EP0082172A1

EP0082172A1 - Method and device for continuously monitoring an installation containing a fluid

Info

Publication number: EP0082172A1
Application number: EP19820901969
Authority: EP
Inventors: Friedrich Dolezalek; Rolf Hartmann; Matthias Selders
Original assignee: Battelle Institut eV
Current assignee: Battelle Institut eV
Priority date: 1981-06-27
Filing date: 1982-06-25
Publication date: 1983-06-29
Also published as: WO1983000226A1; DE3125388A1

Abstract

Procédé de surveillance en continu d'une installation contenant un fluide, permettant de localiser une fuite, dans lequel on place à proximité de l'installation, ou en contact avec celle-ci, un guide d'onde à caractéristique de conductivité constante. Toute fuite dans l'installation se traduit par une modification locale correspondante de la conductivité du guide d'onde. On envoie dans le guide d'onde des impulsions électromagnétiques et optiques dont les réflexions aux endroits où se produisent les fuites de fluide permettent de localiser ces fuites en fonction du temps de parcours.A method of continuously monitoring an installation containing a fluid, making it possible to locate a leak, in which a waveguide with constant conductivity characteristic is placed near the installation, or in contact with it. Any leak in the installation results in a corresponding local modification of the conductivity of the waveguide. Electromagnetic and optical pulses are sent into the waveguide, the reflections of which at the points where fluid leaks occur make it possible to locate these leaks as a function of travel time.

Description

10 Method and device for continuous

Monitoring of systems containing fluid media

The invention relates to a method and devices for the continuous monitoring of systems containing fluid media, in particular liquids, such as pipelines, containers and the like, leak points being ascertained and located.

20 ....

Various methods are known for monitoring pressure-carrying pipes and containers in heating, air conditioning, chemical and reactor plant technology. In the high pressure test with liquid, emerging drops or stains

25 fertilize on a lime paint for leaks. For high-pressure testing with gas, the point where a leak is suspected is wetted with soapy water and then checked for bubbles. Both methods are not suitable for the continuous monitoring of plants in operation and also require a high level of personnel expenditure. According to another method, the plants are filled under pressure with a medium which contains a test gas. A control person can then use locate the leak with a test gas leak detector. This process can also be carried out during operation. However, it requires that a certain constant test gas concentration is constantly present in the medium. In reactor plants, for example, this is not possible or too cumbersome. It has also been proposed to lay a gas-filled, permeable hose parallel to the system, which is periodically sucked off. The leakage medium emerging in vapor form from the vessel to be tested diffuses through the hose wall and locally forms a steam plug in the hose which during the

Suction with a sensitive detector is detected. This method can only be carried out with leak media which have a suitably high vapor pressure and can diffuse through the hose wall. A method is also known in which a bare wire through which current flows is laid along a water-carrying pipe within the insulation. At the location of a leak, the escaping water causes the insulation to become wet and thus an electrically conductive connection between the pipe and the wire. This • event can be monitored by monitoring the electrical

Determine resistance between tube and wire; the leakage is then carried out potentiometrically. However, if two or more leaks occur at the same time, separate detection and location are not possible. In addition, a location based on direct current potential measurement in the electrolyte is susceptible to faults and is not precise. Another method, in which a moisture-sensitive strip is applied to critical points in water-bearing systems, does not offer any possibility of localization along the strip. The strips consist of paper impregnated with ammonium nitrate, on which two copper strips are glued insulated from each other. The emerging moisture leads to a reduction in the electrical resistance between the strips and thus enables the

OM Leak detection as in the previously discussed example. In order to monitor various possible leak points independently of one another, a detector strip must be attached separately at each such point. The main disadvantage of this method, in addition to the lack of location, is the need for a high level of circuitry in order, for example, to be able to monitor approximately 5000 measuring points. Finally, a method is known that is based on the principle of ultrasound emission. Leakages that occur can be recognized by their characteristic emission patterns, classified according to size and located. However, this method is not sensitive enough to be able to detect even the smallest leaks, for example less than 100 kg of escaping liquid per hour.

The present invention is based on the object of specifying a method with which the occurrence of even the smallest leaks in pressure-carrying containers, valves, pipelines and the like can be continuously monitored during the intended operation, a simultaneous location and Classification according to size is possible. Further, the method ^'ge furnish, exiting leakage media in liquid or gaseous Aggregatzu≤tand should detect within a very short time. Another object of the invention is to monitor leakage of very large systems, for example the total of approximately

10,000 m long pipelines of a nuclear power plant, to be made possible with a single central detection apparatus. Advantageously, this central apparatus should be installed outside the plant and not require any mass transport into or out of the plant. A further problem to be solved by the invention is to get by with as few openings as possible in the container wall.

OMPI - -

It has now been shown that this object can be achieved with a method in which electromagnetic linear, including optical, electromagnetic waves are provided in a linearly extended waveguide with locally constant transmission properties, which is arranged in the immediate vicinity of the system or in direct contact with the system Pulses are sent, the leakage medium causing a local change in the forwarding properties of the waveguide and the reflection of the pulses occurring at the leakage point being detected, the size of which is detected and located over the running time. In the sub-claims 2 to 4 advantageous embodiments of the method are described.

The device according to the invention consists of a linearly extended waveguide with locally constant transmission properties, which is arranged in the immediate vicinity of the system or in direct contact with the system, with a local change in the transmission properties of the waveguide occurring at the leak and with one Pulse - reflectometer or its optoelectric equivalent is connected. Some preferred embodiments of the device according to the invention are explained in subclaims 6 to 1.

The advantages achieved by the invention are to be seen essentially in the fact that several leaks can be detected with a location accuracy of approximately + 0.5%. It is also possible to classify the leak by size. A line break or short circuit is also detected. The measuring time is short and is approx. 1 second. The measuring line is easy to lay and retrofitting is easy. The invention is explained in more detail with reference to the accompanying drawings. It shows in schatic simplification

Figu 1 the measurement setup and Figure 2 the record for the evaluation of the measurement result

The device according to the invention consists of waveguides 1 which are connected via a multiplexer 2 with a pulse reflectometer, e.g. consisting of a pulse generator 5 and a Sa pling system 4, are connected. According to this embodiment, the waveguide consists of a high-frequency ribbon line with a porous dielectric, which has hydrophilic or hygroscopic properties. As a result of the water penetrating into the pores of the dielectric, the dielectric constant increases drastically and the wave resistance at the location of the leak is reduced accordingly. A fed into the ribbon cable

The most electrical pulse of approximately 10 seconds duration runs along the line and is reflected wherever leakage-related deviations of the wave resistance from the desired value ^{* "'"} occur. The height and width of a reflected pulse corresponds to the degree and the local extent of the moisture penetration of the strip conductor and, together with the rapid development of the disturbance, enables the leak classification. Due to the temporal relationship of the leak pulse to the test pulse or its reflection at the end of the line, the leak can be located with meter accuracy. The evaluation can be done either on the Oszillo graph screen or using a registration strip. The recording then has approximately the form shown in FIG. 2. In this sketch, the reflection coefficient is? depending on the term in, us entered. Since both the length of the line and the running time are known over the entire line (reflection c)), a localization can be carried out if a leak occurs in a) or b). The high-frequency ribbon cable for an embodiment of the detection system according to the invention consists of two metal foils with a porous dielectric lying between them and protruding slightly to the side. The leakage medium can thus enter the dielectric and cause the change in the forwarding properties of the strip conductor. The use of coaxial cables instead of ribbon conductors is carried out analogously to the exemplary embodiment explained above. Even when using optical fibers for optical pulses, nothing changes in the measurement setup. In principle, only a luminescence or laser diode should be provided for converting the electrical pulses into light. A photodiode or a photo ultiplier can be used to convert the reflected light pulse into an electrical pulse.

To achieve an enrichment of the leak medium, the dielectric of the coaxial cable or ribbon conductor can contain absorption materials. With water or water-containing leak media, e.g. the dielectric is in the form of a textile structure and is hygroscopically impregnated.

It is essential for the accuracy of the measurement that a complete reflection of the pulse at the end of the waveguide is ensured. In the case of coaxial cables or ribbon conductors, this can be done by leaving the line end open. When using optical fibers as waveguides, they would have to be mirrored accordingly at the end of the line.

In the case of pipelines, the waveguides are arranged parallel to the pipeline and, in the case of containers, preferably meanderingly covering the container surface. They can be in direct contact with the system or can be installed at a short distance from the system.

C * According to a further embodiment, the forwarding properties of the waveguides used cannot be changed directly by the leakage medium, but rather by means of a suitable device. In this case, the measuring line is placed at suitable 5 points at certain intervals, especially at critical ones

Provide the system to be monitored with devices that react to the leak medium. For optical fibers that are sensitive to pressure, such a device can e.g. consist of materials which experience an increase in volume when moisture enters and thus exert pressure on the lic fiber. For this, however, the outer covering of the optical fiber would have to be removed accordingly. If high-frequency cables or strip conductors are used, such devices can consist of moisture-sensitive switches.

According to a further embodiment, in particular for monitoring pipelines, the waveguide arranged parallel to the pipeline 0 can only be made sensitive to the Lec mediuum at suitable or critical points. For example, a coaxial cable can be provided at the intended locations with a ribbon cable or ribbon cable loop that is sensitive to the leak medium. In this case, the transitions must be carried out largely without reflection. Small reflections at these points can be used as calibration marks for the localization of the individual sensor, i.e. the tape line or tape line loop can be used. If optical fibers were used instead of HF ribbon cables, the glass fibers could only be made sensitive to the leak medium at critical points, e.g. by changing the cladding.

CI.IFI

.//K_ WIl-O The following example shows the sensitivity of a tape line with a hydrophilic dielectric for the detection of steam leak. Such a line with 50 ohm wave resistance consists, for example, of a sandwich made of 7 mm wide copper foil with an approx. 15 mm wide and 1 mm thick strip of polypropylene nonwoven as a dielectric. The fleece is wetted by a chemical pretreatment. The tape line is provided with a self-adhesive coating and is preferably applied to the inside of the insulation cover of a steam line to be monitored. There it is protected against any splash or condensate water that does not originate from a leak to be detected. An old native solution, in particular for retrofitting, is also the laying on the outside of the insulation, the condensation water reaching the strip line via regularly arranged bores.

Commercially available polypropylene fleece has a dielectric constant E = 1.23 in air, with water saturation (approx. 72% by volume) the dielectric constant is approx. = 65. This reduces the characteristic impedance according to the proportionality —.___ / _ Λ ■

from 5 _c 0_ X1 = 5s. '-n - a „uf r _ή 6, o9 -U π = - ^ss y' -Ω-

This leads to a reflection of the test pulse with a

Reflectance of

t? = ^{50 "6} ' ⁹ • 100% = 76%. 50 + 6, 9

This is easy to measure because commercial reflectometers already detect reflections with 5 = 0.5%. For a clear reflection of e.g. To generate 13%, a water content of 1% in the fleece is sufficient. That is 35 ul water on 0.5 m tape. When the steam condenses completely from a 1 kg / hour leak on an insulation length of 500 mm, this amount of water is deposited on the protruding part of the fleece strip in approx. 30 seconds. The response time to be expected in the case of a 1 kg / hour leak results from the addition of this time and the time until the condensation (1 to 2 minutes) as 1.5 to 2.5 minutes. If there are major leaks and / or the condensed water comes together on the strip, the response times are even shorter. The same applies to hygroscopically impregnated dielectrics, since these already react to an increased air humidity and so there is no need for condensation.

Claims

1. Method for continuous monitoring of fluids

Systems containing media, in particular liquids, such as pipelines, containers and the like, in which leaks are detected and located, are characterized in that they are arranged in a close proximity to the system or in direct contact with the system Extensive waveguides with locally constant conduction properties electromagnetic, including optical pulses are sent, with the leak medium causing a local change in the transmission properties of the waveguide and that the reflection of the impulses at the leakage point is detected, detected in terms of size and over the running time is located.

2. The method according to claim 1, characterized in that RF coaxial cables or HF-Band¬ conductors are used to forward RF pulses.

3. The method according to claim 1, characterized in that an optical fiber bundle or a single optical fiber is used for forwarding optical pulses.

_Q_ ..

4. The method according to any one of claims 1 to 5, characterized in that a complete reflection of the pulses is provided at the end of the waveguide.

5. Apparatus for carrying out the method according to claim 1 to 4, characterized in that it consists of a linearly extended waveguide (1) with locally constant conduction properties, which is in the immediate vicinity of the system or in direct contact with the system, a local change in the transmission properties of the waveguide (1) taking place at the leak and that the waveguide (1) is connected to a pulse reflectometer (3, 4).

6. The device according to claim 5, characterized in that the waveguide (1) is arranged parallel to the pipeline in pipelines and meandering in the case of containers.

-7. Apparatus according to claim 5 or 6, characterized in that an optical fiber bundle or a single optical fiber is used as the waveguide (1).

8. Apparatus according to claim 5 or 6, characterized in that an RF coaxial cable or a as a waveguide (1)

HF band conductor is used.

9. Device according to one of claims 5 to δ, characterized ge indicates that the sheathing of the waveguide (1) is permeable to the leak medium.

OMPI _, -

10. The device according to claim 9, characterized in that the waveguide (1) is in connection with an absorption material, which favors an enrichment of the leak medium, preferably by reversible absorption.

11. The device according to claim 9, characterized in that the dielectric of the RF coaxial cable or HF ribbon conductor is porous and optionally contains the absorption material ent.

12. The device according to one of claims 5 to 8, characterized ge indicates that the waveguide is provided at certain intervals, preferably at critical points in the system, with devices that change the conduction properties of the waveguide upon contact with the leak medium.

13. The device according to one of claims 5 to 12, characterized in that the end of the optical fiber is mirrored and the RF coaxial cable or RF ribbon cable is open or ^' short-circuited.