CN113340984A

CN113340984A - Focusing probe for eddy current defect detection of metal component and using method thereof

Info

Publication number: CN113340984A
Application number: CN202110650710.9A
Authority: CN
Inventors: 付跃文; 陶爱军; 邢仁飞; 黄文丰; 杨帆; 余兆虎
Original assignee: Nanchang Hangkong University
Current assignee: Nanchang Hangkong University
Priority date: 2021-06-11
Filing date: 2021-06-11
Publication date: 2021-09-03
Anticipated expiration: 2041-06-11
Also published as: CN113340984B

Abstract

A focusing probe for detecting eddy current defects of metal components and a using method thereof are disclosed, wherein an opening of a U-shaped magnetic core is vertically downward, a first excitation coil is respectively wound in the middle of the U-shaped magnetic core and the middle sections of two legs, a second excitation coil is wound on the periphery of a cylindrical magnetic core, and second detection coils are respectively arranged at the upper end and the lower end of two sides which are symmetrical to the central axis of the second excitation coil. The exciting coil is connected with a pulse signal transmitter; the detection coil is connected with the detection signal receiver; and drawing voltage attenuation curve graphs of different time windows by using the time as an abscissa and the normalized induced voltage as an ordinate according to the attenuation voltage data received by the computer so as to judge the local corrosion and wall thickness conditions of the test piece. The method realizes effective detection of local defects and thickness of the stainless steel plate to be detected under the long-term condition of large lift-off height, has higher detection sensitivity, and has great application value in local corrosion and wall thickness detection of the metal member of the pipeline with the coating layer.

Description

Focusing probe for eddy current defect detection of metal component and using method thereof

Technical Field

The invention belongs to the field of electromagnetic nondestructive detection, and particularly relates to a focusing probe for detecting eddy current defects of a metal component with a coated pipeline and a using method thereof.

Background

The pipeline of the pressure-bearing equipment is easy to corrode under the conditions of high temperature, high pressure and corrosive liquid and gas medium transportation, and local corrosion is mainly used. To preserve heat and prevent corrosion outside the pipe, the pipe is often protected with a coating layer of several tens to hundreds of millimeters thickness. Therefore, the detection of the wall thickness reduction and the local corrosion of the metal component pipeline under the condition of not removing the coating layer has important significance^[1-]。

The pulse eddy current inspection (PECT) is a non-contact inspection method, which can inspect metal members without detaching a coating layer. The technology has the characteristics of large penetration depth of an incident electromagnetic field, strong defect depth detection capability, rich detection information and the like^[3-]。

The pulse eddy current probe is generally composed of an excitation unit and a receiving unit, the most common structure is that the excitation unit and the receiving unit are coaxially arranged, and the cylindrical probe is widely applied to detecting the defects of a test piece and reducing the wall thickness^[5-]。

The sensitivity of the probe to the detection of a local defect depends on the variation of the secondary magnetic field generated by the eddy currents concentrated around the defect. The cylindrical probe induces an eddy current field on a test piece to have a blind area, and a detection signal is generated by the induction of the receiving coil, so that the receiving coil is required to be placed in an eddy current field gathering area to obtain higher detection sensitivity^[7]. Therefore, the focusing performance of the probe (i.e., the focusing characteristics of the eddy current distribution on the specimen) is a key factor that affects the detection sensitivity of the probe.

Fu and the like improve the diffusion distribution of eddy current by changing the excitation structure of the probe, thereby improving the detection sensitivity of the probe, developing research on the spatial distribution rule of the eddy current at three placing (radial, transverse and longitudinal) positions of the cylindrical excitation coil, and analyzing the influence of the existence of a blind area of an eddy current field on the detection capability of the probe. Meanwhile, the cylindrical probe which is placed longitudinally is clear to have higher detection sensitivity when the wall thickness of the metal component pipeline is detected^[8]。

Xie et alThe energy conversion relationship of the detection coil in air and a test piece is analyzed, and a cylindrical probe with the detection coil coaxially arranged above the excitation coil is provided. The detection sensitivity of the probe depends on the energy conversion efficiency of the detection coil, and the energy conversion efficiency is obviously influenced by lift-off, so that the detection capability of the probe is obviously reduced during lift-off^[9]。

Purna Chandra Rao and the like can detect the buried depth defect of 25 percent of thickness change of the bottom of a stainless steel plate by receiving the induced magnetic field change of a test piece by a GMR magnetic sensor arranged in the center of the bottom of an annular exciting coil, but the detection effect is poor under a certain lift-off height^[10]。

The probe developed by d.g.park et al consists of two series-connected ferrite cylindrical excitation coils and two differentially connected Hall magnetic sensors, is capable of generating a strong excitation magnetic field and suppressing interference through a differential structure. Can detect 20% thickness change of the stainless steel plate under low lift-off (25mm), but has poor detection capability under large lift-off^[11]。

And X.Wu and the like are based on a cylindrical coaxial coil analytical model, the relation between the induced voltage variation and the thickness of the test piece is obtained through derivation, and the thickness is quantified by using the voltage peak time characteristic. The probe can be used for detecting the average wall thickness of a pipeline under a coating, but the detection capability of the probe on local corrosion is still required to be improved under certain lift-off^[12]。

Disclosure of Invention

The invention aims to provide a focusing probe for detecting eddy current defects of a metal component and a using method thereof. The method solves the problems of effectively detecting the local corrosion defect and the thickness of the stainless steel plate under the condition of large lift-off, and the problems of detecting the local defect of the metal component by pulse eddy current and accurately positioning the defect under the condition of a coating layer.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions. A focusing probe for eddy current defect detection of metal members comprises a U-shaped probe body and a cylindrical probe body,

the U-shaped probe body is composed of a U-shaped magnetic core, a first exciting coil and a first detecting coil, wherein the opening of the U-shaped magnetic core is vertically downward, the first exciting coil is wound in the middle of the U-shaped magnetic core and the middle sections of two legs respectively, the first detecting coil is placed under the central axis of the U-shaped magnetic core and on the front side of one leg, the first detecting coil positioned on the front side of one leg is tangent to the first exciting coil wound in the middle section of the leg of the U-shaped magnetic core, and the bottom surface of the first detecting coil is flush with the bottom planes of the two legs of the U-shaped magnetic core;

the cylindrical probe body consists of a cylindrical magnetic core, a second excitation coil and a second detection coil, the second excitation coil is wound on the outer periphery of the cylindrical magnetic core, and the second detection coils are respectively arranged at the upper ends and the lower ends of two sides which are axially symmetrical to the central axis of the second excitation coil, wherein the bottom surface of the second detection coil at one side is flush with the bottom end of the second excitation coil, and the bottom surface of the second detection coil at the other side is flush with the top end of the second excitation coil; the second detection coil is tangent to the second excitation coil.

Further, the first detection coils in the U-shaped probe body are in a circular shape and are connected in series with each other.

Further, the second detection coil of the cylindrical probe body is in a circle shape and is in differential connection.

Furthermore, the wire diameters of the first exciting coil and the second exciting coil are both 0.1-2 mm, and the number of turns is 50-2000 turns.

Further, the wire diameter of the first detection coil and the wire diameter of the second detection coil are both 0.01-1 mm, and the number of turns is 200-10000 turns.

The use method of the focusing probe for the eddy current defect detection of the metal component comprises the following operation steps:

1) the pulse eddy current detector is provided with a pulse signal transmitter, a detection signal receiver and a computer, and the excitation coil is connected with the pulse signal transmitter; the detection coil is connected with the detection signal receiver;

2) the parallel movement detection of the U-shaped probe body and the cylindrical probe body on the stainless steel plate to be detected is respectively used, the U-shaped probe body moves along the connecting line direction of two legs of the U-shaped magnetic core, and the cylindrical probe body moves along the connecting line direction of two second detection coils: exciting coils on the U-shaped probe body and the cylindrical probe body are respectively excited by bipolar square waves with equal width, the U-shaped probe body and the cylindrical probe body are lifted to a height of 10-110 mm from one end of a stainless steel plate to be detected, a detection point is selected at intervals of 0.1-1000 mm, the detection signal receiver receives an induced voltage signal on the detection coil and acquires voltage data, and the induced voltage signal is sent to a computer for processing;

3) drawing voltage attenuation curve graphs of different time windows by using time as an abscissa and normalized induced voltage as an ordinate for attenuation voltage data received by a computer;

4) and reflecting the defect information of the stainless steel plate near the receiving coil through the time section curve graph so as to judge the local corrosion and the wall thickness of the test piece.

The invention can effectively detect the local defects and the thickness of the detected stainless steel plate under the long-term condition of larger lift-off height, has higher detection sensitivity compared with the traditional eddy current detection probe, and has larger application value in the local corrosion and wall thickness detection of the metal component of the pipeline with the coating layer.

Drawings

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

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

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

FIG. 4 is a front view of a cylindrical probe body 02 of the present invention;

FIG. 5 is a left side view of a cylindrical probe body 02 of the present invention;

FIG. 6 is a top view of a cylindrical probe body 02 of the present invention;

FIG. 7 is a schematic flow chart of the detection system of the present invention;

FIG. 8a is a thickness dimension view of a stainless steel sheet 34 to be inspected with a local defect according to the present invention;

FIG. 8b is a plan view of a stainless steel sheet 34 to be inspected with a local defect according to the present invention;

FIG. 9 is a schematic view of the magnetic field variation during the detection process of the present invention;

FIG. 10 is a schematic diagram of the detection profile generation of the present invention;

FIG. 11 is a simulated model view of a U-shaped probe body 01 of the present invention;

FIG. 12 is a simulated model view of a cylindrical probe body 02 of the present invention;

FIG. 13 is a graph of eddy current density of the U-shaped probe body 01 for different lift-off configurations of the present invention;

FIG. 14 is a graph of the eddy current density of a cylindrical probe body 02 under different lift-off conditions in accordance with the present invention;

FIG. 15 is a diagram of a selected area selection for the U-shaped probe body 01 of the present invention producing eddy current power losses on a test piece;

FIG. 16 is a graphical representation of selected areas of the cylindrical probe body 02 of the present invention producing eddy current power losses on a test piece;

FIG. 17 is a graph of eddy current power loss for selected areas of the U-shaped probe body 01 of the present invention at various locations;

FIG. 18 is a plot of eddy current power loss ratio for selected areas at different locations for a U-shaped probe body 01 of the present invention;

FIG. 19 is a graph of eddy current power loss for selected areas of a cylindrical probe body 02 of the present invention at various locations;

FIG. 20 is a plot of eddy current power loss ratio for selected areas at various locations for a cylindrical probe body 02 of the present invention;

FIG. 21 is a diagram showing the result of the detection of the local corrosion defect of the stainless steel plate of the U-shaped probe body 01 of the present invention when it is lifted off at 40 mm;

FIG. 22 is a diagram showing the result of the detection of the local corrosion defect of the stainless steel plate of the U-shaped probe body 01 of the present invention when lifted off at 50 mm;

FIG. 23 is a chart of the results of localized corrosion defect detection of a cylindrical probe body 02 of the present invention at 20mm lift-off;

FIG. 24 is a chart of the results of localized corrosion defect detection of a cylindrical probe body 02 of the present invention at 30mm lift-off;

FIG. 25 is a normalized induced voltage attenuation curve diagram of the U-shaped probe body 01 of the invention for detecting the thickness of a stainless steel plate of 2-10mm under the condition of being lifted away from 110 mm;

FIG. 26 is a graph of the slope of the attenuation curve and the percentage change in thickness of a stainless steel plate 2-10mm when the U-shaped probe body 01 is lifted away from the stainless steel plate 110 mm;

FIG. 27 is a normalized induced voltage attenuation curve diagram of the thickness detection of a stainless steel plate of 2-10mm under the condition that a cylindrical probe body 02 is lifted off by 100 mm;

FIG. 28 is a graph of the slope of the attenuation curve versus the percentage of change in thickness for a 2-10mm thickness test of a stainless steel plate with a lift-off of 100mm for a cylindrical probe body 02 according to the present invention;

in the figure: the probe comprises a U-shaped probe body, 11, a first excitation coil, 12, a first detection coil and 13, a U-shaped magnetic core;

02. a cylindrical probe body, 21, a second excitation coil, 22, a second detection coil, 23, a cylindrical magnetic core;

03. a pulse eddy current detector, 31, a pulse signal transmitter, 32, a detection signal receiver, 33, a computer, 34, a detected stainless steel plate, 35, a coating layer;

171. 181. asymmetric V-shaped waveform signal characteristics, 191, 201. asymmetric double V-shaped waveform signal characteristics.

Detailed Description

The invention is further described below with reference to the figures and examples. Referring to fig. 1 to 6, a focusing probe for eddy current flaw detection of a metal member comprises a U-shaped probe body 01 and a cylindrical probe body 02, wherein the U-shaped probe body 01 is composed of a U-shaped magnetic core 13, a first excitation coil 11 and a first detection coil 12, the opening of the U-shaped magnetic core 13 is vertically downward, the first excitation coil 11 is respectively wound in the middle of the U-shaped magnetic core 13 and in the middle of two legs, the first detection coil 12 is respectively placed under the central axis of the U-shaped magnetic core 13 and on the front side of one leg, the first detection coil 12 in the front side of one leg is tangent to the first excitation coil 11 wound in the middle of the leg of the U-shaped magnetic core 13, and the bottom surface of the first detection coil 12 is flush with the bottom planes of the two legs of the U-shaped magnetic core 13; the first detection coils 12 in the U-shaped probe body 01 are circular and connected in series with each other. The cylindrical probe body 02 is composed of a cylindrical magnetic core 23, a second excitation coil 21 and a second detection coil 22, the second excitation coil 21 is wound on the outer periphery of the cylindrical magnetic core 23, the second detection coil 22 is respectively arranged at the upper end and the lower end of two sides which are axially symmetrical with the axis of the second excitation coil 21, the bottom surface of the second detection coil 22 at one side is flush with the bottom end of the second excitation coil 21, and the bottom surface of the second detection coil 22 at the other side is flush with the top end of the second excitation coil 21; the second detection coil 22 is tangent to the second excitation coil 21. The second detection coil 22 of the cylindrical probe body 02 is in a circular shape and differentially connected.

The wire diameters of the first exciting coil 11 and the second exciting coil 21 are both 0.1-2 mm, and the number of turns is 50-2000. The wire diameters of the first detection coil 12 and the second detection coil 22 are both 0.01-1 mm, and the number of turns is 200-10000.

1) the pulse eddy current detector 03 is provided with a pulse signal transmitter 31, a detection signal receiver 32 and a computer 33, and an excitation coil is connected with the pulse signal transmitter 31; the detection coil is connected with a detection signal receiver 32;

2) the parallel movement detection is performed on the stainless steel plate 34 to be detected by using the U-shaped probe body 01 and the cylindrical probe body 02 respectively, and the U-shaped probe body 01 moves in the direction of the connecting line of the two legs of the U-shaped magnetic core 13, and the cylindrical probe body 02 moves in the direction of the connecting line of the two second detection coils 22: exciting coils on the U-shaped probe body 01 and the cylindrical probe body 02 are respectively excited by bipolar square waves with equal width, the U-shaped probe body 01 and the cylindrical probe body 02 are lifted to a height of 10-110 mm from one end of a stainless steel plate 34 to be detected, a detection point is selected at intervals of 0.1-1000 mm, the detection signal receiver 32 receives an induced voltage signal on the detection coil and acquires voltage data, and the voltage data are sent to the computer 33 for processing;

3) drawing voltage attenuation curve graphs of different time windows by taking time as an abscissa and normalized induced voltage as an ordinate according to attenuation voltage data received by the computer 33;

As shown in FIG. 7, the detection system of the present invention is schematically illustrated, wherein a pulse signal transmitter 31 transmits a pulse signal to a first exciting coil 11 of a U-shaped probe body 01, and simultaneously transmits a synchronization signal to a detection signal receiver 32, the U-shaped probe body 01 moves on the surface of a clad layer 35 on a detected stainless steel plate 34 (the dimension of which is illustrated in FIGS. 8 and 8b) with a local defect, transmits the detection signal to the detection signal receiver 32, and the detection signal receiver 32 transmits the detection signal to a computer 33 for storage, processing and display.

The host model of the pulse eddy current detector used in the invention is WTEM-1QII, the host comprises a pulse signal transmitter 31 and a detection signal receiver 32, the computer 33 is a palm computer, and the application program is WTEM-1 transient electromagnetic prospecting system V3.9.

The detection principle is as follows: in the detection, a bipolar square wave current signal is switched on to the first excitation coil 11 (or the second excitation coil 21) of the U-shaped probe body 01 (or the cylindrical probe body 02). The first excitation coil 11 (or the second excitation coil 21) generates a periodic magnetic field in the surrounding space after being energized. This magnetic field is called the primary magnetic field. When the square wave signal of the excitation current is turned off instantaneously, a rapidly attenuated induced magnetic field is induced around the square wave signal, the attenuated induced magnetic field induces a pulse eddy current in the stainless steel plate 34 to be detected, and the magnetic field induced by the pulse eddy current is called a secondary magnetic field. When the excitation current is turned off, the primary magnetic field disappears, and at this time, the first detection coil 12 (or the second detection coil 22) receives the attenuation signal of the secondary magnetic field, and detects the attenuation change of the magnetic field, and such attenuation information is reflected in the voltage condition induced by the first detection coil 12 (or the second detection coil 22) (as shown in fig. 9). During defect detection, the slopes of the voltage attenuation curves of the U-shaped probe body 01 (or the cylindrical probe body 02) at the positions where the test piece is defective and the position where the test piece is not defective are different, and the slope of the voltage attenuation curve at the position where the test piece is defective is larger than that at the position where the test piece is not defective, so that whether the test piece is defective or not can be judged; during the thickness measurement, since the induced voltage attenuation slopes of the stainless steel plates 34 to be measured with different thicknesses are different, quantitative analysis can be performed according to the slopes, so as to achieve the purpose of measurement.

The pulse eddy current detector 03 is connected with the used U-shaped probe body 01 (or cylindrical probe body 02) and stably provides square wave pulse excitation for the U-shaped probe body 01 (or cylindrical probe body 02). Placing the U-shaped probe body 01 (or the cylindrical probe body 02) at the position 160mm away from the left end of the center position of the stainless steel plate 34 to be detected, starting detection, arranging a coating 35 with a certain height between the U-shaped probe body 01 (or the cylindrical probe body 02) and the stainless steel plate 34 to be detected, slowly moving the U-shaped probe body 01 (or the cylindrical probe body 02) to the other end at a constant speed, selecting acquisition points every 5mm, acquiring voltage data on the first detection coil 12 (or the second detection coil 22), and finally drawing a voltage attenuation curve and a sectional view thereof.

The cross-sectional view of the normalized voltage decay curve (as shown in fig. 10) is a section vector of the voltage decay curve at different detection points, and when the U-shaped probe body 01 (or the cylindrical probe body 02) is used for detecting the stainless steel plate 34, the voltage decay rate is different between the defective part and the non-defective part, and if a defect exists near the first detection coil 12 (or the second detection coil 22), the voltage decay rate is faster. Therefore, the curve near the defective detection point appears abrupt and the curve in the non-defective area is relatively horizontal in the normalized voltage decay curve section.

The specific principle of the normalized voltage attenuation curve profile is as follows:

for each measurement point of the detected stainless steel plate 34 with localized corrosion, the voltage of the first detection coil 12 (or the second detection coil 22) is sampled at the off time. The induced voltage is logarithmically attenuated, and the window length is logarithmically increased, so that the detection signal information can be better reserved. The sampling value of each time window is obtained by averaging after 5 times of superposition. Thus, the resulting voltage vector at the ith measurement station is as follows:

V_i＝[v_i1 v_i2 … v_i(N-1) v_iN]

where N is the total number of time windows per off time.

Assuming that a total of M points are measured, the voltage vectors of the M sampling points can be synthesized into a matrix M:

wherein, the ith row of the matrix M represents the ith measuring point.

The slicing vector S of the jth time window can be obtained from the matrix M_j：

S_j＝[v_1j v_2j … v_(M-1)j v_Mj]

Wherein, the matrix S_jRepresenting voltage vectors of different measuring points of the voltage attenuation curve at a certain moment, and if no defect exists, slicing the vector S under an ideal condition_jEach voltage value of which is equal. After considering noise interference, finding S_jIf one voltage value is lower than other voltage values, the measuring point corresponding to the voltage value is considered to have a defect. In general, when slicing vector S_jWhen the voltage extreme value appears, the point is considered to be located at the center of the defect.

The U-shaped probe body 01 is moved from the left end to the right end of the stainless steel plate 34 to be detected, and the local defects are identified by adopting the characteristics of the asymmetric V-shaped signals. The detection process of the cylindrical probe body 02 is the same as that of the U-shaped probe body 01, the signal generated by the local defect detection of the cylindrical probe body 02 is characterized by an asymmetric double-V-shaped waveform, and the asymmetry of the signal characteristic is derived from the asymmetry of the magnetic field at the placement area of the second detection coil 22.

Establishing a three-dimensional finite element simulation model of the pulse eddy current test by using a multi-physics finite element simulation software COMSOL, and respectively carrying out finite element simulation on the U-shaped probe body 01 and the cylindrical probe body 02 test model (shown in figures 11 and 12); FIG. 13 is a graph of the maximum eddy current density distribution of the U-shaped probe body 01 at 10 to 110mm lift-off with the origin of coordinates at 500X 5mm³The center of the stainless steel plate 34 is the starting point. The eddy current on the surface of the complete test piece is distributed in a butterfly shape, wherein the uniform eddy current gathering area is located in the area right below the U-shaped probe body 01, and the vortex-shaped eddy current area is located in the areas on the left side and the right side of the U-shaped probe body 01. As the lift-off distance increases, the area of the eddy current collection region expands, the eddy current strength decreases, and the area of the focus region of the U-shaped probe body 01 expands while the focus position remains unchanged. Placing the first detection coil 12 inWhen the center of the U-shaped probe body 01 is arranged below, the detection sensitivity of detecting local defects when the U-shaped probe body 01 is lifted away is highest. FIG. 14 is a plot of the maximum eddy current density at 10 to 110mm lift-off for a cylindrical probe body 02 with the origin of coordinates 500X 5mm³The center of the stainless steel plate 34 is the starting point. According to the graph, the eddy current distribution on the surface of the complete test piece is in a vortex shape, and the eddy current density changes from weak to strong and then weakens along the radial direction of the cylindrical probe body 02 from inside to outside. The eddy current on the test piece just below the center of the second excitation coil 21 is weak, so that a detection blind area exists. The center of the cylindrical probe body 02 is offset from the position of the vortex gathering area. As the lift-off distance increases, the blind zone continues to expand, and the vortex gathering area shifts accordingly. In order to obtain a higher detection sensitivity, the eddy current collection area is selected as an optimum placement position for the second receiving coil 22 of the cylindrical probe body 02. Under each lift-off height, the offset of the vortex focal region relative to the blind zone is a fixed value.

Selecting 15 multiplied by 5mm in a simulation model³The eddy current loss power of the U-shaped probe body 01 in the stainless steel plate 34 to be inspected is calculated by area calculation and is simulated by 30X 5mm³Local area induced eddy current disturbances. The power dissipated by eddy currents in the selected area on the specimen at different locations is obtained by moving the selected area from left to right (in the same direction) (as shown in fig. 15 and 16). The initial position of the selected area is located at the leftmost lower end (equivalent to being located at 500X 5mm) of the tested stainless steel plate 34 of used 1/4³The center of the stainless steel plate 34 to be detected), 9 positions are selected in total, the interval between different positions is 15mm, and fig. 17 is a simulation result diagram of the U-shaped probe body 01 under the condition; the eddy current loss power of the selected area at different positions is divided by the eddy current loss power of the whole stainless steel plate 34 to be detected (1/4 with the size of the actual steel plate) to obtain the power ratio of eddy current dissipation at the local area, so as to quantitatively describe the degree of eddy current "gathering" generated by excitation of the U-shaped probe body 01 and the cylindrical probe body 02 on the test piece of the stainless steel plate 34 to be detected, and the simulation result is shown in fig. 18. Simulation experiments using a cylindrical probe body 02 under the same conditions resulted in a plot of eddy current power loss for selected regions at different positions as shown in FIG. 19 and for different positions as shown in FIG. 20And (3) determining the eddy current loss power ratio of the area. It can be seen that the U-shaped probe body 01 is superior in focusing performance to the cylindrical probe body 02 and has higher detection sensitivity in detecting a local defect under lift-off.

The present invention will be described in detail with reference to examples, but the present invention is not limited to the embodiments, but a focusing probe for eddy current flaw detection of metal members and a method for using the same.

Example 1:

the following examples are specific examples of the detection of local corrosion defects of the stainless steel plate 34 to be detected by the U-shaped probe body 01:

(1) the material of the test piece using the stainless steel plate 34 to be tested was 304L stainless steel, the electrical conductivity was 1.379MS/m, and the relative magnetic permeability was 1.003. The experiment used 1 block of material with a thickness of 30X 1.5mm³500X 5mm of (Length X Width X depth) Square groove³The stainless steel plate test piece 34 is tested, and a square groove at the center of the stainless steel plate 34 is used for simulating the local corrosion defect of the steel plate.

(2) The U-shaped probe body 01 detects the stainless steel plate 34 to be detected, the specific parameters of the excitation coils of the two probes are shown in Table 1, and the detection coils of the two probes use the preferred parameters. The first excitation coil 11 of the U-shaped probe body 01 was energized with a current of 1.50A, and the experimental excitation frequency was 8 Hz.

TABLE 1 two kinds of parameter tables for probe exciting coil

(3) The U-shaped probe body 01 is placed at the position 160mm away from the left end of the center of the stainless steel plate 34 to be detected, the pulse eddy current detector 03 is opened, the probe is moved uniformly and slowly, a sampling point is selected every 5mm for detection, and data are collected and recorded at the same time.

(4) After the U-shaped probe body 01 is detected, storing the acquired voltage data and drawing a normalized induced voltage attenuation curve and a normalized induced voltage time profile curve chart;

(5) and observing the voltage peak value change when the U-shaped probe body 01 advances to the simulated defect in the time profile curve chart of the normalized induced voltage.

(6) The number 6-8 time window range capable of well identifying the defect signals in the computer is selected to display the detection result in consideration of the detection object and the lift-off distance, for example, the detection result under the lift-off condition of 40mm is shown in fig. 21, the detection result under the lift-off condition of 50mm is shown in fig. 22, and the local defects can be well identified by utilizing the characteristics of the asymmetric V-shaped waveform signals.

Example 2:

the cylindrical probe body 02 was inspected for local corrosion defects in accordance with the method of use and the U-shaped probe body 01 of example 1, and the stainless steel sheet 34 to be inspected was inspected again.

The window range of No. 4-6 which can better identify the defect signal in the computer is selected to display the detection result by considering the detection object and the lift-off distance, for example, the detection result under the lift-off condition of 20mm is shown in FIG. 23, and the detection result under the lift-off condition of 30mm is shown in FIG. 24. Local defects can be well identified by using the characteristics of the asymmetric double-V-shaped waveform signals.

Example 3:

the following examples are specific examples of the thickness measurement of the stainless steel plate 34 to be measured by the U-shaped probe body 01:

(1) the material of the test piece used is 304L stainless steel, the electric conductivity is 1.379MS/m, and the relative magnetic conductivity is 1.003. In the experiment, 6 test pieces of 500X 2mm each of which was made of 6 stainless steel plates 34 to be examined were used³(Length. times. Width. times. thickness), 2 blocks 500. times.500. times.1 mm³The stainless steel plate 34 to be inspected. The stainless steel sheets 34 to be inspected having different thicknesses are used to simulate the thickness variation of the steel sheets.

(2) The probe detects the stainless steel plates 34 to be detected with different thicknesses, the parameters of the U-shaped probe body 01 are consistent with those in the table 1, and the excitation current and the frequency are also consistent with those in the embodiment 1.

(3) The U-shaped probe body 01 is placed at the center of the stainless steel plate 34 to be detected for detection, a coating layer 35 with the thickness of 100mm is arranged between the U-shaped probe body 01 and the stainless steel plate 34 to be detected, the number of the blocks of the stainless steel plate 34 to be detected is gradually increased, and the detection result under the thickness of 2-10mm is drawn (a normalized induced voltage attenuation curve graph is shown in figure 25, and a curve graph of the percentage of the slope of the attenuation curve and the change of the thickness is shown in figure 26). The thickness of the steel plate can be quantitatively detected by calibrating the thickness through the slope of the voltage attenuation curve according to the experimental result.

Example 4:

the cylindrical probe body 02 and the U-shaped probe body 01 of example 3 were subjected to the same measurement method, and the test pieces of the stainless steel plate 34 to be tested were tested again.

FIG. 27 is a normalized induced voltage decay curve of the cylindrical probe body 02 at 100mm lift-off for the stainless steel plate 34 to be inspected having a thickness of 2 to 10 mm. Fig. 28 is a graph of the slope of the attenuation curve versus the percentage change in thickness, whereby the thickness can be calibrated by the slope of the voltage attenuation curve for quantitative determination of the thickness of the steel sheet.

From experimental detection results, the cylindrical probe body 02 can detect local corrosion defects of the stainless steel plate 34 to be detected under the condition of being lifted off by 30mm and 10% uniform thickness change under the condition of being lifted off by 100mm, and can quantify the defects and the thickness of the stainless steel plate according to the characteristics of the double-V-shaped waveform signal and the slope of the voltage attenuation curve. The U-shaped probe body 01 can detect local corrosion defects of the stainless steel plate 34 to be detected after being lifted off by 50mm and 10% uniform thickness change under 110mm, and the defects and the thickness of the stainless steel plate are quantified according to the characteristics of V-shaped waveform signals and the slope of a voltage attenuation curve. The eddy current focusing area when the cylindrical probe body 02 is lifted off deviates from the center of the probe, and the eddy current focusing area of the U-shaped probe body 01 is positioned right below the center of the probe; the offset of the cylindrical probe body 02 lifted to be less than 30mm relative to the defect is a fixed value; the center of the U-shaped probe body 01 under different lift-off has no detection offset relative to the defect position; the concentration distribution of the eddy current is a key factor influencing the detection sensitivity of the probe.

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Claims

1. a focusing probe for eddy current defect detection of metal members is characterized by comprising a U-shaped probe body and a cylindrical probe body,

2. The focusing probe for eddy current flaw detection of metal members according to claim 1, wherein the first detection coils in the U-shaped probe body are circular and connected in series with each other.

3. The focusing probe for eddy current flaw detection of metal members according to claim 1, wherein the second detection coil of the cylindrical probe body is circular and differentially connected.

4. The focusing probe for eddy current flaw detection of metal members according to claim 1, wherein the wire diameters of the first exciting coil and the second exciting coil are both 0.1-2 mm, and the number of turns is 50-2000 turns.

5. The focusing probe for eddy current flaw detection of metal member according to claim 1, wherein the first and second detection coils each have a wire diameter of 0.01 to 1mm and a number of turns of 200 to 10000.

6. A method of using a focusing probe according to claim 1, characterized in that it is operated as follows: