Magnetic aggregation probe for variable cross-section pulsed eddy current detection

Abstract

The invention is suitable for the technical field of electromagnetic nondestructive testing, and provides a variable cross-section pulsed eddy current testing magnetic aggregation probe which comprises a coil, an upper magnetic core, a lower magnetic core and a magneto-dependent sensor, the upper magnetic core is located in the coil, the magneto-dependent sensor is located between the upper magnetic core and the lower magnetic core, and the cross-section aperture of all or at least part of the area of the upper magnetic core is gradually reduced from top to bottom. And the section aperture of all or at least partial region of the lower magnetic core is gradually reduced from bottom to top. In the structure, the magneto-dependent sensor is located at the necking position formed by the integral structure of the upper magnetic core and the lower magnetic core, on one hand, the upper magnetic core can gather and emit an excitation magnetic field, the diverging area of the magnetic field is reduced, and the defect resolution is improved; and on the other hand, the lower magnetic core gathers the magnetic field fed back to the necking part and then conducts the magnetic field to the upper magnetic core, and the magnetic field can be captured by the magneto-dependent sensor at the necking position, so that the strength of a feedback signal is improved, the signal-to-noise ratio of the signal is improved, and the detection sensitivity is obviously improved compared with an existing mode.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic nondestructive testing, and in particular relates to a magnetic focusing probe for variable-section pulse eddy current testing. Background Art

[0002] In the industrial field, metal pipes and pressure vessels are widely used to transport and store high-temperature, high-pressure and corrosive liquids or gaseous media, which causes corrosion of metal pipes and pressure vessels. Corrosion causes the wall thickness of pipes and pressure vessels to decrease, and the pressure-bearing performance to decrease, which can cause accidents such as leakage and explosion, resulting in casualties and economic losses. Therefore, it is necessary to conduct in-service non-destructive testing and evaluation of the corrosion of pipelines on a regular basis.

[0003] The pulsed eddy current method is an electromagnetic nondestructive testing method that can detect the wall thickness of metal components in service outside the coating. It uses pulse current excitation instead of sinusoidal current excitation to excite a pulse magnetic field outside the inspected component, so that pulse eddy currents are induced inside the inspected component. Then, the degree of corrosion of the metal component is evaluated by detecting the attenuation process of the pulsed eddy current electromagnetic field. One of the advantages of the pulsed eddy current method is that it uses a short-duration pulse current instead of sinusoidal current excitation, which reduces the active power of the system and can generate a transient strong magnetic field without causing significant heating of the coil probe. In addition, the square wave pulse electromagnetic wave has strong penetrating power and can penetrate tens or even hundreds of millimeters thick insulation layers to detect metal pipes.

[0004] Most of the existing pulsed eddy current technologies use air-core coils or coils with uniform cross-section magnetic cores as excitation units, and use coils or Hall, TMR, GMR, etc. as sensors to receive signals. The probe structure that uses coils to receive signals has a large probe size, low sensitivity to defects, and difficulty in identifying small defects. Receiving sensors such as Hall, TMR, and GMR are small in size, so the probe size can be reduced, but because of the small receiving area, it is difficult for them to receive all the magnetic field signals, and most of the magnetic field signals are lost, so there are also large errors in detection. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a magnetic focusing probe for variable cross-section pulse eddy current testing, aiming to solve the technical problems of low resolution, difficult signal focusing and low signal-to-noise ratio in existing pulse eddy current defect detection methods.

[0006] The present invention adopts the following technical solution:

[0007] The variable-section pulse eddy current detection magnetic focusing probe comprises a coil, an upper magnetic core, a lower magnetic core and a magnetic sensitive sensor, wherein the upper magnetic core is located inside the coil, and the magnetic sensitive sensor is located between the upper and lower magnetic cores. The cross-sectional diameter of the upper magnetic core gradually decreases from top to bottom, or at least in part of the area, and the cross-sectional diameter of the lower magnetic core gradually decreases from bottom to top, or at least in part of the area, and the magnetic sensitive sensor is located at the necked position formed by the overall structure of the upper and lower magnetic cores.

[0008] Furthermore, the upper and lower magnetic cores are an integrated structure or are separately arranged; if they are an integrated structure, the necked positions of the upper and lower magnetic cores are hollow tube structures, and the magnetic sensor is located in the hollow tube structure.

[0009] Furthermore, the maximum cross-sectional diameter of the upper magnetic core is greater than the maximum cross-sectional diameter of the lower magnetic core.

[0010] Furthermore, the cross section of the coil is a hollow rectangle or a hollow circle.

[0011] Furthermore, the cross section of the coil is uniform from top to bottom, or has a variable cross section that is thicker at the top and thinner at the bottom.

[0012] The beneficial effects of the present invention are as follows: the magnetic core of the structure of the present invention is divided into an upper magnetic core and a lower magnetic core, the two magnetic cores can be an integral structure or a separate design, the cross-section of the upper magnetic core is larger at the top and smaller at the bottom, and the cross-section of the lower magnetic core is smaller at the top and larger at the bottom, and a magnetic sensitive sensor is arranged at the necking position between the upper and lower magnetic cores. Through this structural design, the upper magnetic core can gather and emit the magnetic field, reducing the area of ​​magnetic field divergence, so that the area of ​​small-size defects accounts for a higher proportion in the area of ​​the excitation magnetic field, thereby improving the defect resolution; the lower magnetic core gathers the feedback magnetic field to the necking part and then transmits it to the upper magnetic core, where the magnetic field will be captured by the magnetic sensitive sensor at the necking position, thereby increasing the strength of the feedback signal and improving the signal-to-noise ratio, and the detection sensitivity is significantly improved compared with the existing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the structure of a magnetic focusing probe provided by an embodiment of the present invention;

[0014] Figure 2 yes Figure 1 Magnetic field distribution diagram of the magnetic focusing probe structure shown;

[0015] Figure 3 is another structural schematic diagram of a magnetic focusing probe provided in an embodiment of the present invention;

[0016] Figure 4 It is a comparative data diagram of the magnetic focusing probe of this embodiment compared with the existing probe. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] In order to illustrate the technical solution of the present invention, a specific embodiment is provided below for illustration.

[0019] like Figure 1 , 2 As shown, the variable-section pulse eddy current detection magnetic focusing probe provided in this embodiment includes a coil 2, an upper magnetic core 12, a lower magnetic core 11 and a magnetic sensitive sensor 3, wherein the upper magnetic core 12 is located inside the coil 2, and the magnetic sensitive sensor 3 is located between the upper and lower magnetic cores. The cross-sectional diameter of the upper magnetic core 12 gradually decreases from top to bottom or at least in part, and the cross-sectional diameter of the lower magnetic core 11 gradually decreases from bottom to top or in part, and the magnetic sensitive sensor 3 is located at the necking position formed by the overall structure of the upper and lower magnetic cores.

[0020] In this structure, at least the upper magnetic core is coaxially placed at the center of the coil. The cross-sectional shape of the coil is not limited, for example, it can be a hollow rectangle or a hollow circle, that is, the coil is circular or rectangular when viewed from top to bottom, and of course it can also be other shapes. The coil is used as an excitation coil to excite the magnetic field. The coil can have a uniform cross-section from top to bottom or a variable cross-section structure with a thick top and a thin bottom. Figure 1 In the structure shown, the cross section of the coil is uniform and consistent from top to bottom. Figure 3 In another structure shown, the cross section of the coil is thicker at the top and thinner at the bottom.

[0021] The structural feature of this magnetic focusing probe is the use of upper and lower magnetic cores. The magnetic cores are soft magnetic materials with high magnetic permeability, high saturation magnetic flux density, and low electrical conductivity. The cross-sectional changes of the entire magnetic core structure change from large to small and then to large, similar to an asymmetric hourglass shape, and the maximum cross-sectional diameter of the upper magnetic core is larger than the maximum cross-sectional diameter of the lower magnetic core. In actual production, the upper and lower magnetic cores are an integrated structure or separately set (the diagram shows that the principle structure is shown as a separate setting), that is, the necking part at the narrowest position between them can be disconnected or hollow connected. If it is an integrated structure, the necking position of the upper and lower magnetic cores is a hollow tube structure, and the magnetic sensor is located in the hollow tube structure. The magnetic core of this structure can enhance the intensity of the excitation magnetic field while concentrating the magnetic field as much as possible and passing through the magnetic sensor.

[0022] During the test, a square wave pulse current is first passed into the excitation coil. Under the action of the excitation current, the coil generates an excitation magnetic field in the form of a pulse ( Figure 2As shown in the figure, 4 is the mark of magnetic flux lines), the excitation magnetic field is gathered and emitted through the upper magnetic core whose cross section changes from large to small. Compared with the magnetic core with the same cross section, the emitted magnetic field is gathered to reduce the divergence area of ​​the magnetic field, which can be more sensitive to small area defects, so that the area of ​​small-size defects accounts for a higher proportion in the excitation magnetic field area, thereby improving the defect detection resolution.

[0023] After the emitted excitation magnetic field encounters the metal conductor detection object 5, an eddy current 6 is generated in the metal conductor detection object 5, and a feedback magnetic field is generated in the form of a magnetic field. The feedback magnetic field is collected and received by the lower magnetic core whose cross section decreases from bottom to top, and then transmitted to the magnetic sensor. Since the magnetic sensor is located at the necking part of the overall structure of the upper and lower magnetic cores, most of the feedback magnetic field will be attracted and conducted by the lower magnetic core and gathered at the necking part to be captured by the magnetic sensor, thereby improving the signal strength and enhancing the signal-to-noise ratio.

[0024] like Figure 4 As shown in the comparative data diagram, signal ① in the diagram is the signal of the magnetic focusing probe using the variable cross-section magnetic core of this embodiment, signal ② is the signal of the existing uniform cross-section magnetic core probe, and signal ③ is the signal of the non-magnetic probe. The ordinate in the diagram is the signal strength of the magnetic sensitive sensor, and the abscissa is the signal decay time. It can be clearly seen that at the same decay time, the signal strength with the magnetic core is significantly greater than the signal strength without the magnetic core, and the signal strength amplitude of the variable cross-section magnetic core probe of the present invention is significantly stronger than the signal strength amplitude of the ordinary magnetic core. Therefore, from the comparison of the signal amplitude with the decay of the decay, it is explained that the present invention successfully enhances the signal strength and thus improves the signal-to-noise ratio of the overall signal.

[0025] Finally, it is particularly important to explain that in the upper and lower magnetic cores of this embodiment, the upper magnetic core may have a portion of the middle area having a variable cross-section from top to bottom, such as Figure 1 The structure shown in the figure may also be a structure in which the entire upper magnetic core has a variable cross-section from top to bottom, such as Figure 3 The trapezoidal shape shown is within the protection scope of this embodiment. Similarly, the magnetic core can be a variable cross-section structure or a partial variable cross-section structure.

[0026] In summary, the present invention provides a pulsed eddy current detection magnetic focusing probe that gathers magnetic fields and amplifies collected signals. On the one hand, the magnetic field generated by the excitation coil is gathered by the upper magnetic core and then emitted. The magnetic field is gathered to reduce the divergence area, which can be more sensitive to small area defects and improve the defect detection resolution. On the other hand, the pulsed eddy current magnetic field signal fed back by the defect detection is gathered as much as possible by the lower magnetic core and received by the magnetic sensitive sensor, thereby improving the signal-to-noise ratio of the signal and enhancing the detection performance.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A magnetic focusing probe for variable cross-section pulsed eddy current testing, characterized in that: The magnetic focusing probe includes a coil, an upper magnetic core, a lower magnetic core and a magnetic sensitive sensor. The upper magnetic core is located inside the coil, and the magnetic sensitive sensor is located between the upper and lower magnetic cores. The cross-sectional diameter of the upper magnetic core gradually decreases from top to bottom or at least in part of the area. The cross-sectional diameter of the lower magnetic core gradually decreases from bottom to top or at least in part of the area. The magnetic sensitive sensor is located at the necked position formed by the overall structure of the upper and lower magnetic cores.

2. The variable cross-section pulse eddy current detection magnetic focusing probe as claimed in claim 1, characterized in that: The upper and lower magnetic cores are an integrated structure or are separately arranged; if they are an integrated structure, the necked positions of the upper and lower magnetic cores are hollow tube structures, and the magnetic sensor is located in the hollow tube structure.

3. The variable cross-section pulsed eddy current detection magnetic focusing probe according to claim 1, characterized in that: The maximum cross-sectional diameter of the upper magnetic core is greater than the maximum cross-sectional diameter of the lower magnetic core.

4. The variable cross-section pulsed eddy current detection magnetic focusing probe according to any one of claims 1 to 3, characterized in that: The cross section of the coil is a hollow rectangle or a hollow circle.

5. The variable cross-section pulsed eddy current detection magnetic focusing probe as claimed in claim 4, characterized in that: The cross section of the coil is uniform from top to bottom, or has a variable cross section that is thicker at the top and thinner at the bottom.

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