JP3729686B2 - Defect detection method for piping - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piping defect detection method, and more particularly to a piping defect detection method using ultrasonic waves.
[0002]
[Prior art]
In a petroleum plant, a chemical plant, and the like, a system in which a large number of pipes are arranged and supported on a rack (rack) standing on the ground at predetermined intervals is frequently used. Since rainwater stays at the contact portion between the pipe and the pedestal, these pipes are corroded particularly at the contact portion when used outdoors for many years.
[0003]
Conventionally, in order to detect the corrosion of the pipe at the contact portion with the gantry, a technique has been adopted in which one pipe is lifted from the gantry and visually inspected. However, it was extremely inefficient to check a huge number of long pipes by such a method.
[0004]
The applicant has applied for an invention of a method for detecting corrosion in piping as described above in Japanese Patent Application No. 10-006479. In the prior application, ultrasonic waves are emitted obliquely from the ultrasonic transducer toward the inside of the pipe, and the presence or absence of corrosion and the depth thereof are detected from the received waveform of the ultrasonic wave transmitted through the pipe in the circumferential direction.
[0005]
[Problems to be solved by the invention]
In the prior invention, an ultrasonic transducer in which an ultrasonic beam is diffused, that is, an ultrasonic transducer with low directivity, is used so that the ultrasonic wave spreads over the entire thickness of the pipe. In addition, a receiver having high directivity is used as the ultrasonic receiver that receives the ultrasonic wave transmitted through the pipe. Thus, the presence or absence of corrosion and the amount thereof are estimated from the received waveform of ultrasonic waves that pass through the pipe in a certain direction. However, in this prior invention, a complicated calculation is required to estimate the amount of corrosion.
[0006]
In addition, when a pipe has a particularly large diameter and a defect exists inside the pipe, it is important to specify the defect position in order to determine the repair position. However, in the prior invention, the defect position in the circumferential direction cannot be detected.
[0007]
An object of the present invention is to further improve the above-mentioned invention of the prior application, and to provide a defect inspection method for piping in which the amount of corrosion of the piping can be easily detected, and a defect inspection method for piping in which the defect position of the piping can be easily identified. And
[0008]
[Means for Solving the Problems]
In the pipe defect detection method according to the present invention, in the first viewpoint, the incident angle in the pipe measured in a direction perpendicular to the extending direction of the cylindrical pipe and from the perpendicular standing on the pipe surface is 54 ° to 90 °. An ultrasonic wave is emitted toward the pipe so that it is within the range of °, and the transmitted wave propagating in the circumferential direction of the pipe or the reflected ultrasonic wave reflected by the defect is detected, and the transmitted wave or the reflected wave is detected. It is characterized by detecting the size of a piping defect based on the amplitude of ultrasonic waves.
[0009]
According to the pipe defect detection method of the first aspect of the present invention, the ultrasonic wave is substantially uniform inside the pipe (thick part) by selecting the incident angle of the ultrasonic wave in the range of 54 ° to 90 °. Therefore, the depth of the defect can be measured by the amplitude of the transmitted ultrasonic wave or the reflected ultrasonic wave reflected from the defect.
[0010]
In addition, according to the second aspect, the pipe defect detection method of the present invention is configured to inject ultrasonic waves into a pipe at a predetermined angle with respect to a perpendicular extending on the pipe surface in a direction orthogonal to the extending direction of the cylindrical pipe. A method of detecting defects in a pipe by detecting ultrasonic waves that are emitted toward the pipe and propagate in the circumferential direction in the pipe,
Based on the return time until the ultrasonic wave passing through a specific position is reflected by the defect and returns to the specific position, an angle from the specific position to the position where the defect exists is detected from the pipe center. It is characterized by that.
[0011]
According to the pipe defect detection method of the second aspect of the present invention, an ultrasonic waveform is observed at a specific position until the ultrasonic wave passing through the specific position is reflected by the defect and returns to the specific position. By measuring this time, it is possible to easily detect the angular difference between the specific position and the position where the defect exists.
[0012]
If the ultrasonic velocity is V , the ultrasonic return time is t, and the pipe radius (outer diameter) is R, the angle β between the specific position and the defect is β = t × V / 2R.
As required. As the speed V , in the case of a steel cylindrical pipe, 3623 m / s, which is the speed of a transverse wave in terms of material, is used.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a sectional view of a pipe showing the principle of a pipe defect detection method according to an embodiment of the present invention. The ultrasonic transducer 11 that emits ultrasonic waves is disposed, for example, near the top (point P1) on the cross section passing through the position where the defect 21 is considered to exist in the pipe 20. The ultrasonic transducer 11 is brought into contact with the outer surface of the pipe 20 via the contact 12 and is inclined at a predetermined angle from a perpendicular line standing on the outer surface.
[0014]
The ultrasonic wave receiver 13 for detecting ultrasonic waves is a position about 60 ° before the position where the defect 21 is supposed to exist in the vicinity of the installation point P1 of the ultrasonic transducer 11 and in the traveling direction of the ultrasonic wave. Place at P2. Instead of the point P1, a point P3 that is symmetrical to the point P2 inside the pipe across the defect 21 may be selected. The ultrasonic receiver 13 preferably has a weak directivity. In this case, it is possible to detect an ultrasonic wave that passes through (transmits or reflects) the pipe 20 in the forward and reverse directions (thick part). The ultrasonic receiver 13 installed at the point P2 is particularly convenient for detecting the position where the defect 21 exists.
[0015]
As shown in FIG. 2, the incident angle of the ultrasonic wave to the pipe 20 is selected so that the angle θ _i from the vertical line standing on the pipe surface on the outer surface of the pipe 20 is 45 °. When an angle of θ _i = 45 ° is selected, the ultrasonic wave immediately after entering the pipe is obtained because the tip of the contact 2 of the ultrasonic vibrator 11 has a width and the ultrasonic wave is refracted on the pipe surface. Becomes a wave having a spread of 54 to 90 ° centered at 70 ° from the perpendicular to the pipe (θ _a = 45 °, θ _b = 90 °). An ultrasonic wave having an incident angle of 54 to 90 ° inside the pipe propagates in the circumferential direction almost uniformly throughout the pipe.
[0016]
FIG. 3 is a timing chart of an ultrasonic waveform (force: mN) generated by the ultrasonic transducer. As the ultrasonic wave, a burst waveform having a center frequency of 5 MHz is preferable, and has a duration of, for example, within 0.6 seconds. The ultrasonic wave used in the present invention, that is, the ultrasonic wave actually propagated through the pipe and detected by the ultrasonic wave receiver 13 was confirmed to be a transverse wave by the result of measuring the ultrasonic velocity. When an ultrasonic wave having a center frequency of 5 MHz is incident on the pipe, the center frequency of the ultrasonic wave propagating in the circumferential direction in the pipe changes to about 4.6 MHz. However, as shown in FIG. 4, the velocity of the ultrasonic wave is a transverse wave velocity of 3263 m / s and does not change by propagating through the pipe.
[0017]
Taking a piping defect occurring at a position in contact with the gantry as an example, the defect 21 is shown at the bottom of the piping in the drawing of FIG. A part of the ultrasonic wave propagating in the circumferential direction in the pipe 20 is reflected by the defect, and the other part passes through the defect and is detected by the ultrasonic receiver 13. If the defect is large, the amplitude of the passing ultrasonic wave is reduced, and conversely, the amplitude of the reflected ultrasonic wave is increased. Accordingly, first, the presence or absence of a defect can be detected by measuring the amplitude of the passing ultrasonic wave or the reflected ultrasonic wave at the point P1 or P2. Further, the defect 21 exists from the point P2 by detecting the return time until the ultrasonic wave detected when passing through the point P2 is subsequently reflected by the defect 21 and detected again as the reflected wave at the point P2. A central angle β up to the position to be obtained is obtained. In this case, it is not necessary to measure the amplitude.
[0018]
In order to detect the transmitted wave and the reflected wave, it is preferable to arrange the ultrasonic receiver 13 at the position of the point P2 shown in FIG. The ultrasonic receiver 13 preferably has a weak directivity in order to detect both transmitted waves and reflected waves. In selecting the point P2, in order to identify the incident wave and the reflected wave in terms of time, a point between the ultrasonic incident point P1 and the position where the defect 21 is supposed to exist is selected. In terms of apparatus, the reflected wave receiver 13 is preferably installed in the vicinity of the vibrator 11 so that the reflected wave can be widely detected.
[0019]
Here, an example in which the angle β between the point P2 and the position where the defect 21 exists is detected. V is the velocity of the ultrasonic wave (transverse wave), t is the time from the detection time of the ultrasonic wave detected at the position of the point P2 until the ultrasonic wave is reflected by the defect 21 and is detected again at the position of the point P2. When the average radius inside the pipe is R, the angle β (radian) measured at the center of the circular pipe formed by the position of the point P2 and the position where the defect 21 exists is
β = t × V / 2R
As required. As the velocity V , a transverse wave velocity of 3263 m / s is selected.
[0020]
In order to confirm the effectiveness of the detection of the corrosion depth of the defect and the detection of the defect position in the present invention, a simulation was performed. In this simulation, a steel cylindrical pipe (circular pipe) having an inner diameter of 54 mm is adopted as an analysis target, and there is no defect on the surface of the circular pipe, a defect having a depth of 1 mm, and a depth of 1.5 mm. And those having a defect of 2 mm depth were selected. The steel pipe has a Young's modulus of 206 GPa, a Poisson's ratio of 0.28, and a density of 7700 kg / cm ³ .
[0021]
The contact 12 attached to the ultrasonic transducer 11 is made of polyimide (Young's modulus is 4.39 GPa, Poisson's ratio is 0.38, and density is 1410 kg / cm ³ ). The attenuation coefficient of the front end portion of the contact 12 was 1.7 dB, the attenuation coefficient of the rear end portion was 50 times that of the front end portion, and the attenuation of the circular tube 20 was not considered. The diameter of the ultrasonic transducer 11 was 4 mm, and the incident angle of the ultrasonic wave was 45 ° on the outer surface of the circular tube so that a central angle of 70 ° was generated after refraction on the surface of the circular tube. The external force having the waveform shown in FIG. 3 is input on each node on the end face of the ultrasonic transducer 11.
[0022]
5 (a) to 5 (d), each of a circular tube having no defect, a circular tube having a defect having a depth of 1 mm, a circular tube having a defect having a depth of 1.5 mm, and a circular tube having a defect having a depth of 2 mm. The received waveform at the incident point (point P1) is shown. In each figure, the waveform observed after 60 μs is the waveform observed after one round of the circular tube, and it can be understood that the amplitude changes depending on the presence or absence of the defect and the size of the defect.
[0023]
FIGS. 6 (a) and 6 (b) show the received waveforms at points P2 and P3 of the circular tube having no defect, respectively. As can be understood from FIG. 5A, the amplitude of the waveform A2 received after making one round of the pipe at the point P2 is attenuated from the waveform A1 received first. Further, comparing these waveforms A1 and A2 with the received waveform A3 at the point P3, this attenuation is mainly due to the attenuation gradually received when passing through the inside of the pipe, and is almost proportional to the transmission distance of the pipe. I can understand.
[0024]
FIGS. 7A and 7B are waveforms obtained by subjecting the waveforms of FIGS. 6A and 6B to wavelet transformation, respectively. Wavelet transform is a technique generally used for frequency analysis of a single wave (burst wave), and a timing chart showing the progress of a wave having a maximum amplitude frequency is obtained. From the figure, the difference t = 20.002 μs between the passing time of the ultrasonic point P2 and the passing time of the point P3 can be obtained with high accuracy. The ultrasonic wave passing speed V is determined by the separation distance L and the time difference t in the pipe between the points P2 and P3.
V = L / t = 65.33 mm / 20.02 μs = 3263 m / s
It can be confirmed that the traveling ultrasonic wave is a transverse wave.
[0025]
FIG. 8A shows an ultrasonic waveform received at a point P2 in a pipe having a defect of 1 mm. As described above, since the ultrasonic velocity V _T is measured, it can be seen that the first observed ultrasonic wave B1 is a transmitted wave that has entered the pipe from the ultrasonic transducer and has arrived. It can also be seen that the next observed ultrasonic wave B2 is a reflected wave reflected by a defect. A waveform obtained by wavelet transform of this waveform is shown in FIG. From the figure, the time difference between the transmitted wave C1 and the reflected wave C2 of which the transmitted wave is reflected by the defect 21 is obtained as 19.46 μs, and thereby, between the position of the point P2 and the position where the defect 21 exists. The angle β seen at the center of the tube is
β = t × V _/ 2R = 19.46 _μs × 3.263 _{mm / μs} / 2 × 30 mm
= 1.0583 rad = 60.64 °
Is calculated.
[0026]
FIG. 9 shows an example of a waveform received by the ultrasonic receiver 13 in which an ultrasonic wave is actually incident on the defect-free circular tube having the shape and material shown in the simulation and is arranged at the point P1. Show. Comparing the waveform of FIG. 9 with the waveforms of FIGS. 6A and 6B, it can be understood that the simulation simulates the result of this experiment fairly accurately.
[0027]
FIG. 10 shows the relationship between the size of the defect and the amplitude of the transmitted ultrasonic wave obtained from the simulation results of FIGS. 5A to 5D in comparison with the relationship obtained from the actually measured received waveform. ing. The horizontal axis is the ratio of the depth D of the defect to the total thickness T of the pipe (defect ratio) r = D / T, and the vertical axis is the maximum amplitude A ₀ obtained with the pipe having the defect and the pipe without the defect. The ratio (amplitude ratio) A ₁ = A _d / A ₀ with respect to the maximum amplitude A _d at the corresponding position obtained in ( ₁ ). As shown in the figure, the simulation result and the actual measurement result are in good agreement, which shows that the size of the defect can be measured by the method of the present invention.
[0028]
11 (a) to 11 (d) show the amplitude distribution in the pipe cross section 50 μs after the incidence of the ultrasonic wave on the pipe with no defect and the pipe with the defects of 1 mm, 1.5 mm, and 2 mm, respectively. The simulation result is shown as a schematic perspective view. As can be understood from the figure, as the defect becomes larger, the amplitude of the transmitted wave becomes smaller and the amplitude of the reflected wave becomes larger. Therefore, the defect size can be determined by the amplitude of the reflected wave instead of the determination of the defect size by the graph of FIG. 10 or Expression (1). As described above, the method for determining the size of the defect based on the amplitude of the reflected wave is used in combination with the above-described method for determining the position of the defect 21 based on the time difference between the transmitted wave and the reflected wave at the specific position P2. it can. In particular, it is preferable to employ this method when detecting defects on the inner surface of the pipe.
[0029]
As mentioned above, although this invention was demonstrated based on the suitable embodiment example, the defect detection method of the piping of this invention is not limited only to the structure of the said embodiment example, From the structure of the said embodiment example. Various modifications and changes are also included in the scope of the present invention.
[0030]
【The invention's effect】
As described above, according to the pipe defect detection method of the present invention, there is an advantage that it is possible to easily measure the corrosion amount of the pipe and detect the defect position, which cannot be easily recognized visually.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a pipe showing the principle of a pipe defect detection method of the present invention.
FIG. 2 is an enlarged view of the surface of a pipe showing the incident angle of ultrasonic waves.
FIG. 3 is a waveform diagram of ultrasonic waves incident on a pipe.
FIG. 4 is a graph of the frequency and speed of ultrasonic waves transmitted through a pipe.
FIGS. 5A to 5D are simulation diagrams of observed waveforms at a point P1 of each circular tube having no defect, a defect of 1 mm, a defect of 1.5 mm, and a defect of 2.0 mm, respectively.
FIGS. 6A and 6B are observation waveform diagrams of points P2 and P3 of a circular tube having no defect, respectively.
7A and 7B are waveform diagrams after wavelet conversion of the waveforms of FIGS. 6A and 6B, respectively.
FIGS. 8A and 8B are a waveform chart of an ultrasonic wave observed at a point P2 of a pipe having a defect of 1 mm and a waveform chart after wavelet conversion, respectively.
FIG. 9 is an actual observation waveform diagram of ultrasonic waves at a point P1 of a pipe having no defect.
FIG. 10 is a graph of actual measurement and simulation results showing the relationship between the size of a defect and the amplitude of an observed ultrasonic wave.
FIGS. 11A to 11D are perspective views showing simulation results of transmitted waves of respective pipes having no defect, a defect of 1 mm, a defect of 1.5 mm, and a result of 2 mm, respectively.
[Explanation of symbols]
11 Ultrasonic vibrator 12 Contact 13 Ultrasonic receiver 20 Piping 21 Defect

Claims (3)

An ultrasonic wave is emitted into the pipe in a direction perpendicular to the extending direction of the cylindrical pipe and inclined at a predetermined angle from a vertical line standing on the pipe surface, and an ultrasonic wave propagating in the pipe in the circumferential direction is emitted. A method for detecting defects in piping by detecting,
Based on the return time until the ultrasonic wave passing through a specific position is reflected by the defect and returns to the specific position, an angle from the specific position to the position where the defect exists is detected from the pipe center. A defect detection method for piping, characterized in that. Assuming that the velocity of the ultrasonic wave is V , the return time is t, and the radius of the pipe is R, the angle β between the specific position and the defect is β = t × V / 2R
The piping defect detection method according to claim 1, which is obtained as follows. The ultrasound is shear waves, a defect detection method of a pipe according to claim 1 or 2.

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