JPH09119919A - Eddy current flaw detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a high sensitivity detection while preventing generation of a dead band by providing a means for selecting a coil to be controlled by a control means by operating any one of a plurality of switches. SOLUTION: A plurality of coils 101a-101h, 102a-102h are arranged annularly with each coil overlapping its adjacent coil partially. The eddy current flaw detector comprises a plurality of function switches for making a first coil 102a and adjacent second and third coils 102h, 102b among a plurality of the coils selectively function, a means for controlling the first coil 102a to function as flaw detecting means and to excite the coils 102h, 102b, and a means for selecting the coils 102, 102b, 102c in first to third coils contiguous in the same direction as the coils to be controlled by the control means at a specified timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-sensitivity eddy current flaw detector applied to inspection work of metal thin tubes such as heat exchanger tubes.

[0002]

2. Description of the Related Art FIG. 7 is a diagram showing the overall structure of a conventional eddy current flaw detector of this type. In FIG. 7, reference numeral 21 denotes a subject capillary, and the subject capillary 21 has a defect 22. 210 is a probe, and this probe 210
Is composed of detection coils 201, 202 and the like, and moves in the direction indicated by arrow L. The probe 210 is connected to the flaw detector 212 via a cable 211.

The flaw detector 212 applies an alternating current to the detection coils 201 and 202 via the cable 211 and processes an amplified signal of an impedance change or an induced voltage change of the detection coils 201 and 202. The flaw detector 212 is connected to a recorder 215 such as a pen recorder via a cable 213. A chart 216 is output from the recorder 215. On the chart 216, 217 is a waveform drawn by the recorder 215 (pen recorder), and 218 is a defect signal (that is, a signal indicating a defect due to a flaw in the subject thin tube 21) in the waveform. .

FIG. 8 is a view for explaining the principle of the detection coils 201 and 202 which are the sensor section shown in FIG. 7, and FIG. 8A is a side sectional view of the subject thin tube 21,
FIG. 8B is a front sectional view of the subject thin tube 21. In FIG. 8, the same parts as those in FIG. 7 are designated by the same reference numerals. In FIG. 8A, reference numerals 221 and 222 denote magnetic fields generated by the detection coils 201 and 202, respectively.
Further, as shown in FIG. 8B, the detection coils 201, 2
02 has a circular cross section.

FIG. 9 is a diagram showing an example of electrical connection of the eddy current flaw detector. In FIG. 9, the same parts as those in FIGS. 7 and 8 are designated by the same reference numerals. In FIG. 9, reference numeral 233 denotes an oscillator, and this oscillator 233 has variable impedances 231 and 232 and detection coils 201 and 202.
It is connected to the. Variable impedance 231, 232
Is for adjusting the unevenness of the characteristics of the detection coils 201 and 202, and the oscillator 233 is for the detection coils 201 and 202.
Apply alternating current to the.

Further, variable impedances 231 and 23
2, an amplifier / signal processor 234 is connected to the detection coils 201 and 202 and the oscillator 233. The amplifier / signal processor 234 amplifies the impedance change or induced voltage change of the detection coils 201 and 202 and performs signal processing, and outputs the processing result to the recorder 215 via terminals 235 and 236. The variable impedance 231, 232, the oscillator 233, the amplifier / signal processor 234, and the terminals 235, 236 constitute the flaw detector 212.

7 to 9, the probe 210 is moving inside the subject thin tube 21 in the direction shown by the arrow L in FIG.
The detection coils 201 and 202 provided in the
The cable 2 can be
An alternating current flows through 11. As described above, the detection coils 101 and 102 have a circular shape, and when an alternating current flows, alternating magnetic fields 221 and 222 as shown in FIG.

The alternating magnetic fields 221 and 222 interlink with the subject thin tube 21, and eddy currents flowing in the circumferential direction of the subject thin tube 21 are generated in the portions close to the detection coils 201 and 202. In the portion where the defect 22 does not exist in the subject thin tube 21, the eddy current becomes uniform over the entire circumference. However, when the detection coils 201 and 202 approach defect 22, defect 2
The eddy current does not flow in the portion 2 and the flow of the eddy current changes in the portion. Further, an alternating magnetic field is generated by the eddy current flowing, and this alternating magnetic field is generated by the detection coil 2.
01, 202 acts on the magnetic field generated by the detection coil 20
Affects the impedance value of 1,202.

As described above, the flow of the eddy current flowing through the sample thin tube 11 changes at the defect 22. Therefore, when the detection coils 201 and 202 approach that portion, the induced voltage or impedance of the detection coils 201 and 202 changes.

As shown in FIG. 9, the detection coil 201,
Reference numeral 202 denotes a variable impedance 231, 232 inside the flaw detector 212, an oscillator 233, an amplifier
It is connected to the signal processor 234 and the like. The variable impedances 231 and 232 remove the induced voltage or the difference in impedance caused by the difference in characteristics that occurs when both the detection coils 201 and 202 are arranged in the portion of the subject capillary 21 where the defect 22 does not exist. It is provided for. In the sound part where the defect 12 does not exist, nothing is output from the amplifier / signal processor 234 (voltage 0 V is output).

The output from the flaw detector 212, that is, the output from the amplifier / signal processor 234 is input to the recorder 215 through the cable 213 as shown in FIG. The probe 210 is moved in the direction indicated by the arrow L in the center of the subject thin tube 21. Then, as the probe 210 passes through the portion of the defect 22, a signal 218 caused by the defect 22 is generated in the waveform 217 of the chart 216 of the recorder 215. When the operator confirms the presence or absence of this signal 218, the defect 2 in the subject thin tube 21 is detected.
The presence or absence of 2, that is, the soundness of the subject thin tube 21 can be known.

As described above, in the conventional eddy current flaw detector, the probe 210 is moved in the axial direction inside the subject capillary 21 to determine whether the subject capillary 21 has a defect, that is, the subject capillary 21. It is possible to know the soundness and is widely used for the inspection of thin tubes of various heat exchangers.

[0013]

In the detection coil concentric with the cross-sectional shape of the subject thin tube 21 shown in FIG. 8, an eddy current flows in the circumferential direction of the fleshy part of the subject thin tube 21 as described above. The strength of the eddy current is uniform all around. Therefore, there is a problem in that the detection sensitivity is reduced for defects (cracks, etc.) having a small area distributed in a part of the subject thin tube 21 in the circumferential direction. In order to solve this problem, the following methods have been considered.

10 (a) and 10 (b) are actual application 5
It is sectional drawing for demonstrating the principle of the division | segmentation type detection coil of the eddy current flaw detection apparatus currently disclosed by 6-57376, (a) is a sectional side view, (b) is a front sectional view. FIG.
The split type detection coil indicated by 0 divides one detection coil into a plurality (four). A switching method is adopted to improve the handling and workability.

In FIGS. 10A and 10B, 2
01a to 201d (201d is not shown) and 202a
Reference numerals 202 to 202d respectively denote detection coils. Defects (cracks, etc.) with a small area in the circumferential direction of the split type detection coil 2
The detection sensitivity to 2 is improved by about 4 times as compared with the normal detection coil shown in FIG. 8 because the entire circumference is shared by the four coils.

11 (a) and 11 (b) are diagrams showing the magnetic field strength distribution of the conventional detection coil, FIG. 11 (a) is the magnetic field strength distribution by the normal detection coil shown in FIG. 8, and FIG. 11 is a magnetic field strength distribution by the split type detection coil shown in FIG. 10. In the case of a normal detection coil as shown in FIG. 11A, one magnetic field intensity distribution 31 is formed, and in the case of a split type detection coil as shown in FIG. 11B, a plurality of magnetic field intensity distributions 31a to 31a. It consists of 31e.

As shown in FIG. 11B, the detection coils 201a to 201d and 202a to 202d shown in FIG.
The intensity distribution of each magnetic field generated by is about 1/4 of the normal detection coil shown in FIG. 8 in the circumferential direction. As described above, in the split-type detection coil, each intensity distribution in the circumferential direction of the magnetic field is narrow. Therefore, for a defect having a small area in the circumferential direction, the ratio of acting on the defect in all the magnetic fields generated by one detection coil. And the detection sensitivity for such small area defects is improved.

FIG. 12 and FIG. 13 are disclosed in Japanese Patent Application No. 56-57376 in order to effectively take out the detection result from the above-mentioned split type detection coil in consideration of workability and handleability. FIG. 12 is an overall configuration diagram of an eddy current flaw detector to which the split detection coil is applied, FIG.
3 is a diagram showing a connection state of each detection coil and a semiconductor switch. 12 and 13, the same parts are designated by the same reference numerals.

In FIG. 12, reference numeral 250 is a multiplexer, and this multiplexer 250 is composed of a plurality of semiconductor switches. The multiplexer 250 includes the detection coils 201a to 201d and 202a to 20d.
2d is connected, and the flaw detector 220 is connected via a signal line 251. Further, a recorder 215 is connected to the flaw detector 220 via a cable 221.

211a to 211d and 2 shown in FIG.
Reference numerals 12a to 212d denote semiconductor switches inside the multiplexer 250. These semiconductor switches 211a-21
The 1d and 212a to 212d are controlled by the flaw detector 220 so that each pair is simultaneously turned on in pairs (for example, 211a and 212a). Thereby, the detection coils 201a-
One pair of 201d and 202a to 202d (for example, when 211a and 212a are turned on, 201a and 2
02a) At the same time, it is connected to the flaw detector 220 via the signal line 251. The signal line 251 is connected to the multiplexer 250.
It is a signal line for transmitting the signal processed in (1) to the flaw detector 220.

The output corresponding to the detection result of the above-mentioned pair of detection coils is sent from the flaw detector 220 to the cable 22.
1 is transmitted to the recorder 215. Waveforms 217a to 217d are drawn on the chart 216 of the recorder 215, and a signal 218 due to a defect is generated on the waveform 217a corresponding to the detection coil pair that has passed through the defective portion 22. By observing this, the operator can know the presence of a defect in the subject thin tube 21. With the eddy current flaw detector having such a configuration, flaw detection with high sensitivity to a defect (a crack or the like) having a small area in the circumferential direction of the subject capillary can be performed.

However, in the conventional flaw detection device for the split type detection coil which aims to improve the detection sensitivity to the defect having a small area in the circumferential direction as described above, as shown in FIG. Magnetic field strength (for example, between the magnetic field strengths 31a and 31b) is lower than other portions (the magnetic field strengths 31a to 31e of the respective detection coils), and the defect detection sensitivity of the magnetic field strength between the respective detection coils is reduced. That is, there is a problem that a dead zone occurs.

It is an object of the present invention to provide an eddy current flaw detector which has no portion where the magnetic field strength is weakened over the entire circumference of an object to be inspected, has high sensitivity of detection and does not generate a dead zone. .

[0024]

In order to solve the above problems and achieve the object, the eddy current flaw detector of the present invention is constructed as follows. An eddy current flaw detector according to the present invention is an eddy current flaw detector that performs flaw detection based on the magnetic field strength of an eddy current generated by a plurality of coils, wherein the plurality of coils are annularly arranged so as to partially overlap adjacent coils. , A plurality of switches for selectively operating the first coil of the plurality of coils and the second and third coils adjacent to the first coil, and detecting the flaw detection of the first coil A control unit that functions as a unit and controls so as to excite the second and third coils, and a coil to be controlled by the control unit is the same as the first to third coils at predetermined timings. Selection means for selecting by operating any of the plurality of switches so that the coils are adjacent to each other in the direction.

As a result of taking the above-mentioned means, the following actions will occur. According to the eddy current flaw detector of the present invention, a plurality of coils are arranged in an annular shape so as to partially overlap adjacent coils, and the first coil functions as a unit for detecting flaw detection, and the first coil The second and third coils adjacent to are controlled to be excited. Then, the control target is selected by activating any of the plurality of switches so as to make each coil adjacent to the first to third coils in the same direction at a predetermined timing.

As a result, the eddy currents generated by the coils always overlap at each timing (every time), so that the magnetic field distribution completely overlaps the magnetic field distribution at the timing before and after that. Therefore, there is no part where the magnetic field strength is weakened over the entire circumference of the inspection target. As a result, it is possible to realize an eddy current flaw detector that has a highly sensitive detectability, does not generate a dead zone, and can significantly improve the detectability for defects (such as cracks) having a small area existing in the circumferential direction of the inspection target.

[0027]

1 is a sectional view showing a split type detection coil of an eddy current flaw detector according to an embodiment of the present invention, (a) is a side sectional view, and (b) is a front sectional view. Is. FIG.
At 101a-101h and 102a-102h
(101b, 101c, and 101d are not shown) are detection coils, and these detection coils 101a to 101h and 102a to 102h are annularly and evenly arranged along the circumference of the subject thin tube 11. Further, the respective detection coils 101a to 101h and 102a to 102h are
Each of them is arranged so as to partially overlap the adjacent coil.

2 (a) to 2 (c) are views showing the shape of each of the detection coils 101a to 101h and 102a to 102h, and FIG. 2 (a) shows the state as viewed in the circumferential direction of the subject thin tube 11. FIG. 2B is a diagram showing a state of the subject thin tube 11 viewed in the axial direction, and FIG. 6C is a diagram showing a state of the subject thin tube 11 viewed from the side surface. As shown in FIG. 2A, one detection coil has a rectangular shape.

FIG. 3 shows each of the detection coils 101a to 10a.
It is a figure which shows the connection state of 1h and 102a-102h. Detection coils 101a to 101h and 102a to 102
Each h is a pair (for example, 101a
And 102a are connected to the multiplexer 131). A flaw detector (not shown) is connected to the multiplexer 131 via a signal line 132. The configuration of the eddy current flaw detector is the same as that of the detection coil 2 shown in FIG.
01a to 201d and 202a to 202d, the multiplexer 250 and the signal line 251 are replaced with the above-described detection coils 101a to 101h and 102a to 102h, the multiplexer 131 and the signal line 132, respectively.

FIG. 4 shows the above-mentioned detection coils 101a to 101a.
It is a figure which shows the connection state of 101h and 102a-102h and a semiconductor switch. In FIG. 4, 111a-11
1h, 112a to 112h, 113a to 113h, and 114a to 114h are semiconductor switches, respectively, and constitute a multiplexer 131.

As shown in FIG. 4, the detection coils 101a.about.
101h and 102a to 102h are paired one by one (for example, 101a and 102a are paired),
It is connected. Then, the detection coils 101a to 101
h are semiconductor switches 111a to 111h and 1 respectively.
13a to 113h are connected one by one (for example,
Semiconductor switches 111a and 11 are provided on the detection coil 101a.
3a is connected), the detection coils 102a to 102
h are semiconductor switches 112a to 112h and 1 respectively.
14a to 114h are connected one by one (for example,
Semiconductor switches 112a and 11 are provided on the detection coil 102a.
4a is connected).

Further, the detection coils 101a to 101h, 1
02a-102h and semiconductor switches 111a-11
1h, 112a to 112h, 113a to 113h, 11
4a to 114h are connected to the corresponding signal lines 132, respectively.

FIG. 5 shows the detection coils 101a-101.
It is a figure which shows the state of eddy current at each timing A, B, C of h and 102a-102h in the circumferential direction. FIG.
121a to 121c (122a to 122c)
Indicates the eddy current generated in the subject thin tube 11 at each timing A, B, and C.

FIG. 6 shows the detection coils 101a-101.
h and timings A, B, and C of 102a to 102h
It is a figure showing distribution of magnetic field strength at time. At the timing "A" in FIG. 5, the magnetic field intensity distribution 141 as shown in FIG. 6A acts on the subject thin tube 11, and the timing "B".
Then, the magnetic field strength distribution 142 as shown in FIG. Further, at the timing "C", the magnetic field distribution 143 as shown in FIG.

In the eddy current flaw detector, the semiconductor switch 11 inside the multiplexer 131 is provided by a flaw detector (not shown).
1a to 111h, 112a to 112h, 113a to 11
3h and 114a-114h are activated at appropriate times. As a result, as shown in FIG. 5, at the timing "A", the detection coils 101h (102h) and 1
01b (102b) is excited, the detection coil 101a
(102a) acts as a detector.

Similarly, at the timing "B", the detection coils 101a (102a) and 101c (102c) are excited, causing the detection coil 101b (102b) to act as a detector, and at the timing "C", the detection coil 101b.
(102b) and 101d (102d) are excited,
The detection coil 101c (102c) acts as a detector. In this way, three adjacent coils (three pairs) are operated as one group.

The flaw detector selects the coil of this group by
Each time the timing advances by one (for example, from timing A to timing B), it moves by 45 ° in one circumferential direction (for example, 101h and 101a and 101b to 101a and 10).
1b and 101c) by activating the corresponding semiconductor switch. As a result, when the timing advances by eight, the selection of the coils of the first group moves one round in the one circumferential direction, and further such circumferential movement is repeated.

By exciting two coils on both sides of the three adjacent coils in this manner, a portion corresponding to the subject thin tube 11 at a position where one coil for the purpose of center detection is present. The eddy currents that flow at each timing A, B, C
121a, 121b, 1 shown in FIG.
21c. When there is a defect in the portion corresponding to the subject thin tube 11, the flow of the eddy current generated at each timing changes, and this influence changes the voltage induced in the detection coil at each timing to detect the defect. To be done.

The distribution of the magnetic field strength acting on the subject thin tube 11 at each timing is shown in FIG. 6. The magnetic field distribution range is shifted by 45 ° in the circumferential direction each time the timing advances. Further, as shown in FIG. 6, each magnetic field distribution 141, 142, 14 generated at each timing A, B, C
Since No. 3 has a portion that overlaps the magnetic field distribution at the timing before and after that, there is no portion where the magnetic field strength becomes weak over the entire circumference of the subject thin tube as shown in FIG. 11B.

As described above, according to the present embodiment,
The distribution of the magnetic field acting on the subject thin tube 11 at each timing A, B, and C is about 90 °, and this is transferred by 45 ° with each advance of the timing. As a result, the magnetic field distribution generated at each timing completely overlaps the magnetic field distribution at the timings before and after that, and there is no part where the magnetic field strength becomes weaker over the entire circumference of the subject thin tube 11. As a result, it has the same high-sensitivity detectability as the conventional split-type detection coil flaw detector, and since there is no part where the magnetic field strength weakens, no dead zone occurs and defects with a small area existing in the circumferential direction. The detectability for (cracking, etc.) will be greatly improved.

The present invention is not limited to the above-mentioned embodiment, and can be carried out by appropriately modifying it without changing the gist. (Modification) (1) In the above-mentioned embodiment, the subject having a tubular shape is described, but the present invention is not limited to the subject having a tubular shape, and can be applied to a subject having a flat plate shape or the like. (2) In the above embodiment, an example of using the coils as a pair (self-comparison method) has been described, but the present invention can be similarly applied when the coils are not used as a pair (standard comparison method). (3) In the above-described embodiment, the state in which eight coils are arranged around the entire circumference has been described, but the number of coils is not limited to eight, and the eddy current flaw detector of the present invention is theoretically provided that the number of coils is four or more. Operate.

[0042]

According to the present invention, it is possible to provide an eddy current flaw detector which has no sensitive magnetic field strength over the entire circumference of an object to be inspected, has a high sensitivity and has no dead zone.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a split type detection coil of an eddy current flaw detector according to an embodiment of the present invention.

FIG. 2 is a diagram showing a shape of a detection coil and an embodiment of the present invention.

FIG. 3 is a diagram showing a connection state of each detection coil according to the embodiment of the present invention.

FIG. 4 is a diagram showing a connection state between a detection coil and a semiconductor switch according to the embodiment of the present invention.

FIG. 5 is a diagram showing a state of an eddy current according to the embodiment of the present invention.

FIG. 6 is a diagram showing a distribution of magnetic field strength according to the embodiment of the present invention.

FIG. 7 is a diagram showing an overall configuration of an eddy current flaw detector according to a conventional example.

FIG. 8 is a diagram for explaining the principle of a detection coil according to a conventional example.

FIG. 9 is a diagram showing an example of electrical connection of an eddy current flaw detector according to a conventional example.

FIG. 10 is a sectional view for explaining the principle of a split type detection coil of an eddy current flaw detector according to a conventional example.

FIG. 11 is a diagram showing a magnetic field strength distribution of a detection coil according to a conventional example.

FIG. 12 is an overall configuration diagram of an eddy current flaw detection apparatus to which a split type detection coil according to a conventional example is applied.

FIG. 13 is a diagram showing a connection state between a detection coil and a semiconductor switch according to a conventional example.

[Explanation of symbols]

 11 ... Subject thin tube 101a-101h ... Detection coil 102a-102h ... Detection coil 131 ... Multiplexer 132 ... Signal line 111a-111h ... Semiconductor switch 112a-112h ... Semiconductor switch 113a-113h ... Semiconductor switch 114a-114h ... Semiconductor switch 121a- 121c ... Eddy current flow method 122a-122c ... Eddy current flow method 141-143 ... Magnetic field intensity distribution 21 ... Subject thin tube 22 ... Defect 201 ... Detection coil 202 ... Detection coil 210 ... Probe 211 ... Cable 212 ... Flaw detector 213 ... cable 215 ... recorder 216 ... recorder chart 217 ... chart waveform 218 ... defect waveform 221 ... magnetic field direction 222 ... magnetic field direction 231 ... variable impedance 232 ... variable impedance 233 ... Oscillator 234 ... Amplification / signal processor 201a-201d ... Detection coil 202a-202d ... Detection coil 3a, 3c ... Current flowing in coil 4a-4d ... Current flowing in coil 250 ... Multiplexer 251 ... Signal line 220 ... Flaw detector 225a-225d Adjusting knob 226a to 226d ... Adjusting knob 227 to 229 ... Adjusting knob 221 ... Cable 215 ... Recorder 216 ... Recorder chart 217a to 217d ... Waveform on chart 218 ... Waveform due to defect 211a to 211d ... Semiconductor switch 212a to 212d ... Semiconductor switch 31 ... Magnetic field intensity distribution by normal detection coil 31a to 31e ... Magnetic field intensity distribution

Claims (1)

[Claims] 1. An eddy current flaw detector that performs flaw detection based on the magnetic field strength of an eddy current generated by a plurality of coils, wherein the plurality of coils are annularly arranged so as to partially overlap adjacent coils. A plurality of switches for selectively operating the first coil of the coils and the second and third coils adjacent to the first coil; and causing the first coil to function as means for detecting flaw detection. Further, a control means for controlling the second and third coils to be excited, and a coil to be controlled by the control means are adjacent to the first to third coils in the same direction at every predetermined timing. An eddy current flaw detector, comprising: selection means for selecting one of the plurality of switches by operating it so as to form each coil.