Leakage flux detection probe

Abstract

To provide a leakage flux inspection probe capable of detecting a crack extending from a weld toe to a column base material of a metal column at an early stage.SOLUTION: A leakage flux inspection probe 10 comprises a magnetic sensor 15 provided in a central portion of a U-shaped magnetized core 11 and a cubic sensor case 13 for housing the U-shaped magnetized core 11, where the U-shaped magnetized core 11 is diagonally placed in the sensor case 13 such that the magnetic sensor 15 is positioned near an edge of the sensor case 13.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a leakage magnetic flux inspection probe and a crack evaluation system, and particularly to a leakage magnetic flux inspection probe and a crack evaluation system capable of detecting cracks at an initial stage.

Background Art

[0002] Conventionally, inspections at sites where damage including cracks in metal columns is expected mainly rely on visual inspections. As a result of visual inspections, when cracks are suspected, a penetration test or a magnetic particle test is carried out at the relevant site to confirm the presence of cracks. In any non-destructive test, it is necessary to remove coatings, plating, etc. in advance. Also, in visual inspections, the inspection results may be affected by the experience and skills of the inspector, and it may be difficult to detect cracks from above the coating film.

[0003] FIGS. 10(A) to 10(D) are diagrams showing a site where crack generation in a metal column is suspected and its specific position. FIG. 10(A) is a diagram showing a crack 27 in the axial direction of the welded part, FIG. 10(B) is a diagram showing a crack 28 in the circumferential direction of the welded part, FIG. 10(C) is a cross-sectional view showing a cross-section in the axial direction of the welded part shown in FIGS. 10(A) and 10(B), and FIG. 10(D) is a cross-sectional view showing a cross-section in the circumferential direction. Referring to FIGS. 10(A) to 10(D), cracks 27 and 28 occur near the welded part 30 between the metal column 125 and the rib 29. The cracks 27 and 28 include cracks that occur along the welded stop end (cracks that do not progress to the column base material) and cracks that occur in the column plate thickness direction (cracks that progress to the column base material). In the figure, the occurrence direction is also shown at the site where crack generation is expected. Among these, in the leakage magnetic flux inspection probe, cracks at an initial stage that have progressed from the welded stop end to the column base material part are the detection targets.

[0004] Also, an apparatus for inspecting cracks in a conventional welded part is disclosed, for example, in Japanese Patent Application Laid-Open No. 2019-20273 (Patent Document 1).

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-20273 (Abstract, etc.) [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Figure 11(A) is a perspective view showing a typical leakage flux inspection probe 110, and Figure 11(B) shows the typical leakage flux inspection probe 110 detecting the presence of a crack 121 in an object under inspection, where a protruding portion 118 has been welded. Referring to Figures 11(A) and 11(B), the typical leakage flux inspection probe 110 includes a U-shaped magnetization core 111 housed vertically in a cubic sensor case 113, and a magnetization coil 112 wound around the center of the U-shaped magnetization core 111, with a rectangular magnetic sensor 115 formed in the center of the U-shaped magnetization core 111 to detect the crack.

[0007] Figure 12 shows an image illustrating the detection of a crack extending laterally from the end of a fillet weld 120 using the leakage flux inspection probe 110 described in Figure 11. Figure 12(A) shows a case where the crack is short and cannot be detected by the magnetic sensor 115, while Figure 12(B) shows a case where the crack 121 is long and can be detected by the magnetic sensor 115.

[0008] Referring to Figure 12(A), a rectangular leakage flux inspection probe 110 is positioned in a plan view close to the weld toe 122 of the fillet weld 120, with its longitudinal direction aligned to detect the crack 121. Here, the magnetic sensor 115 that detects the crack 121 is located in the small rectangular central part of the inspection probe 110, and the area from the position of the rectangular leakage flux inspection probe 110 close to the weld toe 122 to the detection part of the magnetic sensor 115 becomes a dead zone 123 where the crack 121 cannot be detected. Therefore, if the length of the crack 121 is shorter than the dead zone 123, the crack 121 cannot be detected.

[0009] On the other hand, Figure 12(B) shows the case where the length of the crack 121 exceeds the dead zone 123. Referring to Figure 12(B), here the length of the crack 121 is longer than the dead zone 123, so this crack 121 becomes detectable.

[0010] Figure 13 shows a method for detecting cracks that have progressed from the weld toe to the base material of a metal column using a leakage flux inspection probe 110. Figure 13(A) shows the direction of movement of the leakage flux inspection probe 110, and Figure 13(B) shows the leakage flux density detected by the crack. Referring to Figures 13(A) and 13(B), the leakage flux inspection probe 110 is scanned along the rectangular electrical equipment opening 126 provided in the metal column 125 and the weld toe 122 of the fillet weld 120 of the base plate rib 124, the surface of the material is magnetized with a magnetization coil 112, and the magnetic flux leaking from the crack on the material surface is detected by a magnetic sensor 115. At this time, the north pole 116 and south pole 117 of the U-shaped magnetization core 111, which sandwiches the central magnetic sensor 115, are moved along the opening 126 for electrical equipment and the weld toe 122 of the fillet weld 120 of the base plate rib.

[0011] Furthermore, the number of turns in the conventional magnetization coil 112 is optimal for each type of test object, and for this particular test object, 300 or more turns was optimal.

[0012] In other words, the crack 121 is detected when the magnetic sensor 115 passes over the crack 121 and detects the leakage magnetic flux (Figure 13(B)). If the length of the crack 121 is short (Figure 12(A)), the crack cannot be detected, so in order to detect shorter cracks in the initial stages, it was necessary to move the magnetic sensor 115 closer to the end of the sensor case 113 to reduce the dead zone.

[0013] Generally, the magnetization core 111 of the leakage flux inspection probe 110 uses a U-shaped core perpendicular to the surface to be inspected. Increasing the number of turns of the magnetization coil 112 to improve the signal-to-noise ratio physically increases the distance from the end of the sensor case 113 to the magnetic sensor 115, increasing the dead zone. Since it is not possible to reduce the distance from the end of the sensor case 113 to the magnetic sensor 115, there was a problem in that it was not possible to detect cracks 121 that had progressed from the weld toe 122 of the metal column 125 to the column base material in an early stage.

[0014] This invention was made to solve the above-mentioned problems, and aims to provide a leakage magnetic flux inspection probe that can detect cracks that have progressed from the weld toe of a metal column to the column base material at an early stage.

[0015] Another objective of this invention is to develop a crack evaluation system that can determine cracks in the parts of a metal column that could lead to its collapse, without being affected by the experience or skill of the inspector. [Means for solving the problem]

[0016] The leakage flux inspection probe according to this invention comprises a magnetic sensor provided in the center of a U-shaped magnetization core, a rectangular parallelepiped case housing the U-shaped magnetization core, and the U-shaped magnetization core positioned diagonally within the case such that the magnetic sensor is located near the end of the case.

[0017] Preferably, the number of turns of the magnetization coil is 300 or more.

[0018] More preferably, the end of the case on the side where the magnetic sensor is located is chamfered.

[0019] In another aspect of the present invention, the crack evaluation system includes steps of detecting a crack with a leakage magnetic flux inspection probe, quadrature demodulating the detection data, adjusting the X-axis component to be zero when a certain amount of the Y-axis component is detected, detecting a phase based on the adjusted detection data, and determining a crack depth based on the detected phase.

[0020] Preferably, the certain amount of the Y-axis component is 0.2V.

Advantages of the Invention

[0021] According to the present invention, since it has a magnetizing core arranged obliquely, the magnetic sensor can be moved closer to the case end without depending on the number of turns of the magnetizing coil, and the dead zone can be reduced.

[0022] As a result, a crack that has progressed from the welded end of the metal column to the column base material part can be detected at an initial stage.

Brief Description of the Drawings

[0023] [Figure 1] It is a perspective view showing an improved leakage magnetic flux inspection probe according to an embodiment of the present invention. [Figure 2] It is a diagram showing an image of crack detection when using the improved leakage magnetic flux inspection probe. [Figure 3] It is a diagram showing a leakage magnetic flux inspection probe. [Figure 4] It is a diagram showing the apparatus main body. [Figure 5] It is a block diagram showing the configuration of the crack evaluation system. [Figure 6] It is a flowchart showing the operation of the crack evaluation system. [Figure 7] It is a diagram showing a method for evaluating crack depth. [Figure 8] It is a diagram showing the X-axis origin correction function. [Figure 9] It is a diagram showing an example of a display screen of measurement results. [Figure 10]This figure shows examples of crack formation in metal pillars. [Figure 11] This is a diagram showing a typical leakage flux detection probe. [Figure 12] This figure shows an image of crack detection using a typical magnetic flux leakage detection probe. [Figure 13] This figure shows an image of a crack inspection system using a magnetic flux leakage detection probe. [Modes for carrying out the invention]

[0024] Hereinafter, one embodiment of this invention will be described with reference to the drawings. First, in this embodiment, a leakage flux inspection probe having a diagonally arranged magnetization core (hereinafter referred to as a "diagonal magnetization core") is used, so this leakage flux inspection probe having a diagonal magnetization core will be described.

[0025] Figure 1(A) is a perspective view showing a leakage flux inspection probe (inclined probe) 10, which is an inspection probe according to one embodiment of the present invention, and Figure 1(B) is a diagram showing the state in which a crack 121 originating from the weld toe 122 of a fillet weld 120 is detected using the leakage flux inspection probe 10.

[0026] First, referring to Figure 1(A), the leakage flux inspection probe 10 is modified by tilting the magnetization core 11 located inside the leakage flux inspection probe 10, thereby bringing the magnetic sensor 15 closer to the edge of the sensor case 13 than in the conventional inspection probe 110. Specifically, the leakage flux inspection probe 10 includes an angled magnetization core 11 housed in a cubic sensor case 13, the U-shaped magnetization core 11 includes a magnetization coil 12 wound around its center, and a rectangular magnetic sensor 15 formed in the center of the U-shaped magnetization core 11 detects cracks.

[0027] In the leakage flux inspection probe 10 having an angled magnetization core 11, the U-shaped magnetization core is positioned at an angle such that the detection part of the magnetic sensor 15 is located in the center near one side of the bottom of the sensor case 13.

[0028] Furthermore, as shown in Figure 1(B), the sensor case 13 of the leakage flux inspection probe 10 has a predetermined thickness at the end where the magnetic sensor 15 is located. In order to bring the magnetic sensor 15 as close as possible to the weld toe 122, which is the measurement area, the end of the sensor case 13 on the side where the magnetic sensor 15 is located is chamfered as shown by angle α in the figure. Here, it is preferable that α = 30° or less.

[0029] By arranging them in this way, even if the magnetization coil 12 wound around the center of the U-shaped magnetization core 11 becomes larger, the leakage flux inspection probe 10 can be accommodated within the sensor case 13.

[0030] In this embodiment, the number of turns of the magnetization coil 12 is 300 or more.

[0031] Next, we will describe the process of detecting cracks using the leakage flux inspection probe 10. Here, we will describe the detection of early-stage cracks originating from the weld toe 122, which are difficult to measure. Referring to Figure 1(B), the leakage flux inspection probe 10 is positioned close to the weld toe 122. At this time, the magnetized core 11, which is positioned at an angle, is positioned close to the weld toe 122.

[0032] Figure 2 shows an image of crack detection in this embodiment. Referring to Figure 2, since the diagonally positioned magnetized core 11 is positioned close to the weld toe 122, the crack length a reaches the detection part of the magnetic sensor 15, and the detection part of the magnetic sensor 15 can detect the crack 21.

[0033] Next, a scanning jig for a leakage flux inspection probe will be described. Figure 3 shows the scanning jig 35, which houses the leakage flux inspection probe 10 shown in Figure 1, installed on a cylindrical inspection surface 40. Referring to Figure 3, the scanning jig 35 housing the leakage flux inspection probe 10 includes a probe holder 37 for holding the leakage flux inspection probe 10 and a main block 39. The main block 39 has a built-in magnet and can be attracted to the inspection surface 40.

[0034] Furthermore, the device includes a hand-tightening knob 36 for securing the leakage flux inspection probe 10 to the probe holder 37, and the main block 39 and the flux probe 10 are connected by a retaining spring 41 to press the probe holder 37 onto the inspection surface 40. The main block 39 is provided with a bearing 42 to move axially on the cylindrical inspection surface 40.

[0035] Although not shown in the diagram, as described above, the U-shaped magnetization coil is positioned diagonally so that the magnetic sensor is close to the welded area.

[0036] Next, the main body of the device will be described. Figure 4 shows the main body of the device 47. The main body of the device 47 can be used with both the leakage flux method and the eddy current method. The main body of the device 47 is common to both the leakage flux method and the eddy current method probes, and has a replacement port 48 for switching between the leakage flux inspection probe 10 and the eddy current inspection probe 17 for each type of inspection. A mobile phone 49 may also be used as a display unit. Here, the mobile phone 49 is shown mounted in the center of the main body of the device 47.

[0037] Next, a method for evaluating cracks using the leakage flux method will be described. Figure 7 shows a crack evaluation using the leakage flux method in this embodiment. Referring to Figure 7, by quadrature detection of the sensor output of the magnetic sensor of the leakage flux inspection probe, the lift-off noise during magnetic sensor scanning and the signal at the time of crack detection can be separated. In addition, the crack depth is evaluated by utilizing the fact that the phase differs depending on the crack depth. The specific evaluation method will be described later.

[0038] Here, "lift-off" refers to the separation or tilting of the magnetic sensor and the inspection surface, or the distance between the magnetic sensor and the inspection surface. The lift-off signal is the signal generated when the lift-off changes. Origin correction is performed while the magnetic sensor and the inspection surface are in contact, and a lift-off signal is generated when the magnetic sensor is separated from the inspection surface. Typically, the lift-off signal is adjusted to be horizontal to the X-axis direction.

[0039] Furthermore, lift-off noise refers to noise caused by lift-off occurring during leakage flux inspection probe scanning, and it is characterized by a fluctuation in the signal in the X-axis direction.

[0040] Next, the configuration of the measuring device 47 that performs X-axis origin correction when using a leakage flux inspection probe and its control details will be described. Figure 5 is a block diagram showing the configuration of the measuring device 47. Referring to Figure 5, the measuring device 47 includes a control unit 50 and a transceiver 56 connected to the control unit 50 that receives detection data from the leakage flux inspection probe 10 and the eddy current flaw detection probe 17 and transmits it to the control unit 50. The control unit 50 includes a CPU 51 that controls the entire measuring device, an interface 52, an input / output unit (I / O) 53, a memory 54 and a display unit 55.

[0041] Figure 6 is a flowchart showing the operation of the crack evaluation system performed by the CPU 51 of the control unit 50 shown in Figure 5. Referring to Figure 6, the crack evaluation system detects cracks with a leakage flux inspection probe and quadrature-detects the detected data (S11). This makes it possible to separate the lift-off noise during sensor scanning from the signal at the time of crack detection. In addition, the crack depth is evaluated by utilizing the fact that the phase differs depending on the crack depth. Specifically, since the lift-off signal is adjusted to be in the X-axis direction (0°), the crack signal has a Y-axis component and a phase difference occurs. However, if the crack depth is simply evaluated from the phase, the origin is shifted in the X-axis direction due to the lift-off noise generated during sensor scanning, making it impossible to accurately determine the phase. Therefore, here, it is determined whether or not a certain amount of Y-axis component is detected, and if a certain amount of Y-axis component is detected (YES in S12), the X-axis component is set to 0 (S13), and then the phase is determined (S14) to determine the crack depth (S15).

[0042] This S13 process is called the X-axis origin correction function. This X-axis origin correction function cancels the lift-off noise generated during sensor scanning, allowing for accurate phase determination and evaluation of crack depth.

[0043] Next, we will explain the specific evaluation. Figure 7 shows an example of an actual measurement. Referring to Figure 7, here the X-axis has a lift-off of 0°, a penetration of 25°, is 55° at d=0.5mm, is 50° at d=1.0mm, is 45° at d=2.0mm, and is 38° at d=4.0mm.

[0044] Next, the X-axis origin correction in this embodiment will be described. Figure 8 shows this correction method. Referring to Figure 8, lift-off noise 16 is generated as indicated by the arrow in the figure. However, if crack depth is simply evaluated from the phase, the origin is shifted in the X-axis direction due to the lift-off noise 16 generated during sensor scanning, making it impossible to accurately determine the phase.

[0045] This system determines whether the lift-off signal exceeds the threshold for X-axis origin correction shown by the dotted line in the figure, and corrects the X signal to 0 when it exceeds the threshold. In other words, we have developed an X-axis origin correction function that sets the X-axis component to 0 when a certain amount of Y-axis component is detected. The X-axis origin correction function cancels the lift-off noise 16 generated during sensor scanning, allowing for accurate determination of the phase, which is the Y-axis component, and evaluation of the crack depth.

[0046] Furthermore, this fixed amount of the Y-axis component is preferably 0.2V.

[0047] Next, an example of a display screen for measurement results will be described. Figure 9 shows the measurement results of a crack signal using the leakage flux method. When the phase of the crack signal obtained by the leakage flux method using a leakage flux inspection probe is set to be horizontal, the phase is approximately 25° to 55° depending on the crack depth. Therefore, a threshold is set using polar coordinates, signals other than the crack signal are removed, and the crack depth is estimated and evaluated from the phase difference.

[0048] Figure 9(A) is a graph showing the measurement results of a flat plate specimen in polar coordinates, Figure 9(B) is data showing the signal intensity for each crack depth, Figure 9(C) is data showing the X-axis component (solid line) and Y-axis component (dotted line), Figures 9(D) and 9(E) are diagrams showing the display results on the measuring device, Figure 9(D) is an example of the display of the data shown in Figure 9(A), and Figure 9(E) is a diagram showing the measurement results of Figures 9(B) and 9(C).

[0049] Referring to Figure 9(A), the solid lines in the figure show the measurement data, the dashed lines show the thresholds, and the dotted lines show the thresholds for X-axis origin correction. Below the dotted lines, a solid line along the X-axis shows the lift-off signal. In the figure, the numbers and the word "penetration" attached to the solid lines indicate the crack depth.

[0050] Refer to Figure 9(B), which shows the crack depth for each measurement data shown in Figure 9(A).

[0051] Furthermore, referring to Figure 9(D), the measuring device is equipped with a balance button and a start / stop button. The balance button is used to correct the origin, and the start / stop button is used to start and stop the measurement.

[0052] While embodiments of this invention have been described with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications can be made to the illustrated embodiments within the same scope as the present invention or within the scope of equivalents. [Industrial applicability]

[0053] According to this invention, cracks that have progressed from the weld toe of a metal column to the column base material can be detected at an early stage, making it advantageous to use as a magnetic flux leakage inspection probe. [Explanation of symbols]

[0054] 10. Leakage flux detection probe 11. Magnetized core 12. Magnetization coil 13 Sensor Case 14 Sensor board 15 Magnetic Sensor 16. Lift-off noise 20 Protrusion 29 Ribs 30 Welded section 121 Crack 122 Weld toe 125 Metal Pillar

Claims

1. A magnetic sensor is provided in the center of the U-shaped magnetization core, A rectangular parallelepiped sensor case housing the aforementioned U-shaped magnetization core, A leakage flux inspection probe comprising the U-shaped magnetization core positioned diagonally within the sensor case such that the magnetic sensor is located near the end of the sensor case.

2. The leakage flux inspection probe according to claim 1, wherein the number of turns of the magnetization coil is 300 or more.

3. The leakage flux inspection probe according to claim 1, wherein the end of the sensor case on the side where the magnetic sensor is located is chamfered.

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