Leak detection
The leak detection , or leak detection is to locate hidden leaks at about pipework installations or flat roofs performed. Various measurement and location techniques are used to record the position of the leak.
techniques
Electronic moisture measurements
In , capacitive or resistance measurement method moisture priorities can be determined.
Resistance moisture measurement
After this type of measuring device was initially used in woodworking and forestry, the measurement of mineral substances has also been possible for a long time, thus ensuring that it can be used in building moisture measurements.
Mode of action
The electrical resistance of a building material is determined with the help of two electrodes. The resistance changes depending on the humidity of the test substance and is displayed on the measuring device in manufacturer-specific units. A conversion table enables the measured values to be determined in percentages of moisture, taking into account various building materials.
The electrodes used are mainly dependent on the building material to be measured and its accessibility. Surfaces can be measured with different impact electrodes. For deeper layers, which always appear interesting for moisture measurement, measuring probes are particularly suitable, which can be inserted into the depths via boreholes or joints.
Capacitive humidity measurement
The dielectric method enables the measurement of tiled areas or of screeds with underfloor heating underneath, where drilling is far too great a risk. It is sufficient to place the measuring device on the surface of the building material to be measured.
Mode of action
Increased humidity values are not only expressed in an increase in electrical conductivity, but also in an increase in permittivity . This actually measures the capacitance of a capacitor, which is the heart of the measuring device.
The capacitance of the capacitor changes depending on the dielectric (separating material of the capacitor plates). I.e. If there is material with a higher moisture content in the stray field of the capacitor, this is reflected in a higher dielectric constant / permittivity number. The capacitance of the capacitor also changes and is converted and displayed in the measuring device as a percentage by weight .
Line location
Electrically conductive (metallic) lines are measured in their course and in the laying depth.
Electro-acoustic leak detection
Following the previously measured course of the line, you "listen" to the lines. Leakage noises are amplified, so leaks can be pinpointed.
A ground microphone or contact microphone, also known as a geophone , is used to record typical sound waves that occur in the event of a leak in water or heating pipes, namely:
- due to the structure-borne sound vibration of the pipe (caused by the leakage of water at the leak)
- This oscillation varies in strength depending on the nature of the pipe and spreads to both sides of the leak. The noise can be heard directly on the line with special microphones. The following applies: the louder the noise, the closer to the leak point A and vice versa.
- due to the actual leak noise (movement of the water)
- The leak sound spreads spherically and can only be heard at the leak point. A floor microphone is used to amplify the audibility of the noise.
Diffusion tube process
The diffusion tube method is a measuring method that is able to measure and localize gases , vapors and liquids from a leaking pipe / container in the vicinity with high sensitivity. The physical operating principle is based on the fact that the so-called “sensor hose” used is pressure-tight, but represents a permeable diffusion membrane for gases and vapors .
functionality
The sensor tube is z. B. laid along the pipeline to be monitored and flushed with clean air in periodic cycles (typically 1 × per day). The hose is depressurized between the measuring cycles. If the medium carried in it reaches the wall of the sensor hose as a result of a leak in the pipeline, it diffuses through the hose wall and after a few hours forms a high gas concentration at the point of contact inside the hose. This happens regardless of whether the leak medium reaches the sensor hose in liquid or vapor form, if the leak medium on the sensor hose is dissolved in water (e.g. if the pipeline and sensor hose are laid below the groundwater level or in the river bed / seabed) ( Henry's Law ). Since the diffusion process described works for most chemical substances, a long, extended air sample is created inside the sensor hose, which is analyzed by specific gas sensors at the outlet of the hose section during the cyclic rinsing of the hose . If the limit value is exceeded, the leak location can be determined very precisely from the transit time and flow velocity.
Advantages over conventional methods
The diffusion hose method is to be classified as a complementary method to the standard method and is characterized by its high sensitivity, especially for the detection of creeping leaks, as an early stage of major corrosion damage.
Gas leaks
Escaping gas can often be recognized by its smell. The exact location of the leak can be carried out by painting or spraying the containers, fittings and pipelines with a wetting agent ( detergent diluted with water or a special leak spray). The leak can then be determined by the formation of bubbles. When the gas pressure is low, water-based leak detection agent can undesirably temporarily seal leaks in pipe connections that have been sealed with hemp . In this case, gas sensors should be used instead , which often also have better sensitivity.
Tracer gas process
Leaked pipes are emptied and filled with an easily detectable sample gas. The sample gas emerges from the leak. The leak can be limited in this way.
The pipe system is filled with a pre-calculated amount of a suitable gas mixture (usually forming gas 95/05, 95% nitrogen , 5% hydrogen ) and sealed with a slightly increased overpressure. The gas escapes at the leak point and diffuses through relatively dense components such as concrete, screed and floor coverings and can be detected with the aid of the tracer gas measuring device. The sensor, which has a selective sensitivity for the gas used, already reports traces of gas in the single-digit ppm range (ppm - part per million).
Thermography
Method for making leaks in hot water and heating pipes visible. At outside temperatures below around 15 ° C, it is also suitable for checking the airtightness of buildings in conjunction with the blower door test .
A thermogram created with the infrared camera shows the distribution of heat radiation in the thermographed area. Here, darker areas (blue to black) correspond to the areas with lower surface temperatures, the lighter areas (yellow to white) show the areas with the greater thermal radiation. The entire temperature field is shown in the selected measuring range by a continuous color scale.
Radiometric moisture measurement
Mode of action
In radiometric moisture measurement, a neutron probe works on the principle of neutron deceleration. The neutrons emitted by the radiation source are slowed down by hydrogen atoms. The slower neutrons are picked up by detectors in the device and evaluated electronically. The value determined in this way then provides information about the moisture content of the components examined.
The non-destructive measurement can be carried out with layer thicknesses of up to 20 cm. The measured values show an overview of the moisture distribution in the examined area or component. Since the measured values are dimensionless and only allow a very rough assessment of the degree of moisture penetration, i. d. Usually further moisture measurements are necessary in order to be able to make quantitative statements.
application areas
Insulation layers of flat roofs and screeds can be examined for extent and degree of moisture penetration without damage. On the basis of the qualitative measurement of the moisture, the detection of leaks and holes in the roof membrane is almost always given. Areas to be rehabilitated can be precisely delimited with the probe. Other important areas of application are the location of leaks in underfloor heating and pipelines as well as the investigation of cellar and wall areas.
In the area of flat roof analysis, this test method enables comprehensive statements about the tightness of seals. As a result, important aspects arise with regard to the renovation of damp insulation. Especially considering the ecological component - whether the demolition and disposal of the insulation material can be avoided - the drying of the insulation layer of flat roofs has an enormous economic advantage.
safety
The neutron probe requires special training on the part of the user as well as a number of special permits for handling and transport, since radiation-intensive material is used for the measurement.
Fixed or integrated sensor-based leakage location
The sensor-based leak location is used to find soaked thermal insulation and is often used on flat roofs. Communication with the sensors is based on the RFID standard , which enables wireless transmission of the moisture status to an external reader. The prerequisite for the implementation of the localization is the installation of batteryless sensors in new buildings or renovations in the corresponding components.
Mode of action
A number of sensors are pushed into the insulation boards at regular intervals or at particularly endangered places in new buildings or renovations and then initially read in with a roof scanner. Then each individual sensor can be read with the reader through several layers of insulation, sealing, gravel and greenery. Each sensor can be queried whether it is wet or dry in its environment. The sensor-based leakage location system is marketed in Germany as an integrated roof control.
Electro-impulse method
The leak search with the electro-impulse method is suitable, among other things, for finding holes and cracks in the sealing of flat roofs with and without load. This method is also used in the area of parking decks and terraces. However, these must be non-conductive seals.
Mode of action
A current pulse with approx. 40 V DC voltage is applied to the underside of the seal via a protective conductor. A ring line with a negative pole is laid on the surface of the seal around the area to be tested. By wetting the sealing with water, the prerequisite for the 40 V voltage under the sealing is created to allow a direct current to flow at the defective point of the roof sealing (similar to a cable). The direct current now tries to flow to the negative pole of the ring main. The change in potential that forms in the area of the leak can now be measured with the pulse receiver. It is thus possible to move step by step in the direction of the leakage (change in potential) until the potential no longer changes. This is where the leak is located.
Hydrostatic process
The tightness of a pipeline is tested by filling it with compressed air. This method is useful when several pipelines are close together and it is not known which of them has a leak.
Mode of action
The air pressure inside the pipeline is monitored with a manometer. If the pressure remains the same during the test, the line is tight. If the pressure drops, there is a leak. The tracer gas method or an electro-acoustic method can then be used to precisely locate the leak.
DC sparking method
Leak detection using the DC spark method is suitable for locating holes and cracks on non-conductive coatings without loading.
Mode of action
The DC sparking method uses high voltage that is transferred to the seal to be tested via a copper brush. This method can be used to locate holes and porosity in freely accessible, non-conductive coatings. It is not suitable for conductive surfaces. The devices used have a variable sensitivity and are equipped with acoustic and visual organization mechanisms. The DC spark method can also be used to locate points and seams.
Electro-acoustic processes on flat roofs and coatings
The electro-acoustic method is suitable for finding (locating) holes and cracks on seals with and without load.
Mode of action
Alternating current is used in the electro-acoustic process. In a closed circuit, a specific voltage is generated at a defined resistance. The electro-acoustic process makes use of this physical law, whereby the laying of a ring line is not necessary here. The roof must first be moistened (closed film of moisture on the waterproofing), an additional earthing option should be available on the roof surface. The main unit contains a sine wave generator that generates a voltage of approx. 5 V at a frequency of 1 kHz. This voltage is connected to the roof ground. The mobile handset contains a variable resistor across which a voltage drops. This voltage changes depending on the distance between the sensor and the leak. The handset converts this voltage into tones that can be heard through headphones. The closer the leak is, the higher the tone becomes. The leak is at the point where the highest note is reached.
Individual evidence
- ↑ Bayer CO pipeline - modern leak detection and location system
- ↑ Detection of Trace Hydrocarbons and Toxic Components in the Environment, IPC2012, Calgary ( page no longer available , search in web archives )
- ↑ Leak detection system for flat roofs. (No longer available online.) Archived from the original on November 17, 2015 ; accessed on November 13, 2015 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
