JP5800696B2 - Remote field eddy current flaw detection system and remote field eddy current flaw detection method - Google Patents

Description

  The present invention relates to a remote field eddy current flaw detection system and a remote field eddy current flaw detection method using a probe having one or more excitation coils and two or more detection coils.

  A large number of magnetic heat transfer tubes are regularly arranged in the heat exchanger of the power plant. The magnetic heat transfer tube is U-shaped and has a straight pipe part with a length of several meters and a curved pipe part with various curvatures. A curved pipe is a straight pipe that is bent, and has a shape change at various curvatures and a flattened pipe.

  A remote field eddy current flaw detection method is known as one of inspection methods for magnetic heat transfer tubes. It is characterized by a probe structure in which an excitation coil and a detection coil are spaced apart. Since the excitation coil and the detection coil are arranged apart from each other, the direct magnetic field due to the excitation coil does not reach the detection coil, and only a weak indirect magnetic field due to the eddy current spreading to the magnetic heat transfer tube can be detected.

  On the other hand, since one defect is affected by the positions of the excitation coil and the detection coil, two defect signals are observed in the flaw detection waveform. When there are a plurality of defects in the tube axis direction, the flaw detection waveforms overlap, strengthening or canceling each other, resulting in a complicated waveform, making it difficult to detect the defects.

  Various probes have been proposed for such problems. For example, in Patent Document 1, two detection coils are arranged adjacent to each other in a steel pipe to be flaw-detected, and excitation coils separated from the detection coils are connected differentially. Remote field eddy current flaw detection systems have been proposed for placement at desired locations within a steel pipe.

  As a result, the differential output of the waveform due to the influence of the excitation coil becomes zero, only the waveform due to the influence of the detection coil is detected, and the flaw detection signal is easily distinguished.

JP-A 64-35261

  Furthermore, the probe described in Patent Document 1 has an excitation coil and a detection coil that are flexibly connected, which facilitates insertion into a curved portion of the U-shaped tube.

  However, in the remote field eddy current flaw detection by the probe described in Patent Document 1, noise caused by the bending shape is mixed with the flaw detection signal at the curved portion of the U-shaped tube, and it becomes difficult to detect the defect.

  That is, one excitation coil and two detection coils are arranged substantially parallel to the tube axis direction, and this arrangement is maintained in the tube straight portion, but this arrangement (between coils) is maintained in the bent portion according to the bending shape. Distance and angle). When the curvature is small (the curvature radius is large), it can be regarded as a detection error. However, as the curvature becomes large (the curvature radius becomes small), noise caused by the bending shape cannot be ignored.

  In addition, in the bent portion of a test tube having the same curvature as the inspection target tube and having no defects, the noise can be theoretically removed by acquiring noise in advance and subtracting it from the detection signal. It is necessary to accurately match the speed and inspection position, which is difficult to apply in practice.

  An object of the present invention is to provide a remote field eddy current flaw detection system and a remote field eddy current flaw detection method capable of improving the defect detection performance by reducing noise in the bent pipe portion.

(1) In order to achieve the above object, the present invention includes at least one excitation coil, and a first detection coil and a second coil that are arranged at positions away from the excitation coil and are arranged close to each other. Remote field eddy current comprising a probe having a detection coil, and an arithmetic processing device that obtains a flaw detection signal by phase detection of output voltages of the first detection coil and the second coil when the probe scans the inside of the magnetic tube In the flaw detection system, the first detection coil has a first inner detection coil and a first outer detection coil disposed on the outer axis of the first inner detection coil on a concentric axis of the first inner detection coil, The second detection coil includes a second inner detection coil and a second outer detection coil disposed on the outer axis of the second inner detection coil on a concentric axis of the second inner detection coil. Detection Yl and second outer detection coils are differentially connected to each other, said first inner detection coil and the second inner detection coil are differentially connected to each other, the arithmetic processing unit, when there is no defect in the portion to be detected A first signal that is a differential output between the first outer detection coil and the second outer detection coil is the same as a second signal that is a differential output between the first inner detection coil and the second inner detection coil. As described above, a first function unit that adjusts at least one of the first signal and the second signal using a preset first matrix, a first signal adjusted by the first function unit, and a first function A second function unit that compares two signals to obtain a difference, and a third function unit that corrects the signal obtained by the second function unit using a second matrix set in advance to a signal indicating the size of the defect It shall have .

  A difference between the inside and the outside is generated between the differential output of the first outer detection coil and the second outer detection coil and the differential output of the first inner detection coil and the second inner detection coil. If there is no defect in the detected part, the difference between the inside and outside is constant if the curvature of the tube is constant. However, if the detected part is defective, the difference between the inside and outside changes. By detecting this change as a flaw detection signal, a defect can be detected.

In addition, when there is no defect in the detected part, the first signal and the second signal after the calculation by the first function part are the same, and the calculation result by the second function part becomes zero. On the other hand, when the detected part is defective, the first signal and the second signal after the calculation by the first function part are not the same, the calculation result by the second function part is output, and the defect is detected by the third function part. A flaw detection signal indicating the size of the image is output.

  Thereby, a clearer flaw detection signal can be detected, and the defect detection performance in the curved pipe portion can be improved.

( 2 ) In the above (1), it is preferable that a curved portion of a U-shaped magnetic tube is a target for flaw detection.

( 3 ) In order to achieve the above object, the present invention includes at least one excitation coil, and a first detection coil and a second coil that are arranged at positions away from the excitation coil and are arranged close to each other. In a remote field eddy current flaw detection method for obtaining a flaw detection signal by causing a probe having a detection coil to scan the inside of a magnetic tube and phase-detecting the output voltages of the first detection coil and the second coil, the first detection coil comprises: A first inner detection coil and a first outer detection coil disposed on the outer axis of the first inner detection coil on a concentric axis of the first inner detection coil, the second detection coil being a second inner detection coil; And a second outer detection coil disposed outside the second inner detection coil on a concentric axis of the second inner detection coil, and the first outer detection coil and the second outer detection coil are different from each other. Dynamically connected The first inner detection coil and the second inner detection coil are differentially connected to each other, and are differential outputs of the first outer detection coil and the second outer detection coil when there is no defect in the detected portion. The first signal and the second signal, which are differential outputs of the first inner detection coil and the second inner detection coil, are set to be the same by using a first matrix set in advance. A first step of adjusting at least one of the second signals, a second step of comparing the first signal adjusted in the first step with the second signal to obtain a difference, and a preset second And a third step of correcting the signal obtained in the second step to a signal indicating the size of the defect using a matrix .

  According to the present invention, it is possible to improve the defect detection performance by reducing noise in the bent pipe portion.

1 is an overall configuration diagram of a remote field eddy current flaw detection system. It is a schematic block diagram of a probe. It is a schematic block diagram of a detection coil. It is a functional block diagram of an arithmetic processing unit. It is the schematic of a test object pipe. It is a flaw detection result by a prior art. It is a flaw detection result by this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

~Constitution~
FIG. 1 is an overall configuration diagram of a remote field eddy current flaw detection system. The remote field eddy current flaw detection system includes a probe 101, an insertion / extraction machine 102, a flaw detector 103, a processing unit 104, a personal computer 105, and a monitor 106, and flaws an inspection target tube 107.

  FIG. 2 is a schematic configuration diagram of the probe 101. The probe 101 has a structure in which a guide 201, an excitation coil 202, and a detection coil 203 are connected by a flexible tube 204. The guide 201 is a smooth member. The exciting coil 202 has a structure in which a conducting wire is wound on a single layer.

  The detection coil 203 is a characteristic configuration of the present embodiment. FIG. 3 is a schematic configuration diagram of the detection coil 203. The detection coil 203 has a structure in which a large-diameter outer coil 301 and a small-diameter inner coil 302 have a two-layer structure on a concentric axis, and coils 303 and 304 having the same structure are arranged in two rows in the axial direction. The two outer coils 301 and 303 are differentially connected to each other, and the two inner coils 302 and 304 are similarly differentially connected.

  The tube 204 is a hard material that has flexibility and large tensile strength and is difficult to buckle. Electrically, the excitation coil 202 of the probe 101, the outer coils 301 and 303 of the detection coil 203, and the inner coils 302 and 304 are connected to the flaw detector 103 via cables. The flaw detector 103 is connected to the personal computer 105 and the monitor 106 via the arithmetic processing unit 104.

  The probe 101 is inserted to the starting position in the inspection target tube by the insertion / extraction machine 102 and is extracted from the probe inlet side by the insertion / extraction machine 102 in a state where a voltage is applied to the excitation coil 301. At that time, the flaw detector 103 receives the output voltage of the detection coil 203 and performs phase detection to acquire a flaw detection signal. The flaw detection signal has an in-phase signal (X) and a different-phase signal (Y) for one output voltage, and is sent to the arithmetic processing unit 104. The arithmetic processing unit 104 performs the following arithmetic processing, and the personal computer 105 displays the result on the monitor 106.

~control~
Next, arithmetic processing by the arithmetic processing unit 104 will be described. FIG. 4 is a functional block diagram of the arithmetic processing unit 104. The arithmetic processing unit 104 includes a first function unit 104a, a second function unit 104b, and a third function unit 104c.

  There are four flaw detection signals obtained from the probe 101. X1 signal and Y1 signal which are differential outputs of the outer coil 301 and the outer coil 303, and X2 signal and Y2 signal which are differential outputs of the inner coil 302 and the inner coil 304. Each flaw detection signal is a value at the same time or at the same position.

  The first functional unit 104a performs matrix transformation on the X2 signal and the Y2 signal using the matrix A (elements a11, a12, a21, and a22) (step 1). The matrix A is set in advance before the flaw detection so that the X2 signal and the Y2 signal when there is no defect in the detected portion are the same as the X1 signal and the Y1 signal. It can be set from a calibration test or a specific value can be entered. When setting from the calibration test, X1 signal, Y1 signal, X2 signal, and Y2 signal are acquired in the curved part of the test tube with the same curvature as the inspection target tube, and the matrix A that satisfies the above conditions is set. To do. Here, the matrix A is set for each curvature.

  Note that the X1 signal and the Y1 signal may be matrix-transformed and adjusted to be the same as the X2 signal and the Y2 signal.

  The second function unit 104b performs a difference operation between the X1 signal and the Y1 signal and the X2 signal and the Y2 signal after conversion by the matrix A (step 2).

  When there is no defect in the detected part, the X2 signal and Y2 signal after conversion by the matrix A are the same as the X1 signal and the Y1 signal (step 1), and when the difference calculation is performed, it becomes zero (step 2). On the other hand, if the detected part is defective, the X2 signal and the Y2 signal after conversion by the matrix A are not the same as the X1 signal and the Y1 signal (step 1). Instead, the X3 signal and the Y3 signal are output.

  The third function unit 104c performs matrix transformation on the X3 signal and the Y3 signal using the matrix B (elements b11, b12, b21, b22) (step 3). The matrix B is set in advance before the flaw detection so that the X3 signal and the Y3 signal are corrected to the X signal and the Y signal indicating the size of the defect. Under the condition of matrix A, flaw detection is performed with a test tube provided with a simulated defect (for example, φ1 mm hole), and the elements of matrix B are set so that the X signal and the Y signal have target amplitudes. The matrix B is set corresponding to the matrix A.

  When there is no defect in the detected part, the X3 signal and the Y3 signal are zero, and the X signal and the Y signal after conversion by the matrix B are also zero (step 3). On the other hand, if the detected part has a defect, the matrix B outputs an X signal and a Y signal indicating the size of the defect (step 3).

~effect~
The effect of this embodiment will be described using a specific example. FIG. 5A is a schematic view of a tube to be inspected, which is a magnetic heat transfer tube having a curvature of 45 mm and provided with a plurality of φ3 mm through holes. In addition, No. The three defects are provided with two holes on the back and front.

  FIG. 5B is a result of flaw detection of the Y signal by the conventional technique (one excitation coil and two detection coils). In the prior art, there is a problem that the defect detection performance in the bent pipe portion is not good. For example, No. which is a curved pipe part. The flaw detection signals for 2-4 defects are particularly unclear.

  FIG. 5C shows a flaw detection result according to the present embodiment (one excitation coil, detection coil 2 × 2). The flaw detection result of the Y signal at the excitation frequency f = 1 kHz is shown with the elements a11 = a22 = 1.8 and a12 = a21 = 0 of the matrix A, and the elements b11 = b22 = 10.3 and b12 = b21 = 0 of the matrix B. Bending noise at the curved pipe part is reduced, and the flaw detection signal from the φ3mm through hole is clearly detected. In particular, no. In the defect of 3, the amplitude is larger than that of the other defects. Thereby, the defect detection performance in a curved pipe part can be improved.

DESCRIPTION OF SYMBOLS 101 Probe 102 Insertion / extraction machine 103 Flaw detector 104 Arithmetic processor 104a 1st function part 104b 2nd function part 104c 3rd function part 105 Personal computer 106 Monitor 107 Inspection object pipe 201 Guide 202 Excitation coil 203 Detection coil 204 Flexible tube 301 Outer coil (first outer detection coil)
302 Inner coil (first inner detection coil)
303 outer coil (second outer detection coil)
304 inner coil (second inner detection coil)

Claims (3)

At least one excitation coil;
A probe having a detection coil including a first detection coil and a second coil, which are arranged at a position away from the excitation coil and arranged close to each other;
A remote field eddy current flaw detection system comprising: an arithmetic processing unit that obtains a flaw detection signal by phase-detecting output voltages of the first detection coil and the second coil when the probe scans the inside of a magnetic tube;
The first detection coil has a first inner detection coil and a first outer detection coil disposed outside the first inner detection coil on the concentric axis of the first inner detection coil;
The second detection coil has a second inner detection coil and a second outer detection coil disposed outside the second inner detection coil on the concentric axis of the second inner detection coil,
The first outer detection coil and the second outer detection coil are differentially connected to each other,
The first inner detection coil and the second inner detection coil are differentially connected to each other ,
The arithmetic processing unit includes:
When there is no defect in the detected part, a first signal which is a differential output between the first outer detection coil and the second outer detection coil, and a differential output between the first inner detection coil and the second inner detection coil. A first function unit that adjusts at least one of the first signal and the second signal by using a first matrix set in advance so that a certain second signal is the same;
A second function unit that compares the first signal adjusted by the first function unit with the second signal to obtain a difference;
A remote field eddy current flaw detection system comprising: a third function unit that corrects a signal obtained by the second function unit to a signal indicating a defect size using a second matrix set in advance . The remote field eddy current flaw detection system according to claim 1,
A remote field eddy current flaw detection system characterized in that a curved portion of a U-shaped magnetic tube is targeted for flaw detection. A probe having at least one excitation coil and a detection coil including a first detection coil and a second coil, which are arranged at a position apart from the excitation coil and arranged in proximity to each other; 1 In the remote field eddy current flaw detection method for obtaining flaw detection signals by phase detection of the output voltage of the detection coil and the second coil
The first detection coil has a first inner detection coil and a first outer detection coil disposed outside the first inner detection coil on the concentric axis of the first inner detection coil;
The second detection coil has a second inner detection coil and a second outer detection coil disposed outside the second inner detection coil on the concentric axis of the second inner detection coil,
The first outer detection coil and the second outer detection coil are differentially connected to each other,
The first inner detection coil and the second inner detection coil are differentially connected to each other,
When there is no defect in the detected part, a first signal which is a differential output between the first outer detection coil and the second outer detection coil, and a differential output between the first inner detection coil and the second inner detection coil. A first step of adjusting at least one of the first signal and the second signal using a preset first matrix so that a certain second signal is the same;
A second step of comparing the first signal adjusted in the first step with the second signal to obtain a difference;
A remote field eddy current flaw detection method comprising: a third step of correcting the signal obtained in the second step to a signal indicating a defect size using a second matrix set in advance .

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