Ultrasonic flaw detection method

Abstract

This invention provides an ultrasonic flaw detection method that can correct deviations in the flaw detection range caused by fluctuations in the water gap, thereby preventing the occurrence of undetected areas. [Solution] When a water gap WG exists between the ultrasonic transducer 1 and the surface M1 of the material to be inspected facing it, and the arrival times of the primary bottom surface reflected wave Wb1 and secondary bottom surface reflected wave Wb2 of the material to be inspected M when a normal water gap WGo exists are B1o and B2o, respectively, and when the arrival times of the primary bottom surface reflected wave Wb1 and secondary bottom surface reflected wave Wb2 of the material to be inspected M when a changed water gap WG exists are B1 and B2, respectively, the start time T1 of the inspection range R is corrected by the correction time ΔT calculated by the following formula (1). ΔT=(2×B1-B2)-(2×B1o-B2o)…(1)

Description

Technical Field

[0001] The present invention relates to an ultrasonic flaw detection method, and particularly to an ultrasonic flaw detection method in which a water film is interposed between the outer circumference of a bar material and an ultrasonic probe to perform flaw detection.

Background Art

[0002] Fig. 3 shows an example of ultrasonic flaw detection of a round bar material M. In Fig. 3, an ultrasonic probe 1 is provided so as to be close to and face the outer circumference of the material to be flaw detected M. The flaw detection ultrasonic wave W oscillated from the ultrasonic probe 1 is reflected by the facing surface M1 (surface) of the material to be flaw detected M and returns to the ultrasonic probe 1 as a surface reflection wave Wa, and is further reflected by the bottom surface M2 of the material to be flaw detected M and returns to the ultrasonic probe 1 as a bottom surface reflection wave Wb, where it is received.

[0003] If there is a flaw inside the material to be flaw detected M, the flaw detection ultrasonic wave W is reflected by the flaw portion and returns to the ultrasonic probe 1 as a flaw reflection wave Wd. Since the flaw reflection wave Wd occurs between the surface reflection wave Wa and the bottom surface reflection wave Wb, as shown in Fig. 4(2), a flaw detection range R is set in an appropriate range between them, and only the flaw reflection wave Wd is detected. Note that Fig. 4(1) shows the positional relationship corresponding to the signal waveform in Fig. 4(2) with the material to be flaw detected M as a round bar.

[0004] By the way, a predetermined gap of about several millimeters is provided between the ultrasonic probe 1 and the surface M1 of the material to be flaw detected (round bar) M that moves relative to the longitudinal direction, and a water film is formed in the gap to form a water gap WG so that the flaw detection ultrasonic wave efficiently enters the round bar M.

[0005] On the other hand, the flaw detection range R is set within a certain time range after a certain time Ta based on the oscillation time Ts of the flaw detection ultrasonic wave. However, when the water gap WG fluctuates, for example, increases, as shown in Fig. 5 drawn in comparison with Fig. 4, the arrival times of the surface reflection wave Wa and the bottom surface reflection wave Wb are delayed, so that the flaw detection range R is relatively displaced from its original position and an undetected region RU occurs.

[0006] Therefore, in order to prevent this, Patent Document 1 provides a guide roller on the ultrasonic probe, which is kept in constant contact with the surface of the round bar material, thereby preventing fluctuations in the water gap. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6070004 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, even with guide rollers installed, the water gap can fluctuate due to mechanical wear of the rollers themselves or parts of the guide mechanism, making it unavoidable that undetected areas may occur.

[0009] Therefore, the present invention aims to solve these problems by providing an ultrasonic flaw detection method that can correct deviations in the flaw detection range due to fluctuations in the water gap and prevent the occurrence of undetected areas. [Means for solving the problem]

[0010] To achieve the above objective, the present invention provides an ultrasonic flaw detection method in which, when a water gap (WG) exists between an ultrasonic transducer (1) and the surface (M1) of a material to be inspected (M) facing it, the arrival times of the primary bottom surface reflected wave (Wb1) and secondary bottom surface reflected wave (Wb2) of the material to be inspected (M) when a normal water gap (WGo) exists are B1o and B2o, respectively, and when a changed water gap (WG) exists, the arrival times of the primary bottom surface reflected wave (Wb1) and secondary bottom surface reflected wave (Wb2) of the material to be inspected are B1 and B2, respectively, and the start time (T1) of the flaw detection range (R) is corrected by a correction time ΔT calculated by the following formula (1). ΔT=(2×B1-B2)-(2×B1o-B2o)…(1) Furthermore, the present invention is particularly applicable when the material to be inspected is a round bar.

[0011] 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]

[0012] According to the ultrasonic flaw detection method of the present invention, it is possible to effectively prevent the occurrence of undetected areas by correcting deviations in the detection range due to fluctuations in the water gap. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows the positional relationship and time course of the primary and secondary bottom-reflected waves. [Figure 2] This figure shows the time evolution of reflected waves when the water gap is normal and when the water gap is fluctuating. [Figure 3] This is a schematic cross-sectional view showing an example of ultrasonic testing on a round bar material. [Figure 4] This figure shows the positional and temporal relationship of the flaw detection area before water gap fluctuations. [Figure 5] This figure shows the positional and temporal relationship of the flaw detection area after water gap fluctuations. [Modes for carrying out the invention]

[0014] 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.

[0015] A simple method for calculating the water gap WG is to multiply the time difference between the oscillating reflected wave Ws (see FIGS. 4 and 5) generated when the flaw detection ultrasonic wave W is oscillated from the ultrasonic probe 1 and the surface reflected wave Wa generated by the reflection of the flaw detection ultrasonic wave on the surface of the round bar M facing the ultrasonic probe 1 by the underwater speed of the ultrasonic wave. However, since the water gap WG in water film flaw detection is small, the oscillating reflected wave Ws and the surface reflected wave Wa overlap, and the water gap WG cannot be calculated by the above method. Therefore, the bottom reflected wave Wb generated by the reflection of the flaw detection ultrasonic wave W on the bottom surface M2 of the round bar M is used as follows. This will be described with reference to FIG. 1.

[0016] In FIGS. 1(1) and (2), there are shown the positional relationships and time courses B1 and B2 of the overlapping oscillating reflected wave Ws and surface reflected wave Wa, the primary bottom reflected wave Wb1 that is reflected once on the bottom surface M2 of the round bar M and returns to the ultrasonic probe 1, and the secondary bottom reflected wave Wb2 that is reflected once on the bottom surface of the round bar M and then further reflected on the surface M1 of the round bar steel M and reflected twice on the bottom surface M2 and returns to the ultrasonic probe 1.

[0017] Here, the time B1 from the oscillation of the flaw detection ultrasonic wave W until the primary bottom reflected wave Wb1 is received is represented by the following formula (1). In the following formulas, C1 is the sound speed in water and C2 is the sound speed in the round bar M. B1 = 2×WG / C1 + 2×D / C2…(1)

[0018] Also, the time B2 from the oscillation of the flaw detection ultrasonic wave W until the secondary bottom reflected wave Wb2 is received is represented by the following formula (2). B2 = 2×WG / C1 + 4×D / C2…(2)

[0019] From the above formulas (1) and (2), the water gap WG can be calculated by the following formula (3). WG = (2×B1 - B2) / 2×C1…(3)

[0020] Therefore, when the water gap changes from the normal water gap WGo to WG, the delay time ΔT of the reflected wave can be obtained by the following formula (4). Therefore, by correcting the start time of the flaw detection range R by this time ΔT, the flaw detection range R can be set at an appropriate time. ΔT = 2(WG - WGo) / C1 = (2×B1 - B2) - (2×B1o - B2o)…(4) Here, B1o and B2o are the times until the first bottom surface reflected wave and the second bottom surface reflected wave are received, respectively, when the normal water gap is WGo.

[0021] When the reception times B1 and B2 of the first bottom surface reflected wave Wb1 and the second bottom surface reflected wave Wb2 after the water gap variation are 28.4 μs and 54.8 μs, respectively, and the reception times B1o and B2o of the first bottom surface reflected wave Wb1 and the second bottom surface reflected wave Wb2 when the normal water gap is WGo are 27.8 μs and 54.2 μs, respectively, and ΔT = 0.6 μs from Equation (4). Therefore, if the start time T1 of the detection range R in the case of the normal water gap WGo shown in Fig. 2(1) is delayed and corrected by 0.6 μs as a whole as shown in Fig. 2(2), the occurrence of the undetected area RU can be prevented.

[0022] In the above embodiment, the case where the test object is a round bar has been described, but it is not limited thereto, and for example, it may be a flat plate. Also, as described above, the present invention can accurately correct even when the water gap varies due to mechanical wear or the like of each part of the guide mechanism, and can prevent the occurrence of an undetected area. Furthermore, depending on the unevenness and deflection state of the surface of each test object, it is also possible to accurately correct the influence of the water gap as a position that is not affected by the ultrasonic probe when performing flaw detection, and prevent the occurrence of an undetected area.

Explanation of Symbols

[0023] 1... Ultrasonic vibrator, M... Test object, M1... Surface, M2... Bottom surface, R... Detection range, T1... Start time, WG, WGo... Water gap, Wb1... First bottom surface reflected wave, Wb2... Second bottom surface reflected wave.

Claims

1. An ultrasonic flaw detection method in which, when a water gap exists between an ultrasonic transducer and the surface of the material to be inspected that it faces, the arrival times of the primary and secondary bottom-reflected waves of the material to be inspected when a normal water gap exists are B1o and B2o, respectively, and when a changed water gap exists, the arrival times of the primary and secondary bottom-reflected waves of the material to be inspected are B1 and B2, respectively, and the start time of the flaw detection range is corrected by a correction time ΔT calculated by the following formula (1). ΔT=(2×B1-B2)-(2×B1o-B2o)…(1)

2. The ultrasonic testing method according to claim 1, wherein the material to be inspected is a round bar.

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