Ultrasonic flaw detection method

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]

[0001] The present invention relates to an ultrasonic flaw detection method, and more particularly to an ultrasonic flaw detection method suitable for detecting flaws in small diameter rods. [Background technology]

[0002] When flaws in a round bar are detected in-line using the water immersion method, for example, flaw detection equipment such as that shown in Figure 1 is used. In Figure 1, a rotating cylindrical housing 1 is filled with water, and guide sections 13 are provided at the center of both end walls 11 and 12 of the housing 1, allowing the round bar M to pass through while ensuring liquid-tightness with packing. As the round bar M passes through the center of the housing 1, an ultrasonic probe 2 attached to the peripheral wall of the housing 1 revolves around the round bar M together with the housing 1 to detect flaws therein. A focusing probe that focuses ultrasonic waves at a single point is often used as the ultrasonic probe 2 to improve detection sensitivity, and as shown in Patent Document 1, ultrasonic waves are usually focused at the center of the round bar M. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2010-133856 Summary of the Invention [Problem to be solved by the invention]

[0004] The guide section 13 provided in the housing 1 has a large inner diameter to accommodate variations in the diameter of the round bar M, and small-diameter round bar M is relatively free to move and become misaligned as it passes through the guide section 13. Because the small-diameter round bar M has a large curvature, even a slight misalignment d causes the ultrasonic waves Us emitted from the ultrasonic probe 2 to be significantly refracted (refraction angle θ), significantly changing their path and causing them to deviate from the detection area, resulting in a significant decrease in flaw detection sensitivity, as shown in Figure 3. This is shown in Figure 3, where a misalignment of a 50 mm diameter round bar M does not significantly decrease flaw detection sensitivity, but a slight misalignment of a 6 mm diameter round bar M (hereinafter referred to as φ6 mm) significantly decreases flaw detection sensitivity.

[0005] Therefore, the present invention is intended to solve such problems, and has an object to provide an ultrasonic flaw detection method that can maintain high flaw detection sensitivity even when a small diameter bar material is displaced. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides an ultrasonic flaw detection method for detecting flaws in a bar material (M) by outputting ultrasonic waves from a focused ultrasonic probe (2) to the bar material (M), the method comprising: positioning the bar material (M) so that two intersections of a side surface of the bar material (M) with a central axis (O) of the focused ultrasonic probe (2) are within a region on the central axis (O) where the sound pressure distribution in the near field of the probe (2) is maximum and the sound pressure in the focused ultrasonic field of the probe (2) is equal to or greater than a predetermined value; Ultrasonic It is placed in a region closer to the focused ultrasonic probe 2 than the focal point P. A round bar is suitable as the bar M, but it is not limited to this and a square bar may also be used.

[0007] 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]

[0008] According to the ultrasonic flaw detection method of the present invention, high flaw detection sensitivity can be maintained even when a small diameter bar material is displaced. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an overall perspective view of a flaw detection facility. [Figure 2] FIG. 1 is a cross-sectional view of the flaw detection equipment. [Figure 3] 10A and 10B are diagrams showing a decrease in sensitivity due to positional deviation of round rod bodies with different diameters. [Figure 4] FIG. 1 illustrates the sound pressure spread at different axial positions of the focused sound field of an ultrasonic probe. [Figure 5] FIG. 2 is a diagram showing the positional relationship between an ultrasonic probe and a round bar material. [Figure 6] FIG. 1 is a diagram showing an amplitude distribution in the axial direction of the near field of an ultrasonic probe. [Figure 7] FIG. 1 is a diagram showing the amplitude distribution in the axial direction of the focused sound field of an ultrasonic probe. [Figure 8] FIG. 10 is a diagram showing an example of the positional relationship between an ultrasonic probe and a round bar in comparison with a conventional method. [Figure 9] FIG. 10 is a diagram showing an example of change in flaw detection sensitivity with respect to positional deviation of the same round bar material, in comparison with a conventional method. [Figure 10] FIG. 10 is a diagram showing the depth position of a flaw in a round bar material. [Figure 11] FIG. 10 is a diagram showing an example of the change in flaw detection sensitivity with respect to the depth position of a flaw in a round bar material. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] The flaw detection equipment in this embodiment is the same as that shown in FIG. 1, which has already been explained, and the focused ultrasonic probe (hereinafter simply referred to as the probe) used in this embodiment is circular in plan view.

[0012] The sound pressure distribution of probe 2 increases toward the focal point (focus point), reaching a maximum near the focal point, but the sound pressure distribution near the focal point is very narrow (line A in Figure 4). This is the reason why, as mentioned above, when the small-diameter round bar material M is misaligned, the ultrasonic path changes due to refraction, causing a significant decrease in flaw detection sensitivity. On the other hand, near probe 2, the sound pressure distribution becomes wider, but a sufficiently large sound pressure cannot be obtained (line B in Figure 4). In contrast, at an appropriate position between probe 2 and the focal point, a large sound pressure can be maintained while also ensuring a sufficiently wide sound pressure distribution (line C in Figure 4).

[0013] Therefore, in this embodiment, as shown in Fig. 5, the round bar M is positioned in an area 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 oscillation surface of the probe 2 to the outer circumferential 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.

[0014] Here, the sound field of probe 2 is expressed by the following formula (1), and is composed of a near field close to probe 2 and a far field far from probe 2. In the formula, A(x) is the amplitude at water distance x (sound pressure ratio to the average sound pressure just before probe 2), C is the speed of sound of ultrasound in water, λ is the wavelength of ultrasound in water, calculated as C / f, where f and D are as described above.

[0015] JPEG0007742023000001.jpg31130

[0016] Incidentally, when inspecting small diameter round bar materials, the frequency is increased to ensure distance resolution, and the transducer is enlarged to ensure sound pressure, so when the round bar material M is positioned in an area closer to the probe 2 than the focal point P as described above, it is often positioned in the near field. In this near field, the sound pressure change on the central axis O (Fig. 5) of the probe 2 repeatedly reaches a maximum at a predetermined interval.

[0017] Figure 6 shows the change in sound pressure in the near field when the ultrasonic frequency f is 15 MHz, the probe diameter D is 12 mm, and the focusing distance F is 100 mm. As is clear from Figure 6, in the near field, the sound pressure change repeatedly reaches a maximum at regular intervals, but in the maximum regions near the water distances of 40 mm, 50 mm, 70 mm, and 118 mm, if a small diameter round bar with a diameter of 6 mm is used, the entire round bar can be contained within the region where an amplitude of 0.8 or more can be ensured.

[0018] On the other hand, when considering a focused sound field, the change in sound pressure on the central axis of the probe is given by the following equation (2): where A(x), x, λ, f, D, F, and C are as described above, and J is the focusing coefficient.

[0019] JPEG0007742023000002.jpg45128

[0020] Figure 7 shows the change in sound pressure 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 focal distance is 100 mm. Note that in Figure 7, the amplitude is not actually 0 at water distances of 65 mm or less, and this is an area that cannot be calculated using equation (2) above. Therefore, the rod M must be positioned at a water distance of 65 mm or more. On the other hand, although the amplitude A(x) increases near the water distance of 100 mm, where the focal point P of the ultrasonic wave Us is located, as mentioned above, the sound pressure distribution near the focal point P becomes very narrow, so ultimately it is best to set the water distance x for positioning the rod M at 70 mm.

[0021] To confirm the effectiveness of this embodiment, a 6 mm diameter round bar M with a 0.4 mm diameter horizontal hole (SDH) formed in its center as a pseudo flaw Df was used. A conventional method was used to focus the ultrasonic waves Us output from the probe 2 at the center of the round bar M, as shown in Figure 8(1). Another method was used to focus the ultrasonic waves Us behind the round bar M, as shown in Figure 8(2). The method of this embodiment was used to position the round bar M within the maximum amplitude region at a water distance of 70 mm, closer to the probe 2 than the focal point P of the ultrasonic waves Us output from the probe 2. The results are shown in Figure 9. In Figure 8, MD is the diameter of the round bar M.

[0022] As is clear from Figure 9, in the conventional method, flaw detection sensitivity drops significantly when the position of the round bar M is displaced, whereas in the method of this embodiment, flaw detection sensitivity remains sufficiently high even when the position of the round bar M is displaced. Furthermore, even when the flaw depth in the round bar M increases by 1 mm from the center a to b and c as shown in Figure 10, flaw detection sensitivity remains sufficiently high as shown in Figure 11. Note that lines a, b, and c in Figure 11 correspond to the flaw positions a, b, and c in Figure 10. This is because flaws of any depth can be detected with sufficient sensitivity because the round bar M is located within the maximum amplitude region at a water distance of 70 mm as shown in Figure 6.

[0023] Although the above embodiment uses a round bar as the target for flaw detection, the method of the present invention can also be applied to square bars. Furthermore, a probe having a rectangular shape extending in the longitudinal direction of the bar in a plan view can be used. Furthermore, instead of rotating the probe, multiple probes can be installed at predetermined intervals around the circumference. [Explanation of symbols]

[0024] 1...housing, 2...focused ultrasonic probe, M...round bar material, P...focused point, Us...ultrasound.

Claims

1. An ultrasonic flaw detection method for detecting flaws in a bar material by outputting ultrasonic waves from a focused ultrasonic probe to the bar material, wherein two intersections of a side surface of the bar material with a central axis of the focused ultrasonic probe are positioned within a region on the central axis where the sound pressure distribution in the near field of the probe is maximum and the sound pressure in the focused sound field of the probe is equal to or greater than a predetermined value, and the bar material is positioned within a region closer to the focused ultrasonic probe than the focal point of the ultrasonic waves.

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

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