JP6421632B2 - Ultrasonic flaw detection method and system for continuous casting nozzle - Google Patents

Description

  The present invention relates to an ultrasonic flaw detection method and system for a continuous casting nozzle.

  In the steel industry, in a process of continuously casting refined molten steel, a continuous casting nozzle (hereinafter also simply referred to as a nozzle) is used as a refractory for pouring molten steel from a tundish into a mold. If the nozzle for continuous casting causes breakage or abnormal melting during use, it leads to quality contamination of the molten steel, and has a significant effect on yield and productivity.

  In order to prevent breakage and abnormal melting during use of a continuous casting nozzle, a refractory manufacturer has conventionally used an X-ray transmission device as typified by Patent Document 1 to manufacture a nozzle during production. Inspects the presence or absence of defects inherent in the steel, confirms that there are no defects, and then sells them to steel manufacturers. This is because breakage or abnormal melting during use of the nozzle for continuous casting occurs frequently due to a defect inherent in the nozzle. Here, the defect to be inspected is not a spherical sealed pore having a size of 100 μm or less, which is inevitably contained during the production of a continuous casting nozzle, but a layered void generated during production due to variations in production conditions. It is.

  The defect detection method using the X-ray transmission device of the continuous casting nozzle is, for example, as shown in FIG. 12, placing the continuous casting nozzle 100 on the rotary stage 201 and rotating the nozzle 100 from the X-ray source 200. A defect is detected from the difference in density of the dose of X-rays irradiated with X-rays and transmitted through the nozzle 100.

Here, as shown in FIG. 12, the continuous casting nozzle 100 has a cylindrical shape, and includes an alumina-graphite portion 101 and a zirconia-graphite portion 102 of a highly corrosion-resistant material disposed in the powder portion. In many cases, it comprises a plurality of compositions.
However, when the X-ray transmission method is applied to the portion 102 where the zirconia-graphite is disposed in the continuous casting nozzle 100, the atomic zirconium constituting the zirconia has a large atomic weight, that is, the X-ray absorption ability is high. In addition, a phenomenon occurs in which it is difficult to make a difference in density in the dose of transmitted X-rays. For this reason, the portion 102 where zirconia-graphite is disposed has a problem that only a defect having a thickness of about 500 μm or more can be detected.

Japanese Patent Laid-Open No. 62-232547

Ultrasonic flaw detection method (revised new edition), published by Japan Society for the Promotion of Science, Nikkan Kogyo Shimbun (July 30, 1974)

  An ultrasonic flaw detection method as described in Non-Patent Document 1 is known as a defect detection method for a material having a homogeneous structure having a single composition. The ultrasonic flaw detection method irradiates a material having a defect with ultrasonic waves having a frequency of 1 MHz to 5 MHz, and analyzes an ultrasonic waveform reflected from the material (reflection method) or an ultrasonic waveform transmitted through the material. A defect is detected by analysis (transmission method).

Ultrasound is excited from the probe, and there are the following three methods for irradiating the material with the excited ultrasound.
(1) Contact method: A probe 302 is brought into contact with the surface of an object to be inspected via a contact substance 301, and ultrasonic waves excited from the probe 302 are transmitted toward the object to be inspected through the contact substance 301. A method in which a reflected wave is detected by the probe 302 or a transmitted wave is detected by another probe 304 brought into contact with the surface of the object to be inspected via a contact substance 303 (FIGS. 13 and 14).
(2) Water immersion method: The probe 401 and the probe 401 are immersed in water while the probe 401 is installed at a certain distance from the surface of the test object, and excited from the probe 401. The transmitted ultrasonic wave is transmitted toward the object to be inspected using water as a medium, and the reflected wave is detected by the probe 401, or the receiving probe installed at a position away from the surface of the object to be inspected by a certain distance. A method of detecting a transmitted wave by the child 402 (FIGS. 15 and 16).
(3) Air propagation method: With the probe 401 installed at a certain distance from the surface of the object to be inspected, the ultrasonic wave excited from the probe 401 is directed to the object under test using air as a medium. The transmitted wave is detected by the probe 401, or the transmitted wave is detected by the receiving probe 402 installed at a certain distance from the surface of the object to be inspected (FIG. 15, FIG. 16).

The inventor of the present application considered applying an ultrasonic flaw detection method to a continuous casting nozzle.
Here, in the case of applying the ultrasonic flaw detection method by the reflection method, in a material having a homogeneous structure composed of a single composition, if a defect containing air is present in the material, a solid phase composed of a single composition and Since the acoustic impedance of air (gas phase) is significantly different, it is completely reflected on the surface of the defect (interface between different phases of the solid phase and the gas phase), so that the defect can be detected.
However, in the continuous casting nozzle 100 having a plurality of compositions, for example, when the reflection method is applied to a portion 102 where zirconia-graphite is disposed, the acoustic impedance of zirconia and graphite is different, and thus the nozzle 100 is irradiated. The ultrasonic waves are partially reflected at the interface between zirconia and graphite. Therefore, it is clear that the ultrasonic flaw detection method using the reflection method cannot accurately detect defects because the interface between zirconia and graphite is erroneously detected as a defect in any of the contact method, water immersion method, and air propagation method. It was.

  The present invention has been made in view of the above points, and an object of the present invention is to apply an ultrasonic flaw detection method for a continuous casting nozzle and detect a defect with high accuracy.

Means for solving the above problems are as follows.
[1] An ultrasonic flaw detection method for a continuous casting nozzle,
A transmission probe installed at a position away from the inner surface of the continuous casting nozzle;
Using a receiving probe installed at a position away from the outer surface of the continuous casting nozzle so as to be opposed to the transmission probe and the thickness of the continuous casting nozzle,
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
In the probe for transmission, the surface facing the inner surface of the continuous casting nozzle is a convex shape having the same curvature as the inner surface,
The ultrasonic flaw detection method for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. .
[2] An ultrasonic flaw detection method for a continuous casting nozzle,
A transmission probe installed at a position away from the outer surface of the continuous casting nozzle;
Using a receiving probe installed at a position away from the inner surface of the continuous casting nozzle so as to be opposed to the transmission probe and the thickness of the continuous casting nozzle,
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
The surface facing the outer surface of the nozzle for continuous casting in the probe for transmission is a concave shape having the same curvature as the outer surface,
The ultrasonic flaw detection method for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. .
[3] The frequency f causing resonance in the thickness direction of the continuous casting nozzle is:
f = V / λ = n · V / (2d)
V: Longitudinal wave velocity propagating inside the continuous casting nozzle d: Wall thickness of the continuous casting nozzle λ: Wavelength of the ultrasonic wave n: Frequency at which a natural number is established [1] or [2] The ultrasonic flaw detection method of the nozzle for continuous casting as described.
[4] The ultrasonic testing method for a continuous casting nozzle according to any one of [1] to [3], wherein the continuous casting nozzle is provided with a zirconia-graphitic material. .
[5] An ultrasonic flaw detection system for a continuous casting nozzle,
A transmission probe installed at a position away from the inner surface of the continuous casting nozzle;
A receiving probe installed at a position away from the outer surface of the continuous casting nozzle so as to be opposed to the transmission probe and the thickness of the continuous casting nozzle;
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
In the probe for transmission, the surface facing the inner surface of the continuous casting nozzle is a convex shape having the same curvature as the inner surface,
The ultrasonic flaw detection system for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. .
[6] An ultrasonic flaw detection system for a continuous casting nozzle,
A transmission probe installed at a position away from the outer surface of the continuous casting nozzle;
A probe for reception installed at a position away from the inner surface of the nozzle for continuous casting so as to be opposed to the probe for transmission and the thickness of the nozzle for continuous casting;
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
The surface facing the outer surface of the nozzle for continuous casting in the probe for transmission is a concave shape having the same curvature as the outer surface,
The ultrasonic flaw detection system for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. .

  According to the present invention, it is possible to detect a defect with high accuracy by applying an ultrasonic flaw detection method to a nozzle for continuous casting.

It is a figure which shows the outline | summary of the ultrasonic flaw detection by the ultrasonic flaw detection system which concerns on embodiment. It is an external view which shows the probe for transmission which concerns on embodiment. It is a figure which shows the outline | summary of the ultrasonic flaw detection by the ultrasonic flaw detection system which concerns on embodiment. It is a figure which shows the example of the waveform of the transmitted wave detected with the probe for reception. It is a figure for demonstrating the model which analyzes the waveform of the ultrasonic wave which permeate | transmits a nozzle. It is a figure which shows the computer simulation result (amplitude of a received wave) at the time of using the ultrasonic wave of frequency 400kHz, and not having a defect. It is a figure which shows the computer simulation result (amplitude of a received wave) at the time of using a 400-kHz ultrasonic wave and a defect. It is a figure which shows the computer simulation result (amplitude of a received wave) at the time of using the ultrasonic wave of frequency 430.8kHz, and not having a defect. It is a figure which shows the computer simulation result (amplitude of a received wave) at the time of using a ultrasonic wave with a frequency of 430.8 kHz and having a defect. It is a figure which shows the sample used in the Example. It is a figure which shows the sample used in the Example. It is a figure for demonstrating the outline | summary of experiment. It is a figure which shows the outline | summary of the ultrasonic flaw detection method by the ultrasonic flaw detection system which concerns on embodiment. It is a figure for demonstrating the detection method of the defect using the X-ray transmissive apparatus of the nozzle for continuous casting. It is a figure for demonstrating the outline | summary of the reflection method based on the contact method. It is a figure for demonstrating the outline | summary of the permeation | transmission method based on the contact method. It is a figure for demonstrating the outline | summary of the reflection method based on the water immersion method or the air propagation method. It is a figure for demonstrating the outline | summary of the permeation | transmission method based on the water immersion method or the air propagation method.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
In the present invention, an ultrasonic flaw detection method is applied to a nozzle for continuous casting, and a transmission method based on a water immersion method or an air propagation method is adopted.
FIG. 1 is a diagram illustrating an outline of ultrasonic flaw detection by the ultrasonic flaw detection system according to the embodiment.
As shown in FIG. 12, the continuous casting nozzle targeted in the present embodiment includes an alumina-graphite portion 101 and a zirconia-graphite portion 102 of a highly corrosion-resistant material disposed in the powder portion. A continuous casting nozzle 100 having a plurality of compositions.

As shown in FIG. 1, the transmission probe 1 is installed at a position away from the inner surface (inner peripheral surface) 100a of the continuous casting nozzle 100 in plan view. Further, the receiving probe 1 is disposed at a position away from the outer surface (outer peripheral surface) 100b of the continuous casting nozzle 100 so as to face the transmitting probe 1 across the thickness of the continuous casting nozzle 100. 2 is installed.
As shown in FIG. 2, the surface 1a facing the nozzle inner surface 100a in the probe 1 for transmission is formed into a convex shape having the same curvature as the nozzle inner surface 100a. In the receiving probe 2, the surface 2a facing the nozzle outer surface 100b has a flat shape.
The frequency of the ultrasonic wave transmitted from the transmission probe 1 is 1 MHz or less, and is a frequency that causes resonance in the thickness direction of the continuous casting nozzle 100.

With reference to FIG. 3, the outline | summary of the ultrasonic flaw detection by the ultrasonic flaw detection system which concerns on embodiment is demonstrated. In FIG. 3, the transmission probe 1 is illustrated in a simplified manner, but as described above, the surface 1a facing the nozzle inner surface 100a has a convex shape having the same curvature as the nozzle inner surface 100a. ing. Scanning probes 1 and 2 are arranged facing each other across the thickness of nozzle 100 for continuous casting, and scanning is performed while moving probes 1 and 2 in the longitudinal direction of nozzle 100 while transmitting and receiving ultrasonic waves. To do.
FIG. 4 shows an example of the waveform of the transmitted wave detected by the receiving probe 2. It can be seen that at the position where the defect is inherent, the ultrasonic wave is reflected and thus does not pass through, and the ultrasonic waveform is not obtained.
In addition, the ultrasonic flaw detection method to which the present invention is applied may be applied to the entire continuous casting nozzle 100, or the X-ray transmission method is applied to the alumina-graphite portion 101 as usual, and the zirconia-graphite is applied. An ultrasonic flaw detection method to which the present invention is applied may be applied to the quality portion 102.

Here, the reason why the permeation method based on the water immersion method or the air propagation method is employed will be described.
As described above, the ultrasonic flaw detection method includes a contact method, a water immersion method, and an air propagation method. When a transmission method based on the contact method is applied to the cylindrical continuous casting nozzle 100, for example, The probe 1 for transmission is brought into close contact with the inner surface 100a of the nozzle through the contact substance, and the probe 2 for reception is brought into close contact with the outer surface 100b of the nozzle through the contact substance. Therefore, it is necessary to synchronize the probes 1 and 2 for transmission and reception and move them on the same circle. Such an operation is very complicated and takes a long time, and becomes a factor that hinders the productivity of the nozzle for continuous casting, and thus it is difficult to apply it to an actual manufacturing process. Considering the above, a permeation method based on a water immersion method or an air propagation method is adopted.

  Next, the surface shape of the probe 1 for transmission is made convex, and the frequency of the ultrasonic wave transmitted from the probe 1 for transmission is 1 MHz or less and resonates in the thickness direction of the nozzle 100 for continuous casting. The reason why the frequency is used to cause the problem will be explained.

As described above, in the ultrasonic flaw detection method using the reflection method, the interface between zirconia and graphite is erroneously detected as a defect, so that there is a problem that the defect cannot be detected accurately.
Therefore, an attempt is made to apply the ultrasonic flaw detection method by the transmission method. In a continuous casting nozzle, for example, when an ultrasonic wave having a frequency of 1 MHz to 5 MHz is used at a portion where zirconia-graphite is disposed, pores having a size of 100 μm or less are unavoidably formed in the zirconia-graphite. As a result of interference between the pores and the ultrasonic waves, the pores are erroneously detected as defects in any of the contact method, the water immersion method, and the air propagation method because they are contained and the wavelength of the transmitted ultrasonic waves is short. I found that there was a problem.
Accordingly, the ultrasonic frequency is set to 1 MHz or less. On the other hand, when an ultrasonic wave having a frequency of 1 MHz or less is used, since the wavelength of the ultrasonic wave is long, the attenuation of the ultrasonic wave increases in the process of passing through the nozzle 100. As a result, the contact method, the water immersion method, the air propagation method. In either case, a problem was found that defects could not be detected accurately.

The inventor of the present application considers that the attenuation of the ultrasonic wave in the propagation process inside the nozzle is greatly influenced by the surface shape of the probe 1 for transmission and its installation position. In the case of applying the ultrasonic flaw detection method using the transmission method described above, the waveform of the ultrasonic wave passing through the nozzle was analyzed by computer simulation using the model shown in FIG.
The model in FIG. 5 is a model in which a zirconia-graphite nozzle 100 having an inner diameter of 200 mm, an outer diameter of 300 mm, and a thickness of 50 mm is an object, and a defect 51 having a width of 15 mm and a thickness of 0.5 mm is introduced at the center of the thickness. It has become.
The width of the probes 1 and 2 for transmission / reception is 20 mm × 20 mm or less. If the widths of the probes 1 and 2 are more than 20 mm × 20 mm, the projected cross-sectional area of the probes 1 and 2 becomes too larger than the projected cross-sectional area of the defect inherent in the continuous casting nozzle 100 and transmits. This is because the waveform of the ultrasonic wave cannot be accurately analyzed, and a highly accurate defect cannot be detected.
FIG. 5 shows a model in which the probe 1 for transmission is arranged on the nozzle inner surface 100a side and the probe 2 for reception is arranged on the nozzle outer surface 100b side. A model in which the probe 1 was arranged on the nozzle outer surface 100b side and the receiving probe 2 was arranged on the nozzle inner surface 100a side was similarly constructed.

As shown in Table 1, in the transmission method based on the water immersion method or the air propagation method, the attenuation state of the received wave is determined by various combinations A to F of the surface shape of the probe 1 for transmission and its installation position. Analyzed. In any of the combinations A to F, the surface 2a facing the nozzle outer surface 100b in the receiving probe 2 has a flat shape.
As a result, the transmission probe 1 is installed at a position away from the nozzle inner surface 100a, and the surface 1a facing the nozzle inner surface 100a in the transmission probe 1 is the same as the nozzle inner surface 100a. It was ascertained that the ultrasonic wave attenuation was reduced with the combination E having a convex shape having a curvature of.
Further, the transmitting probe 1 is installed at a position away from the nozzle outer surface 100b, and the surface 1a facing the nozzle outer surface 100b in the transmitting probe 1 is the same as the nozzle outer surface 100b. It was ascertained that with the combination C having a concave shape having a curvature, the attenuation of the ultrasonic wave becomes small.

  Further, in the combination E, the attenuation state of the ultrasonic wave when the ultrasonic wave having a frequency of 1 MHz or less was used was subjected to a computer simulation by changing the frequency. As a result, in the transmission method based on the water immersion method or the air propagation method, it was found that the attenuation can be significantly suppressed when the frequency of the ultrasonic wave is a frequency that causes resonance in the thickness direction of the nozzle 100. .

Here, the frequency causing resonance in the thickness direction of the nozzle 100 can be obtained as follows. That is, since resonance occurs when the formula (1) is established, the frequency f at which the formula (2) is established is obtained.
2d = n · λ (1)
d: Nozzle wall thickness (mm)
λ: Wavelength of ultrasonic wave (m)
n: Natural number f = V / λ = n · V / (2d) (2)
V: Longitudinal wave velocity propagating through zirconia-graphite; 10770 (m / s)

Here, n is selected to be 4 in order to show a representative example of a frequency of 1 MHz or less. In this case, the frequency that causes resonance in the thickness direction with a thickness of 50 mm, that is, the frequency that satisfies Equation (2) is 430.8 KHz.
In combination E, the result of computer simulation of the amplitude of the waveform of the ultrasonic wave transmitted from the probe 1 for transmission and received by the probe 2 for reception will be described.
FIG. 6A and FIG. 6B show the results when ultrasonic waves having a frequency of 400 kHz are used. FIG. 6A shows the amplitude of the received wave when there is no defect, and FIG. 6B shows the amplitude of the received wave when there is a defect.
7A and 7B show the results when using ultrasonic waves with a frequency of 430.8 kHz. FIG. 7A shows the amplitude of the received wave when there is no defect, and FIG. 7B shows the amplitude of the received wave when there is a defect.
The accuracy of ultrasonic flaw detection can be evaluated by the ratio of the waveform energy (the time integral value of the absolute amplitude value) of the received wave when there is no defect and when there is a defect, and is small if the ratio is smaller than 1. It shows that the flaw detection accuracy is high.
When the ratio of the waveform energy of the received wave in the time zone from 190 μs to 270 μs after ultrasonic irradiation is obtained, it becomes 0.93 when ultrasonic waves having a frequency of 400 kHz (FIGS. 6A and 6B) are used, whereas frequency 430 When ultrasonic waves of .8 KHz are used (FIGS. 7A and 7B), the value is 0.68, and when a frequency that causes resonance in the thickness direction of the nozzle 100 is used, higher flaw detection accuracy can be obtained. In the ultrasonic flaw detection method by the transmission method based on the water immersion method or the air propagation method, it is said that if the waveform energy ratio is 0.7 or less, the flaw can be flawed with a significant difference. The time zone for measuring the received wave is set to the time zone after 190 μs and 270 μs after the ultrasonic irradiation because the waveform of the received ultrasonic wave is constant.

The reason why the probes 1 and 2 for transmission / reception are installed at a certain distance from the inner surface 100a and the outer surface 100b of the continuous casting nozzle 100 is to make the sound pressure of the ultrasonic waves uniform. . If the probes 1 and 2 are not installed at positions apart from each other by a certain distance, the sound pressure of the ultrasonic waves becomes uneven, and accurate flaw detection cannot be performed. The distance is given by D ² / 4λ, where D is the width of the probes 1 and 2 and λ is the wavelength of the ultrasonic wave. Therefore, it is desirable that the probes 1 and 2 are installed at positions that are separated from the inner surface 100a and the outer surface 100b of the continuous casting nozzle 100 by at least D ² / 4λ. In this example, the widths of the probes 1 and 2 are 20 mm and λ are 25 mm, and the probes 1 and 2 for transmission and reception are separated from the inner surface 100a and the outer surface 100b of the continuous casting nozzle 100 by 4 mm or more, respectively. Install in a different position.

The following experiment was conducted in order to demonstrate that defects can be detected with high accuracy by the ultrasonic flaw detection method to which the present invention is applied.
As shown in FIGS. 8 and 9, a sample 3 in which an artificial defect 31 (layered gap) is formed in the zirconia-graphite material distributed to the continuous casting nozzle is prepared, and the defect inherent in the sample is produced. An experiment to detect 31 was conducted.
The components of the zirconia-graphitic material are zirconia 82 mass% and graphite 18 mass%. When the defect 31 is filled with embryo soil obtained by kneading zirconia and graphite with a phenol resin into a frame, a combustible organic material having a width of 20 mm × a height of 30 mm × a thickness of 0.01 mm is mixed and molded. It was formed by firing at 1000 ° C. in a nitrogen atmosphere to burn off the combustible organic material.
Sample 3 has a cylindrical shape with an inner diameter of 65 mm, an outer diameter of 130 mm, and a height of 150 mm. There are two types of defects 31: one arranged concentrically with respect to the central axis at a position 60 mm from the bottom surface of the cylindrical sample (FIG. 8) and one arranged so as to extend in the radial direction (FIG. 9). Was made. It has been confirmed that the defect 31 having a thickness of 0.01 mm cannot be detected by the conventional X-ray transmission method when arranged concentrically and when arranged in the radial direction.

FIG. 10 shows an outline of the experiment.
The transmission probe 1 is installed inside the cylindrical sample 3 at a position 10 mm away from the inner surface. The width of the probe 1 is 20 mm × 20 mm, and the surface shape thereof is a convex shape having the same curvature as that of the inner surface of the sample 3.
The receiving probe 2 is installed outside the cylindrical sample 3 at a position 10 mm away from the outer surface. The width of the probe 2 is 20 mm × 20 mm.
In the ultrasonic flaw detection with respect to the sample 3, in the circumferential direction of the sample 3, the probe 1 installed on the inner side is fixed, and the probe 2 installed on the outer side by the rotation drive motor 4 is rotated at the rotation angle 2. This was done by scanning concentrically at a time. The longitudinal direction of the sample 3 was performed by raising the probes 1 and 2 in parallel by 0.5 mm by the vertical drive motor 5.
In addition, the ultrasonic flaw detection based on the water immersion method was implemented by performing the same method as the ultrasonic flaw detection method based on the air propagation method in water.

  The frequencies that cause resonance in the thickness direction of the sample 3 used in the examples are d = 32.5 mm, V = 10770 (m / s), and n = natural numbers (1, 2, 3, 4, 5, 6). The frequency at 1 MHz or less is 166, 331, 497, 663, 828, and 994 KHz.

The flaw detection test was conducted by changing the frequency of the ultrasonic wave transmitted from the probe 1 for transmission to 166, 331, 497, 663, 828, and 994 KHz.
The result of a flaw detection test of defects arranged concentrically as shown in FIG. 8 in the water immersion method using ultrasonic waves having a frequency of 166 KHz will be described.
For the received wave at each measurement point in the area where the defect is inherent, the waveform energy in the time zone from 190 μs to 270 μs after ultrasonic irradiation is calculated, and the average waveform energy at the measurement point when there is a defect is calculated from the calculated value. Calculated. The reason why the time zone for measuring the received wave is set to the time zone after 190 μs and 270 μs after ultrasonic irradiation is that the waveform of the received ultrasonic wave is constant.
On the other hand, for the received wave at each measurement point in a region that does not include a defect having the same surface area as the region in which the defect is inherent, the waveform energy in the time zone from 190 μs to 270 μs after ultrasonic irradiation is calculated, and the calculated value From this, the average waveform energy at the measurement point when there was no defect was calculated.
As a result, when the ratio of the average waveform energy when there is a defect to the average waveform energy when there is no defect is 0.36, the defect can be detected with high accuracy.

In addition, the results of a flaw detection test for defects arranged in the radial direction shown in FIG.
For the received wave at each measurement point in the area where the defect is inherent, the waveform energy in the time zone from 190 μs to 270 μs after ultrasonic irradiation is calculated, and the average waveform energy at the measurement point when there is a defect is calculated from the calculated value. Calculated.
On the other hand, for the received wave at each measurement point in a region that does not include a defect having the same surface area as the region in which the defect is inherent, the waveform energy in the time zone from 190 μs to 270 μs after ultrasonic irradiation is calculated, and the calculated value From this, the average waveform energy at the measurement point when there was no defect was calculated.
As a result, the ratio of the average waveform energy when there is a defect and the average waveform energy when there is no defect is 0.47, and the defect can be detected with high accuracy.

  From the above, in both the water immersion method and the air propagation method, both the concentric and radial defects can be detected with high accuracy.

Although the present invention has been described together with the embodiments, the above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention is interpreted in a limited manner by these. It must not be. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.
As shown in FIG. 11, the probe 1 for transmission is installed at a position away from the outer surface 100b of the nozzle 100 for continuous casting, as shown in FIG. Further, the receiving probe 2 is installed at a position away from the inner surface 100a of the continuous casting nozzle 100 so as to face the transmitting probe 1 across the thickness of the continuous casting nozzle 100. You may make it do. In this case, the surface 1a facing the nozzle outer surface 100b in the probe 1 for transmission is formed into a concave shape having the same curvature as the nozzle outer surface 100b.

1: Probe for transmission 1a: Surface 2: Probe for reception 2a: Surface 3: Sample 31: Defect 100: Nozzle for continuous casting 100a: Inner surface 100b: Outer surface 101: Part of alumina-graphite 102: Zirconia-graphite part

Claims (6)

An ultrasonic flaw detection method for a continuous casting nozzle,
A transmission probe installed at a position away from the inner surface of the continuous casting nozzle;
Using a receiving probe installed at a position away from the outer surface of the continuous casting nozzle so as to be opposed to the transmission probe and the thickness of the continuous casting nozzle,
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
In the probe for transmission, the surface facing the inner surface of the continuous casting nozzle is a convex shape having the same curvature as the inner surface,
The ultrasonic flaw detection method for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. . An ultrasonic flaw detection method for a continuous casting nozzle,
A transmission probe installed at a position away from the outer surface of the continuous casting nozzle;
Using a receiving probe installed at a position away from the inner surface of the continuous casting nozzle so as to be opposed to the transmission probe and the thickness of the continuous casting nozzle,
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
The surface facing the outer surface of the nozzle for continuous casting in the probe for transmission is a concave shape having the same curvature as the outer surface,
The ultrasonic flaw detection method for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. . The frequency f causing resonance in the thickness direction of the continuous casting nozzle is:
f = V / λ = n · V / (2d)
V: Longitudinal wave velocity propagating inside the continuous casting nozzle d: Wall thickness of the continuous casting nozzle λ: Wavelength of ultrasonic wave n: Frequency at which a natural number is established Ultrasonic flaw detection method for continuous casting nozzle.   The ultrasonic testing method for a continuous casting nozzle according to any one of claims 1 to 3, wherein the continuous casting nozzle is provided with a zirconia-graphite material. An ultrasonic flaw detection system for a continuous casting nozzle,
A transmission probe installed at a position away from the inner surface of the continuous casting nozzle;
A receiving probe installed at a position away from the outer surface of the continuous casting nozzle so as to be opposed to the transmission probe and the thickness of the continuous casting nozzle;
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
In the probe for transmission, the surface facing the inner surface of the continuous casting nozzle is a convex shape having the same curvature as the inner surface,
The ultrasonic flaw detection system for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. . An ultrasonic flaw detection system for a continuous casting nozzle,
A transmission probe installed at a position away from the outer surface of the continuous casting nozzle;
A probe for reception installed at a position away from the inner surface of the nozzle for continuous casting so as to be opposed to the probe for transmission and the thickness of the nozzle for continuous casting;
A transmission method based on a water immersion method or an air propagation method in which an ultrasonic wave transmitted from the transmission probe is received by the reception probe and a defect is detected by analyzing the received wave. Adopt
The surface facing the outer surface of the nozzle for continuous casting in the probe for transmission is a concave shape having the same curvature as the outer surface,
The ultrasonic flaw detection system for a continuous casting nozzle, characterized in that the frequency of the ultrasonic wave transmitted from the transmission probe is 1 MHz or less and a frequency that causes resonance in the thickness direction of the continuous casting nozzle. .

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