1. A U-shaped magnetic conductor focusing probe, the probe body is formed by U-shaped magnetic conductor, exciting coil and two hollow cylindrical detection coils, characterized by that, the said U-shaped magnetic conductor opening is placed horizontally vertically downward, wherein a magnetic foot is wound with exciting coil, the back is placed a detection coil tangent to exciting coil; a detection coil tangent to the magnetic pin is arranged on the front surface of the other magnetic pin, and the bottom surfaces of the two detection coils are flush with the bottom surface of the U-shaped magnetic conductor magnetic pin; the two detection coils are in differential connection with each other.

2. The U-shaped magnetic conductor focusing probe according to claim 1, wherein the wire diameter of the detection coil is 0.01-4 mm, and the number of turns is 1-200000 turns.

3. The U-shaped magnetic conductor focusing probe according to claim 1, wherein the exciting coil has a wire diameter of 0.05-10 mm and a number of turns of 10-50000 turns.

4. A pulsed eddy current inspection method using the U-shaped magnetic conductor focusing probe of claim 1, characterized by the following steps:

1) connecting an excitation coil on the probe body to a pulse signal driver, and connecting two detection coils to a signal receiver;

2) detecting the stainless steel plate to be detected by using a probe body: switching on equal-width bipolar square wave pulse excitation to an excitation coil, lifting a probe body away from the probe body by 10-110 mm, moving a magnetic pin provided with the excitation coil around a U-shaped magnetic conductor in the direction of the other magnetic pin, moving the probe body to the other end along one end of the center line of a detected stainless steel plate, selecting a detection point every 0.1-200 mm, receiving voltage signals of two detection coils by a signal receiver, collecting attenuation voltage data, and transmitting the data to a computer;

3) drawing a normalized voltage attenuation curve graph by using the acquired attenuation voltage data as a horizontal coordinate and the normalized voltage as a vertical coordinate through a computer, and dividing a sampling time window for the voltage attenuation curve graph; taking the position of the probe as an abscissa and the normalized voltage as an ordinate, and drawing a normalized voltage-time profile curve chart;

4) the normalized time section curve chart reflects the detection signal characteristics of the probe body passing through different defects, and the existence condition of the defects is judged.

Background

The pipeline with the cladding layer has wide application in the industrial fields of chemical industry, nuclear power, petroleum and the like. The field working condition is bad usually, and the steel pipe receives the corruption easily, and then leads to the failure to lead to the incident. The research on how to implement effective detection and defect state evaluation on the coating ferromagnetic pipeline has very important significance on regular detection and maintenance of the steel pipe through the coating and prolonging of the use of industrial facilities.

The pulse eddy current technology is a new technology developed based on eddy current detection, a pulse square wave signal is adopted as excitation, and if a detected component has defects, the flow direction of pulse eddy current in the component and an electromagnetic field generated by the pulse eddy current in the component can be changed. The pulse square wave excitation contains various frequency components and rich frequency spectrum content, so that the signal has stronger penetrating power and can scan and detect defects at different depths at one time and identify the wall thickness change^[1-2]. Therefore, the pulse eddy current technology is suitable for detecting the pressure-bearing equipment pipeline without stopping and detaching the coating layer.

For the external detection of the coating layer pipeline, the traditional nondestructive detection method such as single eddy current detection frequency spectrum, less carried frequency domain information, limited penetration depth and insufficient detection capability on depth defects needs equipment to stop production and remove the coating layer so as to couple a probe and the pipeline surface, the process is complex, errors can occur during secondary packaging of the coating layer, and new potential safety hazards can be caused due to infirm bonding. The digital ray detection can distinguish the thinning condition of the inner wall and the outer wall of the pipeline, but the method has a plurality of limitations in the aspects of cost, efficiency, pollution, safety and the like^[3]。

The cylindrical probe can identify 5% thickness change of the ferromagnetic plate, but the probe cannot identify the thickness change under large lift-off^[4]. A probe composed of two ferrite cylindrical excitation coils connected in series and two Hall magnetic sensors connected in difference can generate strong excitation magnetic field and can inhibit interference through a differential structureAnd the thickness change of 20 percent of the stainless steel plate lifted by 25 millimeters can be detected by improving the signal-to-noise ratio of the probe^[4]However, the local corrosion defect of the stainless steel plate could not be detected. Since the detection signal is induced by the receiving coil, the detection sensitivity of the probe for the local defect depends on the variation of the secondary magnetic field generated by the eddy current concentrated around the defect.

Disclosure of Invention

The invention aims to provide a pulse eddy current detection focusing probe for a pipeline of pressure-bearing equipment with a coating layer and a using method thereof, which solve the problems that the local defects of the pipeline cannot be effectively detected and the thickness change cannot be effectively identified under the condition of large lift-off, clarify the influence of the eddy current distribution of the probe on a detected member on the local corrosion defects and improve the sensitivity of the probe.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions. A U-shaped magnetic conductor focusing probe comprises a probe body, a probe cover and a probe cover, wherein the probe body is composed of a U-shaped magnetic conductor, an excitation coil and two hollow cylindrical detection coils, an opening of the U-shaped magnetic conductor is vertically and horizontally placed downwards, one magnetic pin is wound with the excitation coil, and the back surface of the U-shaped magnetic conductor is provided with the detection coil tangent to the excitation coil; a detection coil tangent to the magnetic pin is arranged on the front surface of the other magnetic pin, and the bottom surfaces of the two detection coils are flush with the bottom surface of the U-shaped magnetic conductor magnetic pin; the two detection coils are in differential connection with each other.

Furthermore, the wire diameter of the detection coil is 0.01-4 mm, and the number of turns is 1-200000 turns.

Furthermore, the diameter of the exciting coil is 0.05-10 mm, and the number of turns is 10-50000 turns.

A pulse eddy current detection method of a U-shaped magnetic conductor focusing probe comprises the following operation steps:

1) connecting an excitation coil on the probe body to a pulse signal driver, and connecting two detection coils to a signal receiver;

2) detecting the stainless steel plate to be detected by using a probe body: switching on equal-width bipolar square wave pulse excitation to an excitation coil, lifting a probe body away from the probe body by 10-110 mm, moving a magnetic pin provided with the excitation coil around a U-shaped magnetic conductor in the direction of the other magnetic pin, moving the probe body to the other end along one end of the center line of a detected stainless steel plate, selecting a detection point every 0.1-200 mm, receiving voltage signals of two detection coils by a signal receiver, collecting attenuation voltage data, and transmitting the data to a computer;

3) drawing a normalized voltage attenuation curve graph by using the acquired attenuation voltage data as a horizontal coordinate and the normalized voltage as a vertical coordinate through a computer, and dividing a sampling time window for the voltage attenuation curve graph; taking the position of the probe as an abscissa and the normalized voltage as an ordinate, and drawing a normalized voltage-time profile curve chart;

4) the normalized time section curve chart reflects the detection signal characteristics of the probe body passing through different defects, and the existence condition of the defects is judged.

The invention realizes the effective detection of the local defect and the identification thickness of the stainless steel plate under the condition of large lift-off, improves the detection sensitivity of the probe, can detect the defect of the pipeline with the coating layer under the condition of large lift-off, is key to research the influence of eddy distribution generated on the pipeline when the probe is lifted-off on the detection of the local defect, solves the problem of the detection of the defect of the pipeline with the coating layer, and has great guiding significance for the detection of the local corrosion defect and the thickness of the pipeline with the coating layer in the industry.

Drawings

FIG. 1 is a front view of a probe body 01 of the present invention;

FIG. 2 is a left side view of the probe body 01 of the present invention;

FIG. 3 is a top view of a probe body 01 of the present invention;

FIG. 4 is a schematic view of a detection system according to the present invention;

FIG. 5 is a plan view of a stainless steel sheet 25 to be inspected having a local corrosion defect according to the present invention;

FIG. 6 is a diagram showing the thickness dimension of a stainless steel sheet 25 to be inspected having a local corrosion defect according to the present invention;

FIG. 7 is a size chart of a stainless steel sheet 07 of the present invention having a thickness of 2 mm;

FIG. 8 is a dimension diagram of a stainless steel plate 08 to be inspected having a thickness of 1mm according to the present invention;

FIG. 9 is a schematic diagram of the detection method of the present invention;

FIG. 10 is a graph illustrating normalized induced voltage decay curves and voltage time profiles under lossy and non-destructive conditions during an inspection process according to the present invention;

FIG. 11 is a schematic view of the eddy current distribution on the surface of a test piece when the probe body 01 is lifted away from 40mm according to the present invention;

FIG. 12 is a schematic view of the eddy current distribution on the test piece surface when the probe body 01 is lifted away from 110mm according to the present invention;

FIG. 13 is a diagram showing the results of the present invention for detecting the local corrosion defect of the stainless steel plate when the probe body 01 is lifted 40mm away;

FIG. 14 is a graph showing the result of detecting the voltage attenuation curve of a stainless steel plate with a thickness of 2-10 mm when the probe body 01 is lifted away from 110 mm.

In the figure: 01. the probe body, 11. the exciting coil, 12. the detecting coil, 13. the U-shaped magnetic conductor;

02. a pulse eddy current detector, 21, a pulse signal driver, 22, a signal receiver, 23, a computer, 24, a coating layer, 25, a stainless steel plate to be detected, and 26, a local corrosion defect;

07. a first test piece; 08. a second test piece; 91. primary magnetic field, 92 secondary magnetic field, 93 eddy current field.

Detailed Description

The invention is further described below with reference to the figures and examples. Referring to fig. 1 to 3, a pulsed eddy current test focusing probe, a probe body 01 is composed of an excitation coil 11, a detection coil 12 and a U-shaped magnetic conductor 13. Both detection coils 12 are hollow cylindrical coils, connected in a differential manner. The U-shaped magnetic conductor 13 is horizontally placed with its opening facing vertically downward, with one leg wound with an excitation coil 11, the back side horizontally placed with a detection coil 12, and the other leg horizontally placed with a detection coil 12 on the front side.

As shown in FIG. 4, the detection system of the present invention is schematically illustrated, the pulse eddy current detector 02 includes a pulse signal driver 21, a signal receiver 22 and a computer 23, wherein the pulse signal driver 21 transmits a pulse signal to the exciting coil 11 of the probe body 01 and simultaneously transmits a synchronizing signal to the signal receiver 22, the probe body 01 moves on the surface of the coating layer 24 on the stainless steel plate 25 to be detected, and the detection signal is transmitted to the signal receiver 22 and processed, stored and displayed by the computer 23.

The pulse detector 02 used in the invention is shown in fig. 4, the model of the host is WTEM-1QII, the host comprises a pulse signal driver 21 and a signal receiver 22, the computer 23 is a WINDOWS palm computer, and the application program is a WTEM-1 transient electromagnetic prospecting system V3.9.

The detection principle is shown in fig. 9: in the detection, a bipolar square wave current signal is applied to the exciting coil 11. The excitation coil 11 is energized to generate a periodic transient magnetic field in the surrounding space, i.e., a primary magnetic field 91. When the excitation current is rapidly switched off from the square wave direct current section, the surrounding magnetic field is rapidly attenuated, due to electromagnetic induction, the stainless steel plate 25 to be detected can induce an eddy current field 93, and the magnetic field generated by the eddy current field 93 is a secondary magnetic field 92. When the excitation current is turned off, the primary magnetic field 91 is zero, and the secondary magnetic field 92 changes in response to the voltage induced in the detection coil 12. When the probe body 01 passes through the local corrosion defect 26 of the stainless steel plate 25 to be inspected, the attenuation of the induced voltage of the detection coil 12 becomes fast, and therefore, the detection information of the defect is obtained by measuring the attenuation change of the induced voltage of the detection coil 12. When the probe body 01 detects stainless steel plates 25 to be detected with different thicknesses, the attenuation slope of the induced voltage of the detection coil 12 increases as the thickness of the stainless steel plate 25 to be detected decreases, so that the thickness information can be quantitatively analyzed from the attenuation slope.

The pulse eddy current detector 02 is connected with the probe body 01, the pulse signal driver 21 provides stable pulse signals for the probe body 01, the probe body 01 is placed at the center of the stainless steel plate 25 to be detected through the coating layer 24, the position 160mm away from the left end starts detection, the probe body 01 slowly moves towards the right end, and induced voltage data on the detection coil 12 are collected when the probe body 01 moves 5 mm. The obtained induced voltage data at each detection position is used to plot a voltage decay curve and a cross-sectional view thereof (as shown in fig. 10).

The normalized voltage-time profile (as shown in fig. 8) is based on the following principle:

the voltage of the detection coil 12 is sampled for each measurement point of the stainless steel plate 25 to be inspected. The induced voltage is divided by the excitation current for normalization. The total number of sampling time windows is N. The length of the time window increases logarithmically. Thus for the ith measurement point, the normalized voltage can be expressed as a vector as follows:

V_i＝[v_i1,v_i2,...,v_iN]

wherein: n is the sampling time window number of the normalized voltage attenuation curve of each detection point. v. of_iNNormalized voltage for the ith measurement point for the nth time window.

M points are measured along the tube, the vectors of the M measurement points forming a matrix W:

the row vector of the matrix W represents a normalized voltage attenuation curve of a certain measuring point, and the column vector is a normalized voltage value corresponding to the same time of a descending curve from the 1 st point to the Mth detecting point. And a curve drawn by taking the coordinate of the detection point as an abscissa and taking a certain column vector as an ordinate is called a normalized voltage-time profile curve of the test piece at the moment corresponding to the column vector.

Wherein: the ith row of the matrix W represents the ith measurement point. Column j represents the jth time window, from which the time profile vector can be obtained:

S_j＝[v_1j,v_2j,...,v_Mj],j＝1,2,...,N

S_jrepresenting the voltage at different measurement points of the voltage-time curve at the same time. v. of_MjThe normalized voltage of the jth time window, mth measurement point is indicated. Ideally, if no defect is present, the time profile vector S_jThe voltage value of each measurement point in (a) is equal, i.e.:

v_1j＝v_2j＝...＝v_Mj,j＝1,2,...,N

if there is a defect, the voltage of the Mth measuring point appearsIf the voltage value is smaller than the voltage value of the measurement point where no defect exists, the defect is detected at the Mth measurement point. Time profile vector S_jIf the minimum value appears, the position corresponding to the minimum value can be used as the central position of the defect. Therefore, if there is a local corrosion defect 26 around a certain measurement position in the stainless steel plate 25 to be inspected, when the detection coil 12 of the probe body 01 passes through the local corrosion defect 26, a dip signal appears at the corresponding position on the normalized voltage-time profile curve, and the minimum value of the dip of the curve is the central position of the local corrosion defect 26.

A three-dimensional finite element simulation model of the pulsed eddy current test is established by using the multiphysics finite element simulation software COMSOLmutiphics. The distribution and direction of eddy currents excited by the probe body 01 when lifted off by 40mm are shown in fig. 9, and induced eddy current fields 93 are gathered. The distribution and direction of eddy currents excited by the probe body 01 when lifted off by 110mm are shown in fig. 10, and the induced eddy current field 93 is gathered.

The present invention is described in detail below with reference to examples, but the design of a U-shaped magnetic conductor focusing probe and the pulsed eddy current detection method thereof are not limited to the examples.

Example 1:

specific examples of the local corrosion defect detection of the stainless steel plate 25 (shown in FIG. 5) by the probe body 01 are as follows:

(1) the stainless steel plate 25 of 304L was used, and had an electric conductivity of 1.379MS/m, a relative magnetic permeability of 1.003, and a size of 500X 5mm³(Length. times. Width. times. depth) of 30X 1.5mm at the center of the stainless steel plate 25 to be inspected³The square groove of (2) was used to simulate a local corrosion defect 26 of the steel plate.

(2) The probe body 01 detects the stainless steel plate 25 to be detected, the exciting current applied to the exciting coil 11 is 2.335 amperes, the frequency is 8Hz, the two-stage gain is 8 multiplied by 1, and 5-time signals are collected and superposed for averaging;

(3) placing the probe body 01 at the position 160mm away from the left end of the center of a stainless steel plate 25 to be detected through a 40mm coating layer 24, turning on a power supply of a pulse eddy current detector 02, slowly moving the probe body 01, selecting a sampling point every 5mm, controlling a computer 23 to detect, and collecting and recording induced voltage data;

(4) after the probe body 01 finishes detection, storing the acquired voltage data and drawing a normalized voltage attenuation curve graph and a normalized voltage time profile curve graph;

(5) and observing the change of the minimum value of the induced voltage when the probe body 01 advances to the simulated local corrosion defect 26 in the normalized voltage time profile curve.

(6) FIG. 13 is a time sectional view of the stainless steel plate 25 to be inspected measured in a window from time No. 6 to time No. 8 when the probe body 01 is lifted 40mm away.

Example 2:

specific examples of thickness identification of the probe body 01 for the first test piece 07 (shown in fig. 7) and the second test piece 08 (shown in fig. 8) are listed below:

(1) using 6 first test pieces 07 and second test pieces 08 with different thicknesses and made of 304L, wherein the size of four first test pieces 07 is 500 multiplied by 2mm³(Length. times. Width. times. thickness), two second test pieces 08 were 500. times.500. times.1 mm in size³The electric conductivity was 1.379MS/m, and the relative magnetic permeability was 1.003. The wall thickness of the steel plate is simulated to change by 2-10 mm by using the first test piece 07 and the second test piece 08 with different thicknesses.

(2) The probe body 01 detects a first test piece 07 and a second test piece 08 with different thicknesses, the exciting current applied to the exciting coil 11 is 2.335 amperes, the frequency is 8Hz, the two-stage gain is 8 multiplied by 1, and 5-time signal superposition is acquired for averaging;

(3) placing the probe body 01 at the centers of a first test piece 07 and a second test piece 08 through a 110mm coating layer, turning on a power supply of a pulse eddy current detector 02, gradually changing the number of the first test piece 07 and the second test piece 08, controlling a computer 23 to detect, and acquiring and recording induction voltage data under the thickness of 2-10 mm;

(4) after the probe body 01 is detected, the collected voltage data is saved, and a normalized voltage attenuation curve graph (shown in fig. 14) under different thicknesses is drawn.

The focusing performance due to the eddy current distribution is a key factor affecting the detection sensitivity of the probe. In order to detect the defects of the coating layer pipeline under the condition of large lift-off, the invention provides a research result of the influence of eddy distribution generated on the pipeline on local defect detection when a probe is lifted off. The excitation magnetic field is improved by changing the excitation structure of the probe, so that the eddy current is gathered and distributed, and the detection sensitivity of the probe is improved. The magnetic conductor loop can effectively guide the magnetic field distribution, so that the eddy current distribution generated by the probe on the test piece is changed, and the problem of detecting the defects of the pipeline with the cladding layer is solved.

Reference documents:

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[2]Fu Y,Lei M,Li Z,et al.Lift-off effect reduction based on the dynamic trajectories ofthe received-signal fast Fourier transform in pulsed eddy current testing[J].Ndt&E International,2017,87:85–92.

[3]Robers M,Scottini R S.Pulsed eddy current in corrosion detection.Proceedings ofthe 8^th ECNDT,Barcelona,Spain,2002

[4]Angani C S,Park D G,Kim C G,et al.Dual core differential pulsed eddy current probe to detect the wall thickness variation in an insulated stainless steel pipe[J].Journal ofMagnetics,2010,15(4):204-208。