Pulsed eddy current detection system and method

Abstract

The invention relates to the technical field of detection, in particular to a pulsed eddy current detection system and method. The system comprises an iron core coil probe, a data acquisition device, a host and a pulse excitation device. Wherein the iron core coil probe comprises an iron core bundle, a detection coil, an excitation coil and a heat dissipation shell, the iron core bundle comprises a plurality of iron cores, the detection coil is wound on the outer surface of the iron core bundle, the excitation coil is wound on the outer surface of the detection coil, and the heat dissipation shell covers the iron core bundle, the detection coil and the excitation coil. The iron core coil probe sequentially comprises an iron core bundle, a detection coil, an excitation coil and a heat dissipation shell from inside to outside. The middle of the coil probe is filled with the iron core material, and the heat dissipation shell is arranged, so that the detection effect of pipeline detection is improved.

Description

Technical Field

[0001] The present invention relates to the field of detection technology, and in particular to a pulsed eddy current detection system and a pulsed eddy current detection method. Background Art

[0002] In the petroleum, chemical, electric power, metallurgy and other industrial fields, metal pipes are usually used to transport high-pressure, high-temperature and corrosive gas or liquid media. Due to medium wear and fluid accelerated corrosion, the pipe wall will be corroded and thinned, or even perforated, which may easily cause accidents such as medium leakage and explosion. Pipe wall corrosion will lead to a decrease in the pressure bearing performance of the pipeline, which seriously threatens production safety. Therefore, it is necessary to conduct non-destructive testing and evaluation of pipe wall corrosion on a regular basis to ensure the safe operation of the pipeline.

[0003] The current pulsed eddy current detection technology mostly uses a hollow excitation coil as the pulsed magnetic field excitation source. The pulsed magnetic field generated by this hollow probe method has a large distribution area, which results in the detection signal obtained by the pulsed eddy current field detection sensor being weak, noisy, and having poor detection effect. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a pulsed eddy current detection system and method for solving the above problems.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present application provides a pulsed eddy current detection system for pipeline detection. The pulsed eddy current detection system includes an iron core coil probe, a data acquisition device, a mainframe, and a pulse excitation source. The iron core coil probe includes an iron core bundle, a detection coil, an excitation coil, and a heat dissipation shell. The iron core bundle includes multiple iron cores. The detection coil is wound on the outer surface of the iron core bundle. The excitation coil is wound on the outer surface of the detection coil. The heat dissipation shell covers the iron core bundle, the detection coil, and the excitation coil. The iron core coil probe is composed of an iron core bundle, a detection coil, an excitation coil, and a heat dissipation shell from the inside to the outside.

[0007] Furthermore, the core coil probe is placed parallel to the pipeline.

[0008] Furthermore, the heat dissipation housing includes a metal housing and a plastic pad. The metal housing is symmetrically arranged with the iron core bundle as the center. The plastic pads are respectively connected to the metal housings to cover the iron core bundle, the detection coil and the excitation coil together.

[0009] Furthermore, a thermally conductive silicone layer is provided between the heat dissipation housing and the excitation coil.

[0010] Furthermore, the pulse excitation device includes: a current A / D analog-to-digital converter, a D / A digital-to-analog converter, a power amplifier circuit and a sampling resistor. The sampling resistor is used to sample the output result of the excitation coil and transmit the output result to the host through the voltage A / D analog-to-digital converter. The host outputs the pulse excitation current to the excitation coil through the D / A digital-to-analog converter and the power amplifier circuit.

[0011] Furthermore, the data acquisition device includes a data acquisition card and a voltage A / D analog-to-digital converter. The data acquisition card is respectively connected to the voltage A / D analog-to-digital converter and the two ends of the sampling resistor, and is used to collect the induced voltage time domain signal at both ends of the detection coil and the excitation current flowing through the sampling resistor. The voltage A / D analog-to-digital converter is used to convert the induced voltage analog signal of the detection coil into an induced voltage discrete digital signal and transmit it to the host.

[0012] In a second aspect, the present application provides a pulse eddy current detection method, which is applied to pipeline detection, and the method includes: step 1: the iron core coil probe is placed parallel to the pipeline to be detected; step 2: the pulse excitation device is controlled by the host to output an excitation digital signal to the iron core coil probe, and the data acquisition device obtains the induced voltage and excitation current fed back by the iron core coil probe, and saves them in the host; step 3: the host determines the detection data of the pipeline detection point based on the induced voltage and the excitation current, and the detection data includes the inversion information of the pipeline wall thickness, the relative magnetic permeability of the iron core coil probe and the coil coupling coefficient; step 4: the host compares the detection data with the pre-tested standard pipeline detection data to determine the detection result corresponding to the pipeline detection point.

[0013] Furthermore, step 2 includes: step 2-1: the host outputs an excitation digital signal with a continuous pulse width of 10 to 100 ms and an amplitude of 0.1 to 1 V; step 2-2: the host controls the D / A digital-to-analog converter to convert the excitation digital signal into a corresponding excitation analog signal; step 2-3: the host outputs the excitation analog signal to the power amplifier circuit, and after amplification by the power amplifier circuit, outputs an excitation current with a continuous pulse width of 10 to 100 ms and an amplitude of 1 to 5 A to the iron core coil probe; step 2-4: the data acquisition device obtains the induced voltage and excitation current at both ends of the iron core coil probe, and saves them in the host.

[0014] Furthermore, step 3 includes: step 3-1: the host corrects the induced voltage and the excitation current according to the coil coupling coefficient of the core coil probe to determine the time domain expression of the induced voltage; step 3-2: the host solves the time domain expression to determine the time domain analytical solution of the induced voltage; step 3-3: the host determines the detection data of the pipeline detection point based on the time domain analytical solution, and the detection data includes the inversion information of the pipeline wall thickness, the relative magnetic permeability of the core coil probe and the coil coupling coefficient.

[0015] Furthermore, step 4 includes: step 4-1: placing the iron core coil probe at the pipeline reference point to determine the standard pipeline detection data, the standard pipeline detection data including the pipeline wall thickness corresponding to the pipeline reference point, the relative magnetic permeability of the iron core coil probe and the inversion information of the coil coupling coefficient; step 4-2: the host determines the relative change of the pipeline wall thickness of the pipeline detection point relative to the pipeline reference point according to the ratio of the inversion results of the pipeline wall thickness corresponding to the pipeline detection point and the pipeline reference point; step 4-3: the host determines the detection result corresponding to the pipeline detection point based on the relative change of the pipeline wall thickness.

[0016] It can be seen from the above technical solutions that the advantages and positive effects of the pulsed eddy current detection system and method proposed in the present invention are:

[0017] By filling the middle of the coil probe with an iron core material with high magnetic permeability and high saturation magnetic flux density, the magnetic resistance of the magnetic circuit between the coil probe and the inspected pipeline is reduced, so that under the same detection conditions, the same size of pulse magnetic field is excited, and the required excitation current and probe size are smaller. In addition, a heat dissipation shell is set outside the coil to dissipate the heat of the coil, which is conducive to increasing the amplitude of the pulse excitation current, ensuring the reliability of the detection results during long-term continuous scanning, while enhancing the excitation magnetic field strength and signal strength, and improving the signal-to-noise ratio of the detection signal. By placing the iron core coil probe parallel to the pipeline, the eddy current can be focused in a smaller area without spreading outward, improving the effect of magnetic field concentration, and helping to limit the eddy current distribution area to a smaller area on the pipeline elbow, so as to better distinguish whether it is a change in the wall thickness of the pipeline elbow itself or a local thinning defect caused by corrosion. By setting a plastic pad of the heat dissipation shell to isolate the metal shell, the metal shell is blocked from forming eddy currents in the circumferential direction, thereby significantly reducing the intensity of the eddy current in the probe shell and improving the signal-to-noise ratio of the detection signal. By setting a thermal conductive silicone layer between the heat dissipation shell and the excitation coil, the heat dissipation efficiency of the coil is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above content and the following specific embodiments of the present invention will be better understood when read in conjunction with the accompanying drawings. It should be noted that the accompanying drawings are only examples of the technical solutions claimed for protection.

[0019] Figure 1 It is a structural schematic diagram of a detection pipeline provided by the present invention;

[0020] Figure 2 is a cross-sectional view of an iron core coil probe provided by the present invention;

[0021] Figure 3 It is a structural diagram of an iron core coil probe provided by the present invention;

[0022] Figure 4 It is a schematic diagram of the axis position of an iron core coil probe and a pipeline provided by the present invention;

[0023] Figure 5 It is a schematic diagram of the dimensions of an iron core coil probe and a pipeline provided by the present invention;

[0024] Figure 6 It is a structural schematic diagram of a pulsed eddy current detection system provided by the present invention;

[0025] Figure 7 It is a flow chart of a pulse eddy current detection method provided by the present invention.

[0026] The reference numerals are described as follows:

[0027] Core coil probe 10;

[0028] Excitation coil 1;

[0029] Detection coil 2;

[0030] Thermal conductive silicone layer 3;

[0031] Plastic mat 4;

[0032] Metal housing 5;

[0033] Core bundle 6;

[0034] Host 20;

[0035] D / A digital-to-analog converter 21;

[0036] Power amplifier circuit 22;

[0037] Current A / D analog-to-digital converter 23;

[0038] Voltage A / D analog-to-digital converter 24;

[0039] Sampling resistor 25. DETAILED DESCRIPTION

[0040] The detailed features and advantages of the present invention are described in detail in the specific implementation modes below, and the contents are sufficient to enable any person skilled in the art to understand the technical contents of the present invention and implement them accordingly. Moreover, according to the description, claims and drawings disclosed in this specification, those skilled in the art can easily understand the relevant objects and advantages of the present invention.

[0041] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0042] In the description of this embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0044] Please refer to Figure 1 , Figure 1 In order to detect the schematic diagram of pipeline structure, the present invention aims to improve the detection accuracy of the pipe wall thickness d in the pipeline.

[0045] In one embodiment of the present invention, a pulsed eddy current testing system may include an iron core coil probe, a data acquisition device, a host computer and a pulse excitation device.

[0046] Please refer to Figure 2 and Figure 3 As shown, the core-coil probe 10 may include a core bundle 6, a detection coil 2, an excitation coil 1, and a heat dissipation shell. The core bundle 6 includes a plurality of cores, the detection coil 2 is wound on the outer surface of the core bundle 6, the excitation coil 1 is wound on the outer surface of the detection coil 2, the heat dissipation shell covers the core bundle 6, the detection coil 2, and the excitation coil 1. The core-coil probe 10 includes the core bundle 6, the detection coil 2, the excitation coil 1, and the heat dissipation shell from the inside to the outside.

[0047] It can be understood that by filling the middle of the coil probe with an iron core material with high magnetic permeability and high saturation magnetic flux density, the magnetic resistance of the magnetic circuit between the coil probe and the inspected pipeline is reduced, so that under the same detection conditions, the same size of pulse magnetic field is excited, and the required excitation current and probe size are smaller. In addition, a heat dissipation housing is provided outside the coil to dissipate heat from the coil, which is conducive to increasing the amplitude of the pulse excitation current, ensuring the reliability of the detection results during long-term continuous scanning, and at the same time enhancing the excitation magnetic field strength and signal strength, and improving the signal-to-noise ratio of the detection signal.

[0048] Furthermore, the core coil probe 10 may be placed in parallel along the pipeline.

[0049] Specifically, please refer to Figure 4 and Figure 5 The iron core coil probe 10 can be placed in the pipeline, and the iron core coil probe 10 is consistent with the axial direction of the pipeline.

[0050] It can be understood that the traditional coil probe design places the coil axis perpendicular to the pipeline axis. The eddy current field of this placement method will diffuse outward over time, and as the probe is lifted off, the eddy current distribution area of ​​the probe will increase. When this probe mode is used to detect small-diameter pipes, especially elbows and tees, the resolution of local corrosion is relatively low and it is easy to miss detection.

[0051] In the present invention, by placing the core coil probe 10 parallel to the pipeline, the eddy current can be focused in a smaller area without spreading outward, which has the effect of magnetic field concentration and is conducive to improving the detection resolution. Furthermore, for occasions with elbows, the middle part of the probe can be filled with an iron core material with high magnetic permeability and high saturation magnetic flux density to reduce the magnetic resistance of the magnetic circuit between the coil probe and the pipeline being inspected, and the eddy current distribution area is limited to a smaller area on the elbow, so as to better distinguish whether it is a change in the wall thickness of the elbow itself or a local thinning defect caused by corrosion. Under the same detection conditions, the same size of pulse magnetic field is stimulated, and the required excitation current and probe size are also smaller.

[0052] In one embodiment, the heat dissipation housing may include a metal housing 5 and a plastic pad 4. The metal housing 5 is symmetrically arranged with the core bundle 6 as the center. The plastic pads 4 are respectively connected to the metal housing 5 and together cover the core bundle 6, the detection coil 2 and the excitation coil 1.

[0053] It can be understood that filling the coil probe with an iron core and using the metal shell 5 to dissipate heat outside the coil are both beneficial to enhancing the excitation magnetic field strength and signal strength. In addition, the pulsed eddy current probe dissipates heat through the metal shell 5, which can increase the amplitude of the pulsed excitation current and ensure the reliability of the detection results during long-term continuous scanning. That is, when the iron core coil probe 10 of the present invention performs pulsed eddy current nondestructive testing on small-diameter pipelines, the coil probe can generate a spatially concentrated pulsed strong magnetic field while ensuring sufficient detection signal strength and improving the signal-to-noise ratio of the signal.

[0054] Furthermore, plastic sheets may be provided between the metal shells 5 to insulate the metal shells 5 and prevent the metal shells 5 from forming eddy currents in the circumferential direction, thereby reducing the intensity of the eddy currents in the heat dissipation shell.

[0055] In one embodiment, a thermally conductive silicone layer 3 is provided between the heat dissipation housing and the excitation coil 1 .

[0056] It can be understood that by providing a thermally conductive silicone layer 3 between the heat dissipation housing and the excitation coil 1, the heat dissipation efficiency of the coil is further improved.

[0057] For further information, please refer to Figure 6The pulse excitation device may include a current A / D analog-to-digital converter 23, a D / A digital-to-analog converter 21, a power amplifier circuit 22 and a sampling resistor 25. The sampling resistor 25 is used to sample the output result of the excitation coil 1 and transmit the output result to the host 20 through the current A / D analog-to-digital converter 23. The host 20 outputs a pulse excitation current to the excitation coil 1 through the D / A digital-to-analog converter 21 and the power amplifier circuit 22.

[0058] In one embodiment, the data acquisition device includes a data acquisition card (not shown) and a voltage A / D analog-to-digital converter 24. The data acquisition card is respectively connected to the two ends of the voltage A / D analog-to-digital converter 24 and the sampling resistor 25, and is used to collect the induced voltage time domain signal at both ends of the detection coil 2 and the excitation current flowing through the sampling resistor 25. The voltage A / D analog-to-digital converter 24 is used to convert the induced voltage analog signal of the detection coil 2 into an induced voltage discrete digital signal, and transmit it to the host 20.

[0059] It can be understood that the two ends of the detection coil 2 are externally connected to a voltage A / D analog-to-digital converter 24, and the voltage A / D analog-to-digital converter 24 is connected to the host 20. The host 20 is also connected to the D / A digital-to-analog converter 21 and the current A / D analog-to-digital converter 23. The D / A digital-to-analog converter 21 is connected to the input of the power amplifier circuit 22, and the output of the power amplifier circuit 22 is connected to the sampling resistor 25 and then connected to the excitation coil 1. The sampling resistor 25 is also connected to the current A / D analog-to-digital converter 23. The host 20 can realize signal acquisition through a data acquisition card, and process the signal, display the results, store data, etc., so as to facilitate the subsequent determination of the wall thickness change information of the detected point of the pipeline.

[0060] In one embodiment, the preparation of the core coil probe 10 may include the following steps:

[0061] Step 1, select cylindrical electrical pure iron (i.e. DT4) wire with a diameter of 1 to 3 mm, cut it into small pieces of equal length, and brush a uniform layer of insulating paint on the surface and end of each core, dry it, and then arrange it closely to form a large cylindrical core bundle 6, and make the air gap between the cores as small as possible, and finally glue it firmly.

[0062] Step 2: tightly wind the enameled wire outside the cylindrical iron core bundle 6 to obtain a cylindrical detection coil 2, and tightly wind the copper enameled wire outside the detection coil 2 to form a cylindrical excitation coil 1.

[0063] Step 3, evenly apply insulating thermally conductive silicone on the outside of the excitation coil 1 to form a thermally conductive silicone layer 3, and tightly bond two semi-circular ring-shaped metal shells 5 to the insulating thermally conductive silicone. The gap between the two half metal shells 5 is separated and insulated by a plastic pad 4.

[0064] Step 4: Place the axis of the cylindrical coil probe parallel to the axis of the pipeline being tested.

[0065] Please refer to Figure 7 The present invention also provides a pulsed eddy current detection method, which may include the following steps:

[0066] Step 1: Place the core coil probe parallel to the pipe to be tested.

[0067] Step 2: The host controls the pulse excitation device to output an excitation digital signal to the core coil probe. The data acquisition device obtains the induced voltage and excitation current fed back by the core coil probe and saves them in the host.

[0068] Step 3: The host determines the detection data of the pipeline detection point based on the induced voltage and the excitation current. The detection data includes the inversion information of the pipeline wall thickness, the relative magnetic permeability of the core coil probe, and the coil coupling coefficient.

[0069] Step 4: The host compares the test data with the pre-tested standard pipeline test data to determine the test results corresponding to the pipeline test points.

[0070] In one embodiment, step 2 may include the following steps:

[0071] Step 2-1: The host 20 outputs an excitation digital signal with a continuous pulse width of 10 to 100 ms and an amplitude of 0.1 to 1 V.

[0072] Step 2-2: The host 20 controls the D / A converter 21 to convert the excitation digital signal into a corresponding excitation analog signal.

[0073] Step 2-3: The host 20 outputs the excitation analog signal to the power amplifier circuit 22. After amplification by the power amplifier circuit 22, an excitation current with a continuous pulse width of 10 to 100 ms and an amplitude of 1 to 5 A is output to the core coil probe 10.

[0074] Step 2-4: The data acquisition device obtains the induced voltage and excitation current at both ends of the core coil probe 10 and stores them in the host 20.

[0075] In one embodiment, step 3 may include the following steps:

[0076] Step 3-1: The host 20 corrects the induced voltage and the excitation current according to the coil coupling coefficient of the core coil probe 10, and determines the time domain expression of the induced voltage.

[0077] Step 3-2: The host 20 solves the time domain expression to determine the time domain analytical solution of the induced voltage.

[0078] Step 3-3: The host 20 determines the detection data of the pipeline detection point based on the time domain analytical solution, and the detection data includes the inversion information of the pipeline wall thickness, the relative magnetic permeability of the core coil probe 10, and the coil coupling coefficient.

[0079] In one embodiment, step 4 may include the following steps:

[0080] Step 4-1: Place the core coil probe 10 at the pipeline reference point to determine standard pipeline detection data, which includes the pipeline wall thickness corresponding to the pipeline reference point, the relative magnetic permeability of the core coil probe 10, and the inversion information of the coil coupling coefficient.

[0081] Step 4-2: The host 20 determines the relative change in the pipe wall thickness of the pipe inspection point relative to the pipe reference point according to the ratio of the pipe wall thickness inversion results corresponding to the pipe inspection point and the pipe reference point.

[0082] Step 4-3: The host 20 determines the detection result corresponding to the pipeline detection point based on the relative change in the pipeline wall thickness.

[0083] Furthermore, for ease of understanding, the entire pulsed eddy current testing method will be fully described below.

[0084] Steps for placing the core coil probe 10:

[0085] The axis of the cylindrical iron core coil probe 10 is placed parallel to the axis of the pipeline to be inspected.

[0086] Signal acquisition steps:

[0087] Step SAP-1, the two ends of the excitation coil 1 are connected to the output of the power amplifier circuit 22 after passing through the sampling resistor 25, and the two ends of the detection coil 2 are connected to the input end of the voltage A / D analog-to-digital converter in the data acquisition card;

[0088] Step SAP-2, using the host 20 to program and output an excitation digital signal with a continuous pulse width of 10 to 100 ms and an amplitude of 0.1 to 1 V; after passing through the D / A digital-to-analog converter, it becomes an excitation analog signal with a continuous pulse width of 10 to 100 ms and an amplitude of 0.1 to 1 V, and outputs it to the power amplifier circuit 22; after the power amplifier circuit 22 amplifies the power, it outputs a pulse excitation current with a continuous pulse width of 10 to 100 ms and an amplitude of 1 to 5 A to the excitation coil 1;

[0089] Step SAP-3, use the data acquisition card to collect the excitation current i(t) (unit A) flowing through the sampling resistor 25, and store the collected excitation current i(t) in the host 20; at the same time, use the data acquisition card to collect the induced voltage time domain signal u(t) (unit V) at both ends of the detection coil 2, and store the collected induced voltage signal u(t) in the host 20.

[0090] In this process, the pulse eddy current continuous scanning system can be used to collect the pulse excitation current and induced voltage time domain signals.

[0091] It should be noted that the pulsed eddy current continuous scanning system is a technology well known to those skilled in the art and will not be described in detail here.

[0092] Parameter inversion steps for the inspected metal pipeline parameters:

[0093] After obtaining the induced voltage at both ends of the detection coil 2 according to the signal acquisition steps, how to invert the detection point Q of the pipeline under inspection from the detection signal? j Wall thickness d j The change of is the key to signal processing in pulse eddy current detection of wall thickness corrosion. In the present invention, when the coil probe prepared in step 1 performs pulse eddy current detection on the pipeline, when the pulse excitation current i(t) is passed through the excitation coil 1, the time domain expression of the induced voltage at both ends of the detection coil 2 is:

[0094]

[0095] π is 3.14; e is the base of natural logarithm, which is 2.72; σ is the conductivity of the steel bar under test, in S / m; μ0 is the magnetic permeability of vacuum, which is 4π×10 -7 H / m; μ r is the relative magnetic permeability of the steel bar under test; r1 is the inner radius of the pipe under test; r2 is the outer radius of the pipe under test; i(t) is the pulse excitation current, in A; i′(t) represents the derivative of the pulse excitation current with respect to time; “*” represents the convolution operation

[0096] K m (x) is the m-th order modified Bessel function of the second kind,

[0097] The coefficients in the formula are:

[0098] F nu (ξ)=δ ξ υ ξ A m (ξ)D m (ξ)-ε ξ B m (ξ)C m (ξ)-A m (ξ)B m (ξ)r 22 ;

[0099] F de (ξ)=[δ ξ υ ξ A m(x)+e ξ B m (x)] 2 -e ξ d ξ u ξ [C m (ξ)+D m (x)] 2 -d ξ u ξ A m (ξ)[C m (ξ)r 22 +D m (ξ)r 11 ]+e ξ B m (ξ)[D m (ξ)r 22 +C m (ξ)r 11 ]+A m (ξ)B m (ξ)r 11 r 22 ;

[0100]

[0101] A m (r1,r2,ξ)=J m (r1ξ)Y m (r2ξ)-J m (r2ξ)Y m (r1ξ);

[0102] B m (r1,r2,ξ)=[J′ m (r1ξ)Y′ m (r2ξ)-J′ m (r2ξ)Y′ m (r1ξ)]r1r2;

[0103] C m (r1,r2,ξ)=[J′ m (r1ξ)Y m (r2ξ)-J m (r2ξ)Y′ m (r1ξ)]r1;

[0104] D m (r1,r2,ξ)=[J m (r1ξ)Y′ m (r2ξ)-J′ m (r2ξ)Y m (r1ξ)]r2;

[0105] J m (x) and Y m (x) are the first and second type m-order Bessel functions, respectively, J′ m (x) and Y′ m (x) represents its derivative with respect to x respectively;

[0106] ξ dek is the denominator expression F de (ξ)=0, the kth positive real root, F′ de (ξ) represents the denominator F de (ξ) is the derivative of the variable ξ; κ is the coil coupling coefficient, which has a typical value of 1 and is related to the change in curvature at the elbow.

[0107] C d (λ,m) is the coil coefficient of the excitation coil 1, and its expression is:

[0108]

[0109] h d is the height of the excitation coil 1; r di and r do are the inner radius and outer radius of the excitation coil 1 respectively; the turn density of the excitation coil 1 N p is the number of turns of the excitation coil 1; x0 is the distance between the pipeline axis and the cylindrical coil axis; C p (λ,m) is the coil coefficient of detection coil 2, and its expression is the same as C d (λ,m) are the same, just replace the corresponding excitation coil 1 parameters with the detection coil 2 parameters.

[0110] Based on the time domain analytical solution of the induced voltage of the metal pipeline pulse eddy current detection model, the least squares problem between the measured value of the induced voltage time domain signal and the theoretical calculated value is established. j The wall thickness, magnetic permeability and coupling coefficient at the point are inverted. The specific steps are as follows:

[0111] Step 1: Check the pipeline inspection point Q j Wall thickness d j , relative magnetic permeability μ r , the coil coupling coefficient κ is set as an unknown parameter, that is, the parameter vector to be inverted x = (d, μ r ,κ) T ;

[0112] Step 2: According to the signal acquisition steps, detect point Q on the inspected pipeline j The discrete time-domain induced voltage measurement data at both ends of the detection coil 2 collected by the data acquisition card are (t1,u1),(t2,u2),…,(tm ,u m ), and compare it with the theoretical value of the induced voltage u(x, t) calculated by equation (1), and minimize the sum of squares of the errors between the measured value and the calculated value of the induced voltage signal to invert the parameter x, that is, to establish the least squares problem:

[0113]

[0114] Let the residual function r i (x) = u i -u(x,t i ),i=1,2,…,m, and the residual function vector r(x)=(r1(x),r2(x),…,r m (x) T .

[0115] Step 3: In the host 20, an iterative algorithm is used to solve the optimal solution x of the least squares problem (2) * , the calculation steps of the iterative algorithm are:

[0116] (1) Given an initial point (where d (1) =1~30mm, κ (1) =0.1~10), allowable error ε>0 (generally ε=10 -3 ), set k = 1;

[0117] (2) The parameter vector of step k Substituting into the calculation formula (1), the theoretical value of the induced voltage u(x) at each time point ti is calculated. (k) ,t i ), and then subtract it from the measured value of the induced voltage ui to calculate the residual function value

[0118] r i (x (k) )=u i -u(x (k) ,t i ),i=1,2,…,m,

[0119] And get the residual function vector r (k) ; Then, the first-order partial derivative of the induced voltage theoretical curve with respect to the wall thickness d is further calculated by formula (1):

[0120]

[0121] Theoretical curve of induced voltage versus relative magnetic permeability μ r The first partial derivative of

[0122]

[0123] And the first-order partial derivative of the induced voltage theoretical curve with respect to the lift-off l

[0124] i=1,2,…,m,

[0125] Get the m×3 matrix A k =(a ij ) m×3 ;

[0126] (3) Solving the equations

[0127]

[0128] Find the direction vector b (k) ;

[0129] (4) From the parameter vector x (k) Departure along b (k) Perform a one-dimensional search and find the step length α k , so that f(x (k) +α k b (k) )=m α inf(x (k) +αb (k) ), and let x (k+1) =x (k) +α k b (k) ;

[0130] (5) If ||x (k+1) -x (k) ||≤ε, then stop the calculation and get the optimal solution of the least squares problem (2) Otherwise, set k:=k+1 and return to step (2).

[0131] The optimal solution of the least squares problem (2) is obtained by the above iterative algorithm Then, the detection point Q on the inspected pipeline is obtained. j Inversion results of wall thickness at Inversion results of relative magnetic permeability Inversion results of coil probe lift-off distance The inversion results With detection point Q j The location information is matched and saved in the host 20.

[0132] It can be understood that the process in which the host 20 analyzes and processes the induced voltage detection signal to invert the wall thickness, relative magnetic permeability and coupling coefficient of the detection point of the ferromagnetic pipeline being inspected is called the parameter inversion step.

[0133] The parameter inversion results are used to detect the relative change in wall thickness at different detection points on the pipeline (wall thickness detection).

[0134] It is understandable that the outer coating of the inspected pipeline is unevenly laid, or the coupling between the probe and the elbow varies at the elbow. Due to the hysteresis characteristics of ferromagnetic materials, the magnetic permeability of each inspected ferromagnetic pipeline may change, so it is impossible to use standard test blocks to calibrate the electrical conductivity and magnetic permeability of the component.

[0135] In the present invention, the wall thickness inversion result at the reference point can be used as a reference value to eliminate the influence of the electromagnetic parameters of the inspected pipeline on the inspection result. The specific steps are:

[0136] Step 1: Place the coil probe in the probe preparation step at the reference point Q0 on the inspected pipe. The wall thickness at the reference point Q0 is d0.

[0137] Step 2: According to the signal acquisition step, the time domain signal data of the induced voltage at both ends of the detection coil 2 at the reference point is acquired and stored in the host;

[0138] Step 3: According to the parameter inversion steps, the least squares problem is established using the detection signal at the reference point Q0 to invert the wall thickness, relative magnetic permeability and probe coupling coefficient at the reference point Q0. is the inversion result of the wall thickness at the reference point Q0.

[0139] Step 4: Move the coil probe to the inspection point Q of the inspected pipeline j According to the signal acquisition steps and parameter inversion steps, the detection point Q is obtained. j The inversion results of wall thickness, relative magnetic permeability and probe coupling coefficient at Q is the detection point j The inversion result of the wall thickness at the detection point Q j The location information is matched and stored in the host.

[0140] Step 5: Set the detection point Q j Wall thickness inversion results Inversion results of wall thickness at reference point Compare and get the ratio of the two wall thickness inversion results In the present invention, the detection point Q j Wall thickness d j The ratio of the wall thickness d0 at the reference point Q0 is the same as the The relationship between The detection point Q on the inspected pipeline is calculated from this j Relative change in wall thickness relative to the reference point Q0.

[0141] Move the coil probe to the next inspection point Q of the inspected pipelinej+1 Repeat steps 4 and 5 to get the detection point Q j+1 Relative change in wall thickness relative to reference point Q0. Match the test results with the location information of the test points and save them in the host. Until the relative change in the wall thickness of the entire tested pipeline relative to the wall thickness of the reference point Q0 is depicted, and the degree of wall thickness corrosion at each test point is described with a gradient color block, so as to find the location of the wall thickness corrosion thinning of the tested pipeline and make a quantitative assessment of the wall thickness corrosion degree.

[0142] It can be understood that the accuracy of the wall thickness detection results at the elbow can be guaranteed by inverting the parameters using the precise mathematical expression of the model. In the precise mathematical expression of the derived pipeline pulse eddy current detection model, the coil coupling coefficient κ is used to correct the influence of the curvature change at the small-diameter pipe elbow on the detection signal. In the parameter inversion step, the coupling coefficient κ is treated as an unknown parameter, and the precise analytical expression of the model is used to determine the wall thickness and coupling coefficient values ​​at each detection point, which can significantly reduce the influence of the pipe curvature change on the wall thickness detection results when detecting small-diameter pipe elbows.

[0143] The detection effect of the present invention will be fully described below.

[0144] The test objects are two 20# steel elbow pipes with the same material, 60mm diameter and 5.7mm wall thickness. One of the intact elbow pipes is used as a reference test block, and the other elbow pipe is processed with a rectangular thinning defect of about 80×60mm on the outer ridge as a comparison test block. The actual remaining wall thickness at the defect is about 4.9mm measured by ultrasonic thickness measurement, which is 85.9% of the 5.7mm on the reference elbow side ridge.

[0145] The middle position of the side ridge of the reference test block is selected as the reference point Q0, and the center position of the rectangular defect processed on the outer ridge of the comparison test block is selected as the detection point Q1. The thickness of the insulation layer varies in the range of 0 to 60 mm.

[0146] The pulse eddy current detection was performed on two elbow pipe test blocks using the iron core coil probe 10 and the pulse eddy current detection method designed in the present invention. It was measured that when the coil probe was lifted off 0 mm, the remaining wall thickness at point Q1 relative to the reference point was 81%, with an error of -4.9%; when the probe was lifted off 40 mm, the remaining wall thickness at point Q1 relative to the reference point was 86.7%, with an error of 0.8%; when the probe was lifted off 60 mm, the remaining wall thickness at point Q1 relative to the reference point was 86.9%, with an error of 1.0%.

[0147] In addition, two 20# steel elbows with the same material, diameter of 34mm and wall thickness of about 5.0mm were used. One of the intact elbows was used as a reference test block, and a rectangular thinning defect of about 60×40mm was processed on the outer ridge of the other elbow as a comparison test block. The actual remaining wall thickness at the defect was measured by ultrasonic thickness measurement method, which was about 4.5mm, compared with 5.15mm on the side ridge of the reference elbow, and the remaining wall thickness was 87.4%.

[0148] The middle position of the side ridge of the reference test block is selected as the reference point Q0, and the center position of the rectangular defect processed on the outer ridge of the comparison test block is selected as the detection point Q2. The thickness of the insulation layer varies in the range of 0 to 10 mm.

[0149] The two elbow test blocks were subjected to pulse eddy current testing using the coil probe and detection method designed in the present invention. It was measured that when the coil probe was lifted off 0 mm, the remaining wall thickness at point Q2 relative to the reference point was 82.6%, with an error of -4.8%; when the probe was lifted off 5 mm, the remaining wall thickness at point Q2 relative to the reference point was 84.1%, with an error of -3.3%; when the probe was lifted off 10 mm, the remaining wall thickness at point Q1 relative to the reference point was 83.7%, with an error of -3.7%.

[0150] It can be seen that for small-diameter pipe elbows with diameters of 60 mm and 34 mm, the maximum deviation between the relative change in wall thickness at the rectangular thinning defect on the outer ridge of the elbow detected by the method of the present invention and the ultrasonic thickness measurement method test result does not exceed 5.0%, which verifies the feasibility and reliability of the method of the present invention in detecting the relative change in wall thickness of small-diameter pipe elbows.

[0151] The terms and expressions used herein are for descriptive purposes only, and the present invention should not be limited to these terms and expressions. The use of these terms and expressions does not mean to exclude any equivalent features of the illustrations and descriptions (or parts thereof), and it should be recognized that various modifications that may exist should also be included in the scope of the claims. Other modifications, variations and substitutions may also exist. Accordingly, the claims should be deemed to cover all such equivalents.

[0152] Similarly, it should be pointed out that although the present invention has been described with reference to the current specific embodiments, ordinary technicians in this technical field should realize that the above embodiments are only used to illustrate the present invention, and various equivalent changes or substitutions may be made without departing from the spirit of the present invention. Therefore, as long as the changes and modifications to the above embodiments are within the scope of the essential spirit of the present invention, they will fall within the scope of the claims of the present invention.

Claims

1. A pulsed eddy current detection system, applied to pipeline detection, comprising an iron core coil probe, a data acquisition device, a host, and a pulse excitation device, characterized in that: The core-coil probe comprises a core bundle, a detection coil, an excitation coil and a heat dissipation shell, wherein the core bundle comprises a plurality of cores, the detection coil is wound around the outer surface of the core bundle, the excitation coil is wound around the outer surface of the detection coil, and the heat dissipation shell covers the core bundle, the detection coil and the excitation coil, wherein the core-coil probe comprises the core bundle, the detection coil, the excitation coil and the heat dissipation shell from the inside to the outside.

2. The pulsed eddy current testing system according to claim 1, characterized in that: The core coil probe is placed parallel to the pipeline.

3. The pulsed eddy current testing system according to claim 1, characterized in that: The heat dissipation housing comprises a metal housing and a plastic pad. The metal housing is symmetrically arranged with the iron core bundle as the center. The plastic pads are respectively connected to the metal housings to cover the iron core bundle, the detection coil and the excitation coil together.

4. The pulsed eddy current testing system according to claim 1, characterized in that: A heat-conducting silica gel layer is provided between the heat dissipation housing and the excitation coil.

5. The pulsed eddy current testing system according to claim 1, characterized in that: The pulse excitation device includes: a current A / D analog-to-digital converter, a D / A digital-to-analog converter, a power amplifier circuit and a sampling resistor. The sampling resistor is used to sample the output result of the excitation coil and transmit the output result to the host through the current A / D analog-to-digital converter. The host outputs a pulse excitation current to the excitation coil through the D / A digital-to-analog converter and the power amplifier circuit.

6. The pulsed eddy current testing system according to claim 1, characterized in that: The data acquisition device includes a data acquisition card and a voltage A / D analog-to-digital converter. The data acquisition card is respectively connected to the voltage A / D analog-to-digital converter and the two ends of the sampling resistor, and is used to collect the induced voltage time domain signal at the two ends of the detection coil and the excitation current flowing through the sampling resistor. The voltage A / D analog-to-digital converter is used to convert the induced voltage analog signal of the detection coil into an induced voltage discrete digital signal, and transmit it to the host.

7. A pulsed eddy current detection method, applied to pipeline detection, characterized in that: include: Step 1: The core coil probe is placed parallel to the pipeline to be tested; Step 2: The host controls the pulse excitation device to output an excitation digital signal to the core coil probe, and the data acquisition device obtains the induced voltage and excitation current fed back by the core coil probe and stores them in the host; Step 3: The host determines the detection data of the pipeline detection point according to the induced voltage and the excitation current, wherein the detection data includes the inversion information of the pipeline wall thickness, the relative magnetic permeability of the core coil probe, and the coil coupling coefficient; Step 4: The host compares the detection data with pre-tested standard pipeline detection data to determine the detection result corresponding to the pipeline detection point.

8. The pulsed eddy current testing method according to claim 7, characterized in that: The step 2 comprises: Step 2-1: The host outputs the excitation digital signal with a continuous pulse width of 10 to 100 ms and an amplitude of 0.1 to 1 V; Step 2-2: the host controls the D / A digital-to-analog converter to convert the excitation digital signal into a corresponding excitation analog signal; Step 2-3: The host outputs the excitation analog signal to the power amplifier circuit, and after amplification by the power amplifier circuit, outputs the excitation current with a continuous pulse width of 10 to 100 ms and an amplitude of 1 to 5 A to the iron core coil probe; Step 2-4: The data acquisition device obtains the induced voltage and the excitation current at both ends of the core coil probe, and stores them in the host.

9. The pulsed eddy current testing method according to claim 7, characterized in that: The step 3 comprises: Step 3-1: the host corrects the induced voltage and the excitation current according to the coil coupling coefficient of the iron core coil probe to determine the time domain expression of the induced voltage; Step 3-2: the host solves the time domain expression to determine a time domain analytical solution of the induced voltage; Step 3-3: The host determines the detection data of the pipeline detection point based on the time domain analytical solution, and the detection data includes the inversion information of the pipeline wall thickness, the relative magnetic permeability of the core coil probe, and the coil coupling coefficient.

10. The pulsed eddy current testing method according to claim 7, characterized in that: The step 4 comprises: Step 4-1: placing the core coil probe at a pipeline reference point, and determining the standard pipeline detection data, wherein the standard pipeline detection data includes inversion information of the pipeline wall thickness corresponding to the pipeline reference point, the relative magnetic permeability of the core coil probe, and the coil coupling coefficient; Step 4-2: The host determines the relative change in the pipe wall thickness of the pipe detection point relative to the pipe reference point according to the ratio of the pipe wall thickness inversion results corresponding to the pipe detection point and the pipe reference point; Step 4-3: The host determines the detection result corresponding to the pipeline detection point based on the relative change in the pipeline wall thickness.

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