Method and device for magnetic nondestructive inspection

Abstract

To provide a rapid magnetic nondestructive inspection method and the like that allow inspection accuracy to be secured although lift-off is increased.SOLUTION: In a magnetic nondestructive inspection method, an AC magnetic field is applied to an inspected object, and a leakage magnetic flux leaking from the inspected object is detected in order to detect flaws in a crack generated in a weld zone of the inspected object. In the magnetic nondestructive inspection method, a magnetic sensor probe in which a first magnetic pole part, a first magnetic sensor, a second magnetic sensor, and a second magnetic pole part are arranged in parallel in that order in a prescribed direction, is moved in the prescribed direction parallel to a welding line direction of the weld zone, in a lift-off state from the weld zone, a phase of a difference vector between a magnetic field vector detected with the first magnetic sensor, and a magnetic field vector detected with the second magnetic sensor is calculated, in order to specify a crack of the weld zone from information obtained by associating a phase of the calculated difference vector and a moving distance of the magnetic sensor probe.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a magnetic nondestructive testing method for detecting cracks occurring in a welded portion of an object to be tested by applying an AC magnetic field to the object to be tested and detecting leakage magnetic flux leaking from the object to be tested. [Background technology]

[0002] Eddy current testing and magnetic leakage flux testing are known as non-destructive magnetic methods for inspecting crack defects in steel structures. Eddy current testing generates eddy currents by applying an AC magnetic field to the object using an application coil. When there is a crack defect, the distribution of eddy currents becomes disrupted, causing a change in the secondary AC magnetic field generated by the eddy currents. This change is detected by a coil or magnetic sensor placed in the same location as the application coil.

[0003] On the other hand, magnetic leakage flux testing is a method in which a magnetic flux is introduced into the object and the magnetic flux leaking from the surface of the defect is detected by a coil or magnetic sensor placed at a different location from the point where the magnetic flux was introduced. A U-shaped yoke or similar is used to introduce the magnetic flux, forming a magnetic circuit between the object and the magnetic flux. Therefore, steel structures, which are magnetic bodies that can form a magnetic circuit, are the subject of inspection. The magnetic flux introduced here can be a DC magnetic field only, a DC and AC magnetic field combined, or an AC magnetic field only.

[0004] In general magnetic leakage flux testing, a large magnetic field is applied to the steel material being inspected, causing magnetic saturation, in order to increase the magnetic flux leaking from the object being inspected. However, applying a large magnetic field requires a large current to be passed through the application coil, which requires a large current source. This makes it unsuitable for field inspections at sites where steel structures are present. As an approach to miniaturizing the equipment, reports have been made on the use of highly sensitive magnetic sensors, such as magnetoresistive elements (MR elements), in the detection section, which can detect weak magnetic fields leaking even when a weak magnetic field is applied.

[0005] To make it easier to determine the location of defects in magnetic leakage flux testing, a method has been reported in which multiple magnetic sensors are used to perform detection processing and capture changes in the detection results.One known method involves arranging multiple magnetic sensors in a line, detecting the output of each magnetic sensor, and comparing the phase-adjusted parameters of the strength and phase of the magnetic field vector obtained with the location of the magnetic sensor to determine the location of the defect (see, for example, Patent Document 1).

[0006] In wide weld lines, the location of cracks is unknown. Therefore, a method of detecting cracks in welds generally involves swinging a magnetic sensor probe across the weld line in a direction perpendicular to the weld line, over a width wider than the weld line, to detect signal changes due to cracks (see, for example, Non-Patent Document 1).

[0007] In magnetic leakage flux testing, which involves swinging a magnetic sensor probe to inspect, the strength and phase of the signal are examined within the amplitude range where signal changes of both positive and negative polarities are generally obtained, and cracks are determined from these changes.Since information on the location and length of cracks is important in inspections, locations where abnormal signals are detected are generally marked with a marker or similar so that they can be identified later.

[0008] In steel structures, fatigue cracks generally occur frequently at welds, which are the joints between steel materials. Unlike smooth steel, welds have uneven surfaces due to the presence of weld beads. This causes problems with magnetic measurements, as lift-off fluctuates, resulting in changes in magnetic signal strength. Lift-off refers to the distance from the weld of the test object to the detection point.

[0009] This made it difficult to distinguish whether the signal change was due to a crack or simply to the bead shape. Furthermore, because the bead is uneven, it was not possible to bring the detector and weld into close contact, so it was necessary to increase the lift-off to stabilize the measurement. Recently, it has become common for anti-corrosion coatings (e.g., resin coatings) to be applied to welds, making it particularly necessary to increase the lift-off.

[0010] For example, the steel deck plates under expressways are structures over several tens of meters long, with deck plates reinforced with U-ribs and other elements, and have extremely long welds. Furthermore, the width of the road surface is supported by dozens of U-ribs, so there are an extremely large number of welds. For this reason, it takes time to inspect all of the long welds formed on steel structures, and rapid inspections are required. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-13087 [Patent Document 2] Japanese Patent Application Publication No. 2018-71983

[0012] [Non-Patent Document 1] "Crack detection for welded joint with surface coating using unsaturated AC magnetic flux leakage" IEEE Transactions on Magnetics, vol. 58, 6201205 (2022) Summary of the Invention [Problem to be solved by the invention]

[0013] The inventors conducted a test to detect cracks in the welded portion using the structure shown in FIG. 10 of Patent Document 2, that is, a yoke arranged in an arch shape between the steel deck plate and the U-rib. However, the input magnetic flux diffuses into the steel plate, reducing the amount of magnetic flux leaking from cracks in the weld, making it impossible to accurately detect cracks in the weld.In other words, because conventional magnetic leakage flux testing requires the yoke material to be in close contact with or close to the weld, there was a need for a magnetic leakage flux testing method that could accurately identify cracks while increasing the lift-off.

[0014] Furthermore, Patent Document 2 employs a method of inspection in which a detector is scanned in a direction perpendicular to the weld line, which does not allow for continuous measurement and therefore requires a long time for inspection.

[0015] An object of the present invention is to provide a rapid magnetic nondestructive inspection method and the like that can ensure inspection accuracy even when the lift-off is large. [Means for solving the problem]

[0016] In order to solve the above problems, the magnetic non-destructive testing method of the present invention is (1) a magnetic non-destructive testing method that applies an AC magnetic field to a test object and detects leakage magnetic flux leaking from the test object to detect cracks that have occurred in a welded portion of the test object, characterized in that a magnetic sensor probe having a first magnetic pole portion, a first magnetic sensor, a second magnetic sensor, and a second magnetic pole portion arranged in this order in a predetermined direction is lifted off the welded portion and moved in the predetermined direction parallel to the weld line direction of the welded portion, the phase of the difference vector between the magnetic field vector detected by the first magnetic sensor and the magnetic field vector detected by the second magnetic sensor is calculated, and cracks in the welded portion are identified from information linking the phase of this calculated difference vector with the movement distance of the magnetic sensor probe.

[0017] (2) The magnetic nondestructive testing method described in (1) above, characterized in that the magnetic sensor probe is supported by a non-magnetic lift-off adjustment adapter at a position lifted off from the weld.

[0018] (3) The magnetic nondestructive inspection method described in (2) above, characterized in that the test objects include a first test object and a second test object formed in a plate shape, the first test object is joined by the welded portion in a state where it is inclined relative to the second test object, and the lift-off adjustment adapter is not in contact with the welded portion and is housed between the first test object and the second test object in a state where it can move in the predetermined direction.

[0019] (4) The magnetic nondestructive inspection method according to (3) above, characterized in that the lift-off adjustment adapter has a trapezoidal cross section.

[0020] In order to solve the above problems, the magnetic nondestructive inspection device of the present invention is (5) a magnetic sensor probe having a first magnetic pole portion, a first magnetic sensor, a second magnetic sensor, and a second magnetic pole portion arranged in this order in a predetermined direction, a distance detection means for detecting the movement distance of the magnetic sensor probe, and an analysis means for detecting and analyzing signals output from the first magnetic sensor and the second magnetic sensor, and is a magnetic nondestructive inspection device that detects leakage magnetic flux leaking from the material under test to detect cracks that have occurred in a welded portion of the test piece, characterized in that when the lifted-off magnetic sensor probe is moved in the predetermined direction parallel to the weld line direction of the welded portion, the analysis means calculates the phase of the difference vector of the magnetic field vectors detected by the first magnetic sensor and the second magnetic sensor, and stores this calculated phase in association with the movement distance detected by the distance detection means.

[0021] (6) A magnetic nondestructive testing device according to (5) above, characterized in that it has a non-magnetic lift-off adjustment adapter for lifting off the magnetic sensor probe.

[0022] (7) A magnetic non-destructive testing device used for the test object described in (3) above, characterized in that the lift-off adjustment adapter has a trapezoidal cross section.

[0023] (8) A magnetic nondestructive testing device according to (5) or (6) above, characterized in that the first magnetic pole part is made up of a yoke and an application coil wound around the yoke, the second magnetic pole part is made up of a yoke and an application coil wound around the yoke, the application coils of the first magnetic pole part and the second magnetic pole part have opposite winding directions, the yoke of the first magnetic pole part is one end of an open-loop shaped yoke, and the yoke of the second magnetic pole part is the other end of the open-loop shaped yoke. [Effects of the Invention]

[0024] According to the present invention, it is possible to ensure inspection accuracy even when the lift-off is large, and to realize a rapid magnetic nondestructive inspection method. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a schematic diagram of a magnetic nondestructive inspection device adapted for use with a flat-plate-shaped object to be inspected. [Figure 2] FIG. 2 is an enlarged view of the magnetic sensor probe of FIG. [Figure 3] FIG. 10 is an explanatory diagram showing a method for determining the phase of a difference vector. [Figure 4] This is a schematic diagram of a magnetic non-destructive testing device compatible with U-ribs. [Figure 5] This is a modified example of FIG. [Figure 6] This is another modification of FIG. [Figure 7] This is another modification of FIG. [Figure 8] 10 is a graph showing changes in magnetic field vector strength, magnetic field vector phase, difference vector strength, and difference vector phase depending on the position. [Figure 9] 10 is a graph showing the relationship between the difference vector phase and the position when line scanning cracks (three locations) formed in a flat steel plate. [Figure 10] FIG. 10 is a graph showing the amount of phase change of the difference vector when the lift-off is changed in FIG. [Figure 11]10 is a graph showing the relationship between the difference vector phase and the position when line scanning cracks (three locations) formed in a welded portion of steel material. [Figure 12] This is a graph showing the relationship between the difference vector phase and position when line scanning cracks (three locations) formed in the welds of the U-rib and steel deck. [Figure 13] FIG. 13 is a graph showing the amount of phase change of the difference vector when the lift-off is changed in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.

[0027] (First embodiment) FIG. 1 is a schematic diagram of a magnetic nondestructive inspection device compatible with a flat-plate-shaped object to be inspected. FIG. 2 is an enlarged view of the magnetic sensor probe of FIG. 1. In these figures, the X-axis, Y-axis, and Z-axis are three axes that are perpendicular to one another, and the X-axis direction corresponds to the "predetermined direction" described in the claims. The object to be inspected 1-1 is flat-plate-shaped and is constructed by joining the side end faces of multiple steel materials together by welding (not shown). The weld line direction of this weld extends in the X-axis direction. The weld line is an imaginary line that represents the weld as a single line.

[0028] The leakage magnetic flux flaw detector is a device that detects cracks in welds by detecting leakage magnetic flux leaking from the test object 1-1, and includes a magnetic sensor probe 6, an AC current source 9 for an applied coil, a magnetic sensor circuit 10, and a signal analysis device 11.

[0029] The magnetic sensor probe 6 includes a yoke 2-1, an apply coil 3-1A, an apply coil 3-1B, a first magnetic sensor 4A, and a second magnetic sensor 4B, and these elements are housed in a fixed state in a housing box 30. Hereinafter, when there is no need to particularly distinguish between the apply coil 3-1A and the apply coil 3-1B, these will also be collectively referred to as the apply coil 3-1. Furthermore, when there is no need to particularly distinguish between the first magnetic sensor 4A and the second magnetic sensor 4B, these will also be collectively referred to as the magnetic sensor 4.

[0030] The yoke 2-1 is formed in a U-shape, with an application coil 3-1A wound around one end (left side in the figure) and an application coil 3-1B wound around the other end (right side in the figure). The application coils 3-1A and 3-1B are wound in opposite directions and are connected to an AC source 9 for the application coils. Known materials can be used for the yoke 2-1. The shape of the yoke 2-1 may be an open loop shape such as a U-shape, C-shape, or arc shape in addition to the U-shape, but a U-shape or a U-shape is preferred. The open loop shape means a shape in which both ends are open and not closed so as to straddle the magnetic sensor 4.

[0031] The yoke 2-1 and the application coil 3-1 cooperate to form a magnetic pole section (magnetic field application means) that applies an AC magnetic field to the welded portion of the test piece 1-1. For ease of explanation, the yoke 2-1 and application coil 3-1A on the left side of the figure will be referred to as the first magnetic pole section 20A, and the yoke 2-1 and application coil 3-1B on the right side of the figure will be referred to as the second magnetic pole section 20B. Furthermore, when there is no need to particularly distinguish between the first magnetic pole section 20A and the second magnetic pole section 20B, they will also be collectively referred to as the magnetic pole section 20. If inspection is possible even with a weak magnetic field (for example, if the inspection object 1-1 is a thin plate), the first magnetic pole portion 20A and the second magnetic pole portion 20B may each be configured with only an application coil.

[0032] The magnetic pole portion 20 and the welded portion are arranged side by side in the Z-axis direction. In other words, the inspection is performed with the magnetic pole portion 20 arranged directly above the welded portion. It is preferable that the welded portion and the magnetic pole portion are arranged so that their center lines are aligned in the same plane in the Z-axis direction, but they may be tilted at an angle of ±45° or less from the Z-axis direction. Also, a part of the magnetic pole portion 20 may be located away from directly above the welded portion.

[0033] The AC current source 9 for the apply coil also outputs a frequency signal of the AC current it is outputting to the signal analyzer 11 . The first magnetic sensor 4A and the second magnetic sensor 4B are provided between the first magnetic pole portion 20A and the second magnetic pole portion 20B, and the first magnetic sensor 4A, the second magnetic sensor 4B, and the second magnetic pole portion 20B are arranged in this order in the X-axis direction (corresponding to a predetermined direction). In other words, the direction in which the first magnetic pole portion 20A, the first magnetic sensor 4A, the second magnetic sensor 4B, and the second magnetic pole portion 20B are arranged is parallel to the direction of the weld line of the welded portion.

[0034] Any of a magnetoresistance element, a magneto-impedance element, a Hall element, a superconducting quantum interference element, etc. can be used for the magnetic sensor 4. The output of each magnetic sensor of the pair of magnetic sensors 4 is detected by a signal analyzer 11 using the signal of the AC current source for the application coil as a time reference signal. In other words, a sensor signal synchronized with the applied AC magnetic field is obtained from the magnetic sensor 4, and this sensor signal is delayed with respect to the applied magnetic field signal. This delayed time is expressed with the time of the applied magnetic field signal as the reference, and is expressed as the phase at the time of detection. The distance between the first magnetic sensor 4A and the second magnetic sensor 4B in the X-axis direction may be about 3 mm. Here, when the center of the gap between the first magnetic sensor 4A and the second magnetic sensor 4B is defined as X1 and the center of the yoke 2-1 in the X-axis direction is defined as X2, it is desirable that the positions of X1 and X2 in the X-axis direction be approximately the same. In this specification and the drawings, CH1 corresponds to the first magnetic sensor 4A, and CH2 corresponds to the second magnetic sensor 4B.

[0035] The magnetic sensor probe 6 is supported by a lift-off adjustment adapter 5-1 made of a flat, non-magnetic material. Wheels 7 are rotatably attached to the sides of the lift-off adjustment adapter 5-1. However, the wheels 7 may also be attached to the storage box 30. The lift-off adjustment adapter 5-1 is not particularly limited as long as it is made of a non-magnetic material, but it is preferable that it be made of a synthetic resin such as polyolefin, nylon, or fluororesin from the standpoint of easy handling of the device during inspection and compactness. When the wheels 7 come into contact with the upper surface of the test object 1-1, the lift-off adjustment adapter 5-1 is lifted off the test object 1-1. In other words, the magnetic sensor probe 6 supported by the lift-off adjustment adapter 5-1 is lifted off from the welded portion of the test object 1-1.

[0036] By rotating the wheel 7 around an axis extending in the Y-axis direction, the magnetic sensor probe 6 can be moved in the direction of the weld line (X-axis direction) while being lifted off from the object under test 1-1. The power means may be automatic, using an actuator or the like, or may be manual (the same applies to the second embodiment).

[0037] As described above, because the magnetic pole portion 20 and the weld are aligned in the Z-axis direction, the magnetic flux of the magnetic pole portion 20 can easily enter the weld directly, increasing the amount of magnetic flux leaking from cracks in the weld. Therefore, even if the lift-off is increased to avoid unevenness in the weld, sufficient inspection accuracy can be ensured. Furthermore, since the inspection is performed while moving the magnetic sensor probe 6 in the weld line direction (X-axis direction), crack detection can be performed continuously along the weld line.

[0038] The magnetic sensor probe 6 is further provided with a rotary encoder 8 as a distance detection means. The rotary encoder 8 moves together with the magnetic sensor probe 6 to detect the distance traveled from the starting point of the inspection, and outputs the detection result to a signal analyzer 11. That is, when the magnetic sensor probe 6 moves, the disk of the rotary encoder 8 rotates, thereby making it possible to detect the distance traveled.

[0039] However, the distance detection means is not limited to the rotary encoder 8, and other means may be used. For example, other means may be used to determine the movement distance of the magnetic sensor probe 6 by analyzing image data obtained from an imaging device placed near the magnetic sensor probe 6 to determine position coordinates. Alternatively, a highly accurate GPS may be installed in the magnetic sensor probe 6, and the movement distance may be determined based on position information transmitted from the GPS.

[0040] The magnetic sensor circuit 10 outputs the magnetic fields detected by the first magnetic sensor 4A and the second magnetic sensor 4B as electric signals to the signal analyzer 11. The signal analyzer 11 receives the electric signals and analyzes the in-phase component B x and quadrature component B y This processing can be achieved by analog processing using a lock-in amplifier, or digital processing using a fast Fourier transform (FFT).

[0041] In-phase component B x and the quadrature component B y The output signals of the first magnetic sensor 4A and the second magnetic sensor 4B can be expressed as magnetic field vectors B1 and B2, respectively. d =B2-B1, and calculate the X component of the difference vector (B dx ) and Y component (B dy) the intensity R and phase θ can be obtained (see Figure 3). By storing the phase θ of this difference vector in association with the movement distance detected by the rotary encoder 8, the position, length, etc. of the crack can be determined. The storage means may be a flash memory or a hard disk. Note that the number of peak values ​​obtained is not limited to one, and is the same as the number of cracks.

number

[0042] (Second embodiment) A second embodiment of the present invention will be described in detail with reference to the drawings. Elements having the same uses and functions as those of the first embodiment will be given the same reference numerals and detailed descriptions thereof will be omitted in some cases. FIG. 4 is a schematic diagram of a magnetic nondestructive inspection device compatible with U-ribs. The X-axis, Y-axis, and Z-axis are three mutually orthogonal axes, and unlike the first embodiment, the Y-axis corresponds to the "predetermined direction" described in the claims. The test objects include a first test object 1-2 and a second test object 1-3 formed in a plate shape, and the first test object 1-2 is joined to the second test object 1-3 by a weld M while being inclined relative to the second test object 1-3. The first test object 1-2 is typically a U-rib, and the second test object 1-3 is typically a steel deck for a road. The angle between the U-rib and the steel deck often exceeds 90 degrees (e.g., approximately 100 degrees). As such, in steel structures having welds, welding is often performed at angled locations.

[0043] As in the first embodiment, the first magnetic pole portion 20A, the first magnetic sensor 4A, the second magnetic sensor 4B, and the second magnetic pole portion 20B are arranged in this order in the Y-axis direction (weld line direction). The Y-axis direction in Fig. 2 corresponds to the X-axis direction (weld line direction) in Fig. 1.

[0044] The first magnetic pole portion 20A, the first magnetic sensor 4A, the second magnetic sensor 4B and the second magnetic pole portion 20B are housed in a fixed state in a storage box 30, and this storage box 30 is fixed to a lift-off adjustment adapter 5-1.

[0045] Here, since the surface of the welded portion M is uneven, it is necessary to ensure a large lift-off. Therefore, in this embodiment, the cross section of the lift-off adjustment adapter 5-1 is made trapezoidal so that the outer surface conforms to the first inspection object 1-2 and the second inspection object 1-3 while avoiding contact with the welded portion M, thereby increasing the lift-off. However, the cross section of the lift-off adjustment adapter 5-1 is not limited to a trapezoid, and may have any structure that avoids contact with the welded portion M and can "appropriately support" the magnetic sensor probe 6. For example, as shown in Figures 5 and 6, it may have a polygonal shape in which the area facing the welded portion M is retracted toward the side where the magnetic sensor probe 6 is located. Also, as shown in Figure 7, the lift-off adjustment adapter 5-1 may be formed by placing separated triangular prisms at both ends of the bottom of the storage box 30.

[0046] Here, "properly supported" means supporting the magnetic sensor probe 6 so that it does not move within the XZ plane (in other words, supporting the magnetic sensor probe 6 so that the postures of the first magnetic pole portion 20A, the first magnetic sensor 4A, the second magnetic sensor 4B, and the second magnetic pole portion 20B are maintained). In the illustrated example of FIGS. 4 to 6, the outer surface of the lift-off adjustment adapter 5-1 and the rotary encoder 8 are in contact with the second object under test 1-3, so the magnetic sensor probe 6 does not fall to the right in the drawings during inspection.

[0047] 4 to 6, at least a portion of the lift-off adjustment adapter 5-1 slides against the object under test during testing, causing frictional resistance. Therefore, to reduce the frictional resistance, it is desirable to construct the lift-off adjustment adapter 5-1 from a material with a low coefficient of friction or to apply a low-friction treatment (for example, coating with fluororesin) to the surface of the lift-off adjustment adapter 5-1.

[0048] However, the lift-off adjustment adapter 5-1 is not an essential element of the present invention. Since the technical idea of ​​the present invention is to perform crack detection while moving the magnetic sensor probe 6 in the direction of the weld line while increasing the lift-off, for example, by attaching rolling members such as wheels to the storage box 30 instead of the lift-off adjustment adapter 5-1, the magnetic sensor probe 6 may be moved in the direction of the weld line in a lift-off state.

[0049] 4, the tilt direction of the magnetic sensor probe 6 is indicated by an arrow T (hereinafter referred to as the arrangement direction T). The arrangement direction T is preferably approximately parallel to the bisector of the first device under test 1-2 and the second device under test 1-3. However, as long as an imaginary line drawn from the weld M in a direction parallel to the direction in which the bisector extends passes through part of the magnetic sensor 4, the magnetic flux of the magnetic pole portion 20 can be appropriately applied to the weld M, and therefore parallelism is not an essential requirement of the present invention. In other words, the arrangement direction T may be inclined with respect to the direction of the bisector.

[0050] The rotary encoder 8 fixed to the housing box 30 will not be described again.

[0051] By moving the magnetic sensor probe 6 in the Y-axis direction and storing the phase θ of the difference vector in association with the distance traveled detected by the rotary encoder 8, the position and size of the crack can be identified.

[0052] As described above, according to this embodiment, crack inspection can be continuously performed while increasing the lift-off, even for a weld M that is welded at an angle. Furthermore, as shown in Fig. 4 and other figures, by arranging the magnetic sensor probe 6 so as to face the weld M, the magnetic flux of the magnetic pole portion 20 can easily enter the weld M, so that inspection accuracy can be ensured even when the lift-off is increased.

[0053] Here, an adjustment means for adjusting the attitude (angle) and lift-off amount of the containing box 30 may be mounted on the magnetic sensor probe 6. This allows the attitude (angle) and lift-off amount of the containing box 30 to be appropriately set according to the shape of the object to be inspected. For example, the adjustment means can be realized by cooperation of an imaging device, a Lidar (Light Detection And Ranging) scanner that can optically detect the distance to the object to be inspected, the shape of the object, and a position (angle) sensor.

[0054] The present invention will be specifically described below with reference to examples. (First Example) Example 1 corresponds to the first embodiment. A slit was artificially formed in a steel plate with no welds, and the relationship between position and intensity or phase was investigated when line scanning was performed along the slit. Figure 8 shows the results, with the horizontal axis representing the position (travel distance) read by the rotary encoder. The vertical axis of Figure 8(a) represents the intensity of the magnetic field vector, the vertical axis of Figure 8(b) represents the phase of the magnetic field vector, the vertical axis of Figure 8(c) represents the intensity of the difference vector, and the vertical axis of Figure 8(d) represents the phase of the difference vector. The slit was positioned 30 mm from the starting point of the inspection, and the lift-off was 2 mm.

[0055] Referring to Figures 8(a) and 8(b), it can be seen that the intensity and phase of the magnetic field vector both showed maximum and minimum peak signals before and after the crack location, making it difficult to identify the crack location. The reason the intensity and phase waveforms of CH1 and CH2 are opposite is because the magnetic sensors are positioned symmetrically about the center of the yoke. Furthermore, it was completely impossible to identify the crack location from the intensity waveform of the difference vector. On the other hand, a waveform corresponding to the crack location was detected in the phase waveform of the difference vector, and it was found that the crack location and the peak position of the phase signal waveform coincided.

[0056] Furthermore, slit-shaped cracks were formed at three locations along a straight line on the unwelded steel plate. The crack lengths were 10 mm, 20 mm, and 30 mm, respectively. Figure 9 shows the phase change of the difference vector when line scanning was performed along this straight line. Referring to this figure, waveforms corresponding to each crack location were obtained, and it was found that the signal change width increased as the crack length increased, indicating that the crack length and signal change width corresponded. In this way, it was found that since phase changes corresponding to cracks could be obtained, each crack could be separated and identified, and since position information could also be obtained from the rotary encoder, it was possible to determine the location and size of the crack.

[0057] Furthermore, the effect of lift-off was also investigated. The amount of phase change corresponding to each crack length when lift-off was changed was investigated, and the results are shown in Figure 10. As the lift-off increases, signal attenuation increases and the phase signal-to-noise ratio deteriorates, so there is a limit to the lift-off, but it was found that for a 10 mm crack, the lift-off can be increased to about 10 mm. For a 20 mm long crack, the lift-off can be increased to about 14 mm. For a 30 mm long crack, the lift-off can be increased to about 18 mm.

[0058] The side edges of two steel plates were welded together, and cracks measuring 10 mm, 20 mm, and 30 mm were formed at three locations along the weld, as described above. The relationship between position and the phase of the difference vector was investigated by line scanning along the weld line direction. Figure 11 shows the results, with the vertical and horizontal axes defined as in Figure 9. Comparing this figure with Figure 9, the signal changes obtained were almost identical to those of a crack formed in a flat plate without welding. This indicates that the phase of the difference vector allows signal changes at the crack location to be obtained without being affected by the unevenness of the bead (weld). Thus, by using the phase of the difference vector of a pair of magnetic sensors, it was found that the crack signal could be obtained without being affected by the unevenness of the weld.

[0059] (Second Example) The second example corresponds to the second embodiment. The thickness of the specimen 1-2 (U-rib) was 6 mm, and the thickness of the specimen 1-3 (deck plate) was 12 mm. The angle between the U-rib and the deck plate was set to 100 degrees, and these U-rib and deck plate were welded together. As in the first example, cracks of lengths 10 mm, 20 mm, and 30 mm were formed in the weld. Using the lift-off adjustment adapter with a trapezoidal cross section shown in Figure 4, line scanning was performed along the weld line while maintaining the yoke inclination angle at 50 degrees. The lift-off was 10 mm. Figure 12 shows the results, with the vertical and horizontal axes defined in the same way as in Figure 11. Phase changes similar to those in Figure 11 were detected, demonstrating that cracks of all lengths could be properly detected.

[0060] For the second embodiment, the effect of lift-off was also investigated using the method described in the first embodiment. The results are shown in Figure 13. The definitions of the vertical and horizontal axes are the same as in Figure 10. For a 10 mm crack, it was found that lift-off could be increased to approximately 15 mm. For cracks with lengths of 20 mm and 30 mm, it was found that lift-off could be increased to approximately 20 mm.

[0061] From the above, it was found that the magnetic sensor probe of the present invention can be used for inspection even under high lift-off conditions, and can detect cracks in welds without being affected by the structure of the plate, angle, etc. It was also found that the location and length of a crack can be estimated from the phase of the difference vector between the outputs of the two magnetic sensors and the position information of the rotary encoder.

[0062] The present invention can be widely used to detect defects such as cracks in steel structures, and can be applied to a wide range of fields, particularly in detecting cracks in welds of steel structures such as bridges, buildings, factory plants, power generation facilities, and railways, which has previously been difficult to do. [Explanation of symbols]

[0063] 1-1 Test subject 1-2 First test object 1-3 Second test object 2-1 York 3-1 3-1A 3-1B Applied coil 4 Magnetic Sensors 4-1 First magnetic sensor 4-2 Second magnetic sensor 5-1 Lift-off adjustment adapter 6 Magnetic Sensor Probes 8 rotary encoders 9 AC current source for the applied coil 10 Magnetic sensor circuit 11 Signal analysis equipment 20 Magnetic pole part 20A First magnetic pole part 20B Second magnetic pole part

Claims

1. A magnetic nondestructive inspection method for detecting cracks occurring in a welded portion of an object to be inspected by applying an AC magnetic field to the object to be inspected and detecting leakage magnetic flux leaking from the object to be inspected, comprising: a magnetic sensor probe, in which a first magnetic pole portion, a first magnetic sensor, a second magnetic sensor, and a second magnetic pole portion are arranged in this order in a predetermined direction, is lifted off the welded portion and moved in the predetermined direction parallel to the weld line direction of the welded portion; calculating a phase of a difference vector between a magnetic field vector detected by the first magnetic sensor and a magnetic field vector detected by the second magnetic sensor; and identifying a crack in the welded portion from information linking the calculated phase of the difference vector with the moving distance of the magnetic sensor probe. A magnetic non-destructive testing method characterized by:

2. the magnetic sensor probe is supported by a non-magnetic lift-off adjustment adapter at a position where it is lifted off from the welded portion; 2. The magnetic nondestructive inspection method according to claim 1.

3. the test objects include a first test object and a second test object formed in a plate shape, the first object to be inspected is joined by the welded portion in a state inclined relative to the second object to be inspected, the lift-off adjustment adapter is housed between the first test object and the second test object in a state of being out of contact with the welded portion and movable in the predetermined direction; 3. The magnetic nondestructive inspection method according to claim 2.

4. The lift-off adjustment adapter has a trapezoidal cross section.

4. A magnetic nondestructive inspection method according to claim 3.

5. a magnetic sensor probe in which a first magnetic pole portion, a first magnetic sensor, a second magnetic sensor, and a second magnetic pole portion are arranged in this order in a predetermined direction; distance detection means for detecting the distance traveled by the magnetic sensor probe; an analysis means for detecting and analyzing signals output from the first magnetic sensor and the second magnetic sensor; A magnetic non-destructive inspection device for detecting a crack occurring in a welded portion of an object to be inspected by detecting leakage magnetic flux leaking from the object to be inspected, When the lifted-off magnetic sensor probe is moved in the predetermined direction parallel to the weld line direction of the weld, the analysis means calculates the phase of a difference vector between the magnetic field vectors detected by the first magnetic sensor and the second magnetic sensor, and stores the calculated phase in association with the movement distance detected by the distance detection means. A magnetic non-destructive testing device characterized by:

6. a non-magnetic lift-off adjustment adapter for lifting off the magnetic sensor probe; 6. A magnetic nondestructive inspection device according to claim 5.

7. A magnetic non-destructive inspection device used for the object to be inspected according to claim 3, The lift-off adjustment adapter has a trapezoidal cross section.

7. A magnetic nondestructive inspection device according to claim 6.

8. the first magnetic pole portion comprises a yoke and an application coil wound around the yoke, the second magnetic pole portion comprises a yoke and an application coil wound around the yoke, the application coils of the first magnetic pole portion and the second magnetic pole portion are wound in opposite directions, the yoke of the first magnetic pole portion is one end of an open loop-shaped yoke, and the yoke of the second magnetic pole portion is the other end of the open loop-shaped yoke; 7. A magnetic nondestructive inspection device according to claim 5 or 6.

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