JPH10123099A - Apparatus and method for evaluating metallic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate a degree of deterioration of a metallic material simply and speedily. SOLUTION: An apparatus 1 is provided with a transmitter 2 generating an a.c., and an inspection coil 3 for detecting a state change of a metallic material by generating an eddy current to the metallic material by the a.c. A voltage change of the inspection coil 3 resulting from the state change of the metallic material is detected by a bridge 4. A frequency spectrum of signals of the voltage change detected by the bridge 4 is obtained by a frequency FFT means 9b. A characteristic amount such as a primary moment or the like of the frequency spectrum obtained by the FFT means 9b or a characteristic amount such as a length of an envelope at a time area, etc., is analyzed by a characteristic amount-analyzing means 9c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal material such as a steel pipe or a steel plate and, more particularly, to an evaluation device and a method for non-destructively evaluating the degree of material deterioration up to the occurrence of cracks. .

[0002]

2. Description of the Related Art Conventionally, an eddy current inspection method and an ultrasonic inspection method have been used for nondestructively inspecting a metal material such as a steel pipe.

In the former method, an eddy current is generated in the metal material, and a change in the state of the metal material such as a change in magnetic permeability caused by a crack or the like is determined by a change in the output voltage and phase of the search coil. To estimate the shape defects generated in the material such as cracks. Moreover, a phase detector or the like is often provided in order to remove noise due to lift-off of the search coil. However, this method only evaluates the change in magnetic permeability or conductivity caused by a shape defect such as a crack, and evaluates the material in order to discover material deterioration or the like before the occurrence of a crack. It was impossible to do.

In the latter method, an ultrasonic pulse is transmitted to a material, a reflected pulse reflected by a defect such as a crack is received, and the degree of a flaw is determined by the sharpness, size and reception time of the reflected pulse. And seeking position. However, even with this method, it is impossible to perform the material evaluation as described above because a reflected pulse caused by a crack or the like is used.

On the other hand, when an ultrasonic pulse is incident on a material, a minute backscattered wave caused by generation of minute voids or inclusion of impurities, which is one mode of material deterioration, is analyzed, whereby the material deterioration is reduced. Methods for assessing the degree have also been proposed. However, in this method, it is necessary to bring the ultrasonic probe into contact with the surface of the material via grease or the like, or to apply ultrasonic waves to the material immersed in the water tank. Therefore, when the material surface was rough or the material itself was a large-sized structure and could not be immersed in a water tank, the test could not be performed.
Further, since it is difficult to move the probe at a high speed while being in contact with the surface of the material, the probe is not suitable when a simple and quick inspection is required.

[0006]

DISCLOSURE OF THE INVENTION In view of such a conventional situation, the present invention provides a metal material evaluation apparatus and an evaluation method capable of easily and quickly evaluating the degree of deterioration of a metal material. With the goal.

[0007]

In order to achieve the above object, a metal material evaluation apparatus according to the present invention is characterized in that a transmitter for generating a continuous wave or a pulse wave and a metal material for a continuous wave or a pulse wave are used. A search coil for generating an eddy current to detect a change in the state of the metal material; a voltage change detection unit for detecting a change in voltage of the search coil due to the change in the state of the metal material; There is provided a frequency spectrum analyzing means for obtaining a frequency spectrum of a signal of a voltage change detected by the means, and a feature quantity analyzing means for analyzing a feature quantity in the frequency spectrum obtained by the frequency spectrum analyzing means.

On the other hand, a feature of the metal material evaluation method according to the present invention is that an eddy current is generated in the metal material by a continuous wave or a pulse wave, and a change in the state of the metal material is detected as a voltage change in the search coil. The object is to obtain a frequency spectrum of a signal of a voltage change of a search coil and to evaluate a metal material by analyzing a feature amount in the frequency spectrum.

Another feature of the present invention is that the above-mentioned "frequency spectrum analyzing means" is omitted, and the "characteristic amount analyzing means" is replaced with the "characteristic in the time domain of the signal of the voltage change detected by the voltage change detecting means." Means for analyzing the quantity. "

[0010] Here, the "exploration coil" may be composed of at least a first coil made of metal material which is brought close to the test body and a second coil which is brought close to the standard body for comparison. In this case, the "voltage change detection means" firstly determines a voltage change of the search coil caused by a change in the state of the metal material.
It may be configured by a circuit that detects the unbalanced output of the second coil, for example, a circuit such as a bridge.

In one embodiment of the present invention, “an unbalanced output of the first and second coils due to a change in the state of the metal material”
Is sent to the frequency spectrum analysis means without passing through the phase detector in order to maintain the state change including the deterioration information of the metal material. The characteristic amount analysis means analyzes characteristic amounts such as a first moment described later, and can evaluate the degree of material deterioration based on the analyzed characteristic amounts. Further, according to another embodiment of the present invention, it has been confirmed that it is possible to analyze the "length of the envelope" or the like as a feature amount in the time domain and evaluate the degree of deterioration of the material.

Since the search coil and the metal material are basically in non-contact with each other, even if the surface of the metal material is rough or a non-metal film is interposed, a state change due to material deterioration or the like can be reliably and quickly performed. Can be caught. In addition, since the characteristic amount in the frequency spectrum is detected instead of the phase change in the signal of the voltage change of the search coil, it is possible to evaluate not only the defect of the shape but also the deterioration of the material.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, an evaluation device 1 according to the present embodiment evaluates a degree of material deterioration until a crack is generated or a crack generation state in a steel pipe as an example of a metal material. The evaluation device 1 is generally composed of a transmitter 2, a search coil 3, a bridge 4, a personal computer 9, and the like. The personal computer 9 has a hard disk,
Removable hard disk, CD-ROM, RAM,
Copy the software stored on a flexible disk etc. to C
A general-purpose product that realizes functions described later by performing arithmetic processing in the PU is used.

As shown in FIG. 2, the above-mentioned steel tube S is divided into a test tube S1 as a test object to be subjected to material evaluation and a standard tube S2 as a standard body for comparison. The test tube S1 and the standard tube S2 have the same shape and the same size.

In the present embodiment, the search coil 3 includes a first coil 3a approaching the test tube S1, and a second coil 3b approaching the standard tube S2. These first and second coils 3 a and 3 b constitute a part of the bridge 4. The transmitter 2 transmits an AC signal having a sine curve as shown in FIG. 10A which is an example of a continuous wave for generating an eddy current using a crystal transmitter or the like, and the first and second coils 3a. , 3b, an eddy current is generated in the test tube S1 and the standard tube S2 by electromagnetic induction. The output of the transmitter 2 is in a state where the high-frequency side noise is cut by the filter 2a.
A magnetic flux is generated in the search coil 3 of the bridge 4.

The bridge 4 is provided with the first and second coils 3
a, 3b and first and second variable resistors 4a, 4b. These first and second variable resistors 4a and 4b
When both the test tube S1 and the standard tube S2 are normal,
This is for adjusting the voltage of the output terminal 4c to be “zero”. Then, a state change of the steel tube S due to a change in the material of the test tube S1 or the like is detected as an unbalanced output of the first coil 3a and the second coil 3b. Note that the automatic balancer 5 of FIG. 1 adjusts the imbalance of the bridge 4 due to a cause unrelated to a change in the material of the test tube S1 such as a fluctuation in the power supply voltage.

Here, two different forms of the search coil 3 are illustrated in FIG. The search coil 3 shown in FIGS. 3A and 3B is a bobbin type, and has only one search coil 3 wound around one steel pipe S around the concentric axis of the steel pipe S. . The search coil 3 according to this aspect is suitable for detecting a material abnormality (including a crack or the like) continuous in the longitudinal direction L of the steel pipe S. On the other hand, in the axial type search coil shown in FIGS. 3C and 3D, a plurality of search coils 3 are radially arranged on the inner surface of the steel pipe S. Then, each radial section of the steel pipe S is configured to be inspected by the corresponding search coil 3. Each search coil 3
Has a coil body 3y wound around a small bobbin 3x, and the center axis of the winding of the coil body 3y in each search coil 3 coincides with the circumferential direction of the steel pipe S. The search coil 3 according to this embodiment is suitable for detecting a material abnormality continuous in the circumferential direction of the steel pipe S, and the members indicated by reference numerals 3 to 8 in FIG. It is provided.

The output of the bridge 4 shown in FIG.
After being amplified through the A / D converter 8 and converted into a digital signal by the A / D converter 8, various signal processing described later is performed by the personal computer 9 by digital processing. The personal computer 9 stores the unbalanced output of the bridge 4 in the memory 9a, analyzes the data of the unbalanced output signal in the FFT means 9b by a fast Fourier transform algorithm, and obtains the frequency spectrum of the unbalanced output signal. Further, in the frequency spectrum of the unbalanced output signal, a characteristic amount described later is converted into a characteristic amount analyzing unit 9c.
And displays the analysis result in a display mode such as B scan or C scan using the CRT monitor 10 or the color printer 11.

FIG. 4 shows the relationship between the frequency distribution curve P (f) obtained by the FFT means 9b and each characteristic amount obtained by the characteristic amount analyzing means 9c. Further, examples of the feature amounts used in the present invention are listed below. 1) The frequency fp corresponding to the peak value Pt of P (f) 2) The frequency fa, fb corresponding to the value Pm 6 dB down from the peak value Pt 3) The width of the frequency of 6 dB down (fb-fa) 4) The first moment ∫ (P (f) · f) df / ∫P (f) d
f5) ∫P (f) df (however, limited to an integrated value between 0.01 and 0.04 MHz)

When performing the inspection, the first coil 3a is inserted into the test tube S1, the second coil 3b is inserted into the standard tube S2, and the voltage between the output terminals 4c of the bridge 4 is set by the first and second variable resistors 4a and 4b. The balance of the bridge is adjusted so that becomes zero. Then, the coils 3a and 3b are moved in the longitudinal direction in the test tube S1, and the characteristic amount analysis means 9c
Analysis results of each feature in the frequency domain by CRT
It is displayed on the monitor 10 and output to the printer 11.

In the embodiment of the search coil 3 shown in FIG. 3A, each characteristic amount is displayed on the CRT monitor 10 and the printer 11 in a B-scan format. On the other hand, in the mode of the search coil 3 in FIG. 3C, the inner surface of the test tube is developed on a plane for each channel of each search coil 3, and each feature amount is displayed in a C-scan format by color display. In the latter mode, when only one search coil 3 is provided, the search coil 3 is moved in the longitudinal direction L of the steel pipe S while rotating the search coil 3 in the circumferential direction of the steel pipe S. ,
Similarly, the internal state of the steel pipe S may be displayed in a C-scan format.

Next, a second embodiment of the present invention will be described with reference to FIGS. The same components as those in the first embodiment are denoted by the same reference numerals.

The present embodiment is different from the first embodiment in that each of the first and second coils 3 includes primary coils 3c and 3d for excitation and secondary coils 3a and 3a for reception. 3b, and that an operational amplifier circuit including an operational amplifier 4d is used as the above-described voltage change detection means 4. Further, in the present embodiment, each steel pipe S is transmitted from the transmitter 2 using a pulse wave as shown in FIG.
An eddy current is generated.

When a pulse wave as shown in FIG. 7A is applied to the primary coils 3c and 3d by the transmitter 2, if there is a material difference between the test tube S1 and the standard tube S2,
The differential output of the secondary side coils 3a and 3b is obtained from the output terminal 4c of the operational amplifier circuit as shown by signals K1 and K2 in FIG. 7B. FIG. 8 shows that, of the signals K1 and K2,
Sound material signal Ka (t) and degraded material signal Kb indicated by broken line
It is a graph which shows the relationship with (t).

Here, the "length of the envelope" described later is
The signal Ka (t) of the sound material shown in FIG. 8 will be described as an example. The value Xb corresponding to 10% of the peak value Xp of the signal will be described.
Is the length of the envelope between two points of the signal Ka (t). According to the comparison between the two signals, it can be seen that the peak value Xp and the envelope length of the signal tend to increase as the material deteriorates. In the present embodiment, the received signal is analyzed by the feature amount analyzing unit 9c without passing through the FFT unit 9b. The analysis in the feature amount analysis means 9c in this case is as follows.
This is to calculate the signal peak value and the length of the envelope as each feature amount in the time domain, and output the analysis results to the CRT monitor 10 and the printer 11 as before.

[0026]

Next, a first embodiment according to the first embodiment will be described. In the present embodiment, FIG.
An inspection using the search coil of the mode shown in FIG. The steel pipe S used for the inspection is a SUS304 stainless steel pipe having a diameter of 22 mm and a thickness of 1.2 mm. 0.5 to 1.0 in a range of 20 to 30 mm with respect to the longitudinal direction.
The search coil 3 was moved at a constant pitch such as mm to sample data. The frequency of the alternating current in the transmitter 2 was 70 kHz, and the sampling rate in the FFT means 9b was 781 kHz. The threshold of the low-pass function in the filter 7 was set to 200 kHz.

As the test tube S1, a tube degraded in five stages at intervals of 20% using an ultrasonic fatigue tester was used. 100% means the occurrence of cracks. FIG.
In (a), the ranges indicated by reference numerals G1, G2, G3, G4, and G5 indicate the degree of deterioration of 100, 80, 60, and 4 respectively.
They correspond to 0 and 20 percent, respectively. Each sample point corresponding to the degree of deterioration G1 to G5 is represented by the vertical axis representing the first moment and the horizontal axis representing the above 0.01 to 0.04 MHz.
The graphs with integration values ΔP (f) df between the symbols G1 to G5
Were plotted for each range. From this test result, it was confirmed that there was a correlation between the degrees of deterioration G1 to G5 and the first moment and the feature amount of ΔP (f) df.

Next, a second example according to the first embodiment will be described. In this embodiment, the axial type coils shown in FIGS. 3C and 3D are used as the search coils, and the filter 7 shown in FIG.
The difference is that it is configured as a 0 kHz low-pass filter. Other conditions are the same as in the first embodiment. In the present embodiment, as shown in FIG.
5 shows the correlation between the first moment and the width of the frequency of 6 dB down (fb-fa), and the degree of the deterioration and the fixed width of the frequency width of 6 dB down (fb-fa) are also constant. Was also confirmed.

On the other hand, a third example according to the second embodiment will be described with reference to FIG. The degree of deterioration G1 to G5 of the test tube in this embodiment is the same as in the first embodiment. According to the present embodiment, it has been found that both the length of the signal envelope and the magnitude of the signal peak value increase as the degree of deterioration progresses.

Finally, the possibility of another embodiment of the present invention will be described. In the above embodiment, the search coil 3 is configured as an insertion coil that is inserted into the steel pipe S.
A penetrating coil located outside the steel pipe S or an upper coil facing the surface of the specimen may be used. In each of the above embodiments, the search coil 3 is configured as a self-induction type that generates an eddy current in the steel pipe S and detects a state change of the steel pipe S. However, a mutual induction type in which a primary coil that generates an eddy current in the steel pipe S by electromagnetic induction and a secondary coil that detects a change in state of the steel pipe S such as magnetic permeability may be provided separately.

In the first and second embodiments, a continuous wave or a pulse wave as shown in FIGS. 10A and 10E is used. As the continuous wave, a sawtooth wave in FIG.
A square wave of (c), a wave after detection of a sine wave of (d), a chirp wave in which a sine wave having a constant frequency gradually attenuates, or the like can be used. As the pulse wave, FIG.
In addition to the intermittent pulse wave of (e), a pulse wave with a narrow interval as shown in (f) may be used. Further, the degree of deterioration of the material can be estimated using the above-described feature amount in the frequency domain using the pulse wave, and the degree of deterioration of the material can be estimated using the above-described feature amount in the time domain using the continuous wave.

In the above embodiment, the inspection object is made of a material that is hardly magnetic, and the change in the state is mainly detected as a change in conductivity. However, in the present invention, the inspection object may be a magnetic material, and the change in the state may be detected mainly as a change in the magnetic permeability. The “state change” of a metal material is caused not only by a shape defect such as a crack, but also by a void or metal embrittlement.

According to the present invention, not only a phase difference of a signal is detected but also information not conventionally used by a phase detection or a filter provided at a subsequent stage of a bridge is analyzed by a characteristic amount in a time domain or a frequency domain, and inspection is performed. Capture changes in the material of the target. Therefore, for example, a signal of a tube sheet and a signal of a crack in a steam generator, which were conventionally buried in a phase difference between signals and difficult to discriminate, can be discriminated.

[0034]

As described above, according to the features of the metal material evaluation apparatus and the evaluation method according to the present invention, not only the detection of a shape defect but also the deterioration of the material can be performed by a simple non-contact method. It has become possible to catch it reliably and quickly.

It should be noted that the reference numerals in the claims are merely for convenience of comparison with the drawings, and the present invention is not limited to the configuration of the accompanying drawings by the description. .

[Brief description of the drawings]

FIG. 1 is a logical block diagram of the present evaluation device.

FIG. 2 is a circuit diagram partially illustrating a relationship between a transmitter, a bridge, and a coil, in principle, and illustrating the relationship;

3A and 3B show a relationship between a search coil and a steel pipe, and FIG. 3A is a longitudinal sectional view of a steel pipe showing a first embodiment, taken along a longitudinal direction;
(B) is a sectional view taken along line AA of (a), (c) is a view corresponding to (a) according to the second embodiment, and (d) is a sectional view taken along line BB of (c).

FIG. 4 is a graph showing a relationship between a frequency distribution curve and a feature amount in a feature amount analysis unit.

FIG. 5 (a) shows the degree of deterioration, the first moment, and the 0.01 to 0.04MH of the steel pipe according to the embodiment of FIG. 3 (a).
3B is a graph showing a correlation with the integral value between z, and FIG. 3B shows the relationship between the degree of deterioration of the steel pipe according to the embodiment of FIG. 3C, the first moment, and the frequency width (fb-fa) of 6 dB down. It is a graph which shows a correlation.

FIG. 6 is a diagram corresponding to FIG. 2 according to a second embodiment of the present invention.

FIG. 7A is a graph showing an input pulse generated by a transmitter in the second embodiment, and FIG. 7B is a graph showing a received pulse detected by a secondary coil.

FIG. 8 is a graph showing the relationship between the reception time and the time when the reception pulses of the sound material and the deteriorated material are compared and displayed.

FIG. 9 is a graph showing one correlation between the degree of deterioration of the steel pipe according to the second embodiment shown in FIG. 6, and the values of the envelope length and peak intensity of the received pulse.

FIG. 10 is a graph showing a relationship between time and intensity of a continuous wave and a pulse wave generated by a transmitter.

[Explanation of symbols]

 Reference Signs List 1 evaluation device 2 transmitter 3 search coil 3a first coil (first secondary coil) 3b second coil (second secondary coil) 3c first primary coil 3d second primary coil 3x Bobbin 3y Coil body 4 Bridge 4a First variable resistor 4b Second variable resistor 4c Output terminal 4d Operational amplifier 5 Automatic balancer 6 Amplifier 7 Filter 8 A / D converter 9 Personal computer 9a Memory 9b FFT means 9c Feature analysis means 10 CRT monitor 11 Printer S Steel pipe (metal material) S1 Test tube (test body) S2 Standard pipe (standard body)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takuichi Imana 1-18-14 Kitahorie, Nishi-ku, Osaka-shi Non-Destructive Inspection Co., Ltd.

Claims (5)

[Claims] An oscillator (2) for generating a continuous wave or a pulse wave, and an eddy current is generated in the metal material (S) by the continuous wave or the pulse wave to detect a state change of the metal material (S). A voltage change detection means (4) for detecting a voltage change of the search coil (3) caused by a change in the state of the metal material (S).
A frequency spectrum analyzing means (9b) for obtaining a frequency spectrum of the signal of the voltage change detected by the voltage change detecting means (4);
An evaluation apparatus for a metal material, comprising: a feature amount analyzing means (9c) for analyzing a feature amount in the frequency spectrum obtained in b). 2. A transmitter (2) for generating a continuous wave or a pulse wave, and an eddy current is generated in the metal material (S) by the continuous wave or the pulse wave to detect a state change of the metal material (S). A voltage change detection means (4) for detecting a voltage change of the search coil (3) caused by a change in the state of the metal material (S).
An evaluation apparatus for a metal material, comprising: a characteristic amount analyzing unit (9c) for analyzing a characteristic amount in a time domain of a signal of a voltage change detected by the voltage change detecting unit (4). 3. The search coil (3) includes a first coil (3a) that is at least close to the test object (S1) of the metal material (S) and a second coil that is close to a comparison standard (S2). A coil (3b), wherein the voltage change detecting means (4) detects a voltage change of the search coil (3) caused by a state change of the metal material (S) with the first and second coils (3b).
3. The metal material evaluation device according to claim 1, wherein the device is detected as an unbalanced output of a, 3b). 4. An eddy current is generated in the metal material (S) by a continuous wave or a pulse wave, and a state change of the metal material (S) is detected as a voltage change of the search coil (3). A) a metal spectrum evaluation method for obtaining the frequency spectrum of the signal of the voltage change and evaluating the metal material (S) by analyzing the characteristic amount in the frequency spectrum. 5. An eddy current is generated in the metal material (S) by a continuous wave or a pulse wave to detect a state change of the metal material (S) as a voltage change of the search coil (3). A) a metal material evaluation method for evaluating the metal material (S) by analyzing a characteristic amount of a voltage change signal in a time domain.