JP5372866B2 - Eddy current flaw detection method and eddy current flaw detection system - Google Patents

Description

  The present invention relates to an eddy current flaw detection method and an eddy current flaw detection system.

  In the eddy current flaw detection of the heat exchanger heat transfer tube, the presence or absence of a defect signal is confirmed while inserting and extracting the probe. As a confirmation method, there is known a method in which the relationship between the defect size and the signal amplitude value is grasped experimentally in advance, and the threshold value corresponding to the defect size of the detection target and the amplitude value of the observation signal are compared and evaluated. For example, in Patent Document 1, the difference signal obtained by subtracting the reference signal from the flaw detection signal is subjected to threshold processing to determine the presence / absence of a flaw. Embodiment 4 of Patent Document 1 also describes an example in which a multi-coil probe is adopted as a probe. In general, a multi-coil probe has a structure in which a plurality of coils are arranged on the outer periphery of a casing, and has a plurality of channels (CH). Each channel uses a part of the entire circumference of the tube as a detection range, and a plurality of channels complement each other to inspect the entire circumference of the tube.

JP 2001-296279 A

  However, the sensitivity of each channel has a distribution, and even if a plurality of channels are combined, there is a portion with low sensitivity between the channels. In the heat transfer tube inspection, since the circumferential position of the defect is unknown, it is required to determine the threshold value in consideration of the positional relationship between the defect and each channel.

  Therefore, an object of the present invention is to improve the reliability of inspection by increasing the accuracy of estimating a defect size from an observation signal.

In the present invention, the maximum amplitude value (S ₁ ) at an arbitrary position in the length direction of the heat transfer tube and the amplitude value detected by a channel adjacent to the channel detecting the maximum amplitude value (S ₁ ) (S ₂ > S ₃ ). A large amplitude value (S ₂ ) is obtained, a correction coefficient (A) is determined from the amplitude ratio (S ₂ / S ₁ ) of the maximum amplitude value (S ₁ ) and the adjacent amplitude value (S ₂ ), and correction is performed. The defect size is calculated by comparing the amplitude value (AS ₁ ) with a threshold value.

  According to the present invention, it is possible to improve the accuracy of the inspection by increasing the accuracy of estimating the defect size from the observation signal.

It is a flowchart showing the signal processing of eddy current flaw detection with a multi-coil probe. It is a block diagram showing the structure of an eddy current flaw detection system. It is a schematic diagram of the screen showing the tube arrangement | sequence of a heat exchanger. It is a figure which shows the length direction position of a heat exchanger tube. It is a schematic diagram showing the structure of a multi-coil probe. It is a figure showing the cross section of a multi-coil probe. It is an example of the correction figure for calculating a correction coefficient. It is an example of the sensitivity distribution of a multi-coil probe. It is an example of a calibration test body. It is an example of an estimated diagram for calculating a defect size. It is an example of a flaw detection image of an outer surface simulated defect having a thickness of 50% t. It is an example of the signal waveform of the external surface simulation defect of thickness 50% t depth.

  FIG. 1 shows a signal processing flow of eddy current flaw detection in the multi-coil probe according to the present embodiment. FIG. 2 is a block diagram showing the configuration of the eddy current flaw detection system. The eddy current flaw detection system 20 includes a monitor 21, a computer 22, an eddy current flaw detector 23, an insertion / extraction machine 24, and a multi-coil probe 25.

  In the signal processing flow of FIG. 1, the computer 22 processes the position data from the insertion / extraction machine 24 and the flaw detection data from the eddy current flaw detector 23. The monitor 21 is a device for displaying data from the computer 22 and performing operations.

In FIG. 1, a tube to be inspected is selected from the tube arrangement diagram on the monitor 21 (S101), flaw detection data with a multi-coil probe is acquired, and an image is displayed (S102). The flaw detection data is a signal amplitude value with respect to the position of the multi-coil probe, and has data of a plurality of channels (CH). A signal processing range is selected (S103), and a position (i) for signal processing is designated (S104). A search is made for CH (j) having the maximum amplitude value at the position (i), and the amplitude value (i, j) is set to S ₁ (S105). By comparing adjacent CH amplitude value of (j-1) (i, j-1) amplitude values of adjacent CH (j + 1) (i , j + 1), a large value to S ₂ (S106). A correction coefficient A is determined from the relationship between S ₂ / S ₁ and the correction coefficient, and a correction amplitude value AS ₁ is calculated (S107). A threshold value (S _th ) is set in advance and compared with the corrected amplitude value AS ₁ (S108). When the correction amplitude value is smaller than the threshold value (AS ₁ <S _th ), the defect size is set to zero (S201). If the corrected amplitude value is larger than the threshold value (AS ₁ > S _th ), the defect size is calculated from the estimated diagram with the value of AS ₁ and stored (S202). It is confirmed whether the signal processing of the selected range is completed (S109). If not completed, the process returns to (S104) to perform signal processing at the next position (i + 1). If completed, a graph of the defect size with respect to the position is displayed (S110). If there is a processing step (S202) in the entire signal processing within the selected range, it is determined that there is a defect, and if there is no defect, it is clearly indicated on the inspection target tube in the tube arrangement diagram (S111).

  Next, the signal processing flow of FIG. 1 will be described in detail for each item.

  In S101, the tube arrangement (FIG. 3A) corresponding to the heat exchanger is displayed on the monitor 21, and the apparatus user selects the same tube as the inspection target tube 32 on the monitor display. The flaw detection data is stored corresponding to the tube display 31, and the signal processing result is clearly shown on the tube display 31.

  In S102, flaw detection data is acquired by the eddy current flaw detection system 20. In the flaw detection method, the multi-coil probe 25 is inserted into the tube and scanned by the insertion / extraction machine 24. The position of the multi-coil probe 25 in the heat transfer tube length direction is acquired by referring to the encoder value, the feed amount of the insertion / extraction machine, or the time. FIG. 3B shows the position (i) in the heat transfer tube length direction. Corresponding to the position, the X amplitude value and the Y amplitude value are acquired from the eddy current flaw detector 23. The flaw detection data is displayed as an image (C scope) with respect to the heat transfer tube length direction position of the multi-coil probe as the X amplitude value, Y amplitude value, or total amplitude value (root mean square value) of each channel.

  In S103, the apparatus user selects a start position and an end position with two cursors or the like on the image display. Alternatively, a method of automatically setting to a predetermined position may be used. The start position and the end position may be selected within the target range.

  In S104, the position (i) for signal processing in the selection range is designated. Usually, the starting position (i = 0) of the selection range is designated first.

In S105, a search is made for CH (j) having the maximum amplitude value at the position (i = 0). The amplitude value is an X amplitude value, a Y amplitude value, or a total amplitude value. Maximum amplitude value (i, j) is stored as S _1.

In S106, compared to obtain the amplitude (i, j-1) amplitude values of adjacent CH (j + 1) (i , j + 1) adjacent CH (j-1), stores a larger value as S _2.

In S107, the value of S ₂ / S ₁ is calculated and the correction coefficient A is determined from the correction diagram. The correction diagram represents the sensitivity ratio between channels based on the theoretical sensitivity distribution, and varies depending on the multi-coil probe. For example, in the case of the multi-coil probe shown in FIG. 4, the correction diagram is shown in FIG. 4A, in the multi-coil probe, excitation coils 42 and detection coils 43 are alternately arranged on the outer peripheral surface of a casing 41 at a 45-degree pitch. The excitation coil 42 and the detection coil 43 have the same structure, and are connected with their channel positions shifted in angle. FIG. 4B is a sectional view taken along line AA of the detection coil. When the detection coils 43 are arranged as shown, the sensitivity distribution in a single channel is represented by a solid line in FIG. The sensitivity distribution of the channel with the angle shifted is represented by a dotted line in FIG. Each channel complements the insensitive part, but a low sensitivity part of about 70% of the maximum sensitivity appears. Therefore, the sensitivity of two channels at a certain position is set as S ₁ and S ₂ (<S ₁ ), and a correction coefficient A for correcting the sensitivity from the value of the sensitivity ratio (S ₂ / S ₁ ) to the maximum sensitivity S ₀ is introduced. . In FIG. 5, when S ₂ / S ₁ = 0, S ₁ corresponds to S ₀ and the correction coefficient A is A = 1. When S ₂ / S ₁ = 1, the correction coefficient A is A = 1.4 in order to correct S ₁ to be equivalent to S ₀ . Even in the case of 0 <(S ₂ / S ₁ ) <1, in order to correct S ₁ to be equivalent to S ₀ , the correction coefficient is calculated in the range of 1 <A <1.4. In the above description, S ₀ , S ₁ , and S ₂ are expressed as sensitivities, but actually, the correction coefficient A is calculated by associating the sensitivity with amplitude values. A correction amplitude value AS ₁ is obtained from the integration of the correction coefficient A and the maximum amplitude value S ₁ and used for threshold determination in the next step.

In S108, it is compared with a threshold S _th correction amplitude value AS _1. When AS ₁ <S _th , the process proceeds to S201 where the defect size at position (i) is set to zero. When AS ₁ ≧ S _th , the process proceeds to S202, and the defect size at the position (i) is calculated from the estimated diagram. The estimated diagram represents the relationship between the defect size and the maximum amplitude value. For example, the relationship of FIG. 8 is obtained in the calibration specimen 71 of FIG. Before flaw detection, data is acquired with the simulated defect 72 of the calibration specimen 71, and data interpolation is performed to obtain an estimated diagram. A defect size corresponding to the value of the correction amplitude value AS ₁ is calculated from the estimated diagram.

  In S109, it is confirmed whether the signal processing of the selected range is completed. If incomplete, position (i) is set to position (i + 1) and signal processing is performed again from S104. If complete, perform the next step.

  In S110, the defect size is plotted and displayed with respect to the position of the selected range.

  In S111, if there is a processing step (S202) in the entire signal processing within the selected range, it is determined to be defective, and if there is no defect, it is clearly indicated in the inspection target tube of the tube arrangement diagram.

Thus, the maximum amplitude value of an arbitrary position in the length direction of the heat transfer tube (S ₁₎ and the channel CH (j-1) adjacent to the channel CH (j) for detecting the maximum amplitude value (S _1), A large amplitude value (S ₂ ) among amplitude values (S ₂ > S ₃ ) detected by CH (j + 1) is acquired, and an amplitude ratio (A ₂ ) between the maximum amplitude value (S ₁ ) and the adjacent amplitude value (S ₂ ) ( The correction coefficient (A) is determined from S ₂ / S ₁ ), and the correction amplitude value (AS ₁ ) is compared with the threshold value S _th to calculate the defect size. A value can be used. If it is a correction amplitude value, it is possible to determine the threshold value in consideration of the positional relationship between the defect and each channel. Therefore, it is possible to increase the accuracy of estimating the defect size from the observation signal and improve the reliability of the inspection.

  The effect of signal processing in eddy current flaw detection with the multi-coil probe according to the present embodiment will be confirmed. In the eddy current flaw detection system 20, the multi-coil probe 25 is connected to the eddy current flaw detector 23 with a cable, and an electric signal for excitation or detection is transmitted and received. The eddy current flaw detector 23 is connected to the computer 22 with a cable to electrically transmit / receive flaw detection conditions and flaw detection signals. The insertion / extraction machine 24 inserts / extracts the multi-coil probe 25 via a cable and transmits a position reference signal to the computer 22. The eddy current flaw detection system can be realized by general equipment. The multi-coil probe 25 has the coil arrangement of FIG. 4 and is connected with the channel position shifted by 22.5 degrees.

Figure 9 is a flaw detection image of an eddy current flaw detection system 20, FIG. 10 is a signal waveform of the channel (CH1 and CH2) corresponding to the amplitude value S ₁ and the amplitude value S _2. An outer surface crack having a thickness of 50% t was detected at S ₁ = 1.4 V and S ₂ = 1.4 V, and S ₂ / S ₁ = 1. From the correction diagram of FIG. 5, the correction coefficient A is A = 1.4, and the correction amplitude value AS ₁ is AS ₁ = 2.0V. Here, assuming that the threshold value is an amplitude S _th = 0.2 V corresponding to an outer surface crack with a depth of 20% of the thickness, the defect size is equivalent to a depth of 50% using the estimated diagram of FIG. Calculated. Thereby, the estimation accuracy of the defect size can be improved and the reliability of the inspection can be improved.

20 Eddy current flaw detection system 21 Monitor 22 Computer 23 Eddy current flaw detector 24 Insertion / extraction machine 25 Multi-coil probe 31 Tube display 32 Tube to be inspected 41 Case 42 Excitation coil 43 Detection coil 71 Calibration specimen 72 Simulated defect

Claims (4)

In eddy current testing method for testing a heat transfer tube using the multi-coil probe, the maximum amplitude value of an arbitrary position (S ₁₎ in the length direction of the heat transfer tube, the channel for detecting the maximum amplitude value (S ₁₎ A large amplitude value (S ₂ ) is acquired from amplitude values (S ₂ > S ₃ ) detected by adjacent channels, and an amplitude ratio (S) between the maximum amplitude value (S ₁ ) and the adjacent amplitude value (S ₂ ). ₂ / S ₁ ), a correction coefficient (A) is determined, and the defect size is calculated by comparing the correction amplitude value (AS ₁ ) with a threshold value.   2. The eddy current flaw detection method according to claim 1, wherein the sensitivity characteristic in the tube circumferential direction of the multi-coil probe is corrected by representing the amplitude ratio of at least two channels. In an eddy current flaw detection system that flaws a heat transfer tube using a multi-coil probe,
Among the maximum amplitude value (S ₁ ) at an arbitrary position in the length direction of the heat transfer tube and the amplitude value (S ₂ > S ₃ ) detected by a channel adjacent to the channel detecting the maximum amplitude value (S ₁ ) To obtain a large amplitude value (S ₂ ), determine a correction coefficient (A) from the amplitude ratio (S ₂ / S ₁ ) of the maximum amplitude value (S ₁ ) and the adjacent amplitude value (S ₂ ), and correct the amplitude An eddy current flaw detection system comprising a computer that calculates a defect size by comparing a value (AS ₁ ) with a threshold value.   4. The eddy current flaw detection system according to claim 3, wherein the sensitivity characteristics in the tube circumferential direction of the multi-coil probe are corrected by representing the amplitude ratio of at least two channels.

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