JP2023077504A - Supersonic flaw detection method - Google Patents

Abstract

To provide a supersonic flaw detection method that can maintain high flaw detection sensitivity even when a small diameter bar material is misaligned.SOLUTION: A round bar material M has an outer diameter that fits within a region where sound pressure distribution of near sound field of a convergence ultrasonic probe 2 is maximal and sound pressure of a convergence sound field of the convergence ultrasonic probe 2 is above a specified value. The round bar material M is positioned within a region closer to the probe 2 concerned than a convergence point P of supersonic Us emitted from the convergence ultrasonic probe 2; and flaw detection of the round bar material M is performed.SELECTED DRAWING: Figure 5

Description

TECHNICAL FIELD The present invention relates to an ultrasonic flaw detection method, and more particularly to an ultrasonic flaw detection method suitable for flaw detection of small-diameter bars.

In the case of in-line flaw detection of round bars by the water immersion method, for example, flaw detection equipment as shown in FIG. 1 is used. In FIG. 1, a rotating columnar housing 1 is filled with water, and a round bar M is placed at the center of both end walls 11 and 12 of the housing 1 while ensuring liquid tightness with packing. A guide portion 13 is provided for passing through. An ultrasonic probe 2 provided on the peripheral wall of the housing 1 rotates around the round bar M passing through the central part of the housing 1 to detect flaws thereof. I do. As the ultrasonic probe 2, a focusing probe that focuses ultrasonic waves to one point is often used in order to improve detection sensitivity. I am trying to let

JP 2010-133856

By the way, the guide portion 13 provided in the housing 1 has a margin in its inner diameter in order to cope with variations in the diameter of the round bar M. relatively freely displaced, resulting in positional deviation. Since the small-diameter round bar M has a large curvature, as shown in FIG. 2, even if there is a slight displacement d, the ultrasonic wave Us emitted from the ultrasonic probe 2 is greatly refracted (refractive angle θ). There was a problem that the path changed greatly and deviated from the flaw detection area, and the flaw detection sensitivity greatly decreased. This is shown in FIG. 3, where a round bar M with a diameter of 50 mm does not have a significant drop in flaw detection sensitivity even if it is misaligned, but a round bar M with a diameter of 6 mm (hereinafter referred to as φ6 mm) has a slight misalignment. Also, the flaw detection sensitivity is greatly reduced.

Therefore, the present invention is intended to solve such problems, and an object of the present invention is to provide an ultrasonic flaw detection method capable of maintaining high flaw detection sensitivity even when a small-diameter bar is displaced. .

In order to achieve the above object, in the ultrasonic flaw detection method of the present invention, in a region closer to the probe (2) than the focal point (P) of the ultrasonic waves (Us) output from the focused ultrasonic probe (2) , a bar having an outer diameter in which the sound pressure distribution of the near-field sound field of the focused ultrasonic probe (2) is maximal and the sound pressure of the focused sound field of the focused ultrasonic probe (2) falls within a region equal to or greater than a predetermined range. (M) is positioned and flaw detection is performed on the bar (M). A round bar is suitable as the bar (M), but it is not limited to this, and a square bar may be used.

The symbols in parentheses above refer to the corresponding relationship with specific means described in the embodiments described later.

According to the ultrasonic flaw detection method of the present invention, it is possible to maintain high flaw detection sensitivity even when a small-diameter bar is displaced.

1 is an overall perspective view of a flaw detection equipment; FIG. It is a cross-sectional view of flaw detection equipment. It is a figure which shows the sensitivity fall accompanying the position shift of the round-bar body from which diameters differ. FIG. 4 illustrates the spread of sound pressure at different axial positions of the focused sound field of an ultrasound probe; It is a figure which shows the positional relationship of an ultrasonic probe and a round bar material. FIG. 4 is a diagram showing the amplitude distribution in the axial direction of the near-field sound field of the ultrasonic probe; FIG. 4 is a diagram showing the amplitude distribution in the axial direction of the focused sound field of the ultrasonic probe; It is a figure which shows an example of the positional relationship of an ultrasonic probe and a round-bar material by comparison with a conventional method. FIG. 5 is a diagram showing an example of change in flaw detection sensitivity with respect to positional deviation of the same round bar, in comparison with a conventional method. It is a figure which shows the depth position of the crack in a round-bar material. FIG. 5 is a diagram showing an example of change in flaw detection sensitivity with respect to the depth position of flaws in a round bar.

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

The flaw detection equipment in this embodiment is the same as that shown in FIG. 1, and the focused ultrasonic probe (hereinafter simply referred to as probe) is circular in plan view in this embodiment.

The sound pressure distribution of the probe 2 increases toward the focal point (focus) and reaches a maximum near the focal point, but the sound pressure distribution near the focal point becomes very narrow (line A in FIG. 4). This is the reason why, when the small-diameter round bar M is displaced, the ultrasonic wave path changes due to refraction, which greatly reduces the sensitivity of flaw detection. On the other hand, in the vicinity of the probe 2, although the sound pressure distribution becomes wider, a sufficient sound pressure cannot be obtained (line B in FIG. 4). On the other hand, at an appropriate position between the probe 2 and the focal point, it is possible to secure a sufficiently wide sound pressure distribution while maintaining a large sound pressure (line C in FIG. 4).

Therefore, in this embodiment, as shown in FIG. 5, the round bar M is positioned in a region closer to the probe 2 than the focal point P of the ultrasonic waves Us output from the probe 2 . In FIG. 5, x is the water distance from the center of the oscillating surface of the probe 2 to the outer peripheral surface of the round bar M, D is the diameter of the probe, f is the frequency of the oscillating ultrasonic waves, and F is the focal distance.

Here, the sound field of the probe 2 is represented by the following equation (1) and is composed of a near-field sound field close to the probe 2 and a far-field sound field far from the probe 2 . In the formula, A(x) is the amplitude at water distance x (ratio of sound pressure to the average sound pressure immediately before probe 2), C is the speed of ultrasonic waves in water, and λ is the wavelength of ultrasonic waves in water. /f, where f and D are as described above.

By the way, especially in the flaw detection of a small-diameter round bar, the frequency is increased in order to secure the distance resolution, and the vibrator is increased in order to secure the sound pressure. Positioning it in a region closer to the probe 2 than the point P often results in positioning it in the near field. In this short-distance sound field, the change in sound pressure on the center axis O (FIG. 5) of the probe 2 repeatedly becomes maximum at predetermined intervals.

FIG. 6 shows changes in sound pressure in the near-field sound field when the frequency f of ultrasonic waves is 15 MHz, the probe diameter D is 12 mm, and the focal distance F is 100 mm. As is clear from FIG. 6, in the near-field sound field, the sound pressure change repeatedly reaches its maximum at predetermined intervals. In the case of a small-diameter round bar of φ6 mm, the entire round bar can be accommodated within a region where an amplitude of 0.8 or more can be secured.

On the other hand, considering a focused sound field, the change in sound pressure on the center axis of the probe is given by the following equation (2). where A(x), x, λ, f, D, F, C are as described above and J is the focusing factor.

FIG. 7 shows the sound pressure change in the focused sound field when the frequency f of the ultrasonic wave Us is 15 MHz, the probe diameter D is 12 mm, and the focusing distance is 100 mm. In addition, in FIG. 7, the water distance of 65 mm or less is actually not an amplitude of 0, but a region that cannot be calculated by the above equation (2). Therefore, the round bar M must be positioned at a water distance of 65 mm or more. On the other hand, although the amplitude A(x) becomes large near the water distance of 100 mm where the focal point P of the ultrasonic wave Us is, the sound pressure distribution near the focal point P becomes very narrow as described above. The water distance x for positioning the material M is preferably set to 70 mm.

In order to confirm the effect of the present embodiment, as shown in FIG. A conventional method of focusing the ultrasonic wave Us output from the probe 2 at the center of the round bar M, and a method of focusing the ultrasonic wave Us behind the round bar M as shown in FIG. With respect to the method of the present embodiment in which the round bar M is positioned within the maximum amplitude region with a water distance of 70 mm closer to the probe 2 than the focal point P of the ultrasonic wave Us output from the probe 2, the positional deviation of the round bar M We compared the change in flaw detection sensitivity for This is shown in FIG. In addition, in FIG. 8, MD is the diameter of the round bar M. As shown in FIG.

As is clear from FIG. 9, in the conventional method, if the round bar M is displaced, the sensitivity of flaw detection drops significantly. Sensitivity remains sufficiently high. Furthermore, even if the depth of the flaw in the round bar M increases by 1 mm from the center a to b and c as shown in FIG. 10, the flaw detection sensitivity is maintained sufficiently high as shown in FIG. Lines a, b, and c in FIG. 11 correspond to flaw positions a, b, and c in FIG. This is because flaws of any depth can be detected with sufficient sensitivity because the round bar M is contained within the maximum amplitude region of the water distance of 70 mm shown in FIG.

In the above embodiment, a round bar is used as a flaw detection target, but the method of the present invention can also be applied to a square bar. Also, as the probe, a rectangular probe extending in the longitudinal direction of the bar in plan view can be used. Furthermore, instead of rotating the probes, a plurality of probes may be installed at predetermined intervals in the circumferential direction.

1 -- housing, 2 -- focused ultrasonic probe, M -- round bar, P -- focal point, Us -- ultrasonic wave.

Claims (2)

In a region closer to the probe than the focal point of the ultrasonic waves output from the focused ultrasound probe, the sound pressure distribution of the near-field sound field of the focused ultrasound probe is maximum and the focused sound field of the focused ultrasound probe. An ultrasonic flaw detection method in which a rod having an outer diameter that falls within a region where the sound pressure of (1) is greater than or equal to a predetermined value is positioned and flaw detection is performed on the rod. 2. The ultrasonic flaw detection method according to claim 1, wherein the bar is a round bar.

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