JP5028211B2 - Eddy current flaw detector and eddy current flaw detection method - Google Patents

Description

  The present invention relates to an eddy current flaw detection apparatus and an eddy current flaw detection method using an eddy current flaw detection sensor having a pair of exciting coils and a detection coil arranged therebetween.

  For example, a heat exchanger tube installed in a coolant purification system or the like of a nuclear power plant is regularly inspected to check whether or not a defect such as a crack has occurred. The heat exchanger tube of the heat exchanger is formed, for example, in a U shape, and both ends thereof are inserted into the through holes of the tube plate (magnetic material) and fixed. Specifically, for example, as shown in FIG. 6, the tube diameter of the heat transfer tube 1 is expanded from the inside to form a tube expansion portion 1 a, and the outer peripheral surface of the tube expansion portion 1 a is the inner peripheral surface of the through hole 2 a of the tube plate 2. It is fixed in close contact with. Since thermal stress due to temperature fluctuations acts on the heat transfer tube 1, the region near the deformed portion (portion between the expanded portion 1 a and the unexpanded portion 1 b) 1 c in the non-expanded portion 1 b is shown in FIG. There is a possibility that a circumferential crack E on the outer peripheral surface side indicated by a dotted line may occur. Therefore, in the maintenance and inspection of the heat transfer tube 1, it is necessary to detect the presence or absence of the circumferential crack E.

  As an inspection method of the heat transfer tube 1, for example, an eddy current flaw detection method using an eddy current flaw detection sensor having an exciting coil and a detection coil can be considered. In this eddy current flaw detection method, an eddy current is induced in the heat transfer tube 1 by an exciting coil, and a change in the eddy current caused by a defect of the heat transfer tube 1 is detected by a detection coil to determine the presence or absence of a defect. It is. However, the deformed portion 1c and the tube plate 2 of the heat transfer tube 1 exist near the region where the circumferential crack E is likely to occur in the non-expanded tube portion 1b of the heat transfer tube 1, and the deformed portion 1c and the tube of the heat transfer tube 1 exist. Since the change in the eddy current caused by the plate 2 is detected as noise, it is difficult to detect the circumferential crack E.

  7A and 7B (however, in FIG. 7A, when the circumferential crack E does not occur, FIG. 7B shows the circumferential crack E. As shown in FIG. 2, an eddy current flaw sensor having a pair of exciting coils 3 </ b> A and 3 </ b> B and a detection coil 4 disposed therebetween is proposed (for example, see Non-Patent Document 1).

  The exciting coils 3A and 3B are arranged so that the coil axis direction is substantially perpendicular to the inspection surface (inner peripheral surface) of the heat transfer tube 1 and spaced apart from each other in the circumferential direction of the heat transfer tube 1, and are opposite to each other. The exciting current is allowed to flow. Thereby, in the area | region between exciting coil 3A, 3B, the eddy current by exciting coil 3A, 3B is piled up, and the eddy current of the axial direction (left-right direction in a figure) of the heat exchanger tube 1 is strengthened.

  The detection coil 4 is arranged such that the coil axial direction is the axial direction of the heat transfer tube 1, and detects a change in eddy current in the circumferential direction of the heat transfer tube 1. Thereby, the circumferential crack E is detected, reducing the detection noise resulting from the deformation | transformation part 1c and the tube sheet 2 of the heat exchanger tube 1. FIG. If it demonstrates in detail, the deformation | transformation part 1c of the heat exchanger tube 1 will be formed substantially equally over the perimeter. Therefore, as indicated by arrows in FIG. 7A, the eddy current in the axial direction of the heat transfer tube 1 due to the excitation coils 3 </ b> A and 3 </ b> B is detoured to one side and the other side in the circumferential direction by the deformed portion 1 c of the heat transfer tube 1. For example, the amplitude of the voltage applied to the exciting coils 3A and 3B is the same (in other words, the amplitude of the exciting current is the same), and the magnitude of the eddy current by the exciting coil 3A is the same as the magnitude of the eddy current by the exciting coil 3B. By arranging the detection coil 4 on the symmetry axis L between the exciting coils 3A and 3B, the above-mentioned bypass currents on the one side and the other side in the circumferential direction are canceled at the detection position of the detection sensor 4. The detection noise caused by the deformed portion 1c of the heat transfer tube 1 can be reduced. Similarly, the detection noise caused by the tube sheet 2 existing over the entire outer periphery of the heat transfer tube 1 can be reduced. On the other hand, the circumferential crack E of the heat transfer tube 1 is locally generated in the circumferential direction. Therefore, as indicated by the arrows in FIG. 7B, the eddy current in the axial direction of the heat transfer tube 1 due to the exciting coils 3A and 3B is biased to one of the circumferential direction one side or the other side by the circumferential crack E. Detour. And since the detection sensor 4 detects this biased detour current, the presence or absence of the circumferential crack E can be detected. At this time, the detection signal of the detection sensor 4 includes the signal (S) due to the circumferential crack E and the noise (N) due to the deformed portion 1c of the heat transfer tube 1 and the tube plate 2, but as described above, the noise ( N) is reduced.

Masashige Shigeshi et al., “Development of Eddy Current Flaw Sensors for Inspection of Heat Transfer Tube Expanded Parts”, 2006 Autumn Meeting Lecture Summary Collection, Japan Nondestructive Inspection Association, p187-188

However, there are the following problems in the above-described prior art.
That is, in the above prior art, for example, the amplitude of the voltage applied to each of the exciting coils 3A and 3B is the same (in other words, the amplitude of the exciting current is the same), and on the symmetry axis L between the exciting coils 3A and 3B. By arranging the detection coil 4, the bypass currents on the one side and the other side in the circumferential direction are canceled at the detection position of the detection coil 4, and detection noise is reduced due to the deformed portion 1 c of the heat transfer tube 1 and the tube plate 2. It comes to plan. However, since the position accuracy of the detection coil 4 is limited due to manufacturing reasons, the balance of the detour currents on the one side and the other side in the circumferential direction is slightly unbalanced at the detection position of the detection coil 4, and the detection is slightly detected. Noise is generated. Further, even if the position accuracy of the detection coil 4 is high, if the distance (lift-off) of the excitation coils 3A and 3B with respect to the inspection surface of the heat transfer tube 1 is different, the magnitude of the eddy current by the excitation coil 3A and the magnitude of the eddy current by the excitation coil B are different. Therefore, the balance of the detour currents on the one side and the other side in the circumferential direction at the detection position of the detection coil 4 is slightly unbalanced, and detection noise is slightly generated. Therefore, there is room for improvement in terms of reduction of detection noise, that is, improvement of the SN ratio.

  An object of the present invention is to provide an eddy current flaw detection method and an eddy current flaw detection device that can reduce detection noise and increase the S / N ratio and improve the detection accuracy of defects.

(1) In order to achieve the above object, the present invention is arranged so that the coil axis direction is substantially perpendicular to the examination surface of the subject and spaced apart from each other in the coil radial direction. A pair of exciting coils for inducing current, the coil axial direction is substantially parallel to the inspection surface of the subject, and the coil axial direction is substantially perpendicular to a linear direction connecting the center positions of the pair of exciting coils. In the eddy current flaw detection method using an eddy current flaw detection sensor having a detection coil disposed between the pair of excitation coils and detecting a change in eddy current induced in the subject, the excitation of the pair A first procedure for inputting and setting a first voltage pattern having different amplitudes of voltages to be applied to the coils, and adjusting voltages based on the first voltage pattern to apply voltages having different amplitudes to the pair of exciting coils. You A second procedure for creating first detection data based on the detection signal of the detection coil and recording the first detection data is different from a second procedure in which the amplitudes of the voltages applied to the pair of excitation coils are different. A third procedure for inputting and setting the voltage pattern, and adjusting the voltage based on the second voltage pattern to apply voltages having different amplitudes to the pair of excitation coils, and based on the detection signal of the detection coil A fourth procedure for creating second detection data and recording the second detection data, and confirming the magnitude of noise in the first detection data and the second detection data, In order to determine which of the voltage pattern and the second voltage pattern is preferable, the method includes a fifth procedure for displaying the first detection data and the second detection data.
(2) In order to achieve the above object, the present invention is arranged so that the coil axis direction is substantially perpendicular to the examination surface of the subject and spaced apart from each other in the coil radial direction, and the subject is swirled. A pair of exciting coils for inducing current, the coil axial direction is substantially parallel to the inspection surface of the subject, and the coil axial direction is substantially perpendicular to a linear direction connecting the center positions of the pair of exciting coils. wherein disposed between the pair of exciting coils so that, in the above eddy current testing apparatus having an eddy current testing sensor and a detection coil for detecting a change of the induced eddy currents in the object, the excitation of the pair a voltage pattern setting means amplitude of the voltage applied respectively to the coils to input setting different voltage patterns, respectively to the excitation coils of the pair in accordance with the voltage pattern input set by the voltage pattern setting means An excitation voltage adjusting means for adjusting the amplitude of the voltage to be pressurized, the detected data generating means for generating a detection data based on a detection signal of the detection signals, respectively corresponding to the plurality of voltage pattern set by the voltage pattern setting means And detecting data recording means for recording a plurality of detection data created by the detection data creating means, and confirming the magnitude of noise in the plurality of detection data, and any of the plurality of voltage patterns is preferable. In order to determine whether or not, detection data display means for displaying the plurality of detection data is provided.

  According to the present invention, the detection noise can be reduced and the SN ratio can be increased, and the defect detection accuracy can be improved.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In addition, this embodiment makes the heat exchanger tube 1 of the heat exchanger mentioned above a test object, and attaches | subjects the same code | symbol to the part equivalent to the above, and abbreviate | omits description suitably.

  FIG. 1 is a diagram illustrating the eddy current flaw detection sensor according to the present embodiment together with the cross-sectional structure of the heat transfer tube 1. FIG. 2A is a radial sectional view showing the structure of the eddy current flaw detection sensor, and FIG. 2B is a partially enlarged view showing the arrangement direction of the excitation coil and the detection coil in FIG. FIG.

  In FIG. 1, FIG. 2A and FIG. 2B, an eddy current flaw detection sensor 5 includes a cylindrical main body case 6 that can be inserted into the heat transfer tube 1, and a circumferential direction in the main body case 6. For example, there are four exciting coils 7A to 7D arranged at intervals, and four detecting coils 8A to 8D arranged between the exciting coils 7A to 7D, respectively. That is, a combination of the excitation coils 7A and 7B and the detection coil 8A (first channel), a combination of the excitation coils 7B and 7C and the detection coil 8B (second channel), and a combination of the excitation coils 7C and 7D and the detection coil 8C. (Third channel), and has four channels consisting of combinations (fourth channel) of excitation coils 7D, 7A and detection coil 8D.

  The exciting coils 7A to 7D are arranged so that the coil axis direction (vertical direction in FIG. 2B) is substantially perpendicular to the inspection surface (inner peripheral surface) of the heat transfer tube 1. In addition, in the exciting coils 7A to 7D, exciting currents that are opposite to each other are passed through adjacent exciting coils, so that eddy currents from the exciting coils are superimposed in the region of each channel, and the axial direction of the heat transfer tube 1 The eddy current is strengthened.

  The detection coils 8 </ b> A to 8 </ b> D are arranged such that the coil axial direction (the direction perpendicular to the inner surface of FIG. 2B) is the axial direction of the heat transfer tube 1 (in other words, the coil axial direction is the heat transfer tube 1. The coil axis direction is substantially perpendicular to the linear direction connecting the center positions of the exciting coils in each channel), and the vortex in the circumferential direction of the heat transfer tube 1 A change in current is detected. Thereby, the circumferential crack E is detected, reducing the detection noise resulting from the deformation | transformation part 1c and the tube sheet 2 of the heat exchanger tube 1. FIG.

  Next, an eddy current flaw detector provided with the eddy current flaw detection sensor 5 will be described with reference to FIG. FIG. 3 is a block diagram showing the configuration of the eddy current flaw detector according to the present embodiment.

  In FIG. 3, the eddy current flaw detection apparatus includes an eddy current flaw detection sensor 5, a winder 10 that feeds out or winds up a lead wire 9 connected to the eddy current flaw detection sensor 5, and a lead of the winder 10. A voltage is applied to the excitation coils 7A to 7D of the eddy current flaw sensor 5 via the position control circuit 11 for controlling the amount of extension of the line 9 and the voltage regulator 12, and from the detection coils 8A to 8D of the eddy current flaw sensor 5. An eddy current flaw detector 13 for inputting a detection signal (induced voltage signal), a computer (electronic computer) 14 connected to the position control circuit 11 and the eddy current flaw detector 13, and a monitor 15 connected to the computer 14. It has.

  The computer 14 is configured to store setting information set in advance or setting information set in accordance with an operator's input in a storage device (not shown). Then, the computer 14 outputs setting information including, for example, the moving speed and moving amount of the eddy current flaw detection sensor 5 to the position control circuit 11, and the position control circuit 11 drives and controls the winder 10 based on this setting information. The eddy current flaw detection sensor 5 is moved in the axial direction of the heat transfer tube 1. Further, the computer 14 outputs setting information including, for example, the frequency and amplitude of the excitation voltage to the eddy current flaw detector 13, and the eddy current flaw detector 13 adjusts the voltage based on the setting information (however, the voltage amplitude). The details of the adjustment will be described later). The excitation coils 7A to 7D of the eddy current flaw detection sensor 5 are applied. In addition, the computer 14 inputs detection signals from the detection coils 8A to 8D of the eddy current flaw detection sensor 5 via the eddy current flaw detector 13, and performs predetermined calculation processing on the detection signals, for example, the detection coils 8A to 8D. Detection data (waveform data) associated with the detection positions is generated, and the detection data and the like are displayed on the monitor 15.

  Here, as a major feature of the present embodiment, the computer 14 can input and set the amplitude of the voltage applied to the exciting coils 7A to 7D, and the setting signal of the eddy current flaw detector 13 corresponding to this setting information is the voltage regulator. 12 is output. The voltage adjuster 12 adjusts the amplitude of the voltage applied to the exciting coils 7A to 7D according to the setting signal. Detailed functions of the voltage regulator 12 will be described with reference to FIG. FIG. 4 is a block diagram showing detailed functions of the voltage regulator.

  In FIG. 4, a voltage regulator 12 has exciting coils 7A to 7D connected in parallel, and is connected in series to the exciting coils 7A to 7D, respectively, and adjusts the amplitude of the voltage applied to the exciting coils 7A to 7D. 16A to 16D (however, a power amplifier may be used instead of these voltage dividers) and a control unit 17 (such as a CPU) for controlling the voltage dividers 16A to 16D based on a setting signal from the eddy current flaw detector 13. is doing.

  Next, the operation of the eddy current flaw detector according to this embodiment will be described.

  First, one of the plurality of heat transfer tubes 1 to be inspected is selected, and the eddy current flaw detection sensor 5 is arranged at the inspection start position in the heat transfer tube 1. Then, the operator inputs and sets the first voltage pattern with different amplitudes of the voltages applied to the excitation coils 7 </ b> A to 7 </ b> D of the eddy current flaw detection sensor 5 using the computer 14. Thereafter, when the operator inputs an inspection start instruction with the computer 14, the winder 10 is driven and the eddy current flaw detection sensor 5 moves in the axial direction of the heat transfer tube 1. At the same time, the exciting coils 7A to 7D of the eddy current flaw sensor 5 are excited by the eddy current flaw detector 13 and the voltage regulator 12, and the change of the eddy current induced in the heat transfer tube 1 is detected by the detection sensors 8A to 8D. Detected. Then, the computer 14 acquires detection signals of the detection sensors 8A to 8D via the eddy current flaw detector 13, and creates first detection data in which the positions of the detection sensors 8A to 8D are associated based on the detection signals. The created first detection data is recorded in the storage device and displayed on the monitor 15. The operator visually checks the first detection data displayed on the monitor 15 to confirm the magnitude of noise caused by the deformed portion 1c of the heat transfer tube 1 and the tube sheet 2, and the circumferential crack E and the like. Determine if there is a defect.

  Thereafter, the eddy current flaw detection sensor 5 is returned to the inspection start position in the same heat transfer tube 1, and the operator inputs and sets the second voltage pattern with the computer 14, and the heat transfer tube 1 is re-inspected in the same procedure as described above. . As a result, the computer 14 creates second detection data, records the created second detection data in the storage device, and causes the monitor 15 to display the second detection data. The operator visually checks the second detection data displayed on the monitor 15 to confirm the magnitude of noise caused by the deformed portion 1c of the heat transfer tube 1 and the tube sheet 2, and the circumferential crack E and the like. Recheck for defects. Thereafter, the operator displays the first detection data and the second display data on the monitor 15 and compares the magnitudes of noises. Which of the first voltage pattern and the second voltage pattern is preferable? Judging. For example, when it is determined that neither the first voltage pattern nor the second voltage pattern is preferable, the third voltage pattern is input and set, and the heat transfer tube 1 is re-inspected in the same procedure as described above. Then, the magnitude of noise in the third voltage pattern is checked to determine whether the third voltage pattern is preferable. On the other hand, when it is determined that any one of the voltage patterns is preferable, the voltage pattern is input and set by the computer 14 and the process proceeds to the inspection of the other heat transfer tube 1.

  As described above, in this embodiment, the amplitude of the voltage applied to the excitation coils 7A to 7D by the voltage regulator 12 so that the detection noise caused by the deformed portion 1c of the heat transfer tube 1 and the tube plate 2 is reduced. Make them different from each other. This can reduce detection noise caused by the influence of the positional accuracy of the detection sensors 8A to 8D in each channel, the difference in lift-off of the exciting coils 7A to 7D, and the S / N ratio. Therefore, the detection accuracy of defects such as circumferential cracks E can be improved.

  Moreover, in order to confirm the effect of this embodiment mentioned above, this inventor performed the numerical calculation using the calculation model shown to Fig.5 (a). The simulated heat transfer tube 18 in this calculation model is a cylindrical tube made of stainless steel (SUS316) having an outer diameter of 15.9 mm and a wall thickness of 2.3 mm, and the inner peripheral surface of the cylindrical tube having an axial dimension of about 0.2 mm. The deforming portion 18a is provided over the entire circumference. The eddy current flaw detection sensor 19 has the same structure as that of the eddy current flaw detection sensor 5, and one lift-off of the pair of exciting coils in each channel is 0.8 mm and the other is 0.9 mm. The voltage condition applied to one excitation coil (in other words, the excitation coil having a small lift-off) is fixed at Vo, and the voltage condition applied to the other excitation coil (in other words, the excitation coil having a large lift-off) is set to Vo, Numerical calculation was performed by changing to 1.2Vo or 1.5Vo. As a result, detection data as shown in FIG. 5B was obtained. In FIG. 5B, the horizontal axis represents the position of the detection sensor in the axial direction of the simulated heat transfer tube 18 (however, zero corresponds to the position of the deformed portion 18a of the simulated heat transfer tube 18), and the vertical axis represents Represents the amplitude of the detection signal. As is clear from this result, when the voltage applied to the pair of exciting coils in each channel is different (in the case of the voltage conditions 1.2 Vo and 1.5 Vo), the voltage is the same (in the voltage condition Vo). Detection noise can be reduced as compared with the case (1).

  In the above-described embodiment, the eddy current flaw detection sensor 5 is configured such that the excitation coils 7A to 7D and the detection coils 8A to 8D are arranged at equal intervals in the circumferential direction of the main body case 6, and the heat transfer tube is used by the winder 10. The case of moving only in one axial direction has been described as an example, but the present invention is not limited to this. That is, for example, the excitation coil and the detection coil may be locally arranged in the circumferential direction of the main body case. In this case, the eddy current flaw detection sensor may be rotated in the circumferential direction of the heat transfer tube. Even in such a modification, the same effect as described above can be obtained.

  Moreover, in the said one Embodiment, although demonstrated taking the case where the heat exchanger tube 1 of a heat exchanger was made into a test object, it is not restricted to this. That is, for example, it may be applied to a case where pipes for other uses are to be inspected and the purpose is to reduce detection noise caused by a support member or the like existing all around the outer circumference of the pipe. Good. In such a case, the same effect as described above can be obtained.

It is a figure showing the eddy current flaw sensor which comprises one Embodiment of the eddy current flaw detector of this invention with the cross-sectional structure of the heat exchanger tube to be examined. It is the radial direction sectional view showing the structure of the eddy current flaw detection sensor which constitutes one embodiment of the eddy current flaw detector of the present invention, and the partial enlarged view showing the arrangement direction of the excitation coil and the detection coil. It is a block diagram showing the whole structure of one Embodiment of the eddy current flaw detector of this invention. It is a block diagram showing the detailed function of the voltage regulator which comprises one Embodiment of the eddy current flaw detector of this invention. It is a figure for demonstrating the effect of one Embodiment of the eddy current flaw detector of this invention, and each represents the detection data of the detection sensor which is a calculation model and a calculation result. It is a figure showing the cross-sectional structure of the heat exchanger tube of the test target in a prior art. It is a figure showing the structure and arrangement | positioning of the eddy current flaw detection sensor in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat transfer tube 5 Eddy current flaw detection sensor 7A-7D Excitation coil 8A-8D Detection sensor 12 Voltage regulator (excitation voltage adjustment means)
14 Computer (input setting means)

Claims (2)

A pair of exciting coils for inducing an eddy current in the subject, the coil axis direction being substantially perpendicular to the test surface of the subject and being spaced apart from each other in the coil radial direction; Arranged between the pair of excitation coils so as to be substantially parallel to the test surface of the subject and so that the coil axis direction is substantially perpendicular to the linear direction connecting the center positions of the pair of excitation coils, In an eddy current flaw detection method using an eddy current flaw detection sensor having a detection coil for detecting a change in eddy current induced in a subject,
A first procedure for inputting and setting first voltage patterns having different amplitudes of voltages applied to the pair of exciting coils, respectively;
A voltage is adjusted based on the first voltage pattern to apply voltages having different amplitudes to the pair of exciting coils, and first detection data is generated based on a detection signal of the detection coil. A second procedure for recording the detection data of
A third procedure for inputting and setting a second voltage pattern having different amplitudes of voltages applied to the pair of excitation coils,
A voltage is adjusted based on the second voltage pattern to apply voltages having different amplitudes to the pair of exciting coils, and second detection data is created based on a detection signal of the detection coil. A fourth procedure for recording the detection data of
In order to confirm the magnitude of noise in the first detection data and the second detection data, and to determine which of the first voltage pattern and the second voltage pattern is preferable, An eddy current flaw detection method comprising: first detection data; and a fifth procedure for displaying the second detection data . A pair of exciting coils for inducing an eddy current in the subject, the coil axis direction being substantially perpendicular to the test surface of the subject and being spaced apart from each other in the coil radial direction; Arranged between the pair of excitation coils so as to be substantially parallel to the test surface of the subject and so that the coil axis direction is substantially perpendicular to the linear direction connecting the center positions of the pair of excitation coils, In an eddy current flaw detector comprising an eddy current flaw detection sensor having a detection coil for detecting a change in eddy current induced in a subject,
Voltage pattern setting means for inputting and setting voltage patterns having different amplitudes of voltages applied to the pair of excitation coils,
An excitation voltage adjusting means for adjusting the amplitude of the voltage applied respectively to the exciting coils of the pair in accordance with the voltage pattern input set by the voltage pattern setting means,
Detection data creating means for creating detection data based on the detection signal of the detection signal;
Detection data recording means for recording a plurality of detection data created by the detection data creation means corresponding to the plurality of voltage patterns set by the voltage pattern setting means;
In order to confirm the magnitude of noise in the plurality of detection data and to determine which of the plurality of voltage patterns is preferable, a detection data display means for displaying the plurality of detection data is provided. An eddy current flaw detector characterized by

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