Eddy current flaw detection device and flaw detection method

Abstract

To prevent flaws from being overlooked.SOLUTION: An eddy current flaw detector includes: a probe body 210 having a contact surface 214 with a flaw detection target; excitation coils (first excitation coil 224, second excitation coil 234) provided in the probe body 210; a first detection coil 222 provided in the probe body 210 and having a center axis substantially orthogonal to the contact surface 214; a second detection coil 232 provided in the probe body 210 and having a central axis forming an acute angle with the central axis of the first detection coil 222; an excitation unit that applies the alternating current to the excitation coils and generates an induced current due to electromagnetic induction in the flaw detection target; and a detection unit that detects a second detection signal based on the induced current through the second detection coil 232 while detecting a first detection signal based on the induced current through the first detection coil 222.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an eddy current flaw detection device and a flaw detection method. [Background technology]

[0002] Conventionally, steel bridge inspections have been carried out by visual inspection and magnetic particle testing (MT). If paint cracks or rust are found during visual inspection, the paint is first peeled off from the cracked or rusted areas to expose the metal parts. Then, magnetic particle testing is used to detect the presence or absence of flaws (cracks) in the metal parts.

[0003] However, magnetic particle testing requires the removal of the coating, which increases costs due to the need for personnel and increased manpower.

[0004] Therefore, a technology has been studied that uses an eddy current flaw detector to perform flaw detection through the coating film (for example, Patent Document 1). In this case, if the detection signal obtained by the eddy current flaw detector exceeds a predetermined threshold, it is determined that a flaw exists. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5191873 Summary of the Invention [Problem to be solved by the invention]

[0006] The detection signal in an eddy current flaw detector reaches a maximum when the direction of the central axis of the detection coil coincides with the depth direction of the flaw.

[0007] However, the depth direction of the flaw cannot be visually observed from above the paint film. Furthermore, the location of the crack in the paint film and the location of the flaw may not coincide, making it impossible to confirm the location of the flaw from above the paint film. Therefore, skilled techniques are required to align the direction of the central axis of the detection coil with the depth direction of the flaw, and depending on the skill level of the inspection technician, there is a risk of misjudgment of the flaw due to errors in the signal strength of the detection signal or the flaw being overlooked.

[0008] In view of the above problems, the present disclosure aims to provide an eddy current flaw detection device and flaw detection method that can prevent flaws from being overlooked. [Means for solving the problem]

[0009] In order to solve the above problem, an eddy current flaw detector according to one aspect of the present disclosure includes: The first and second plates are joined by a weld. a probe body having a contact surface with an object to be inspected; an excitation coil provided in the probe body; a first detection coil provided in the probe body and having a central axis substantially perpendicular to the contact surface; a second detection coil provided in the probe body and having a central axis that forms an acute angle with the central axis of the first detection coil; an excitation unit that applies an AC current to the excitation coil to generate an induced current in the object to be inspected by electromagnetic induction; and a detection unit that detects a second detection signal based on the induced current through the second detection coil while detecting a first detection signal based on the induced current through the first detection coil. The device is configured to be able to detect flaws that may occur in an object to be inspected, the flaws extending in a first direction, and the flaws that extend in a second direction different from the first direction. do.

[0010] The first and second detection coils may be provided between the excitation coil and the contact surface.

[0011] The second detector coil may have a central axis that forms an angle of 35° or more and 55° or less with respect to the central axis of the first detector coil.

[0012] In order to solve the above problem, a flaw detection method according to one aspect of the present disclosure includes: The first and second plates are joined by a weld.The probe body has a contact surface with the object to be inspected, an excitation coil provided in the probe body, a first detection coil provided in the probe body and having a central axis that is approximately perpendicular to the contact surface, and a second detection coil provided in the probe body and having a central axis that forms an acute angle with the central axis of the first detection coil. The flaw detection device is configured to be able to detect flaws that may occur in an object to be inspected, the flaws extending in a first direction, and the flaws that may occur in a second direction different from the first direction. A flaw detection method using an eddy current flaw detection device, comprising the steps of applying an alternating current to an excitation coil to generate an induced current in an object to be detected by electromagnetic induction; detecting a second detection signal based on the induced current through a second detection coil while detecting a first detection signal based on the induced current through a first detection coil; and notifying the presence of a flaw when the difference between the signal strength of the first detection signal and the signal strength of the second detection signal is equal to or greater than a predetermined value. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to prevent defects from being overlooked. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating an object to be inspected by an eddy current flaw detector according to this embodiment. [Figure 2] FIG. 2 shows an eddy current flaw detector according to this embodiment, which includes a probe and a control unit. [Figure 3] FIG. 3 is a diagram illustrating the probe according to this embodiment. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a diagram illustrating the relationship between a flaw occurring in the support and the first and second detection coils. [Figure 6] FIG. 6 is a functional block diagram of the control unit according to this embodiment. [Figure 7] FIG. 7 is a flowchart showing the processing flow of the flaw detection method according to this embodiment. [Figure 8] FIG. 8 is a diagram illustrating a detection signal when the contact surface is in contact with the object to be flaw-detected and there is no flaw. [Figure 9] FIG. 9 is a diagram illustrating a detection signal when the contact surface is in contact with the object to be flaw-detected and there is a flaw. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Dimensions, materials, and other specific numerical values ​​shown in the embodiments are merely examples for ease of understanding and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present disclosure are not shown.

[0016] Fig. 1 is a diagram illustrating an object 10 to be inspected by an eddy current flaw detector 100 according to this embodiment. In Fig. 1 of this embodiment and Fig. 5 described later, the X axis (horizontal direction, road width direction), Y axis (horizontal direction, road length direction), and Z axis (vertical direction) that intersect perpendicularly are defined as shown in the figure.

[0017] 1, the object 10 to be inspected is, for example, a steel bridge. The object 10 to be inspected includes a support 20 and a pavement 30.

[0018] The support body 20 is a deck slab made of steel members. The support body 20 supports the vertical downward load of a vehicle. The surface of the support body 20 is covered with a paint film. The support body 20 includes a first plate 22, a second plate 24, and a welded portion 26.

[0019] The first plate 22 is a steel plate extending in a substantially horizontal direction. The second plate 24 is a steel plate standing vertically downward from the first plate 22. The second plate 24 is welded (for example, fillet welded) to the first plate 22. The welded portion 26 is a portion formed as a result of welding the first plate 22 and the second plate 24 together.

[0020] The pavement 30 is laid on the first plate 22. The pavement 30 is made of asphalt or the like. Vehicles run on the pavement 30.

[0021] Fatigue caused by vehicles passing over the pavement 30 over time can cause cracks or other defects in the welds 26 of the support body 20. The cracks propagate from the welds 26 toward the first plate 22 or from the welds 26 toward the second plate 24.

[0022] Therefore, an eddy current flaw detector 100 shown in FIG. 2 and other figures below inspects the support 20 for flaws.

[0023] [Eddy current flaw detection device 100] 2, the eddy current flaw detector 100 according to this embodiment includes a probe 110 and a control unit 120. Each component will be described below.

[0024] [Probe 110] 3 is a diagram illustrating the probe 110 according to this embodiment. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG.

[0025] As shown in FIGS. 3 and 4, the probe 110 includes a probe body 210, a first coil unit 220, and a second coil unit 230.

[0026] The probe body 210 includes a grip portion 212, a contact surface 214, and an inclined surface 216. The probe body 210 is made of, for example, plastic.

[0027] The gripping portion 212 is, for example, a rectangular prism-shaped portion, and is held by an inspection technician.

[0028] The contact surface 214 is provided at the tip 210a of the probe main body 210. The contact surface 214 is a flat surface that can come into contact with the object 10 under test. That is, an inspection engineer holds the gripping portion 212 and brings the contact surface 214 into contact with the object 10 under test to perform flaw detection. When performing flaw detection, the inspection engineer brings the contact surface 214 into contact with the object 10 under test so that the depth direction in FIG. 4 coincides with the Y-axis direction in FIG. 1. In this embodiment, the area of ​​the contact surface 214 is smaller than the cross-sectional area of ​​the gripping portion 212.

[0029] The inclined surface 216 is provided between the grip portion 212 and the contact surface 214. In this embodiment, the probe body 210 has four inclined surfaces 216. The inclination angles of the four inclined surfaces 216 may be equal or different.

[0030] The first coil unit 220 is composed of a first detection coil 222 and a first excitation coil 224. The second coil unit 230 is composed of a second detection coil 232 and a second excitation coil 234. The first coil unit 220 and the second coil unit 230 have substantially the same configuration except for the angle they make with the contact surface 214 and their positions within the probe body 210. Furthermore, the first coil unit 220 is provided at a different position in the depth direction in FIG. 4 from the second coil unit 230.

[0031] The first detection coil 222 is provided inside the probe body 210. The central axis of the first detection coil 222 is perpendicular to the contact surface 214. In other words, the angle α between the central axis of the first detection coil 222 and the contact surface 214 is 90°.

[0032] The first excitation coil 224 (excitation coil) is provided inside the probe body 210. The first excitation coil 224 is provided farther away from the contact surface 214 than the first detection coil 222. In other words, the first detection coil 222 is provided between the first excitation coil 224 and the contact surface 214. This makes it possible to suppress input of noise due to the AC current applied by the first excitation coil 224 to the first detection coil 222.

[0033] The central axis of the first excitation coil 224 (the depth direction in FIG. 4) is perpendicular to the central axis of the first detection coil 222.

[0034] The second detection coil 232 is provided inside the probe body 210. The angle β formed between the central axis of the second detection coil 232 and the central axis of the first detection coil 222 is an acute angle (greater than 0° and less than 90°). The angle β is, for example, equal to or greater than 35° and equal to or less than 55°. In this embodiment, the angle β is 45°.

[0035] The second excitation coil 234 (excitation coil) is provided inside the probe body 210. The second excitation coil 234 is provided farther from the contact surface 214 than the second detection coil 232. In other words, the second detection coil 232 is provided between the second excitation coil 234 and the contact surface 214. This makes it possible to suppress input of noise due to the AC current applied by the second excitation coil 234 to the second detection coil 232.

[0036] The central axis of the second excitation coil 234 (the depth direction in FIG. 4) is perpendicular to the central axis of the second detection coil 232.

[0037] Fig. 5 is a diagram illustrating the relationship between a flaw occurring in the support 20 and the first and second detection coils 222 and 232. In Fig. 5, dashed lines indicate flaws. In Fig. 5, thick lines indicate the direction 222a of the central axis of the first detection coil 222 and the direction 232a of the central axis of the second detection coil 232.

[0038] In the support body 20, stress is applied in a direction in which the first plate 22 and the second plate 24 move apart or in a direction in which the first plate 22 and the second plate 24 move closer to each other. For this reason, as shown in FIG. 5, flaws propagate from ends 26a, 26b of the welded portion 26. Furthermore, flaws often propagate toward direction A, direction B, direction C, or direction D in the support body 20. Direction A is a direction (Z-axis direction in FIG. 5) perpendicular to the in-plane direction of the first plate 22 (XY in-plane direction in FIG. 5). Direction B is a direction (X-axis direction in FIG. 5) perpendicular to the in-plane direction of the second plate 24 (YZ in-plane direction in FIG. 5). Direction C is a direction that forms a 45° angle with the in-plane direction of the first plate 22. Direction D is a direction that forms a 45° angle with the in-plane direction of the second plate 24.

[0039] When an inspection technician scans the probe 110 over the support 20, the probe 110 scans the first plate 22, the weld 26, and the second plate 24 in that order, or the second plate 24, the weld 26, and the first plate 22 in that order.

[0040] Here, when contact surface 214 of probe 110 contacts first plate 22 and inclined surface 216 contacts welded portion 26, direction 222a of central axis of first detection coil 222 can be made to roughly coincide with direction A. Furthermore, since angle β formed between the central axis of first detection coil 222 and the central axis of second detection coil 232 is 45°, when direction 222a of central axis of first detection coil 222 is made to coincide with direction A, direction 232a of central axis of second detection coil 232 can be made to coincide with direction C.

[0041] Similarly, when contact surface 214 of probe 110 contacts second plate 24 and inclined surface 216 contacts welded portion 26, direction 222a of central axis of first detection coil 222 can be made to roughly coincide with direction D. Furthermore, since angle β formed between the central axis of first detection coil 222 and the central axis of second detection coil 232 is 45°, when direction 222a of central axis of first detection coil 222 is made to coincide with direction D, direction 232a of central axis of second detection coil 232 can be made to coincide with direction B.

[0042] Therefore, with the contact surface 214 in contact with the first plate 22, the probe 110 according to this embodiment can align a flaw that has propagated in direction A with the direction 222a of the central axis of the first detection coil 222, and can align a flaw that has propagated in direction B with the direction 232a of the central axis of the second detection coil 232. Similarly, with the contact surface 214 in contact with the second plate 24, the probe 110 according to this embodiment can align a flaw that has propagated in direction D with the direction 222a of the central axis of the first detection coil 222, and can align a flaw that has propagated in direction C with the direction 232a of the central axis of the second detection coil 232.

[0043] [Control Unit 120] 6 is a functional block diagram of the control unit 120 according to this embodiment. As shown in FIG. 6, the control unit 120 includes an excitation unit 310, a detection unit 330, an A / D converter 340, a central control unit 360, a memory 370, and a display device 380.

[0044] The excitation unit 310 applies an AC current to the first excitation coil 224 and the second excitation coil 234, and generates an induced current in the object 10 (support 20) under test by electromagnetic induction. In this embodiment, the excitation unit 310 includes a function generator 312 and an amplifier 314.

[0045] Function generator 312 (indicated by "F / G" in FIG. 6) generates an AC signal of a first frequency and an AC signal of a second frequency different from the first frequency. The AC signals from function generator 312 are output to amplifier 314 and detection unit 330.

[0046] The amplifier 314 (denoted by "B / P" in FIG. 6) amplifies the AC signal of the first frequency generated by the function generator 312 and applies the AC current to the first excitation coil 224. Similarly, the amplifier 314 amplifies the AC signal of the second frequency generated by the function generator 312 and applies the AC current to the second excitation coil 234. This generates an induced current in the object 10 under test due to electromagnetic induction. The amplifier 314 is, for example, a bipolar power supply.

[0047] The detection unit 330 is configured with, for example, a lock-in amplifier (indicated by "L / I" in FIG. 6). The detection unit 330 extracts the frequency component of the current applied to the first excitation coil 224 (a first detection signal based on an induced current) from the AC voltage detected by the first detection coil 222 based on an AC signal (a reference signal) of a first frequency output from the function generator 312. Similarly, the detection unit 330 extracts the frequency component of the current applied to the second excitation coil 234 (a second detection signal based on an induced current) from the AC voltage detected by the second detection coil 232 based on an AC signal (a reference signal) of a second frequency output from the function generator 312.

[0048] The A / D converter 340 (denoted by "A / D" in FIG. 6) converts the output value (analog signal) of the detection unit 330 into a digital signal.

[0049] The central control unit 360 is configured by a semiconductor integrated circuit including a CPU (central processing unit). The central control unit 360 reads programs and parameters for operating the CPU from the ROM. The central control unit 360 manages and controls the entire eddy current flaw detection apparatus 100 in cooperation with RAM as a work area and other electronic circuits.

[0050] The memory 370 is composed of a ROM, a RAM, a flash memory, a HDD, etc. The memory 370 stores programs and various data used by the central control unit 360.

[0051] The display device 380 is configured with a liquid crystal display, an organic EL (Electro Luminescence) display, or the like.

[0052] In this embodiment, the central control unit 360 also functions as a determination unit 362 and a notification unit 364 .

[0053] The determination unit 362 determines whether or not there is a flaw based on the signal strength of the first detection signal detected through the first detection coil 222 and the signal strength of the first detection signal detected through the second detection coil 232. The determination of whether or not there is a flaw by the determination unit 362 will be described in detail later.

[0054] When the determining unit 362 determines that there is a flaw, the notifying unit 364 causes the display device 380 to display a message to that effect.

[0055] [Flaw detection method] Next, a flaw detection method for detecting flaws in the object 10 to be detected using the eddy current flaw detection device 100 will be described. Fig. 7 is a flowchart showing the processing flow of the flaw detection method according to this embodiment. As shown in Fig. 7, the flaw detection method according to this embodiment includes a current application step S110, a signal detection step S120, a first determination step S130, a first notification step S140, a second determination step S150, a second notification step S160, a third determination step S170, and a third notification step S180. Each step will be described below.

[0056] [Current application process S110] The current application step S110 is a step in which the excitation unit 310 applies an AC current to the first excitation coil 224 and the second excitation coil 234, thereby generating an induced current in the object to be detected 10 by electromagnetic induction. As described above, the excitation unit 310 applies an AC current of a first frequency to the first excitation coil 224, and applies an AC current of a second frequency to the second excitation coil 234.

[0057] [Signal detection step S120] The signal detection step S120 is a step in which the detection unit 330 detects a second detection signal S2 based on the induced current through the second detection coil 232 while detecting a first detection signal S1 based on the induced current through the first detection coil 222. In this embodiment, the detection unit 330 simultaneously detects the first detection signal S1 and the second detection signal S2.

[0058] Fig. 8 is a diagram illustrating a detection signal when the contact surface 214 is in contact with the object 10 under test and there is no flaw. Fig. 9 is a diagram illustrating a detection signal when the contact surface 214 is in contact with the object 10 under test and there is a flaw.

[0059] As shown in FIGS. 8 and 9, the detection signal is represented by a Lissajous waveform. The Lissajous waveform indicates fluctuations in the sine component (amplitude, vertical axis in FIGS. 8 and 9) and cosine component (phase, horizontal axis in FIGS. 8 and 9) of the detection signal with respect to the excitation voltage. In the eddy current flaw detector 100, the probe 110 is brought into contact with a standard test piece for calibration, and adjustment (origin correction) is performed so that the reference point of the Lissajous waveform becomes the origin (0,0). Then, after the origin correction is performed, flaw detection is performed using the eddy current flaw detector 100. Therefore, the reference point of the Lissajous waveform becomes the origin (0,0). In the Lissajous waveform, the sine component and cosine component of the detection signal fluctuate with the origin as the reference point.

[0060] As shown in Fig. 8, when there is no flaw, the fluctuation range of the sine component of the detection signal is approximately zero. On the other hand, as shown in Fig. 9, when there is a flaw, the fluctuation range of the sine component of the detection signal becomes larger than when there is no flaw.

[0061] Therefore, the detection unit 330 determines the fluctuation range of the sine component of the detection signal as the signal strength Sc of the detection signal. Note that the signal strength Sc of the detection signal is the value from the minimum value (negative peak) to the maximum value (positive peak) of the vertical axis (sine component) of the Lissajous waveform.

[0062] [First judgment step S130] 7, the determination unit 362 determines whether the signal strength Sc of the first detection signal S1 is equal to or greater than a threshold value Th and whether the signal strength Sc of the second detection signal S2 is equal to or greater than a threshold value Th. The threshold value Th is determined in advance based on the depth of the flaw that is desired to be detected.

[0063] If it is determined that the signal strength Sc of the first detection signal S1 is equal to or greater than the threshold value Th and that the signal strength Sc of the second detection signal S2 is equal to or greater than the threshold value Th (YES in S130), the determination unit 362 proceeds to a first notification step S140. On the other hand, if it is determined that either or both of the signal strength Sc of the first detection signal S1 and the signal strength Sc of the second detection signal S2 are not equal to or greater than the threshold value Th (NO in S130), the determination unit 362 proceeds to a second determination step S150.

[0064] [First notification step S140] The notification unit 364 causes the display device 380 to display a message stating "A flaw has been detected or lift-off has occurred."

[0065] Even if there is no flaw, when the contact surface 214 and the object 10 are separated, noise (lift-off signal) occurs, causing the sine component of the detection signal to fluctuate. Since the separation distance between the first detection coil 222 and the object 10 and the separation distance between the second detection coil 232 and the object 10 are substantially equal, the lift-off signal is detected through both the first detection coil 222 and the second detection coil 232.

[0066] Furthermore, even if the contact surface 214 is in contact with the object 10 to be detected, if the flaw is larger than a predetermined size, a detection signal based on the flaw will be detected through both the first detection coil 222 and the second detection coil 232.

[0067] Therefore, when the signal strength Sc of the first detection signal S1 and the signal strength Sc of the second detection signal S2 are equal to or greater than the threshold value Th (YES in S130), the alarm unit 364 notifies that a flaw has been detected or that the noise is due to the separation (lift-off) between the contact surface 214 and the object 10 to be detected.

[0068] When the first notification step S140 is executed, the inspection engineer checks whether or not there is a visual defect. If the inspection engineer does not find any defects, the current application step S110 to the first determination step S130 may be repeated again.

[0069] Then, after the inspection engineer has finished checking for the presence or absence of flaws, the inspection engineer moves the probe 110 and repeats the process from the current application step S110.

[0070] [Second judgment step S150] The determination unit 362 determines whether the signal strength Sc of the first detection signal S1 is equal to or greater than the threshold value Th, or whether the signal strength Sc of the second detection signal S2 is equal to or greater than the threshold value Th.

[0071] If it is determined that either the signal strength Sc of the first detection signal S1 or the signal strength Sc of the second detection signal S2 is equal to or greater than the threshold value Th (YES in S150), the determination unit 362 proceeds to a second notification step S160. On the other hand, if it is determined that the signal strength Sc of the first detection signal S1 or the signal strength Sc of the second detection signal S2 is not equal to or greater than the threshold value Th (NO in S150), the determination unit 362 proceeds to a third determination step S170.

[0072] [Second notification process S160] The notification unit 364 causes the display device 380 to display a message indicating that a flaw has been detected.

[0073] As described above, the distance between the first detection coil 222 and the object 10 to be detected is substantially equal to the distance between the second detection coil 232 and the object 10 to be detected, so the lift-off signal is detected through both the first detection coil 222 and the second detection coil 232.

[0074] However, a detection signal based on a flaw that is equal to or smaller than a predetermined size will be detected through either the first detection coil 222 or the second detection coil 232.

[0075] Therefore, the notification unit 364 notifies that a flaw has been detected when it determines that either the signal strength Sc of the first detection signal S1 or the signal strength Sc of the second detection signal S2 is equal to or greater than the threshold value Th (YES in S150). In addition, the notification unit 364 notifies that a flaw has been detected when it determines that the difference between the signal strength Sc of the first detection signal S1 and the signal strength Sc of the second detection signal S2 is equal to or greater than a predetermined value (YES in a third determination step S170 described later).

[0076] This allows the notification unit 364 to notify of flaws with high accuracy.

[0077] Then, the inspection engineer moves the probe 110 and repeats the process from the current application step S110. [Third judgment step S170] The determination unit 362 determines whether the difference between the signal strength Sc of the first detection signal S1 and the signal strength Sc of the second detection signal S2 is equal to or greater than a predetermined value.

[0078] If it is determined that the difference between the signal strength Sc of the first detection signal S1 and the signal strength Sc of the second detection signal S2 is equal to or greater than a predetermined value (YES in S170), the determination unit 362 proceeds to the second notification step S160. On the other hand, if it is determined that the difference between the signal strength Sc of the first detection signal S1 and the signal strength Sc of the second detection signal S2 is not equal to or greater than the predetermined value (NO in S170), the determination unit 362 proceeds to the third notification step S180.

[0079] [Third notification process S180] The notification unit 364 causes the display device 380 to display a message indicating that the body is "healthy (no flaws)."

[0080] Then, the inspection engineer moves the probe 110 and repeats the process from the current application step S110.

[0081] As described above, the eddy current flaw detector 100 according to this embodiment includes the first detector coil 222 and the second detector coil 232. As a result, the eddy current flaw detector 100 can detect flaws in various directions and depths simply by scanning the probe 110 along the object 10 (support 20) under test without changing the angle of the probe 110. Therefore, flaws can be detected regardless of the skill level of the inspection technician, and it becomes possible to prevent flaws from being overlooked.

[0082] Although the embodiments have been described above with reference to the accompanying drawings, it goes without saying that the present disclosure is not limited to the above-described embodiments. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0083] For example, in the above-described embodiment, the probe 110 includes the first detector coil 222 and the second detector coil 232. However, the probe 110 may include three or more detector coils. For example, the probe 110 may include a first detector coil, a second detector coil, and a third detector coil. In this case, the central axis of the first detector coil is perpendicular to the contact surface 214. The angle between the central axis of the first detector coil and the central axis of the second detector coil is, for example, 45°, and the angle between the central axis of the first detector coil and the central axis of the third detector coil is, for example, 90°. Furthermore, the angle between the central axis of the first detector coil and the central axis of the second detector coil is, for example, 30°, and the angle between the central axis of the first detector coil and the central axis of the third detector coil is, for example, 60°.

[0084] In the above embodiment, the probe 110 includes the first excitation coil 224 and the second excitation coil 234. However, there is no limit to the number of excitation coils. For example, the probe 110 may include one excitation coil, or three or more excitation coils.

[0085] Furthermore, in the above embodiment, the case where the central axis of first detection coil 222 is perpendicular to contact surface 214 (angle α is 90°) has been exemplified. However, the central axis of first detection coil 222 may be approximately perpendicular to contact surface 214. "Approximately perpendicular" means that the angle α formed between the central axis of first detection coil 222 and contact surface 214 is within a range of 90°±1°, that is, a range of 89° to 91°.

[0086] In the above embodiment, the threshold value Th of the signal strength Sc of the first detection signal S1 and the threshold value Th of the signal strength Sc of the second detection signal S2 are equal to each other. However, the threshold value Th of the signal strength Sc of the first detection signal S1 and the threshold value Th of the signal strength Sc of the second detection signal S2 may be different.

[0087] In the above embodiment, a steel bridge is used as an example of the object 10 to be inspected. However, the object 10 to be inspected only needs to include at least the first plate 22, the second plate 24, and the welded portion 26. In other words, the object 10 to be inspected may have a corner weld such as a T-joint. The object 10 to be inspected may be, for example, the wall surface of a steel bridge or a plant.

[0088] This disclosure can contribute, for example, to Goal 12 of the Sustainable Development Goals (SDGs), "Ensure sustainable consumption and production patterns." [Explanation of symbols]

[0089] 10. Object to be inspected 100 Eddy current flaw detection equipment 210 Probe body 214 Contact surface 222 First detection coil 224 First excitation coil (excitation coil) 232 Second detection coil 234 Second excitation coil (excitation coil) 310 Excitation section 330 Detector

Claims

1. A probe body having a contact surface with an object to be inspected, in which a first plate and a second plate are joined by a weld; an excitation coil provided in the probe body; a first detection coil provided in the probe body, the first detection coil having a central axis substantially perpendicular to the contact surface; a second detection coil provided in the probe body and having a central axis that forms an acute angle with the central axis of the first detection coil; an excitation unit that applies an AC current to the excitation coil and generates an induced current in the object to be detected by electromagnetic induction; a detection unit that detects a second detection signal based on the induced current through the second detection coil while detecting a first detection signal based on the induced current through the first detection coil; Equipped with An eddy current flaw detection device configured to be able to detect flaws that may occur in the object to be detected and that extend in a first direction, and flaws that extend in a second direction different from the first direction.

2. The eddy current flaw detector according to claim 1 , wherein the first detection coil and the second detection coil are provided between the excitation coil and the contact surface.

3. The eddy current flaw detector according to claim 1 or 2, wherein the second detection coil has a central axis that forms an angle of 35° or more and 55° or less with respect to the central axis of the first detection coil.

4. A flaw detection method using an eddy current flaw detection device comprising: a probe body having a contact surface with an object to be detected, in which a first plate and a second plate are joined by a weld; an excitation coil provided in the probe body; a first detection coil provided in the probe body, the central axis of which is approximately perpendicular to the contact surface; and a second detection coil provided in the probe body, the central axis of which forms an acute angle with the central axis of the first detection coil, and which is capable of detecting flaws that may occur in the object to be detected, the flaws extending in a first direction and flaws extending in a second direction different from the first direction, applying an alternating current to the excitation coil to generate an induced current in the object to be detected by electromagnetic induction; detecting a second detection signal based on the induced current through the second detection coil while detecting a first detection signal based on the induced current through the first detection coil; a step of notifying that there is a flaw when a difference between the signal strength of the first detection signal and the signal strength of the second detection signal is equal to or greater than a predetermined value; A flaw detection method comprising:

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