JP4144703B2 - Tube inspection method using SH waves - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tube inspection method using ultrasonic SH waves. More specifically, the present invention relates to a pipe inspection method for inspecting a water supply pipe or the like by receiving, with a probe, an SH wave that propagates through a pipe wall and transmits or reflects a damaged portion.
[0002]
[Prior art]
Conventionally, in the inspection of a pipe, an inspection is performed using a longitudinal wave or an SV wave. For example, Patent Document 1 describes a method for evaluating thinning by measuring the wall thickness of a tube using a cylindrical wave that vibrates the entire cylinder. However, in the method described in the same document, since the cylindrical wave to be used has a vibration component (L mode) in the tube thickness direction, when inspection is performed in a state where liquid such as water exists in the tube The ultrasonic wave is attenuated by the fluid. Therefore, it was necessary to perform an inspection with the liquid in the tube removed. In addition, since the detectable damaged part is determined by the ratio to the cross-sectional area of the pipe, it was not suitable for local damage inspection.
[0003]
On the other hand, the thing of patent document 2 is known as a pipe inspection method using the SH wave which vibrates in parallel with respect to the pipe surface. This technique focuses on the detection of damage in a welded portion with a flange for supporting a tube located 90 ° away from the probe in the tube circumferential direction. In paragraph 0015 of the same document, “the incident angle λ of the ultrasonic wave is an angle substantially equal to an angle called a critical angle at which the refraction angle of the ultrasonic wave incident on the specimen 10 such as steel is just 90 degrees”. It is described. Therefore, this technique is a method using surface waves propagating in the vicinity of the tube surface as shown in FIG. The surface SH wave easily spreads in the entire tube circumferential direction Y as shown in FIG. As a result, with this surface SH wave, it is difficult to accurately identify the position of the damaged portion in the tube circumferential direction, and damage inside the tube wall cannot be detected.
[0004]
[Patent Document 1]
JP 2002-328119 A [Patent Document 2]
Japanese Patent Laid-Open No. 9-72887
[Problems to be solved by the invention]
An object of the present invention is to provide an SH wave tube inspection method that can perform highly accurate tube inspection even when liquid is present in the tube and can specify the position of the damaged portion in the tube circumferential direction. It is to provide.
[0006]
[Means for Solving the Problems]
The feature of the tube inspection method using the SH wave according to the present invention is that the SH wave is transmitted from the probe to the tube wall, and the SH wave propagated through the tube wall and transmitted or reflected from the damaged portion is probed. A tube inspection method using an SH wave for inspecting a tube by receiving the signal from the probe toward the inside of the tube wall from the probe toward the longitudinal direction of the tube, and an incident angle of the SH wave in the tube wall. Is to transmit an SH guide wave, which is a burst wave. Here, unlike the “surface SH wave” described in Patent Document 2, the “SH guide wave” refers to an SH wave in which the entire wall thickness of the tube wall vibrates. Since the vibration direction of the SH guide wave is parallel to the tube wall surface, the SH guide wave is not attenuated by the liquid even if the liquid exists in the tube. The SH guide wave is transmitted in the tube longitudinal (tube axis) direction due to the sharpness of the directivity, so that the position of the defect (damage) in the tube circumferential direction can be accurately specified.
[0007]
According to the experiments by the inventors, the incident angle when transmitting the SH wave to the tube wall is smaller than the critical angle of the SH wave in the tube wall, and this SH wave is used as a burst wave inside the tube wall. It was found that the SH guide wave can be propagated inside the tube wall by making it incident.
[0008]
In addition to the features of the tube inspection method according to the present invention, the probe may be scanned in the tube circumferential direction by the probe. As described above, the position of the damaged portion can be easily specified using the sharp directivity of the SH guide wave. Note that a simple and highly accurate inspection can be performed by transmitting and receiving the SH wave with one probe.
[0009]
【The invention's effect】
As described above, according to the feature of the tube inspection method using the SH wave according to the present invention, since the SH wave is not attenuated by the liquid in the tube by using the SH guide wave, the presence or absence of the liquid in the tube is taken into consideration. This makes it possible to perform precise pipe inspections using sharp directivity. As a result, it has become possible to perform inspection without interrupting the use of the pipe, and it has been possible to contribute to improving the reliability and operating rate of facilities and the like.
[0010]
In addition, since the SH guide wave having sharp directivity is used, it is possible to easily and accurately specify the position of the damaged portion in the tube circumferential direction by scanning in the tube circumferential direction.
[0011]
Other objects, configurations, and effects of the present invention will become apparent from the following embodiments of the present invention.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in more detail with reference to the accompanying drawings.
The pipe inspection method using SH waves according to the present invention is mainly intended for inspection of water supply / hot water supply pipes, drain pipes, oil supply pipes and the like in plants and the like. As shown in FIG. 1, these are used to detect damages such as defects and thinning in the inner and outer surfaces 12 and 13 of the pipe 10 and the inside of the pipe wall 11 and to specify a damage position. In the present embodiment, a fluid W such as water remains in the water supply pipe 10.
[0013]
FIG. 1 shows a block diagram of a pipe inspection apparatus 1 used in the pipe inspection method according to the present invention. The tube inspection device 1 generates a burst wave with an oscillator 3 a controlled by a personal computer 7, and transmits an SH guide wave from the pipe outer surface 12 to the tube wall 11 via the probe 2. The transmitted SH guide wave is transmitted / reflected at the damaged portion and received again by the probe 2. The received reflected wave is amplified by the receiver 3b and the preamplifier 4, converted into a digital signal by the A / D converter 6 with the noise removed by the filter 5, processed by the personal computer 7, and the result is obtained. Displayed on the monitor 8.
[0014]
As shown in FIG. 2A, the probe 2 generally has a vibrator 21 and a wedge 22, and a shear wave excited by the vibrator 21 is applied to the tube wall 11 via the acrylic wedge 22 as an SH wave. As incident. At that time, a highly viscous transverse wave contact medium is interposed between the wedge 22 and the tube wall outer surface 12. This probe 2 is a variable SH probe capable of appropriately adjusting the incident angle θ given by the angle formed by the probe attachment center axis L1 and the normal L2 of the tube wall outer surface 12. And in order to generate SH guide wave inside this tube wall 11, this incident angle (theta) is adjusted to a value sufficiently smaller than 27 degree | times which is the critical angle of SH wave in the tube wall 11 which is steel materials. There is a need. According to experiments by the inventors, it has been found that an angle of about 19 degrees is appropriate as the incident angle θ for generating the SH guide wave propagating in the tube longitudinal direction X.
[0015]
Here, the relationship between the propagation characteristics of the SH wave and the incident angle θ will be briefly described with reference to FIGS.
First, as shown in FIG. 6A, when the incident angle θ ′ is 27 degrees which is the critical angle of the SH wave, the SH wave incident on the tube wall 11 propagates on the tube wall outer surface 12 as an SH surface wave. It was confirmed. Therefore, although it is suitable for detecting the surface damage of the tube wall 11, it is not suitable for the damage inspection in the tube wall inner surface 13 and the tube wall 11. Further, as shown in FIG. 6B, the surface SH wave easily goes around in the tube circumferential direction Y not only along the tube axis direction X but also along the tube outer surface. Thus, the surface SH wave cannot identify the position of the damaged portion in the tube circumferential direction.
[0016]
On the other hand, as shown in FIG. 2A, when the incident angle θ is adjusted to 19 degrees, which is sufficiently smaller than 27 degrees, which is the critical angle of the SH wave, and the SH wave is incident on the tube wall 11, the incident SH wave is obtained. Becomes a guide wave that enters the tube wall 11 at a refraction angle of 45 degrees and propagates in the tube longitudinal direction X while reflecting between the outer surface 12 and the inner surface 13 of the tube wall 11. Therefore, by analyzing this SH wave, it is possible to inspect not only the tube wall outer surface 12 but also the tube wall inner surface 13 and the tube wall 11 inside. By the way, in order to reach the incident SH wave to the tube inner surface 13, the incident SH wave is not a pulse wave but a burst wave composed of a plurality of waves. This is because the energy is large and an SH guide wave can be generated efficiently by transmitting a plurality of waves.
[0017]
FIG. 2B schematically shows the displacement direction and the magnitude of the force acting on each point in the thickness direction when the SH guide wave is propagated inside the tube wall 11. A shearing force acts on the tube wall 11 immediately below the tube circumferential position of the probe 2, and this shearing force propagates only in the tube axis direction X. In other words, since the SH guide wave does not easily propagate in the tube circumferential direction Y, the directivity with respect to the tube axis direction X is strong as a result.
[0018]
According to experiments by the inventors described later, no SH wave was observed at a position shifted by 45 degrees in the tube circumferential direction from the position of the probe (transmitter) 2 tube circumferential direction. Also from this experimental result, the SH wave hardly spreads in the tube circumferential direction Y, is a very directional wave propagating in the tube axis direction X, and the sound speed is different from other SH waves. Therefore, by using this SH guide wave, it is possible to observe only the damaged part at the pipe circumferential position where the probe 2 is installed, and the pipe circumferential direction position of the damaged part can be specified.
[0019]
Next, an actual procedure for inspecting a pipe using the pipe inspection method according to the present invention will be briefly described. First, the probe 2 is installed on the pipe outer surface 12 with a contact medium interposed. Then, after performing the above-described inspection at this position, the probe 2 is moved in the tube circumferential direction Y by a predetermined angle, and the above-described inspection is performed for each movement position. When the defect signal is received, the coordinates of the damaged part are specified by the difference in generation time of the defect echo S1 and the tube circumferential direction Y position of the probe 2. By performing such inspection over the entire pipe circumference, it is possible to grasp the damage in the entire range.
[0020]
[Example 1]
The inventors have used the SV wave (L mode) in order to demonstrate that the tube inspection method using the SH guide wave according to the present invention is also applicable when the liquid inside the tube 14 is present. And a comparison experiment with the case of using the SH guide wave according to the present invention. In this example, 3B piping having an artificial flaw on the pipe outer surface 12 was used as a test body, and the probe 2 was installed on the pipe outer surface 12 at a position where the distance to the artificial flaw was 1500 mm.
[0021]
3A and 3B show received waveforms when SV waves are used. FIG. 3A shows the amplitude when water W does not exist inside the tube 14 and FIG. 3B shows the amplitude when water W exists inside the tube 14. It is a time-series distribution of values, and the gain is 36 dB for each. In FIG. 6A, an artificial flaw echo S1 is observed at 0.88 ms, and an end face echo S2 is observed at 1.0 ms, respectively, which clearly shows that the artificial flaw is captured. On the other hand, when water W was present inside the tube 14, neither artificial flaw echo S <b> 1 nor end face echo S <b> 2 was observed as shown in FIG.
[0022]
On the other hand, FIG. 4 shows a received waveform obtained by an experiment using the SH guide wave according to the present invention. FIG. 4A shows a time-series waveform of amplitude values when water is not present in the pipe interior 14 and FIG. 4B is a time series waveform of amplitude values when water W is present in the pipe interior 14, and the gain is set to 36 dB. In both (a) and (b), an artificial flaw echo S1 is observed at 0.82 ms, and an end face echo S2 is observed at 0.93 ms. The SH guide wave is not attenuated by the liquid W inside the tube 14. It was confirmed that the wave propagated through the tube wall 11.
[0023]
[Example 2]
In order to demonstrate that the SH guide wave is a directional sharp wave, the inventors have arranged the probe 2 at the same circumferential position as the artificial flaw and the probe 2 from the position to the tube. A comparative experiment was performed with the case where it was arranged at a position shifted by 45 degrees in the circumferential direction Y. In this example, a 2B pipe having an artificial flaw on the tube outer surface 12 was used as a test body, and the probe 2 was installed on the tube outer surface 12 having a distance to the artificial flaw of 4000 mm and a distance to the tube end surface of 4500 mm.
[0024]
FIG. 5 (a) shows a received waveform when the probe 2 is arranged at the same circumferential position as the artificial flaw, and the artificial flaw echo S1 is 2.55 ms and the end face echo S2 is 2.8 ms. Observed. On the other hand, FIG. 5B shows a received waveform when the probe 2 is arranged at a position shifted by 45 degrees in the tube circumferential direction Y from the probe position of FIG. S2 was observed, but no artificial flaw echo was observed. The inventor conducted similar comparative experiments by appropriately changing the distance to the flaw detection part and the tube size, and obtained similar experimental results. Therefore, it was found that the SH guide wave is a wave having a sharp directivity that propagates in the tube circumferential direction Y almost without spreading.
[0025]
Finally, reference is made to the possibilities of other embodiments of the invention. Moreover, it is also possible to implement by combining each embodiment shown below suitably. In addition, the same code | symbol is attached | subjected to the member similar to the said embodiment.
[0026]
In the above embodiment, the state in which the liquid W is present in the pipe interior 14 is recalled, but the present invention can be implemented regardless of the presence or absence of the liquid W.
[0027]
In the above-described embodiment, a case where transmission / reception is performed by one probe has been described. However, it is also possible to perform inspection by separately installing a transmitter and a receiver. However, since the SH guide wave is a wave having a sharp directivity, the transmitter and the receiver need to be close to each other in the tube circumferential direction Y. Therefore, the above embodiment is excellent in practicality.
[0028]
In the above-described embodiment, the case of inspecting 2B piping and 3B piping has been described as an example. However, if a small-diameter tube that does not require a support member or the like to be in contact with the outer surface of the tube, high-accuracy tube inspection is possible. According to the experiments by the inventors, it has been confirmed that the pipe inspection method according to the present invention is sufficiently useful if the pipe diameter is at least a small diameter pipe of 3 inches or less.
[0029]
In the said embodiment, the case where the corrosion part in the pipe outer surface 12 was detected as a damaged part was demonstrated as an example. However, it is also possible to perform damage inspections such as corrosion, defects, voids, and foreign matter contamination in the tube inner surface 13 and the tube wall 11.
[0030]
In the above embodiment, the case where local corrosion has occurred as a damaged portion has been described as an example. However, it is also possible to grasp the three-dimensional shape of the damaged portion by appropriately scanning the tube circumferential direction Y and / or the tube longitudinal direction X.
[0031]
In addition, the code | symbol entered in the term of the claim is only for the convenience of contrast with drawing, and this invention is not limited to the structure of an accompanying drawing by this entry.
[Brief description of the drawings]
FIG. 1 is a block diagram of a tube inspection apparatus used in a tube inspection method using SH waves according to the present invention.
2A and 2B are diagrams for explaining an SH guide wave, in which FIG. 2A is a cross-sectional view in the longitudinal direction of the tube, and FIG. 2B is a cross-sectional view in the direction perpendicular to the tube axis.
FIG. 3 is a reception waveform when a tube inspection is performed using an SV wave (L mode), (a) shows a reception waveform when there is no water in the tube, and (b) shows a reception waveform when there is water in the tube. Each is shown.
4A and 4B are reception waveforms when a tube inspection is performed using an SH wave according to the present invention. FIG. 4A shows a reception waveform when there is no water in the tube, and FIG. 4B shows a reception waveform when there is water in the tube. Each is shown.
FIG. 5 is a received waveform at each position when the position of the probe is shifted by 45 ° in the pipe circumferential direction, and (a) is a case where the probe is placed at the same pipe circumferential position as the artificial flaw. , (B) respectively show received waveforms when the probe is displaced 45 degrees from the position of the artificial flaw in the pipe circumferential direction.
6A and 6B are diagrams for explaining a surface SH wave, where FIG. 6A is a cross-sectional view in the longitudinal direction of the tube, and FIG. 6B is a cross-sectional view in the direction perpendicular to the tube axis.
[Explanation of symbols]
1: tube inspection device, 2: probe, 3a: oscillator, 3b: receiver, 4: preamplifier, 5: filter, 6: A / D converter, 7: personal computer, 8: monitor, 10: tube, 11: Tube wall, 12: Tube wall outer surface, 13: Tube wall inner surface, 14: Inside tube, 21: Vibrator, 22: Wedge, W: Water (liquid), L1: Probe mounting center axis, L2: Tube wall outer surface Normal, X: Pipe axis (pipe longitudinal) direction, Y: Pipe circumferential direction, θ, θ ′: Incident angle

Claims (4)

  An SH wave tube inspection method for inspecting a tube by transmitting an SH wave from the probe to the tube wall and receiving the SH wave transmitted through the tube wall and transmitted through or reflected from the damaged portion by the probe. The incident angle from the probe toward the inside of the tube wall in the longitudinal direction of the tube is smaller than the critical angle of the SH wave in the tube wall, and the SH wave is a burst wave. A tube inspection method using an SH wave that transmits an SH guide wave.   The tube inspection method using SH waves according to claim 1, wherein a liquid is present inside the tube.   3. The tube inspection method using SH waves according to claim 1, wherein the tube is scanned in the tube circumferential direction by the probe.   The tube inspection method using an SH wave according to claim 1, wherein the SH wave is transmitted and received by one probe.

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