JP2013011526A - Ultrasonic flaw detection method and ultrasonic flaw detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately detect a flaw in a steel product.SOLUTION: A transmitting/receiving section 3 transmits an ultrasonic pulse signal while scanning an ultrasonic probe 2 and receives a flaw detection signal caused by the ultrasonic pulse signal. A storage section 5 stores flaw detection signals for a plurality of pulses received by the transmitting/receiving section 3. A subtraction signal acquiring section 7a takes out a flaw detection signal predetermined pulses before a flaw detection signal subject to processing from the stored flaw detection signals, as a subtraction signal. A subtraction processing section 7b subtracts the subtraction signal from the flaw detection signal subject to the processing. Echo noise can be thus removed therefrom to provide a flaw echo signal with a high S/N ratio and with reduced noise, so that the flaw in a steel product can be highly accurately detected.

Description

  The present invention relates to an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus for inspecting an internal defect of a subject using ultrasonic waves.

  Conventionally, there has been proposed an ultrasonic flaw detection method for nondestructive inspection of defects inside a subject using ultrasonic waves. In this ultrasonic flaw detection method, in general, an ultrasonic probe (ultrasonic probe) is in contact with a subject such as a steel pipe or a steel plate, and ultrasonic waves are transmitted to the subject, and echo signals from the subject are transmitted. (Flaw detection signal) is received, and a defect echo signal reflected by the defect is detected with a predetermined threshold, thereby inspecting a defect such as a flaw inside the subject. However, since this flaw detection signal includes noise, a defect echo signal having a high S / N ratio cannot be obtained, and there is a case where a minute defect cannot be inspected with high accuracy.

  By the way, the noise included in the flaw detection signal is synchronized with the flaw detection signal due to not only the electrical noise mixed randomly in the flaw detection signal in time but also the shape of the test material and the arrangement of the ultrasonic probe. There is echoic noise mixed in at a certain time. For example, the surface echo signal in the defect inspection close to the surface of the steel material, the bottom echo signal in the defect inspection close to the bottom surface, and the echo signal whose propagation speed is different due to mode conversion between the longitudinal wave and the transverse wave It can be a cause of noise.

  Against this background, there has been proposed a signal processing technique for obtaining a defect echo signal having a high S / N ratio by reducing the influence of echo noise on ultrasonic flaw detection. For example, Patent Literature 1 and Patent Literature 2 describe flaw detection signal waveforms obtained at adjacent positions among flaw detection signals obtained by transmitting ultrasonic waves while relatively scanning the subject and the ultrasonic probe. It is described that the surface echo signal and the bottom surface echo signal are removed by performing a difference calculation on.

  Patent Document 3 discloses a method for calculating a difference between flaw detection signal waveforms obtained by adjacent ultrasonic probes among flaw detection signals obtained by transmitting ultrasonic pulses from a plurality of ultrasonic probes. It is described that the defect echo signal becomes obvious by reducing the influence of the echo signal and the bottom echo signal.

  In Patent Document 4, ultrasonic waves are transmitted while relatively scanning an object and a plurality of ultrasonic probes, the transmission intensity of ultrasonic waves that have passed through the object is detected, and adjacent ultrasonic probes are detected. It is described that a defect is detected by calculating the difference in transmission intensity detected by a child to reduce the influence of transmission intensity fluctuation due to surface contamination or the like.

Japanese Patent Laid-Open No. 9-152428 JP 2002-243703 A JP 2004-12369 A JP 2005-106597 A

  However, according to the techniques described in Patent Document 1 and Patent Document 2, if the length of the defect is longer than the distance between adjacent positions, the defect echo signal is included in both flaw detection signals. For this reason, if the difference calculation between the flaw detection signal waveforms at adjacent positions is performed, not only the echo noise but also the defect echo signal is reduced, and the defect may be missed. In order to solve such a problem, Patent Document 1 considers that a defect echo signal is not included in the flaw detection signal waveform at the immediately preceding position when a defect echo signal is detected. It describes that the difference calculation with the flaw detection signal waveform at the position immediately before the detection of the defect echo signal is performed instead of the flaw detection signal waveform at the adjacent position. However, in general, in ultrasonic flaw detection, in order to prevent a minute defect from being missed, the sampling interval of the flaw detection signal is set smaller than the ultrasonic beam width, so that the defect echo signal gradually increases and appears. . For this reason, when a defect echo signal is detected at a predetermined threshold, it is highly likely that the defect detection signal is included in the flaw detection signal immediately before the defect echo signal. In any case, the defect echo signal may be reduced. there were.

  In addition, according to the techniques described in Patent Document 3 and Patent Document 4, since there are variations in characteristics of a plurality of ultrasonic probes, the signal waveforms detected by adjacent ultrasonic probes are: Even with the same noise factor, it is not always the same, and the noise reduction effect is low. In addition, the defect detection based on the transmission intensity described in Patent Document 4 has low detection accuracy.

  This invention is made in view of the above, Comprising: It aims at providing the ultrasonic flaw detection method and ultrasonic flaw detection apparatus which can detect the defect in steel materials with high precision.

  In order to solve the above-described problems and achieve the object, an ultrasonic flaw detection method according to the present invention transmits an ultrasonic pulse signal while scanning an ultrasonic probe, and flaw detection caused by the ultrasonic pulse signal. In the ultrasonic flaw detection method for continuously inspecting defects in steel materials by receiving signals, a step of storing flaw detection signals for a plurality of received pulses and a flaw detection signal to be processed from the stored flaw detection signals Taking out the flaw detection signal before the predetermined number of pulses as a subtraction signal, subtracting the subtraction signal from the flaw detection signal to be processed, and based on the flaw detection signal obtained by subtracting the subtraction signal, Inspecting for defects.

  The ultrasonic flaw detection method according to the present invention is the ultrasonic flaw detection method according to the present invention, wherein the predetermined number of pulses is an ultrasonic wave from when a flaw detection signal before the predetermined number of pulses is received to when the flaw detection signal to be processed is received. The scanning amount of the probe is equal to or longer than the total length of the defect to be detected and the beam width of the ultrasonic pulse signal, and is equal to or shorter than the length at which the waveform of the echo noise in the flaw detection signal does not change. It is characterized by that.

  In the ultrasonic flaw detection method according to the present invention as set forth in the invention described above, the subtraction signal is obtained by synchronously averaging a plurality of flaw detection signals before the predetermined number of pulses.

  The ultrasonic flaw detection method according to the present invention is characterized in that, in the above invention, when the received flaw detection signal is stored, the boundary flaw signal is aligned and stored based on a reference.

  Further, the ultrasonic flaw detection apparatus according to the present invention transmits an ultrasonic pulse signal while scanning an ultrasonic probe, and receives a flaw detection signal resulting from the ultrasonic pulse signal, thereby continuously in a steel material. In the ultrasonic flaw detector for inspecting a defect, a means for storing the received flaw detection signals for a plurality of pulses, and a flaw detection signal a predetermined number of pulses before the flaw detection signal to be processed from the stored flaw detection signal as a subtraction signal Means for taking out, means for subtracting the subtraction signal from the flaw detection signal to be processed, and means for inspecting a defect in the steel material based on the flaw detection signal obtained by subtracting the subtraction signal. Features.

  According to the present invention, since the echo noise is removed from the flaw detection signal, it is possible to obtain a defect echo signal having a reduced S / N ratio with reduced noise. It is possible to detect a defect such as a minute defect.

FIG. 1 is an explanatory diagram for explaining a flaw detection signal obtained by transmitting an ultrasonic pulse signal from an ultrasonic probe. FIG. 2 is a waveform diagram illustrating a flaw detection signal obtained from one ultrasonic pulse signal transmitted from the ultrasonic probe. FIG. 3 is a block diagram schematically showing the configuration of the ultrasonic flaw detector according to the embodiment of the present invention. FIG. 4 is a block diagram schematically showing the configuration of an ultrasonic flaw detector according to another embodiment of the present invention. FIG. 5 is a flowchart showing an ultrasonic flaw detection processing procedure by the ultrasonic flaw detector. FIG. 6 is an explanatory diagram for explaining the ultrasonic flaw detection processing. FIG. 7 is an explanatory diagram of a method of selecting N. FIG. 8 is an explanatory diagram of a method of selecting N. FIG. 9 is an explanatory diagram of a method for selecting N and Na. FIG. 10 is an explanatory diagram of a method for selecting N and Na. FIG. 11 is a diagram illustrating the effect of aligning the flaw detection signal with the boundary echo signal as a reference.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus according to the present invention will be described with reference to the drawings. In addition, this invention is not limited by this embodiment.

  First, a flaw detection signal obtained by transmitting an ultrasonic pulse signal from an ultrasonic probe will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram for explaining a flaw detection signal obtained through transmission through an object S when an ultrasonic pulse signal P is transmitted from the surface A to the bottom surface B of the object S having a defect F inside. FIG. 2 is a diagram illustrating a flaw detection signal waveform obtained from the ultrasonic pulse signal P for one pulse transmitted as shown in FIG.

  As shown in FIG. 1, the ultrasonic pulse signal P incident on the surface A of the subject S passes through the bottom surface B through various paths and is received as a flaw detection signal. For example, the path T1 in FIG. 1 is the shortest path through which the ultrasonic pulse signal P passes only through the healthy part without the defect F. Like the peak corresponding to the path T1 shown in FIG. It is received as a flaw detection signal in the shortest time. On the other hand, the path T2 is the longest path through which the ultrasonic pulse signal P is reflected by the bottom surface B and the surface A while passing through only the healthy part and then passes through the bottom surface B, and is a peak corresponding to the path T2 shown in FIG. Furthermore, it takes a long time until the ultrasonic pulse signal P is received as a flaw detection signal. A path F1 is a path through which the ultrasonic pulse signal P is reflected by the bottom surface B and the defect F and then passes through the bottom surface B. A path F2 is a bottom surface after the ultrasonic pulse signal P is reflected by the defect F and the surface A. This is a path through B. A path F1 and a path F2 in which the ultrasonic pulse signal P is reflected by the defect F are longer than the path T1 and shorter than the path T2, and are between the peak corresponding to the path T1 and the peak corresponding to the path T2 in FIG. appear.

  Between the peak corresponding to the path T1 and the peak corresponding to the path T2 in FIG. 2, in addition to the defect echo signal reflected by the defect F such as the path F1 and the path F2 described above, the surface A of the subject S A large number of echo noises or ultrasonic probes received after passing through only a healthy part while being reflected obliquely on the bottom surface B or surface A while being incident obliquely on the surface or having undergone mode conversion between longitudinal and transverse waves. Echo noise due to reverberation reflected in the tactile element is included. The present invention performs signal processing for reducing the influence of such echo noise and making a defective echo signal stand out.

  FIG. 3 is a block diagram schematically showing the configuration of the ultrasonic flaw detector according to the embodiment of the present invention. As shown in FIG. 3, the ultrasonic flaw detector 10 transmits an ultrasonic wave for nondestructive inspection of a defect of a subject, and receives a flaw detection signal resulting from the transmitted ultrasonic wave. An input unit 4 for inputting various information, a storage unit 5 for storing examination data of the subject, a display unit 6 for displaying the examination result of the subject, and each component of the ultrasonic flaw detector 10. And a control unit 7 for controlling.

  The flaw detection signal acquisition unit 1 includes an ultrasonic probe (ultrasonic probe) 2 and a transmission / reception unit 3, and transmits an ultrasonic signal of an electrical signal transmitted from the transmission / reception unit 3 to the outside from the ultrasonic probe 2. While transmitting as a sound wave, the ultrasonic wave received with the ultrasonic probe 2 is output to the transmission / reception part 3 as a flaw detection signal of an electrical signal. The ultrasonic probe 2 is realized by using a piezoelectric vibrator or the like, transmits an ultrasonic wave to the outside by applying a pulse signal from the transmission / reception unit 3, receives the ultrasonic wave from the outside, and converts it into an electric signal. The transmission / reception unit 3 outputs an ultrasonic pulse signal to the outside via the ultrasonic probe 2 by applying a pulse signal having a resonance frequency of the ultrasonic probe 2 or a frequency in the vicinity thereof to the ultrasonic probe 2.

  In the present embodiment, the ultrasonic probe 2 that transmits ultrasonic waves and the ultrasonic probe 2 that receives ultrasonic waves are configured separately, and are arranged so as to face each other with the subject interposed therebetween. .

  The input unit 4 is realized by using an input device such as a power switch and an input key, and inputs various instruction information to the control unit 7 in response to an input operation by the operator. For example, the input unit 4 inputs to the control unit 7 instruction information such as the start or end of flaw detection of the subject, instruction information for instructing display of flaw detection data of the subject, and the like.

  The storage unit 5 is realized using a storage medium such as a hard disk, and stores various types of information such as examination data of the subject instructed by the control unit 7. In particular, in the present embodiment, as will be described later, the storage unit 5 always stores a plurality of (five (N + Na)) or more flaw detection signals corresponding to pulses transmitted before the latest ultrasonic pulse signal. Yes.

  The display unit 6 is realized by using a display device such as a liquid crystal display, and displays various information instructed to be displayed by the control unit 7. Specifically, the display unit 6 displays inspection data of the subject by ultrasonic flaw detection (for example, defect information such as minute flaws). The display unit 6 may display waveform information of a flaw detection signal obtained from the subject to be examined.

  The control unit 7 is realized using a memory that stores a processing program and the like and a CPU that executes the processing program, and controls each component of the ultrasonic flaw detector 10 described above. The control unit 7 includes a subtraction signal acquisition unit 7a that acquires a subtraction signal and a subtraction processing unit 7b that performs signal processing for subtracting the subtraction signal from the flaw detection signal, and performs ultrasonic flaw detection processing to be described later. Run.

  The control unit 7 can also be realized using an FPGA. FIG. 4 shows the configuration of an ultrasonic flaw detector when the control unit 7 is realized using an FPGA. In this case, as shown in FIG. 4, the storage unit 5 uses a memory and is configured to be included in the control unit 7, and realizes ultrasonic flaw detection processing described below on hardware. Other configurations are the same as those in FIG.

  Next, an ultrasonic flaw detection processing procedure performed by the ultrasonic flaw detector 10 will be described with reference to FIGS. FIG. 5 is a flowchart showing an ultrasonic flaw detection processing procedure, and FIG. 6 is an explanatory diagram for explaining the ultrasonic flaw detection processing. The flowchart shown in FIG. 5 starts, for example, when the operator operates the input unit 4 to input an ultrasonic flaw detection instruction to the subject, and the ultrasonic flaw detection process proceeds to the process of step S1.

  In the process of step S1, the control unit 7 is always transmitted to the storage unit 5 before the ultrasonic pulse signal corresponding to the flaw detection signal to be subjected to the ultrasonic flaw detection processing (for example, the latest flaw detection signal received). Processing for storing at least (N + Na) times of flaw detection signals obtained from the ultrasonic pulse signal is started. The flaw detection signal to be stored is at least a flaw detection signal corresponding to each pulse from the latest ultrasonic pulse signal up to the pulse (N + Na) times before. That is, as shown in FIG. 6, when performing the ultrasonic flaw detection process on the flaw detection signal corresponding to the i-th pulse with the latest ultrasonic pulse signal as the i-th pulse, the control unit 7 stores in the storage unit 5. At least (N + Na) flaw detection signals corresponding to the (i−N−Na) to i th pulses are stored. Thereby, the process of step S1 is completed and the ultrasonic flaw detection process proceeds to the process of step S2.

  It should be noted that the values of N and Na are specified in advance before the process of step S1, for example, when the operator operates the input unit 4.

  Each time an ultrasonic pulse signal is transmitted, a flaw detection signal corresponding to the latest ultrasonic pulse signal is received. Therefore, the control unit 7 newly stores in the storage unit 5 each time a flaw detection signal corresponding to the (i + 1) th ultrasonic pulse signal is received. At the same time, the control unit 7 may delete the oldest one of the flaw detection signals stored in the storage unit 5. That is, in this case, the control unit 7 may delete the flaw detection signal corresponding to the (i−N−Na) th pulse.

  In the process of step S2, as shown in FIG. 6, the subtraction signal acquisition unit 7a corresponds to the pulse Na times from (N + Na) times to N times before the i-th ultrasonic pulse signal from the storage unit 5. A flaw detection signal is taken out and a known synchronous addition averaging process is performed to obtain a subtraction signal.

Here, the amplitude at the j-th sampling point (all n) of the flaw detection signal corresponding to the i-th pulse is x (i, j), and the flaw detection signal corresponding to this i-th ultrasonic pulse signal When performing ultrasonic flaw detection, the amplitude r (i, j) at the j-th sampling point of the subtraction signal can be expressed by the following equation (1). Note that the position of the sampling point is proportional to the time after the ultrasonic pulse signal is transmitted.

  By performing the above arithmetic processing, the processing in step S2 is completed, and the ultrasonic flaw detection processing proceeds to processing in step S3.

  In the process of step S3, the subtraction processing unit 7b performs a process of subtracting the subtraction signal acquired in step S2 from the flaw detection signal to be subjected to the ultrasonic flaw detection process, as shown in FIG. In the present embodiment, the flaw detection signal corresponding to the latest ultrasonic pulse signal is the target of ultrasonic flaw detection processing.

Here, for the flaw detection signal corresponding to the i th pulse, the amplitude y (i, j) at the j th sampling point of the signal obtained by subtracting the subtraction signal from the flaw detection signal is expressed by the following equation ( 2).

  The control unit 7 inspects the defect of the steel material by detecting the defect echo signal of the subject included in the signal obtained by the above subtraction process. Thereby, the process of step S3 is completed and a series of ultrasonic flaw detection processes are completed.

  By performing the above ultrasonic flaw detection process, if the flaw detection signal at the sound part is used as a subtraction signal, the subtraction signal is subtracted from the flaw detection signal including the defect echo signal, thereby performing flaw detection at the sound part. Echo noise that is equally included in the signal and the flaw detection signal at the defective portion can be removed. As shown in FIG. 6, the signal y (i, j) obtained as a result of performing the above-described ultrasonic flaw detection processing on the flaw detection signal in the defect portion including the defect echo signal is indicated by a dotted line in FIG. As shown in the enclosed part, the intensity (amplitude) of the defect echo signal stands out, and the possibility of missing the defect echo signal is reduced. A defect can be determined by setting an appropriate threshold for the intensity of the defect echo signal.

  Note that the subtraction signal is not the flaw detection signal immediately before the flaw detection signal to be subjected to ultrasonic flaw detection processing, but is a flaw detection signal corresponding to a pulse N times or more before, so that a subtraction signal can be used even when detecting a long defect. The possibility of applying the flaw detection signal at the defect portion to the defect portion can be reduced.

  Here, with reference to FIG. 7 and FIG. 8, the method for selecting N will be described. 7 and 8 are diagrams for explaining the defect detection accuracy. The intensity of the defect echo signal received by transmitting an ultrasonic pulse signal while scanning the ultrasonic probe on a line passing over the defect. It is an image figure which shows the relationship between and the number of pulses. FIG. 7 shows the case of scanning over a very small spot-like defect, and FIG. 8 shows the case of scanning over a defect (continuous defect) whose length is longer than the beam width of the ultrasonic pulse signal. As shown in FIG. 7, when the defect is a very small dot and its length is sufficiently shorter than the scanning amount between pulses (the product of the pulse time interval and the scanning speed of the ultrasonic probe), A peak centered right above appears, and the width of the base corresponds to the ultrasonic beam width. On the other hand, as shown in FIG. 8, when the defect length is longer than the beam width, a trapezoidal peak corresponding to the defect length appears, and the skirt width is the sum of the defect length and the beam width. It corresponds to.

  Based on this, in the present embodiment, N is selected so that the scanning amount between N pulses is sufficiently longer than the length of the defect. As a result, the subtraction process is performed by applying the flaw detection signal at the defect portion to the subtraction signal, thereby preventing the reduction to the defect echo signal.

  However, N is selected so that the shape of the subject does not change at a position separated by the scanning amount between N pulses. When the shape of the subject changes, the waveform of the echo noise included in the flaw detection signal at the healthy part is different from the waveform of the echo noise of the flaw detection signal that is the target of the ultrasonic flaw detection process. I can not expect.

  In addition, the subtraction signal is obtained by synchronously averaging the flaw detection signals corresponding to a plurality of (Na times) pulses, resulting in electrical random noise included in each flaw detection signal or bubbles in the acoustic contact medium. The effect of instantaneous echo noise is reduced.

  By obtaining the subtraction signal by synchronously averaging the flaw detection signals corresponding to a plurality of (Na times) pulses, the flaw detection signal obtained at the sound part after the ultrasonic probe has passed the defect is further detected. When performing an ultrasonic flaw detection process, even when a flaw detection signal including a defect echo signal at a defective portion that has passed through is included in the subtraction signal, the influence of the defect echo signal can be reduced. When the process of subtracting the subtraction signal including the defect echo signal from the flaw detection signal in the healthy part, an event is detected in which the virtual echo signal is detected as if there is a defect in the healthy part. Even if a defect echo signal is included in the subtraction signal, the influence can be reduced, and the generation of a virtual echo signal can be reduced.

  FIG. 9 and FIG. 10 show the intensity of the defect echo signal when the ultrasonic flaw detection process of the present embodiment is applied by changing the above N and Na. In both FIG. 9 and FIG. 10, the horizontal axis indicates the combination of N and Na, and the vertical axis indicates the defect echo signal intensity after ultrasonic flaw detection processing corresponding to each combination in the case of continuous defects, Each of the cases without defects is shown. N = raw and Na = raw are defect echo signal intensities when ultrasonic flaw detection processing is not performed.

  FIG. 9 shows a case where Na is set to 4 and N is changed, and N = 1 means that a flaw detection signal corresponding to an adjacent ultrasonic pulse signal is included in the subtraction signal. According to FIG. 9, when N = 1, the defect echo signal intensity after the ultrasonic flaw detection process is reduced for any defect, and the reduction of the defect echo signal intensity is improved as N is increased. I understand. Although N depends on the capacity of the storage unit 5, it is desirable to set N to 50 or more.

  FIG. 10 shows a case where N is 30 and Na is changed, and Na = 1 means that a single flaw detection signal is used as a subtraction signal. According to FIG. 10, it can be seen that the reduction of the defect echo signal intensity is improved as Na is increased. It is desirable to set Na to 10 or more.

  As described above, according to the ultrasonic flaw detection processing of the present embodiment, since the echo noise that is equally included in the flaw detection signal in the healthy part can be removed, if there is a defect echo signal, it can be made to stand out. There is little risk of overlooking any flaws. Further, even for a long defect, the echo noise can be reduced with a simple process to make the defect echo signal stand out.

  When performing the ultrasonic flaw detection process of the above-described embodiment, the position of the echo may be blurred due to the influence of the subject's vibration or the like. It is desirable to match the time positions of noise. For the alignment of the flaw detection signals, for example, boundary echo signals such as surface echo signals and bottom surface echo signals as indicated by peaks corresponding to the paths T1 and T2 in FIG. For example, this can be realized by providing boundary echo detection means and storing the flaw detection signal in the storage unit 5 with reference to the detected boundary echo signal.

  FIG. 11 illustrates the effect of aligning the flaw detection signals with reference to the boundary echo signal. The upper part of FIG. 11 shows the flaw detection signal, and the middle part and the lower part show a part of the upper part of the flaw detection signal on the horizontal axis. Among these, the middle stage shows the flaw detection signal before the subtraction process, and the lower stage shows the flaw detection signal after the subtraction process is performed with N = 50 and Na = 4. The flaw detection signal before the subtraction process at the middle stage and the flaw detection signal after the subtraction process at the lower stage are a flaw detection signal that is not aligned by the boundary echo signal, and a flaw detection signal that is aligned with reference to the peak corresponding to the path T1. , Shows flaw detection signals aligned on the basis of the peak corresponding to the path T2. According to FIG. 11, if the flaw detection signals are not aligned by the boundary echo signal, the echo fluctuates due to the influence of the vibration of the subject even in the ultrasonic flaw detection processing of the present embodiment, and the flaw detection region is detected. There may be a case where a peak corresponding to noise or the path T2 remains. On the other hand, if the flaw detection signals are aligned based on the peak corresponding to the path T1, the peak corresponding to the path T2 may be reduced but remain in the flaw detection area. However, the flaw detection signal is generated based on the peak corresponding to the path T2. It can be seen that, when aligned, the echo noise in the flaw detection area can be reduced satisfactorily.

1 Flaw Detection Signal Acquisition Unit 2 Ultrasonic Probe (Ultrasonic Probe)
DESCRIPTION OF SYMBOLS 3 Transmission / reception part 4 Input part 5 Storage part 6 Display part 7 Control part 7a Subtraction signal acquisition part 7b Subtraction processing part 10 Ultrasonic flaw detector

Claims (5)

In an ultrasonic flaw detection method for continuously inspecting a defect in a steel material by transmitting an ultrasonic pulse signal while scanning an ultrasonic probe and receiving a flaw detection signal resulting from the ultrasonic pulse signal,
Storing flaw detection signals for the number of received multiple pulses;
Extracting a flaw detection signal that is a predetermined number of pulses prior to the flaw detection signal to be processed from the stored flaw detection signal;
Subtracting the subtraction signal from the flaw detection signal to be processed;
Inspecting a defect in the steel based on the flaw detection signal from which the subtraction signal is subtracted;
An ultrasonic flaw detection method comprising:   The predetermined number of pulses means that the scanning amount of the ultrasonic contact from the time when the flaw detection signal before the predetermined number of pulses is received until the time when the flaw detection signal to be processed is received exceeds the length of the defect to be detected. 2. The ultrasonic flaw detection method according to claim 1, wherein the ultrasonic flaw detection method has a length equal to or longer than a total length of the beam width of the sound wave pulse signal and a length that does not change a waveform of echo noise in the flaw detection signal.   3. The ultrasonic flaw detection method according to claim 1, wherein the subtraction signal is obtained by synchronously averaging a plurality of flaw detection signals before the predetermined number of pulses.   The ultrasonic flaw detection method according to any one of claims 1 to 3, wherein when the received flaw detection signal is stored, the boundary echo signal is stored in alignment with a reference. In an ultrasonic flaw detector that continuously inspects defects in steel by transmitting an ultrasonic pulse signal while scanning an ultrasonic probe and receiving a flaw detection signal resulting from the ultrasonic pulse signal,
Means for storing flaw detection signals for the number of received multiple pulses;
Means for taking out a flaw detection signal a predetermined number of times before the processing target flaw detection signal as a subtraction signal from the stored flaw detection signal;
Means for subtracting the subtraction signal from the flaw detection signal to be processed;
Means for inspecting a defect in the steel based on the flaw detection signal obtained by subtracting the subtraction signal;
An ultrasonic flaw detector characterized by comprising: