Ultrasonic flaw detection method

Abstract

This invention provides an ultrasonic flaw detection method that reliably detects misalignment of the ultrasonic probe, accurately corrects the intensity of the reflected wave from the flaw, and enables reliable flaw detection. [Solution] An ultrasonic probe 1 is positioned opposite the outer surface of a round bar M and moved in the width direction of the round bar M. At each movement position, the ultrasonic probe 1 receives the surface reflected wave Wa and the defect reflected wave Wd from an artificial defect M1 of a predetermined size formed inside the round bar M. The relationship between the center frequency in the frequency band of the surface reflected wave Wa and the movement position of the ultrasonic probe 1 is stored, and the comparison relationship between the intensity of the defect reflected wave Wd at the movement position and the intensity of the defect reflected wave Wd at the direct-facing position is stored. During flaw detection, the intensity of the defect reflected wave Wd at the movement position of the ultrasonic probe 1, which is determined from the center frequency, is corrected based on the comparison relationship.

Description

Technical Field

[0001] The present invention relates to an ultrasonic flaw detection method, and particularly to an ultrasonic flaw detection method capable of accurately performing flaw detection even when an ultrasonic probe is displaced in the cross-sectional width direction of a round bar material.

Background Art

[0002] Fig. 5 shows a cross-section of a round bar material M having a flaw M2 inside. When the ultrasonic probe 1 is at position A facing the outer peripheral surface (surface) forming the arc cross-section of the round bar material M, the flaw detection ultrasonic wave W oscillated from the ultrasonic probe 1 toward the round bar material M enters the surface perpendicularly and travels straight without refraction, is reflected by the internal flaw M2, and returns to the ultrasonic probe 1 again as a flaw reflection wave Wd, and is received with sufficient intensity.

[0003] However, when the ultrasonic probe 1 is displaced in the width direction of the round bar material M (the tangential direction of the arc cross-section at the facing position) to position B, the flaw detection ultrasonic wave W is refracted on the surface of the round bar 1 and deviates from the direction of the internal flaw M2, and because the refractive indices of the shear wave and the longitudinal wave are different and they separate, etc., the intensity of the flaw reflection wave Wd returning to the ultrasonic probe 1 decreases.

[0004] Therefore, in Patent Document 1, a method is disclosed in which the displacement (moving position) of the ultrasonic probe is detected based on the magnitude of the flaw detection ultrasonic wave (bottom surface reflection wave) reflected by the bottom surface of the round bar material, and the intensity of the flaw reflection wave is corrected.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the conventional method described above had a problem in that the intensity of the bottom-reflected wave fluctuated due to Rayleigh scattering and other factors inside the round bar material, making it difficult to accurately detect the misalignment of the ultrasonic probe and correct the intensity of the defect-reflected wave.

[0007] Therefore, the present invention aims to solve these problems by providing an ultrasonic flaw detection method that reliably detects misalignment of the ultrasonic probe, accurately corrects the intensity of the reflected flaw wave, and enables reliable flaw detection. [Means for solving the problem]

[0008] To achieve the above objective, in the present invention, an ultrasonic probe (1) is positioned facing the outer surface of a rod (M) and moved in the width direction of the rod (M). At each movement position, the ultrasonic probe (1) receives the surface reflected wave (Wa) and the defect reflected wave (Wd) from an artificial defect (M1) of a predetermined size formed inside the rod (M). The correspondence between the center frequency in the frequency band of the surface reflected wave (Wa) and the movement position of the ultrasonic probe (1) is stored, and the comparison relationship between the intensity of the defect reflected wave (Wd) at the movement position and the intensity of the defect reflected wave (Wd) at the direct-facing position is stored. During flaw detection, the intensity of the defect reflected wave (Wd) at the movement position of the ultrasonic probe (1), which is determined from the center frequency, is corrected based on the comparison relationship. Furthermore, the present invention is particularly applicable when the material to be inspected is a round bar.

[0009] The symbols in parentheses above are for reference only, indicating the correspondence with the specific means described in the embodiments described later. [Effects of the Invention]

[0010] According to the ultrasonic flaw detection method of the present invention, the movement position of the ultrasonic probe is detected by the change in the center frequency in the frequency band of the surface reflected wave. Therefore, the misalignment of the ultrasonic probe is reliably detected without being affected by Rayleigh scattering, etc., and the intensity of the reflected wave is accurately corrected, enabling reliable flaw detection. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing how an ultrasonic probe receives surface-reflected waves and flaw-reflected waves from a round bar. [Figure 2] This is a waveform diagram of a surface reflected wave. [Figure 3] This graph shows the change in the center frequency of the surface reflected wave with respect to the movement of the ultrasonic probe. [Figure 4] This graph shows the path changes of ultrasonic flaw detection waves emitted from an ultrasonic probe. [Figure 5] This is a cross-sectional view showing the change in the path of the flaw-detecting ultrasound when the ultrasonic probe moves. [Modes for carrying out the invention]

[0012] The embodiments described below are merely examples, and various design improvements made by those skilled in the art without departing from the spirit of the present invention are also included within the scope of the present invention.

[0013] In Figure 1, the ultrasonic probe 1 is positioned directly toward the outer surface of the round bar M (position A in the figure), and flaw detection ultrasonic waves are emitted toward the round bar M. The surface reflected wave Wa reflected from the surface of the round bar M and the flaw reflected wave Wd from the end face of the artificial flaw M1 extending from the bottom surface (right end in the figure) of the round bar M toward the center of the round bar are again received by the ultrasonic probe 1.

[0014] The ultrasonic probe 1 used was a 15MHz broadband single probe with a transducer diameter of φ6mm. The target round bar material M was a steel material with a diameter of φ6mm, and the artificial defect M1 was a flat-bottomed hole with a diameter of φ0.8mm. The focus of the ultrasonic probe 1 was aligned with the center of the round bar material M (i.e., the center of the end face of the artificial defect), and water immersion testing was performed with a water distance of (focal length - round bar radius).

[0015] The ultrasonic probe is moved forward and backward by predetermined amounts in the width direction of the round bar material (tangential direction of the arc cross-section at the forward position) as shown by the dashed line in Figure 1, and surface reflected wave Wa and scratch reflected wave Wd are received at each movement position.

[0016] The surface reflected wave Wa, unlike the bottom reflected wave, does not pass through the round bar M, and therefore does not suffer from the problem of its intensity fluctuating due to Rayleigh scattering, etc. It is a burst wave as shown in Figure 2, which relatively well preserves the shape of the flaw detection ultrasonic wave emitted from the ultrasonic probe 1. Furthermore, according to the inventor's experiments, when the frequency analysis of the surface reflected wave Wa is performed using the Fast Fourier Transform (FFT), the center frequency of the frequency band of the surface reflected wave Wa uniquely changes depending on the movement position of the ultrasonic probe 1. This is shown in Figure 3.

[0017] As shown by the solid line in Figure 3, the center frequency decreases in proportion to the amount of movement, regardless of whether the ultrasonic probe 1 is moved in the forward or reverse direction from its forward position (movement position 0). The dashed line x in Figure 3 is an approximation curve of the experimental values ​​connected by the solid line, and is almost symmetrical with respect to movement position 0. Therefore, the correspondence between movement position and center frequency on this approximation curve x is stored in the memory of the flaw detector (not shown) to which the ultrasonic probe 1 is connected. Since it is almost symmetrical, regardless of whether the movement position is forward or reverse (positive or negative), it is sufficient to store the correspondence between the absolute value of the movement position and the center frequency at that time in the memory.

[0018] On the other hand, the signal intensity of the defect reflection wave Wd at each movement position of the ultrasonic probe 1 is shown by the solid line in Figure 4. According to Figure 4, the signal intensity of the defect reflection wave Wd decreases in proportion to the amount of movement, regardless of whether the ultrasonic probe 1 is moved in the forward or reverse direction from the direct facing position (movement position 0). The dashed line y in the figure is an approximation curve of the experimental values ​​connected by the solid line, and is almost symmetrical with respect to movement position 0. Therefore, the comparison relationship between the signal intensity at each movement position and the signal intensity at the direct facing position on this approximation curve y is stored in the memory of the flaw detector as a correction amount C (Figure 4). Since it is almost symmetrical, regardless of whether the movement position is forward or reverse (positive or negative), it is sufficient to store the absolute value of the movement position and the correction amount C of the signal intensity at that time in the memory.

[0019] During actual flaw detection, the center frequency of the surface reflection wave Wa of the flaw detection ultrasonic wave oscillated from the ultrasonic probe 1 is detected to determine the moving position (position deviation) of the ultrasonic probe 1 (broken line x in FIG. 3), and a correction amount C is added to the signal intensity of the flaw reflection wave Wd (broken line y in FIG. 4) from the moving position to increase the signal intensity. In this way, the intensity of the flaw reflection wave Wd is corrected to enable reliable flaw detection.

[0020] In the above embodiment, the material to be flaw detected is a round bar, but it is not limited to this.

Explanation of Signs

[0021] 1... Ultrasonic probe, M... Round bar (bar), M1... Artificial flaw, Wa... Surface reflection wave, Wd... Flaw reflection wave.

Claims

1. An ultrasonic flaw detection method comprising: moving an ultrasonic probe, which is positioned opposite the outer surface of a rod, in the width direction of the rod, receiving surface reflected waves and fault reflected waves from artificial defects of a predetermined size formed inside the rod at each movement position with the ultrasonic probe; storing the correspondence between the center frequency in the frequency band of the surface reflected wave and the movement position of the ultrasonic probe; storing the comparative relationship between the intensity of the fault reflected wave at the movement position and the intensity of the fault reflected wave at the directly facing position; and correcting the intensity of the fault reflected wave at the movement position of the ultrasonic probe, which is determined from the center frequency, based on the comparative relationship during flaw detection.

2. The ultrasonic flaw detection method according to claim 1, wherein the rod material is a round rod material.

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