JP3036387B2 - Ultrasonic flaw detection method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method and apparatus for non-destructively inspecting defects in a material using ultrasonic waves and measuring the thickness of the material.

[0002]

2. Description of the Related Art FIG. 10 is a functional block diagram of a conventional general ultrasonic flaw detector. In FIG. 10, reference numeral 21 denotes a synchronizing unit for generating and outputting a synchronizing signal necessary for each circuit; 22, a transmitting unit for generating a transmission electric signal based on an output signal from the synchronizing unit 21; A probe that generates an ultrasonic wave based on a transmission electric signal, makes the ultrasonic wave incident on the inside of the subject 24, receives an echo from the inside of the subject, and converts the echo into an electric signal. And 26, a display unit for displaying an output signal from the receiving unit 25.

When inspecting the inside and outside of a material using ultrasonic waves, a probe 23 shown in FIG. 10 is a single-transducer type probe which transmits and receives ultrasonic waves using one transducer. . FIG. 11 shows a flaw detection waveform obtained when the inside and outside of the material are inspected when the probe is used. In FIG. 11A, when the transducer surface of the probe is set so as to be parallel to the material surface, and ultrasonic flaw detection is performed through the water of the medium, FIG.
A flaw detection waveform as shown in FIG. FIG. 11B
(A) is a reflected echo (S echo) from the material surface, (A) is a reflected echo (F echo) from a defect inside the material, and (C) is a reflected echo (B echo) from the bottom surface of the material. Here, the S echo has an extremely large amplitude as compared with the F echo, and is almost saturated in normal flaw detection. A portion having a certain time width and extending from the surface of the material to a depth corresponding to a distance over which the ultrasonic wave propagates in the time width is called a surface dead zone, and it is impossible to detect an internal defect existing therebetween. Generally, in the case of steel inspection using a single element type probe, it is said that a dead zone of about 3.0 [mm] exists.

However, when an inspection is performed for the purpose of detecting lamination or the like of a steel sheet, the dead zone must be as small as possible. Also, due to the extreme difference in acoustic impedance between the couplant (such as water) and steel (impedance of couplant <impedance of steel), the F echo
The amplitude is extremely small compared to the S echo, and in normal inspection inside steel, to increase the amplification sensitivity of the receiving amplifier,
The S echo after the output of the receiving unit 25 in FIG. 10 is saturated, and as shown in FIG. 12, a run-in phenomenon (see A in FIG. 12) is confirmed within a certain period immediately after the S echo, and the amplification of the receiving unit is performed. In many cases, linearity cannot be guaranteed and defect evaluation cannot be performed reliably. As a means for solving this problem, there is a method using a split-type probe (also referred to as a two-transducer vertical probe). This is a probe generally used in an ultrasonic automatic flaw detector for thick steel plates.

FIG. 13 is a view showing the structure of a split-type probe. In FIG. 13, 31 is a transmitting oscillator, 32 is a receiving oscillator, 33 is an acoustic dividing surface, and 34 and 35 are acrylic materials. 0.5 [m] between the probe and the material surface
m], and a medium such as water is interposed to avoid contact between the probe and the material. In this split type probe, the transmitting oscillator 31 and the receiving oscillator 32 are separated,
Since the S echo can be limited to only the leak component from the sound division surface 33, the S echo can be almost completely removed. By using this split type probe, the S echo width can be almost ignored and the run-in phenomenon immediately after the S echo can be eliminated.

FIG. 14 (a) shows a flaw detection waveform when a flaw of a steel plate having a thickness of 60 [mm] is detected using the above-mentioned split type probe. FIG. 14B shows the spectrum of the B echo on the steel bottom surface. FIG. 15 shows a distance amplitude characteristic curve of the B echo. Here, the echo height also tends to decrease gradually when the distance is farther from the focal position, but the echo tends to decrease sharply when the distance is closer to the focal position. From FIG. 14B, the split-type probe can be said to be a narrow-band type probe. Due to this narrow band (in other words, the number of echo waves is large), the following adverse effects cannot be avoided in actual flaw detection.

[0007] The problem of detectability in the near field is shown in FIG. 16.
As shown in (d), φ5.6 [mm] flat bottom artificial defects of various depths are machined, and flaw detection waveforms at that time are shown. FIG. 17 shows the first F echo (F) of the artificial defect at each depth.
1 shows one echo height (amplitude). Generally, FIG.
When the position is closer to the focal position as shown in FIG. 5, the echo sharply drops. The echo reflected multiple times in the water gap and the multiple reflected echoes from the defect interfere with each other because of the large wave number of the echo, so that the presence or absence of the defect can be confirmed. However, since the F1 echo cannot be recognized, the echo height is high. It is impossible to recognize the size (understand the size of the defect). Figures 16 and 1
7, the limit is 1.5 to 2.0 [mm] below the surface, and it is impossible to detect a defect existing in a shallower place.

[0008] The problem of the dead zone limit on the front and back surfaces and the steel front side are as described above. However, the dead band is also a problem on the steel bottom side due to the large number of echo waves. FIG. 18 shows φ5.6 processed near the steel bottom surface.
[Mm] It is a flaw detection waveform of an artificial defect, but 1.0 near the bottom surface.
At about [mm], it is very difficult to recognize the F echo. Therefore, it is impossible to detect a defect of 1.0 mm or less near the bottom.

[0009]

In order to solve the above problem, it is necessary to reduce the number of echo waves. In other words, it is only necessary to increase the bandwidth of the divided probe. But,
Such a method has the following problems. (1) Sensitivity Deterioration Problem FIGS. 19A and 19B show a 25 mm thick STB.
FIG. 3B is a flaw detection waveform (B echo waveform) when the bottom surface of the N1 standard test piece is flaw-detected by a conventional narrow band and wide band split probe. FIGS. 19C and 19D show the spectra of the B echoes in FIGS. 19A and 19B, respectively. The signal-to-noise amplitude ratio (SN ratio) at this time
Are 20.5 [dB] and 9.0 [dB], respectively, and S is about 12 [dB] due to the use of the broadband probe.
N degradation occurs. (2) Leakage noise problem inside the probe In the split-type probe, the transducers are slightly inclined inward so that the transducers on the transmitting side and the receiving side focus on each other. Therefore, at the time of ultrasonic excitation, ultrasonic waves are generated in the vertical and horizontal directions. Here, the ultrasonic waves in the horizontal direction leak to the receiving side through the acoustic division plane. However, since the material of the sound division surface is a material having a very small acoustic impedance such as cork, only a small amount of ultrasonic waves having a low frequency are transmitted. As a result, as shown in FIG. 20B, a leaky echo having the same echo height level as the S echo is detected,
There is a risk of being mistakenly recognized as a defect. By the way, in the conventional narrow band type probe, as shown in FIG.
Since the noise removing coil is inserted into the probe, the band is naturally narrowed by the damping action, and the waveform is as shown in FIG. As described above, in order to increase the bandwidth of the split-type probe, it is indispensable to improve the SN ratio and remove leakage noise.

[0010] Separately, in an automatic ultrasonic flaw detector for a steel plate or the like, in order to mechanically scan the probe,
As shown in FIG. 13, a water gap having a width of about 0.5 [mm] is provided between the acrylic surface of the probe and the steel plate surface, so that the reflected echo in the gap on the transmitting side does not leak to the receiving side. Are divided by surface. However, steel plate burrs,
If the sound dividing surface is worn out due to the undulation, or if the water gap becomes large and the sound dividing surface is separated from the steel plate surface, leakage of the S echo to the receiving side is inevitable. (A) of FIG.
Is an S echo when the water gap is 0.5 [mm]. When the gap becomes 1.5 [mm], the S echo sharply increases, and multiple reflection echoes in the gap clearly appear. On the other hand, in the normal automatic flaw detection, as shown in FIG. 22A, an S echo and a B echo are detected, and an actual flaw detection range (F gate) is set between the S echo and the B echo. . Also, even if the S echo position changes, F
A function that the gate follows (S tracking function) is employed. As shown in FIG. 21B, the increase of the S multiple reflection echo due to the expansion of the water gap is caused by the S tracking function as shown in FIG.
There is also a problem that an erroneous indication of a defect caused by leakage of the multiple reflection echo into the F gate is caused.

[0011]

In the ultrasonic flaw detection method and apparatus according to the first and third aspects of the present invention, transmission and reception of ultrasonic waves are performed separately in a direction perpendicular to the surface to be inspected. An ultrasonic flaw detection method and apparatus for flaw detection existing inside a steel sheet using a split type vertical probe, which is used for transmitting and receiving ultrasonic waves using a chirp wave that changes the frequency within a predetermined rectangular envelope. A transmission wave generating unit that generates a transmission wave and supplies the split vertical probe, a reference wave generation unit that generates a reference wave using a chirp wave that changes the frequency within a predetermined sinusoidal envelope, Correlation processing between a received wave obtained from the split type vertical probe and a reference wave generated by the reference wave generation means, and a correlation processing means using the pulse-compressed signal after the correlation processing for flaw detection. It is provided.

In the ultrasonic flaw detection method and apparatus according to the second and fourth aspects of the present invention, the split type vertical probe separately transmits and receives ultrasonic waves in a direction perpendicular to the surface to be inspected. In the ultrasonic flaw detection method and apparatus for flaw detection existing inside the steel sheet using the method, generating a transmission wave used for transmission and reception of the ultrasonic wave using a chirp wave that changes the frequency within a predetermined pulse width, the division Transmission wave generating means for supplying to the vertical probe, a reference wave generating means for generating a reference wave using a chirp wave having the same or different shape as the transmission wave by the chirp wave, and the split vertical probe. Correlation processing means for performing correlation processing between the obtained reception wave and the reference wave generated by the reference wave generation means, and outputting a pulse-compressed signal after the correlation processing, and a pulse-compressed signal after the correlation processing Against A detection means that performs detection by the polarity of the larger amplitude value of the positive amplitude or negative amplitude of the reflected echo from the inside or bottom of the steel sheet, and uses the detected echo for flaw detection. is there.

[0013]

As a technique for solving the above-mentioned deterioration of the SN ratio, there is a technique called pulse compression known in the field of radar (Radar handbook, Skolnike).
t. , McGraw-Hill Inc. , 1970).

[0014] Figure 23 is an explanatory view of a linear frequency modulated pulse compression radar in FIG (a) is from time t ₁ t ₂
Indicates that that a linear frequency modulation (FM) frequency in a transmission time T (equal to the transmission pulse width) to the f ₁ to f _2, (b) is frequency modulated in such straight The waveform of a wave (this is called a chirp wave) is shown. FIG. 23B shows an example of the pulse compression radar.
By transmitting a frequency-modulated wave as described above as a transmission wave and performing a cross-correlation operation between the reception waveform and the waveform used for transmission, the pulse width in the time axis direction of the reception wave is compressed, and a waveform having a sharp amplitude is formed. In addition, the SN ratio of the received signal is improved. FIG. 23C shows the signal waveform after the cross-correlation calculation processing.

As a document which applies the pulse compression technique to the field of ultrasonic waves, there is an ultrasonic diagnostic pulse compression apparatus disclosed in, for example, JP-A-63-233369. In this apparatus, in order to pulse-compress an ultrasonic echo signal, a cross-correlation process between a complex signal and a reference wave signal via a quadrature detector is performed. In general, two functions f
A correlation function s (τ) as a result of performing a correlation operation between ₁ (t) and f ₂ (t) is defined as the following equation (1).

[0016]

(Equation 1)

When this technique is introduced into ultrasonic flaw detection, by using a chirp wave having a width in the time axis direction as a transmission wave, transmission energy can be reduced as compared with a conventional case where a pulse wave having an extremely short width is used. It can be secured large.
Further, as shown in FIG. 24 (a), since the transmission waveform corresponding to the frequency band of the probe can be set, the conversion efficiency between the electric signal and the ultrasonic wave at the probe is reduced by the conventional pulse wave ((b) of FIG. 24). )), And a margin of sensitivity can be secured. In this way, by using a split type probe, using a chirp wave for a transmission wave, and using a flaw detection signal obtained by performing a correlation process on this reception wave, the noise of the flaw detection signal is reduced, and the probe has a wider band. Can prevent the deterioration of the S / N ratio.

According to the first and third aspects of the present invention, a split type vertical probe which separately transmits and receives ultrasonic waves in a direction perpendicular to the surface to be inspected is provided inside the steel plate. An ultrasonic flaw detection method and apparatus for flaw detection of a flaw that uses a chirp wave that changes the frequency of a transmission wave used for transmission and reception of an ultrasonic wave within a predetermined rectangular envelope, and receives the reception wave and a predetermined sinusoidal envelope A correlation process is performed with a reference wave using a chirp wave whose frequency is shifted in the inside, and a defect inside the steel plate is detected by a pulse-compressed signal after the correlation process.

By employing the ultrasonic flaw detection method using the chirp wave as the transmission wave, the echo has a waveform composed of a sharp main lobe and small side lobes around the main lobe as shown in FIG. Here, a reflection echo from each boundary surface at the time of flaw detection in steel is shown in FIG. 25B. In FIG. 25B, (A) is a reflection echo (BK echo) from a boundary surface between the acrylic surface of the probe and the couplant,
(A) is a reflected echo (S echo) from the interface between the couplant and the steel surface, and (c) is a reflected echo from a defect inside the steel (the interface between the steel and the material change such as air layers and inclusions). F echo) and (d) are reflection echoes (B echoes) from the interface between the steel and the air layer.

Here, regarding the incidence of ultrasonic waves from the medium 1 to the medium 2, the reflectance γ _{12 at the} boundary surface is as follows, where Z ₁ is the acoustic impedance of the medium 1 and Z ₂ is the acoustic impedance of the medium 2. It is obtained as in equation (2). γ ₁₂ = (Z ₂ −Z ₁ ) / (Z ₁ + Z ₂ ) (2) In Expression (2), if the acoustic impedance of the medium 2 is smaller than that of the medium 1, that is, if the reflectance is a negative value, ,
This means that the phase is reversed. If the value becomes a positive value, the phase is not reversed.

In FIG. 25B, the phase inversion of the S echo can be observed with respect to the BK echo (acoustic contact material), the F echo (steel versus air) and the B echo (steel versus air). FIG. 25D shows the acoustic impedance of each medium. Here, the BK echo from FIG.
Since the phases of the F echo and the B echo match, if only the positive component having the peak value of these echoes is detected, the detected waveform is shown in FIG. FIG.
In (c), the conventional S echo component is almost removed. Therefore, considering the polarity of F echo or B echo,
By performing detection based on the polarity with the larger peak amplitude value on either the positive side or the negative side, erroneous recognition of a defect due to the S echo can be prevented.

Further, in the invention according to claims 2 and 4, the split type vertical probe for separately transmitting and receiving ultrasonic waves in the direction perpendicular to the surface to be inspected is provided inside the steel plate. In an ultrasonic flaw detection method and apparatus for flaw detection of an existing defect, a transmission wave used for transmission and reception of an ultrasonic wave uses a chirp wave that transits a frequency within a predetermined pulse width, and a reception wave thereof, and a transmission wave set in advance. Correlation processing with a reference wave using a chirp wave of the same or different shape is performed, and for the pulse-compressed signal after this correlation processing, the positive side amplitude or negative side amplitude of the reflected echo from the inside or bottom surface of the steel plate Among them, detection is performed based on the polarity having the larger amplitude value, and a defect inside the steel plate is detected by an echo after the detection. As a result, the reflection echo (S echo) level on the steel sheet surface can be reduced, and the undulation of the steel sheet during automatic flaw detection,
This is effective in preventing erroneous recognition of a defect due to an increase in S echo due to deterioration of the sound division surface.

[0023]

FIG. 1 is a functional block diagram showing an example of an ultrasonic flaw detector according to the present invention. In FIG. 1, reference numeral 1 denotes a synchronizing unit that generates and outputs a synchronizing signal necessary for each circuit, 2 denotes an FM signal setting unit that sets a frequency modulation signal (chirp signal wave in this example) having a predetermined waveform, and 3 denotes an FM signal setting. The FM signal transmitting section 4 generates an FM signal to be transmitted based on the FM signal set by the section 2 and supplies the signal to the probe 4. The FM signal transmitting section 4 generates an ultrasonic wave based on the transmission signal from the FM signal transmitting section 3 and receives A probe that irradiates an ultrasonic wave into the specimen 5 and converts an echo from the inside of the specimen into an electric signal, 5 is a specimen to be inspected, 6 is a pulse compression unit, 7 is a reference wave setting unit, 8 is a reference wave setting unit. Is a display unit.

In the apparatus shown in FIG. 1, the FM signal set by the FM signal setting unit 2 at a predetermined cycle is output from the FM signal transmitting unit 3 based on a synchronization signal output from the synchronization unit 1 at every predetermined repetitive synchronization. Sent. The probe 4 generates an ultrasonic wave based on the transmitted FM signal and causes the ultrasonic wave to be incident on the subject 5, and an ultrasonic reflection echo from a nonuniform portion of acoustic impedance existing inside and outside the subject. Is captured and converted to an electrical signal and output. The received signal from the probe 4 is
Based on the output signal from the synchronization unit 1, the pulse compression unit 6 performs pulse compression by correlation calculation with the reference wave set by the reference wave setting unit 7, and the result is displayed on the display unit 8.

FIG. 2 is a diagram showing an example of a specific hardware configuration of the apparatus shown in FIG. In FIG. 2, reference numeral 11 denotes a personal computer which performs all the functional operations of the synchronization unit 1, the FM signal setting unit 2, the FM signal transmission unit 3, and the reference wave setting unit 7 in FIG. 12 is a D / A converter,
Reference numeral 13 denotes a transmission amplifier, 14 denotes a divided probe, 15 denotes a reception amplifier, 16 denotes an A / D converter, and 17 denotes an FIR filter. Specific hardware of the pulse compression unit 6 in FIG. It is. As the FIR filter 17, for example, FIG.
May be used. 18 is an oscilloscope, 1
9 is a subject.

In FIG. 2, the FM waveform generated by the personal computer 11 is converted into an analog signal by the D / A converter 12, and is amplified to a required transmission power by the transmission amplifier 13, so that the divided waveform is obtained. It is transmitted into the subject 19 as ultrasonic waves from one of the tentacles 14. The signal received by the other of the divided probes 14 is amplified by the receiving amplifier 15 and is sequentially converted to a digital signal by the A / D converter 6. Then, the received digital signal is correlated with the reference wave generated and output by the personal computer 11 by the FIR filter 17, and pulse compression processing is performed. The waveform after the pulse compression is displayed on the oscilloscope 18. The reason why the personal computer 11 is used here is that the waveform of the transmission wave and the waveform of the reference wave can be set to arbitrary shapes by changing the program.

The digital filter shown in FIG.
Two functions f ₁ (n) and f discretized by the / D converter
A correlation operation as shown in equation (3) of ₂ (n) can be performed. In equation (3), N is the number of samples.

[0028]

(Equation 2)

FIG. 3 is a diagram showing an example of the configuration of the FIR digital filter. In the drawing, + indicates an adder, X indicates a multiplier, and Z ^-1 indicates a delay unit. The output is delayed after a time corresponding to the repetition period.

In the digital filter shown in FIG. 3, a reference waveform for performing a correlation operation with a reception waveform x (τ) discretized into a digital signal is sampled (discretized) at a certain fixed sampling frequency. in the example each discrete data value as 128 c ₀ to c _127, are inputted to one respective × sign multiplier. On the other hand, the discretized reception data x (τ) input from the input terminal for each transmission cycle is
Is directly supplied to the other input of each multiplier, and the reference data c ₀ to c ₁₂₇ are respectively multiplied separately, each multiplication results except the multiplication result between c _{12 7} are respectively 127 delayer and adder Is supplied to one of the inputs of the corresponding adder, which is alternately connected in series. Then, only the result of multiplication with c ₁₂₇ is directly supplied to the first delay unit connected in series in an alternating manner,
The other input of the adder connected in series downstream of the delay unit is supplied with a result of multiplication and c _{12 6.} Then, the output of the last adder in the serial combination becomes the correlation operation output.
Equation (4) shows the result of the above operation.

[0031]

(Equation 3)

The FIR digital filter having the above-described configuration is used to input discrete data x sequentially input from an input terminal.
(Τ) and the scattered data C (i) of the reference waveform are subjected to a convolution operation according to the following equation (5), and y
(Τ). In the equation (5), the signal time is reversed to reverse the direction of the signal, and then the time is shifted. However, the equivalent is obtained by rearranging the arrays C _{0 to} C ₁₂₇ of the discrete data of the reference waveform in the reverse direction. Processing can be performed.

[0033]

(Equation 4)

FIG. 4 is a waveform diagram for explaining the operation of the digital filter shown in FIG. 3. In FIG. 4, after transmitting the frequency modulation wave, the reception signals sequentially obtained as time elapses are divided into time τ to τ + 127. The temporal change of the correlation output, which is the result of sequentially performing the convolution operation (equivalent to the operation for obtaining the similarity between two waveforms) between each of the divided received waveforms and the reference waveform from the beginning of the reception period, is shown. I have. Now the received echo waveform is obtained almost at the center of the time axis,
It can be seen that the reference wave is sequentially shifted in time, and when the phase of the received echo wave coincides with the phase of the reference wave (approximately at the center of the time axis in FIG. 4), the correlation output of the maximum peak is obtained.
The level of this peak differs depending on the similarity.

Embodiment 1 In the first embodiment, the subject is STB-N having a thickness of 25 [mm].
One test piece was used, and the bottom face was inspected. The probes used are a narrow-band split type probe (probe A) having a nominal frequency of 5 [MHz] and a broadband split type probe (probe B) having the same frequency. FIGS. 5A and 5B show flaw detection waveforms by the flaw detector shown in FIG. 10 using the probe A and the probe B. FIG. At this time, the amplitude ratio between the B echo and the noise (S
N ratio) were 20.5 [dB] and 9.1 [dB], respectively. Here, using the probe B and the flaw detector shown in FIG. 2, the conditions (frequency transition width 1 to 9 [MHz], signal time 5 [μsec], and envelope shown in FIGS. The line shows the waveform after the correlation processing with the transmission wave and the reference wave (the transmission wave has a square shape at the signal time and the reference wave has a sine shape at the signal time). SN here
The ratio becomes 28.2 [dB], and the S
The N ratio was improved by 19.1 [dB], and the improvement was 7.7 [dB] compared to the probe A which is usually used.

Embodiment 2 FIG. In Example 2, a steel plate having a thickness of 10 [mm] has a depth from the surface of 3.0 [mm], 2.5 [mm], and 2.0 [mm], respectively.
Two probes (narrow band type: probe) using φ5.6 [mm] flat bottom holes processed at the positions of [mm], 1.5 [mm] and 1.0 [mm] in Example 1 A, Broadband type: Probe B)
Was used to detect flaws. In addition, when the probe A is used, the flaw detector shown in FIG. 10 is used, and when the probe B is used, the flaw detector shown in FIG. 2 is used. , (B) (the frequency transition width is 1 to 9 [MHz], the signal time is 3 [μsec],
As the envelope, a transmission wave having a square shape at the signal time and a reference wave having a sine shape at the signal time were used. 6 (a), (b), (c), (d) and (e) show the flaw detection waveform when the probe A detects a defect at each of the above-mentioned depths, and FIGS. (D), (e), (f),
(G) is a flaw detection waveform when a defect at each depth is detected by the probe B. In the case of the probe A, the depth is 2.0 [m
m], it is difficult to recognize the F echo due to interference with the multiple reflection echo behind the F echo (see FIG. 6C). F echo of a defect existing at a shallower place than this ((d) and (e) in FIG. 6)
Is also difficult to recognize, and the limit of defect recognition is up to a depth of 2.0 [mm]. On the other hand, in the case of the probe B, it is possible to recognize an F echo having a depth of 1.0 [mm] (see FIG. 7G). Therefore, by using the probe B and the flaw detector shown in FIG. 2, the limit of the conventional defect recognition is narrowed from a depth of 2.5 [mm] to a depth of 1.0 [mm],
The flaw detection range can be expanded.

Embodiment 3 FIG. In Example 3, depths of 1.5 [mm], 1.0 [mm] and 0.5 [m] were respectively formed on the bottom surface of a steel plate having a thickness of 20 [mm].
m] with a flat bottom artificial defect of φ5.6 [mm], and flaw detection using the two probes (narrow band type: probe A, broad band type: probe B) used in Example 1. Was done. In addition, when the probe A is used, the flaw detector shown in FIG. 10 is used, and when the probe B is used, the flaw detector shown in FIG. 2 is used. , (B) (the frequency transition width is 1 to 9 [MHz], the signal time is 3 [μsec], and the envelope indicates that the transmission wave is square in the signal time, and the reference wave is the signal. Sinusoidal in time). 8C, 8D, and 8E show flaw detection waveforms when each defect is detected by the probe A, and FIGS. 8F, 8G, and 8H show each defect. It is a flaw detection waveform at the time of flaw detection with the probe B. In the case of the probe A, regarding a defect echo (F echo) having a depth of 1.0 [mm],
It is difficult to recognize the F echo due to interference with the B echo on the bottom surface of the steel plate (FIG. 8D). Similarly, it is difficult to recognize an F echo (FIG. 8E) of a defect present at a deeper place, and the defect recognition is limited to a depth of 1.5 [mm]. On the other hand, in the case of the probe B, the depth is 1.0 [m
m] can be recognized (FIG. 8 (g)).
Therefore, by using the probe B and the flaw detector shown in FIG.
The limit of the conventional defect recognition is narrowed from a depth of 1.5 [mm] to a depth of 1.0 [mm], and the flaw detectable range can be expanded.

Embodiment 4 FIG. In Example 4, a steel plate having a thickness of 20 [mm] was used for the two probes (narrow band type: probe A, broad band type) used in Example 1.
Flaw detection was performed using the probe B). When the probe A is used, the flaw detector shown in FIG. 10 is used, and when the probe B is used, the flaw detector shown in FIG. 2 is used. , (B) (the frequency transition width is 1 to 9 [MHz], the signal time is 3 [μ], respectively).
sec], the envelope indicates that the transmission wave is square in the signal time, and the reference wave is sinusoidal in the signal time.)
Was used. FIG. 9C shows a flaw detection waveform in the case of the probe A,
FIG. 9D shows a flaw detection waveform in the case of the probe B. When measuring the amplitude ratio of the S echo and the B echo (B echo / S echo), the probe A was 31.0 [dB],
Probe B was 32.0 [dB].

Here, in FIGS. 9 (c) and 9 (d),
FIG. 9 shows waveforms when only the negative waveform is detected.
(E) and (f). Here, when measuring the level ratio of the S echo and the B echo (B echo / S echo),
Probe A is 31.0 [dB], and probe B is 35.5 [dB].
B], and a decrease in the S echo level of 3.5 [dB] was confirmed by pulse compression processing using a broadband probe and a chirp wave. Therefore, considering the polarity of the F echo or the B echo and evaluating the defect of the steel sheet using the waveform after detection with the polarity having the larger positive or negative amplitude value, the fluctuation of the water gap, etc. Flaw detection can be performed without being affected by the change in the S echo level due to the above, and application to automatic flaw detection and the like can be expected.

[0040]

As described above, according to the present invention, a defect existing inside a steel sheet using a split type vertical probe that separately transmits and receives ultrasonic waves in a direction perpendicular to the surface to be inspected. In the ultrasonic flaw detection method and apparatus for flaw detection, using a chirp wave that changes the frequency of a transmission wave used for transmission and reception of ultrasonic waves within a predetermined square envelope, the reception wave thereof, and within a predetermined sinusoidal envelope Correlation processing with a reference wave using a chirp wave that changes frequency is performed, and a defect inside the steel plate is detected by a pulse-compressed signal after the correlation processing, so that the frequency is higher than that of a conventional probe. A probe with a wide band can be introduced, and even if the number of transmission waves is increased, it is possible to detect defects existing near the steel sheet surface and bottom surface compared to the conventional one by using a signal with excellent time resolution obtained by pulse compression of the received wave. Of the dead zone There is an effect to decrease.

Further, according to the present invention, an ultrasonic wave detecting a defect existing inside a steel plate by using a split type vertical probe which separately transmits and receives an ultrasonic wave in a direction perpendicular to a surface to be inspected. In the flaw detection method and apparatus, using a chirp wave that changes the frequency of a transmission wave used for transmission and reception of ultrasonic waves within a predetermined pulse width, the received wave, and a chirp wave having the same or different shape as a preset transmission wave are used. A correlation process with the used reference wave is performed. For the pulse-compressed signal after the correlation process, the larger amplitude value of the positive side amplitude or the negative side amplitude of the reflection echo from the inside or the bottom surface of the steel plate is used. Since the detection based on the polarity is performed and the defect inside the steel plate is detected by the echo after the detection, the dead zone can be reduced and the reflection echo (S echo) level on the steel plate surface can be reduced. Ri, swell and of the steel sheet at the time of automatic flaw detection,
This is effective in preventing erroneous recognition of a defect due to an increase in S echo due to deterioration of the sound division surface.

[Brief description of the drawings]

FIG. 1 is a functional configuration diagram showing an example of an ultrasonic flaw detector according to the present invention.

FIG. 2 is a diagram illustrating an example of a specific hardware configuration of the device in FIG. 1;

FIG. 3 is a diagram illustrating a configuration example of an FIR digital filter.

FIG. 4 is a waveform chart for explaining the operation of FIG. 3;

FIG. 5 is an explanatory diagram of various waveforms according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram 1 of various waveforms in a second embodiment according to the related art.

FIG. 7 is an explanatory diagram of various waveforms in Embodiment 2 of the present invention.
It is.

FIG. 8 is an explanatory diagram of various waveforms in Embodiment 3 of the present invention.

FIG. 9 is an explanatory diagram of various waveforms in Embodiment 4 of the present invention.

FIG. 10 is a functional configuration diagram of a conventional general ultrasonic flaw detector.

FIG. 11 is a flaw detection waveform obtained by flaw detection using a conventional general ultrasonic flaw detector.

FIG. 12 is a diagram showing a flaw detection waveform showing a driving phenomenon.

FIG. 13 is a configuration diagram of a split-type probe.

FIG. 14 is an explanatory diagram of various waveforms obtained by a split probe.

FIG. 15 is a diagram showing a distance amplitude characteristic curve.

FIG. 16 is an explanatory diagram of various flaw detection waveforms by a conventional split-type probe.

FIG. 17 is a diagram showing an echo height of an F1 echo by a conventional split-type probe.

FIG. 18 is a diagram showing a flaw detection waveform for a bottom surface vicinity defect.

FIG. 19 is an explanatory diagram of various waveforms obtained by a split-type probe.

FIG. 20 is an explanatory diagram of leakage noise.

FIG. 21 is an explanatory diagram of an increase in S echo due to an increase in a water gap.

FIG. 22 is an explanatory diagram of leakage of an S echo into a flaw detection gate.

FIG. 23 is an explanatory diagram of a linear frequency modulation pulse compression radar.

FIG. 24 is a diagram illustrating a relationship between a transmission wave and a frequency band of a probe.

FIG. 25 is an explanatory diagram of S echo level reduction by detection.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synchronization part 2 FM signal setting part 3 FM signal transmission part 4, 14 Probe 5, 19 Subject 6 Pulse compression part 7 Reference wave setting part 8 Display part 11 Personal computer 12 D / A converter 13 Transmission amplifier 15 Receiving amplifier 16 A / D converter 17 FIR filter 18 Oscilloscope

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (4)

(57) [Claims] 1. An ultrasonic flaw detection method for flaw detection existing inside a steel sheet using a split type vertical probe for separately transmitting and receiving ultrasonic waves in a direction perpendicular to a surface to be inspected, comprising: Using a chirp wave that changes the frequency of a transmission wave used for transmission and reception of sound waves within a predetermined rectangular envelope , the received wave and a chirp wave that changes the frequency within a predetermined sinusoidal envelope are used. An ultrasonic flaw detection method, comprising performing a correlation process with a used reference wave, and flaw-detecting a defect inside the steel plate with a pulse-compressed signal after the correlation process. 2. Ultrasonic wave transmission in a direction perpendicular to a surface to be inspected.
Steel plate using split-type vertical probe for separate transmission and reception
Ultrasonic flaw detection method for detecting flaws inside
The transmission wave used for transmitting and receiving ultrasonic waves within a predetermined pulse width.
Using a chirp wave that changes the wave number,
Chirp wave with the same or different shape as the set transmission wave
The correlation processing with the reference wave using is performed. For the pulse-compressed signal after the correlation processing, the larger one of the positive side amplitude and the negative side amplitude of the reflection echo reflected from the inside or the bottom surface of the steel sheet. An ultrasonic flaw detection method comprising: performing detection according to the polarity of a flaw; and detecting flaws inside the steel sheet by an echo after the detection. 3. An ultrasonic flaw detector for detecting a defect existing inside a steel plate by using a split type vertical probe which separately transmits and receives ultrasonic waves in a direction perpendicular to a surface to be inspected. using a chirp wave to transition frequencies in shape envelope towards generates a transmission wave to be used for transmission and reception of ultrasonic waves, before
Transmitting wave generating means for supplying to the split-type vertical probe, reference wave generating means for generating a reference wave using a chirp wave for changing the frequency within a predetermined sinusoidal envelope , the split-type vertical probe Correlation processing means for performing a correlation process between the received wave obtained from the probe and the reference wave generated by the reference wave generation unit, and using the pulse-compressed signal after the correlation process for flaw detection. Ultrasonic flaw detector. 4. Ultrasonic wave transmission in a direction perpendicular to the surface to be inspected.
Steel plate using split-type vertical probe for separate transmission and reception
Ultrasonic flaw detector that detects flaws inside
Use a chirp wave that changes the frequency within a predetermined pulse width.
To generate transmission waves used for transmitting and receiving ultrasonic waves,
Transmission wave generating means for supplying the split vertical probe, and a chirp having the same or different shape as the transmission wave by the chirp wave.
Reference wave generating means for generating a reference wave using a chirp wave, a reception wave obtained from the split vertical probe, and the reference wave
Perform correlation processing with the reference wave generated by the generation means, and
Correlation processor that outputs a pulse-compressed signal after correlation processing
Step, the pulse-compressed signal after the correlation process, the detection of the polarity of the larger amplitude value of the positive amplitude or the negative amplitude of the reflected echo from the inside or bottom of the steel plate, the detection is performed wherein the absence ultrasonic flaw detection apparatus <br/> that a detection means for utilizing the flaw echo after.