KR100993190B1 - Defect detecting apparatus - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flaw detector for detecting defects in composite joints in which a contact medium (couplant) is not available and has high attenuation.

According to the present invention, a defect flaw detector for flaw detection (5) placed on the junction (4) of the flaw detection object (1) by changing the ultrasonic amplitude, the defect flaw detector 100 generates a pulse when the power is applied; A pulse generator 110, a transmission sensor 122 for receiving ultrasonic waves generated by the pulse generator 110 to provide ultrasonic waves to the flaw detector 1, and propagates to the junction portion 4 through the flaw detector (1) A receiving sensor 124 for receiving an acoustic wave to generate an electrical signal, an amplifier 140 for receiving and amplifying the electrical signal generated by the receiving sensor 124, and collecting pulses amplified by the amplifier 140, And a display device 150 for storing and displaying. According to the present invention, there is an advantage that it is easier and more accurate to detect junction defects.

Composites, joints, defects, flaw detection, amplitude, contactless

Description

Defect detecting apparatus

1 is a schematic view showing an outline of a defect inspection apparatus according to the present invention.

2 is a block diagram showing the configuration of a defect inspection apparatus according to the present invention.

Figure 3 is a perspective view showing the external configuration of the sensor assembly which is a main component of the defect inspection apparatus according to the present invention.

Figure 4 is a flow chart showing a defect detection method using a defect detection apparatus according to the present invention.

Figure 5 is a flow chart showing in detail the step of installing the sensor assembly is a step in the defect detection method using a defect detection apparatus according to the present invention.

6 is a graph showing a change in amplitude according to a frequency change in relation to a transmission sensor which is one configuration of a defect detection apparatus according to the present invention;

7 is a graph showing a change in amplitude according to a load change in relation to a load generating means which is one configuration of a defect inspection apparatus according to the present invention.

8 is a damping curve of the pulse according to the change in the distance from the transmitting sensor to the receiving sensor when the load of the load generating means of one component of the defect inspection apparatus according to the present invention is 1440g.

9 is a damping curve of the pulse according to the change in the distance from the transmitting sensor to the receiving sensor when the load of the load generating means of one component of the defect inspection apparatus according to the present invention is 1730g.

10 is a damping curve of the pulse according to the change of the distance from the transmitting sensor to the receiving sensor when the load of the load generating means of one component of the defect inspection apparatus according to the present invention is 2140g.

Fig. 11 is a graph showing the seismic waves at each point by dividing the top surface of the flaw detection object of the flaw detection apparatus according to the present invention into 10 X 15 pieces.

12 to 15 are photographs evaluating defects using a simple attenuation curve method in a defect detection method using a defect detection apparatus according to the present invention.

16 to 19 are photographs evaluating defects using a maximum amplitude comparison method in a defect detection method using a defect detection apparatus according to the present invention.

20 to 23 are photographs evaluating defects using the attenuation curve utilization method in a defect detection method using a defect detection apparatus according to the present invention.

24 to 27 are photographs evaluating defects using a maximum-minimum amplitude utilization method in a defect detection method using a defect detection apparatus according to the present invention.

28 to 31 are photographs in which defects are evaluated by using the attenuation amount in the defect detection method using the defect detection apparatus according to the present invention.

Explanation of symbols on the main parts of the drawings

1. Test object 2. Composite plate

3. Epoxy adhesive 4. Joint

5. Defect 100. Defect flaw detector

110. Pulse generator 120. Sensor assembly

122. Transmitter Sensor 124. Receiver

125. Sensor jig 129. Load generating means

140. Amplifier 150. Display Unit

160. Transport means 162. Rails

164. Feeder S100. Scanning Preparation Stage

S200. Sensitivity correction step S300. Sensor Assembly Installation Step

S320. Sensor assembly mounting process S340. Sensor Assembly Pressurization Process

S400. Pulse generation step S500. Ultrasonic provision step

S600. Acoustic wave receiving step S700. Electric signal amplification stage

S800. Pulse collection display step S900. Sensor Assembly Transfer Step

The present invention relates to a flaw detection device for detecting a defect of the composite joint, more specifically, it is possible to detect the location and size of the defect by providing an ultrasonic wave to the flaw detection object and receiving and analyzing the acoustic wave propagated along the flaw object To a flaw detection device.

In general, the body of the LNG transport ship is able to form the appearance by bonding a plurality of blocks formed of a composite material as an insulating material using an epoxy adhesive.

More specifically, the outer surface of the block is provided with a fibrous composite plate with aluminum foil embedded in the inner part, and then coated with the same composite plate after coating the epoxy adhesive on the composite plate.

At this time, the composite plate is attached over the outer surface of the two blocks to maintain the airtight upper and lower blocks.

And, as described above, a plurality of blocks joined by the composite plate and the epoxy adhesive are not visually confirmed by the joint, and there is a defect in the joint (for example, where the two composite plates are separated because the epoxy adhesive is not evenly applied). The durability is significantly lowered, and it is difficult to maintain up and down.

In general, defect inspection of a composite joint includes radiographic test, infrared test, and ultrasonic test, but the radiographic test cannot be used due to its structure, and the infrared test is difficult to apply.

In the case of the ultrasonic probe business, the reflection wave reflected from the defective part is detected by using a contact medium to detect the defect. When the test sample is thin, high frequency ultrasonic wave is used.

However, if the test specimen is a fibrous composite material and the attenuation of the ultrasonic waves is severe, but the contact medium is used, the contact medium cannot be used because it is difficult to remove the contact medium after the test, and it is difficult to detect defects because the high frequency ultrasonic wave cannot be used. There is this.

An object of the present invention is to solve the above problems, it is possible to detect the location and size of the defect by providing a low frequency ultrasonic wave without contact medium to the flaw detection object and receiving and analyzing the acoustic wave propagated to the junction along the flaw object The present invention provides a defect detection apparatus.

The defect inspection apparatus for flaw detection on the junction of a flaw object by ultrasonic amplitude change WHEREIN: The flaw flaw detection apparatus which flaws the defect posted on the junction part of a flaw object by an ultrasonic amplitude change, The flaw flaw detection apparatus WHEREIN: A pulse generator for generating pulses when power is applied, a transmitting sensor receiving ultrasonic waves generated by the pulse generator and providing ultrasonic waves to the flaw detector, and receiving an acoustic wave propagated to the junction through the flaw detector to generate an electric signal. It characterized in that it comprises a receiving sensor, an amplifier for receiving and amplifying the electrical signal generated by the receiving sensor, and a display device for collecting, storing and displaying the pulses amplified by the amplifier.

The receiving sensor is characterized in that it is provided with a plurality.

The plurality of receiving sensors and the transmitting sensor is characterized in that fixed to the sensor jig.

The pulse generator, the sensor jig and the amplifier are characterized in that they move simultaneously in the same direction by the transfer means.

Ultrasonic waves generated by the transmitting sensor are characterized in that less than 300㎑.

Between the amplifier and the receiving sensor, characterized in that the sensitivity correction means for correcting the received sensitivity of each of the plurality of receiving sensors.

The sensor jig is characterized in that the load generating means for applying the downward load on the flaw detection object and the receiving sensor and the transmitting sensor.

According to such a structure, there exists an advantage which can detect a junction defect easily and correctly.

Hereinafter, with reference to the accompanying FIG. 1, an outline of detecting a defect of a joint using ultrasonic waves will be described before explaining the configuration of the defect inspection apparatus according to the present invention.

1 is a schematic view showing an outline of a defect inspection apparatus according to the present invention.

As shown in the figure, the plurality of flaw objects 1 formed of a composite material is to maintain the state in which the epoxy adhesive 3 is placed between the composite plate (2).

In addition, defects (5) elements, such as pores and foreign substances, may be present in the joint portion 4 in which the epoxy adhesive 3 is disposed, and such defects 5 elements reduce the adhesion between the composite plates 2. As a result, the confidentiality of the flaw detection object 1 becomes difficult.

In addition, such a defect (5) is not visible from the outside of the composite plate (2) it is impossible to visually check.

Accordingly, in the flaw detection apparatus 100 according to the present invention, a transmission sensor 122 for providing ultrasonic waves to the flaw detection object 1 and an elastic wave propagated to the joint portion 4 through the flaw detection object 1 are received and electric A receiving sensor 124 for generating a signal is provided.

Therefore, when the transmission sensor 122 provides the ultrasonic wave to the flaw detection object 1, when the defect 5 is present in the junction 4, the amplitude of the seismic wave is changed, so that the soundness of the junction 4 can be compared. It becomes possible.

The transmitter sensor 122 and the receiving sensor 124 is provided in each of the two in Figure 1, but in the embodiment of the present invention, the receiving sensor 124 is provided with eight pieces of the flaw detection object (1) The entire upper surface was inspected. In addition, the receiving sensor 124 may be provided in more than eight numbers depending on the size of the flaw detection object (1).

In the embodiment of the present invention, first, the low frequency surface wave (elastic wave) is transmitted, and then amplitude is measured to assess the integrity of the junction 4 and, if suspected as a defect 5, additionally analyze the defect (5) as necessary. The study was conducted in the direction of evaluating).

Hereinafter, the configuration of the defect inspection apparatus 100 according to the present invention will be described with reference to FIGS. 2 and 3.

2 is a block diagram showing the configuration of the defect inspection apparatus according to the present invention, Figure 3 is a perspective view showing the external configuration of the sensor assembly which is a main component of the defect inspection apparatus according to the present invention.

As shown in these drawings, the defect detecting apparatus 100 is an apparatus for detecting a defect 5 posted on the junction 4 of an object to be detected by an ultrasonic pulse change, and a pulse generator 110 that generates pulses when power is largely applied. And a sensor assembly configured to receive ultrasonic waves generated by the pulse generator 110 to provide ultrasonic waves to the flaw detector 1 and to receive elastic waves propagated to the junction portion 4 through the flaw detector 1 to generate electrical signals. 120, an amplifier 140 that receives and amplifies the electrical signal generated by the sensor assembly 120, and a display device 150 that collects, stores, and displays the pulses amplified by the amplifier 140. It is composed.

The sensor assembly 120 is for searching for defects 5 of the junction part 4 while moving back and forth while being in contact with the upper surface of the flaw object 1 on the flaw object 1. And a plurality of such sensors are fixed to the sensor jig 125.

That is, the sensor jig 125 forms the exterior of the sensor assembly 120 as shown in FIG. 3, and a plurality of sensor exposure holes (not shown) are formed on the outer surface of the sensor jig 125.

In addition, the above-described transmission sensor 122 and the reception sensor 124 are fitted into the sensor exposure hole.

More specifically, in order to detect the left or right side of the flaw detection object 1, nine sensor exposure holes are formed in the bottom surface of the sensor jig 125, and one of the sensor exposure holes includes The lower end is fixed in an exposed state. The receiving sensor 124 is fixed to the remaining eight sensor exposure holes.

Therefore, the ultrasonic wave generated by one transmitting sensor 122 is separated from the transmitting sensor 122 by the eight receiving sensors 124 arranged in a zigzag shape so that the entire inspection object 1 is inspected. Received as, it is obvious that two sensor jigs 125 should be installed in order to detect the front (including both left and right) of the flaw detection object (1).

One side of the amplifier 140 is provided with sensitivity correction means (not shown) to have the same reception sensitivity under the same conditions. The sensitivity correction means is a configuration for correcting the sensitivity of the plurality of reception sensor 124 and the transmission sensor 122, provided with a number corresponding to the number of the reception sensor 124 and the transmission sensor 122, The same sensitivity can be corrected for the sensor.

Further, the correction of the receiving sensor 124 by the sensitivity correction means (not shown) is performed on the calibration test piece (not shown) before the receiving sensor 124 is inserted into the sensor jig 125 and then the sensor jig 125. It is fixed to the installation.

The load generating means 129 is provided above the sensor assembly 120. The load generating means 129 applies a downward load on the transmitting sensor 122 and the receiving sensor 124 so that the lower ends of the receiving sensor 124 and the transmitting sensor 122 may contact the upper surface of the flaw detection object 1. It is a configuration to ensure that.

That is, since no contact medium is used for the flaw detection object 1, the transmitting sensor 122 and the reception sensor 124 should be mechanically coupled to the flaw detection object 1, in which a load is generated to apply an appropriate pressure. Means 129 are provided.

In the preferred embodiment of the present invention, the load generating means 129 is applied to a metal block having a weight of 1500g or more.

The pulse generator 110 and the amplifier 140 are provided on the left side of the sensor assembly 120. The pulse generator 110 is configured to generate a pulse when power is applied, and is electrically connected to the transmission sensor 122.

Therefore, the pulse generated by the pulse generator 110 is transmitted to the transmission sensor 122, the transmission sensor 122 is provided with such a pulse to generate an ultrasonic wave.

The amplifier 140 is electrically connected between the sensor assembly 120 and the display apparatus 150 to amplify an electric signal. More specifically, the amplifier 140 is located between the receiving sensor 124 and the display apparatus 150. .

In the case of the receiving sensor 124, the ultrasonic sensor is rapidly attenuated while being transmitted along the inspection object 1 even if a sensor having a high sensitivity is used, and thus the transmitting sensor 122 generates a weak electric signal. Difficult to detect).

Therefore, the electrical signal transmitted from the receiving sensor 124 to the display device 150 is preferably amplified through the amplifier 140.

The display device 150 is provided on the left side of the amplifier 140. The display device 150 is configured to collect, store, and display the pulses amplified by the amplifier 140, and may be variously applied to a desktop cup computer and a laptop cup computer within a range in which an arithmetic device is built.

On the other hand, the amplifier 140, the pulse generator 110 and the sensor assembly 120 is configured to detect the defect (5) while being transferred in the longitudinal direction of the flaw detection object (1).

That is, the transfer means 160 is provided below the amplifier 140 and the pulse generator 110. The conveying means 160 is a plurality of rails 162 placed in parallel in the longitudinal direction of the flaw detection object (1) and the transfer table for linear reciprocating movement in the longitudinal direction of the flaw detection object (1) placed on the upper surface of the rail (162) ( 164).

In addition, the amplifier 140 and the pulse generator 110 are seated on the upper left side of the carriage 164, and the sensor assembly 120 is fixed to the lower right side of the carriage 164.

Therefore, when the carriage 164 moves along the rail 162, the amplifier 140, the pulse generator 110, and the sensor assembly 120 are transferred at the same direction and speed.

Hereinafter, a method of flaw detection using the flaw detection device 100 configured as described above will be described with reference to FIGS. 4 and 5.

4 is a flowchart showing a defect detection method using a defect detection apparatus according to the present invention, Figure 5 shows in detail the step of installing the sensor assembly, which is a step in the defect detection method using a defect detection apparatus according to the present invention. Flowchart is shown.

First, the flaw detection object 1, in which a plurality of composite members are coupled, is prepared by the joint portion 4, and the flaw detection object 1 and the rail 162 are placed in parallel (see FIG. 2). S100)

Thereafter, a sensitivity correction step S200 of correcting the sensitivity of the plurality of reception sensors 124 is performed. The sensitivity correction step (S200) is a process of equally correcting the sensitivity of the plurality of reception sensors 124 using the sensitivity correction means.

Thereafter, the transmitting sensor 122 and the receiving sensor 124 are fixed to the sensor assembly 120.

Then, the sensor assembly mounting step (S300) for coupling the sensor assembly 120 to the transfer table 164 to position the sensor assembly 120 above the flaw detection object 1 is performed.

The sensor assembly installation step (S300) is a step of maintaining the state in which the lower end of the transmitting sensor 122 and the receiving sensor 124 in contact with the upper surface of the flaw detection object 1 through a number of processes.

That is, the sensor sensor assembly installation step (S300), the sensor assembly 120 is coupled to the transfer means 160 as shown in Figure 5 so that the sensor assembly 120 is located above the flaw detection object (1) The assembly mounting process (S320) and the sensor assembly 120 is provided with a load generating means 129 on the upper side of the sensor assembly pressure sensor (S340) to apply a load to the flaw detection object (1).

Therefore, the sensor assembly 120 is fixed in a state suspended from the transport table 164, the movement is limited, and the lower end of the transmitting sensor 122 and the receiving sensor 124 by the load of the load generating means 129 By being pressed downward, it comes into contact with the upper surface of the flaw detector 1.

When the sensor assembly installation step S300 is completed according to the above process, a pulse generation step S400 for generating pulses by applying power to the pulse generator 110 is performed.

The pulse generated in the pulse generating step (S400) is transmitted to the transmission sensor 122 that is electrically connected to the pulse generator 110, the transmission sensor 122 receives the pulse to the flaw detection object (1) By providing ultrasonic waves, an ultrasonic wave providing step S500 is followed.

At the same time as the ultrasonic wave providing step S500 is performed, the receiving line TM124 receives an elastic wave transmitted through the flaw detection object 1 to generate an electrical signal.

In this case, the plurality of receiving sensors 124 are arranged to have different distances from the transmitting sensor 122 and detect the defect 5 below each position.

The electrical signal received in the acoustic wave receiving step S600 is amplified by the amplifier 140, followed by the electrical signal amplifying step S700.

The electrical signal amplified by the electrical signal amplification step S700 is transmitted to the display apparatus 150 to be collected, stored, and displayed, and finally, the detection of the defect 5 is completed by the pulse collection display step S800.

Thereafter, the sensor assembly 120 is transferred to the adjacent flaw detection area by the sensor assembly transfer step (S900), and then the flaw detection is repeatedly performed through the sensor assembly pressing process (S340).

In the sensor assembly transfer step (S900), the transfer means 160 helps to linearly move the sensor assembly 120 in the longitudinal direction of the flaw detection object 1, and at the same time, the amplifier 140 and the pulse generator 110 also. The transfer means 160 is transferred in the same direction as the sensor assembly 120.

Therefore, the sensor assembly transfer step (s900) may be converted in the direction before / after the predetermined time of the transfer means 160 according to the length of the flaw detection object (1), to inspect the entire junction of the flaw detection object (1) It is preferable that the operation is continuously performed until the pulse collection display step (* s800) is completed.

In the pulse collection display step S800, the health inside the junction 4 may be evaluated through various methods.

That is, the pulse collection display step (S800), a simple attenuation curve using method for simply displaying the amplitude change according to the distance from the transmitting sensor 122 to the plurality of receiving sensors 124 to evaluate the soundness according to the amount of amplitude attenuation; , Using the maximum amplitude comparison method to compare measured values of the same distance as the maximum amplitude, the attenuation curve method to compare the amplitude of the rest part with the amplitude of a healthy part, and the maximum and minimum amplitude measured at the same distance. Maximum-minimum amplitude use method to evaluate the health with a standardized value, attenuation amount and attenuation curve obtained by subtracting the amplitude measured at the transmitting sensor 122 closest to the transmitting sensor 122 and the amplitude measured at the remaining transmitting sensor 122 The attenuation amount which evaluates the soundness by subtracting the attenuation amount expected for each receiving sensor 124 by the use method detects the defect 5 inside the junction 4 using at least one of the use methods. It is able to.

Experimental results for various methods applied to the pulse collection display step (S800) will be described below.

Hereinafter, the experimental procedure and the results performed according to the defect detection method using the defect detection apparatus according to the present invention will be described below.

First of all, the ultrasonic test method was selected as the most appropriate non-destructive test method to check the bonding state of the junction part 4. Among the ultrasonic test methods, the vertical reflection method and the surface wave method were considered. The research was conducted using the method.

The limitation of the experiment related to the present invention is that it is not possible to use a very important contact medium in the ultrasonic test. In order to perform the experiment without using the contact medium, an optimal frequency should be selected.

Therefore, in the experiments related to the present invention, the variation of the amplitude was observed by experimenting with the transmitting sensor 122 and the receiving sensor 124 having the frequencies of 750, 375, and 175 kHz, respectively. The sensitivity was the best.

That is, Figure 6 is a graph showing a change in amplitude according to the frequency change of the transmission sensor 122 and the reception sensor 124, which is one component of the defect detection apparatus according to the present invention, each frequency used as shown in the figure Of the sensors at 175 kHz, the highest sensitivity was observed.

In other words, as the frequency increases, the sensitivity decreases. However, as shown by the vertical lines in FIG. 6, at a frequency lower than 300 kHz, appropriate sensitivity was obtained for defect detection.

On the other hand, since the contact medium is not used in the flaw detection object 1 in the experiment of the present invention, the load generating means 129 is further provided as described above. In addition, the load generating means 129 confirmed the reception state of the pulse by applying a variety of weights to provide the optimal load to the transmitting sensor 122 and the receiving sensor 124.

That is, FIG. 7 is a graph showing a change in amplitude according to the load change in relation to the load generating means 129 which is one component of the defect inspection apparatus according to the present invention, and the load generating means 129 as shown in FIG. ) Is increased to about 1000g, the amplitude change is not constant, and a deviation occurs and it is unstable.

On the other hand, when the load of the load generating means 129 is more than 1500g it can be seen that the signal amplitude increases linearly as the load increases.

8 to 10 show attenuation curves of pulses different from the distance change from the transmitting sensor 122 to the receiving sensor 124 when the load generating means 129 has loads of 1440g, 1730g, and 2140g. .

8 to 10, the point number of the horizontal axis is set to point number 1 when the separation distance from the transmitting sensor 122 to the receiving sensor 124 is 4 cm, and each point 1 cm away from the point number 1. number 2, point number 3.

As shown in the figure, in point number 1, the amplitude increases as the load increases. After point number 1, the amplitude did not change significantly even if the magnitude of the load changed.

In addition, the amplitude was measured 10 times for each point number, and it can be seen that the deviation of the measured amplitude is severe every time even at the same position. On the other hand, the amplitude at the point number 2 was lower than the amplitude at the point number 3 and the point number 4, and the same pattern is exhibited in all the flaw detection objects 1 regardless of the load magnitude of the load generating means 129.

Therefore, the load generating means 129 is configured to apply a load of 1500g or more, it is of course possible to apply a metal block.

Fig. 11 shows a graph of the seismic waves measured at each point by dividing the top surface of the test object into 10 X 15 pieces.

In FIG. 11, the graph adjacent to the left / right is a graph measured by the receiving sensor 124 located at the same distance from the transmitting sensor 122, and the receiving sensor 124 is farther away from the transmitting sensor 122 toward the upper side. It is a graph measured through.

As shown in the figure, it can be seen that the signal amplitude shows a great difference in each position in the closest place (the lowest point in FIG. 11) to the transmitting sensor 122.

This is similar to the deviation in point number 1 of FIGS. 8 to 10 measured several times in one place, and the circled circle in FIG. 11 indicates the location of the artificially made defect 5 for the experiment.

In more detail, despite the discreteness of the data, it can be seen that the amplitude decreases as the distance increases with some discrete width, and this tendency has an experimentally significant meaning.

In general, ultrasonic waves decrease in amplitude as the propagation distance increases. The measurement amplitude values vary somewhat in width by the surface state of the measuring point, but the amplitude decreases with increasing distance, which is consistent with the theory. If the amplitude at a position is less than the reference value at that distance at that distance, it can be regarded as a defect 5.

In FIG. 11, the vicinity of the circle is not bonded to the artificial defect 5, and it is understood that the amplitude is significantly lower than the surroundings at this point, and the amplitude change according to the unhealthy state of the junction 4 is determined by the flaw detection object 1. Defects 5 (unhealthy joints) can be judged because they are larger than the measurement deviation due to the surface condition of.

Further, in the pulse collection display step S900 of the present invention, the defect 5 can be detected by using one or more of a simple attenuation curve method, a maximum amplitude comparison method, a damping curve method, a maximum-minimum amplitude method, and a damping amount method. .

12 to 15 show photographs evaluating defects using the simple attenuation curve using method, and FIGS. 16 to 19 show photographs evaluating defects using the maximum amplitude comparison method. FIG. 23 shows photographs evaluating defects using the attenuation curve utilization method.

24 to 27 show photographs evaluating defects using the maximum-minimum amplitude utilization method, and FIGS. 28 to 31 show photographs evaluating defects using the attenuation amount usage method.

Where the defect 5 is located on the flaw detection object 1 (inner circle surrounded by the circle) as described above, even if the flaw is detected by applying the above-mentioned multiple use method, a different aspect is observed when compared with the place where the defect 5 does not exist. I can see that it stands out.

The scope of the present invention is not limited to the above-described embodiments, and many other modifications based on the present invention will be possible to those skilled in the art within the scope of the present invention.

In the present invention, the ultrasonic wave is injected to the junction and the amplitude and position of the reflected ultrasonic wave are analyzed to configure the size and position of the defect.

Therefore, there is an advantage that it is easier and more accurate to detect defects in the joints that are not visible to the naked eye.

In addition, since the inside of the joint can be inspected without destroying the flaw object, manufacturing cost is reduced.

Claims (7)

delete delete A flaw flaw detector for flaw detection on the junction of a flaw object by ultrasonic amplitude change, wherein the flaw flaw detector is provided with a pulse generator for generating a pulse when power is applied and a pulse generated by the pulse generator. A transmitting sensor providing ultrasonic waves to the plurality of receiving sensors, a plurality of receiving sensors generating an electric signal by receiving the elastic wave propagated to the junction through the flaw detection object, a sensor jig to which the plurality of receiving sensors and the transmitting sensor are fixed, and the receiving And an amplifier for receiving and amplifying the electrical signal generated by the sensor, and a display device for collecting, storing, and displaying the pulses amplified by the amplifier. Above the sensor jig, And a load generating means for allowing the receiving sensor and the transmitting sensor to apply a downward load on the flaw detection object. 4. The flaw detection apparatus according to claim 3, wherein the pulse generator, the sensor jig, and the amplifier move simultaneously in the same direction by a transfer means. 5. The defect inspection apparatus according to claim 4, wherein the ultrasonic waves generated by the transmitting sensor are 300 kHz or less. The method of claim 5, wherein between the amplifier and the receiving sensor, And a sensitivity correction means for correcting the reception sensitivity of each of the plurality of reception sensors. delete

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