JP3748852B2 - Magnetic flaw detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention applies a magnetic field to a device under test by an exciting coil, and reduces the thickness of piping material due to cracks existing inside the device under test, pinhole defects generated in welds, corrosion, etc. The present invention relates to a magnetic flaw detector that detects an internal magnetic field affected by an internal defect such as the above, and detects a defect of a device under test.
[0002]
[Prior art]
Internal defects such as cracks existing inside the DUT, pinhole defects generated in welds, etc., pipe wall thickness reduction due to corrosion, etc. when a magnetic field is applied to the DUT by the excitation coil In a magnetic flaw detector that detects the internal magnetic field affected by the magnetic force or the electromotive force generated in the pickup coil, not only the presence of a defect but also the position of the defect and the depth of the defect are detected. It is required to specify.
[0003]
Further, in such a magnetic flaw detector, a noise magnetic field is generated due to a local magnetic characteristic change in the DUT, a disturbance in the magnetic field distribution caused by unevenness, a disturbance in the magnetic field distribution caused by surface roughness, etc. However, unless the noise magnetic field and the change in the magnetic field generated by the defect are distinguished, that is, the S / N ratio is not increased, accurate defect detection cannot be performed. Therefore, for example, in Patent Document 1, an eddy current is caused in an object to be measured by an alternating magnetic field generated by an excitation coil provided in a horseshoe-shaped magnetic core, and a pickup coil wound around a leg portion (yoke) of the magnetic core. Therefore, when the eddy current of the object to be measured is disturbed due to the presence of a defect in the object to be measured, the electromotive force generated in the pickup coils provided in both yokes can be detected. In the flaw detection apparatus capable of detecting a defect by detecting a difference, the pickup coil is composed of a gradiometer, and a SQUID element (superconducting quantum interference element) is used for detecting an electromotive force so that a weak electromotive force can be detected. A magnetic flaw detector with improved detection accuracy is shown.
[0004]
Further, in Patent Document 2, in order to obtain the same effect as when a plurality of magnetization levels are given to the magnetizer, a plurality of magnetic sensors whose installation positions are changed along the magnetization direction of the magnetizer are provided, and defects from the inspection object are detected. A device is shown in which a magnetic flux leakage signal is measured by both magnetic sensors, and a detection signal having a high S / N ratio is obtained by utilizing the fact that the received signals differ depending on the distance between the two sensors.
[0005]
Further, in Patent Document 3, a single magnetometer is mixed and supplied with a plurality of frequency alternating currents, a magnetic flux returning from the inspection object is detected by a single magnetic sensor, and the inspection object has a defect. In this case, a leakage magnetic flux flaw detector that isolates noise and efficiently detects only the defect by using the fact that the strength of the leakage magnetic flux returned from the defect of the inspection object differs between high frequency and low frequency .
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-14601 [Patent Document 2]
JP 2000-227419 A [Patent Document 3]
JP 2000-275219 JP
[Problems to be solved by the invention]
However, the apparatus disclosed in Patent Document 1 needs to be able to handle liquid nitrogen in order to use a SQUID element (superconducting quantum interference element), which is inevitably expensive and used in a general place. It is difficult to do. The devices disclosed in Patent Document 2 and Patent Document 3 are intended to obtain a detection signal having a high S / N ratio, and there is no description about estimating the position and depth of a flaw.
[0008]
Therefore, in the present invention, the position and depth of internal defects such as pinhole defects generated in cracks and welded parts, pipe wall defects caused by corrosion, etc. It is an object to provide a magnetic flaw detection apparatus that can be detected.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention
An excitation coil that generates a magnetic flux orthogonally intersecting the DUT by winding a high permeability material around a core formed in a semi-doughnut shape, and a magnetic field induced in the DUT by the magnetic flux generated by the excitation coil is detected. In a magnetic flaw detector composed of a detection coil,
Two detection coils are provided in the core, a means for applying an alternating current in which a plurality of frequency components are multiplexed to the excitation coil, and each frequency at the plurality of frequencies from the magnetic field detected by the two detection coils. Means for detecting frequency change, magnetic potential difference, amplitude value change, etc., and estimating / detecting the position and depth of the defect of the DUT, both ends of the half-doughnut core facing the DUT The first gist is to have an exciting coil wound around the core leaving the vicinity of the portion.
[0010]
That is, when an AC magnetic field is applied to a conductor such as steel, the magnetic flux entering the conductor becomes weaker as the depth increases due to the skin effect, and the detection signal level becomes weaker as the signal source is deeper. This phenomenon becomes more prominent as the excitation frequency is higher and the permeability of the device under test is higher. Therefore, when an alternating current in which a plurality of frequency components are multiplexed is applied to the exciting coil in this way, the level detected by the detecting coil is different between the influence of the low frequency caused by the defect on the magnetic field and the influence of the high frequency on the magnetic field. The frequency varies depending on the defect. For this reason, two detection coils are provided, and each detection coil detects the frequency, magnetic potential difference, and amplitude changed for each superimposed frequency, so that the test object can be cracked or welded with a simple and inexpensive structure. It is possible to provide a magnetic flaw detector capable of estimating and detecting the position and depth of an internal defect such as a pinhole defect generated in a part or the like, a thickness reduction of a piping material due to corrosion, or the like.
[0011]
The invention according to claim 1 comprises two detection coils wound in a double winding between the excitation coil and the core, and the two detection coils are arranged at both ends of the half-doughnut core. The invention according to claim 2 is characterized in that the two coils are separately wound in the vicinity of both end portions of the core where the exciting coil of the core is not wound. It consists of a coil for detection,
Furthermore, the invention described in claim 3 is characterized in that the core is composed of two detection coils separately accommodated in detection coil accommodation holes provided in the vicinity of both end portions facing the device under test.
More to this, it is possible to select the optimum mode by the test object. If both detection coils are provided in the vicinity of both end portions where the core faces the DUT, both detection coils are separated by the distance of the portion of the core facing the DUT. It becomes easier.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. This is just an example.
[0013]
FIG. 1 is a schematic block diagram of an apparatus showing an embodiment of the present invention, and FIGS. 2 to 4 are sectional views showing an embodiment of a detection / excitation sensor according to the present invention. In the figure, 1 is a detection / excitation sensor used in the present invention, 2 is a core made of a high permeability material (amorphous ferrite, high permeability steel plate, etc.) constituting the detection / excitation sensor 1 and formed in a half donut shape, 3 is a device under test Excitation coils 4, 5 for generating magnetic flux orthogonal to the body 6 are wound around the core 2 side of the excitation coil 3, and the magnetic field induced in the DUT 6 by the magnetic flux generated by the excitation coil 3. The detection coil to be detected is wound around the core 2 side of the excitation coil 3 in this figure . Reference numeral 6 denotes a device under test, and 7 an arithmetic unit (CPU), which generates a signal for an alternating magnetic field in which a plurality of frequency components sent to the excitation coil 3 of the detection / excitation sensor 1 are multiplexed, and the detection coil 4. 5 is analyzed by fast Fourier transform, relative amplitude value detection, etc., the position and depth of the defect in the DUT 6 are calculated, and the sweep position of the detection / excitation sensor 1 is instructed. Reference numeral 8 denotes a digital / analog converter (D / A-C) for digital / analog conversion of a signal multiplexed from a plurality of frequency components sent from the arithmetic unit 7, and 9 amplifies the signal from the digital / analog converter 8. , A power amplifier 10 for generating an alternating magnetic field in which a plurality of frequency components are multiplexed by being supplied to the exciting coil 3, 10 and 11 are preamplifiers for amplifying a minute signal detected by the detection coils 4 and 5, and 12 and 13 An analog / digital converter (A / D-C) 14 for analog / digital conversion of signals from the detection coils 4 and 5 amplified by the preamplifiers 10 and 11 and sending them to the arithmetic unit 7, 14 has a motor and its drive circuit. sweeping device for moving so as to sweep the detection and excitation sensor 1 with respect to the test object 6 Te, 3 20 _1, 20 ₂ phases and the test object in the core 2 Detecting coil wound around the portion near to a 21 _1, 21 ₂ is also detecting coil accommodated in the detecting coil housing hole 22 provided in the portion facing the vicinity and DUT core 2 in FIG.
[0014]
FIG. 2 is a cross-sectional view showing a first embodiment of the detection / excitation sensor 1 according to the present invention, and is a core 2 side configured in a semi-doughnut shape with a high permeability material (amorphous ferrite, high permeability steel plate, etc.). The detection coils 4 and 5 are wound on the outer side, and the excitation coil 3 is wound on the outer side. The detection coils 4 and 5 and the excitation coil 3 are arranged on the core 2 side. The detection coils 4 and 5 may be wound around the outside. 3 and 4 are cross-sectional views showing the second and third embodiments of the detection / excitation sensor 1, which are configured in a semi-dough shape with a high permeability material (amorphous ferrite, high permeability steel plate, etc.). winding an exciting coil 3 around the core 2, independently of each winding of the detection coil 20 _1, 20 ₂ at opposite end portions near the test object of the semi-donut-shaped core 2 in the embodiment of FIG. 3 In the embodiment shown in FIG. 4, the detection coils 21 ₁ and 21 ₂ are separately housed in the detection coil housing holes 22 provided in the vicinity of both end portions of the half-doughnut-shaped core 2 facing the object to be tested. Is.
[0015]
In the magnetic flaw detection apparatus of the present invention, any of the detection / excitation sensors 1 in the embodiments shown in FIGS. 2 to 4 may be used. In FIG. 1, the shape shown in FIG. 2 is taken as an example. The case where the detection / excitation sensor 1 is used is shown.
[0016]
When the detection / excitation sensor 1 configured in this way generates an alternating magnetic field that generates a magnetic flux that crosses the test object 6 made of a conductor such as steel at right angles, the test object 6 is caused by the skin effect. The magnetic flux that enters the field becomes weaker as it gets deeper. This phenomenon becomes more prominent as the excitation frequency of the exciting coil 3 is higher and as the magnetic permeability of the DUT 6 is higher. Therefore, when a magnetic field in which a plurality of frequency components are multiplexed is applied to the device under test 6, the piping material flesh caused by cracks, pinhole defects, corrosion, etc. generated deep in the device under test 6. When there is an internal defect such as thickness reduction, the effect of the magnetic field due to the magnetic flux entering by the defect is a value corresponding to each of the multiplexed frequencies, and by detecting the affected magnetic field for each frequency, It becomes possible to estimate and detect the position and depth of the defect.
[0017]
In the magnetic flaw detector according to the first embodiment shown in FIG. 1 configured based on such a concept, a signal for an alternating magnetic field in which a plurality of frequency components are multiplexed is generated by an arithmetic unit (CPU) 7. Then, it is converted into an analog signal by a digital / analog converter (D / A-C) 8, amplified by a power amplifier 9, and given to the detection / excitation sensor 1. Similarly, the arithmetic unit (CPU) 7 moves the detection / excitation sensor 1 relative to the device under test 6, generates a sweep signal for sweeping the entire surface of the device under test 6, and gives it to the sweep device 14. The entire surface of the device under test 6 is swept by moving the detection / excitation sensor 1 or the device under test 6 by the motor of the sweep device 14 or its drive circuit.
[0018]
Therefore, the detection / excitation sensor 1 sweeps the DUT 6 while applying a magnetic flux generated by an alternating magnetic field in which a plurality of frequency components are multiplexed to the DUT 6, and the detection coils 4 and 5 of the detection / excitation sensor 1 The magnetic field generated in the device under test 6 is detected by the magnetic flux generated by the alternating magnetic field and sent to the preamplifiers 10 and 11. Then, the preamplifiers 10 and 11 amplify this detection signal and send it to the analog / digital converters 12 and 13. The analog / digital converters 12 and 13 convert this analog signal into a digital signal and send it to the arithmetic unit 7. Then, the arithmetic unit 7 monitors whether or not the device under test 6 is defective based on the transmitted signal.
[0019]
The magnetic flux applied to the device under test 6 by the exciting coil 3 enters the depth according to the excitation frequency and the magnetic permeability of the device under test 6 as described above, but the device under test 6 is not defective. In this case, there is no change in the magnetic field detected by the detection coils 4 and 5 and the value is almost constant. However, when the device under test 6 has a defect, only the magnetic flux having a frequency equal to or lower than a specific frequency reaches the position where the defect is present, the magnetic field is affected, and a change occurs. Therefore, since the magnetic field detected by the detection coils 4 and 5 changes depending on the excitation frequency, the arithmetic unit 7 performs fast Fourier transform and relative change of the magnetic field of each frequency detected by the detection coils 4 and 5. Using the amplitude value detection, for example, the depth of the defect is detected from the frequency at which the amplitude value has changed and the frequency at which the frequency value has not changed, and the strength of the magnetic field detected by the detection coils 4 and 5 for each specific frequency is detected. The position of the defect is estimated by detecting the magnetic potential difference, and the size of the defect is estimated by changing the frequency of the magnetic flux, and the defect is estimated and detected.
[0020]
In this way, by performing such calculation while sweeping the entire surface of the detection / excitation sensor 1 with respect to the device under test 6 by the sweep device 14, it is generated at a crack or a welded portion of the device under test 6. Pinhole defects, internal defects such as pipe wall thickness reduction caused by corrosion, etc., can be estimated in position and depth, and by displaying the detection results on a display device or the like, the device under test 6 Internal defects can be visually observed.
[0021]
Figure 3 is a second embodiment of the detection and excitation sensor 1 of the present invention, in this second embodiment, opposite end portions near the detection coil 20 _1, 20 ₂ and the test object 6 of the core 2 The excitation coil 3 is wound between the detection coils 20 ₁ and 20 ₂ . By doing so, the detection coils 20 ₁ and 20 ₂ are separated from each other by the distance between both end portions of the core 2 facing the device under test 6, so that the detection of the magnetic potential difference becomes easier.
[0022]
FIG. 4 shows a third embodiment of the detection / excitation sensor 1 according to the present invention. In this third embodiment, both end portions of the detection coils 21 ₁ and 21 ₂ facing the DUT 6 of the core 2 are shown. The exciting coil 3 is housed in a detection coil housing hole 22 provided in the vicinity, and the excitation coil 3 is wound between the detection coils 20 ₁ and 20 ₂ . By doing so, the detection coils 21 ₁ and 21 ₂ are separated from each other by the distance between both end portions of the core 2 facing the device under test 6 as in the second embodiment, so that the magnetic potential difference can be easily detected. Become.
[0023]
【The invention's effect】
As described above, according to the present invention, the excitation coil 3 constituting the detection / excitation sensor 1 generates an alternating magnetic field in which a plurality of frequency components are multiplexed and applies it to the device under test 6 to provide two detections. Because the level detected by the detection coil differs between the influence of the low frequency caused by the defect on the magnetic field and the influence of the high frequency on the magnetic field, and the frequency changes due to the defect. Using the fact that the magnetic flux reaching the defect occurring in the specimen 6 varies depending on the frequency and that the magnetic field is affected by the defect, the frequency, magnetic potential difference, amplitude, etc. changed for each frequency are detected. Estimate and detect the position and depth of internal defects such as pinhole defects generated in cracks and welds of the specimen under test, reduced thickness of piping materials caused by corrosion, etc. Possible and becomes easy, and it is possible to provide a magnetic flaw detector inexpensive structure, is intended to provide a great effect.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of an apparatus showing an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a first embodiment of a detection / excitation sensor according to the present invention.
FIG. 3 is a cross-sectional view showing a second embodiment of the detection / excitation sensor according to the present invention.
FIG. 4 is a cross-sectional view showing a third embodiment of the detection / excitation sensor of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Detection / excitation sensor 2 Core 3 Excitation coil 4, 5 Detection coil 6 Test object 7 Computing device (CPU)
8 Digital / Analog Converter (D / A-C)
9 Power amplifier 10, 11 Preamplifier 12, 13 Analog / digital converter (A / D-C)
14 Sweeping device

Claims (3)

An excitation coil that generates a magnetic flux orthogonally intersecting the DUT by winding a high permeability material around a core formed in a semi-doughnut shape, and a magnetic field induced in the DUT by the magnetic flux generated by the excitation coil is detected. In a magnetic flaw detector composed of a detection coil,
Two detection coils are provided in the core, a means for applying an alternating current in which a plurality of frequency components are multiplexed to the excitation coil, and each frequency at the plurality of frequencies from the magnetic field detected by the two detection coils. Means for detecting frequency change, magnetic potential difference, amplitude value change, etc., and estimating / detecting the position and depth of the defect of the DUT, both ends of the half-doughnut core facing the DUT An excitation coil wound around the core leaving the vicinity of the core and two detection coils wound in a double winding between the excitation coil and the core. The two detection coils A magnetic flaw detector which extends to both end portions of the half-doughnut-shaped core and is wound . An exciting coil that is wound around a core formed of a high permeability material in a semi-doughnut shape and generates a magnetic flux that intersects the DUT perpendicularly, and a magnetic field induced in the DUT is detected by the magnetic flux generated by the exciting coil. In a magnetic flaw detector composed of a detection coil,
Two detection coils are provided in the core, a means for applying an alternating current in which a plurality of frequency components are multiplexed to the excitation coil, and each frequency at the plurality of frequencies from the magnetic field detected by the two detection coils. Means for detecting frequency change, magnetic potential difference, amplitude value change, etc., and estimating / detecting the position and depth of the defect of the DUT, both ends of the half-doughnut core facing the DUT An excitation coil wound around the core leaving the vicinity of the core, and the two detection coils wound separately in the vicinity of both ends of the core where the excitation coil of the core is not wound. A magnetic flaw detection device. An excitation coil that generates a magnetic flux orthogonally intersecting the DUT by winding a high permeability material around a core formed in a semi-doughnut shape, and a magnetic field induced in the DUT by the magnetic flux generated by the excitation coil is detected. In a magnetic flaw detector composed of a detection coil,
Two detection coils are provided in the core, a means for applying an alternating current in which a plurality of frequency components are multiplexed to the excitation coil, and each frequency at the plurality of frequencies from the magnetic field detected by the two detection coils. Means for detecting frequency change, magnetic potential difference, amplitude value change, etc., and estimating / detecting the position and depth of the defect of the DUT, both ends of the half-doughnut core facing the DUT an exciting coil wound on the core, leaving a portion near the core consists of two detecting coils each housed separately in the detection coil housing hole provided at opposite end portions near the test object Magnetic flaw detector characterized by that.

Images