Ultrasonic flaw detection method

Abstract

To provide an ultrasonic flaw detection method capable of performing good flaw detection by excluding the effect of multiple reflected waves even when a simple single vibrator type ultrasonic probe is used.SOLUTION: Flaw detection is performed by inclining a receiving / oscillating surface 11 of an ultrasonic probe 1 for vertically oscillating ultrasonic waves from the receiving / oscillating surface 11 by a predetermined angle θ with respect to a surface of a flaw detection object M under a condition that flaw detection ultrasonic waves Ud oscillated from a center A of the receiving / oscillating surface 11 are reflected by a flaw K on a bottom surface of the flaw detection object M and always received by the receiving / oscillating surface 11 as flaw detection signal waves Ui.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic flaw detection method, and more particularly to an ultrasonic flaw detection method that reduces the influence of multiple reflected waves from the surface and bottom surface of a material to be detected. [Background technology]

[0002] One such ultrasonic flaw detection method is disclosed in Patent Document 1, in which the receiving surface of a phased array ultrasonic probe is tilted significantly in the width direction perpendicular to the direction of movement relative to the surface of the material to be detected, and in this state, ultrasonic waves for flaw detection are generated that form an angle with the tilted receiving surface of the ultrasonic probe and are incident perpendicularly on the surface of the material to be detected. This causes noise-like reflected waves (hereinafter referred to as multiple reflected waves) from the surface of the material to be detected to be reflected back and forth between the tilted receiving surface and the surface of the material to be detected, and are quickly eliminated by exiting to the side of the ultrasonic probe, preventing the multiple reflected waves from affecting the reflected waves (detection signal waves) from flaws in the material to be detected. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2017-49215 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned conventional ultrasonic flaw detection method, by quickly causing the multiple reflected waves to exit to the side and disappear, flaw detection can be performed quickly and efficiently while eliminating the influence of the multiple reflected waves even when the oscillation period of the flaw detection ultrasonic waves emitted from the ultrasonic probe is shortened.To achieve this, as described above, the receiving surface of the ultrasonic probe is tilted significantly in the width direction of the ultrasonic probe relative to the surface of the material to be detected, and the flaw detection ultrasonic waves are emitted at an angle from the receiving surface of the ultrasonic probe so that even in this state, the flaw detection ultrasonic waves are incident perpendicularly on the surface of the material to be detected.

[0005] However, this is based on the assumption that a phased array ultrasonic probe is equipped with multiple ultrasonic transducers. A typical ultrasonic probe equipped with only a single ultrasonic transducer normally emits ultrasonic waves for flaw detection in a direction perpendicular to the receiving surface, making it difficult to emit ultrasonic waves for flaw detection at the desired angle relative to the receiving surface.

[0006] Therefore, the present invention aims to solve such problems and provide an ultrasonic flaw detection method that can eliminate the influence of multiple reflected waves and perform good flaw detection even when a simple single-vibrator ultrasonic probe is used. [Means for solving the problem]

[0007] In order to achieve the above object, in the first invention, the receiving surface (11) of the ultrasonic probe (1) that emits ultrasonic waves for flaw detection vertically from its receiving surface (11) is tilted at a predetermined angle (θ) with respect to the surface of the material (M) to be flaw-detected, under the condition that the ultrasonic waves for flaw detection (Ud) emitted from the center (A) of the receiving surface (11) are reflected by a flaw (K) on the bottom surface of the material (M) to be flaw-detected and are always received by the receiving surface (11) as flaw detection signal waves (Ui).

[0008] According to the first invention, even in a single-transducer ultrasonic probe that radiates ultrasonic waves only in a direction perpendicular to its receiving surface, the influence of multiple reflected waves can be eliminated and good flaw detection can be performed.

[0009] In the second invention, the tilting direction is the depth direction of the ultrasonic probe (1).

[0010] According to the second invention, flaws can be detected well even when the material to be detected is a round bar or the like, in which the distance from the oscillation receiving surface changes in the width direction of the ultrasonic probe.

[0011] In the third invention, the predetermined angle (θ) is further set to an angle range in which at least the first surface reflected wave (Us1) and bottom reflected wave (Ub1) of the multiple reflected waves from the test material (M) are received by the receiving and emitting surface (11), and the surface reflected waves (Us2, Us3, ...) and bottom reflected waves (Ub2, Ub3, ...) of the predetermined number or more are not received by the receiving and emitting surface (11).

[0012] According to the third aspect of the present invention, the influence of multiple reflected waves can be further reliably eliminated, thereby enabling good flaw detection.

[0013] The symbols in parentheses above indicate, for reference, the correspondence with specific means described in the embodiments to be described later. [Effects of the Invention]

[0014] As described above, according to the ultrasonic flaw detection method of the present invention, even when a simple single-transducer ultrasonic probe is used, the influence of multiple reflected waves can be eliminated and good flaw detection can be performed. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an overall perspective view of a round bar during ultrasonic flaw detection. [Figure 2] FIG. 10 is a cross-sectional view of an ultrasonic probe placed at an angle in the depth direction. [Figure 3] 1 is a cross-sectional view showing the geometric conditions under which a flaw detection signal wave is received by an inclined receiving surface of an ultrasonic probe. FIG. [Figure 4] FIG. 1 is a cross-sectional view showing the geometric conditions under which surface multiple reflected waves are not received by an inclined receiving surface of an ultrasonic probe. [Figure 5] FIG. 10 is a cross-sectional view showing the geometric conditions under which bottom-surface multiple-reflected waves are not received by the inclined receiving surface of the ultrasonic probe. [Figure 6] FIG. 10 is a cross-sectional view showing a conventional example in which ultrasonic probes are arranged parallel in the depth direction. [Figure 7] FIG. 10 is a diagram showing multiple reflected waves generated by ultrasonic waves for flaw detection in a conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0016] The embodiments described below are merely examples, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

[0017] Figure 1 shows an example of ultrasonic testing of a round bar material M, which is the material to be tested, with an ultrasonic probe 1 placed above the round bar material M. The ultrasonic probe 1 is cylindrical, and its bottom surface 11 (receiving surface) has a concave, arc-shaped central portion (Figure 6). The ultrasonic probe 1 contains a single ultrasonic vibrator, and the emitted ultrasonic waves are focused into a beam by the receiving surface 11, which has a concave central portion, toward the round bar material M below. In this state, the ultrasonic probe 1 or the round bar material M is moved relatively in the longitudinal direction, and flaws are detected in the longitudinal direction of the round bar material M.

[0018] In order for a single-transducer ultrasonic probe 1 to receive and emit ultrasonic waves well, conventionally, its receiving surface 11 is parallel to the top surface (surface) M1 of the round bar M in the depth direction as shown in Figure 6, so that the flaw detection ultrasonic waves Ud emitted from the center of the ultrasonic probe 1 are incident perpendicularly on the top surface M1 of the round bar M (thick arrow in Figure 6). However, when done this way, the surface reflected waves Us from the top surface of the round bar M and the bottom reflected waves Ub from the lower surface (bottom surface) M2 of the round bar M are reflected back and forth between the receiving surface 11 and the probe, generating multiple reflected waves that act as noise (thin arrow in Figure 6).

[0019] 7, if the oscillation period T of the flaw detection ultrasonic wave Ud from the ultrasonic probe 1 is short, Ub4 of the multiple reflected waves Ub1 to Ub4 (the figure shows only the bottom multiple reflected waves) due to the immediately preceding flaw detection ultrasonic wave Udf appears after the next flaw detection ultrasonic wave Udr to affect as noise the flaw detection signal wave appearing in the flaw detection window set in this region. This effect becomes more severe as the oscillation period T becomes shorter.

[0020] Therefore, in this embodiment, as shown in Fig. 2, the receiving surface 11 of the ultrasonic probe 1 is inclined by an angle θ in the depth direction with respect to the top surface M1 of the round bar M. As shown in the geometric dimension diagram in Fig. 3, this inclination angle θ must satisfy the condition that the flaw detection ultrasonic wave Ud emitted from the center A in the depth direction of the receiving surface 11 is reflected by the flaw K on the bottom surface of the round bar M and is received again by the receiving surface 11 as the flaw detection signal wave Ui, and this satisfies the inequality of the following formula (1). Due to the geometric relationship shown in Fig. 3, this inequality satisfies the inequality of the following formula (2).

[0021]

number

[0022]

number

[0023] In the above equations (1) and (2), L is half the length 2L of the depth direction of the receiving surface, Dw is the distance between the depth direction center A of the receiving surface and the surface M1 of the round bar material M, Df is the distance between the surface M1 of the round bar material M and the flaw K, and φ is the angle (refraction angle) calculated using the following equation (3) from the sound speed in water Cw and the sound speed inside the round bar material Ct.

[0024]

number

[0025] As an example, when L = 6 (mm), Dw = 26.7 (mm), Df = 33.1 (mm), Cw = 1500 m / s, and Ct = 5900 m / s, if θ is set to 0.8 (°), the right-hand side of the above equation (2) becomes 4.391, which satisfies the inequality.

[0026] In this embodiment, the inclination angle θ of the receiving surface 11 can be made extremely small, at about 0.8°, so that the flaw detection ultrasonic waves Ud emitted perpendicularly from the receiving surface 11 are efficiently incident on the round bar M, and in this state, the multiple reflected waves Us, Ub generated on the surface M1 and bottom surface M2 of the round bar M are reflected back and forth between the receiving surface 11 and the surface M1 of the round bar M, and are quickly eliminated after exiting, due to the inclination of the receiving surface 11 in the depth direction. Therefore, even if the oscillation period T (see FIG. 7) between the flaw detection ultrasonic waves Udf, Udr is shortened, it is possible to avoid the multiple reflected waves Us, Ub appearing after the oscillation of the subsequent flaw detection ultrasonic wave Udr and affecting the flaw detection signal wave Ui.

[0027] Table 1 shows the change in the S / N ratio of the flaw detection signal when the tilt angle θ is changed from 0° (not tilted) to 0.8°. As is clear from Table 1, if the tilt angle θ is set to 0.5° or more, the influence of the multiple reflected waves Us and Ub can be eliminated and the S / N ratio can be significantly improved.

[0028] [Table 1]

[0029] Here, the first surface reflected wave Us1 and bottom reflected wave Ub1 of the multiple reflected waves Us and Ub must be incident on the receiving oscillation surface 11 in order to set a flaw detection window between them that captures the flaw detection signal wave Ui. On the other hand, if the oscillation period T of the flaw detection ultrasonic wave Ud is shortened from 1 ms (frequency 1 KHz) to about 0.38 ms (frequency 2.6 KHz), for example, it is the fourth and subsequent multiple reflected waves Us4 and Ub4 that appear after the next flaw detection ultrasonic wave Udr and affect the flaw detection signal wave Ui.

[0030] Therefore, for each tilt angle θ, the condition under which the fourth and subsequent surface multiple reflected waves Us4 are not received by the receiving surface 11 is that, based on the geometric relationship shown in Figure 4, n = 4 and the inequality in the following formula (4) is established. Therefore, by confirming that this inequality is established, it can be confirmed that the fourth and subsequent surface multiple reflected waves Us4 exit and disappear without being received by the receiving surface 11, and do not affect the flaw detection signal wave Ui. As an example, by substituting the specific values ​​shown in paragraph

[0025] above into the following formula (4), the inequality in formula (4) is satisfied.

[0031]

number

[0032] Furthermore, for each tilt angle θ, the condition for the fourth and subsequent bottom multiple reflected waves Ub4 not to be received by the receiving surface 11 is, based on the geometric relationship shown in Figure 5, that the inequality in the following formula (5) be established with n = 4. Therefore, by confirming that this inequality is established, it can be confirmed that the fourth and subsequent bottom multiple reflected waves Ub4 exit and disappear without being received by the receiving surface 11, and do not affect the flaw detection signal wave Ui. As an example, when the specific values ​​shown in paragraph

[0025] above are substituted into the following formula (5), the inequality in formula (5) is satisfied.

[0033]

number

[0034] Although the ultrasonic probe of a single transducer type has been exemplified in the above embodiment, the present invention is not limited to this, and may be of a phased array type, for example. In the above embodiment, the material to be detected is a round bar, but this is not limited to this and may be a square bar or a flat plate, etc. In this case, the inclination direction of the receiving surface does not necessarily have to be the depth direction. [Explanation of symbols]

[0035] 1… Ultrasonic probe, 11… Vibration surface, A… Center of vibration surface, K… Flaw, M… Bar (material to be tested), Ud… Ultrasonic wave for testing, Ui… Testing signal wave, θ… Inclination angle.

Claims

1. An ultrasonic flaw detection method in which the receiving surface of an ultrasonic probe, which emits flaw detection ultrasonic waves vertically from its receiving surface, is tilted at a predetermined angle with respect to the surface of the material to be detected, under the condition that the flaw detection ultrasonic waves emitted from the center of the receiving surface are reflected by flaws on the bottom surface of the material to be detected and are always received at the receiving surface as flaw detection signal waves.

2. The ultrasonic flaw detection method according to claim 1 , wherein the tilting direction is a depth direction of the ultrasonic probe.

3. The ultrasonic flaw detection method according to claim 1 or 2, wherein the predetermined angle is further set to an angle range in which at least the first surface reflected wave and bottom reflected wave of the multiple reflected waves from the material to be detected are received by the receiving / transmitting surface, and the surface reflected waves and bottom reflected waves of the predetermined number of times or more are not received by the receiving / transmitting surface.

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