JP6347462B2 - Phased array ultrasonic inspection method and ultrasonic inspection system - Google Patents

Description

  The present invention relates to a phased array ultrasonic inspection method and an ultrasonic inspection system, and is particularly useful when applied to a case where a long inspection object such as a bolt is inspected from one end face in the longitudinal direction.

  In the roots of the screws of the foundation bolts of nuclear equipment, cracks may occur due to stress concentration when subjected to seismic loads. In nuclear power plants and thermal power plants, which are aged, there have been many reports of fatigue cracks occurring in bolts including foundation bolts. When evaluating the soundness of a bolt in which a crack has been detected, dimensional data relating to the depth of the crack is required.

  An edge echo method and a vertical flaw detection method are known as methods for estimating crack size according to the prior art. Of these, since the reflection echo at the crack surface of the bolt and the end echo due to the crack tip are not separated, it is difficult to apply the end echo method to the estimation of the crack depth of the bolt. In the vertical flaw detection method, it is necessary to scan the longitudinal wave vertical probe on the end face of the bolt, and there is a problem in that a small crack cannot be detected because the echo of the screw portion is obstructed.

  On the other hand, Suh et al. Proposed a method for estimating crack depth in bolts by surface waves propagating on the crack surface (Non-Patent Document 1). However, such an estimation method has a problem that the surface wave attenuates violently on a non-smooth crack surface and it is not easy to receive it.

D. M. Suh and W. W. Kim, A New Ultrasonic Technique for Detection and Sizing of Small Cracks in Studs and Bolts, Journal Nondestructive Evaluation, Vol. 14, No. 4, P.201-206, 1995.

  In view of the above prior art, the present invention can easily and accurately measure the position and size of a crack generated on a long inspection object such as a bolt by flaw detection from one end face in the longitudinal direction. An object of the present invention is to provide a phased array ultrasonic inspection method and an ultrasonic inspection system.

  In order to develop a phased array ultrasonic flaw detection method and an ultrasonic flaw detection system that achieve the above-described object, the present inventors have developed a phased array ultrasonic wave to detect a crack generated in the middle of a bolt that is a long inspection object. The detection method by the flaw detection method was examined.

  Here, in the phased array ultrasonic flaw detection method, ultrasonic waves in different propagation directions and focusing positions can be freely controlled by electronically controlling the transmission / reception timing of each element for an array probe composed of a plurality of elements. Exciting technology. However, estimating the crack depth from the flaw detection results obtained by this method remains a problem. Therefore, we conducted a simulation of wave propagation in bolts using the finite element method, identified features that correlate with the crack depth of the received waveform, and verified them experimentally.

<Examination by simulation>
First, the simulation model will be described. In the simulation model, as shown in FIG. 1, the position of the crack and its dimensions are defined by an axial position P, a length L, and a depth D, respectively.

  Based on the results of flaw detection by the phased array ultrasonic flaw detection method, a simulation of wave propagation in a bolt was carried out in order to investigate a crack depth estimation method. A two-dimensional model of simulation based on the finite element method is shown in FIG. As shown in the drawing, a 32-element linear array probe (hereinafter also referred to as an “array probe”) 1 having a pitch of 0.6 mm and a width of 0.5 mm is connected to one end face of the bolt 2 (right end face in the figure). ). The flaw detection mode was a longitudinal wave, and the refraction angle was changed from −5 to 25 ° in steps of 0.5 °. Α in the figure is a refraction angle (hereinafter referred to as a tip refraction angle) when the central beam of the ultrasonic wave hits the tip of the crack 3. The material of the bolt 2 was carbon steel, and the longitudinal wave sound velocity was set to 5,920 m / s. The diameter and length of the bolt 2 are 30 mm and 200 mm, respectively, and the length of the screw portion 4 is 120 mm. A crack 3 was inserted into the valley of a screw with P = 50 or 100 mm. The width of the crack 3 is fixed to 0.5 mm, and the depth D is changed to 0.5, 1.0, 2.0, 2.5, 4.0, 6.0, 7.5, and 12.5 mm. I let you. The focal position of the ultrasonic beam was set to 60 mm when P = 50 mm, and 110 mm when P = 100 mm.

  A three-dimensional ultrasonic field when the array probe 1 in the figure radiates to the steel material through water was calculated using predetermined software. As main calculation conditions, the horizontal distance was set to 0 mm, the frequency of the input waveform was set to 5 MHz, the sampling frequency was set to 100 MHz, and the spatial resolution was set to 0.1 mm.

<Simulation results and discussion>
1) In the case of a crack with an axial position of 50 mm and a depth of 6 mm Ultrasonic waves with different refraction angles are excited from the array probe 1 (see FIG. 2, the same applies hereinafter), and the received waveform corresponding to each refraction angle is simulated. Calculated. FIG. 3 shows the result of arranging received waveforms corresponding to refraction angles from −5 ° to 20 ° in a fan shape. This result is called a sector (S) scan cross-sectional image. NE and SE in the figure are instructions caused by the crack 3 (see FIG. 2, the same applies hereinafter) and the screw part 4 (see FIG. 2, the same applies hereinafter), and are hereinafter referred to as a crack echo NE and a screw echo SE, respectively. . BW is a bottom echo, and MNE is an instruction based on multiple reflections at the crack 3. The shade of color represents the strength of the echo.

  As shown in FIG. 3, the indication of multiple reflection at the screw echo SE, the crack echo NE, the bottom echo BW, and the crack 3 is clearly observed. In FIG. 3, as shown in the enlarged view of the crack echo NE, the strength of the crack echo NE is high at two locations near the opening and the tip of the crack 3.

  FIG. 4 shows the intensity distribution of the crack echo NE at each refraction angle. As shown in the figure, the intensity of the crack echo NE increases and decreases according to the change in the refraction angle, and reaches a maximum value (peak) when the refraction angle is 8 ° and 15 °. Hereinafter, these two peaks will be considered.

  The peak corresponding to the refraction angle of 15 ° is due to reflection at the corner portion composed of the crack 3 and the screw portion 4. In the model shown in FIG. 2, when the ultrasonic central beam hits the corner portion, the refraction angle is geometrically about 15 °.

  FIG. 5 shows the state of wave propagation at a refraction angle of 15 ° at different times. Red and blue in the figure represent a longitudinal wave and a transverse wave, respectively. L and T mean a longitudinal wave and a transverse wave excited by the array probe 1, respectively. RL and SL indicate longitudinal wave reflected waves at the corner portion and the screw portion 4, respectively. As shown in the figure, the excited longitudinal wave propagates toward the corner portion while being reflected by the screw portion 4, and at the time of 9.5 μs, the longitudinal wave is reflected at the corner portion, and the reflected wave becomes a bolt. 2 is propagated toward the end face of 2 and finally received by the array probe 1.

  On the other hand, the peak corresponding to the refraction angle of 8 ° was found to be mainly due to reflection near the tip of the crack 3 from the wave propagation simulation result. Factors affecting the intensity of the crack echo NE include the intensity of the excited ultrasonic sound field, the rate of reflection of ultrasonic energy at the crack 3, and the scattering at the screw portion 4.

  When P = 50 mm and D = 6 mm, the tip refraction angle α is 7.4 °. The three-dimensional ultrasonic field emitted from the array probe 1 shown in FIG. 2 is calculated, and the intensity of the ultrasonic field at each refraction angle is the maximum intensity when the refraction angle is 0 °. Is normalized and shown in FIG. As shown in the figure, the intensity of the ultrasonic sound field decreases as the refraction angle increases, but the decrease is gradual. For example, when the refraction angle is 7.4 °, the maximum intensity of the ultrasonic sound field is 0.978, whereas when the refraction angle is 10 °, it is 0.962. Thus, even if the refraction angle changes slightly, the intensity change of the ultrasonic sound field is negligible, so that a slight change in the refraction angle does not cause a significant change in crack echo intensity.

  The reflection of the ultrasonic wave near the tip of the crack 3 varies greatly depending on the refraction angle. The state of the change represented by sound rays is shown in FIG. The thick line in the figure indicates the center beam, and the broken line indicates the scattering of the ultrasonic wave at the screw portion 4. FIG. 4A shows a case where the center beam of the ultrasonic wave hits the tip of the crack 3. At this time, about half of the excited ultrasonic energy is reflected by the crack 3, and the rest passes through the crack 3. The reflected ultrasound is finally received by the array probe 1 while being scattered by the screw portion 4. When the refraction angle is smaller than the tip refraction angle α, the proportion of ultrasonic energy reflected by the crack 3 decreases. On the other hand, as shown in (b) of the figure, the ratio increases as the refraction angle increases. When a certain refraction angle is reached, all ultrasonic energy is reflected as shown in FIG. Even if the refraction angle is further increased, the ratio of reflected ultrasonic waves does not increase. It is considered that the intensity of the crack echo NE is amplified mainly by an increase in the ratio of reflected ultrasonic waves. On the other hand, as shown in FIG. 7, the influence of scattering at the screw portion 4 accumulates as the refraction angle increases. The scattering results in a decrease in the energy of the ultrasonic waves returning to the array probe 1 and a decrease in the intensity of the crack echo NE. Thus, it is considered that a peak is formed in the vicinity of the tip refraction angle α by the interaction between the reflection at the tip of the crack 3 and the scattering at the screw portion 4.

<For different crack depths>
The intensity distribution of the crack echo NE at the refraction angle when the depth of the crack 3 was changed was calculated and normalized with the maximum value when the depth of the crack S was 0.5 mm. FIG. 8 shows the intensity distribution of the crack echo NE at the refraction angle when P = 50 mm. As shown in the figure, when the crack 3 is shallow, only one peak is observed. When the crack depth is 2 mm or more, respective peaks P1 and P2 corresponding to the corner portion and the tip vicinity of the crack 3 are observed. The refraction angle corresponding to the peak P1 (hereinafter referred to as the peak P1 refraction angle) is constant regardless of the depth of the crack 3. The intensity of the peak P1 is amplified as the depth of the crack 3 increases, and the depth of the crack 3 is saturated at 2 mm. On the other hand, with respect to the peak P2, the corresponding refraction angle (hereinafter referred to as the peak P2 refraction angle) and intensity decrease and amplify as the crack 3 becomes deeper. Table 1 shows the peak P2 refraction angle obtained from the figure.

  As shown in the table, in the case of the shallow crack 3, since the peak P1 and the peak P2 are not separated, they are indicated by the refraction angle of the peak P1. For reference, the tip refraction angle α is also shown in the table. As shown in the table, when the crack depth is changed from 2 mm to 12.5 mm, the refraction angle of the peak P2 is reduced from 13.5 ° to 2 °. Both of these values are somewhat larger than the tip refraction angle α.

  On the other hand, the intensity distribution of the crack echo NE at the refraction angle in the case of P = 100 mm is shown in FIG. As shown in the figure, when the depth of the crack 3 is less than 4 mm, only one peak is observed, whereas when the crack 3 becomes deeper, two peaks are clearly observed. At the peak P1, the refraction angle is around 7 °, and varies slightly with the change in the depth of the crack 3. This is because since the pitch of the refraction angle is set to 0.5 °, the peak appearing in the figure is not necessarily a true peak. The intensity of the peak P1 is amplified as the crack 3 becomes deeper and is saturated at 6 mm. On the other hand, as in the case of P = 50 mm, the refraction angle of the peak P2 and the intensity of the peak P2 decrease and amplify as the depth of the crack 3 increases. Table 2 shows the refraction angle of the peak P2 obtained from FIG.

  As shown in Table 2, the refraction angle of the peak P2 is slightly larger than the tip refraction angle α, and from 4.8 ° to 1 ° as the depth of the crack 3 changes from 4 mm to 12.5 mm. Change.

  Compared to the case of P = 50 mm, the difference between the refraction angles of the peak P1 and the peak P2 is small, and the change range of the refraction angle of the peak P2 is also narrow. From this, it can be considered that the peak P1 and the peak P2 become difficult to separate as the axial position increases.

  As described above, the refraction angle of the peak P2 changes depending on the depth of the crack 3 in any axial direction, and has a strong correlation with the depth of the crack 3. If this correlation is used, it is considered that the crack depth in the bolt 2 can be estimated from the flaw detection result obtained by the phased array ultrasonic flaw detection method.

That is, as a result of the simulation experiment, the following knowledge was obtained.
1) In the case of the shallow crack 3, there is only one peak of the distribution of the crack echo intensity at the refraction angle, whereas when the crack 3 becomes deep, there are two peaks. The two peaks are due to the reflection at the crack corner and near the crack tip.
2) Although the peak refraction angle due to reflection near the tip of crack 3 is slightly larger than the tip refraction angle α, it changes depending on the depth of crack 3 and increases with increasing depth of crack 3. Decrease.

  The configuration of the present invention based on such knowledge is as follows.

The first aspect of the present invention is:
In a phased array ultrasonic flaw detection method for performing ultrasonic flaw detection on an inspection object using an array probe composed of a plurality of elements,
The array probe is arranged on one end face of the inspection object, and the echo from the inspection object is digitized by irradiating ultrasonic waves while changing the refraction angle toward the inside of the inspection object. Flaw detection process for obtaining flaw detection data,
Based on the flaw detection data, a crack inspection process for determining the presence or absence of a crack in the inspection object;
When it is determined that a crack exists in the crack inspection process, a maximum echo detection process for detecting a maximum echo from which the echo due to the crack is maximized from the flaw detection data;
An axial position detecting step for specifying an axial position that is a position for giving the maximum echo in a direction where the refraction angle is zero degrees;
Based on the flaw detection data, a peak detection step of detecting a peak that is a maximum value of the echo intensity from an echo intensity distribution characteristic of the echo corresponding to each refraction angle;
A tip refraction angle detection step of selecting a tip refraction angle which is a smaller refraction angle of two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle giving the peak;
It possesses a裂深detection step of Ki for detecting a certain Ki裂深of dimensions in the direction of crack perpendicular to the axial direction on the basis of the tip angle of refraction,
The tip refraction angle detection step includes
When two peaks are detected in the peak detection step, two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle that gives the peak with the smaller refraction angle The phased array ultrasonic flaw detection method is characterized in that the smaller refraction angle is selected to be the tip refraction angle .

According to this aspect, using the knowledge as described above, the maximum value of the echo intensity is obtained from the echo intensity distribution characteristic of the echo corresponding to each refraction angle created based on the flaw detection data, and this maximum value is used. The tip refraction angle is obtained. Since the tip refraction angle gives information on the tip of the crack generated inside the inspection object, the end surface of the inspection object on which the array probe is disposed by using the tip refraction angle. The crack depth can be detected well from the geometrical relationship such as the axial dimension from the end face to the crack. As a result, the soundness of the inspection object can be evaluated. In particular, the area in which the array probe can be disposed is small, and it is useful for flaw detection of bolts, prisms, etc., where the interior of the flaw detection site is buried in another member.
Based on the knowledge, a crack echo originating from the vicinity of the crack tip is identified, and the tip refraction angle is obtained based on this echo. Therefore, the tip refraction angle can be obtained accurately and used. The crack depth can also be determined accurately and accurately.

The second aspect of the present invention is:
The phased array ultrasonic flaw detection method described in the first aspect is the phased array ultrasonic flaw detection method characterized in that the predetermined ratio is half of the echo intensity.

  According to this aspect, the tip refraction angle can be accurately specified based on the knowledge. In particular, when the inspection object is a bolt, the tip refraction angle is detected as a value that is at least smaller than the actual value, so that the depth of the bolt crack can be detected on the safe side. That is, the actual crack depth does not become larger than the measured value, and when the crack depth is used as a guide for the replacement time of the bolt, an accurate measured value can be given.

The third aspect of the present invention is:
An array probe used for phased array ultrasonic flaw detection, comprising a plurality of elements disposed on one end surface of the inspection object and radiating ultrasonic waves toward the inside of the inspection object,
Flaw detection data obtained by changing the refraction angle of the ultrasonic wave by controlling each element and performing flaw detection inside the inspection object and digitizing the echo of the flaw detection result obtained as a result of the ultrasonic irradiation A phased array flaw detector to receive,
The array probe is controlled to perform a predetermined flaw detection by the array probe via the phased array flaw detector, and the flaw detection data transmitted from the phased array flaw detector is processed to perform the inspection. A phased array ultrasonic flaw detection system having an arithmetic processing means for performing ultrasonic flaw detection inside an object,
The arithmetic processing means includes:
Based on the flaw detection data, a crack inspection process for determining the presence or absence of a crack in the inspection object;
When it is determined that there is a crack in the crack inspection process, a maximum echo detection process for detecting a maximum echo that maximizes the echo from the flaw detection data;
An axial position detecting step for specifying an axial position that is a position for giving the maximum echo in a direction where the refraction angle is zero degrees;
Based on the flaw detection data, a peak detection step of detecting a peak that is a maximum value of the echo intensity from an echo intensity distribution characteristic of the echo corresponding to each refraction angle;
A tip refraction angle detection step of selecting a tip refraction angle which is a smaller refraction angle of two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle giving the peak;
A crack depth detection step of detecting a crack depth that is a dimension of a crack in a direction orthogonal to the axial direction based on the tip refraction angle ; and
In the tip refraction angle detection step,
When two peaks are detected in the peak detection step, two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle that gives the peak with the smaller refraction angle The phased array ultrasonic flaw detection system is characterized in that the smaller refraction angle is selected to be the tip refraction angle .

According to this aspect, using the knowledge as described above, the maximum value of the echo intensity is obtained from the echo intensity distribution characteristic of the echo corresponding to each refraction angle created based on the flaw detection data, and this maximum value is used. The tip refraction angle is obtained. Since the tip refraction angle gives information on the tip of the crack generated inside the inspection object, the end surface of the inspection object on which the array probe is disposed by using the tip refraction angle. The crack depth can be detected well from the geometrical relationship such as the axial dimension from the end face to the crack. As a result, the lifetime of the inspection object can be accurately determined. In particular, the area in which the array probe can be disposed is small, and it is useful for flaw detection of bolts, prisms, etc., where the interior of the flaw detection site is buried in another member.
Based on the knowledge, the crack echo caused by the crack tip is specified, and the tip refraction angle is obtained based on this echo. Therefore, the tip refraction angle can be obtained accurately, and this can be used to crack the crack. Depth can also be determined accurately and accurately.

The fourth aspect of the present invention is:
The phased array ultrasonic flaw detection system described in the third aspect is the phased array ultrasonic flaw detection system characterized in that the predetermined ratio is half of the echo intensity.

  According to this aspect, the tip refraction angle can be accurately specified based on the knowledge. In particular, when the inspection object is a bolt, the tip refraction angle is detected as a value that is at least smaller than the actual value, so that the depth of the bolt crack can be detected on the safe side. That is, the actual crack depth does not become larger than the measured value, and when the crack depth is used as a guide for the replacement time of the bolt, an accurate measured value can be given.

  According to the present invention, it is possible to accurately and accurately estimate the crack depth of an inspection object such as a bolt when the phased array ultrasonic flaw detection method is used. In other words, for the bolts with cracks, we obtained the knowledge that the distribution of crack echo intensity at the refraction angle has a strong correlation with the crack depth by using the results of simulations using the finite element method. Since a crack depth estimation method is proposed using the relationship, a desired crack depth can be detected satisfactorily. Specifically, the peak refraction angle due to reflection near the crack tip is slightly larger than the tip refraction angle, but it changes depending on the crack depth and decreases with increasing crack depth. If this relationship is used, the crack depth can be estimated accurately. Incidentally, according to the present invention, when the object to be inspected is a bolt, although the estimated crack depth is larger than the true value, the maximum error can be kept within 2 mm.

It is explanatory drawing which defines and shows the position of the crack in the simulation model, and its dimension by the position P of the axial direction, the length L, and the depth D, respectively. It is explanatory drawing which shows the two-dimensional model (bolt) of the simulation based on a finite element method. It is explanatory drawing which shows the result (S scan cross-sectional image) which arranged the received waveform corresponding to the refraction angle from -5 degrees to 20 degrees which calculated the received waveform corresponding to each refraction angle by simulation. It is a characteristic view which shows the intensity distribution of the crack echo NE in each refraction angle. It is explanatory drawing which shows the mode of wave propagation with a refraction angle of 15 degrees for each different time (6.0 μs, 8.0 μs, 9.5 μs, 10.5 μs, 16.0 μs). FIG. 6 is a characteristic diagram showing the intensity of the ultrasonic sound field at each refraction angle normalized by the maximum intensity of the ultrasonic sound field when the refraction angle is 0 °. FIG. 6 is an explanatory diagram showing an acoustic ray of an ultrasonic wave reflected by a bolt crack, which changes depending on a refraction angle, and (a) shows a case where the central beam of an ultrasonic wave hits the tip of the crack, and (b) shows In the case of a larger refraction angle, (c) shows a case where all ultrasonic energy is reflected. Calculates the intensity distribution of the crack echo NE with respect to the refraction angle when P = 50 mm in a plurality of cases where the crack depth is changed, and is normalized with the maximum value when the crack depth is 0.5 mm. FIG. Calculates the intensity distribution of the crack echo NE with respect to the refraction angle when P = 100 mm in a plurality of cases where the crack depth is changed, and is normalized with the maximum value when the crack depth is 0.5 mm. FIG. 1 is a block diagram showing a phased array ultrasonic flaw detection system according to an embodiment of the present invention. It is a figure regarding the process sequence in the arithmetic processing part in the ultrasonic flaw detection system shown in FIG. 10, (a) is a flowchart which shows a process sequence, (b) is explanatory drawing which shows the geometric relationship of a crack depth. It is explanatory drawing which shows the flaw detection data obtained at a flaw detection process, (a) is S scan data, (b) is B scan data, (c) is A scan data. It is explanatory drawing which shows the volt | bolt which is a test target object used for actual flaw detection. It is explanatory drawing which shows the sector scan image obtained by the flaw detection of the volt | bolt of FIG. FIG. 14 is a characteristic diagram showing echo intensity distributions at different refraction angles when the crack depth of the bolt shown in FIG. 13 is variously changed. It is a characteristic view which shows the measured value of the crack depth of the volt | bolt shown in FIG. 13 in comparison with an actual depth.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 10 is a block diagram showing a phased array ultrasonic flaw detection system according to an embodiment of the present invention. As shown in the figure, the phased array ultrasonic flaw detection system according to this embodiment includes an array probe 1, an arithmetic processing unit 11, a phased array flaw detection device 12, a control device 13, a motor 14, and a display unit 15. Here, the array probe 1 in the present embodiment is a linear array probe in which a plurality of (for example, 32) elements are arranged in a straight line, and one of the bolts 22 that are long inspection objects in the present embodiment. It is pressed against the end face with a spring or the like and brought into contact therewith. The arithmetic processing unit 11 controls the phased array flaw detector 12 and the control device 13. The phased array flaw detector 12 applies a voltage to the array probe 1 to excite ultrasonic waves propagating in the bolts 22 and irradiates the inside of the bolts 22 with ultrasonic waves for flaw detection. The phased array flaw detector 12 also sends flaw detection data representing flaw detection results in the bolts 22 received by the array probe 1 to the arithmetic processing unit 11. In other words, the phased array flaw detector 12 performs flaw detection inside the bolt 22 by changing the refraction angle of the ultrasonic wave by controlling each element of the array probe 1, and flaw detection obtained as a result of the ultrasonic irradiation. The flaw detection data obtained by digitizing the resulting echo is received and sent to the arithmetic processing unit 11. As a result, the flaw detection data is stored in the arithmetic processing unit 11.

  Furthermore, in this embodiment, the control device 13 controls the motor 14 that rotates the array probe 1 on the end face (the upper end face in FIG. 10) of the bolt 22 under the control of the arithmetic processing unit 11. More specifically, the array probe 1 is configured to rotate 360 ° around the central axis OO ′ of the bolt 22, and flaw detection data is obtained by swinging the refraction angle within a predetermined range at each rotation position. collect. More specifically, the flaw detection by the array probe 1 is performed in the clockwise direction in the drawing with the surface OT including the central axis OO ′ as the starting point (0 °) as the center line SS ′ of the upper end surface of the bolt 22. The irradiation range of the ultrasonic wave for flaw detection is swung within the surface OT at each rotation position of the rotation angle θ that is appropriately rotated and changed, and flaw detection data is obtained at each position corresponding to the rotation angle θ of 0 ° to 360 °. collect. The scanning range of the ultrasonic wave in the plane OT is in the range of −β to + φ with respect to the central axis OO ′. Here, the position data of the array probe 1 as the motor 14 is driven is supplied from the control device 13 to the arithmetic processing unit 11. Further, the data processed by the arithmetic processing unit 11 is displayed on the display unit 15.

  In the arithmetic processing unit 11 in the phased array ultrasonic flaw detection system, the following processing is performed. Such processing will be described with reference to FIG. 11A which is a flowchart of processing in this case.

1) Step S1
The bolt 22 that is the inspection object is flawed, and flaw detection data that is a flaw detection result is obtained (flaw detection step). As shown in FIG. 12, the flaw detection data includes (a) S scan data, (b) B scan data, and (c) A scan data.

2) Step S2
In order to determine the presence or absence of a crack in the bolt 22, the flaw detection data is analyzed. Specifically, the data cursor on the B scan data shown in FIG. 12B is moved, and the presence or absence of a crack echo on the S scan data shown in FIG. 12A and the B scan data shown in FIG. Observe.

3) Step S3
Proceed to the process of determining whether there is a crack in the bolt 22 and estimating the crack depth, or end ("END"). Incidentally, since crack echoes are observed in the S and B scan data shown in FIGS. 12A and 12B, the process proceeds to the process of estimating the crack depth.

4) Step S4
An S-scan corresponding to the largest crack echo is obtained. As shown in FIG. 12B, the intensity of the crack echo differs depending on the circumferential position. This is because the crack depth varies depending on the circumferential direction. Since the strength of the crack echo increases as the crack depth increases, the crack depth estimated based on the S scan data corresponding to the maximum crack echo is considered to be the maximum. Therefore, as shown in FIG. 12, the refraction angle cursor is moved so as to pass as strong an echo as possible. Thereafter, the data cursor on the B scan is moved and stopped at a position where the crack echo is maximum on the S scan data. It is assumed that the S scan data at this time corresponds to the maximum crack echo (maximum echo detection step).

5) Step S5
In the direction where the refraction angle is zero degrees, that is, in the direction of the central axis OO ′ (see FIG. 10; the same applies hereinafter), the axial position of the crack, which is the position that gives the maximum crack echo, is obtained (axial position detection step). Specifically, the line on the S scan data is moved so as to overlap with the crack echo and the position thereof is read, and the axial position of the read crack is defined as P. In the case shown in FIG. 12, P = 50 mm.

6) Step S6
Peak P1 or peak P2 is detected based on the number of peaks on the distribution of the crack echo intensity at the refraction angle (peak detection step). Specifically, in order to create an echo intensity distribution, the refraction angle cursor on the S scan data is moved, the crack echo intensities corresponding to different refraction angles are read from the A scan data, and the echo intensity distribution with respect to the refraction angle is calculated. Characteristics (see FIG. 8 and FIG. 9) are obtained (peak detection step).

7) Step S7
If two peaks are detected as a result of the process of step S6, the crack depth is estimated using the peak P2. Specifically, as described above, the refraction angle that gives the peak P2 varies depending on the crack depth, but is slightly larger than the tip refraction angle α. Therefore, it is assumed that the smaller one of the two refraction angles corresponding to the half value of the peak P2 is equal to the tip refraction angle α.

8) Step S8
If only one peak is detected as a result of the process in step S6, the crack depth is estimated using the peak P1. Specifically, it is assumed that the smaller one of the two refraction angles corresponding to the half value of the peak P1 is equal to the tip refraction angle α.

9) Step S9
Using the tip refraction angle α obtained as a result of the processing in steps S7 and S8, D = r−tan (α) (where r is a trough of the screw of the bolt 22) from the geometrical relationship shown in FIG. The crack depth D is obtained using a radius based on. Here, r is the valley diameter of the bolt 22. For example, when r = 26.8 mm, the crack depth D = 7.25 mm when the axial position P (= 50 mm) and the tip refraction angle (= 7.01 °) of the crack obtained from FIG. 12 are substituted. Is required.

  In order to verify the effect of the ultrasonic flaw detection system according to the above-described embodiment, a flaw detection experiment was performed by forming a crack in a bolt to be inspected. FIG. 13 is an explanatory view showing a bolt which is an inspection object used for actual flaw detection. As shown in the figure, the bolts 22 are carbon steel SS400 bolts having a length of 300 mm, and cracks 23 having different depths were applied thereto by electric discharge machining. The diameter of the bolt 22 was 24 mm or 30 mm, and the axial position P of the crack 23 was 50 mm. The depth of the crack 23 was changed to 0.5, 1.0, 2.0, 4.6, and 8 mm. The shape of the crack 23 was determined with reference to the shape of the fatigue crack applied to the bolt specimen.

  The measurement conditions were that the flaw detection mode was set to longitudinal wave, the sound velocity was set to 5,900 m / s, and the refraction angle was changed from −20 ° to 20 ° at a step of 0.2 °. At the time of transmission, the ultrasonic energy is focused at a position 60 mm in the axial direction. At the time of reception, the received waveform was set to be focused at a position in the axial direction of 10 mm to 150 mm for the purpose of improving the axial distance resolution. The digitizer frequency and applied voltage are 50 MHz and 200 V, respectively. Measurement was carried out by rotating the array probe 1 every 0.5 ° about the central axis OO ′ of the bolt 22.

  FIG. 14 shows a cross-sectional image of the sector scan data obtained by detecting the crack 23 having P = 50 mm and D = 6 mm. As shown in the figure, the indication due to multiple reflection at the screw echo SE, the crack echo NE and the crack 23 is clearly observed. Further, in the enlarged view of the crack echo NE, the respective instructions corresponding to the reflection near the tip of the corner portion and the crack 23 are also clear. This is in good agreement with the simulation results of FIG.

  FIG. 15 shows echo intensity distributions of crack echoes at different refraction angles when the depth of the crack 23 is changed to 0.5, 1, 2, 4, 6 and 8 mm. This figure is normalized and shown with the maximum value when the crack depth is 0.5 mm. As shown in the figure, when D ≦ 1 mm, only one peak is observed. When D = 2 mm, the peak P1 and the peak P2 begin to separate. When D ≧ 4 mm, the peak P2 is completely separated from the peak P1 and is clearly observed. Since the centers of the array probe 1 and the end face of the bolt 22 do not coincide somewhat, the refraction angle of the peak P1 slightly varies. Further, the echo intensity changes depending on the contact state of the array probe 1. Since it is difficult to make the contact state constant, the echo intensity will not be discussed. Table 3 shows refraction angles related to the peaks P1 and P2 obtained from FIG.

  As shown in Table 3, the refraction angle of the peak P2 is about 1 ° larger than the tip refraction angle α, and decreases as the crack depth increases. The results in the table are in good agreement with the simulation results in Table 1.

  From the viewpoint of the ultrasonic flaw detection test, a crack such as a fatigue crack excluding a branching stress corrosion crack can be regarded as a crack. As a result of examination by simulation and experiment, the peak of the distribution of crack echo intensity at the refraction angle has a strong correlation with the crack depth, and this interval is used to estimate the depth of the crack generated in the bolt 22. According to the above embodiment, the desired crack depth D can be satisfactorily measured.

  FIG. 16 shows a comparison between the crack depth estimated from the results of the experiment and the actual crack depth (true value). As shown in the figure, although the crack depth is estimated to be somewhat larger than the true value in any case, the maximum error is within 2 mm. This indicates the validity of the estimation method based on the flowchart shown in FIG. As shown in the figure, when the axial position P increases from 50 mm to 100 mm, the error of the estimated crack depth D increases. This is considered to be due to the fact that the ultrasonic energy becomes difficult to converge when the axial position P becomes far.

  The inspection object in the above embodiment has been described by taking a bolt as an example, but it is needless to say that the inspection object is not limited to this. If it is a long object such as a prism, the same actions and effects can be obtained. Furthermore, it is not necessary to limit to a long thing, A block member etc. may be sufficient. However, since the block member has room for other ultrasonic flaw detection methods, the present invention can be said to be particularly useful in the case of the long object.

  In the above embodiment, the array probe is a linear array. However, this may be a matrix array. In the case of a matrix array, many elements are required, but it is not necessary to rotate the array probe.

  In the above embodiment, the array probe of the linear array is rotated 360 ° around the central axis. However, the rotation angle may be set according to the inspection range. In the above embodiment, the array probe 1 is rotated by the motor 14, but the motor 14 is not necessarily required. It can also be configured to manually adjust to a predetermined angle. In the case of using a matrix array, the same effect can be obtained by electronically rotating the ultrasonic beam.

  The present invention is useful in the industrial field in which various plants are maintained and maintained by ultrasonic flaw detection.

1 Array probe 2, 22 Volts 3, 23 Crack α Tip refraction angle D Crack depth P1, P2 Peak

Claims (4)

In a phased array ultrasonic flaw detection method for performing ultrasonic flaw detection on an inspection object using an array probe composed of a plurality of elements,
The array probe is arranged on one end face of the inspection object, and the echo from the inspection object is digitized by irradiating ultrasonic waves while changing the refraction angle toward the inside of the inspection object. Flaw detection process for obtaining flaw detection data,
Based on the flaw detection data, a crack inspection process for determining the presence or absence of a crack in the inspection object;
When it is determined that a crack exists in the crack inspection process, a maximum echo detection process for detecting a maximum echo from which the echo due to the crack is maximized from the flaw detection data;
An axial position detecting step for specifying an axial position that is a position for giving the maximum echo in a direction where the refraction angle is zero degrees;
Based on the flaw detection data, a peak detection step of detecting a peak that is a maximum value of the echo intensity from an echo intensity distribution characteristic of the echo corresponding to each refraction angle;
A tip refraction angle detection step of selecting a tip refraction angle which is a smaller refraction angle of two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle giving the peak;
It possesses a裂深detection step of Ki for detecting a certain Ki裂深of dimensions in the direction of crack perpendicular to the axial direction on the basis of the tip angle of refraction,
The tip refraction angle detection step includes
When two peaks are detected in the peak detection step, two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle that gives the peak with the smaller refraction angle A phased array ultrasonic flaw detection method, wherein a smaller refraction angle is selected to be a tip refraction angle . In the phased array ultrasonic flaw detection method according to claim 1 ,
The phased array ultrasonic flaw detection method characterized in that the predetermined ratio is half of the echo intensity. An array probe used for phased array ultrasonic flaw detection, comprising a plurality of elements disposed on one end surface of the inspection object and radiating ultrasonic waves toward the inside of the inspection object,
Flaw detection data obtained by changing the refraction angle of the ultrasonic wave by controlling each element and performing flaw detection inside the inspection object and digitizing the echo of the flaw detection result obtained as a result of the ultrasonic irradiation A phased array flaw detector to receive,
The array probe is controlled to perform a predetermined flaw detection by the array probe via the phased array flaw detector, and the flaw detection data transmitted from the phased array flaw detector is processed to perform the inspection. A phased array ultrasonic flaw detection system having an arithmetic processing means for performing ultrasonic flaw detection inside an object,
The arithmetic processing means includes:
Based on the flaw detection data, a crack inspection process for determining the presence or absence of a crack in the inspection object;
When it is determined that there is a crack in the crack inspection process, a maximum echo detection process for detecting a maximum echo that maximizes the echo from the flaw detection data;
An axial position detecting step for specifying an axial position that is a position for giving the maximum echo in a direction where the refraction angle is zero degrees;
Based on the flaw detection data, a peak detection step of detecting a peak that is a maximum value of the echo intensity from an echo intensity distribution characteristic of the echo corresponding to each refraction angle;
A tip refraction angle detection step of selecting a tip refraction angle which is a smaller refraction angle of two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle giving the peak;
A crack depth detection step of detecting a crack depth that is a dimension of a crack in a direction orthogonal to the axial direction based on the tip refraction angle ; and
In the tip refraction angle detection step,
When two peaks are detected in the peak detection step, two refraction angles corresponding to the echo intensity at a predetermined ratio to the echo intensity corresponding to the refraction angle that gives the peak with the smaller refraction angle A phased array ultrasonic flaw detection system characterized in that the smaller refraction angle is selected to be the tip refraction angle . The phased array ultrasonic flaw detection system according to claim 3 ,
The predetermined ratio is half of the echo intensity. A phased array ultrasonic flaw detection system, wherein: