Method, device and test piece for locating leaks in landfill sites using eddy current

Abstract

A method, device and test piece for locating a leakage position of a landfill HDPE membrane by using eddy current, the method comprising the following steps: arranging metal test pieces in equal intervals between the HDPE membrane and the GCL layer; when the HDPE membrane leaks, the landfill leachate corrodes the magnesium alloy metal sheet in the metal test piece; the primary magnetic field of the energized detection coil acts on the magnesium alloy metal sheet; under the excitation of the primary magnetic field of the detection coil, the surface of the magnesium alloy metal sheet generates induced eddy current; the induced eddy current is fed back to the detection coil through the secondary magnetic field, so that the impedance of the coil is distorted; the impedance change rule of the coil is analyzed according to the abnormal distribution of the impedance in the array detection coil, so as to obtain the corrosion distribution of the metal sheet under the HDPE membrane; and the inversion positioning algorithm is used to solve the leakage position. The test piece is provided with a metal sheet made of magnesium alloy, and the magnesium alloy contains a rare earth phase containing a rhenium element capable of forming a high-temperature-resistant phase.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental engineering, in particular to a method and device for locating the leakage position of HDPE membrane in landfill and a test piece. BACKGROUND

[0002] In recent years, due to the progress of waste management measures, waste landfills are added everywhere to store and decompose waste. In order to prevent leachate in waste from polluting groundwater, a leachate-proof layer, i.e. HDPE membrane, is laid at the bottom of the landfill. Since the HDPE membrane is subjected to complex stress after the landfill is put into operation, it is easy to be damaged, so it is necessary to monitor the leakage position of the HDPE membrane in the landfill in real time by some methods, so as to repair it in time. The traditional methods for monitoring the leakage position of the HDPE membrane mainly include high-voltage direct current method, transmission line method, optical fiber micro-bending loss method and stress wave method. The high-voltage direct current method needs to lay a certain thickness of clay layer under the membrane to lay the power supply and detection electrodes; the transmission line method is prone to physical displacement of the detection fiber due to the migration of the waste layer; the optical fiber micro-bending loss method has high requirements for the flatness of the foundation layer, otherwise it is easy to cause false detection; and the stress wave method is difficult to correct the wave velocity due to the non-uniform characteristics of the medium under the membrane, which will cause positioning error.

[0003] Among them, the high-voltage direct current method needs to lay a certain thickness of clay layer under the membrane to lay the power supply and detection electrodes; the transmission line method is prone to physical displacement of the detection fiber due to the migration of the waste layer; the optical fiber micro-bending loss method has high requirements for the flatness of the foundation layer, otherwise it is easy to cause false detection; and the stress wave method is difficult to correct the wave velocity due to the non-uniform characteristics of the medium under the membrane, which will cause positioning error. SUMMARY

[0004] In view of the above shortcomings, the technical problem to be solved by the present application is to provide a device and method for locating the leakage position of HDPE membrane in landfill by using eddy current, which has simple structure, low cost and simple operation. The purpose is to provide a detection coil impedance abnormal distribution monitoring system and a magnesium alloy metal detection test piece for realizing real-time positioning of the leakage position of HDPE membrane by using the corrosion characteristics of leachate.

[0005] The present application utilizes the abnormality of eddy current on the surface of the corroded metal sheet, and the closer to the damaged position, the greater the density of leachate, which leads to higher corrosion degree of the metal sheet, and thus increases the abnormality of the eddy current response on the surface of the metal sheet, so as to locate the leakage position of the HDPE membrane.

[0006] In order to achieve the above purpose, the present application provides the following technical solutions:

[0007] The application discloses a device for positioning a leakage position of a HDPE film of a landfill by using eddy current, which utilizes the difference characteristics of eddy current of surfaces before and after corrosion to realize real-time monitoring of the leakage position of the HDPE film by laying a plurality of magnesium alloy metal sheets with equal intervals between the HDPE film and a GCL layer and by analyzing the difference characteristics of impedance of a detection coil when the HDPE film has leakage or not.

[0008] The application discloses a method for positioning a leakage position of a HDPE film of a landfill by using eddy current, which utilizes the difference characteristics of eddy current of surfaces before and after corrosion to realize real-time monitoring of the leakage position of the HDPE film by laying a plurality of magnesium alloy metal sheets with equal intervals between the HDPE film and a GCL layer and by analyzing the difference characteristics of impedance of a detection coil when the HDPE film has leakage or not.

[0009] The application further provides a detection test piece for positioning a leakage position of a HDPE film of a landfill by using eddy current, which is provided with a metal sheet prepared from a magnesium alloy metal, and the magnesium alloy contains a rhenium element capable of forming a high-temperature-resistant rare earth phase.

[0010] Preferably, the metal sheet is provided with a sponge gasket between the metal sheet and the HDPE film.

[0011] The application utilizes eddy current detection to detect the corrosion condition of the magnesium alloy metal sheet laid under the anti-seepage layer, reverses and positions the leakage position of the HDPE film. The data is convenient to store and call, and the damage position of the HDPE film can be sensitively and quickly recognized. The method can effectively overcome the defects of the existing detection methods, such as the power supply electrode cannot be laid, the detection cable is prone to physical displacement, the basic environment requirement is high, and the wave speed correction is difficult.

[0012] Compared with the prior art, the device and the method for positioning a leakage position of a HDPE film of a landfill by using eddy current at least have the following beneficial effects:

[0013] (1) The method needs a detection metal sheet with a relatively small thickness, which can be laid between the HDPE film and a GCL layer (a geosynthetic clay liner), and does not need a clay layer, thereby widening the application scenarios.

[0014] (2) The system array density of the application is large, the displacement error is small, and the system can be corrected by using an algorithm, thereby improving the detection accuracy and realizing self-detection at any time.

[0015] (3) The method can be used for detecting the leakage position of the HDPE film in a landfill, and the detection result is convenient to store and call.

[0016] (3) The working environment requirement is low, and the detection unit can be replaced at any time.

[0017] (4) The detection metal sheet is a uniform medium, and does not need to analyze the error caused by the composition of the leachate.

[0018] The method for locating the leakage position of the HDPE membrane of the landfill by using eddy current will be further described below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a detection principle schematic diagram of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0020] Figure 2 It is a detection unit model structure schematic diagram of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0021] Figure 3 It is an apparent impedance diagram of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0022] Figure 4 It is a normalized apparent impedance diagram of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0023] Figure 5 It is a case implementation schematic diagram of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0024] Figure 6 It is a detection schematic diagram of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0025] Figure 7 It is a signal generator circuit diagram of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0026] Figure 8 It is a signal amplification circuit of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0027] Figure 9 It is a low-pass filter circuit of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current;

[0028] Figure 10 It is a phase-sensitive detection circuit of the method for locating the leakage position of the HDPE membrane of the landfill by using eddy current. DETAILED DESCRIPTION

[0029] The HDPE membrane leakage position monitoring method involved in the present application will be introduced from the aspects of function, composition and working principle.

[0030] As Figure 1 、 Figure 2 shown, the system used in the method for locating the leakage position of the landfill HDPE membrane by using eddy current mainly comprises a detection coil, a magnesium alloy metal sheet and an eddy current detection system.

[0031] Function: the surface eddy current of the corroded metal sheet is distorted under the action of the magnetic field to realize the monitoring of the leakage position of the HDPE membrane.

[0032] The material of the metal sheet of the present application can be selected from magnesium alloy, which has strong activity and is easy to be eroded by the landfill leachate to produce corrosion damage, but the general magnesium alloy has poor high-temperature resistance, therefore, the present application adds rhenium element to form a high-temperature-resistant rare earth phase. The magnesium alloy has good stability under dry air conditions. When the HDPE membrane is damaged and the leachate erodes the magnesium alloy, corrosion defects will be produced, mainly in the following two forms:

[0033] 1. Galvanic corrosion: when Cu, Co, Ni, Fe and other elements appear, the corrosion resistance of the magnesium alloy will be seriously affected, and the corrosion rate will be ten times that of the original; and the leachate contains Cl ions, at this time, the corrosion speed of the magnesium alloy in the humid environment of deionized water is four times that of the original. When the landfill leachate contains the above elements and is humid, the corrosion speed of the magnesium alloy will be accelerated, especially when the leachate contains SO2, the corrosion will be more serious.

[0034] 2. Local corrosion: due to the presence of Cl ions in the leachate, the radius of the Cl ions is relatively small, which can penetrate into the surface of the passivation layer of the magnesium alloy, causing damage to the passivation film and local corrosion.

[0035] Because the landfill leachate is complex and has different acid-base properties, the corrosion mode of the magnesium alloy is mainly the above two modes, and the magnesium alloy has strong conductivity, which is easy to produce eddy current on the surface under the action of the primary magnetic field, therefore, the magnesium alloy with added rhenium element is selected as the detection means.

[0036] Working principle: after the detection coil is energized, a primary magnetic field is excited to act on the magnesium alloy metal sheet, and an eddy current is induced on the surface of the magnesium alloy metal sheet. The size, phase and flow form of the eddy current are affected by the damage position of the metal sheet corroded by the leachate, thereby generating a secondary magnetic field. The secondary magnetic field acts on the detection coil, the impedance change rule of the analysis coil is analyzed, and then the corrosion distribution of the metal sheet under the HDPE membrane is obtained, and then the leakage position is solved according to the inversion positioning algorithm.

[0037] The impedance of the detection coil is represented in the form of series connection of inductance and resistance, which can be represented by the following formula:

[0038] T1=R1+jωL1#(1)

[0039] In formula (1), T1 represents the impedance of the coil itself, ω is the angular frequency of the supply voltage, R1 is the resistance of the detection coil, and L1 is the length of the coil.

[0040] When the coil is energized, the metal sheet is affected by the magnetic field, inducing an induced eddy current, and the secondary magnetic field generated by the induced eddy current affects the current and voltage in the detection coil, which is converted into the detection coil as an equivalent impedance T2:

[0041]

[0042] In formula (2), T2 represents the impedance converted into the detection coil by the secondary magnetic field, M represents the mutual inductance of the detection coil and the metal sheet, ω2 is the angular frequency of the induced eddy current on the surface of the metal sheet, R2 is the equivalent resistance when the metal surface eddy current flows, and L2 is the equivalent resistance length when the metal surface eddy current flows. At this time, the impedance in the detection coil, i.e. the apparent impedance, is:

[0043] T 总 = T1 + T2 (3)

[0044]

[0045] As shown in Figure 2 , it is a single detection unit model of a system for locating the leakage position of the HDPE film in the landfill by using eddy current, in order to prevent foreign matter from entering the system and affecting the detection result, a layer of sponge gasket is arranged on the metal sheet, when the HDPE film is damaged, the leachate corrodes the magnesium alloy metal sheet through the sponge gasket, the primary magnetic field generated by the supply current of the detection coil acts on the metal sheet, so that the surface of the metal sheet generates an eddy current and derives a secondary magnetic field which reacts on the detection coil, changing the impedance of the coil, when the response current is transmitted to the detection system, the impedance distribution of the detection coil can be obtained, and the specific position of the corroded alloy sheet is determined by analyzing whether the impedance distribution is distorted.

[0046] Please also refer to Figure 3 , it is the apparent impedance diagram of the present application, the apparent impedance is divided into resistance and inductance, the horizontal axis RS is the apparent resistance, the vertical axis Xs is the apparent inductance, X2 is the equivalent inductance of the response current, K is the coupling coefficient, and the change curve of the apparent impedance can be obtained according to formula (4), the resistance and inductance are regarded as unknown components, the apparent impedance change plane diagram is obtained, when R2→∞ or X2→∞, T0 and Tm are two extreme points, Figure 3 The positions of the two extreme points in the formula affect the detection result, and normalization processing is required;

[0047] As shown in Figure 4 , it is the normalized apparent impedance diagram of the present application. After processing, it is beneficial to identify the impedance distortion condition, and the detection of the leakage position is more sensitive.

[0048] The design inversion algorithm is used to locate the coordinates of the leakage position. The upper computer records the coordinate information of each detection unit to establish a GCl detection plane, the horizontal direction is the x-axis, and the vertical direction is the y-axis. The detection signals transmitted to the upper computer are used to analyze multiple abnormal points and accurately locate the leakage position of the HDPE film.

[0049] The alloy sheet corrosion positions A (Xa, Ya), B (Xb, Yb), and C (Xc, Yc) are known; ri is the distance between each alloy sheet corrosion position coordinate point and the leakage point, i = a, b, c; X (x, y) is the coordinate of the actual leakage point. Equation set (5) can be established:

[0050]

[0051] The square terms of the unknown node coordinates in the equation set are eliminated to obtain the linear equation set (6):

[0052]

[0053] The matrix representation of equation set (6) is:

[0054] AX = B#(7)

[0055] where the coefficient matrix A and the vector B are:

[0056]

[0057]

[0058] The unknown node is:

[0059]

[0060] The linear equation set with the correction amount is represented as:

[0061] AX+N = B#(11)

[0062] where N is a random error vector. The square of the modulus of the random error vector N = B - AX is required to be minimized, i.e., ||B - AX||2. 2 from the minimum, so that the influence of random errors on the positioning result is minimized.

[0063] ||B - AX||2 2 = (B - AX) T (B - AX) = B T B - B T AX - X T A T B + X T A T AX#(12)

[0064] The formula (12) is a function of X, and the derivative is equal to zero after derivation:

[0065] A T AX-A T B=0#(13)

[0066] Under the condition that the matrix A is full rank, the equation has a unique solution, and the leakage point coordinates are obtained:

[0067] X=(A T A) -1 A T B#(14)

[0068] Case implementation:

[0069] See Figure 5 、 Figure 6 , it is a schematic diagram of a metal detection test piece and a detection process diagram of an example of the present application. Since the slope rarely leaks, the top detection area of the HDPE film bottom library is set, the area is 70cm*70cm, twenty detection units are arrayed, the horizontal and vertical spacing is 10cm, and the diameter of each detection unit is 4cm and the height is 1cm. The detection unit is placed between the HDPE film and the GCL layer, when the HDPE film is damaged, the percolate corrodes the alloy sheet, so that the coil detection signal is distorted, the signal is transmitted to the signal amplification circuit from the coil, the low-pass filter circuit filters out the noise, the phase-sensitive detection circuit obtains the impedance amplitude, phase and other characteristic elements and transmits to the upper computer (impedance analysis machine), and finally the damaged position is located through the algorithm.

[0070] The detection system comprises a signal generation circuit, a detection coil, a signal amplification circuit, a phase-sensitive detection circuit, and a low-pass filter circuit. The obtained signal will be finally uploaded to the upper computer for impedance analysis, and the process is as shown in Figure 6 .

[0071] The induced current of eddy current detection is very small, and the alternating current signal generation circuit outputs ±15V voltage, Figure 7 which is used in the present application, R2 and R3 control the starting adjustment, frequency setting and amplitude stabilization. During the oscillation process, adjusting R4 satisfies the condition R4>2(R1-R3), and the distortion degree of the circuit waveform is low.

[0072] The signal amplification circuit is designed by AD830 differential amplifier, and the signal detected by the detection coil is modulated and amplified by the amplification circuit, as shown in Figure 8 .

[0073] The detection signal is filtered by the low-pass filter circuit to remove the noise, as shown in Figure 9 .

[0074] An AD835 phase-sensitive detection circuit with a bandwidth of 250MHz is designed to process the induced voltage and the excitation voltage to obtain characteristic elements such as amplitude and phase difference. Among them, sinout1 and sinout2 are coupling signals generated by the excitation source, and ux is the output detected signal, as shown in Figure 10 .

[0075] The method has the advantages of thin thickness, no need to lay clay layer in landfill, large array density, small displacement error, self-checking and correcting, easy replacement of detection unit, and easy implementation.

[0076] The above-described embodiments are merely preferred embodiments of the present application, and are not intended to limit the scope of the present application. Various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art without departing from the design spirit of the present application shall fall within the scope of protection of the claims of the present application.

Claims

1. A method for locating a leak in a landfill HDPE membrane using vortex, characterized in that, The metal detection test piece is laid between the HDPE film and the GCL layer in an equidistant manner, when the HDPE film leaks, the landfill leachate corrodes the magnesium alloy metal sheet in the metal detection test piece, the detection coil is energized to excite a primary magnetic field acting on the magnesium alloy metal sheet, under the excitation of the primary magnetic field of the detection coil, an induced eddy current is induced on the surface of the magnesium alloy metal sheet, the induced eddy current is fed back to the detection coil through a secondary magnetic field, so that the impedance of the coil is distorted, the impedance change rule of the coil is analyzed according to the abnormal distribution of the impedance in the array detection coil, so as to obtain the corrosion distribution of the metal sheet under the HDPE film, and then the leakage position is solved according to the inversion positioning algorithm.

2. The method of locating a leak in a landfill HDPE membrane using vortex according to claim 1, wherein, The magnesium alloy metal sheet contains a rhenium element capable of forming a high-temperature-resistant rare earth phase.

3. A method of locating a leak in a landfill HDPE membrane using vortex according to claim 2, characterized in that, The metal detection test piece comprises a magnesium alloy metal sheet and a detection coil, and a sponge gasket is arranged on the magnesium alloy metal sheet.

4. The method of locating a leak in a landfill HDPE membrane using eddy currents of claim 3, wherein, The impedance of the detection coil is represented in a series connection mode of inductance and resistance, and is represented as: ； In formula (1), denotes the impedance of the coil itself, is the supply voltage angular frequency, is the resistance of the detection coil, is the length of the coil; When the coil is energized, the metal sheet is affected by the magnetic field, and induced eddy current is excited. The secondary magnetic field generated by the eddy current affects the current and voltage in the detection coil, which is converted into an equivalent impedance in the detection coil This is embodied: ； In formula (2), M represents the mutual inductance of the detection coil and the metal sheet, is the angular frequency of the induced eddy current on the surface of the metal sheet, is the equivalent resistance of the eddy current flowing on the surface of the metal sheet, is the equivalent resistance length of the eddy current flowing on the surface of the metal sheet; at this time, the impedance in the detection coil, i.e. the apparent impedance, is: ； The leakage position is coordinate-positioned, the coordinate information of each detection unit is recorded, a GCl detection plane is established, the horizontal direction is the x-axis and the vertical direction is the y-axis, a plurality of abnormal points are analyzed according to the detection signal, and the leakage position of the HDPE film is accurately positioned.

5. A method of locating a leak in a landfill HDPE membrane using eddy currents as recited in claim 4, wherein, The positioning calculation method is: Given the alloy sheet corrosion positions A (Xa, Ya), B (Xb, Yb) and C (Xc, Yc); ri is the distance between the alloy sheet corrosion position coordinate points and the leakage point, i=a, b, c; X (x, y) is the coordinate of the actual leakage point, and an equation group (5) is established: ； The square terms of the unknown node coordinates in the equation group are eliminated to obtain a linear equation group (6): ； The matrix representation form of the equation group (6) is: ； Wherein the coefficient matrix A and the vector B are: ； The unknown node is: ； The linear equation group with the correction amount is represented as: ； Where N is a random error vector, and the square of the modulus of the random error vector N = B - AX is required to be the smallest, that is The minimum, so that the influence of random error on the positioning result is minimized, ； Formula (12) is a function of X, and after derivation, the derivative is equal to zero: ； Under the condition that the matrix A is full rank, the equation has a unique solution, and the leakage point coordinate is obtained: 。 6. The method of locating a leak in a landfill HDPE membrane using eddy currents of claim 3, wherein, The eddy current detection system comprises a signal generation circuit, a detection coil, a signal amplification circuit, a phase-sensitive detection circuit and a low-pass filter circuit, the signal detected by the detection coil is transmitted to the signal amplification circuit, the low-pass filter circuit filters out the noise, the phase-sensitive detection circuit obtains the characteristic elements and transmits them to the upper computer, and finally the damage position is located through the algorithm.

7. An apparatus for locating a leak in a landfill HDPE membrane using vortex, characterized by, The main part includes a metal detection test piece and an eddy current detection system, the metal detection test piece comprises a detection coil and a magnesium alloy metal sheet, the eddy current detection system energizes the detection coil to excite a primary magnetic field acting on the magnesium alloy metal sheet, and an eddy current is induced on the surface of the magnesium alloy metal sheet, the size, phase and flow form of the eddy current are affected by the damage position of the metal sheet corroded by the leachate, and then a secondary magnetic field is generated, the secondary magnetic field acts on the detection coil, the eddy current detection system analyzes the impedance change rule of the coil, so as to obtain the corrosion distribution of the metal sheet under the HDPE film, and then the leakage position is solved according to the inversion positioning algorithm.

8. The device for locating the position of a leak in a landfill HDPE membrane using eddy currents according to claim 7, characterized in that, The eddy current detection system includes a signal generation circuit, a detection coil, a signal amplification circuit, a phase-sensitive detection circuit, a low-pass filter circuit, and an impedance analyzer. The signal detected by the detection coil is transmitted from the coil to the signal amplification circuit, filtered by the low-pass filter circuit to remove noise, and the phase-sensitive detection circuit obtains characteristic elements and transmits them to the impedance analyzer. The impedance analyzer locates the damage position through an algorithm.

9. A test piece for locating a leak in a landfill HDPE membrane using eddy current, for use in the method of locating a leak in a landfill HDPE membrane using eddy current as claimed in claim 1, laid between the landfill HDPE membrane and the GCL layer, characterized in that, The device includes a metal sheet made of a magnesium alloy containing rhenium, an element capable of forming a high-temperature resistant rare earth phase.

10. A test kit for locating leaks in landfill HDPE membranes using eddy currents according to claim 9, wherein, The metal sheet is provided with a sponge pad, which is located between the metal sheet and the liquid inlet of the test specimen.

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