Nondestructive detection method and nondestructive detection system for leakage phenomenon

Abstract

To provide a nondestructive detection method and a nondestructive detection system capable of identifying a leakage phenomenon of a fluid in an existing pipeline without performing processing or the like on the pipeline.SOLUTION: A nondestructive detection method for a leakage phenomenon of a fluid in a pipeline includes: an analysis surface installation step of installing an image analysis surface on a surface of a pipe material of the pipeline; an analysis surface imaging step of imaging the image analysis surface by imaging means; a displacement amount measuring step of measuring a circumferential direction displacement amount of the pipe material on the basis of the image captured by the imaging means; and a leakage phenomenon determination step capable of making an analysis on the basis of the measured circumferential direction displacement amount to at least determine the presence or absence of the leakage phenomenon of the fluid. The leakage phenomenon determination step can determine an attenuation behavior in a time-frequency domain based on the circumferential direction displacement amount to at least estimate the presence or absence of a water leakage and a water leakage position.SELECTED DRAWING: Figure 25

Description

Technical Field

[0001] The present invention relates to a non-destructive detection method and a non-destructive detection system for a leakage phenomenon, which are capable of identifying a fluid leakage phenomenon in a pipeline.

Background Art

[0002] Conventionally, there is a water conservancy system that enables water supply and distribution to farmland by utilizing the water pressure in an agricultural pipeline. Water leakage in the agricultural pipeline may lead to disruption of the farming plan associated with loss of agricultural water and a decrease in the yield and quality of crops.

[0003] Since most of the existing pipelines are buried in the ground, it is difficult to efficiently detect water leakage, and the establishment of inspection technology is an issue from the perspective of maintenance and management. Generally, for detecting water leakage in a pipeline, the main aim is to detect a decrease in water pressure. However, at present, pressure gauges can only be installed at limited locations such as air valves in existing facilities.

[0004] Under such circumstances, in the technologies disclosed in Non-Patent Document 1, Non-Patent Document 2, and Patent Document 1, for water leakage in an irrigation pipeline, it has been studied to establish a detailed detection method by adding information on water leakage to the water hammer pressure associated with valve operation and employing numerical simulation.

[0005] Also, in the technology disclosed in Non-Patent Document 3, as a direct measurement method, it has been studied to insert a capsule-type exploration device into a pipeline and identify the water leakage position of the pipeline from the water leakage sound acquired by the exploration device.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Patent Document

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the methods disclosed in Non-Patent Document 1, Non-Patent Document 2, and Patent Document 1, it is essential to install a water pressure gauge in the pipeline to measure the water pressure. In particular, in an existing aging pipeline, it is assumed that it will be difficult to install a water pressure gauge.

[0009] In addition, in the method disclosed in Non-Patent Document 3, it is necessary to insert a φ55 mm × 165 mm capsule with an underwater microphone built into the pipeline. In particular, it is difficult to apply it to pipelines with a small pipe diameter. In addition, when the recovery of the capsule is essential, there are problems such as the need for processing for insertion and recovery in existing pipelines, and the risk in the event that the capsule cannot be recovered.

[0010] Therefore, an object of the present invention is to provide a non-destructive detection method and a non-destructive detection system for a leakage phenomenon that can identify the fluid leakage phenomenon in an existing pipeline without performing processing such as processing on the pipeline.

Means for Solving the Problems

[0011] The present invention is a non-destructive detection method for a fluid leakage phenomenon in a pipeline, including an analysis surface installation step of installing an image analysis surface on the surface of the pipe material of the pipeline, an analysis surface photographing step of photographing the image analysis surface with photographing means, a displacement amount measurement step of measuring the circumferential displacement amount of the pipe material based on the image photographed by the photographing means, and a leakage phenomenon determination step of performing an analysis based on the measured circumferential displacement amount and being able to determine at least the presence or absence of the fluid leakage phenomenon. The leakage phenomenon determination step is characterized in that it is possible to determine the attenuation behavior in the time-frequency domain based on the circumferential displacement amount and estimate at least the presence or absence of water leakage and the water leakage position.

[0012] According to the configuration of the present invention, for example, in a limited space in a manhole, it is possible to identify the presence or absence of water leakage and the water leakage position of the fluid in the existing pipeline without performing processing such as processing on the pipeline.

Brief Description of the Drawings

[0013]

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Mode for Carrying Out the Invention

[0014] Hereinafter, with reference to the drawings, an embodiment of the non-destructive detection method and non-destructive detection system for leakage phenomena of the present invention will be described by taking the method for identifying leakage phenomena in a water supply and distribution pipeline as an example.

[0015] (Model Pipeline Experiment) Prior to the present invention, based on the study flow shown in FIG. 1, a model pipeline as shown in FIG. 2 was fabricated, and experiments were carried out to detect the presence or absence of simulated leakage in the model pipeline, the fluctuation of water pressure caused by valve operation, and the behavior of the pipe body by using a strain gauge and a digital image correlation method (hereinafter referred to as the "DIC method"), which is one of the image analysis techniques.

[0016] The appearance of the above model pipeline is as shown in Figure 2. The specifications of the pipe material of the model pipeline are as shown in Figure 3(a). To explain in more detail, a water tank for storing water is installed at the most upstream, water is flowed from the pipe connected to the water tank, and discharge is carried out by valve operation at the most downstream.

[0017] The dimensions of the water tank are 0.47m×0.47×0.47×1.2m, and it is fixed to the pedestal at a height of 2.9m above the ground. In this experiment, the upstream gate valve is fully opened, and the flow rate is adjusted by operating the ball valve at the end. Also, in order to ensure the pressure head on the downstream side, the model pipeline is installed so that there is a height difference between the most upstream and the most downstream. And by considering storing water up to a height of 1.1m in the most upstream water tank and the height difference of the installation of the model pipeline, a pressure head of about 7.8m is ensured at the most downstream.

[0018] Also, as shown in Figure 3(b), six types of study cases, Case1 to Case6, are set considering the presence or absence of simulated leakage and the measurement positions. That is, it is to verify that the presence or absence of leakage can be detected even in the measurement at a position far from the leakage position. In all study cases, the valve opening is set to 16.9° and water is passed, and when the water level in the water tank drops by 1m, the valve is suddenly closed to generate a water hammer pressure.

[0019] When measuring the water pressure, small pressure sensors (manufactured by Sensiz Co., Ltd., model HTV-100KP) are installed at two locations, near the most upstream water tank and near the most downstream valve. Regarding the water pressure data, recording is carried out by a voltage data logger (manufactured by T&D Co., Ltd., model MCR-4V, sampling: 500Hz) and recording by synchronous connection associated with image measurement (sampling: 50Hz).

[0020] Also, in the study by this experiment, in order to mutually compare with the image analysis results by the above image measurement, the water pressure data obtained by synchronous connection is used. In data analysis, data from 0.5s before closing the valve to 8.192s (2 12 data) is used.

[0021] Also, during the above image measurement, circumferential strain and axial strain are measured using a strain gauge 13 (KFP-5-120-C1-65L1M2, manufactured by Kyowa Electronic Instruments Co., Ltd.). As shown in Fig. 4, the strain gauge 13 is attached to the opposite side (lower part of the pipe body) of the image measurement surface created on the upper part of the pipe body with waterproof tape. The measurement interval by the strain gauge 13 is 500 Hz and is synchronized with the above water pressure measurement. In data analysis, data from 0.5 s before closing the valve to 8.192 s (2 12 data) are used.

[0022] In order to non-contact detect the deformation behavior of the above-mentioned pipe body, the deformation behavior of the pipe body is image-measured in the manner shown in Fig. 4. The above-mentioned DIC method is used so that the deformation behavior of the pipe body can be identified three-dimensionally. In this method, a random pattern is applied to the image analysis surface A installed on the surface of the pipe material to be measured, and the displacement amount is calculated from the dynamics of the pixel group in the digital image by photographing the movement amount of the dots in the random pattern with the CCD cameras 11 and 12.

[0023] Therefore, as shown in Fig. 4, the image analysis surface A with the random pattern is installed at the position corresponding to the crown of the pipe body, and two CCD cameras 11 and 12 are installed so as to look down on the image analysis surface A from directly above. The random pattern of the embodiment is created as a rectangle with a size of 55 mm (horizontal) × 80 mm (vertical). As measurement conditions, the shutter speed is 20 ms, the aperture is 6, and the frame rate is 50 Hz so that water pressure data can also be captured by synchronous connection. Also, as shown in the figure, lighting 20 by a clip light is installed to adjust the brightness. Note that the lighting 20 is not necessarily required, and the lighting 20 is unnecessary during bright daytime hours.

[0024] Regarding the simulated leakage of the model pipeline, as shown in Fig. 2, it is reproduced by providing one leakage hole H with a diameter of 5 mm on the downstream side. Also, in order to measure the water pressure inside the pipe and analyze the deformation behavior of the pipe body, a water pressure gauge is installed at the positions shown in the figure, and image analysis surfaces A are installed at three locations: measurement position 1 (2 m upstream from the valve), measurement position 2 (23 m upstream from the valve), and measurement position 3 (47.3 m upstream from the valve).

[0025] As software for implementing the DIC method, Vic Snap (manufactured by Correlated Solutions) is used for measurement, and Vic 3D (manufactured by Correlated Solutions) is used for analysis. Also, as an evaluation index for the deformation behavior of the pipe body by the DIC method, the circumferential displacement amount (rad) in the cylindrical coordinate system (displayed as dTheta in the study results described later) is used.

[0026] Fig. 5 shows a model in the cylindrical coordinate system. This index represents the displacement amount with respect to the circumferential direction θ from the random pattern of the image analysis surface A in the initial state. And counterclockwise is the positive direction and clockwise is the negative direction with respect to the positive direction of the pipe axis direction Z.

[0027] Fig. 6 shows an example of the analysis results of the above experiment. The time-series data of the circumferential displacement amount at the center coordinates of the random pattern of the image analysis surface A surrounded by a rectangle is extracted and analyzed. In data analysis, data from 0.5 s before closing the valve to 10.24 s (2 9 data) is used.

[0028] (Analysis method) ·Internal pressure acting on a thin-walled cylinder and circumferential strain As a problem in mechanics of materials, in a thin-walled cylinder under the action of internal pressure, the circumferential strain εθ can be obtained by the following formula 1 as the radius changes (Shibuya et al.: Modern Mechanics of Materials 1986).

[0029]

Equation

[0030] Here, R is the inner radius, p is the internal pressure, E is the longitudinal elastic modulus, t is the wall thickness, and ν is the Poisson's ratio. According to the above formula (1), the relationship between the water pressure, which is the internal pressure in the pipeline, and the circumferential strain of the pipe body can be understood.

[0031] · Period associated with water hammer action The water hammer pressure, which is a rapid pressure increase caused by valve closure, repeats reflections at the upstream and downstream ends in the pipeline. That is, this water hammer action transitions as follows: propagation to the free surface ~ reflection from the free surface ~ reflection at the valve position ~ re - reflection at the free surface, as shown in the schematic diagram of Fig. 7. Also, the period T associated with the water hammer action can be expressed by the following formula (2).

[0032]

Equation

[0033] Here, L is the pipeline length and a is the pressure wave propagation speed. By taking the reciprocal of the period T, the vibration frequency associated with the water hammer action can be obtained.

[0034] (Study results) The time series of the water pressure inside the pipe (measured by a water pressure gauge) and the circumferential strain of the pipe body (measured by a strain gauge) will be described.

[0035] In Figs. 8 - 13, the relationship between the water pressure inside the pipe and the circumferential strain is shown in time series for each of the above - mentioned cases. As shown in the illustration, for the circumferential strain, it can be confirmed that the closer the measurement position is to the downstream side (Case1 - 4), the more similar the circumferential strain waveform is to the downstream water pressure waveform, and the closer the measurement position is to the upstream side (Case5, 6), the more similar the circumferential strain waveform is to the upstream water pressure waveform. This is because, as shown in the above formula (1), the deformation of the pipeline is caused by the internal pressure.

[0036] Also, Figs. 14 - 16 show the results of comparing the waveforms of water pressure and circumferential strain with or without leakage at each measurement position (Case1 - 6). In the case of leakage, it can be confirmed that the period tends to become shorter from around the third period of the water hammer pressure waveform.

[0037] Subsequently, the time series of the circumferential strain of the pipe body (measured by a strain gauge) and the circumferential displacement of the pipe body (measured by the DIC method) will be described.

[0038] Figs. 17 to 22 show the relationships between the water pressure and the circumferential displacement (measured by the DIC method) for each of the above cases in time series. As shown in the figures, in Cases 3 and 4 (see Figs. 19 and 20), the best correspondence between the water hammer pressure waveform and the circumferential displacement (dTheta) can be confirmed. In addition, in Cases 5 and 6 (see Figs. 21 and 22), a good correspondence between the water hammer pressure waveform and the circumferential displacement can be confirmed.

[0039] In Cases 1 and 2, it is considered that the vibration caused by noise may have had a significant impact. Fig. 23 shows the results of comparing the waveforms of the water pressure and the circumferential displacement according to the presence or absence of leakage at each measurement position. As shown in the figure, in Cases 3 to 6, similar to the circumferential strain, it can be confirmed that the period of the water hammer pressure waveform tends to be shorter in the case of leakage.

[0040] Next, the frequency distributions of the water pressure inside the pipe (measured by a pressure gauge), the circumferential strain of the pipe body (measured by a strain gauge), and the circumferential displacement of the pipe body (measured by the DIC method) will be described.

[0041] Figs. 24 to 26 show the frequency distributions of the water pressure, the circumferential strain, and the circumferential displacement according to the presence or absence of leakage at each measurement position (Cases 1 to 6). In Cases 3 and 4, where relatively good results were obtained in the time series waveforms, as shown in Fig. 25, it can be confirmed that in the frequency distribution, the frequencies (1) (1.7 Hz) and (2) (peak value) also tend to coincide for the water pressure, the circumferential strain, and the circumferential displacement, respectively.

[0042] In addition, in the case of a water leakage waveform with a shorter period in the time-series waveform, it can be confirmed that the frequency (3) shows a higher value than the frequency (2). The frequency (1) shows approximately 1.7 Hz that can be calculated in advance from the pipeline length and the pressure propagation speed. This can be calculated from the drawing information based on the specifications of the pipe. From this, if waveforms such as those in Case 3 and 4 can be input, from the information on the water hammer pressure waveform due to the sudden closure of the valve, in the case of water leakage, a frequency higher than the frequency due to the water hammer action (1.7 Hz in Fig. (1)) obtained from the drawing information of the pipeline can be obtained, enabling the detection of the presence or absence of water leakage even without actual measurement comparison data for the case without water leakage. Also, as can be seen from the fact that the amplitude spectrum appears lower in the case of water leakage in Fig. (3) than in the case without water leakage in Fig. (2), it becomes possible to grasp the energy loss due to water leakage and detect the presence or absence and scale of water leakage.

[0043] Note that the waveforms in the case of no water leakage in FIGS. 24 to 26 described above are not necessarily obtained only by actual measurement, and can be calculated based on the specifications and drawing information of the pipes in the pipeline by known unsteady flow condition analysis, and various information regarding the leakage phenomenon can be discriminated by comparison with this.

[0044] Next, the time-frequency analysis of the water pressure in the pipe (by a pressure gauge), the circumferential strain of the pipe body (by a strain gauge), and the circumferential displacement amount of the pipe body (by the DIC method) will be described.

[0045] In FIGS. 27 to 38, the results of the time-frequency analysis of the water pressure, the circumferential strain, and the circumferential displacement amount (by the DIC method) are shown for each of the above-described cases. Note that the reason why only the horizontal axis is different for the circumferential displacement amount by the DIC method is due to the difference in the number of data for data analysis. In each case, it can be confirmed that in any of the water pressure, the circumferential strain, and the circumferential displacement amount, the attenuation of the waveform becomes faster in the case of water leakage.

[0046] From this, it became clear that even at the measurement positions 47.3 m upstream from the valve (Case 5, 6), the influence of the water leakage near the valve can be detected by the circumferential strain and the circumferential displacement amount of the pipe body. Thus, by confirming the attenuation mode of the circumferential strain or the circumferential displacement amount, it becomes possible to reliably detect the presence or absence of water leakage even when the measurement position is far from the water leakage hole.

[0047] From each of the above-described examination results, it is possible to detect water leakage only by the measurement using the strain gauge 13 or only by the image measurement using the CCD cameras 11 and 12 for the behavior of the pipe body of the pipeline. In addition, by combining these strain gauges 13 and CCD cameras 11 and 12, it becomes possible to perform detection by image measurement considering the internal pressure information possessed by the circumferential strain, and it becomes possible to improve the detection accuracy and the certainty of the presence or absence of water leakage.

[0048] (System Configuration) Hereinafter, the configuration of the leakage phenomenon identification system 100 in the embodiment of the present invention will be described.

[0049] As shown in FIG. 4, the leakage phenomenon identification system 100 in the embodiment of the present invention at least includes an image analysis surface A installed on the surface of the pipe material of the pipeline, imaging means (CCD cameras 11 and 12) for imaging the image analysis surface A, displacement amount measurement means 101a for measuring the circumferential displacement amount of the pipe material based on the image captured by the imaging means, strain measurement means 101b for measuring the circumferential strain of the pipe material by the strain gauge 13 installed on the pipe material, and leakage phenomenon discrimination means 103 capable of performing analysis based on the measured circumferential displacement amount and circumferential strain and discriminating at least the presence or absence of a fluid leakage phenomenon.

[0050] In this embodiment, as shown in FIG. 4, at least two or more CCD cameras 11 and 12 for photographing the image analysis surface A from different directions are provided as photographing means. However, as long as the photographing means can photograph a three-dimensional image of the image analysis surface A, the number of photographing cameras including CCD cameras may be one or more. And the photographing means (CCD cameras 11 and 12) is connected to a PC incorporating a leakage phenomenon discrimination means 103 and the like.

[0051] Further, the leakage phenomenon discrimination means 103 in the PC includes an analysis means 104 and a learning means 105 that learns at least the circumferential displacement amount of the pipe material (learning step). Analysis is executed based on a predetermined algorithm of the learning means 105. And based on the analysis result, the identification information of the water leakage phenomenon is output to the water leakage information output section 102.

[0052] Also, a measurement facility information input means 106 is connected to the leakage phenomenon discrimination means 103. For example, in addition to the diameter and material of the pipeline, it is possible to input the diameter of the water leakage hole H actually discovered, the distance from the image photographing position to the water leakage hole H, and the like. By using such various information and the circumferential displacement amount of the pipe material as learning data, it becomes possible to identify not only the presence or absence of the water leakage hole H but also the water leakage position and the water leakage scale from the acquired three-dimensional image, and further, it becomes possible to improve the identification accuracy of the water leakage phenomenon.

[0053] (Method for Identifying Water Leakage Phenomenon) In an existing pipeline, since most of it is buried underground, in a manhole with a stop valve or the like, the image analysis surface A is installed on the surface of the exposed pipeline material (analysis surface installation step). And the photographing means (CCD cameras 11 and 12) is installed to photograph the above image analysis surface A with the photographing means (analysis surface photographing step).

[0054] The image captured by the imaging means is sent to a PC, and based on this, the circumferential displacement amount of the pipe material is measured (displacement amount measurement step). Based on the measured circumferential displacement amount of the pipe material, analysis can be performed to determine the presence or absence of a fluid leakage phenomenon (leakage phenomenon determination step). That is, by evaluating the deformation behavior of the pipe body by the above-described DIC method, obtaining the circumferential displacement amount (Figure 5 "θ") in the cylindrical coordinate system, and determining the attenuation behavior in both time and frequency (time-frequency domain), the leakage phenomenon in the pipeline can be identified.

[0055] That is, by determining the attenuation behavior in the above-described time-frequency domain, it becomes possible to detect not only the presence or absence of water leakage and the location of the water leakage but also the outflow form of the water leakage (for example, the presence or absence of a jet flow at the leakage hole, etc.) from the time waveform information.

[0056] Also, from the above-described experimental results, it became clear that it is possible to identify the presence or absence of water leakage even at a measurement location far from the water leakage hole. From this, for example, by arranging the image analysis surface A and the imaging means at two manholes and performing analysis based on the circumferential displacement amount of the pipe material measured at these two manholes and comparing these attenuation behaviors, it becomes possible to estimate not only the presence or absence of water leakage but also the location of the water leakage. And by using the above-described attenuation behavior and the actual location of the water leakage hole, etc. as learning data, it becomes possible to improve the identification accuracy of the water leakage phenomenon.

[0057] (Other embodiments) As described above, regarding the non-destructive detection method and non-destructive detection system for the leakage phenomenon of the present invention, the embodiments have been described by taking the method for identifying the water leakage phenomenon in the water supply and distribution pipeline as an example. However, the present invention is not necessarily limited to the configuration as described above, and various modifications as follows are possible.

[0058] For example, the non-destructive detection method and system for leakage phenomena of the present invention are not necessarily limited to water supply and distribution pipelines, and can be applied to pressurized pipelines for transporting various fluids such as fuel pipelines, gas pipelines, and steam pipelines. By considering the characteristics of the fluid and the characteristics of the pipe body, it is possible to identify the leakage phenomenon of the fluid with high precision.

[0059] In addition, the scale of the deformation of the pipe material depends on the elastic modulus and the second moment of area of the pipe material. Therefore, the non-destructive detection method and system for leakage phenomena of the present invention can be more preferably applied to pipe materials made of vinyl chloride than to steel pipes such as cast iron pipes.

[0060] As described above, the embodiments of the present invention have been described based on the drawings, but the specific configuration is not limited to these embodiments. The scope of the present invention is shown by the claims rather than the description of the above embodiments, and further includes all changes within the meaning and scope equivalent to the claims. In addition, the specific materials, dimensions, shapes, etc. described in the above examples can be changed within the scope of solving the problems of the present invention.

Description of Reference Numerals

[0061] A Image analysis surface 11 CCD camera 12 CCD camera 20 Lighting 100 Identification system for leakage phenomena 101a Displacement measurement means 101b Strain measurement means 102 Leakage information output means 103 Leakage phenomenon discrimination means 104 Analysis means 105 Learning means 106 Measurement facility information input means

Claims

1. A non-destructive detection method for fluid leakage phenomena in a pipeline, comprising: an analysis surface installation step of installing an image analysis surface on the surface of the pipe material of the pipeline; an analysis surface photographing step of photographing the image analysis surface with photographing means; a displacement measurement step of measuring the circumferential displacement amount of the pipe material based on the image photographed by the photographing means; a leakage phenomenon discrimination step of performing analysis based on the measured circumferential displacement amount and being able to discriminate at least the presence or absence of the fluid leakage phenomenon; the leakage phenomenon discrimination step can discriminate the attenuation behavior in the time-frequency domain based on the circumferential displacement amount and estimate at least the presence or absence of water leakage and the water leakage position A non-destructive detection method for leakage phenomena, characterized in that.

2. It has a strain measurement means installation step of installing strain measurement means capable of measuring the circumferential strain of the pipe material on the surface of the pipe material of the pipeline, the leakage phenomenon discrimination step can discriminate the attenuation behavior in the time-frequency domain based on the circumferential displacement amount and the attenuation behavior in the time-frequency domain based on the circumferential strain, and estimate at least the presence or absence of water leakage The non-destructive detection method for leakage phenomena according to Claim 1.

3. The photographing means is at least two or more photographing cameras that photograph the image analysis surface from different directions The non-destructive detection method for leakage phenomena according to Claim 1 or 2.

4. It has a learning step of machine-learning at least the circumferential displacement amount, in the leakage phenomenon discrimination step, it is possible to estimate the presence or absence of water leakage and the water leakage position based on a predetermined algorithm by the machine learning The non-destructive detection method for leakage phenomena according to Claim 1 or 2.

5. It has a learning step of machine-learning at least the circumferential displacement amount, in the leakage phenomenon discrimination step, it is possible to estimate the presence or absence of water leakage and the water leakage position based on a predetermined algorithm by the machine learning The non-destructive detection method for leakage phenomena according to Claim 3.

6. A non-destructive detection system for fluid leakage phenomena in a pipeline, comprising: an image analysis surface installed on the surface of the pipe material of the pipeline; photographing means for photographing the image analysis surface; displacement measurement means for measuring the circumferential displacement amount of the pipe material based on the image photographed by the photographing means; Leakage phenomenon discrimination means capable of performing analysis based on the measured circumferential displacement amount and discriminating at least the presence or absence of the leakage phenomenon of the fluid, Strain measuring means disposed on the surface of the pipe material of the pipeline and capable of measuring the circumferential strain of the pipe material, and having at least A non-destructive detection system for leakage phenomena, characterized by this.

7. The imaging means is at least two or more imaging cameras that image the image analysis plane from different directions. The non-destructive detection system for leakage phenomena according to claim 6.

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