recorder VTR 18. The metering device 11 is connected, via cable 19, to an interface, an image data terminal (IDT) 20, cooperating over a BCD unit 21 with another IDT 22 - both IDTs having so called C videos 23 and 24 respectively. The cable 25 connects the IDT 20 with a discon 26 and a monitor 27 and with the display unit 16. Inspection of a section of a sewer 1 normally takes place between two inspection wells 2. The pulling wire 7 is fetched at the downstream well by a forerunner floated downstream from the upstream well and after lowering the scanning device 3 enclosed in the shell 4 into the sewer 1 the scanning device 3 is pulled on its sledge 6 along the sewer. The advance is controlled by the metering device 10-11 indicating the length of cable 9 rolled off. The signal from the IR scanning device 3 is received by the display unit 16 and are recorded by the VTR 18 and the signals from the metering device 10-11 are computed by the IDT 20 and fed to the display unit 16. The distance figures can be read on the display and also be recorded on the VTR 18. The IR scanning device 3 is pulled through the sewer and the operator is in full control at his display unit and can adjust light, contrast, and sensitivity. The images are recorded and can be evaluated on any later occasion. The thermograms shown on Figs. 3 - 6 are results from an inpection of a sewer 100 meters in lenght and chosen at random and just give some examples of faults. In Figs. 3 - 6 white areas indicate warm and grey to black gra¬ dually colder areas. Fig. 3 and 3a illustrate two flows of water joining at a manhole, the left flow warm and the right flow cold. The wall of the sewer is cold. Fig. 4 and 4a show an area including a joint and a darker area indicates inleaking colder surface water. Fig. 5 and 5a show the influence of cold water sur¬ rounding and penetrating a displaced joint. Colder sur¬ face water seeps in along the joint. Fig. 6 and 6a illustrate how roots have penetrated the sewer wall but not yet to an extent causing leakage. The roots taking water from the contents of the sewer are warmer than the wall behind kept cooler by the surrounding filling material. In a modified embodiment, not shown, the IR sensing device is combined with a TV camera and an appropriate light source. Such TV camera is also connected with the central unit, which is equipped with a display means for the TV image and furthermore with an electronic apparatus for displaying the IR image on top of the TV image or vice versa to form a combined image. Such a combinded IR and TV image is more easily read by the operator and gives <- besides the leak indicating temperature image also a visual picture of the location and shape of the damage or leak. The IR camera and the TV camera might of course e used one at a time but the best result is attained if they are used simultaneously.

Claims: CLAIMS 1. Method for detecting leaks and other defects on inspection of underground sewers and the like channels, wherein a movable detecting and inspection unit (3) com¬ municating with an above ground localized central unit (12) is moved along the sewer (3) and upon travelling along such, by scanning the inside of the sewer with the aid of an IR scanning unit or the like temperature regi¬ stering device, c h a r a c t e r i z e d in adapting the scanning device to register and sense temperatures deviating from the prevailing temperature of the inside of the sewer or the like and being caused by ground or surface water flowing or leaking in, the prevailing tem¬ perature of the sewer being determined by the waste water flowing therethrough; further adapting said scanning de- vice to convey to the central unit (12), which includes display and recording means, signals indicating sensed temperatures and location of areas having such tempera¬ tures; adapting a metering device connected to the scanning unit to simultaneously send to such central unit informa- tion on distance moved and processing the signals received in the central unit to give a thermal picture and location indication. 2. Method according to claim 1, wherein a TV camera device is combined with the IR scanning device and arranged to simultaneously with the IR scanning produce a TV image; said TV camera being adapted to be connected with the central unit display and recording device; and arranging means for producing by overlapping the IR image on the TV image or vice versa a combined image enabling the ope- rator to determine the shape and location of any faults or leaks and the rate of in leaking ground or surface water. 3. Apparatus for detecting leaks and other defects on underground sewers or the like channels, including a water proof IR scanning device or the like (3) temperature sensing device mounted on a sledge or the like carrier (6) movable along such sewer or channel (3) and being equipped with communication means (9) connecting such sledge mounted IR scanner (3) with an above ground central unit (12), wherein the scanning device is arranged to sense and detect temperatures deviating from the prevailing temperature of the sewer and transmit signals containing information about the prevailing temperature and any areas having different temperature due to in leaking ground or surface water to the central unit, a distance metering device connected to the scanning device and adapted to inform the central unit or distance passed and a data processing unit for compiling the signal from the IR scanning unit resulting in a thermographic image with signal from distance metering device for creating a record¬ able position determined image on a display means. 4. Apparatus according to claim 3, wherein the IR scanning device is combined with a TV camera device also communicating with the central unit; said central unit being equipped with means for combining the IR images and the TV images to form and overlap picture indicating both temperature differences, i.e. leaks and the shape and location of leaky sections of the sewer.

Inventors: ERICSSON BO, WETTERVIK LENNART, ERICSSON, BO, WETTERVIK, LENNART
Applicants: ERICSSON BO, WETTERVIK LENNART, ERICSSON, BO, WETTERVIK, LENNART
Application year: 1985
Main classification: G01M3
IPC codes: G01M3