JPH05203632A - Ultrasonic flaw detection device - Google Patents

Abstract

PURPOSE:To improve flaw detection signals and noise S-N ratio for metal materials comprising coarse crystal grains, austenite-based heat-resistant materials, etc., and improve a defect detection ability. CONSTITUTION:A device comprises an ultrasonic probe having an ultrasonic transmitting/receiving means capable of moving an ultrasonic transmitting/ receiving position, filter circuits 10-1, 10-2, 10-3,... 10-n for giving zone characteristics of which specified center frequencies are different from each other to plural detection waveforms obtained by ultrasonic transmission/ reception at the ultrasonic transmitting/receiving positions by the ultrasonic transmitting/receiving means of the ultrasonic probe respectively, and an A/D coverter 13 to digitize the detection waveforms passing through the filter circuit. In addition, a signal processing circuit 16 is provided for comparing data at the same sample point among plural waveform data obtained by the A/D converter 13, and repeating a process of taking the minimum value of them for the data at the sample point for plural sample points.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detector which is most suitable for flaw detection of metal materials such as coarse crystal grains and austenite heat resistant materials.

[0002]

2. Description of the Related Art Defects such as cracks, cavities and non-metal inclusions existing inside a test object such as a metallic material since the material was manufactured,
Alternatively, as a method for inspecting defects such as cracks that are generated due to various external factors after being made into a device / structure, an ultrasonic flaw detection method is often used together with an X-ray inspection.

However, in the ultrasonic flaw detection method, if the ratio of noise echoes depending on the material structure such as a material having a large crystal grain size or an austenitic material is poor as compared with a general steel material, noise is detected. Since the amplitude value is not sufficiently higher than the echo level, it is difficult to distinguish between noise and defect. As a result,
The defect size that can be detected is limited to a large size, and the defect detection capability may be significantly deteriorated.

Therefore, an averaging method is known as a method for removing noise in such electrical signal / waveform measurement. However, this method is effective for noise that enters at random in time, such as electrical noise, but individual noise is the same as the material structure, such as the noise echo that depends on the material structure described above. Even if they are random, they are not temporally random because they are generated from the ultrasonic reflection source called microscopic tissue, and there is no effect if they occur at the same position as ultrasonic waves are transmitted and received.

Further, the probe position is one of the signal processes for extracting the defect echo from the material noise which is random in the traveling direction of the ultrasonic wave, that is, in the beam path direction, but is not random in time. There is a method of obtaining a single flaw detection waveform by adding a plurality of flaw detection waveforms recorded while slightly changing the, and averaging. Specifically, in automatic flaw detection using a probe drive mechanism, the average of multiple flaw detection waveforms with minutely changed ultrasonic transmission / reception positions is used, and among array transducers that have many microvibrators. Although a method of averaging a plurality of flaw detection waveforms obtained by switching the oscillators used is used, material noise is reduced only by averaging, and a sufficient effect can be obtained to improve the S / N ratio. Often not.

Further, a method of frequency-analyzing one flaw detection waveform obtained at a specific ultrasonic wave transmitting / receiving position and utilizing the difference between frequency spectra of defects and material noise to improve the S / N ratio has been studied. As an example, a study by VL Newhouse et al. (Flaw-to-grain EchoEnhancement by SPlit-spect
rum Processing: Ultrasonics, Vol 20, No. 2, 1982) is well known. In this series of studies, as shown in the block diagram of the analysis process shown in FIG. 8, the signal waveform w detected by the ultrasonic probe 2 in contact with the surface of the subject 1 and amplified by the ultrasonic transceiver 21 is A The D / D converter 22 digitizes the digitized data S1 and the frequency analysis means 23 frequency-analyzes the frequency-divided data into a plurality of filters 24 having different center frequencies. Inverse Fourier transform means 25
The plurality of waveforms S2 obtained by the inverse Fourier transform are passed to the data processing unit 26 to be subjected to several kinds of data processing, and finally an analysis processing for obtaining a flaw detection waveform S3 with an improved S / N ratio is performed. ing.

However, this method is effective in improving the S / N ratio of the flaw detection waveform at one ultrasonic wave transmitting / receiving position,
Since it is a software process of a computer, it takes time to process one flaw detection waveform, and therefore this method cannot be adopted for manual flaw detection or automatic flaw detection for inspecting a wide surface.

[0008]

The conventional ultrasonic flaw detection method described above requires an automatic flaw detection method that requires a probe driving mechanism to add the flaw detection waveforms obtained at slightly different ultrasonic transmission / reception positions. Since it uses software processing that requires analysis time using a device or computer, it is possible to improve the S / N ratio and extract defect echoes from material noise, but it is often used in actual equipment. In an ultrasonic flaw detector based on manual work in which the inspector has a hard time distinguishing between a noise echo and a defect echo,
There is no such thing as the above-mentioned processing in automatic flaw detection, software processing, or software processing that can reduce the signal level of material noise and clearly extract a defect echo.

According to the present invention, S / of a flaw detection signal and noise of a metal material composed of coarse crystal grains, an austenitic heat resistant material, etc.
It is an object of the present invention to provide an ultrasonic flaw detector capable of improving the N ratio and enhancing the defect detection capability.

[0010]

In order to achieve the above object, the present invention provides an ultrasonic wave transmitting means for transmitting ultrasonic waves to an object and a plurality of ultrasonic waves for receiving ultrasonic waves from the object at different receiving positions. An ultrasonic probe having receiving means and capable of moving the ultrasonic wave transmitting / receiving positions, and a plurality of ultrasonic waves obtained by transmitting / receiving ultrasonic waves at the ultrasonic wave transmitting / receiving positions by the ultrasonic wave transmitting / receiving means of the ultrasonic probe. A filter circuit that gives different band characteristics with different center frequencies specified for each of the flaw detection waveforms, and digital conversion means that digitizes the flaw detection waveform that has passed through this filter circuit and converts it into waveform data at a plurality of sample points, The data at the same sample point is compared with a plurality of waveform data obtained by this digital conversion means, and the minimum value among them is sampled at that sample point. The process of the data is repeated for a plurality of sample points and a signal processing means for obtaining a single flaw detection waveform.

[0011]

In the ultrasonic flaw detector having such a structure,
By passing a plurality of ultrasonic waves received at different ultrasonic receiving positions through filter characteristics with different center frequencies,
It is possible to obtain a plurality of flaw detection waveforms including a noise waveform whose dominant frequency is different for each reflection source, and a flaw waveform with a frequency characteristic that hardly changes with a slight deviation of the flaw detection position and whose frequency characteristics are in a relatively wide range. By combining the two into a single flaw detection waveform by real-time signal processing, the defect echo amplitude remains the same even in materials with high noise echo levels that depend on the material structure, such as coarse crystal materials and austenite materials. Only the tissue-dependent noise echo can be reduced, the S / N ratio for defect echo detection can be improved, and the flaw detection with high defect detection ability requires an automatic scanning device and computer software. Without doing so, it is possible to easily carry out the manual flaw detection, which is usually the most frequently performed, which requires portability and mobility. That.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing a structural example of an ultrasonic probe used in an ultrasonic flaw detector according to the present invention, and FIG. 2 is a transverse sectional view of the ultrasonic probe. 1 and 2, reference numeral 2 denotes an ultrasonic probe mounted on the surface of the subject 1. In this ultrasonic probe 2, a transmitting ultrasonic transducer 3 is arranged at a central position inside the case 2a, and a plurality of receiving ultrasonic transducers 4-1 are arranged around the transmitting ultrasonic transducer 3. , 4-2, 4-3, ... 4-n are arranged. A backing material 5 for adjusting the ultrasonic waveform characteristics is filled in a gap between the transducers inside the case 2a, and a matching plate 6 for adjusting the acoustic impedances of the transducer and the subject is further provided on the opening surface of the case 2a. Is provided. The signal lines 7 and 8-1, 8-2, and 8-1, 8-2, are independently provided to the transmitting ultrasonic transducer 3 and the receiving ultrasonic transducers 4-1, 4-2, 4-3, ... 4-n. 8-3, ... 8-
n are connected to each other.

FIG. 3 shows an example of the circuit configuration of the ultrasonic flaw detector according to the present invention. In FIG. 3, reference numeral 9 denotes an ultrasonic transmitter that repeatedly applies a high-voltage pulse for exciting an ultrasonic wave to a transmitting ultrasonic oscillator 3 existing at the center of the ultrasonic probe 2. Reference numeral 11 denotes an ultrasonic signal received by the plurality of receiving ultrasonic transducers 4-1, 4-2, 4-3, ... 4-n of the ultrasonic probe 2 and converted into an electric signal. Bandpass filters 10-1, 10-2, 10-3, ... 10 having different center frequencies connected to the respective transducers
Each of the transducer switching devices is input via -n. The transducer switching device 11 switches the input from the receiving ultrasonic transducer every time a high voltage pulse for excitation is applied to the transmitting ultrasonic transducer 3. The ultrasonic signal is provided to the ultrasonic receiver 12. The ultrasonic receiver 12 amplifies the ultrasonic signal selected by the switching of the transducer switching unit 11 and inputs it to the A / D converter 13. The A / D converter 13 converts the ultrasonic signal from the ultrasonic receiver 12 into digital waveform data, and transmits the ultrasonic wave for reception through a waveform memory switcher 14 that operates in synchronization with the vibrator switcher 11. 4-
Waveform memory 1 corresponding to 1, 4-2, 4-3, ... 4-n
5-1, 15-2, 15-3, ... 15-n are respectively stored. Therefore, these waveform memories 15-1, 15-
2, 15-3, ... 15-n include ultrasonic transducers for reception 4-
The number of ultrasonic wave propagation paths obtained by ultrasonic wave transmission / reception that is equal to the number of 1,4-2, 4-3, ... The flaw detection waveform of will be stored.

On the other hand, the waveform memories 15-1, 15-2, 1
The plurality of flaw detection waveforms recorded in 5-3, ...
It is sent to the minimized signal processing circuit 16. The minimization signal processing circuit 16 includes waveform memories 15-1, 15-2, 15-
The ultrasonic wave propagation paths stored in 3, ... 15-n are slightly different, and the frequency characteristics are also combined into a plurality of flaw detection waveforms which are decomposed into waveforms, and one flaw detection waveform in which material noise is reduced To get The flaw detection waveform processed by the minimization signal processing circuit 16 is sent to the D / A converter 17, where it is converted back to an analog waveform and sent to the waveform display CRT 18. This CRT18 for waveform display
Draws an A-scope flaw detection waveform similar to that of a normal flaw detector. Reference numeral 19 is a flaw detection control circuit for controlling a series of operations of each of the above-mentioned components. Next, the operation of the ultrasonic flaw detector constructed as described above will be described.

When ultrasonic waves are radiated from the ultrasonic transducer 3 for transmission to the subject 1 as shown in FIG. 4, the ultrasonic waves for reception are arranged around the ultrasonic transducer 3 for transmission. ultrasonic transducer 4-1, 4-2, 4-3, ... ultrasonic propagation path corresponding to the relative positional relationship between the _{4-n l 1, l 2} , l 3, ... l
After passing _n , ultrasonic transducers for reception 4-1, 4-2, 4-
3, ... 4-n. At this time, in a material having a high noise echo level depending on the material structure such as a coarse crystal grain material or an austenitic material which is the object of the present invention, as shown in FIG. 5, flaw detection waveforms w ₁ and w containing material noise are obtained. ₂ , w ₃ , ... W _n are received, but because the ultrasonic wave propagation path is slightly different for each flaw detection waveform, the material noise included in each flaw detection waveform is random with respect to the beam path direction, Further, the flaw detection waveforms are slightly different. On the other hand, for a defect larger than the crystal grain boundary that causes material noise, the difference in the ultrasonic wave propagation path with respect to the defect size is relatively small. At 2, 4-3, ... 4-n, almost equal defect echoes are received.

On the other hand, focusing on the frequency characteristics of the noise echo and the defect echo, the following is obtained. That is, the frequency characteristic of the defect echo near the beam path L is relatively flat with respect to the frequency as shown in FIG. 6 and includes a wide range of frequency components, but a noise echo near the beam path L'is an example. As shown in FIG. 6, the frequency characteristics are not flat, and there are excellent frequency components, and the noise echo near the beam path L ″ is different from the noise echo near the beam path L ′. It is common for there to be outstanding frequency components.

Therefore, the noise echo and the defective echo having such frequency characteristics have different center frequencies. The band pass filters 10-1, 10-2, 10-3, ... 1
0-n signal waveform after passing through the _{w '1, w' 2,} w '
_3, ... w _'n, the received waveform as shown in FIG. 7 w _1, w
Compared with ₂ , w ₃ , ... W _n , the amplitude value of the noise echo is generally smaller.

[0019] Next flaw detection waveform w processed by the band-pass filter 10 described above _'1, w' _2, w against _'3, ... w' _n, the minimum signal processing circuit 16, the following processing is executed To be done. That is, the flaw detection waveform detected by the i-th transducer is composed of waveform data constituted by m sampling points by digitization, and w ′ (1.2 ... j
... m). Then, paying attention to the jth sampling point, the minimum absolute value min {out of w '(j) ₁ , w' (j) ₂ , w '(j) ₃ , ... w' (j) _n. w '(j) _{i = 1} ... _n }
Is adopted as a representative value of the j-th sample point on the beam path of the flaw detection waveform detected by the n transducers.

By repeating this operation from the first sample point of the flaw detection waveform to the last sample point, that is, the m-th sample point, the ultrasonic transducers for reception 4-1, 4-2, 4 are obtained.
-3, ... 4-n, the flaw detection waveforms obtained by integrating the plurality of flaw detection waveforms detected by W = [min {w ′ (J) _{i = 1} ... _n }]
You will get _{j = 1} ... _n .

As a result, with respect to the material noise, the noise caused by the material structure such as the crystal grain boundaries has a random characteristic in the arrangement arrangement itself such as the crystal grain boundaries. By adopting the minimum value of the amplitude value of the same beam path of the waveform, it can be represented by a small value, and each flaw detection waveform matches the predominant frequency of each noise by the pass band filter with different center frequency. The noise waveform that has passed through the filter will have a small amplitude value, and the effect of being able to adopt the minimum value of the amplitude value of the signal waveform from the band-pass filters with different center frequencies will be synergistic, reducing noise echo. Can be made

On the other hand, regarding the defect echo, the influence of a plurality of flaw detection waveforms on the amplitude value of the same beam path due to a slight difference in the ultrasonic wave propagation path is small, and even when passing through a band pass filter having a different center frequency, the filter frequency is reduced. Since the effect on the amplitude value of each defect echo is small, the representative value data on a certain beam path does not become extremely small even if the minimum value among those values is taken. Therefore, a plurality of waveform data w that is composed of m sample points _{'1, w' 2, w} '3, ... w' Repetitive operation for each determining the minimum value for all sample points _n If returned, the amplitude value level of the material noise becomes small, but the amplitude value of the defect echo does not change.

This means that in the flaw detection of a coarse crystal material or an austenite material, the amplitude of the defect echo, which is buried in the noise echo and difficult to confirm its existence in the normal flaw detection, remains unchanged, and the noise echo depending on the material structure remains. Since the amplitude value can be reduced, the S / N ratio for detecting the defect echo can be improved easily without requiring an automatic scanning device or computer software, and also by manual flaw detection. ..

Although the ultrasonic transducers for transmission and reception shown in FIGS. 1 and 2 are disk type, in short, a plurality of flaw detection waveforms obtained by slightly changing the propagation path of ultrasonic waves are obtained. It is not always necessary to use the disk type as long as it meets the purpose for performing signal processing, and an array probe or the like using a strip-shaped transducer may be used. Further, in the example of FIG.
Although all the flaw detection waveforms necessary for signal processing are recorded by n times of ultrasonic signals equal to the number of 4-2, 4-3, ... 4-n, the ultrasonic receiver and the A / D converter 13 By providing the same number as the number of receiving ultrasonic transducers, it is possible to store the flaw detection waveform in a short time with one ultrasonic transmission.

[0025]

As described above, according to the present invention, a plurality of ultrasonic waves received at different ultrasonic wave reception positions are passed through filter characteristics having different center frequencies.
It is possible to obtain a plurality of flaw detection waveforms including a noise waveform whose dominant frequency is different for each reflection source, and a flaw waveform with a frequency characteristic that hardly changes with a slight deviation of the flaw detection position and whose frequency characteristics are in a relatively wide range. By combining the two into a single flaw detection waveform by real-time signal processing, the defect echo amplitude remains the same even in materials with high noise echo levels that depend on the material structure, such as coarse crystal materials and austenite materials. Only the tissue-dependent noise echo can be reduced. Therefore, it is possible to improve the S / N ratio for detecting the defect echo, and the portability, which is usually the most frequently used, does not require an automatic scanning device or computer software for flaw detection with high defect detection ability. It is possible to provide an ultrasonic flaw detector that can easily realize flaw detection by manual operation that requires mobility.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an ultrasonic probe in an embodiment of the ultrasonic flaw detector according to the present invention.

FIG. 2 is a cross-sectional view showing the ultrasonic probe according to the embodiment.

FIG. 3 is a block circuit diagram showing the circuit configuration of the embodiment.

FIG. 4 is a view for explaining a propagation path of ultrasonic waves transmitted and received by the ultrasonic probe in the embodiment.

FIG. 5 is a diagram showing a flaw detection waveform of a material having a high noise echo level, which is received by the ultrasonic probe in the embodiment.

FIG. 6 is a frequency characteristic diagram of a noise echo and a defect echo in the example.

7 is a signal waveform diagram after the noise echo and the defective echo having the frequency characteristics as shown in FIG. 6 have passed through the bandpass filters having different center frequencies.

FIG. 8 is a block diagram for explaining signal processing for noise reduction by a conventional ultrasonic flaw detector.

[Explanation of symbols]

1 ... Subject, 2 ... Ultrasonic probe, 3 ... Transmission ultrasonic transducer, 4-1,4-2,4-3, ... 4-n ... Reception ultrasonic probe , 9 ... Ultrasonic transmitter, 10-1, 10
-2, 10-3, ... 10-n ... band pass filter, 1
1 ... Transducer selector, 12 ... Ultrasonic receiver, 13 ...
A / D converter, 14 ... Waveform memory switcher, 15-
1, 15-2, 15-3, ... 15-n ... Waveform memory, 1
6 ... Minimization signal processing circuit, 17 ... D / A converter, 18 ... Waveform display CRT, 19 ... Flaw detection control circuit.

Claims (1)

[Claims] 1. An ultrasonic wave transmitting means for transmitting ultrasonic waves to a subject and a plurality of ultrasonic wave receiving means for receiving ultrasonic waves from the subject at different receiving positions, and these ultrasonic wave transmitting / receiving positions are movable. Different ultrasonic probe and the center frequency specified for each of a plurality of flaw detection waveforms obtained by transmitting and receiving ultrasonic waves at each ultrasonic wave transmitting / receiving position by the ultrasonic wave transmitting / receiving means of the ultrasonic probe. A filter circuit that gives a band characteristic, digital conversion means that digitizes the flaw detection waveform that has passed through this filter circuit and converts it into waveform data at a plurality of sample points, and the same for a plurality of waveform data obtained by this digital conversion means Repeat the process of comparing the data at each sample point and setting the minimum value as the data at that sample point for multiple sample points. An ultrasonic flaw detector, comprising: a signal processing unit for obtaining one flaw detection waveform.