JP3531019B2 - Defect identification method by ultrasonic flaw detection - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect identification method by ultrasonic flaw detection suitable for identifying the shape of a defect tip on a steel surface or in steel using ultrasonic waves.

[0002]

2. Description of the Related Art Conventionally, it has been considered difficult to quantitatively grasp a defect in the field of ultrasonic flaw detection, for example, to specify the height or depth of a defect, the shape of a defect, and the like. From the strength, the height of the defect and the sound pressure intensity were assumed to be in a proportional relationship, and the approximate height of the defect was estimated.
However, in reality, the height of the defect and the sound pressure intensity change depending on various conditions such as the shape and inclination of the defect, and it can only be handled as a guide.

FIG. 12 is an explanatory diagram of conventional flaw detection by corner echo. In this figure, 2 is a probe, 3 is a test piece, and 10 is an ultrasonic reflection path. In this figure, even though the defects (a) and (b) have the same defect height, a reflected wave that cannot be detected by the probe 2 is generated in (b) due to the difference in the shape of the ultrasonic reflection surface, and the corner echo is generated. Difference occurs in the reflected sound pressure of the defect, the corner echo sound pressure of the defect (b) becomes a corner echo sound pressure corresponding to the defect (c), and the defect (c)
It is determined that the defect height is equivalent to. In the conventional ultrasonic flaw detection method that uses only such corner echo as a signal, it is very difficult to quantitatively grasp the defect. Recently, a method for accurately measuring the height of a defect using the peak echo at the edge has been proposed and partially put into practical use, but this also does not provide information on the shape of the defect. Absent. As an example of the defect height measurement using the edge peak echo, the case of the bottom opening defect will be described.

FIG. 13 is an explanatory view of general corner echo and end echo. First, in the figure, B is a reflected wave conventionally used in ultrasonic flaw detection, which is called a corner echo. On the other hand, A is a point reflection from the end of the defect, which is a signal preceding the corner echo and is called an end echo.

FIG. 14 is an explanatory diagram of defect height measurement using a general end echo. In the figure, 5 is an end echo waveform, 6 is a corner echo waveform, W is the beam path when the peak of the end echo is obtained, and t is the test piece 3.
Is the plate thickness, θ is the refraction angle, and the defect height H is obtained by the equation (1). H = t-Wcos θ …………………………………………………… (1) As mentioned above, the edge peak echo method is the reflection from the edge of the defect. The probe position where the end echo reaches the peak is obtained, and the defect height is obtained from the ultrasonic beam path distance and the refraction angle at this time.

FIG. 15 is an explanatory diagram for explaining the relationship between the probe frequency and the end echo discrimination. In this figure, 7 is an end echo path and 8 is a corner echo path. To use the edge peak echo method, it is necessary to identify and detect the edge echo, but as shown in this figure, as the defect height becomes lower, the path distance between the edge echo and the corner echo becomes shorter. However, it becomes difficult to distinguish between the two. Therefore, in the end peak echo method which is generally performed conventionally, the frequency is 5 MHz.
Since the following probe is used, the defect height of several mm is the detection limit in order to accurately measure the defect height.

[0007]

A nondestructive inspection technique capable of detecting and identifying a defect existing on the surface and inside of a structural material that cannot be detected by the naked eye is a technique for ensuring the safety and reliability of the structure. Although it is important for the conventional ultrasonic flaw detection method to obtain information on the presence or absence of a defect and the height of the defect, it is impossible to obtain any information on the shape of the defect. Therefore, it was impossible to judge the importance of the defect. Determining the importance of a defect is determining whether or not the defect is a serious problem, that is, whether the possibility of crack growth is large or small.

FIG. 16 is an explanatory view for explaining the types of defects existing on the surface of a general structural material. As shown in this figure, defects of structural materials include those with a sharp tip shape and large crack propagation, and those with welding defects, such as undercuts and blow holes, which have a smooth tip and small crack growth. However, it is necessary to prioritize the repair of defects having a large crack-growing property, but this determination cannot be made by the conventional technique, and therefore all the detected defects have to be treated. This is especially true for chemical plants that have enormous numbers of inspection points and require treatment within a limited period of time.
It becomes a serious problem in power plants. Further, also in the edge peak echo method capable of accurately measuring the defect depth, the detection limit is several mm as described above, and it is difficult to deal with minute defects. Since the end echo itself is a very weak echo, it requires skill to find and identify it.

In the edge peak echo method, an ultrasonic shielding material is installed on the surface of the material to be inspected between the ultrasonic wave incident point and the scratch in order to prevent an interfering echo which hinders the identification of the edge echo. Japanese Patent Application No. 1-6996, Japanese Patent Application No. 59-203199, Japanese Patent Application No. 59-1 discloses a method for detecting flaws from a plurality of directions for a defect to detect an end echo with high accuracy.
Japanese Patent Application No. 19798, Japanese Patent Application No. 58-246338 and the like have been proposed, but these are all for accurately obtaining the beam path length of the end peak echo, and paying attention to the end echo sound pressure intensity itself. There is no. An object of the present invention is to solve the above-mentioned problems, to identify the tip shape of a detected defect, and to judge the importance of the defect.

[0010]

The above object is to provide a defect identification method by ultrasonic flaw detection in which an ultrasonic wave is transmitted from a probe to a subject and an echo reflected from a defect portion is received to identify a defect. A characteristic formula expressing the relationship between the defect shape and the end echo sound pressure level of the model defect is obtained, the end echo sound pressure level of the object is measured, and introduced into the characteristic formula to identify the defect tip shape. It is achieved by In the defect identification method by ultrasonic flaw detection, in which an ultrasonic wave is transmitted from the probe to the subject and an echo reflected from the defect is received to identify the defect, the model defect shape and the end echo of the model defect are previously detected. Obtain the characteristic curve that represents the relationship with the sound pressure level, set the threshold values for the fatigue defect with a sharp tip and the welding defect with a curvature at the tip on the characteristic curve, and set the echo sound pressure level at the end of the subject. measured and compared to the threshold value is achieved by performing the identification of the welding defects tip having a curvature in sharp fatigue defects and tip. In the defect identification method by ultrasonic flaw detection, in which an ultrasonic wave is transmitted from the probe to the subject and an echo reflected from the defect is received to identify the defect, the model defect shape and the end echo of the model defect are previously detected. A characteristic curve representing the relationship with the sound pressure level is obtained, and thresholds for a fatigue defect having a tip curvature R of almost 0 and a welding defect having a tip curvature R of 0.1 mm or more are set on the characteristic curve, and by measuring the end echo sound pressure level compared to the threshold value is achieved by performing the identification of the welding defects tip having a curvature in sharp fatigue defects and tip. The above-mentioned object is a defect identification method by ultrasonic flaw detection in which ultrasonic waves are transmitted from a probe to a subject and an echo reflected from a defect portion is received to identify a defect,
Each echo of an end echo that is a reflection from the defect top for a material on which a model defect is formed in advance, a bottom reflection end echo that is the material bottom reflection of the end echo, and a corner echo that is a reflection from the defect base. By determining the correlation between the path distance and the defect shape between the echoes, measuring the path distance between the echoes of the subject, and identifying the shape of the defect tip using the correlation between the at least one echo path distance and the defect shape. To be achieved. In the defect identification method by ultrasonic flaw detection, in which the ultrasonic wave is transmitted from the probe to the subject and the echo reflected from the defect portion is received to identify the defect, the above-mentioned purpose is to analyze the frequency of the echo and This is achieved by determining whether or not an end echo has occurred.

[0011]

According to the above structure, the sound pressure level of the end echo changes depending on the tip shape of the defect, and the correlation between the tip shape of the defect and the sound pressure level of the end echo is obtained in advance. Then, the tip shape of the defect can be identified by comparing with the end echo sound pressure level of the subject. Also, paying attention to the fact that the path distance between the corner echo and the end echo, and the bottom surface reflection end echo change depending on the defect tip shape, and obtain the correlation between the path distance between each echo and the defect shape in advance. The shape of the tip of the defect of the subject can be identified by setting it in advance. Then, perform frequency analysis of the echo waveform at the time of flaw detection, pay attention to the characteristic that there are two or more frequency peaks when the end echo occurs, and confirm in advance whether or not the end echo occurs from the number of frequency peaks. Due to
The end echo and the corner echo can be easily identified.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. First, the device configuration of this embodiment will be described. FIG. 1 is a block diagram for explaining the device configuration of an embodiment of the present invention. This figure is a basic system diagram of a flaw detector for identifying defects. 1 is a flaw detector, 2 is a probe, 3 is a test piece, 4 is a defect, 11 is a frequency analysis device, and 12 is an automatic sensitivity adjustment device. , 14 is an inter-echo path distance measuring device, 15 is a defect shape identifying device, and 16 is a characteristic curve. The ultrasonic waves emitted from the probe 2 toward the defect 4 in the test piece 3, which is the subject, are reflected by the end of the defect 4 and then captured by the probe 2.
This signal is displayed and recognized as an end echo by the flaw detector 1. At this time, the position of the defect 4 may be detected in advance by normal ultrasonic flaw detection, or may be detected by using the corner echo of this apparatus. Here probe 2
In addition, by using the one having a frequency of 10 MHz or more, it becomes possible to measure a minute defect having a defect height of 0.5 mm or less. The frequency analysis device 11 analyzes the frequency of the ultrasonic reflection echo, and when there are two or more frequency peaks, it is determined that there is an end echo, and the end echo is identified.
Use as supplementary information for identification. The automatic sensitivity adjustment device 12 adjusts the sensitivity level of the flaw detector so that the echo height of the received end echo is a constant value that is arbitrarily set, and outputs the flaw detector sensitivity value at this time to the defect shape identification device 15. . The inter-echo path distance measuring device 14 reads the path distances between the echoes of the corner echo, the end echo, and the bottom reflection end echo from the echo waveform, and outputs the respective numerical values to the defect shape identifying device 15. The defect shape identification device 15 performs the following calculations and determinations based on these data.

1) From the relationship between the defect tip shape and the edge echo sound pressure level (sensitivity of the flaw detector 1) obtained in advance, a sharp tip and a tip having a curvature (having a large crack progressability) A threshold value for determining that the crack propagating property is small) is obtained, and this is compared with the end echo sound pressure level from the test piece 3 to identify and determine the defect tip shape. However, since the relationship between the defect tip shape and the end echo sound pressure level changes depending on the characteristics of the flaw detection system used, the numerical value is not particularly limited. 2) The previously obtained correspondence between the defect tip shape and the end echo sound pressure level is stored as a characteristic curve 16, and the tip shape corresponding to the end echo sound pressure level from the test piece 3 is estimated from this. 3) The tip curvature is obtained from the relational expression obtained in advance from the distance between the echoes. Since the relationship between the defect tip shape and the end echo sound pressure level differs depending on the characteristics of the flaw detector 1 and the probe 2 used, it is necessary to obtain the characteristic curve 16 of the system used for inspection in advance. In the above, the comparison determination is performed using the defect shape identification device 11, but the effect is the same even if a person performs the comparison determination based on the characteristic curve 16.

Next, the identification method of this embodiment will be described. The sound pressure level of the end echo changes depending on the tip shape of the defect. In order to apply this phenomenon to the identification of the tip shape of a defect, the following ultrasonic flaw detection experiment was conducted to confirm the characteristics. The system configuration for the ultrasonic flaw detection test is the same as that shown in FIG. The probe 2 connected to the flaw detector 1 is used to perform flaw detection on the test piece 3 on which various prepared simulated defects have been processed, and the characteristics of the end echo sound pressure level due to the defect tip shape are confirmed. Since the probe 2 handles a weak end echo, a wide-band point-converging type is suitable. Although this is used in this embodiment, a narrow-band, non-converging type is also possible. The frequency of the probe 2 needs to be selected according to the size of the target defect, but at least a frequency of 10 MHz or more is required when dealing with a defect of about 0.5 mm, and a frequency of 10 MHz is used in this experiment. It was used.

FIG. 2 is a perspective view of a test piece simulating a fatigue defect according to an embodiment of the present invention. This figure shows the shape of the test piece for cracks caused by artificial fatigue. FIG. 3 is a perspective view of a test piece simulating a welding defect according to the embodiment of the present invention. This figure shows the shape of a U-shaped machined crack test piece. The test piece 3 is an artificial fatigue crack (defect depth 1.0 mm, 0.5 mm) simulating an actual defect shown in FIG. 2 in which the tip shape is variously changed.
And a machining crack shown in Fig. 3 (defect depth 2.0 m
m, 1.0 mm, 0.5 mm) was prepared as a bottom opening defect in a flat plate test piece.

FIG. 4 is an explanatory view for explaining ultrasonic flaw detection according to the embodiment of the present invention. As shown in the figure, 5 is an end echo waveform and 6 is a corner echo waveform. When flaw detection is performed by the probe 2 from the side opposite to the defect 4, the ultrasonic waves emitted from the flaw 2 travel through the test piece 3 at an incident angle of 45 °, are reflected at the end of the defect 4, and are echoed at the end. A becomes the end echo waveform 5, and the corner echo B becomes the corner echo waveform 6 after a delay corresponding to the defect height from this end echo.
Is observed on the screen of the flaw detector 1. At this time, the sensitivity of the flaw detector 1 required for adjusting the echo height (sound pressure level) of the end echo to a constant value P is obtained as a dB value, and this is compared with each defect tip shape. Table 1 shows the relationship between each tip shape of the defect 4 of the test piece 3 and the end echo sound pressure level (dB).

[0017]

[Table 1]

When the tip has a curvature (tip curvature =
R2.0 to R0.1) is 60 to 72 dB, and 85 to 89 d in the case of a fatigue crack with a sharp tip (tip curvature ≈ 0)
It was B, and a level difference of 10 dB or more was observed between the two, confirming that fatigue cracks could be identified. Also, from this result, it was confirmed that the end echo sound pressure level does not depend on the defect height, but changes depending on the tip shape (tip curvature), and it is possible to estimate the tip shape from this relationship. This is also clear from FIG. 5, which is a graph of Table 1.

FIG. 5 is a chart showing the relationship between the defect tip shape and the end echo sound pressure level according to the embodiment of the present invention. In this figure, the horizontal axis represents the curvature of the defect tip, and the vertical axis represents the sensitivity of the flaw detector 1. Here, the tip curvature of the artificial fatigue crack is 0.005 m
It is plotted assuming m. It can be seen from this figure that the sensitivity of the flaw detector 1 decreases as the curvature of the defect tip increases.

FIG. 6 is an explanatory view showing the relationship between the defect tip shape and the end echo sound pressure level according to the embodiment of the present invention. When the tip is very sharp as in this figure (A), the end echo is a point reflection pure end echo, but this figure (B)
When the tip has a curvature as shown in (C) and (C), the surface echo by the reflecting surface of the tip is dominant in the end echo, and therefore the sound pressure level changes depending on the size of the reflecting surface according to the curvature of the tip. It will be. Therefore, by determining the end echo sound pressure level at this time, the tip shape can be identified. In the defect height measurement using the conventional end peak echo, the main focus was to obtain the beam path length when the end echo reaches the peak, but in the present embodiment, as described above, the sound pressure level itself Focusing on the difference, this is used for defect shape identification. The same effect can be obtained by obtaining the ratio of the sound pressure level of the end echo and the sound pressure level of the corner echo.

Next, the frequency of the probe necessary for identifying the end echo will be described. According to the above-mentioned experiment, when the probe 2 having the frequency of 10 MHz and the angle of inclination of 45 ° is used, the end echo having the defect height of 0.5 mm can be identified, but the end echo of the defect height of 0.25 mm is recognized. It was difficult to identify. This is due to the relationship between the distance between the end echo transmission point and the corner echo transmission point and the wavelength λ.
When it becomes, it is considered that the end echo is in a form overlapping with the corner echo, which makes identification difficult.

FIG. 7 is an explanatory view for explaining the relationship between the probe frequency and the end echo discrimination ability according to the embodiment of the present invention. Here, the frequency of the probe 2 is 10 MHz, but as a result of frequency analysis of the received waveform, the frequency at the time of receiving the end echo is 4
It was confirmed that the frequency was up to 6 MHz. Therefore, it will be examined based on this. Considering that it is possible to identify the end echo if there is one wave in the distance between the transmitting points, the defect height is 1.0 mm and 1.0.
Since there are 7 waves, the critical dimension for one wave is estimated as follows. 1.0mm × 1 wave / 1.7 wave = 0.58mm ……………………………………………………………………………………………………………………………… （………………………………………… （2） Partial echo discrimination limit is 0.58 mm
And is in good agreement with the experimental results. Therefore, the wavelength λ
Is shorter than the distance between the transmitting points, the end echo can be identified, and it can be confirmed that the frequency of the probe 2 must be at least 10 MHz or more to measure the defect height of 0.5 mm. It was

Further, regarding the identification of the end echo, the frequency analysis of the ultrasonic reflection echo was tried, and the following findings were obtained. Figure 8
FIG. 4 is an explanatory diagram illustrating the relationship between the occurrence of an end echo and the number of frequency peaks according to the embodiment of this invention. As a result of performing the frequency analysis of the ultrasonic reflection echoes on all the test pieces shown in FIGS. 2 and 3, as shown in this figure, when the end echoes can be identified at a defect depth of 0.5 mm or more, two or more echo echoes can be identified. Whereas a frequency peak occurs, the edge echo is buried in the corner echo like a defect depth of 0.25 mm, and when it is difficult to identify the edge echo, only one frequency peak occurs. found. If the occurrence of the end echo is confirmed in advance using this characteristic, the end echo can be easily identified and specified. The operation of the defect tip shape identification method focusing on the sound pressure level of the end echo has been described above.
Next, a description will be given of a method of identifying a defect tip shape, focusing on a change in the path distance between echoes of a corner echo, an edge echo, and a bottom reflection edge echo. First, in order to clarify how the change in the defect tip shape affects the path distance of each echo, ultrasonic simulation was performed and ultrasonic path analysis was performed.

FIG. 9 is an explanatory view of a defect subjected to ultrasonic simulation of the embodiment of the present invention. As shown in this figure, the model defect has a height on the bottom surface of 0.5 mm and a radius of 0.5 mm.
It has a semicircular shape of 5 mm. FIG. 10 is a pattern diagram showing an ultrasonic simulation result of the defect shown in FIG. Figure 1
1 is a flaw detection waveform of the ultrasonic simulation of the defect shown in FIG. Here, A, B, C, and D in FIGS. 10 and 11 correspond to each other. Described below is the route through which each echo of the actual flaw detection waveform is reflected when ultrasonic waves are incident on the defect shown in FIG. In FIG. 9, the ultrasonic wave incident from the upper left 45 ° is 45
It is reflected at point a on the cylinder in the ° direction and becomes a reflected wave A. Further, the wave reflected at the left corner b becomes the reflected wave B. Part of the ultrasonic wave incident at point a passes over the defect, is reflected at the right corner c of the defect, part of it goes around in the upper right direction, part of it wraps around the defect surface, and returns to point a It becomes C. The reflected wave B is
Part of the light passes through point a along the defect surface, then is reflected at the right corner c, part of it propagates to the upper right, and part of it propagates along the defect surface in the same way as the reflected wave C and returns to the incident direction. Wave D. The reflected waves A, B, C, D received by the probe 2 are A, B, C, D in FIG. Distance A between each reflected wave
Table 2 shows a comparison between the experimental values of B, AC and CD and the theoretical values obtained from the distances in FIG. The two are in good agreement,
As a result, the ultrasonic path of each reflected wave could be identified.

[0025]

[Table 2]

Next, by utilizing this phenomenon, the curvature R of the defect tip shape can be estimated by the following method. First, A
The ultrasonic path difference corresponding to the path distance between C is

[0027]

[Equation 1]

As described above, the tip curvature estimated by this method is in good agreement with the true value of 0.5 mm, confirming the validity of this estimation method. Although a semicircular defect has been described above as an example, other tip shapes can be estimated by the same ultrasonic analysis. As described above, according to the present embodiment, it becomes possible to obtain information regarding the shape of the defect tip, which was impossible in the past, and it is possible to identify the defect based on this information, and to judge the importance of the defect. It is possible to give it down.

[0029]

According to the present invention, the correlation between the tip shape of the defect and the sound pressure level of the end echo is obtained in advance, and the tip shape of the defect is determined by comparing with the end echo sound pressure level of the subject. It is possible to obtain the effect of enabling identification and judgment of the importance of defects. The shape of the defect tip can be identified by previously obtaining the correlation between the defect shape and the path distance between the corner echo and the edge echo, and the bottom surface reflection edge echo.
Then, the frequency of the echo waveform is analyzed at the time of flaw detection, and the presence or absence of the end echo is confirmed in advance from the number of frequency peaks, whereby the end echo and the corner echo can be easily distinguished.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a device configuration according to an embodiment of the present invention.

FIG. 2 is a perspective view of a test piece simulating a fatigue defect according to an example of the present invention.

FIG. 3 is a perspective view of a test piece simulating a welding defect according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating ultrasonic flaw detection according to an embodiment of the present invention.

FIG. 5 is a chart showing a relationship between a defect tip shape and an end echo sound pressure level according to an example of the present invention.

FIG. 6 is an explanatory diagram showing a relationship between a defect tip shape and an end echo sound pressure level according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram illustrating the relationship between the probe frequency and the end echo discrimination capability according to the embodiment of this invention.

FIG. 8 is an explanatory diagram illustrating a relationship between the occurrence of an end echo and the number of frequency peaks according to the embodiment of this invention.

FIG. 9 is an explanatory diagram of a defect subjected to ultrasonic simulation of an example of the present invention.

10 is a pattern diagram showing an ultrasonic simulation result of the defect shown in FIG.

11 is a flaw detection waveform of the ultrasonic simulation of the defect shown in FIG. 9. FIG.

FIG. 12 is an explanatory diagram of conventional flaw detection by corner echo.

FIG. 13 is an explanatory diagram of general corner echo and end echo.

FIG. 14 is an explanatory diagram of defect height measurement using a general end echo.

FIG. 15 is an explanatory diagram illustrating a relationship between a general probe frequency and end echo discrimination.

FIG. 16 is an explanatory diagram illustrating types of defects existing on the surface of a general structural material.

[Explanation of symbols]

1 flaw detector 2 probe 3 test pieces 4 defects 5 Edge echo waveform 6 corner echo waveform 7 Edge echo path 8 corner echo path 10 Ultrasonic reflection path 11 Frequency analyzer 12 Automatic sensitivity adjustment device 14 Echo distance measuring device 15 Defect shape identification device 16 characteristic curve

Front page continuation (72) Inventor Kasaburo Harumi 4-27-6 Shakujii-cho, Nerima-ku, Tokyo (72) Inventor Yasuo Toyooka 5-3 Takaracho, Kure-shi, Hiroshima Bab Hitachi Engineering Co., Ltd. (72) Inventor Youmei Matsumoto 6-9 Takara-cho, Kure-shi, Hiroshima Babcock Hiritsu Co., Ltd. Kure factory (72) Inventor Orimoto Mana 6-9 Takara-cho, Kure-shi, Hiroshima Babcock Hiritsu Co., Ltd. Kure factory (56) References JP-A-5-332998 (JP, A) JP-A-61-283864 (JP, A) Harumi Kazaburo et al., "Measurement of Minute Defects on Bottom Surface by Ultrasonic Wave (Part 1)", Nihon Proceedings of the 14th Simulation Technology Conference of the Japan Society for Simulation, June 21, 1995, pp. 325-328 (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 29/00-29 / 28 JISST file (JOIS)

Claims (6)

(57) [Claims] 1. In a defect identification method by ultrasonic flaw detection, in which ultrasonic waves are transmitted from a probe to an object and echoes reflected from a defect portion are received to identify a defect, a model defect shape and an edge of the model defect are previously prepared. Obtaining a characteristic formula representing the relationship with the partial echo sound pressure level, measuring the end echo sound pressure level of the subject, by ultrasonic flaw detection characterized by introducing into the characteristic formula to identify the defect tip shape Defect identification method. 2. In a defect identification method by ultrasonic flaw detection, in which ultrasonic waves are transmitted from a probe to an object and echoes reflected from a defect part are received to identify the defect, a model defect shape and an end of the model defect are previously set. Obtain a characteristic curve representing the relationship with the partial echo sound pressure level, set the threshold value of the fatigue defect having a sharp tip and the welding defect having a curvature at the tip on the characteristic curve,
By measuring the end echo sound pressure level of the subject and comparing it with the threshold value, it is possible to distinguish between a fatigue defect having a sharp tip and a welding defect having a curvature at the tip. Defect identification method by ultrasonic flaw detection. 3. A model defect shape and an edge of the model defect in advance in a defect identification method by ultrasonic flaw detection for identifying a defect by transmitting an ultrasonic wave from a probe to an object and receiving an echo reflected from the defect part. A characteristic curve representing the relationship with the partial echo sound pressure level is obtained, and threshold values for a fatigue defect having a tip curvature R of almost 0 and a welding defect having a tip curvature R of 0.1 mm or more are set on the characteristic curve, ultrasonic flaw detection, characterized in that said by comparing with the threshold value to measure the end echo sound pressure level of the subject, and identifies the welding defects tip having a curvature in sharp fatigue defects and tip Defect identification method by. 4. The defect identification method by ultrasonic flaw detection according to claim 2, wherein the welding defect is a blow hole or an undercut. 5. In a defect identification method by ultrasonic flaw detection, in which ultrasonic waves are emitted from a probe to an object and echoes reflected from the defect part are received to identify the defect, a defect top part of a material on which a model defect is formed in advance From the end echo that is a reflection from, the bottom reflection end echo that is the material bottom surface reflection of the end echo, and the path length and the defect shape between the echoes of the corner echo that is the reflection from the defect base. Find the correlation,
A defect shape identification method by ultrasonic flaw detection, characterized in that a path distance between echoes of the subject is measured, and a shape of a defect tip is identified by using a correlation between at least one inter-echo path distance and a defect shape. 6. The ultrasonic flaw detection method according to claim 1 , wherein the frequency analysis of the echo is performed and the presence or absence of an end echo is determined based on the number of frequency peaks. Defect identification method.