JP5981706B2 - Electromagnetic induction type inspection method and electromagnetic induction type inspection device - Google Patents

Description

  The present invention relates to an electromagnetic induction inspection method and an inspection apparatus for inspecting a defect or the like of an inspection object that is a conductor using an electromagnetic induction method.

  Conventionally, an alternating current is applied to the exciting coil, an eddy current is generated on the surface of the object to be inspected by the magnetic flux emitted from the exciting coil, and the detection signal generated in the detection coil (induction coil) in accordance with the fluctuation of the eddy current Many eddy current inspection apparatuses for inspecting defects of an inspection object based on changes have been proposed (for example, Patent Document 1).

  The eddy current inspection apparatus described in Patent Document 1 uses the skin effect, and inspects the surface of a conductor and the vicinity of the surface. In such an eddy current inspection apparatus, it is known that the electromagnetic field generated in the object to be inspected is concentrated near the surface and rapidly attenuates when it reaches a deep part. This is because the eddy current acts only on the surface, and almost no eddy current is generated in the deep part of the detected object.

Japanese Patent Laid-Open No. 11-94805

  The eddy current inspection apparatus described in Patent Document 1 is devised to generate an eddy current near the surface of an object to be inspected by an alternating magnetic field from an exciting coil and to inspect only the surface of the object to be inspected and the vicinity of the surface. It has been done. In addition, as shown in FIG. 17, the greater the distance (depth) from the surface of the object to be detected, the smaller the eddy current generation range, and hence the smaller the inspectable range. There was a problem that it could not be done at all.

  Moreover, in the eddy current inspection apparatus described in Patent Document 1, the eddy current generated by the magnetic flux of the alternating magnetic field has a relatively small range that can be detected on the surface of the object to be inspected, and has a large and complicated shape. There was also a problem that it could not be inspected.

  In modern society, there are many structures that use thick steel materials such as nuclear reactors, railroad rails, piping with heat insulation materials, chemical plants, steel plates, steel bridges, and the like. When these structures are used for several decades, there is a possibility of structural destruction due to corrosion or metal fatigue. For example, in a nuclear reactor, intergranular corrosion may occur from the inside, and in railroad rails, electric corrosion starts on the lower back surface, and corrosion may increase and lead to an accident. However, an inspection method for these structures has not yet been established. In addition, for the corrosion inspection of pipes with a heat insulating material in chemical plants, the heat insulating material is peeled off and the visual inspection is performed, but the length of the pipe may exceed several tens of kilometers. In such a case, all the pipes are visually checked. It is absolutely impossible to inspect with. Further, steel materials used for roads and bridges are also assumed to have defects such as corrosion metal fatigue when decades of use have passed. This inspection method has not yet been established.

  There are a large number of large and complex inspected objects that must be inspected as described above as infrastructure in society, and there is an urgent need to establish inspection methods for these inspected objects.

  Accordingly, it is an object of the present invention to provide an electromagnetic induction inspection method and an electromagnetic induction inspection apparatus that can detect a defect or the like in a deep part even if the inspection object has a large and complicated shape.

  Another object of the present invention is to provide an electromagnetic induction inspection method and an electromagnetic induction inspection apparatus capable of easily and accurately detecting a defect in a deep part of an inspection object.

  Still another object of the present invention is to provide an electromagnetic induction inspection method and an electromagnetic induction inspection apparatus capable of nondestructively detecting a defect in a deep part of an inspection object.

  According to the present invention, an electromagnetic induction sensor having an exciting coil that generates an alternating magnetic field by flowing an alternating current and an induction coil that detects a change in magnetic flux and an object to be inspected are relatively in contact or non-contact at a predetermined speed. While moving, an alternating current is supplied to the exciting coil to supply an alternating magnetic field. Based on the supplied alternating magnetic field and an alternating current generated inside the inspection object due to relative movement, the alternating magnetic field flowing in the inspection object An electromagnetic induction inspection method is provided in which a change in magnetic flux is detected by an induction coil, and the presence or absence of a defect in the inspection object is determined based on a change amount of at least one of a phase component and an amplitude component of a detection output from the induction coil. The

If the object to be inspected is a conductor, an alternating current is generated inside the object to be inspected by moving it relatively at a predetermined speed in one direction while supplying an alternating current to the exciting coil directed toward the object to be inspected. . The following equation is derived based on the results obtained by experiments by the present applicant with reference to Faraday's law, and when moving relatively at a predetermined speed while supplying an alternating current to the exciting coil, It shows that an alternating current is generated inside the inspection object.
i = v × S × B
In the formula, i is an alternating current generated inside the object to be inspected, v is a moving speed of the magnetic flux of the alternating magnetic field supplied from the exciting coil, B is a magnetic flux density of the alternating magnetic field, and S is an alternating magnetic field. Magnetic flux cross section.

  In this way, an alternating current is generated by moving the free electrons existing in the inspection object by moving the excitation coil toward the inspection object at a predetermined speed while supplying an alternating current to the excitation coil. By examining the amount of change in the magnetic flux of the alternating magnetic field that is created, internal defects can be detected even if the object to be inspected is a ferromagnetic, paramagnetic, or diamagnetic material having a thickness of several tens of millimeters or more. Is possible.

  It is preferable to control the magnitude of the alternating current generated in the deep part of the inspection object by adjusting the relative movement speed of the electromagnetic induction sensor and the inspection object. Thereby, it can test | inspect by adjusting the relative movement speed of an electromagnetic induction sensor and a to-be-inspected object according to the thickness of to-be-inspected object.

  It is preferable to control the reach depth of the magnetic flux of the alternating magnetic field inside the object to be inspected by adjusting the voltage applied to the exciting coil while keeping the frequency constant. Thereby, it can test | inspect by adjusting the voltage applied to an exciting coil according to the thickness of a to-be-inspected object.

  It is preferable to control the magnitude of the alternating current generated in the deep part of the inspection object by changing the magnetic flux density of the exciting coil by adjusting the magnitude of the alternating current flowing through the exciting coil. Thereby, it can test | inspect by adjusting the applied current to an exciting coil according to the thickness of a to-be-inspected object.

  According to the present invention, an electromagnetic induction sensor having an excitation coil that generates an alternating magnetic field by flowing an alternating current and an induction coil that detects a change in magnetic flux, and the electromagnetic induction sensor and the object to be inspected are relative to each other at a predetermined speed. The electromagnetic induction sensor and the object to be inspected are relatively contacted or non-contacted by the moving means while an alternating current is supplied to the exciting coil of the electromagnetic induction sensor and an alternating magnetic field is supplied from the electromagnetic induction sensor. The induction coil detects the magnetic flux change of the AC magnetic field flowing in the inspection object based on the supplied alternating magnetic field and the alternating current generated inside the inspection object due to the relative movement, and the detection output from the induction coil Provided is an electromagnetic induction inspection apparatus including a control unit that determines the presence or absence of a defect inside an inspection object based on a change amount of at least one of a phase component and an amplitude component of It is.

  In the electromagnetic induction inspection apparatus of the present invention, an alternating current is generated inside the inspection object, and the inspection object has a thickness of several tens of mm or more by examining the amount of change in the magnetic flux of the alternating magnetic field created by this alternating current. Even in the case of a ferromagnetic material, paramagnetic material, or diamagnetic material, the magnetic flux of an alternating magnetic field can reach the back surface from the surface of the object to be inspected and can detect internal defects and the like. . Further, since an alternating current can flow even in a peripheral portion where the magnetic flux of the alternating magnetic field of the exciting coil does not directly affect, a wider range can be detected. Also, since the magnetic flux of the alternating magnetic field output from the exciting coil can pass through the conductor and non-conductor and reach the target conductor, inspection of the inspection object covered with the conductor and non-conductor It can be performed.

  A speed adjusting means for adjusting the relative movement speed of the electromagnetic induction sensor and the inspection object is further provided, and the magnitude of the alternating current generated in the deep part of the inspection object is controlled by adjusting the relative movement speed by the speed adjustment means. It is preferable to do. Thereby, it can test | inspect by adjusting the relative movement speed of an electromagnetic induction sensor and a to-be-inspected object according to the thickness of to-be-inspected object.

  It is preferable to further include voltage adjusting means for adjusting the voltage applied to the exciting coil in a state where the frequency is constant, and to control the arrival depth of the magnetic flux of the alternating magnetic field inside the inspection object by this voltage adjusting means. Thereby, it can test | inspect by adjusting the voltage applied to an exciting coil according to the thickness of a to-be-inspected object.

  Current adjusting means for adjusting the magnitude of the alternating current flowing through the exciting coil is further provided, and this current adjusting means controls the magnitude of the alternating current generated in the deep part of the object under test by changing the magnetic flux density of the exciting coil. It is preferable. Thereby, it can test | inspect by adjusting the applied current to an exciting coil according to the thickness of a to-be-inspected object.

  The induction coil is preferably wound on the same axis as the exciting coil. As a result, the electromagnetic induction sensor can be reduced in size and the detection accuracy can be ensured.

  The inner diameter of the exciting coil is preferably 20 mm to 150 mm. Thereby, the magnetic flux of the alternating magnetic field which can reach the deep part of the inspection object can be formed.

  The electromagnetic induction sensor further includes a standard electromagnetic induction sensor having an excitation coil and an induction coil having the same configuration as the electromagnetic induction sensor, and the control unit outputs the detection signal output from the induction coil of the electromagnetic induction sensor and the induction coil of the standard electromagnetic induction sensor. It is preferable that the detection signal is compared to determine the presence / absence of a defect inside the inspection object. Thereby, detection accuracy can be improved.

  According to the present invention, an alternating current is formed inside the inspection object, and the amount of change in the magnetic flux of the alternating magnetic field created by the alternating current is examined, so that even a large-sized and complicated inspection object can be placed deep in the inspection object. A defect or the like can be detected easily, quickly, accurately, and nondestructively.

  For example, even if the object to be inspected is a ferromagnetic material, paramagnetic material or diamagnetic material having a thickness of several tens of mm or more, an alternating magnetic field can reach the back surface from the surface of the object to be inspected through the inside. Defects and the like can be detected. Further, since an alternating current can flow even in a peripheral portion where the magnetic flux of the alternating magnetic field of the exciting coil does not directly affect, a wider range can be detected. Moreover, an internal defect etc. can be detected also when there exists a conductor and space between inspection objects, such as piping inspection with a heat insulating material. Further, by detecting the change in the magnetic flux of the alternating magnetic field radiated from the inside of the conductor, it is possible to detect foreign matter, cracks and defects contained in the inspection object with high resolution and high accuracy. In addition, it is possible to inspect structures such as railroad rails and bridges regardless of the shape. Furthermore, even if the surface of the object to be inspected is uneven, it can be inspected in a non-contact manner. Furthermore, since the alternating current generated inside flows sufficiently longer than the width of the magnetic field lines of the alternating magnetic field output from the exciting coil, a wide range of detection can be performed with a single exciting coil operation. In the case of a coating pipe, a pipe with a heat insulating material, etc., the entire circumference of the pipe can be inspected at once by moving the electromagnetic induction sensor in the pipe longitudinal direction. Furthermore, the defect can be detected even if the electromagnetic induction sensor does not pass right above the defect portion of the inspection object. Furthermore, a sufficient distance between the inspection object and the electromagnetic induction sensor can be secured.

It is a figure which shows roughly an example of the state which is test | inspecting using the structure of the electromagnetic induction type inspection apparatus in the 1st Embodiment of this invention, and this electromagnetic induction type inspection apparatus. It is a perspective view which shows roughly the structure of the electromagnetic induction sensor of the electromagnetic induction type inspection apparatus in 1st Embodiment. It is a figure which shows roughly the structure of the electromagnetic induction sensor in the change aspect of 1st Embodiment. It is explanatory drawing which shows generation | occurrence | production of the alternating current by the electromagnetic induction sensor of the electromagnetic induction type test | inspection apparatus in 1st Embodiment. It is a perspective view which shows a part of moving means of the electromagnetic induction type test | inspection apparatus in 1st Embodiment. It is a model figure of the electric signal output from an electromagnetic induction sensor. It is a flowchart which shows roughly the comparison operation of a comparison means. It is a flowchart which shows an example of the electromagnetic induction type inspection method in 1st Embodiment. It is a figure which shows the image of the alternating current generate | occur | produced when test | inspecting a railroad rail using the electromagnetic induction type inspection apparatus in 1st Embodiment. It is a figure which shows the detection result at the time of applying the voltage of 60 mV to an exciting coil. It is a figure which shows the detection result at the time of applying a voltage of 20 mV to an exciting coil. It is a figure which shows roughly the other example of the state currently test | inspected using the electromagnetic induction type inspection apparatus in 1st Embodiment. It is a figure which shows the detection result using the electromagnetic induction type inspection apparatus in 1st Embodiment. It is a figure which shows roughly an example of the state which is test | inspecting using the structure of the electromagnetic induction type inspection apparatus in the 2nd Embodiment of this invention, and this electromagnetic induction type inspection apparatus. It is a figure which shows the detection result using the electromagnetic induction type inspection apparatus in 2nd Embodiment. It is a perspective view which shows the other example of the moving means of an electromagnetic induction type inspection apparatus. It is a figure which shows the mode of the eddy current inside a to-be-inspected object in the case of using the conventional eddy current inspection apparatus.

  Embodiments of an electromagnetic induction inspection method and an electromagnetic induction inspection device according to the present invention will be described below with reference to the drawings.

  FIG. 1 schematically shows an example of the configuration of an electromagnetic induction type inspection apparatus 100 according to the first embodiment of the present invention and a state of inspection using the electromagnetic induction type inspection apparatus 100, and FIG. 1 schematically shows the configuration of an electromagnetic induction sensor.

  As shown in FIGS. 1 and 2, the electromagnetic induction type inspection apparatus 100 according to this embodiment includes an electromagnetic induction sensor 10 having an excitation coil 10 a and an induction coil 10 b, an electromagnetic induction sensor 10, and an object R to be inspected. A moving means 20 that relatively moves in a fixed relative direction at a speed, a detection signal process for determining the presence or absence of defects inside the inspection object R, a control unit 30 that controls the operation of the entire inspection apparatus, and a detection result A display unit 40 for displaying and an AC power source E are provided.

  As shown in FIG. 2, the electromagnetic induction sensor 10 includes an integrated excitation coil 10a and induction coil 10b. The excitation coil 10a and the induction coil 10b are configured to be coaxially stacked.

  The exciting coil 10a is formed on the inner side. For example, after winding an insulation-coated copper wire around a long cylindrical body, the cylindrical body is removed to form a hollow annular shape. The inner diameter of the exciting coil 10a is preferably 20 mm to 150 mm. Thereby, the magnetic flux of the alternating magnetic field which can reach the deep part of the inspection object can be formed. Moreover, it is preferable that the number of coil turns is 200 or more and the frequency of the applied current is 50 kHz or less. In this embodiment, the exciting coil 10a has an inner diameter of 20 mm, an insulation-coated copper wire thickness of 0.3 mm, and a number of turns of 300.

  The induction coil 10b is wound on the outer surface of the exciting coil 10a, and is integrally formed coaxially with the exciting coil 10a. In this embodiment, the induction coil 10b is composed of an insulation-coated copper wire having a thickness of 0.3 mm and a number of turns of 350.

  Note that the shapes of the exciting coil 10a and the induction coil 10b are not limited to the annular shape, and may be, for example, an elliptical ring shape, a rectangular ring shape, or other shapes. Further, the method of forming the coil is not limited to the method of winding the induction coil 10b directly on the outer surface of the exciting coil 10a. For example, the exciting coil 10a and the induction coil 10b may be separately formed and then coaxially and integrally arranged.

  In addition, in the modification of the first embodiment, the electromagnetic induction type inspection apparatus includes an electromagnetic induction sensor 10 and a standard electromagnetic induction sensor 10 ′ having an excitation coil and an induction coil having the same configuration in addition to the electromagnetic induction sensor 10. . In this case, the inspection is performed by comparing the inspection object with the standard inspection object. For example, as shown in FIG. 3, the standard electromagnetic induction sensor 10 ′ is mainly composed of an excitation coil 10a ′ and an induction coil 10b ′ that are identical in structure to the excitation coil 10a and the induction coil 10b of the electromagnetic induction sensor 10. The output signal of the induction coil 10b of the electromagnetic induction sensor 10 is compared with the output signal of the induction coil 10b 'of the standard electromagnetic induction sensor 10' to determine whether there is a defect inside the inspection object. As shown in FIG. 3, the positional relationship between the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ is such that the electromagnetic induction sensor 10 is positioned in the vicinity of the inspection object R1, and the standard electromagnetic induction sensor 10 ′ is set to the inspection object R1. The inspection is performed in the vicinity of the standard inspection object R2 away from the inspection object. In addition, it is also possible to perform inspection while moving the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ at the same speed on the same inspection object without using the standard inspection object R2.

  FIG. 4 illustrates how an alternating current is generated in the inspection object when an alternating current is passed through the exciting coil 10a of the electromagnetic induction sensor 10 in the first embodiment. In FIG. 4, the alternating current i is indicated by an arrow. As shown in FIG. 4A, when the electromagnetic induction sensor 10 moves in the direction V along the inspection object while an alternating current is passed through the exciting coil 10a, the movement direction (arrow) The alternating current i flows in a direction orthogonal to the (V direction). FIG. 4B shows a cross section orthogonal to the moving direction V. As shown in the figure, the width of the alternating magnetic field generated inside the inspection object when an alternating current is passed through the exciting coil 10a is W1, and on the other hand, the alternating magnetic field is induced and flows inside the inspection object by this alternating magnetic field. The width of the alternating current i is W2. This alternating current i is generated over almost the entire width of the object to be inspected.

  The moving means 20 includes a mounting portion 21 on which the electromagnetic induction sensor 10 is mounted, and a driving portion 22 that moves the mounting portion 21 at a predetermined speed along the object to be inspected. The mounting portion 21 is, for example, a sliding type that slides on the object to be inspected as shown in FIG. The electromagnetic induction sensor 10 is mounted on the upper surface of the mounting portion 21. The drive unit 22 is configured to move the mounting unit 21 along the object to be inspected, for example, by driving a motor or the like. A guide rail or the like (not shown) may be provided along the object to be inspected, and the mounting portion 21 may be guided by the guide rail. Moreover, since position information can be obtained by attaching an encoder or the like, the position of the defect can be determined. In addition, you may provide only the mounting part 21, without providing the drive part 22 in the moving means 20. FIG. In that case, the mounting portion 21 is moved manually.

  The control unit 30 controls the operation of the entire inspection apparatus and processes the detection signal output from the induction coil 10b. The control unit 30 includes a control unit 31, a comparison unit 32, a determination unit 33, and a recording unit 34. In the control part 30, the function of each said means is implement | achieved using a computer and software, for example. The control means 31 is for controlling the detection operation of the electromagnetic induction sensor 10 and the movement operation of the moving means 20. The comparison means 32 is for comparing the measured value with the reference value using the change amount of at least one of the phase signal and the amplitude signal output from the induction coil 10b. The determination means 33 is for determining the presence / absence of a defect inside the inspection object based on the comparison result of the comparison means 32. The recording means 34 is for storing and recording the measurement result.

  The control unit 31 further includes a speed adjusting unit that adjusts the moving speed of the electromagnetic induction sensor 10. The moving speed of the electromagnetic induction sensor 10 is set in advance by the speed adjusting unit, and the alternating current is supplied to the deep part of the inspection object R. generate. The control means 31 further includes voltage adjusting means for adjusting the voltage applied to the exciting coil 10a when the frequency is made constant, and the voltage adjusting means presets the voltage applied to the exciting coil 10a to be inspected. The arrival depth of the magnetic flux of the alternating magnetic field inside the object R is controlled. Further, the control means 31 further includes a current adjusting means for adjusting the current flowing through the exciting coil 10a. With this current adjusting means, the current flowing through the exciting coil 10a is preset and the magnetic flux density of the exciting coil 10a is increased. The alternating current generated in the deep part of the inspection object R is increased.

  In this embodiment, the comparison means 32 measures the signal (reference value) Vref obtained by measuring the standard inspection object having no defect with the electromagnetic induction sensor 10 and the inspection object R with the electromagnetic induction sensor 10. The signal (measured value) Vout obtained in this way is compared. Specifically, first, a reference value is acquired from the signal Vref output from the induction coil 10b of the electromagnetic induction sensor 10 for the standard inspection object (S01 in FIG. 7). Next, a measured value is acquired from the signal Vout output from the induction coil 10b of the electromagnetic induction sensor 10 for the object to be inspected (S02 in FIG. 7). Thereafter, the measured value is compared with the reference value (S03 in FIG. 7). For example, as shown in FIG. 6, the amplitude of the signal (measured value) Vout and the amplitude of the signal (reference value) Vref are compared. The phase of the signal (measured value) Vout may be compared with the phase of the signal (reference value) Vref. Further, both the amplitude and the phase may be compared.

  In the modified embodiment of FIG. 3, the comparison means 32 has a signal (reference value) Vref obtained by measuring with the standard electromagnetic induction sensor 10 ′ for the standard inspection object R2 having no defect, and electromagnetic induction for the inspection object R1. A signal (measured value) Vout obtained by measurement with the sensor 10 is compared. Specifically, first, the inspection object R2 is disposed below the standard electromagnetic induction sensor 10 ′, and the inspection object R1 is disposed below the electromagnetic induction sensor 10, and measurement is performed. Thus, the signal (reference value) Vref is acquired from the induction coil 10b ′ of the standard electromagnetic induction sensor 10 ′ (S01 in FIG. 7), and the signal (measured value) Vout is acquired from the induction coil 10b of the electromagnetic induction sensor 10. (S02 in FIG. 7). Thereafter, the measured value is compared with the reference value (S03 in FIG. 7). For example, as shown in FIG. 6, the amplitude of the signal (measured value) Vout and the amplitude of the signal (reference value) Vref are compared. The phase of the signal (measured value) Vout may be compared with the phase of the signal (reference value) Vref. Further, both the amplitude and the phase may be compared.

  The determination unit 33 determines whether or not a defect or the like exists in the inspection object R or R1 based on the comparison result of the comparison unit 32, that is, normality / abnormality of the inspection object. If the phase change amount Δθ (or amplitude change amount ΔΗ) is zero, the inspection object R or R1 is determined to be normal. If it is not zero, the inspection object R is determined to be abnormal. If the above-described phase change amount Δθ and amplitude change amount ΔΗ are converted into data in association with the state of the inspection object in advance in the determination means 33, what is actually the abnormality of the inspection object, that is, corrosion? It is also possible to identify and grasp a specific defect state such as whether the state is the occurrence of a crack.

  The recording unit 34 records the measurement state and the measurement result in a memory or a recording sheet. The recording unit 34 can store the output of the electromagnetic induction sensor 10, the measurement state, the measurement result, and the like, and can read them out when necessary.

  The display part 40 displays a measurement state, a measurement result, etc. For example, the position of the electromagnetic induction sensor 10 is displayed or the measurement result is displayed. On the display unit 40, the measurement state, the measurement result, and the like can be displayed as a graphic or a number.

  The AC power source E includes a sine wave oscillator and a constant current amplifier, and the AC voltage of the angular frequency ω output from the sine wave oscillator becomes a constant current by the constant current amplifier and is supplied to the exciting coil 10a of the electromagnetic induction sensor 10. Is done.

  Next, an inspection method using the electromagnetic induction inspection apparatus 100 in the present embodiment will be described. FIG. 8 is a flowchart illustrating an example of an inspection method in the electromagnetic induction inspection apparatus 100.

  When inspecting using the electromagnetic induction inspection apparatus 100, first, the electromagnetic induction sensor 10 placed on the moving means 20 is installed on the surface of the object to be inspected (S11). Next, the moving speed of the moving means 20 is set (S12), the voltage applied to the exciting coil 10a is set (S13), and the supply current to the exciting coil 10a is set (S14). Thereafter, the inspection is started with the electromagnetic induction sensor 10 moved (S15). That is, the control means 31 relatively moves the electromagnetic induction sensor 10 and the object R to be inspected in a certain direction at a predetermined speed, and supplies an alternating current set to the exciting coil 10a. As a result, an AC magnetic field that moves in a certain direction is applied to the object R to be inspected, and free electrons inside the object R move to generate an alternating current. An alternating magnetic field is generated by the generated alternating current. The generated AC magnetic field is detected and output by the induction coil 10b of the electromagnetic induction sensor 10.

  Next, the electromagnetic induction inspection apparatus 100 compares the measured value with the reference value using at least one of the phase signal and the amplitude signal output from the induction coil 10b (S16). Next, based on this comparison result, it is determined whether or not the difference between the measured value and the reference value is 0 (or a predetermined value defined in advance), and the difference between the measured value and the reference value is 0 (or If it is equal to or less than a predetermined value, it is determined that there is no defect. If the difference between the measured value and the reference value is not zero (or exceeds the predetermined value), it is determined that there is a defect (S17). Next, this measurement result is displayed, and a warning is given when there is a defect (S18).

  According to the electromagnetic induction inspection method of the present invention, an alternating current is excited inside the inspection object R by moving the excitation coil 10a in one direction at a predetermined speed while an alternating current is flowing. This alternating current changes its value when there is a defect in the inspection object, and flows in a wider range than the influence range of the magnetic flux of the alternating magnetic field of the exciting coil 10a. Detection is possible (see FIG. 4B). The speed of relative movement between the electromagnetic induction sensor 10 and the inspection object R is preferably 10 m / min to 30 m / min. When the speed is slower than 10 m / min, an alternating current hardly occurs. On the other hand, when the speed is higher than 30 m / min, it becomes difficult to detect defects and the like.

  Further, since the alternating current i excited by the inspection object R depends on the frequency of the alternating current supplied to the exciting coil 10a, the frequency of the alternating current i generated inside the inspection object is the current supplied to the exciting coil 10a. And the frequency becomes equal. Therefore, it is desirable to select a frequency suitable for the inspection of the inspection object.

  As shown in FIG. 9, the alternating current i is excited over almost the entire width in each part of the inspection object R without being affected by the shape of the inspection object R (for example, railroad rail) having a complicated shape. Is done. By measuring the amount of change in the magnetic flux of the alternating magnetic field formed by this alternating current i, it is possible to easily inspect defects and the like of various shapes of inspection objects.

Verification example 1
As the inspected object R, as shown in FIG. 1, a railway rail R having a pseudo defect C formed thereon was used. Here, three types of cuts were made in the inspection object R as pseudo defects C from the bottom of the rail toward the head. However, only one type of cut is shown in FIG. These cuts were (1) the thickness of the remaining head portion, 30 mm, (2) the remaining head portion thickness of 20 mm, and (3) the remaining head portion thickness of 10 mm. The electromagnetic induction sensor 10 described above was used as the electromagnetic induction sensor.

  As the exciting coil 10a of the electromagnetic induction sensor 10, an insulation-coated copper wire having a thickness of 0.3 mm and a number of turns of 300 is used, and as the induction coil 10b, an insulation-coated copper wire having a thickness of 0.3 mm and a number of turns of 350. The thing of was used. The excitation coil 10a was applied with voltages of 60 mV and 20 mV at a frequency of 6.0 kHz, and the electromagnetic induction sensor 10 was moved in one direction at a constant speed (for example, 30 m / min) for inspection.

  FIG. 10 shows output signals when the applied voltage is 60 mV and the remaining thickness is 10 mm, 20 mm, and 30 mm. As can be seen from the figure, when the applied voltage was 60 mV, all three types of cuts with different depths could be detected. FIG. 11 shows output signals when the applied voltage is 20 mV and the remaining thickness is 10 mm, 20 mm, and 30 mm. As can be seen from the figure, the output signal does not appear when the remaining thickness is 20 mm and 30 mm, and the output signal appears only when the remaining thickness is 10 mm. This indicates that detection was possible when the remaining thickness was 10 mm, but detection was not possible when the remaining thickness was 20 mm and 30 mm.

Verification example 2
As the inspection object, as shown in FIG. 12, a rail having a pseudo defect F as a notch formed on a rail (inspection object) R was used. The electromagnetic induction sensor 10 described above was used as the electromagnetic induction sensor. The excitation coil 10a was tested by applying a voltage of 5 V at a frequency of 4 kHz and moving the electromagnetic induction sensor 10 in one direction at a constant speed (for example, 30 m / min). The distance between the electromagnetic induction sensor 10 and the railroad rail was 3 mm.

  The magnetic flux of the alternating magnetic field applied from the exciting coil 10a proceeds in the vertical direction in the inspection object R. The alternating current excited in the inspection object R by this magnetic field and relative movement flows in a horizontal direction orthogonal to the magnetic flux of the alternating magnetic field. Accordingly, when an alternating current flows in the vicinity of the pseudo defect F of the inspection object R, the alternating current is disturbed, and the alternating magnetic field generated by the alternating current is also disturbed. The magnetic flux having this disturbance is detected by the induction coil 10b of the electromagnetic induction sensor 10 and displayed as a phase signal or an amplitude signal.

  FIG. 13A shows the detected phase signal, and FIG. 13B shows the detected amplitude signal. As is clear from these figures, it is possible to easily and reliably detect a defect in a portion that extends from the railroad rail head to the bottom through a narrow body.

  As described above, the electromagnetic induction type inspection apparatus 100 according to the present embodiment is configured such that the electromagnetic induction sensor 10 having the excitation coil 10a and the induction coil 10b, the electromagnetic induction sensor 10 and the inspection object R are fixed at a predetermined speed. A moving means 20 for moving in the direction, a control unit 30 for determining the presence or absence of defects inside the inspection object R, and a display unit 40 for displaying detection results are provided. When inspecting using this electromagnetic induction type inspection apparatus 100, the control means 31 moves the electromagnetic induction sensor 10 and the object R to be inspected relative to each other in a fixed direction at a predetermined speed, and the alternating current is applied to the exciting coil 10a. Thus, free electrons inside the object to be inspected are converted into alternating current, an alternating magnetic field generated by the excited alternating current is detected by the induction coil 10b, and the phase signal or amplitude signal output from the induction coil 10b The presence or absence of a defect inside the inspection object is determined based on at least one of the change amounts. As a result, even in a large and complex shaped inspection object, a defect or the like in the deep part of the inspection object can be detected easily, quickly, accurately, and non-destructively. By detecting the change in the magnetic flux of the alternating magnetic field radiated from the inside of the inspection object (conductor), it is possible to detect the foreign matter, cracks or defects contained in the inspection object with high resolution and high accuracy.

  FIG. 14 shows a configuration of an electromagnetic induction inspection apparatus 200 according to the second embodiment of the present invention and a state in which a pipe with a heat insulating material is inspected using the electromagnetic induction inspection apparatus 200.

  This embodiment is a case where the piping P with a heat insulating material is used as an inspection object. As the electromagnetic induction sensor, the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ shown in FIG. 3 are used, and the inspection is performed while moving them on the heat insulating material pipe P at the same speed. The other configuration of the present embodiment is substantially the same as that of the embodiment of FIG. 1 and the modification shown in FIG.

Verification example 3
As the object to be inspected, a pipe P with a heat insulating material in which a pseudo defect (not shown) having a length of 40 mm, a width of 20 mm, and a depth of 2 mm was formed was used. In this heat insulating material-attached pipe P, a heat insulating material D (insulator) having a thickness of 60 mm is wound around the outer periphery of a steel pipe P1 having an outer diameter of 120 mm and a wall thickness of 9.0 mm, and the outer periphery is formed by a steel plate having a thickness of 0.3 mm. The plate T is wound and protected.

  The electromagnetic induction sensor 10 includes an excitation coil 10a and an induction coil 10b. The excitation coil 10a is configured by winding an insulation-coated copper wire having a thickness of 0.5 mm on an air core bobbin having an inner diameter of 100 mm, and an induction coil 10a. As the coil 10b, a coil formed by winding an insulation-coated copper wire having a thickness of 0.3 mm on the outside of the exciting coil 10a in 300 coaxial directions was used. Similarly, the electromagnetic induction sensor 10 'includes an excitation coil 10a' and an induction coil 10b '. The excitation coil 10a' is identical to the excitation coil 10a, and the induction coil 10b 'is identical to the induction coil 10b. . The electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ were fixed to the moving means 20 ′ so as to be arranged in a column in the longitudinal direction of the pipe P with a heat insulating material to be inspected. However, these arrangement orders are arbitrary.

  The excitation coils 10a and 10a 'were passed through a current of 400 mA at a frequency of 1.20 kHz, and the electromagnetic induction sensors 10 and 10' were manually moved in one direction at a constant speed (for example, 10 m / min) for inspection.

  As shown in FIG. 14, when the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 'are placed on the moving means 20' and moved on the heat insulating material pipe P at an arbitrary speed V in the longitudinal direction of the pipe, The magnetic flux of the alternating magnetic field applied from the coils 10a and 10a 'passes through the outer plate T and reaches the steel pipe P1, and an alternating current orthogonal to the magnetic flux of the alternating magnetic field is excited in the steel pipe P1. In this case, the excited alternating current flows in the circumferential direction in the steel pipe P1. That is, theoretically, the current is zero. When a part of the steel pipe P1 is defective, the current balance of the theoretical value zero is broken, so that the magnetic flux of the alternating magnetic field generated depending on the alternating current also changes, and the change in the magnetic flux of the alternating magnetic field is caused by the induction coils 10b and 10b. It can be determined whether or not there is a defect based on a change amount of either phase or amplitude.

  FIG. 15 shows a phase signal when the above-described pseudo defect is detected. The curve in FIG. 15 is a reciprocal signal when the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ are moved forward and backward.

  The positional relationship between the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ may be such that the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ are arranged close to each other and move on the object to be inspected. The induction sensor 10 may be separated from the standard electromagnetic induction sensor 10 ', and only the electromagnetic induction sensor 10 may be moved on the inspection object.

  The electromagnetic induction type inspection apparatus 200 according to the present embodiment can obtain the same effects as the electromagnetic induction type inspection apparatus 100 in the embodiment of FIG.

  Moreover, the defect which exists in the steel pipe surface and an internal perimeter is detectable even if the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 'are run at any position in the circumferential direction of the heat insulating material.

  In the above-described embodiment, the example in which the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ are moved in a predetermined direction has been described. However, the present invention is not limited to this. For example, the electromagnetic induction sensor 10 and the standard electromagnetic induction sensor 10 ′ may be fixed and the inspection object may be moved.

  In the above-described embodiment, the functions of the comparison unit 32 and the determination unit 33 are realized by a computer and software. However, the present invention is not limited to this. For example, the functions of the comparison unit and the determination unit may be realized by hardware.

  Furthermore, in the above-described embodiment, the mounting portion 21 of the moving means has a configuration as shown in FIG. 5, but the present invention is not limited to this. For example, in the case of a large object to be inspected, as shown in FIG. 16, the mounting portion 21 ′ may be configured to include wheels. In this case, the frictional force at the time of moving to the surface of the object to be inspected is reduced, and it can move smoothly.

  INDUSTRIAL APPLICABILITY The present invention can be used for the purpose of nondestructively inspecting defects of a test object that is a conductor, particularly a large and complicated shape test object, using an electromagnetic induction method.

DESCRIPTION OF SYMBOLS 10 Electromagnetic induction sensor 10 'Standard electromagnetic induction sensor 10a, 10a' Excitation coil 10b, 10b 'Induction coil 20, 20A Moving means 21, 21' Mounting part 22 Drive part 30 Detection signal processing part 31 Control means 32 Comparison means 33 Determination means 34 Recording means 40 Display unit 100, 200 Electromagnetic induction type inspection device C, F Pseudo defect D Insulation material E AC power supply i Alternating current P Insulation pipe P1 Steel pipe T Outer plate R Railway rail (inspection object)
R1 inspection object R2 standard inspection object

Claims (9)

The electromagnetic excitation sensor having an excitation coil that generates an alternating magnetic field by flowing an alternating current and an induction coil that detects a change in magnetic flux and the object to be inspected are relatively moved in a contact or non-contact state at a predetermined speed, and the excitation is performed. An alternating current is supplied to the coil to supply an alternating magnetic field,
Based on the supplied alternating magnetic field and the alternating current generated in the inspection object due to the relative movement, the magnetic flux change of the alternating magnetic field flowing in the inspection object is detected by the induction coil,
Based on the amount of change in at least one of the phase component and the amplitude component of the detection output from the induction coil, the presence or absence of a defect inside the inspection object is determined ,
An electromagnetic induction inspection method, wherein the magnitude of an alternating current generated in a deep portion of the inspection object is controlled by adjusting a relative movement speed of the electromagnetic induction sensor and the inspection object . By adjusting the voltage applied to the exciting coil in a state in which the frequency constant, the electromagnetic induction according to claim 1, characterized in that controlling the magnetic flux of the penetration depth of the alternating magnetic field in the object to be inspected inside Expression inspection method. The magnitude of the alternating current generated in the deep part of the inspection object is controlled by changing the magnetic flux density of the excitation coil by adjusting the magnitude of the alternating current flowing through the excitation coil. The electromagnetic induction type inspection method according to 1 or 2 . An electromagnetic induction sensor having an excitation coil that generates an alternating magnetic field by flowing an alternating current and an induction coil that detects a change in magnetic flux;
Moving means for relatively moving the electromagnetic induction sensor and the inspection object at a predetermined speed;
An alternating current is supplied to the exciting coil of the electromagnetic induction sensor to supply an alternating magnetic field from the electromagnetic induction sensor, and the electromagnetic induction sensor and the object to be inspected are relatively moved in a contact or non-contact state by the moving means. Detecting a change in magnetic flux of an alternating magnetic field flowing in the inspection object based on the supplied alternating magnetic field and an alternating current generated in the inspection object due to the relative movement, and detecting the induction coil based on at least one of the amount of change in the phase and amplitude components of the detection output from, and a determining controller the presence or absence of the object to be inspected inside the defect,
The apparatus further comprises speed adjusting means for adjusting the relative movement speed of the electromagnetic induction sensor and the inspection object, and the magnitude of the alternating current generated in the deep part of the inspection object by adjusting the relative movement speed by the speed adjustment means. An electromagnetic induction inspection apparatus characterized by controlling the thickness. It further comprises voltage adjusting means for adjusting the voltage applied to the exciting coil in a state where the frequency is constant, and the voltage adjusting means controls the arrival depth of the magnetic flux of the alternating magnetic field inside the inspection object. The electromagnetic induction type inspection apparatus according to claim 4 . The apparatus further comprises current adjusting means for adjusting the magnitude of the alternating current flowing through the exciting coil, and the current adjusting means changes the magnetic flux density of the exciting coil to generate the magnitude of the alternating current generated in the deep part of the inspection object. The electromagnetic induction type inspection apparatus according to claim 4 or 5 , wherein the electromagnetic induction type inspection apparatus is controlled. The electromagnetic induction inspection apparatus according to any one of claims 4 to 6 , wherein the induction coil is wound on the outer peripheral surface of the excitation coil so as to be coaxial with the excitation coil. The inner diameter of the exciting coil, an electromagnetic induction type inspection device as claimed in any one of claims 4 to 7, characterized in that the 20Mm～150mm. The electromagnetic induction sensor further includes a standard electromagnetic induction sensor having an excitation coil and an induction coil having the same configuration as the electromagnetic induction sensor, and the control unit outputs a detection signal output from the induction coil of the electromagnetic induction sensor and the standard electromagnetic induction sensor. The electromagnetic wave according to any one of claims 4 to 8 , wherein the electromagnetic wave is configured to determine whether or not there is a defect in the inspection object by comparing with a detection signal output from an induction coil. Inductive inspection device.

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