JP2004347572A - Ultrasonic flaw detector and ultrasonic flaw detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To nondestructively detect the presence of a corrosion in the vicinity of a boundary between an examination object and another solid matter, in a case that the circumference of the examination object is surrounded by a solid having a property different from that of the object. <P>SOLUTION: An arbitrary waveform creating section 72 creates a burst signal to drive a transmission probe 1, and a signal processing section 75 calculates the height of an echo in the examination object 8 on the basis of an electric signal from a receiving probe 2. This processing is repeated with changing the frequency of a carrier of the burst signal, and the presence/absence of a corrosion in the object 8 is determined on the basis of the change in the height of the echo with the change of the frequency of the carrier. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic inspection device and an ultrasonic inspection method for non-destructively inspecting a boundary portion between solids, and particularly to an ultrasonic inspection device capable of inspecting for the presence or absence of corrosion near the boundary portion. The present invention relates to a flaw detection device and an ultrasonic flaw detection method.
[0002]
[Prior art]
Ultrasonic flaw detectors have been used to non-destructively inspect interfaces between different solids, such as metal structures and supporting structures that support the structures. A conventional ultrasonic flaw detector of this type is disclosed, for example, in Patent Document 1. In the technique described in Patent Literature 1, a transmitting probe is excited by a flaw detector, and an ultrasonic wave is propagated in a pipe. The transmitted ultrasonic echo is received by the receiving probe, and the level of the echo is displayed on the display of the flaw detector. If there is corrosion near the boundary between the pipe rack and the pipe that supports the pipe, ultrasonic waves will cause irregular reflection in this area, so the level of the echo displayed on the flaw detector display will be reduced accordingly. Become. Therefore, Patent Document 1 assumes that if the received echo level is low, it can be determined that corrosion exists between the pipe rack and the pipe.
[0003]
However, even when there is no corrosion, the ultrasonic waves penetrate into the pipe rack, so it is difficult to evaluate the presence or absence of corrosion using only the echo level. Further, this method is a method applicable only when there is nothing other than the pipe rack around the pipe. For example, in a state where the periphery of the pipe is solidified with concrete, it is considered that ultrasonic waves propagate not only inside the pipe but also into concrete. For this reason, the received echo level is reduced regardless of the presence or absence of corrosion. Therefore, it is difficult to apply the method disclosed in Patent Document 1 to the inspection of the corrosion of the pipe near the boundary between the concrete and the pipe.
[0004]
In addition, Patent Literature 2 also discloses a method of inspecting for thinning due to corrosion. In Patent Literature 2, a surface wave is propagated into an inspection target by a transmission probe, and the propagated surface wave is received by a reception probe. If there is corrosion near the boundary between the gantry supporting the inspection target and the inspection target, the surface wave propagates along the corrosion, so that the reception time of the received echo is delayed by that much. Patent Document 2 assumes that corrosion can be evaluated using the delay of the reception time.
[0005]
However, this method is also applicable only when there is nothing other than the gantry around the inspection target part. For example, in a state where the periphery of the inspection target is hardened with concrete or the like, a surface wave along the boundary between the inspection target and the concrete does not propagate. Therefore, corrosion cannot be inspected using the propagation delay time of the surface wave. Therefore, it is difficult to apply the method disclosed in Patent Document 2 to the inspection of corrosion of the inspection target portion near the boundary between the concrete or the like and the inspection target portion.
[0006]
Further, Patent Literature 3 discloses a corrosion inspection method. The technique described in Patent Literature 3 differs from the technique described in Patent Literature 2 in that an SH wave (Shear Horizontal Wave) is used. In the inspection method disclosed in Patent Document 3, an SH wave is transmitted from a probe, and corrosion is evaluated using a reflected SH wave reflected at a corroded place and a transmitted SH wave transmitted through a corroded place. .
[0007]
However, in this method as well, in a state where the periphery of the test object is hardened with concrete or the like, it is considered that ultrasonic waves propagate not only in the test object but also in concrete or the like. For this reason, the received echo level becomes small, and it is considered difficult to secure a sufficient signal-to-noise ratio. Therefore, it is difficult to apply the method disclosed in Patent Document 3 to the inspection of corrosion of the inspection target portion near the boundary between the concrete or the like and the inspection target portion.
[0008]
[Patent Document 1]
JP-A-62-113060
[Patent Document 2]
JP-A-2002-5905
[Patent Document 3]
JP-A-2002-243704
[0009]
[Problems to be solved by the invention]
As described above, when the periphery of the test object is surrounded by a solid having a property different from that of the test object, the corrosion inspection near the boundary between the test object and other solids is conventionally performed. There was a problem that the method shown was difficult.
[0010]
The present invention has been made in order to solve the above-described problem, and when the periphery of a test object is surrounded by a solid having a property different from that of the test object, the test object and another solid It is an object of the present invention to obtain an ultrasonic inspection apparatus and an ultrasonic inspection method capable of nondestructively inspecting for the presence or absence of corrosion near the boundary of an object.
[0011]
[Means for Solving the Problems]
An ultrasonic flaw detector according to the present invention includes a burst signal generating unit that generates a burst signal to drive a transmission probe that is driven by an electric signal and transmits an ultrasonic wave into a test object, and a carrier of the burst signal. A control unit that gives a command to change the frequency to the burst signal generation unit, and based on an electric signal from a receiving probe that converts an ultrasonic wave propagated through the test object into an electric signal, An intensity calculation unit that calculates the intensity of the ultrasonic wave; and a property determination unit that determines a property of the test object based on a change in the intensity of the ultrasonic wave in the test object with respect to the change in the carrier frequency. .
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 shows an ultrasonic inspection system including the ultrasonic inspection device according to Embodiment 1 of the present invention. As shown in FIG. 1, the ultrasonic testing system includes a transmitting probe 1, a receiving probe 2, and a flaw detection control unit (ultrasonic flaw detection device) 7.
[0013]
The transmission probe 1 is driven by an electric signal and generates ultrasonic waves having the same frequency as the frequency of the electric signal. The receiving probe 2 generates an electric signal having the same frequency as the frequency of the received ultrasonic wave (that is, converts the ultrasonic wave into an electric signal). The probes 1 and 2 may be a piezoelectric element type ultrasonic transducer, an EMAT (electro-magnetic acoustic transducer), or another ultrasonic transducer.
[0014]
FIG. 1 shows a state in which the transmission probe 1 and the reception probe 2 are placed on the test object 8. The test object 8 is a part of a metal structure having a uniform small thickness, such as a pipe or a steel plate. Around the test object 8, a surrounding solid 10 such as concrete is arranged. Corrosion 5 may be present in a portion of the test object 8 surrounded by the surrounding solid 10, and in the portion where the corrosion 5 exists, the test object 8 does not contact the surrounding solid 10, but in other portions, Both are in contact. The probes 1 and 2 are arranged on both sides of the surrounding solid 10.
[0015]
The flaw detection control unit 7 includes a control unit 71, an arbitrary waveform generation unit (burst signal generation unit) 72, a transmission unit 73, a reception unit 74, a signal processing unit (strength calculation unit, property determination unit) 75, and an output unit 76. The control unit 71 is connected to the arbitrary waveform generation unit 72, the transmission unit 73, the reception unit 74, the signal processing unit 75, and the output unit 76, and supplies a control signal to these units to control the flaw detection control unit 7. Take control.
[0016]
The arbitrary waveform generator 72 generates a transmission electric signal to drive the transmission probe 1. FIG. 2 shows the waveform of the transmission electric signal generated by the arbitrary waveform generating section 72. This transmission electric signal is a burst signal having the carrier frequency f0. The transmission electric signal is amplitude-modulated so that the amplitudes of the signal at the beginning (rising portion) and at the end (falling portion) become small. This type of amplitude-modulated transmission electric signal is hereinafter referred to as a “modulated burst signal”.
[0017]
The arbitrary waveform generating section 72 is connected to the transmitting section 73, and the transmitting section 73 is connected to the transmitting probe 1. The transmitting section 73 amplifies the modulated burst signal generated by the arbitrary waveform generating section 72 and transmits the amplified modulated burst signal (excitation signal) to the transmitting probe 1, thereby causing the transmitting probe 1 to transmit. Exciting electrically. That is, the excitation signal is converted into an ultrasonic wave in the transmission probe 1. This ultrasonic wave is transmitted to the test object 8. The ultrasonic wave propagates through the test object 8 below the surrounding solid 10 and is received by the receiving probe 2 as an echo of the ultrasonic wave.
[0018]
The receiving probe 2 is connected to a receiving unit 74, and the receiving unit 74 is connected to a signal processing unit 75. The receiving unit 74 amplifies the received electric signal (received echo signal) output from the receiving probe 2 and transmits the amplified received echo signal to the signal processing unit 75. Although not shown, the signal processing unit 75 has an A / D conversion unit and a memory inside. The A / D converter converts the received echo signal from the receiver 74 into a digital signal. The digital signal is stored in a memory in the signal processing unit 75.
[0019]
When the digital signal derived from the ultrasonic echo corresponding to one modulated burst signal is stored in the memory in the signal processing unit 75, the signal processing unit 75 notifies the control unit 71 of the fact, and The control unit 71 supplies a control signal designating another carrier frequency f0 to the arbitrary waveform generation unit 72 in accordance with. In response to the control signal, the arbitrary waveform generator 72 generates a modulated burst signal with a changed carrier frequency f0.
[0020]
By repeatedly measuring the echo for the carrier frequency f0 of the different modulated burst signal, the signal processing unit 75 stores a digital signal derived from each echo for each carrier frequency f0 in an internal memory. As described later, the signal processing unit 75 calculates the intensity (echo height) of the ultrasonic wave in the test object based on these digital signals, and based on the echo height for each carrier frequency f0, the test object. 8 properties are determined. The signal processing unit 75 is connected to an output unit 76 that is, for example, a display device. The signal processing unit 75 notifies the output unit 76 of the property determination result, and the output unit 76 outputs the property determination result (for example, displays the result). ).
[0021]
The range in which the carrier frequency f0 is changed and the number of repetitions are tested based on the frequency characteristics of the transmitting probe 1 and the receiving probe 2 (specifically, a frequency band in which stable transmission and reception are possible). Person decides in advance.
[0022]
A method for inspecting corrosion 5 from these received echo signals will be described below.
When the thickness of the test object 8 is uniform and small (for example, when the wavelength of the ultrasonic wave propagating in the test object 8 is about the same to several times), the ultrasonic wave propagating in the test object 8 Becomes a plate wave. When the transmission probe 1 uses the oblique flaw detection method, which is a commonly used oblique probe, the direction in which the vibration of the plate wave proceeds is parallel to the plane of FIG. Such a plate wave is called a Lamb wave (Lamb wave), but is hereinafter simply referred to as a “plate wave”.
[0023]
The plate wave propagating in the test object 8 shows a complicated propagation form. Further, the propagation form differs depending on the frequency. The result of confirming this state by sound field simulation is shown in FIGS. 3 to 13A.
[0024]
FIG. 3 is a diagram showing conditions of a sound field simulation. In the sound field simulation, the intensity of the ultrasonic energy and the particle displacement vector in various parts at each time were calculated by numerical analysis according to a program developed by the inventor, and the results were displayed on a graphic display software. . In this simulation, it was assumed that the oblique flaw detection method in which the incident angle from the transmitting probe 1 and the incident angle to the receiving probe 2 were 60 ° was used. Acrylic is assumed as the material of the wedge that maintains the incident angle at 60 °, and a steel plate having a thickness of 4.36 mm is assumed as the material of the test object 8. Mortar with a length of 300 mm was assumed as the surrounding solid 10. It was assumed that there was no void between the test object 8 and the surrounding solid 10. Further, as the frequency response characteristics of the probes 1 and 2, a wide band having a center frequency of 1.0 MHz was assumed. For the sake of simulation, an absorption boundary 10A was provided in the surrounding solid 10 to suppress reflected waves unnecessary for analysis.
[0025]
FIG. 4 shows a result of performing a sound field simulation on the assumption that a modulated burst signal having a carrier frequency f0 of 0.7 MHz is used as the transmission electric signal generated by the arbitrary waveform generating section 72. FIG. 4 has a snapshot of the sound field (obtained with the above-mentioned graphic display software) in which the elapsed time differs by 8 μsec, and the top snapshot excites the transmission probe 1. The sound field after 12 μsec is shown, and the bottom snapshot shows the sound field after 92 μsec. The density of the dots in FIG. 4 indicates the intensity of the ultrasonic energy, and the denser the dots, the stronger the ultrasonic energy.
[0026]
At the stage after 12 μsec, the sound has not yet propagated into the test object 8 (steel plate), but remains in the acrylic wedge of the transmitting probe 1. At a stage after 20 μsec, the ultrasonic wave propagates into the steel plate. At this time, the ultrasonic wave in the steel plate is a plate wave. At the stage after 36 sec, the plate wave propagates in the region where the upper and lower sides of the steel plate are air, and reaches the region where the mortar exists on the steel plate after 44 μsec. Thereafter, the plate wave propagates through the steel sheet while leaking energy into the mortar.
[0027]
FIG. 5 is an enlarged view of the snapshot of the sound field after 92 μsec shown in FIG. 4 and further shows the particle displacement vector at that stage. As shown in FIG. 5, the direction of the particle displacement is the same in the vicinity of the upper surface and the lower surface of the steel sheet. That is, when it vibrates upward near the upper surface of the steel plate, it also vibrates upward near the lower surface of the steel plate, and when it vibrates downward near the upper surface of the steel plate, it vibrates downward also near the lower surface of the steel plate. Such a plate wave is called an asymmetric mode plate wave. The plate wave shown in FIG. 5 is a plate wave called a zero-order asymmetric mode (A0 mode) in this technical field among the asymmetric modes.
[0028]
The plate wave in the A0 mode propagates to the receiving probe 2 while leaking energy into the mortar, and is received. FIG. 6 shows an echo received by the receiving probe 2. The vertical axis represents the voltage output from the receiving probe 2, that is, the amplitude of the ultrasonic wave. In normal ultrasonic flaw detection, as shown in FIG. 6, since only the change in the amplitude of the received echo is known, it cannot be determined whether the echo is an A0 mode plate wave. By observing the form of the particle displacement vector as illustrated in FIG. 5 obtained by the sound field simulation, it can be determined that the ultrasonic wave propagation mode is the A0 mode.
[0029]
FIG. 7 shows the result of performing the same sound field simulation by changing the carrier frequency f0 to 1.0 MHz, similarly to FIG. Until the plate wave propagating in the steel plate reaches the region under the mortar, the state of the ultrasonic energy is substantially the same as that in FIG. 4, but the state in which the ultrasonic wave propagates in the region under the mortar is different. As can be seen from a comparison between FIG. 4 and FIG. 7, when the carrier frequency f0 is 1.0 MHz, the energy of the plate wave propagating through the steel plate under the mortar is reduced because energy leaks from the steel plate to the mortar quickly. Very small (ie, the dots are coarser on FIG. 7). When the carrier frequency f0 is 1.0 MHz, a plate wave other than the A0 mode propagates at a later stage of the elapsed time.
[0030]
FIG. 8 is an enlarged view of the snapshot of the sound field after 92 μsec shown in FIG. 7 and further shows the particle displacement vector at that stage. As shown in FIG. 8, it can be confirmed that a plate wave propagating later than the A0 mode plate wave exists in the steel plate. The plate wave is directed in a direction in which the direction of particle displacement is different between the upper surface and the lower surface of the steel plate. That is, when vibrating upward near the upper surface of the steel plate, it vibrates downward near the lower surface of the steel plate, and when vibrating downward near the upper surface of the steel plate, it vibrates upward near the lower surface of the steel plate. Such a plate wave is called a symmetric mode plate wave. The plate wave of the symmetric mode shown in FIG. 8 is a plate wave called a zero-order symmetric mode (S0 mode) in this technical field among the symmetric modes.
[0031]
Actually, even when the carrier frequency f0 shown in FIG. 4 is 0.7 MHz, the S0 mode ultrasonic wave propagates, but its attenuation is much larger than when the carrier frequency f0 is 1.0 MHz. Therefore, when the carrier frequency f0 is 0.7 MHz, the plate wave in the S0 mode is already invisible at a stage after 92 μsec. At the stage after 44 μsec in FIG. 4, the plate wave propagating slightly behind the A0 mode ultrasonic wave is actually a S0 mode plate wave. That is, since the attenuation of the S0 mode plate wave is relatively small due to the change of the carrier frequency f0 to 1.0 MHz, the S0 mode plate wave has the same amplitude as the A0 mode as shown in FIG. And propagates through the steel sheet.
[0032]
When the carrier frequency f0 of the modulated burst signal is 1.0 MHz, the A0-mode and S0-mode plate waves leak very much energy into the mortar, resulting in very weak vibrations. It propagates to child 2 and is received, albeit slightly. FIG. 9 shows an echo received by the receiving probe 2.
[0033]
FIG. 10 shows a result of performing the same sound field simulation by changing the carrier frequency f0 to 1.4 MHz, similarly to FIG. Until the plate wave propagating in the steel plate reaches the region under the mortar, the state of the ultrasonic energy is substantially the same as that in FIG. 4, but the state in which the ultrasonic wave propagates in the region under the mortar is different. As can be seen by comparing FIG. 4 with FIG. 7 and FIG. 10, when the carrier frequency f0 is 1.4 MHz, a relatively large amplitude is generated even in a later stage while energy is leaked from the steel plate into the mortar. The plate wave is maintained and propagated. That is, the diffusion of energy is slower than in other cases.
[0034]
FIG. 11 is a diagram in which the snapshot of the sound field after 92 μsec shown in FIG. 10 is enlarged, and the particle displacement vector at that stage is also shown. As shown in FIG. 11, a plate wave having a vibration displacement vector that cannot be said to be the A0 mode or the S0 mode propagates in the steel plate. Since this plate wave has energy concentrated below the steel plate, it is considered that the leakage of energy into the mortar is small. Hereinafter, the plate wave of such vibration displacement is referred to as “pseudo-plate wave”.
[0035]
Since the pseudo plate wave has a small energy leakage into the mortar, it is received by the receiving probe 2 as a signal having a relatively large amplitude. FIG. 12 shows an echo received by the receiving probe 2.
[0036]
The mode of the propagating plate wave and the received echo have been described above based on the sound field simulation in which the carrier frequency f0 of the modulated burst signal is changed. A similar simulation was performed by changing the carrier frequency f0 from 0.5 MHz to 1.5 MHz at intervals of 0.1 MHz, and the frequency-echo height characteristics (changes in the intensity of the ultrasonic wave in the test specimen with respect to the change in the carrier frequency). Is shown in FIG. 13 (A). FIG. 13A also shows three types of simulation results. One is a simulation result in the case where the mortar described so far is completely bonded to the steel plate, and is shown as “no void” in FIG. 13 (A).
[0037]
Further, in addition to the simulation described above, it is assumed that a void 11 simulating corrosion is provided between the surrounding solid 10 which is mortar and the test object 8 which is a steel plate as shown in FIG. The result of performing the same simulation and obtaining the frequency-echo height characteristic is shown as “with air gap”. Further, the frequency-echo height characteristics simulated ignoring the mortar are shown as “no mortar”. In the case of “without mortar”, the echoes in the A0 mode and the S0 mode propagate and are received. FIG. 13A shows the echo height in the A0 mode. The echo height here is the maximum amplitude of the echo. Each curve in FIG. 13A is represented by a relative echo height based on the maximum echo height in the case of “without mortar”.
[0038]
As can be seen from FIG. 13 (A), in the case of “no air gap” where the mortar and the steel plate are completely bonded, the characteristics clearly changed near the carrier frequency of 1.0 MHz. This is because, as can be seen from the simulation results shown in FIGS. 4 to 12, A0 mode echoes are mainly received in the frequency band from 0.5 MHz to 1.0 MHz, and weak S0 mode echoes are obtained at 1.0 MHz. This is mainly because the pseudo plate wave is mainly received in the frequency band from 1.0 MHz to 1.5 MHz. That is, in a state where the mortar and the steel plate are completely bonded, the mode of the echo received near the carrier frequency of 1.0 MHz is switched, so that the characteristics as shown in FIG. 13A are obtained. As described above, since the mode of the received echo is switched, the echo height has the lowest peak, and there is a frequency at which the change tendency of the echo height changes rapidly. Hereinafter, this frequency is referred to as a “transition frequency”. In the case of “no air gap” where the mortar and the steel sheet are completely bonded, it can be assumed that there is no corrosion between the mortar and the steel sheet. It can be said that it exists.
[0039]
On the other hand, in the case of "with air gap", characteristics similar to the frequency-echo height characteristics in the case of "without air gap" were shown, but the change was relatively gradual. For this reason, although the lowest peak of the echo height exists, the transition of the change tendency is gradual, and the transition frequency cannot be clearly obtained. In the case of “with voids”, it can be assumed that a part of the steel sheet is corroded near the boundary between the steel sheet and the mortar. Therefore, when a part of the steel plate is corroded near the boundary between the steel plate and the mortar, it can be said that the transition frequency exists but does not clearly appear.
[0040]
On the other hand, in the case of “without mortar”, a monotonous characteristic having the highest peak around the carrier frequency of 0.8 MHz was shown. That is, a situation where the transition frequency does not exist is brought about. In the case of "without mortar", it can be assumed that the steel plate is completely corroded and there is a gap between the steel plate and the mortar, so if the steel plate is completely corroded near the boundary between the steel plate and the mortar Can be said to have no transition frequency.
[0041]
The above relationships can be summarized as follows.
(1) In the case of no corrosion, the transition frequency is clearly obtained.
(2) When a part of the steel sheet is corroded near the boundary between the steel sheet and the mortar, the transition frequency exists but does not clearly appear.
(3) When the steel sheet is totally corroded near the boundary between the steel sheet and the mortar, there is no transition frequency.
[0042]
The frequency-echo height characteristics can be obtained by actual measurement without simulation. Therefore, by judging the presence or absence of a clear transition frequency from the actually measured frequency-echo height characteristics, whether the steel sheet is completely adhered to the mortar, a part of the steel sheet is corroded, or the steel sheet is completely corroded Can be determined. However, in consideration of actual flaw detection, it is often sufficient to be able to determine the presence or absence of corrosion regardless of the degree of corrosion. Therefore, a process and a method for determining whether or not there is corrosion without outputting an inspection result of "partially corroded" will be described below.
[0043]
FIG. 14 is a flowchart for explaining the corrosion inspection method according to the first embodiment. Hereinafter, each step of realizing the corrosion determination method will be described in detail again with reference to the flowchart of FIG.
[0044]
In step ST1, the control unit 71 drives the arbitrary waveform generation unit 72, the transmission unit 73, the reception unit 74, the signal processing unit 75, and the output unit 76 to an operable state. In step ST1, the control unit 71 sets the first carrier frequency f0 at which flaw detection is started, and supplies a control signal designating the carrier frequency f0 to the arbitrary waveform generation unit 72. Further, the control unit 71 notifies the signal processing unit 75 of the carrier frequency f0.
[0045]
In step ST2, the arbitrary waveform generator 72 generates a modulated burst signal based on the carrier frequency f0 set by the controller 71, and transmits the modulated burst signal to the transmitter 73.
[0046]
In step ST3, the transmission unit 73 excites the transmission probe 1. Before executing the inspection method, the tester sets the incident angle of the ultrasonic wave from the transmitting probe 1 to an angle at which the A0 mode and S0 mode plate waves are efficiently excited. As a result, the plate waves of the A0 mode and the S0 mode propagate into the inspection object 8.
[0047]
In step ST4, the receiving probe 2 receives an echo. The angle of incidence of the ultrasonic wave on the receiving probe 2 may be the same as or different from the angle of incidence from the transmitting probe 1. Before executing the inspection method, the tester sets the incident angle on the receiving probe 2 so that the A0 mode and S0 mode plate waves propagated in the test object 8 can be efficiently received. Keep it.
[0048]
In step ST5, the receiving echo signal from the receiving probe 2 is amplified by the receiving unit 74 and sent to the signal processing unit 75.
[0049]
In step ST6, the A / D converter inside the signal processing unit 75 converts the received echo signal sent to the signal processing unit 75 into a digital reception echo signal, and converts the resulting digital reception echo signal into a signal processing unit. 75 in the internal memory. At this time, the carrier frequency f0 of the modulated burst signal notified from the control unit 71, that is, the carrier frequency f0 corresponding to the digital reception echo signal is stored together with the digital reception echo signal.
[0050]
In step ST7, it is determined whether or not flaw detection has been performed using all the predetermined carrier frequencies. If flaw detection has been performed using all carrier frequencies, the process proceeds to step ST9. After step ST9, only the processing in the signal processing unit 75 is performed, and the transmission unit 73 and the reception unit 74 do not participate in the processing. On the other hand, when the flaw detection is not performed using all the predetermined carrier frequencies, the process proceeds to step ST8. Here, the predetermined carrier frequency is predetermined by a person who performs a test based on the frequency characteristics of the probes 1 and 2 (specifically, a frequency band in which stable transmission and reception can be performed). In the case of a 1 MHz probe, for example, f0 = 0.5 MHz, 0.6 MHz, 0.7 MHz, 0.8 MHz,..., 1.3 MHz, 1.4 MHz, and 1.5 MHz. However, the method of determining the carrier frequency varies depending on the case, and the range of the change and the frequency interval may be selected so that the characteristic shown in FIG. 13A clearly appears.
[0051]
In step ST8, the control section 71 changes the carrier frequency. That is, a carrier frequency f0 not yet used for flaw detection is selected from predetermined carrier frequencies, and a control signal designating the carrier frequency f0 is supplied to the arbitrary waveform generator 72. Further, the control unit 71 notifies the signal processing unit 75 of the carrier frequency f0. Then, the process returns to step ST2, and repeats the processes from step ST2 to step ST7 until all the predetermined carrier frequencies are used for flaw detection.
[0052]
In step ST9, the signal processing unit 75 reads out all the carrier frequencies stored in the memory in step ST6 and the digital reception echo signals corresponding thereto.
[0053]
In step ST10, the signal processing unit 75 functions as an intensity calculation unit, and calculates an echo height for each carrier frequency f0 based on these digital reception echo signals, thereby obtaining a frequency-echo height characteristic (that is, a carrier The change in the intensity of the ultrasonic wave in the test specimen with respect to the change in frequency) is obtained. The echo height here is the maximum amplitude of the echo.
[0054]
In step ST11, the signal processing unit 75 functions as a property determining unit, and checks whether there is a transition frequency from the frequency-echo height characteristics. That is, the lowest peak of the echo height is obtained, and when the difference between the echo height of the carrier frequency near the carrier frequency corresponding to the lowest peak and the echo height of the lowest peak exceeds the threshold, it is determined that the transition frequency exists. . For example, when there is a lowest peak of the echo height at the carrier frequency of 1.0 MHz, the carrier frequency at the carrier frequency (for example, 0.9 MHz and / or 1.0 MHz) closest to 1.0 MHz is used. The difference between the echo height and the lowest peak is determined, and if the difference exceeds the threshold, it is determined that a transition frequency exists. In this case, 1.0 MHz as the carrier frequency corresponding to the lowest peak is the transition frequency. By making such a determination, when a transition frequency actually exists but does not clearly appear, it is determined that the transition frequency does not exist.
[0055]
If it is determined that the transition frequency exists, the signal processing unit 75 notifies the output unit 76 of a property determination result indicating that there is no corrosion in the test object 8 in step ST12. The result of the property determination is output, and the process ends.
[0056]
On the other hand, if it is determined that the transition frequency does not exist, in step ST13, the signal processing unit 75 notifies the output unit 76 of a property determination result indicating that corrosion is present in the test object 8, and the output unit 76 outputs the property determination result and ends the process.
In this way, the properties of the test object 8 can be determined based on the echo height for each carrier frequency f0.
[0057]
In the above ultrasonic flaw detection method, the modulation burst signal (see FIG. 2) created in step ST2 depends on the extent to which the amplitude modulation needs to be applied. . In some cases, a burst signal without amplitude modulation may be used. An operation section (not shown) is provided, which allows a tester to operate the arbitrary waveform generator 72 to adjust the degree of amplitude modulation.
[0058]
The method of changing the carrier frequency f0 in step ST8 may be a uniform increase or a uniform decrease within the range of the frequency required for flaw detection, or the carrier frequency may be increased or decreased at non-uniform intervals. You may. The carrier frequency may be changed at random. The carrier frequency initially set in step ST1 may be within the required frequency range, and need not be the lower limit or the upper limit of the required frequency.
[0059]
Further, the intervals of all carrier frequencies used for flaw detection may be equal intervals (for example, 0.1 MHz intervals as described above), but may not be equal intervals. For example, it may be determined in advance that f0 = 0.5 MHz, 0.7 MHz, 0.9 MHz, 1.0 MHz, 1.1 MHz, 1.3 MHz, and 1.5 MHz are used as carrier frequencies.
[0060]
It is desirable that the frequency characteristics of the transmission probe 1 and the reception probe 2 (specifically, the frequency band in which stable transmission and reception can be performed) are wide so that the transition frequency can be detected. After calculating the echo height, the echo height is corrected based on the frequency characteristics of these probes (the relationship between the frequency and the transmission / reception performance of ultrasonic waves) to obtain a frequency-echo height characteristic, The presence or absence of a transition frequency may be determined from the frequency-echo height characteristics.
[0061]
The incident angles of the transmission probe 1 and the reception probe 2 are preferably set so that the plate waves in the A0 mode and the S0 mode can be efficiently transmitted and received. The sheath differs depending on the frequency at which the transmitting probe 1 and the receiving probe 2 operate. Therefore, it is preferable that these incident angles can be appropriately changed in accordance with a change in the thickness of the test object 8 or a frequency band in which the transmitting probe 1 and the receiving probe 2 operate.
[0062]
As described above, according to the first embodiment, the property of the test object 8 is determined based on the change in the intensity of the ultrasonic wave in the test object 8 with respect to the change in the carrier frequency of the burst signal. When the periphery of the object 8 is surrounded by the surrounding solid 10 having a property different from that of the test object 8, the presence or absence of corrosion near the boundary between the test object 8 and the surrounding solid 10 can be easily and non-destructively determined. Can be inspected.
[0063]
Embodiment 2 FIG.
In the first embodiment described above, the flaw detection control unit 7 itself determines the presence or absence of corrosion in the test object 8, but as the second embodiment of the present invention, the flaw detection control unit 7 provides information that facilitates the determination. Then, a tester may determine the presence or absence of corrosion based on this information. For example, the output unit 76, which is a display device, may display the frequency-echo height characteristics in a graph such as a line graph.
[0064]
In the second embodiment, after the signal processing unit 75 calculates the echo height for each carrier frequency f0 to obtain the frequency-echo height characteristic (step ST10 in FIG. 14), the signal processing unit 75 Notifies the output unit 76 of the echo height corresponding to each carrier frequency f0 to the output unit 76, and the output unit 76 outputs the frequency-echo height characteristic, and ends the processing. Also in this embodiment, when the periphery of the test object 8 is surrounded by the surrounding solid 10 having a property different from that of the test object 8, the presence or absence of corrosion near the boundary between the test object 8 and the surrounding solid 10 Can be easily and nondestructively inspected.
[0065]
Embodiment 3 FIG.
Next, an ultrasonic inspection method and an ultrasonic inspection apparatus according to Embodiment 3 of the present invention will be described. Since the configuration of the system according to the third embodiment is the same as that of FIG. 1, the description is omitted, and the operation is described below.
[0066]
In the first embodiment, a burst signal is generated in the arbitrary waveform generator 72, flaw detection is performed by changing the carrier frequency f0 of the burst signal, and the relationship between the carrier frequency and the echo height or the presence or absence of corrosion 5 is inspected. In this case, since the flaw detection is repeatedly performed while changing the carrier frequency, it takes time to determine the presence or absence of the corrosion 5. On the other hand, in the third embodiment, the transmission probe 1 is excited by an electric signal having a wide frequency band, that is, a different frequency, and the frequency spectrum of the echo received by the reception probe 2 is obtained. The presence or absence of corrosion 5 is determined from this frequency spectrum. According to this, the determination result can be obtained in a shorter time than in the method of performing flaw detection by changing the carrier frequency of the burst signal.
[0067]
FIG. 15 is a diagram illustrating an example of a transmission electric signal generated by the arbitrary waveform generation unit (transmission electric signal generation unit) 72 according to the third embodiment. The signal having the wide frequency band may be a spike-like transmission electric signal as shown in FIG. In the third embodiment, the presence or absence of corrosion 5 is determined by exciting the transmission probe 1 once with a spike-like signal as shown in FIG. 15 instead of changing the carrier frequency of the burst signal to perform flaw detection. I do.
[0068]
FIG. 16 is a flowchart illustrating a corrosion inspection method according to the third embodiment. Hereinafter, each step of realizing the corrosion determination method will be described in detail with reference to the flowchart of FIG.
[0069]
In step ST21, the control unit 71 drives the arbitrary waveform generation unit 72, the transmission unit 73, the reception unit 74, the signal processing unit 75, and the output unit 76 to an operable state. Also, in step ST21, the arbitrary waveform generating section 72 generates a spike-like transmission electric signal and transmits it to the transmission section 73. Here, the spike-like signal may be a signal having a positive amplitude as well as a signal having a negative amplitude as shown in FIG. Further, an impulse signal is also included in the spike signal.
[0070]
In step ST22, the transmission unit 73 amplifies the spike transmission electric signal generated by the arbitrary waveform generation unit 72, and excites the transmission probe 1 at a different frequency.
In step ST23, the echo is received by the receiving probe 2. The receiving probe 2 converts the received echo into an echo reception signal.
In step ST24, the receiving echo signal from the receiving probe 2 is amplified by the receiving unit 74 and sent to the signal processing unit 75.
[0071]
In step ST25, the A / D converter inside the signal processing unit 75 converts the received echo signal sent to the signal processing unit 75 into a digital reception echo signal, and converts the resulting digital reception echo signal into a signal processing unit. 75 in the internal memory. In step ST26, the signal processing unit 75 reads the digital reception echo signal stored in the memory in step ST25.
[0072]
In step ST27, the signal processing unit 75 functions as a characteristic calculation unit, and obtains, as a spectrum, a frequency-echo height characteristic representing a relationship between echo heights for different frequencies based on the digital reception echo signal. As a method for obtaining the spectrum, a fast Fourier transform can be used, but another method may be used. When using the fast Fourier transform, the original signal is often multiplied by various window functions (for example, rectangle, Hamming, Hanning, Kaiser, etc.). The frequency may be determined as appropriate according to the frequency characteristics of the probe 1 and the receiving probe 2.
[0073]
In step ST28, the signal processing unit 75 functions as a property determination unit, and checks for the presence or absence of a transition frequency from the frequency-echo height characteristic as the spectrum obtained in step ST27. That is, the lowest peak of the echo height is obtained, and when the difference between the echo height of the frequency near the frequency corresponding to the lowest peak and the echo height of the lowest peak exceeds the threshold, it is determined that the transition frequency exists. For example, if there is the lowest peak of the echo height at the frequency of 1.0 MHz, the echo height at the frequency used for the flaw detection closest to 1.0 MHz (for example, 0.9 MHz and / or 1.0 MHz). Is determined, and when the difference exceeds a threshold, it is determined that a transition frequency exists. In this case, 1.0 MHz as the frequency corresponding to the lowest peak is the transition frequency. By making such a determination, when a transition frequency actually exists but does not clearly appear, it is determined that the transition frequency does not exist.
[0074]
If it is determined that the transition frequency exists, the signal processing unit 75 notifies the output unit 76 of a property determination result indicating that there is no corrosion in the test object 8 in step ST29, and the output unit 76 The result of the property determination is output, and the process ends.
[0075]
On the other hand, when it is determined that the transition frequency does not exist, in step ST30, the signal processing unit 75 notifies the output unit 76 of a property determination result indicating that corrosion is present in the test object 8, and the output unit 76 outputs the property determination result and ends the process.
In this manner, the properties of the test object 8 can be determined based on the relationship between the echo heights for different frequencies included in the spiked transmission electric signal output once.
[0076]
In the above-described ultrasonic flaw detection method, in step ST1, the spike-shaped transmission electric signal is created by the arbitrary waveform generating section 72. If the frequency of the ultrasonic wave propagating to the test object 8 is wide, the transmission electric signal is May not be a spike, and may be, for example, a stepped signal.
[0077]
As in the first embodiment, the frequency characteristics of the transmission probe 1 and the reception probe 2 (specifically, a frequency band in which stable transmission and reception can be performed) are wide so that a transition frequency can be detected. It is desirable. After calculating the echo height, the echo height is corrected based on the frequency characteristics of these probes (the relationship between the frequency and the transmission / reception performance of ultrasonic waves) to obtain a frequency-echo height characteristic, The presence or absence of a transition frequency may be determined from the frequency-echo height characteristics.
[0078]
Further, similarly to the first embodiment, the incident angles of the transmission probe 1 and the reception probe 2 are preferably set so that the plate waves in the A0 mode and the S0 mode can be transmitted and received efficiently. However, this varies depending on the thickness of the test object 8 and the frequency at which the transmitting probe 1 and the receiving probe 2 operate. Therefore, it is preferable that these incident angles can be appropriately changed in accordance with a change in the thickness of the test object 8 or a frequency band in which the transmitting probe 1 and the receiving probe 2 operate.
[0079]
As described above, according to the third embodiment, the property of the test object 8 is determined based on the relationship between the intensity of the ultrasonic wave in the test object 8 and the different frequencies of the transmission electric signal. When the periphery of the object 8 is surrounded by the surrounding solid 10 having a property different from that of the test object 8, the presence or absence of corrosion near the boundary between the test object 8 and the surrounding solid 10 can be easily and non-destructively determined. Can be inspected. In the flaw detection step, if a single transmission electric signal is output, a frequency-echo height characteristic is obtained as a spectrum from a reception echo signal corresponding to the transmission electric signal, so that a determination result can be obtained in a short time.
[0080]
Embodiment 4 FIG.
In the third embodiment described above, the flaw detection control unit 7 itself determines the presence or absence of corrosion in the test object 8, but as the fourth embodiment of the present invention, the flaw detection control unit 7 provides information that facilitates the determination. Then, a tester may determine the presence or absence of corrosion based on this information. For example, the output unit 76, which is a display device, may display the frequency-echo height characteristics in a graph such as a line graph.
[0081]
In the fourth embodiment, after the signal processing unit 75 obtains the frequency-echo height characteristic as a spectrum (step ST27 in FIG. 16), the signal processing unit 75 outputs the frequency-echo height characteristic to the output unit 76. To the output unit 76, and the output unit 76 outputs the frequency-echo height characteristic, and ends the processing. Also in this embodiment, when the periphery of the test object 8 is surrounded by the surrounding solid 10 having a property different from that of the test object 8, the presence or absence of corrosion near the boundary between the test object 8 and the surrounding solid 10 Can be easily and nondestructively inspected, and a judgment result can be obtained in a short time.
[0082]
【The invention's effect】
As described above, according to the present invention, when the periphery of a test object is surrounded by a solid having a property different from that of the test object, the presence or absence of corrosion near the boundary between the test object and another solid Is easily and nondestructively inspected.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an ultrasonic inspection system including an ultrasonic inspection device according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing a waveform of a transmission electric signal used in Embodiment 1 of the present invention.
FIG. 3 is a schematic diagram showing conditions of a sound field simulation in which the principle of the embodiment of the present invention has been discovered.
FIG. 4 is a diagram illustrating a sound field simulation result when a carrier frequency is 0.7 MHz.
FIG. 5 is a diagram showing a particle displacement vector when a carrier frequency is 0.7 MHz.
FIG. 6 is a diagram illustrating a change in amplitude of a received echo signal when the carrier frequency is 0.7 MHz.
FIG. 7 is a diagram showing a sound field simulation result when the carrier frequency is 1.0 MHz.
FIG. 8 is a diagram showing a particle displacement vector when the carrier frequency is 1.0 MHz.
FIG. 9 is a diagram showing a change in amplitude of a received echo signal when the carrier frequency is 1.4 MHz.
FIG. 10 is a diagram showing a sound field simulation result when the carrier frequency is 1.4 MHz.
FIG. 11 is a diagram showing a particle displacement vector when the carrier frequency is 1.4 MHz.
FIG. 12 is a diagram illustrating a change in amplitude of a received echo signal when the carrier frequency is 1.4 MHz.
13A is a diagram showing frequency-echo height characteristics obtained by simulation under three conditions, and FIG. 13B is a schematic diagram showing one of the conditions.
FIG. 14 is a flowchart for explaining a corrosion inspection method according to the first embodiment.
FIG. 15 is a diagram showing a waveform of a transmission electric signal used in the third embodiment.
FIG. 16 is a flowchart illustrating a corrosion inspection method according to the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Transmitting probe, 2 receiving probe, 5 corrosion, 7 flaw detection control unit (ultrasonic flaw detector), 8 test object, 10 surrounding solid, 10A absorption boundary, 11 void, 71 control unit, 72 optional Waveform generation unit (burst signal generation unit, transmission electrical signal generation unit), 73 transmission unit, 74 reception unit, 75 signal processing unit (strength calculation unit, property determination unit, characteristic calculation unit), 76 output unit.

Claims (8)

A burst signal generation unit that generates a burst signal to drive a transmission probe that is driven by an electric signal and transmits an ultrasonic wave into a test object,
A control unit that gives a command to change the carrier frequency of the burst signal to the burst signal generation unit,
Based on an electric signal from a receiving probe that converts the ultrasonic wave propagated in the test object into an electric signal, an intensity calculation unit that calculates the intensity of the ultrasonic wave in the test object,
An ultrasonic flaw detector comprising: a property determining unit configured to determine a property of the test object based on a change in intensity of the ultrasonic wave in the test object with respect to the change in the carrier frequency. The property determination unit determines the peak of the change in the intensity of the ultrasonic wave in the test object with respect to the change in the carrier frequency, and the intensity of the ultrasonic wave in the test object with respect to the carrier frequency near the carrier frequency corresponding to the peak. The method according to claim 1, wherein when the difference from the peak exceeds a threshold value, it is determined that there is no corrosion in the specimen, and otherwise, it is determined that there is corrosion in the specimen. Ultrasonic flaw detector. A burst signal generation unit that generates a burst signal that drives a transmission probe that is driven by an electric signal and transmits an ultrasonic wave into a test object,
A control unit that gives a command to change the carrier frequency of the burst signal to the burst signal generation unit,
Based on an electric signal from a receiving probe that converts the ultrasonic wave propagated in the test object into an electric signal, an intensity calculation unit that calculates the intensity of the ultrasonic wave in the test object,
An output unit that outputs a frequency-echo intensity characteristic indicating a change in the intensity of the ultrasonic wave in the test object with respect to the change in the carrier frequency. A transmission electric signal generation unit that generates transmission electric signals having different frequencies to drive a transmission probe that is driven by an electric signal and transmits ultrasonic waves into a test object,
A frequency-echo intensity characteristic representing a relationship between the intensity of the ultrasonic wave in the test object with respect to the different frequency, based on an electric signal from a receiving probe that converts the ultrasonic wave propagated in the test object into an electric signal. A characteristic calculation unit that calculates
An ultrasonic flaw detector comprising: a property determining unit that determines a property of the test object based on the frequency-echo intensity characteristic. The property determination unit obtains a peak of the intensity of the ultrasonic wave in the test object for a different frequency, and a difference between the intensity of the ultrasonic wave in the test object and the peak for a frequency near the frequency corresponding to the peak is a threshold. The ultrasonic flaw detector according to claim 4, wherein when the value exceeds the threshold value, it is determined that there is no corrosion in the test piece, and otherwise, it is determined that there is corrosion in the test piece. A transmission electric signal generation unit that generates transmission electric signals having different frequencies to drive a transmission probe that is driven by an electric signal and transmits ultrasonic waves into a test object,
A frequency-echo intensity characteristic representing a relationship between the intensity of the ultrasonic wave in the test object with respect to the different frequency, based on an electric signal from a receiving probe that converts the ultrasonic wave propagated in the test object into an electric signal. A characteristic calculation unit that calculates
An ultrasonic flaw detector including an output unit for outputting the frequency-echo intensity characteristic. From the measurement result of the intensity of the ultrasonic wave in the test sample measured by propagating the ultrasonic wave into the test sample while changing the carrier frequency, the peak of the change in the intensity of the ultrasonic wave in the test sample with respect to the change in the carrier frequency. ,
If the difference between the intensity of the ultrasonic wave in the test piece and the peak for the carrier frequency near the carrier frequency corresponding to the peak exceeds a threshold, it is determined that there is no corrosion in the test piece, and In the case of (1), it is determined that there is corrosion in the specimen. From the measurement results of the intensity of the ultrasonic wave in the test object for each frequency measured by propagating ultrasonic waves having different frequencies into the test object, determine the peak of the intensity of the ultrasonic wave in the test object for different frequencies,
When the difference between the intensity of the ultrasonic wave in the specimen and the peak for the frequency near the frequency corresponding to the peak exceeds the threshold, it is determined that there is no corrosion in the specimen, and in other cases (C) determining that there is corrosion in the specimen.

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