JPH095301A - Eddy-current flaw detector - Google Patents

Abstract

PURPOSE: To improve the detectability of an eddy current flaw detector against defects near the weld of a metal to be inspected and, at the same time, to improve the reliability of various kinds of equipment and to remarkably improve the availability of the flaw detector. CONSTITUTION: After the output of a flow detector is converted into a digital value by means of an A/D converter 11 and the digital value is stored in a data string basic memory 12, the waveform of signals from a weld is extracted by means of an extractor 13. By turning back the extracted data string near the point at which the waveform of the signals from the weld shows the maximum value, a correlation coefficient calculator 15 finds the correlation coefficient of the waveform while the turning back point is successively moved and a maximum correlation coefficient value extractor 16 extracts the maximum value and stores the maximum condition in a maximum correlation coefficient condition storing memory 18. Then a signal waveform computing element 20 reduces the waveform of signals against the weld by finding the difference between each data under the condition of the turning back point when the correlation coefficient becomes the maximum and, after the computed data string is stored in a memory 21, a D/A converter 22 converts the data string into an analog value and outputs the analog vale to a recorder for recording.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detector used for confirming the soundness of a metal flat plate or the like.

[0002]

2. Description of the Related Art As shown in FIG. 5, a conventional eddy current flaw detector for flaw detection on a flat plate or the like is used in which a detection coil 101 is connected to a flaw detector 120 via a connection cable 140. Further, in FIG. 5, 110 is a flat plate which is a target object metal, 111 is a defect in the object metal, 131 is a magnetic field generated by the detection coil 101, and 132 is a metal body generated by the magnetic field generated by the detection coil 101. Eddy current 133 flowing inside is a magnetic field generated by the eddy current 132.

The detection coil 101 includes a connection cable 14
Through 0, a fixed size (amplitude) from the flaw detector 120,
An alternating current of constant frequency is supplied. Detection coil 10
When an alternating current flows through the detection coil 10,
1, a magnetic field 131 is generated, and this magnetic field 131 interlinks with the detection coil 101 itself and the object metal 110,
Eddy current 132 is generated in the object metal 110. This eddy current 132 is generated concentrically with the detection coil 101 when the object metal 110 has no defect. A magnetic field 133 is also generated by this eddy current 132, and this magnetic field 133 also interlinks with the detection coil 101.

These alternating magnetic fields 131 and 133 interlink with the detection coil 101, whereby the detection coil 1
The impedance of 01 changes. When the defect 111 exists in the object metal 110, the flow method of the eddy current 132 changes as compared with the case where there is no defect. At this time, eddy current 13
Since the magnetic field 133 generated by 2 also changes as compared with the case where there is no defect, the impedance of the detection coil 101 changes. This change in impedance is converted into a voltage by an electronic circuit built in the flaw detector 120 and displayed on the screen 121 of the flaw detector 120. Further, the converted voltage is transmitted to the recorder 135 and displayed as a record.

The position signal 142 of the detection coil 101 is also input to the recorder 135, and a signal waveform appears corresponding to the position of the detection coil 101. By observing this signal waveform, the presence or absence of a defect can be known. It can be done and is used as a method to confirm the soundness of various equipment components.

[0006]

However, in the above-described conventional flaw detection apparatus, when flaw detection is performed around the welded portion 113 of the object metal 110 as shown in FIG. 6, noise generated from the welded portion 113 (specific to welding) Signal), the signal due to the defect becomes unclear, and the detectability decreases.

FIG. 6 shows a state in which a metal to be inspected (flat plate or the like) 110 having a butt welded portion 113 is being inspected, 101 is a detection coil, 130 is a connection cable,
151 is an arrow indicating the scanning direction of the detection coil 101,
2 is an arrow indicating the direction of the object metal 110, 111 is a surface defect in the object metal 110, and 112 is the object metal 110.
It is a surface defect in the vicinity of the butt weld portion 113 inside. Figure 6
In, the detection coil 101 is scanned across the welded portion 113 in the direction of arrow 151 indicating the scanning direction of the detection coil 101.

The eddy current flaw detection is a technique for detecting a defect by a change in the shape and electromagnetic characteristics of the metal to be inspected. Even if the flaw is not a defect, a signal is generated even if the shape of the metal in the inspection or the electromagnetic characteristic is changed. appear. The welded portion 113 generally has a different shape from the base material portion, and the electromagnetic characteristics also change. Also, along with this shape change and characteristic change,
In general, it has a considerably greater effect than defects. Therefore, in the welded portion 113, a signal generated by the welded portion having a considerably larger amplitude than that of the defect is generally generated, and the signal generated by the defect is hidden, so that the defect detectability is deteriorated. FIG. 7 shows the adverse effect phenomenon caused by this welding.

FIG. 7 shows a signal waveform obtained when a butt-welding object is flaw-detected by a conventional flaw-detecting apparatus. In each of FIGS. 7A, 7B and 7C, a detection coil is shown. 6 is a signal waveform when 101 is scanned in the direction of an arrow X indicating the direction of the object metal 110 in FIG. 6, and FIG. 7A is an example of a signal waveform when the detection coil 101 is scanned in a defect-free portion. , (B) is an example of a signal waveform when a portion of the defect 111 separated from the weld 113 is scanned, and (c) is a signal waveform when a portion of the defect 112 near the weld is scanned. In these signal waveforms (a), (b), and (c), 201 is a signal waveform due to the defect 112 existing near the butt weld 113, 31 is a signal waveform due to the defect 111 distant from the weld 113, and 30 Is a signal waveform by the butt welding portion 113. As shown in this figure, the signal waveform due to the defect 111 separated from the welded portion 113 is clearly recognized, and this defect 111 can be detected. However, the signal waveform of the defect 112 in the vicinity of the weld 113 is not clear because it overlaps with the signal waveform of the weld 113 (because the shape and electromagnetic characteristics of the weld are not uniform), and the signal of the weld 113 is not uniform. Because the waveform is not uniform,
It becomes difficult to identify the presence or absence of a defect, which makes detection difficult.

As described above, the conventional flaw detector has a problem that it is difficult to detect a defect existing in the vicinity of the welded portion. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an eddy current flaw detector that can reduce the signal waveform of a welded portion and improve the detectability of a defect near the welded portion.

[0011]

An eddy current flaw detector according to the present invention comprises a detection coil which scans on a metal to be inspected including a welded portion to detect the generation of a magnetic field and the magnetic field from the metal to be inspected.
A flaw detector that processes a detection signal from the detection coil and outputs flaw detection data corresponding to a defect in the metal to be inspected, a data string storage unit that stores the flaw detection data output from this flaw detector, and a storage unit that stores the flaw detection data. Welding portion waveform extracting means for extracting the signal waveform of the welding portion from the generated data string, and the central position indicating the maximum value of the welding portion signal waveform extracted by this extracting means is extracted, and the vicinity of this central position is a turning point. As a correlation coefficient calculation means for calculating the correlation coefficient of each data point, and the difference of each data is obtained under the condition of the turning point when the correlation coefficient obtained by this means becomes maximum, and the signal waveform for the welded portion is obtained. It is characterized by comprising a calculating means for reducing and a recorder for recording flaw detection data in which unnecessary signal waveforms are reduced by the calculating means.

[0012]

After storing all the flaw detection data in the memory, the signal processor folds the data string near the point showing the maximum value of the welding signal waveform, obtains the correlation coefficient, and sequentially moves the fold points. Calculate the correlation coefficient. By calculating the difference of each data under the condition of the turning point when the correlation coefficient calculated in this way becomes maximum, the signal waveform due to welding is minimized and the calculated difference of each data is converted into an analog value. And output to the recorder. As a result, the signal waveform for the welded portion can be reduced, and the detectability for defects near the welded portion can be improved.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. 1 is a diagram showing an overall configuration of an eddy current flaw detector according to an embodiment of the present invention, FIG. 2 is a functional block diagram of a signal processor, FIG. 3 is an explanatory diagram of how to obtain a maximum value of a correlation coefficient, Figure 4
FIG. 6 is a diagram showing an example of a signal waveform when scanning the periphery of a welded portion.

In FIG. 1, 100 is a signal processor,
Others are the same as those of the conventional flaw detector shown in FIG. The output of the flaw detector 120 is input to the signal processor 100, and the output of the signal processor 100 is input to the recorder 135.

The recorder 135 has a flaw detector 120.
A processed signal of the output from the sensor and the position signal of the detection coil 101 are transmitted by a cable 141 connecting the signal processor 100 and the recorder 135. Others are the same as those of the conventional flaw detection apparatus shown in FIG. 5, and therefore, the same reference numerals as those in FIG. 5 are given and detailed description thereof will be omitted.

FIG. 2 shows a detailed internal structure of the signal processor 100. In the figure, 11 is A / D
Converter, 12 is data string basic memory, 13 is welded portion waveform extractor, 14 is data string rearrangement and storage memory, 15
Is a correlation coefficient calculator, 16 is a correlation coefficient maximum value extractor, 17
Is a correlation coefficient calculation reference point adder / subtractor, 18 is a correlation coefficient maximum condition storage memory, 19 is a line number adder, 20 is a signal waveform calculator, 21 is a calculation data string storage memory, 22 is a data string output D / A It is a converter.

The signal processor 100 configured as described above.
The output data (flaw detection data) from the flaw detector 120 and a signal indicating the position of the detection coil (position signal) are converted into digital values by the A / D converter 11. The flaw detection data and position signals converted into these digital values are all stored in the data string basic memory 12.

The detection coil 101 is scanned as indicated by an arrow 151 indicating the scanning direction of the detection coil 101 shown in FIG. 6, and is scanned over the entire range of the metal 110 to be inspected, which is detected during this period. A signal indicating the position of the coil 101 and output data of the flaw detector 120 (flaw detection data)
All are stored in the data string basic memory 12.

After all the flaw detection data and position signals in the required range are stored in the data string basic memory 12, the welding waveform extractor 13 causes the detection coil 101 to scan each time (the direction of the object metal is changed). For each scan in the X direction indicated by the arrow 152), the center of the welding signal waveform in the data for each scan is extracted by searching for the maximum value of the voltage of the flaw detection data, and the detection coil corresponding to this center position is extracted. Record the position of 101.

The data string rearranging and storing memory 14 is
Detection coil 10 extracted by the weld waveform extractor 13.
The flaw detection data string for each scan is rearranged and stored, with the position of 1 as the folding point.

The correlation coefficient calculator 15 obtains the correlation coefficient of each data point with respect to the data string rearranged at the folding point and calculates the sum. FIG. 3 illustrates the data sequence for obtaining the correlation coefficient. This drawing shows one scan of the detection coil 101 (the object metal 110 shown in FIG. 6).
Of the signal waveform obtained by one scan in the X direction of the arrow 152 indicating the direction of
3 is an enlarged view of the time axis (scanning distance axis), in which the correlation coefficient calculator 15 indicates points "+1" and "-1" for each point in the data (set of point data) of FIG. The correlation coefficient is calculated for the voltage values of “+2” and “−2”, and for the voltage values of “+2” and “−2” between “+1” and “−1”. The correlation coefficient for each folded point is calculated, and the sum of all of them is calculated.

The correlation coefficient maximum value extractor 16 stores the data folding point and the value obtained by the correlation coefficient calculator, and generates a signal to the correlation coefficient calculation reference point addition / subtractor 17. Correlation coefficient calculator 1 stored so far
The output value of 5 is compared. Correlation coefficient calculation reference point adder / subtractor 1
Reference numeral 7 sequentially adds and subtracts the reference point every time the correlation coefficient is calculated for each line, and the data return point is sequentially shifted. By sequentially changing the folding point, the correlation coefficient at each folding point is obtained, and the maximum correlation coefficient extractor 16 determines the condition (reference point = folding point) that maximizes the correlation coefficient.

This maximum condition is stored in the correlation coefficient maximum condition storage memory 18. In this way, the condition that the correlation coefficient for the data string (data line) for one scan in the X direction is maximum (reference point = turning point) is stored in the maximum correlation coefficient storage memory 18.

When the condition that the correlation coefficient of the data string for one scan in the X direction becomes maximum (reference point = folding point) is stored in the maximum correlation coefficient storage memory 18, the maximum correlation coefficient storage is performed. The memory 18 generates a signal to the line number adder 19 and also transmits to the signal waveform calculator 20 the condition that the correlation coefficient becomes maximum.

The line number adder 19 receives the signal from the correlation coefficient maximum condition storage memory 18, increments the line number (data string number) by "1", and extracts the increased line number from the welding portion waveform. The data sequence transmitted to the device 13 and corresponding to the next X-direction scanning is performed in the same manner as described above.

The signal waveform calculator 20 receives from the correlation coefficient maximum condition storage memory 18 the condition that the correlation coefficient is maximum (reference point = folding point), and folds the data on the basis of this point to set the interval between the points. Is obtained (data for obtaining the difference is retrieved from the data string basic memory 12). An implementation method for folding back and obtaining the difference between the points is, for example, "-" in FIG.
Subtract the voltage value at the "+1" point from the voltage value at the "1" point,
The voltage value at the point "+2" is subtracted from the voltage value at the point "-2", and so on.

The calculated voltage value is stored in the calculation data string storage memory 21 together with the position signal. After performing this for all the data subjected to flaw detection, the arithmetic data string storage memory 21 sends flaw detection data and a detection coil position signal to the data string output D / A converter 22 at an appropriate timing to Output D / A converter 22
Outputs each analog voltage.

Since the output of the data string output D / A converter 22 is connected to the input of the recorder 135 as shown in FIG. 1, the output of the data string output D / A converter 22 is transferred to the recorder 135 as before. It is drawn in the same way as in.

An example of the signal waveform drawn on the recorder 135 is shown in FIG. FIG. 4A shows an example of a signal waveform by the conventional apparatus, 31 is a signal waveform by the defect 111 separated from the weld 113, and 30 is a signal waveform of the weld 113.
FIG. 4B shows an example of a signal waveform by the device of the present invention.
Is a signal waveform due to the defect 111 separated from the weld 113,
32 is a signal waveform due to the defect 112 near the weld 113.

As shown in FIG. 4A, in the conventional apparatus, a signal (31 in the figure) can be clearly recognized and detected for the defect 111 separated from the welded portion 113, but the defect 112 near the welded portion can be detected. Since it occurs together with the signal from the welded portion 113, it cannot be identified and is difficult to detect.

However, in the apparatus according to the present invention as shown in FIG. 7B, the signal processor 100 finds the reference point at which the correlation coefficient is maximum, and the difference between the data is obtained and outputted. The signal due to the defect is greatly reduced, and only the signal due to the defect can be recognized, and the signal waveform 32 due to the defect 112 near the welded portion can be clearly identified and detected. The signal from the weld 113 does not occur uniformly because the shape of the weld and the electromagnetic characteristics fluctuate, but a reference point for signal processing is extracted and processed for each signal line corresponding to one scan. Therefore, the signal due to welding is greatly reduced, and the defect can be detected.

In the present embodiment, the shape of the object metal is a flat plate for the sake of simplicity of explanation, but the present invention is also applicable to the object metal such as a pipe or a tube. Further, although all the devices in the above-described embodiments have been described as analog type, when the flaw detector recorder or the like is digital type, the A / D converter and the D / A converter for signal processing are unnecessary.

[0033]

As described above, according to the present invention, the signal processor is provided between the flaw detector and the recorder, and the signal waveform is reduced by the signal processor with respect to the welded portion of the object metal. Therefore, the detectability for defects existing in the vicinity of the welded portion is improved, and as a result, the reliability of various devices can be improved and the operating rate can be greatly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a flaw detection apparatus according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a signal processor in the embodiment.

FIG. 3 is an explanatory diagram of how to obtain a maximum value of a correlation coefficient in the same embodiment.

FIG. 4 is a diagram showing an example of signal waveforms when a periphery of a welded portion is scanned by a conventional apparatus and an apparatus of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional flaw detection device.

FIG. 6 is a view showing a state in which a metal to be inspected having a butt welding portion is being detected by a conventional flaw detection device.

FIG. 7 is a diagram showing a signal waveform when a test metal of a butt weld portion is scanned by a conventional flaw detector.

[Explanation of symbols]

 11 A / D Converter 12 Data Sequence Basic Memory 13 Weld Waveform Extractor 14 Data Sequence Sorting and Storage Memory 15 Correlation Coefficient Calculator 16 Correlation Coefficient Maximum Value Extractor 17 Correlation Coefficient Calculation Reference Point Adder / Subtractor 18 Phase Number of relations Maximum condition storage memory 19 Line number adder 20 Signal waveform calculator 21 Calculated data string storage memory 22 Data string output D / A converter 30 Signal waveform of weld zone 31 Signal waveform due to defect away from weld zone 32 Weld zone Signal waveforms due to defects in the vicinity 100 Signal processor 101 Detection coil 110 Specimen metal 111 Surface defects in the specimen metal 120 Flaw detector 121 Screen of flaw detector 131 Magnetic field generated by the detection coil 132 Eddy current flowing in the subject metal 135 Recorder 151 Arrow indicating the scanning direction of the detection coil 152 Arrow indicating the direction of the object metal

Claims (1)

[Claims] 1. A detection coil for scanning a metal to be inspected including a welded part to detect the generation of a magnetic field and a magnetic field from the metal to be inspected, and a detection signal from the detection coil to process defects in the metal to be inspected. A flaw detector that outputs corresponding flaw detection data,
Data string storage means for storing the flaw detection data output from the flaw detector, weld portion waveform extraction means for extracting the signal waveform of the weld portion from the data sequence stored in the storage means, and the extraction means Correlation coefficient calculating means for extracting the central position showing the maximum value of the welded part signal waveform and calculating the correlation coefficient of each data point with the vicinity of this central position as the turning point, and the correlation coefficient calculated by this means Equipped with a calculating means for calculating the difference between the respective data under the condition of the turning point at the time of maximum to reduce the signal waveform to the welded portion, and a recorder for recording the flaw detection data in which the unnecessary signal waveform is reduced by the calculating means. An eddy current flaw detector characterized in that