JPH06337263A - Ultrasonic flaw detection method - Google Patents

Abstract

PURPOSE:To provide a method for inspecting the internal flaw of a material, e.g. a thick steel pipe, using a transverse ultrasonic wave in which the echo signal from a flaw can be obtained with high S/N ratio by reducing the noise signal of multiplex echo caused by the side lobe of an ultrasonic wave impinging obliquely on the material significantly. CONSTITUTION:A wide band probe 3 is excited alternately with a flaw detection frequency f1 for maximizing the amplitude of echo from a flaw and a flaw detection frequency f2 (>f1) for obtaining a high amplitude of multiplex echo every period of a synchronizing signal. A receiving signal thus obtained is detected by a detector 16 through a wide band receiver 15. The detection signals for respective frequencies are picked up by analog switches 17, 18 and the timings thereof are matched by a delay unit 19. A differential amplifier 22 then produces a definitely discriminated echo signal from the flaw.

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 more particularly, to an ultrasonic flaw detection method for externally inspecting flaws (defects) inside a test material using transverse ultrasonic waves.

[0002]

2. Description of the Related Art Ultrasonic waves are made incident on the inside of a test material such as metal from a probe, and reflected echoes from the inside of the test material are received through the probe to detect the inside of the test material. Defects (defects)
Conventionally, an ultrasonic flaw detection method for inspecting a test material without destroying the test material has been known. Of these ultrasonic flaw detection methods, when inspecting for flaws in the welded portion of flat plate butt welding and for crack defects on the outer or inner and outer surfaces of the metal pipe, ultrasonic waves are applied from the probe to the surface of the material to be inspected. Angle-angle flaw detection is performed in which the light is obliquely incident.

Here, if the material to be tested is solid, even if the ultrasonic waves incident from the probe are only longitudinal waves, the refracted waves inside the material to be tested include longitudinal waves and transverse waves. If these refracted waves have the relationship shown in FIG. 6 with respect to the incident wave, the Snell's law of the following equation is established.

[0004]

[Equation 1]

In the above equation, v _i is the ultrasonic wave in the medium I of FIG. 6, that is, the sound velocity of the longitudinal wave, v _S is the sound velocity of the transverse wave in the medium II, v _L is the sound velocity of the longitudinal wave in the medium II,
θ _i is the incident angle of the incident wave, θ _S is the refraction angle of the transverse wave in the medium II, and θ _L is the refraction angle of the longitudinal wave in the medium II.

In the conventional ultrasonic flaw detection, the medium I is
Acrylic glass of the angle probe, or water (when the steel pipe is flawed), Medium II is the test material.

As described above, the ultrasonic wave is emitted from the probe at an incident angle θ.
_When it is incident at _i , as shown in FIG. 7, it is reflected by the inner surface 62a and the outer surface 62b of the pipe wall of the test material 61, and the reference numeral 63
Propagate along the route indicated by. If there is a flaw (defect) on the inner and outer surfaces, the flaw is reflected there, and the echo returns to the probe 60.

However, when the longitudinal wave and the transverse wave are mixed in the test material 61, both of them have different propagation paths and sound velocities, and therefore the reflected wave of the echo received by the probe 60 cannot be distinguished, Therefore, the position of the flaw cannot be specified. for that reason,
In oblique-angle flaw detection in which ultrasonic waves are obliquely incident on the test material 61,
It is usual to make the incident angle θ _i larger than the critical angle so that only transverse waves exist in the test material 61.

Here, the above-mentioned critical angle is the incident angle θ _i when the refraction angle θ _L of the longitudinal wave in the medium II is 90 °, and assuming that the medium I in FIG. Assuming that the sound velocity v _i of the sound wave is about 1450 m / sec, the medium II is ordinary steel, and the sound velocity v _L of the longitudinal wave in the medium II is 5950 m / sec, from the equation (1), the incident angle (critical Angle θ _i is about 14.1 ° (= sin ~ ¹ (1450
/ 5950)). At this time, the refraction angle θ _S of the transverse wave in the medium II is about 32.5 °, and in principle, only the transverse wave exists in the medium II.

Further, in FIG. 7, since only one flaw can be detected, when the steel pipe is used as the test material, the steel pipe and the probe 6 are used.
By fixing either one of 0 and rotating the other, flaw detection is performed over the entire circumference, and by moving the steel pipe in the axial direction as well, flaw detection is performed over substantially the entire length.

[0011]

However, in the above-mentioned conventional ultrasonic flaw detection method, the material to be inspected has a large t / D (where t is the thickness of the tube and D is the outer diameter of the tube). 20% or more)
In the case of a thick-walled steel pipe, as shown in FIG.
When an ultrasonic wave is incident from the outside at a relatively large incident angle θ _i that is equal to or greater than the critical angle, the ultrasonic wave enters from the outer surface 70a of the thick steel pipe 70 and passes through the thin inner surface 70b, but the thick inner surface 70c. Propagate on the route 72 that does not reach. Therefore, the inner surface defect 71 cannot be detected.

As a countermeasure against this, the refraction angle θ _S of the transverse wave in the thick steel pipe 70 may be reduced. Then, in order to reduce θ _S , it is necessary to reduce the incident angle θ _i .
However, as described above, if the transverse wave and the longitudinal wave are mixed in the thick-walled steel pipe 70, there arises a problem, so that θ _i cannot be made smaller than the critical angle, and there is a limit.

Therefore, if the incident angle θ _i is reduced to a value as close as possible to the critical angle within the above limit,
As shown in FIG. 9, among the ultrasonic waves emitted from the probe 60, the main lobe 8 which is an ultrasonic wave component in the main emission direction.
0a reaches the thick inner surface 70c of the thick steel pipe 70,
A side lobe 80b, which is an ultrasonic wave component obliquely radiated from the probe 60, is incident on the outer surface 70a of the thick-walled steel pipe 70 at an angle that is substantially vertical. Therefore, the side lobes 80b are multiply reflected by the inner and outer surfaces 70a and 70b of the thick-walled steel pipe 70.

The energy of the side lobe 80b is smaller than the energy of the main lobe 80a.
However, the above-mentioned multiple reflection is caused by the tube wall having a size extremely larger than the wavelength of the ultrasonic wave, while the flaw to be inspected is not so large as compared with the above wavelength. Therefore, on the CRT display screen of the ultrasonic flaw detector, as shown in FIG. 10, the amplitudes of echoes (multi-echoes) M1, M2, M3, and M4 due to multiple reflection are the echoes of the echo F originally reflected from the flaw that should be inspected. It may not be negligible compared to the amplitude. In FIG. 10, T is a transmitted wave, and S is a surface echo generated because the ultrasonic side lobes from the probe are incident on the tube surface at an angle close to vertical.

The present invention has been made in view of the above points, and significantly reduces unnecessary signals due to multiple echoes generated by side lobes of ultrasonic waves obliquely incident on a material to be inspected, and a reflected echo from a flaw. It is an object of the present invention to provide an ultrasonic flaw detection method for inspecting a flaw by obtaining a signal with a good S / N ratio.

[0016]

In order to achieve the above-mentioned object, an ultrasonic flaw detection method of the present invention is based on respective reflected echo signals obtained by using two flaw detection frequencies in a time-division manner, The above problem is solved by canceling the multiple echo signals.

That is, according to the present invention, the ultrasonic wave is reflected obliquely from inside the thick-walled steel pipe by injecting the ultrasonic wave obliquely from the probe into the thick-walled steel pipe having a ratio of thickness to outer diameter of a predetermined value or more. In the ultrasonic flaw detection method of receiving a reflection echo of and performing a flaw inspection of a thick steel pipe, using a probe having a wideband transmission / reception frequency characteristic as the above-mentioned probe, within a transmission / reception frequency band of the probe, And a first transmission signal having a first flaw detection frequency at which the amplitude of a reflection echo from a flaw in the thick-walled steel pipe is approximately maximum, and within a transmission / reception frequency band of the probe, and
The probe is time-divisionally excited by the flaw detection frequency and the second transmission signal having the second flaw detection frequency different from the flaw detection frequency, and immediately after being excited by the first transmission signal, it is excited by the second transmission signal. One of the first reception signal of the probe in the previous period and the second reception signal of the probe in the period immediately before being excited by the first transmission signal immediately after being excited by the second transmission signal Is delayed and synchronized, and then a flaw inspection is performed based on a signal obtained by differentially amplifying both received signals.

[0018]

[Operation] For thick-walled steel pipes with a ratio of thickness to outer diameter of a specified value or more,
In the ultrasonic flaw detection method in which the ultrasonic wave is obliquely incident from the probe to receive the reflection echo of the transverse ultrasonic wave reflected from inside the thick-walled steel pipe and inspect the thick-walled steel pipe for flaws, the flaw detection frequency is increased. Then, the ability of flaw detection is increased, but the reflected echo from the flaw is further increased in attenuation of ultrasonic waves due to transverse ultrasonic waves. Therefore, due to the canceling effect of these two factors, there is an optimum flaw detection frequency at which the amplitude of the reflection echo from the flaw becomes maximum. This optimum flaw detection frequency is the first flaw detection frequency in the present invention.

On the other hand, the multiple echoes caused by multiple reflections caused by the side lobes from the probe being incident on the outer surface of the thick-walled steel pipe at an angle close to vertical are mainly longitudinal wave reflection echoes. The effect of attenuation due to propagation in the medium is less than that of transverse waves, and the amplitude of multiple echoes does not change much even when the flaw detection frequency is changed.

In view of the above points, the present invention provides a probe having a wide range of transmission / reception frequency characteristics with a first transmission signal having the first flaw detection frequency and a second flaw detection frequency. The first received signal is obtained by the ultrasonic wave based on the first transmitted signal and the second received signal is obtained by the ultrasonic wave based on the second transmitted signal by exciting in a time division manner with the second transmitted signal To get Here, in the second received signal, the reflected echo from the flaw is sufficiently smaller than that in the first signal, while the multiple echo from the tube wall is not smaller than that in the flaw. , The second flaw detection frequency is selected.

Since the first and second received signals are obtained in a time division manner, in the present invention, one of the first and second received signals is delayed by a time equal to one cycle of the ultrasonic flaw detector. After performing the synchronization, the one signal delayed and the other signal not delayed are differentially amplified. In this differentially amplified signal, the amplitude waveform of the reflected echo from the flaw is smaller than that of the first received signal, but the amplitude of the multiple echo is further reduced, so the signal portion of the reflected echo from the flaw is reduced. And the signal part of the multiple echo can be clearly distinguished.

[0022]

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an ultrasonic flaw detector to which the method of the present invention is applied. In the figure, an ultrasonic flaw detector 1 is connected to a probe 3 via a coaxial cable 2. The probe 3 is a wide band probe having a wide range of transmission / reception frequency characteristics, and the ultrasonic transducer inside is the ultrasonic flaw detector 1.
When it is excited by the transmission signal from, the ultrasonic wave is generated, the ultrasonic wave is made incident on the test material, and the ultrasonic echo from the test material is received.

The above-mentioned test material has, for example, a tube thickness of t,
A thick-walled steel pipe 4 having a ratio t / D exceeding 20%, where D is the outer diameter of the pipe, and is, for example, a stainless steel pipe or a high alloy steel pipe used in a high temperature environment. Ultrasonic waves (main lobes) are obliquely incident on the outer surface of the test material from the probe 3 at an angle close to the critical angle. As a result, as described above, the transverse ultrasonic waves propagate inside the thick-walled steel pipe 4 and are reflected by the crack flaws formed on the inner surface or the like. Also, multiple echoes are generated due to the side lobes from the probe 3. Since the above side lobes are incident on the thick-walled steel pipe 4 at an angle close to vertical, that is, at an angle equal to or less than the critical angle, this multiple echo includes a longitudinal wave. The above t / D value changes depending on the material of the thick-walled steel pipe 4.

Next, the structure of the ultrasonic flaw detector 1 will be described. The synchronization signal oscillator 11 oscillates and outputs a synchronization signal having a constant cycle, which activates the operation of each part of the ultrasonic flaw detector 1.
The switching signal generator 12 generates a first switching signal and a second switching signal, which are synchronized with the above synchronization signal. As will be described later, the first and second switching signals are symmetrical square waves having opposite phases. With these first and second switching signals, the transmission frequency is changed to f ₁ and f _{2 for} each cycle of the synchronization signal.
The inspection is performed by alternately switching to.

The transmission oscillator 13 receives the synchronization signal from the synchronization signal oscillator 11 and the first and second switching signals from the switching signal generator 12 as input signals, and the frequency from the time when the synchronization signal is input. A burst sine wave having a predetermined number of cycles of f ₁ or f ₂ is oscillated. This burst sine wave has a frequency of f ₁ when the first switching signal is at a high level.
When the second switching signal is at high level, the frequency is f ₂ . The transmitter 14 receives the burst sine wave from the transmission oscillator 13 and amplifies it into a large-amplitude signal that excites the probe 3. The transmitter 14 also has a circuit for matching with the coaxial cable 2.
include.

The receiver 15 uses the probe 3 to make the thick-walled steel pipe 4
The echo signal converted into an electric signal by receiving the reflected echo from is input, and a circuit for amplifying the echo signal has a wide-band reception frequency characteristic so as to correspond to the selection of the transmission frequency. The detector 16 envelope-detects the received echo signal from the receiver 15. The analog switch 17 is a circuit that transmits the input detection signal to the output when the first switching signal is at the high level, and when the first switching signal is at the low level,
Cut off input and output. The analog switch 18 is a circuit that transmits the input detection signal to the output when the second switching signal is at the high level, and shuts off the input and the output when the second switching signal is at the low level.

The delay device 19 is a circuit for delaying the output detection signal of the analog switch 17 for a period of one cycle of the synchronizing signal and performing time synchronization (synchronization) with the output detection signal of the analog switch 18, which will be described later. As described above, the circuit configuration shown in FIG. The amplifiers 20 and 21 are delay devices 1 respectively.
9. Amplify each output signal of the analog switch 18 to a predetermined amplitude.

The differential amplifier 22 differentially amplifies the amplified detection signals from the amplifiers 20 and 21, and outputs a differential amplified signal of a level corresponding to the level of the difference between these input signals. The sweep signal generator 23 synchronizes with the synchronization signal, and only when the second switching signal is at a high level,
The differential amplified signal from the differential amplifier 22 is the CRT display 24.
Generates a sweep signal as displayed by. The CRT display 24 is a cathode ray tube (CR) that displays a differentially amplified signal.
T), a horizontal deflection circuit that amplifies the differential amplified signal to the amplitude and DC potential required for display, a brightness and focus adjustment circuit, and the like.

The delay device 19 is constructed as shown in FIG. As shown in the figure, the delay device 19 has four input terminals 31 to 34 and one output terminal 35. 31
Is an input terminal of the sync signal from the sync signal oscillator 11,
Reference numerals 32 and 33 are input terminals for the first and second switching signals, and 34 is an input terminal for an output detection signal of the analog switch 17.

The clock oscillator 41 receives the synchronizing signal, and oscillates and outputs a clock pulse which is the basis of the conversion command signal of the AD converter 48 and the DA converter 51 from the falling edge of the pulse. The repetition frequency of this clock pulse is determined from the upper limit of the frequency band of the received echo signal. The address counter 42 is reset at the rising edge of the sync signal, and then the clock oscillator 4
It is a digital counter that starts counting clock pulses from 1. The count value of this counter 42 is
It becomes the address signal of the memory 52.

The address upper limit detection circuit 43 outputs an address upper limit detection signal of logic "1" when all the bits of the output of the address counter 42 become logic "1", and stops the oscillation operation of the clock oscillator 41. To do. AND circuit 44
When the first switching signal from the input terminal 32 is at a high level, the clock pulse is passed and supplied to the delay line 45 and the AD converter 48. A-D converter 4
Reference numeral 8 outputs a digital signal of the amplitude value of the detection signal from the input terminal 34 at the rising time of the clock pulse from the AND circuit 44.

Here, assuming that the number of bits of the address counter 42 is N and the repetition frequency of the clock pulse is f _C , the AD converter 48 outputs the input detection signal A-
D conversion can be time is _{(2N-1) / f C} . Also,
Assuming that the sound velocity of the ultrasonic wave propagating in the thick-walled steel pipe 4 is V, the ultrasonic wave is incident on the thick-walled steel pipe 4 in the flaw detection range, and the ultrasonic wave is reflected from a flaw in the thick-walled steel pipe 4 to detect the probe. until it is received by 3, because it is half the round-trip distance of the ultrasonic wave becomes {(2N-1) / f C} V / 2.

Three-state buffer circuits 49 and 5
0 is provided in the same number as the number of bits of the A / D converter 48 and the D / A converter 51. When the first and second switching signals are at high level, the input signal is transmitted to the output and low level. When, the output becomes high impedance. Therefore, when the first switching signal is at the high level, the digital signal from the AD converter 48 is input to the memory 52 through the three-state buffer circuit 49, and this period is the second
Since the switching signal of 3 is low level, the output of the three-state buffer circuit 50 becomes high impedance, and the memory 52 and the three-state buffer circuit 50 are separated.

On the other hand, when the first switching signal is at the low level, the output of the three-state buffer circuit 49 becomes high impedance and the memory 52 and the three-state buffer circuit 49 are separated from each other. , And the second switching signal is at a high level, the digital signal read from the memory 52 is input to the DA converter 51 through the three-state buffer circuit 50. The three-state buffer circuits 49 and 50 are
The active state and the output high impedance state are repeated alternately for each cycle of the synchronization signal, and when one is in the active state, the other is set to the output high impedance state.

The delay line 45 receives the clock pulse from the AND circuit 44 until the detected signal is converted into a digital signal by the AD converter 48, and then is stably input to the memory 52 through the three-state buffer circuit 49. Then, the data is input to the memory 52 as a write clock after being delayed by a time required for the writing. The AND circuit 46 passes the clock pulse from the clock oscillator 41 and supplies it to the delay line 47 when the second switching signal from the input terminal 33 is at a high level.

In the delay line 47, the output of the address counter 42 is increased by "1" in response to the clock pulse from the AND circuit 46, the stored content of the new address is read from the memory 52, and the three-state buffer circuit 5 is supplied.
It is delayed by a time required for stable input to the D-A converter 51 through 0 and is supplied to the D-A converter 51 as a conversion clock. The DA converter 51 performs digital-analog conversion on the read output data of the memory 52 based on the delayed clock pulse, and outputs the analog signal to the output terminal 35.

As described above, the delay device 19 of FIG. 2 continuously outputs the output detection signal of the analog switch 17 at high speed during the period when the flaw detection frequency is f ₁ and the first switching signal is at the high level. The AD signal is converted into a digital signal by the A / D converter 48, the digital signal is sequentially written into the memory 52, and subsequently, during the period when the flaw detection frequency is f ₂ and the second switching signal is at the high level, the memory 52 outputs the signal. Read the digital signals in the order in which they were written and read them
After being converted into an analog signal by the DA converter 51 continuously at high speed, it is output to the output terminal 35. This output analog signal has the same waveform as that of the input terminal 34 and is a signal delayed for one period of the synchronizing signal.

Next, the operation of the ultrasonic flaw detector 1 configured as shown in FIG. 1 will be described with reference to FIGS. 3 (A) and 4 with a constant period T ₀ from the synchronization signal oscillator 11.
The switching signal generator 1 outputs the synchronization signal a shown in FIG.
2, the transmission oscillator 13, the delay device 19, and the sweep signal generator 23, respectively. 4 is an enlarged time chart of the time axis of the time chart of FIG.

The switching signal generator 12 inverts the level every time the rising edge of the synchronizing signal a is input, and
It generates a first switching signal b shown in FIG. 3B and a second switching signal c shown in FIG. 3C, which have opposite phases to each other. That is, these switching signals b and c are symmetrical square waves having a period 2T ₀ , which is obtained by dividing the synchronizing signal a by 1/2.

The transmission oscillator 13 receives the first and second switching signals b and c and the synchronization signal a as input signals, and the first switching signal b is at a high level (synchronization signal a
Period T ₀ ), the period is 1 / second as shown in FIG. 4B from the time when the falling edge of the synchronizing signal a is input.
For example, the sine wave of f ₁ is oscillated and output for three cycles, and during the period when the second switching signal c is at high level (the period T ₀ of one cycle of the synchronization signal a), the falling edge of the synchronization signal a is input. Therefore, a sine wave having a cycle of 1 / f ₂ is similarly oscillated and output for 3 cycles. That is, the transmission oscillator 13 alternately outputs the burst sine wave of the frequency f _{1 and} the burst sine wave of the frequency f ₂ for each cycle of the synchronization signal a. The cycle number (wave number) of these burst sine waves is experimentally set according to the material size and shape of the thick-walled steel pipe 4.

By the way, when a test piece having the same size and the same or similar material as the thick-walled steel pipe 4 and a known flaw is preliminarily flaw-detected, the amplitude of the echo signal obtained by the reflection echo from the flaw is as shown in FIG. As indicated by III in 5, the flaw detection frequency f ₁
The characteristic has a peak at. On the other hand, the multiple echoes due to multiple reflections that occur because the ultrasonic side lobes from the probe are incident on the outer surface of the test piece at an angle that is nearly vertical,
As described above, since it is mainly a reflection echo of a longitudinal wave, the influence of attenuation due to propagation in the medium is smaller than that of a transverse wave,
As indicated by IV in FIG. 5, the amplitude of the multiple echo does not change so much even if the flaw detection frequency is changed. Therefore, in the present embodiment, as shown in FIG. 5, the flaw detection frequency f ₂ when the amplitude of the multiple echo is larger than that of the reflected echo from the flaw is obtained.
Select.

Therefore, in this embodiment, as shown in FIG. 4, the transmission oscillator 13 oscillates and outputs the burst sine wave of the frequency f ₁ while the first switching signal b is at the high level. , The burst sine wave of the frequency f ₂ is oscillated and output while the second switching signal c is at the high level. The transmitter 14 in FIG. 1 outputs a signal in which the burst sine waves of these two frequencies are combined in time series as shown in FIG. 4 (B), and causes the probe 3 to cycle T _{0 of the} synchronization signal a. Frequency f _{1 for} each
Alternatively, it is time-divisionally excited at f ₂ .

As a result, when the echo signal from the probe 3 is envelope-detected by the detector 16 through the wide band receiver 15, a detection signal d as shown in FIG. 3D is obtained.
The detection signal d 1 is a detection signal d ₁ obtained when the flaw detection frequency is f ₁ when the first switching signal b is at a high level.
And a detection signal d ₂ obtained when the flaw detection frequency is f ₂ and the second switching signal c is at a high level.

As shown in FIG. 3D, the detected signals d ₁ and d ₂ are multiplexed by a signal portion T due to the transmitted wave, a reflected echo signal portion S from the surface of the thick steel pipe 4, and a side lobe. Echo signal portion Mi (here, i = 1 to 5)
And a reflected echo signal portion F from the flaw. Since the detected signal d ₁ is a signal when the flaw detection frequency is the above f ₁ , the amplitude of the reflected echo signal portion F from the flaw is larger than the amplitude of the multiple echo signal portion M _i due to the side lobe. On the other hand, since the detection signal d ₂ is a signal when the flaw detection frequency is f ₂ , the amplitudes of the multiple echo signal portions M1 to M3 due to the side lobes are larger than the amplitude of the reflection echo signal portion F from the flaw. Is also large.

The analog switch 17 receives the detected signal d
Is input, and the input detection signal during the period when the first switching signal b is at the high level is selected and output to the delay device 19. Therefore,
In the delay device 19, as shown in FIG.
Only ₁ is entered. The other analog switch 18
Also, the detection signal d is input, and the input detection signal during the period when the second switching signal c is at the high level is selected and output to the amplifier 21. Therefore, only the detection signal d ₂ is input to the amplifier 21, as shown in FIG.

As described above, since the delay device 19 delays the input signal for the period T ₀ of the synchronizing signal a, the delay device 19 delays the detection signal d ₁ as shown in FIG. 3 (F). with a delay time T _0, and outputs a detection signal d ₃ the transmission period matches that of the detection signal d _2.

The differential amplifier 22 differentially amplifies the differential detection signal d ₃ input via the amplifier 20 and the detection signal d ₂ input via the amplifier 21 to obtain a differential detection signal. A differential amplified signal having a level obtained by subtracting the level of the detected signal d ₂ from the level of d ₃ is generated and output. Therefore, the differential amplified signal has a signal waveform in which the level of the echo signal portion F from the flaw is clearly discriminated from the other signal portion (noise signal), as indicated by h in FIG.

This differential amplified signal h is displayed on the CRT display 24.
Are supplied to and displayed here. Since the differential amplified signal h has a waveform in which the amplitude of the multiple echo signal portion Mi (noise signal) due to side lobes is greatly reduced, CR
The T display 24 can display the echo signal from the flaw with a good S / N ratio. The differential amplifier 22 may be configured to output only a signal portion having a predetermined level or higher in the differentially amplified signal h.

As described above, according to this embodiment, the signal portion of the reflected echo from the flaw and the signal portion of the multiple echo can be clearly discriminated in the differential amplified signal.
It is possible to detect flaws by clearly identifying the echo from the flaw.

The present invention is not limited to the above embodiment. For example, the receiver 15 has been described as a circuit having a wideband frequency characteristic capable of receiving at least the frequencies f ₁ and f ₂ , but the frequency of a relatively narrow band centered on the frequency f ₁ is interlocked with the switching of the transmission frequency. The band may be switched to a relatively narrow frequency band centered on the frequency f ₂ .

[0052]

As described above, according to the present invention, the received signals obtained in time division at different flaw detection frequencies are synchronized and then differentially amplified, so that the echo signal from the flaw has a side lobe. It is possible to obtain a differential amplification signal having a signal waveform clearly distinguished from the multiple echo signal by
It is possible to accurately and clearly inspect an echo from a flaw inside the thick-walled steel pipe where D is a predetermined value, for example, 20% or more, with a good S / N ratio.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of an embodiment of a delay device.

FIG. 3 is a time chart for explaining the operation of FIG.

FIG. 4 is a time chart for explaining the operation of the main part of FIG.

FIG. 5 is a characteristic diagram illustrating a flaw detection frequency in an example of the present invention.

FIG. 6 is an explanatory diagram of refracted waves when an ultrasonic wave is incident on a solid.

FIG. 7 is a diagram illustrating a flaw detection method for a steel pipe.

FIG. 8 is a diagram illustrating a problem of the conventional method.

FIG. 9 is a diagram illustrating a problem of the conventional method.

FIG. 10 is a diagram showing various echoes on the screen in the conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ultrasonic flaw detector 3 ... Probe 4 ... Thick steel pipe 11 ... Synchronous signal oscillator 12 ... Switching signal generator 13 ... Transmitting oscillator 14 ... Transmitter 15 ... Receiver 16 ... Wave detector 17, 18 ... Analog switch 19 ... delay device 22 ... differential amplifier 24 ... CRT display device 41 ... clock oscillator 42 ... address counter 48 ... AD converter 51 ... DA converter 52 ... memory

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Saito 2-16-46 Minami Kamata, Ota-ku, Tokyo Within Tokimec Co., Ltd.

Claims (1)

[Claims] 1. A reflection echo of a transverse ultrasonic wave reflected from the inside of a thick-walled steel pipe by injecting ultrasonic waves obliquely from a probe into the thick-walled steel pipe having a ratio of thickness to outer diameter of a predetermined value or more. In the ultrasonic flaw detection method for inspecting the flaw of the thick-walled steel pipe by receiving, as the probe, a probe having a wideband transmission / reception frequency characteristic is used, within the transmission / reception frequency band of the probe, And,
A first transmission signal having a first flaw detection frequency at which the amplitude of a reflection echo from a flaw in the thick steel pipe is approximately maximum, and a first flaw detection frequency within the transmission / reception frequency band of the probe And the second transmission signal having a second flaw detection frequency different from that of the probe, the probe is time-divisionally excited, and immediately after being excited by the first transmission signal, it is excited by the second transmission signal. A first reception signal of the probe in a previous period and a second reception signal of the probe in a period immediately after being excited by the second transmission signal and before being excited by the first transmission signal An ultrasonic flaw detection method, characterized in that, after delaying one of the signals and performing synchronization, a flaw inspection is performed based on a signal obtained by differentially amplifying both received signals.