JP2022052676A - Metal crack inspection device using magnetic sensor - Google Patents

Abstract

To provide a metal crack inspection device that can obtain a defect signal directly above a crack in a metallic structure or a metal material, such as a steel plate, regardless of the location of the crack.SOLUTION: In a non-destructive inspection device that detects a magnetic field of eddy current generated in a metal inspected object by applying an AC magnetic field to the inspected object with magnetic sensors, as an application method, a linear wiring parallel to a surface of the inspected object is provided, and a pair of magnetic sensors having a sensitivity axis for detecting a magnetic field perpendicular to the surface of the inspected object are provided at axisymmetric positions across the linear wiring. As a first-order differential magnetic sensor that takes difference by the pair of magnetic sensors, a change in the magnetic field due to a crack in the magnetic field created by the eddy current is detected.SELECTED DRAWING: Figure 2

Description

According to the present invention, an AC magnetic field is applied to a metal object to be inspected to generate an eddy current in the object to be inspected, and a secondary magnetic field generated by this eddy current is detected to detect defects in the object to be inspected. The present invention relates to a metal crack inspection device using a sensor.

Conventionally, an eddy current flaw detection method and a leakage magnetic flux flaw detection method are known as methods for magnetically inspecting defects generated in an inspected object such as a metal structure. In particular, in the eddy current flaw detection method, an eddy current is generated in the inspected object by applying an AC magnetic field to the inspected object using an applied coil, and the eddy current generated in the inspected object is the eddy current in the inspected object. It is inspected by utilizing the fact that it is disturbed by the presence of defects such as scratches on the magnet. The eddy current turbulence may be detected as a change in the inductance of the applied coil itself, or may be detected by a magnetic sensor including a detection coil provided separately from the applied coil. Here, the magnetic sensor includes a thin film device such as a Hall element, a magnetoresistive element (MR), and a magnetic impedance element (MI), and the detection coil is also included in the magnetic sensor as a broad classification.

For surface crack inspection, a detection coil is generally used as a magnetic sensor. In the method using the detection coil, since the frequency characteristic of the sensitivity of the detection coil has a characteristic proportional to the frequency, the sensitivity becomes low at a low frequency, and the sensitivity becomes zero especially at a direct current, so that the measurement cannot be performed. Therefore, in the eddy current inspection method using the detection coil, the frequency of the applied magnetic field is set to a high frequency of several tens of kHz or more for inspection. The frequency of the applied magnetic field is related to the skin depth as a distance parameter that the applied magnetic field reaches the inside of the metal, and the skin depth is inversely proportional to the square root of the frequency. Therefore, the eddy current flaw detection method using the detection coil is widely used for inspecting cracks generated on the surface of the object to be inspected. Inspection using the detection coil is limited to cracks on the surface, but on the other hand, the detection coil measures the magnetic flux obtained by multiplying the magnetic flux density by the coil area, so it is possible to detect abnormalities over a wide area. The coil shape can be freely taken as various coil shapes such as a first-order differential coil and a second-order differential that can cancel the environmental magnetic flux.

The magnetic sensor of the thin film device can detect the magnetic field at a local position as the magnetic flux density. Therefore, a detailed magnetic field distribution can be measured. However, since it detects magnetic noise such as the distribution of local magnetism of the object to be inspected such as steel, multiple magnetic sensors are used to remove it, and arithmetic processing such as the difference in the output of each magnetic sensor is performed. The way to do it is taken. In this way, how to use the magnetic sensor of the coil or thin film device as the detection means needs to be selected in the crack inspection device according to the measurement target and the inspection requirement specifications.

In optimizing the inspection device, it is important to select the magnetic sensor to be used, how to apply the applied magnetic field to the object to be inspected, and to optimize the arrangement of the magnetic sensor. As a method of applying the applied magnetic field, an upper coil is generally used in which the central axis of the applied coil faces the surface of the object to be inspected in a direction perpendicular to the central axis. In this case, the distribution of the eddy current generated in the object to be inspected becomes circular, for example, in the circular application coil, like the shape of the upper coil. Further, in a tangential coil in which the central axis of the coil of the square coil is parallel to the surface of the object to be inspected and one side is parallel to the surface of the subject, there is an effect that eddy currents flow intensively near one parallel side ( For example, Non-Patent Document 1). There is also an application wire method in which a wire arranged parallel to the surface of the subject is applied without using a coil (Non-Patent Document 2). Similar to the tangential coil, an eddy current is generated in parallel with the applied wire.

When a detection coil is used for the upper coil, a detection coil whose central axis is oriented in the same direction as the central axis of the upper coil for application is often used. Similarly, many magnetic sensors of thin film devices have the magnetic field detection direction of the magnetic sensor aligned with the central axis of the upper coil. On the other hand, there is one in which two magnetic sensors are arranged on the same side by removing from the central axis of the upper coil to take the differential of the output of each magnetic sensor (Non-Patent Document 3). In this case, changes in the eddy current distribution due to cracks in a region smaller than the area of the upper coil can be captured. Further, in the case of the applied wire, the sensitivity axes of the magnetic sensor of the thin film device are arranged so as to be orthogonal to each other directly above the applied wire. As a result, the coupling of the applied magnetic field by the applied wire to the magnetic sensor is weakened, and the signal which is the secondary magnetic field generated by the eddy current can be detected accurately. Further, since a magnetic field can be applied to a local portion by the application wire, minute defects can be detected.

As the application wire, a figure eight differential coil is used as the application coil, and the adjacent sides thereof are combined to form a linear wiring. As a detection magnetic sensor, there is one in which two detection coils of the first derivative are connected and arranged on a linear wiring as a second derivative coil (Non-Patent Document 4). In some cases, the figure 8 application coil and the figure 8 detection coil are arranged so as to be orthogonal to each other (Patent Documents 1 and 2).

JP-A-2019-39779 International Publication No. WO00 / 08458

Japan Nondestructive Testing Association, "Eddy Current Testing I", pp. 32-43 Keiji Tsukada, Hiroto Shobu, Yuto Goda, Takumi Kobara, Kenji Sakai, Toshihiko Kiwa, and Mohd Mawardi Saari, "Integrated magnetic sensor probe and excitation wire for nondestructive detection of submillimeter defects", IEEE Magnetics Letters, vol. 10, No. 1, pp. 8105105-1-5 (2019) Keiji Tsukada, Minoru Hayashi, Yoshihiro Nakamura, Kenji Sakai, and Toshihiko Kiwa, "Small eddy current testing sensor probe using a tunneling magnetoresistance sensor to detect cracks in steel structures", IEEE Transactions on Magnetics, vol. 54, No. 11,6202205 (2018) Proceedings of the 2018 Autumn Lecture Meeting of the Japan Nondestructive Inspection Association, Yuto Goda, Tetsuro Hirata, Kenji Sakai, Toshihiko Kiwa, Akira Tsukamoto, Keiichi Tanabe, Keiji Tsukada Development of lift-off crack inspection method, 2018

Generally, when a crack occurs, what was initially localized grows longer over time. In this case, you need to know how the crack is growing. However, in many of the conventional eddy current inspection methods, a defect signal is obtained at the end of the crack, but there is a problem that the defect signal cannot be obtained or becomes weak at the middle portion of the crack. In the method of arranging two magnetic sensors away from the central axis in the applied coil on the same side and taking the difference, a signal was obtained even in the middle of the crack. However, the pattern of the obtained signal was a signal change separated on both sides along the crack, and the largest signal could not be obtained immediately above the crack. Therefore, when the magnetic sensor probe was two-dimensionally scanned and imaged, a magnetic field pattern matching the shape of the crack could not be obtained.

Also, in areas covered with pavement such as concrete and asphalt, such as road slabs, the distance between the magnetic sensor and the steel slab when trying to inspect using a crack inspector from above the road. That is, since the lift-off becomes large, there is a problem that the detected magnetic field generated by the eddy current due to the crack becomes small. Therefore, there is a method of detecting a weak magnetic field by using an ultrasensitive superconducting quantum interference element (SQUID) as a magnetic sensor (Patent Document 1).

In the case where the side where the applied coil of the figure 8 is combined is linear wiring and the second derivative detection coil is used, the first derivative of many turns is overlapped, so that the positional relationship between the two is deviated and balanced. It was sometimes difficult. Further, since half of the second derivative coil is located in the linear wiring, there is a problem that the signal change cannot be obtained when the direction of the crack is parallel to the linear wiring. Further, when the structure of the detection coil becomes complicated and the number of channels is increased, there is a problem that it is difficult to image the detailed crack shape. Further, in the case where the figure 8 application coil and the figure 8 detection coil were arranged so as to be orthogonal to each other, there was a direction that could not be detected due to the direction of the crack.

In order to image cracks, a method of line scanning using a multi-channel magnetic sensor probe in which multiple magnetic probes consisting of a combination of an applied coil and a magnetic sensor are arranged is a two-dimensional method for one magnetic probe. The inspection speed is faster and the inspection position accuracy is higher than the scanning method. However, when a multi-channel magnetic sensor probe is formed, the structure becomes complicated and the applied magnetic field distribution due to the adjacent applied coil changes, so that the obtained data may differ from that when a single magnetic probe is used. Because it happened, it was necessary to pay attention to its arrangement.

In view of this situation, the present inventor can obtain a large signal change even under a large lift-off inspection condition, and can obtain a large signal change in the entire region directly above a long crack regardless of the direction of the applied coil. The present invention was achieved by developing a magnetic probe that can be easily imaged from the resulting result.

The metal crack inspection device using the magnetic sensor of the present invention is non-destructive by detecting the magnetic field of the eddy current generated in the metal object to be inspected by applying an AC magnetic field to the object to be inspected. In the inspection device, as an application method, a pair of linear wirings parallel to the surface of the inspected object are provided, and a pair of sensitivity axes having a sensitivity axis for detecting a magnetic field perpendicular to the surface of the inspected object at a line-symmetrical position straddling the linear wiring. As a primary differential magnetic sensor provided with a magnetic sensor and taking a difference by a pair of magnetic sensors, it detects a change in the magnetic field due to a crack in a magnetic field created by an eddy current.

Further, the magnetic sensor for non-destructive inspection of the present invention is also characterized in the following points.
(1) A magnetic sensor array in which a plurality of primary differential magnetic sensors are arranged along a linear wiring.
(2) In a pair of magnetic sensors, each magnetic sensor is provided with a cancel coil that generates a magnetic field opposite to the magnetic field direction created by the linear wiring.

According to the present invention, since the magnetic field is applied to the object to be inspected by the linear wiring, a linear eddy current can be generated. This linear eddy current can generate changes in the eddy current at various angles, whether perpendicular or parallel to the crack extension direction. Here, by arranging a pair of magnetic sensors across the linear wiring and adopting the difference, that is, the configuration of the first-order differential magnetic sensor, a large signal change can be obtained immediately above the crack. The magnetic field created by the eddy current becomes spatially wider as the magnetic field strength becomes weaker as the distance between the object to be inspected and the magnetic sensor increases. Since a pair of magnetic sensors are arranged across the linear wiring here, the distance between the magnetic probe composed of the linear wiring and the pair of magnetic sensors and the subject is lifted off by the magnetic sensors separated from each other. It is possible to efficiently detect the magnetic field distribution that has spread greatly.

Furthermore, by arranging a plurality of primary differential magnetic sensors along the linear wiring, it became easy to image cracks. In this imaging, a large signal change can be obtained just above the crack, so that the signal distribution corresponding to the crack shape can be obtained, and the crack shape can be recognized. Here, the applied magnetic field created by the linear wiring is applied not only to the object to be inspected but also to each of the pair of magnetic sensors. Therefore, by providing a cancel coil that removes the applied magnetic field entering the magnetic sensor, it is possible to reduce the applied magnetic field component coupled to the magnetic sensor. With this cancel coil, it is possible to obtain a signal having a high SN, that is, a ratio of the magnetic field components generated by the eddy current in the signal detected by the magnetic field sensor.

It is a schematic explanatory drawing of the metal crack inspection apparatus which concerns on this invention. It is a schematic explanatory drawing of the magnetic sensor probe of the metal crack inspection apparatus which concerns on this invention. Using the magnetic sensor probe shown in FIG. 2 according to the present invention, a detection signal is obtained when an inspected object having an artificial crack in a steel plate is line-scanned so that the linear wiring in the magnetic sensor probe is orthogonal to the crack. It shows the phase change of. It is a schematic explanatory drawing of the multi-channel magnetic sensor probe using the multi-channel primary differential type magnetic sensor in the metal crack inspection apparatus which concerns on this invention. Using the multi-channel magnetic sensor probe according to the present invention, the phase change of the detection signal when scanning an object to be inspected in which an artificial crack is provided in a steel plate is mapped. The multi-channel magnetic sensor probe according to the present invention is rotated 90 degrees to map the phase change of the detection signal when scanning an object to be inspected having an artificial crack in a steel plate. It is a schematic explanatory drawing of the multi-channel magnetic sensor probe which used the linear wiring which concerns on this invention as one side of a tangential coil. It is a schematic explanatory drawing of the multi-channel magnetic sensor probe which used the linear wiring which concerns on this invention as the adjacent side of the figure 8 coil. It is a schematic explanatory drawing of the magnetic sensor probe which provided the cancellation coil in each magnetic sensor in the magnetic sensor probe of FIG. 2 which concerns on this invention. It is a relationship diagram of the applied magnetic field in FIG. 9 which concerns on this invention, and the magnetic field created by a cancel coil.

In the non-destructive inspection magnetic sensor and non-destructive inspection device of the present invention, the AC magnetic field applied to the object to be inspected is generated by a linear wiring in which an AC current is applied, and an eddy current generated by the applied magnetic field is generated. It is a metal crack inspection device that can inspect cracks by measuring the differential output of a set of magnetic sensors on both sides across a linear wiring.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Members having similar uses and functions are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 1, the non-destructive inspection apparatus of the present invention detects an AC power source 20 that generates an AC magnetic field applied to the inspected object T and a magnetic field of eddy current generated in the inspected object T by the AC magnetic field. The magnetic sensor probe 30 is provided with a signal analyzer 21 for analyzing the output signal of the magnetic sensor probe 30. The magnetic sensor probe 30 is driven by the magnetic sensor power supply 22. The signal analyzer 21 uses the signal of the AC power supply 20 as a trigger to lock in and detect the output signal of the magnetic sensor probe 30, and analyzes the signal strength and phase. As the body T to be inspected, a steel plate having a thickness of 7 mm having an artificial crack defect d having a length of 20 mm formed by electric discharge machining was used.

As shown in FIG. 2, the magnetic sensor probe is provided with a linear wiring 31 parallel to the surface of the subject (xy plane) near the object T to be inspected, and is driven by the AC power supply 20. A set of magnetic sensors 32a and 32b are installed on both sides so as to straddle the linear wiring 31 at line-symmetrical positions, and these magnetic sensors 32a and 32b are oriented in the direction perpendicular to the surface of the object T to be inspected, z in the figure. The magnetic field in the direction is detected. The outputs of the set of magnetic sensors 32a and 32b are processed for difference signals and amplification by the differential amplifier 23, and the first-order differential magnetic sensor 33 is formed by the configuration of the set of magnetic sensors 32a and 32b. ..

As the magnetic sensor, an anisotropic magnetoresistive element (AMR), which is a thin film type magnetic sensor, was used in this embodiment. In addition to AMR, tunnel type MR elements, giant MR elements, MI elements, Hall elements, and detection coils can be used. In the case of the detection coil, instead of using two magnetic sensors, the coil that is wound in opposite directions like a figure eight is connected in series, and one coil becomes a first-order differential magnetic sensor as it is. Can be used.

Since the linear wiring 31 is connected to the AC power supply 20, wiring can be freely performed where it is not necessary to apply an applied magnetic field to the object T to be inspected. Here, as shown in FIG. 2, the linear wiring 31 is arranged on both sides in a direction away from the inspected body T to form a U-shaped wiring pattern.

In the present embodiment, the signal analyzer 21 is configured by a personal computer in which the required program is installed, but it may be performed by an analog circuit such as a lock-in amplifier.

In the inspected object T in which the artificial crack defect d is formed by using the above-mentioned non-destructive inspection device, the linear wiring 31 is orthogonal to the length direction of the artificial crack d, and the central portion of the artificial crack defect d is formed. FIG. 3 shows a graph of the phase change of the signal when the magnetic sensor probe 30 is line-scanned so as to cross. The alternating current output from the alternating current power supply 20 was set to 50 kHz at 10 mA. As shown in FIG. 3, it can be seen that the signal with the largest signal change immediately above the crack is obtained, that is, the signal corresponding to the position of the crack is obtained. Here, as a signal, lock-in detection obtains two orthogonal components, a real number component and an imaginary number component, and these signals can be displayed in terms of signal strength and phase. There is also a method of displaying a Lissajous waveform of a real number component on the x-axis and an imaginary number component on the y-axis. This Lissajous waveform display method is a method suitable for inspecting so as to make an inspection place with a thin magnetic sensor probe such as a pencil type. However, skill is required to judge the test method and test result.

In the present invention, a signal change corresponding to the location of the crack was obtained even in the central part of the crack, and in order to take advantage of this feature, a multi-channel magnetic sensor probe was manufactured so that anyone could easily understand the image. As shown in FIG. 4, the multi-channel magnetic sensor probe 30a forms a sensor array in which a plurality of primary differential magnetic sensors are arranged in a linear wiring 31a. In the figure, three first-order differential magnetic sensors 33a, 33b, 33c are used, but the number is not particularly limited and the channel can be determined according to the region to be inspected.

FIG. 5 shows an image of data obtained by scanning a 10-channel magnetic sensor probe 30b in the y direction in the figure. The direction of the artificial crack defect d and the direction of the linear wiring are orthogonal to each other. The change in phase is imaged, and the signal change corresponding to the size of the artificial crack defect d is obtained. As described above, this magnetic sensor probe has a feature that the shape of the crack can be inspected from the feature that the signal change corresponding to the position of the defect can be obtained not only at the end of the crack but also at the intermediate position.

FIG. 6 shows an image of data obtained by scanning a 10-channel magnetic sensor probe 30b in the y direction in the figure in the same direction as the direction of the artificial crack defect d and the direction of the linear wiring. There is. Here, since the length of the magnetic sensor probe is not enough for the length of the artificial crack defect, scanning is performed in two regions. It is an image of the phase change, and the signal change corresponding to the size of the artificial crack defect d is obtained as in FIG. As described above, this magnetic sensor probe has a feature that the shape of a crack can be inspected regardless of the direction of the defect. This makes it possible for anyone to obtain easy-to-understand test results.

FIG. 7 shows a third embodiment. In the previous embodiment, one linear wiring was used, but the allowable value of the current is limited. Since the pavement is thick like a steel deck of a road, the attenuation of the applied magnetic field strength becomes large when the lift-off is large. Therefore, when it is desired to apply a stronger magnetic field, it is necessary to use a plurality of linear wirings 31b as shown in FIG. As a method of constructing a plurality of coils, there is a method of using a tangential coil 34 whose coil surface is perpendicular to the object to be inspected. In this case, a coil is formed, but the magnetic field created by the side far from the object to be inspected has little effect.

As shown in FIG. 8, as a method of forming a plurality of linear wirings, there is a method of using a figure eight coil 35. Here, it is necessary to make the current flow in the opposite phase as shown by the arrow in the figure. As a result, the sides where the two coils are in contact are in the same direction, and a plurality of linear wirings 31c can be formed. In the case of this configuration, the magnetic field is applied to the object T to be inspected even around the side of the coil other than the linear wiring, but the influence is small because it is separated from the linear wiring 31c.

The first-order differential magnetic sensor in the above embodiment has a configuration in which the magnetic sensor is arranged at a line-symmetrical position across the linear wiring. In this case, not only the magnetic signal generated by the eddy current but also the applied magnetic field created by the AC current flowing through the linear wiring is directly detected in each magnetic sensor, and if the differential of each magnetic sensor output is taken, the environment etc. Although the magnetic noise of the can be attenuated, the applied magnetic field cannot be removed. Therefore, as shown in FIG. 9, cancel coils 36a and 36b for removing the applied magnetic field coupled to the magnetic sensors 32c and 32d in the first-order differential magnetic sensor 33d are provided. The operation method of the cancel coils 36a and 36b is shown in FIG. Since an alternating current is passed through the linear wiring 31d, an applied magnetic field rotated in an annular shape is generated around the linear wiring 31d so as to be represented by Ampere's law. Since the figure is an alternating current, the direction of the current and the direction of the applied magnetic field at a certain moment are shown. An applied magnetic field is applied to the magnetic sensor in the foreground of the figure in the negative direction of the z-axis. On the other hand, an applied magnetic field is applied to the magnetic sensor on the back side in the positive direction of the z-axis. Therefore, if the differential between the two magnetic sensors is taken, the signal due to the applied magnetic field is doubled, and a large offset signal is carried in addition to the magnetic signal due to the eddy current. Therefore, the cancel coil generates a cancel magnetic field in the positive direction on the z-axis opposite to the applied magnetic field in the front magnetic sensor, and a cancel magnetic field in the negative direction in the z-axis in the back magnetic sensor. By generating it, the influence of the applied magnetic field can be reduced. By providing this cancel coil in each magnetic sensor, it becomes possible to detect a high SN signal.

Since the distance between the pair of magnetic sensors can be freely designed with the configuration of the present invention, it is possible to capture the magnetic field due to the spatially spread eddy current in the case of a large lift-off such as inspection of a steel deck of a road. For example, in the case of a lift-off of 80 mm, it has become possible to detect a large signal change due to a crack by separating the distances between the magnetic sensors of the first-order differential magnetic sensor by the same degree.

Since the object to be inspected is a flat surface, the linear wiring is uniaxial in Cartesian coordinates, but if the object to be inspected is a cylindrical pipe, for example, the linear wiring is a wiring that is shaped along the circumference of the cylinder. However, it can take various forms.

The magnetic sensor for non-destructive inspection and the non-destructive inspection apparatus of the present invention can be widely used for detecting crack defects generated in metallic structures and metal materials such as steel plates. In particular, defect detection inspection in a wide range of fields such as steel structures where it was difficult to determine the growth status of cracks where there are complicated shapes, such as bridges and buildings, factory plants, power generation equipment, and railways. Can be made possible, and effective maintenance can be made possible.

20 AC power supply 21 Signal analyzer 22 Power supply for magnetic sensor 23 Differential amplifier 30, 30a, 30b, 30c, 30d Magnetic sensor probe 31, 31a, 31b, 31c, 31d Linear wiring 32a, 32b, 32c, 32d Magnetic sensor 33 , 33a, 33b, 33c, 33d Primary differential magnetic sensor 34 Tungential coil 358-shaped coil 36a, 36b Cancellation coil T Inspected object d Artificial crack defect

Claims (5)

In a non-destructive inspection device that detects cracks by detecting the magnetic field generated by the eddy current generated in the inspected object by applying an AC magnetic field to the metal inspected object with a magnetic sensor.
A linear wiring is provided, and an alternating current is applied to the linear wiring to generate the alternating magnetic field. The pair of magnetic sensors are arranged at line-symmetrical positions across the linear wiring and the pair of magnetic sensors. A metal crack inspection device equipped with a first-order differential magnetic sensor that measures the difference in the output of. A metal crack inspection device in which a plurality of the first-order differential magnetic sensors are arranged along the linear wiring. The metal according to claims 1 and 2, wherein the linear wiring uses a tangential coil in which a coil surface is arranged perpendicular to the subject, and the tangential coil is a parallel portion closest to the subject. Crack inspection device. The metal according to claim 1 to 3, wherein one side of a figure eight coil made of a pair of coils energizing an alternating current in the opposite direction is brought close to each other, and one side of the differential coil brought close to each other is used as the linear wiring. Crack inspection device. The metal crack inspection apparatus according to claim 1 to 4, wherein each of the first-order differential magnetic sensors is provided with a cancel coil that cancels or attenuates the AC magnetic field.

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