JP4413089B2 - Inspection method for buried pipes - Google Patents

Description

The present invention relates to a buried pipe inspection method for performing deterioration diagnosis by inspecting a buried pipe by a shock elastic wave method.

Recently, in sewage pipes and agricultural water pipes, accidents such as depression and water leakage are increasing due to corrosive wear and breakage of buried pipes over time. For this reason, appropriate deterioration diagnosis and appropriate repair / updating based on the diagnosis result are required.
In this deterioration diagnosis of sewage pipes and agricultural water pipes, in general, in order to determine the order of repair and reconstruction works and the construction method, ranking of the degree of deterioration between the element areas constituting the survey basin and quantitative It is necessary to grasp the progress of the deterioration level.
Conventionally, visual inspection or visual inspection is performed using a TV camera, and the physical properties of the sample obtained by removing the core are investigated as necessary. It is difficult to accurately and quantitatively grasp the degree of deterioration. Or, in order to collect quantitative data, it is necessary to remove a large number of cores, and the strength of the healthy tubular body is inevitably lowered, and the work cost is inevitably increased.

As a nondestructive test method, an ultrasonic method, a percussion method, and a shock elastic wave method are known.
However, in the ultrasonic method, since the ultrasonic wave as an input wave has a high frequency and low energy, it is difficult for the input wave to propagate through the concrete, and it is not suitable for the inspection of concrete products.
In the percussion method, the signal is received by a non-contact acoustic device such as a microphone, so it is easily affected by ambient noise, and is easily affected by the back side of the impact point. Quantitative analysis and diagnosis However, there are problems such as easy individual differences, and there is a problem in diagnostic accuracy.
The shock elastic wave method is a method in which an elastic wave is input to an object to be inspected by mechanical impact such as impact, and a frequency spectrum of a waveform received by a vibrator in contact with the object to be inspected is obtained. The present applicant has already proposed a diagnosis system for buried pipes using the shock elastic wave method. (For example, Patent Document 1, Non-Patent Document 1, etc.)

JP 2004-028976 A Minagi, Kamada, Nozaki, Funabashi, Basic research on deterioration diagnosis method of concrete sewage pipes by elastic waves, Annual report of concrete engineering, 2002, VOL24, No1, p1539-1544

The basic configuration of this diagnostic system will be described as follows.
In FIG. 11 (a), p is an underground pipe, a is an input point for inputting an elastic wave by an impulse hammer or the like, and b is a receiving point (output point) for receiving a propagating elastic wave by a vibration sensor. .
The propagation of elastic waves is discussed in terms of mass m, spring constant k, damping coefficient c, etc., and since spring constant k is given by the ratio of acting force and displacement, in the case of a tube, the spring constant is the bending stiffness EI of the tube. Be evaluated.
If the input at the input point is an impulse I shown in FIG.
Arrives at the receiving point through reflection at the tube end, reflection and transmission at a defect such as a crack, and the incoming wave x includes the relative positional relationship between the output point and the receiving point, and the input and output points. Relative positional relationship with the pipe end, relative positional relationship between the input and output points and the defective part, bending rigidity of the tube, damping coefficient, specific gravity of the tube, elapsed time, etc. are involved. L is a variable related to the relative positional relationship between the input point, the output point, and the pipe end, L ′ is a variable related to the relative positional relationship between the input point or the output point, and the defect location, and the bending rigidity of the tube EI, damping coefficient c, pipe specific gravity m, elapsed time t

で表すことができ、その波形は、出力点と受振点との相対的位置関係や入力点や出力点
と管端との相対的位置関係Ｌ、入力点や出力点と欠陥箇所との相対的位置関係Ｌ’、管体
の曲げ剛性EI、減衰係数ｃ、管の比重ｍ等によって異なる。 x = x (EI, c, m, L, L ′, t)
Can be expressed as
Thus, if the input elastic wave is f (t) as shown in FIG.
Output X is

The waveform can be expressed by the relative positional relationship between the output point and the receiving point, the relative positional relationship L between the input point, the output point, and the pipe end, and the relative position between the input point, the output point, and the defective portion. It differs depending on the positional relationship L ′, the bending rigidity EI of the tube, the damping coefficient c, the specific gravity m of the tube, and the like.

Fig. 12 (b) shows a type 1 of a JIS A 5303B type nominal fume pipe with a nominal diameter of 250mm and a length of 2m. The waveform of the vibration-receiving elastic wave is shown. (B) in FIG. 12 shows a frequency spectrum obtained by fast Fourier transform of the waveform,
It has a maximum peak at the natural vibration frequency.
In this frequency spectrum, the following difference occurs between the healthy product and defective product (of course, the input value, the relative positional relationship between the input point and the receiving point, and the environmental conditions such as the amount of water in the pipe are the same comparison) ).
(1) Spectral intensity value of maximum peak The deteriorated product has a smaller peak peak spectral intensity value (spectrum intensity value at the natural frequency) than a healthy product. The reason for this is presumed that the presence of defects such as cracks makes it difficult for elastic waves to propagate.
(2) Natural vibration frequency The natural vibration frequency of the deteriorated product shifts to the low frequency side compared to the healthy product. The reason for this is presumably because the bending rigidity of the tubular body decreases when there are defects such as cracks.
(3) Number of peaks Particularly when the defect is a crack in the tube axis direction, the number of peaks having a certain strength or more is reduced. The reason is presumed that although the concrete portion having a mass divided by the crack in the axial direction of the pipe vibrates separately, the attenuation becomes remarkable due to the interaction in the coupled vibration.
With these (1) to (3) as determination points, deterioration diagnosis is performed according to the flow shown in FIG. 13, for example.
That is, the received wave frequency spectrum of each pipe body in the section of the buried pipe to be inspected is obtained, the number of spectra having a maximum peak spectral intensity value of 40% or more is obtained from each frequency spectrum, and the number of peaks is 2 or less. For those with axial cracks, those with 3 or more peaks are marked as circumferential cracks if the maximum peak intensity value is significantly reduced compared to the sound wave frequency spectrum of healthy products. If the degree of decrease is small, it is determined that the tube thickness is reduced.

In the deterioration diagnosis of the buried pipe, it is necessary to measure the frequency spectrum of the received wave under the same measurement conditions and the same environmental conditions for each pipe body.
Therefore, in order to make the sound pipe body the same as the measurement condition and the environmental condition (pipe water amount 0%), FIG.
As shown in FIG. 3, the inspection robot 1 ′ is mounted on the carriage so that the vibration sensor B and the impulse hammer A can be moved up and down respectively. Is introduced into the inspection section of the buried pipe, and the relative positional relationship between the vibration sensor B and the impulse hammer A and the input value of the impulse hammer A are made the same as those of the healthy pipe, and the frequency spectrum of the received wave of each pipe one after another Is measuring.
As the amount of water in the pipe attenuates the propagation elastic wave and causes a substantial increase in the mass of the pipe body, the amount of water in the pipe affects the received waveform, as is apparent from the above-described basic equation [1] of the vibration waveform. It causes differences in the frequency spectrum.
Thus, draining the examination section has the significance of aligning the environmental conditions with respect to the amount of water with reference to 0% of the amount of water in the pipe, and is effective in increasing the diagnostic accuracy.
However, the span between manholes in the buried pipeline is long, and the amount of water between the spans of the sewage pipeline and the agricultural water pipeline in use is large, and the draining operation is extremely difficult.

Therefore, the present inventor has intensively studied the influence of the amount of water in the pipe on the received wave frequency spectrum in an actual buried pipe, and unexpectedly, the natural vibration frequency and the number of peaks of the received wave frequency spectrum are almost unchanged. First of all, it was found that the intensity of the spectrum (crest value) only changed.
This fact indicates that the decrease in the peak value of the received elastic wave due to the release of a part of the output elastic wave in the pipe water in proportion to the increase in the amount of water in the pipe, the change in the received elastic wave due to the change in the damping coefficient or mass. It is presumed that the result appears stronger.

The purpose of the present invention is to perform a shock elastic wave test sequentially on each pipe connected to each other in the buried pipe, and analyze and determine the frequency spectrum of the received wave in each test to perform a deterioration diagnosis. Even if there is a water amount, it is possible to perform deterioration diagnosis based on a unified standard by correcting the frequency spectrum corresponding to the water amount, and to facilitate the work by omitting the water draining operation.

In the buried pipe inspection method according to the present invention, an elastic wave is input to a predetermined inner surface portion of the embedded tube in a state where water is present in the tube, and a propagation elastic wave is transmitted from the input portion to the inner surface portion of the tube at a predetermined interval. the tube in the water level measured co Upon geophone obtains a frequency spectrum with respect to a reference level of the geophone wave is corrected by a correction factor for the pipe water level obtained in advance the intensity values of the frequency spectrum of the geophone wave, the frequency It is characterized by analyzing the spectrum and diagnosing deterioration of buried pipes.

Even if there is water in the pipe, the frequency spectrum of the received wave obtained by measurement in that state can be corrected to the frequency spectrum when the water volume is constant (for example, 0% water), and the deterioration diagnosis of the buried pipe can be performed It can be done without being affected. Accordingly, it is not necessary to drain water from the inspection section of the buried pipeline, and the preparation work for the shock elastic wave test in the inspection section can be simplified.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a drawing for explaining a shock elastic wave test method used in the present invention.
In FIG. 1, p is a tubular body, A is an impact tool for inputting an elastic wave to a predetermined location on the inner surface of the tubular body,
B is a vibration sensor brought into contact with a predetermined location on the inner surface of the tube at a predetermined distance from the input point, and C is a computer that records the received wave of the vibration sensor and displays a frequency spectrum by fast Fourier transform.
The hitting tool A can always be hit with the same force and length of time, for example, a hammer or a steel ball that strikes a hammer or steel ball with a constant force (for example, an impulse hammer), from a certain height. What can drop a steel ball can be used, and it is particularly preferable to use one that can measure the recorded data of input information and reflect it at the time of analysis.
The vibration sensor B may be any method of picking up vibration acceleration, vibration speed, and vibration displacement, and the sensor element is a piezoelectric type such as a resistance wire strain gauge, a semiconductor gauge utilizing the piezo effect, and a piezoelectric ceramic. An acceleration pickup or the like can be used, and an AE sensor for AE wave detection can also be used. The vibration sensor can be brought into contact with the inner surface of the tube by using an adhesive tape, an adhesive, or pressing by hand, but it is preferable to use an inspection robot that handles the vibration sensor or hammer with an arm described later.
Since the vibration sensor and the hammer may come into contact with water, acidic water, or basic water, it is preferable to use a corrosion-resistant metal such as an aluminum alloy or SUS.

In order to perform a shock elastic wave test of a tubular body, in FIG. 1, an elastic wave is input by a striking tool A, a propagated elastic wave is received by a vibration sensor B, and the received wave is recorded in a computer C. The recorded waveform is subjected to fast Fourier transform to obtain the frequency spectrum of the received wave.
The input duration is 100 to 150 μs, while the vibration receiving time is 0 to 800 × 10 μs.
s, and the frequency of the frequency spectrum is 0 to 10 kHz, preferably 0.5 to 8 kHz. (A cut of less than 0.5 kHz is to eliminate noise)
Relative positional relationship between input, input position and receiving position in order to make the test condition for each pipe body the same when conducting the shock elastic wave test sequentially on the pipes connected to each other in the inspection section of the buried pipe Are made substantially the same. In this case, if the interval between the input position and the vibration receiving position is short, the distance from the propagation elastic wave from the output position to the vibration receiving position by reflecting the tube defect portion becomes long.
Because the attenuation during propagation becomes large and it becomes difficult to reflect the defect information of the tube in the received waveform.
The interval between the input position and the vibration receiving position is preferably ¼ or more of the tube length.
In order to eliminate the influence of the magnitude of the input, it is preferable to use a transfer function obtained by the received wave / input wave as received information.

In the present invention, even if there is a water amount in the defective pipe, the defect information such as the natural vibration frequency of the received wave, the number of peaks of the frequency spectrum of the received wave is substantially unchanged, and the peak value of the received wave is not changed. It is only substantially different, and the ratio of the difference is substantially equal to that of the healthy pipe. Therefore, if the relationship between the amount of water in the pipe and the peak value of the received wave is obtained for the healthy pipe, the amount of water exists. This is based on an unexpected finding that the frequency spectrum at the reference water amount (usually 0% water amount) can be obtained by correcting the spectral intensity of the frequency spectrum of the received wave of the defective tube.

First, this basic matter is verified.
(A) Calculation of correction formula for pipe water volume of received wave in healthy pipe This correction formula was calculated as follows.
For a healthy tube sample, a nominal diameter of 250 mm and a length of 2 m based on Type B of JISA 5303
A concrete fume tube was used.
The elastic wave input position and the vibration receiving position are 1950 mm apart on the top of the inner surface of the tube, and the inspection apparatus has a first arm 11a and a second arm 11b on the carriage as shown in FIG. 1
An inspection robot having an impulse hammer A supported at the tip of the arm 11a and a vibration sensor B supported at the tip of the second arm 11b is used, and GH-313 manufactured by Keyence Corporation is used as the vibration sensor.
A, Keyence Corporation GA-245 was used for the receiving amplifier, Keyence Corporation NR-2000 was used for the data logger, and Abu Boutique Co., Ltd. was used for the fast Fourier transform program.
As shown in FIG. 3 (A), the healthy sample is placed on a soil having a thickness of 200 mm, and further embedded in a soil cover thickness of 500mm as shown in FIG. 3 (B). (The distance from the impact hammer impact location to the receiving location is 1950 mm)
Install the weir plate so that the upper part is left open at both ends of the sample (fix the acrylic plate with adhesive), operate the inspection robot to bring the vibration sensor into contact with the inner surface of the sample, and adjust the water level in the tube Tap water was injected so as to be 0%, 10%, 30%, and 50%, and a shock elastic wave test was performed for each water level to record the waveform of the received wave. FIG. 4A shows the waveform of the received wave at a water level of 0%.
The received waveform for each water level is converted into an absolute value ((b) in FIG. 4 is a waveform obtained by converting the absolute value of the waveform shown in (b) in FIG. 4), integrated over a time interval of 0 to 700 × 10 μs,
Integral value ratio y = (integrated value of received wave at water level x%) / (integrated value of received wave at 0% water level)
Is calculated and shown in FIG.
[Formula 2] y = −0.005x + 1
Got.
The ratio y of the integral values means (received wave energy at water level x%) / (received wave energy at water level 0%).
Similarly, the frequency spectrum of the received wave is obtained by changing the water level ((a) in FIG.
% (B) shows the frequency spectrum of the received wave at a water level of 50%), and integrates in the frequency range of 0.5 to 10 kHz.
Integral value ratio y = (integrated value of received wave frequency spectrum at water level x%) / (integrated value of received wave frequency spectrum at 0% water level)
As a result, the same formula as [Formula 2] was obtained.
From this correction equation, the correction coefficient for the water level changed in units of 10% is as follows.

(B) Correlation between the correction equation y and the received wave frequency spectrum of the defective tube body It was confirmed that there was a correlation as follows.
As the defective tube body, the fume tube is dropped as shown in FIG. 6 (a), and a circumferential crack is 0.15 mm wide (equally spaced in the circumferential direction 5) at the center of the tube body as shown in FIG. 6 (b). Average value in points)
The defective tube was embedded in the same manner as the healthy sample, and weir plates were fixed to both ends of the tube so that water could be injected to a predetermined water level.
Even if the amount of water is present in the defective pipe, the spectrum intensity (crest value) of the received wave frequency spectrum of the defective pipe is corrected by the correction equation y as follows, at the reference water level (usually 0 water level). A received wave frequency spectrum can be obtained.
The left view of FIG. 7 (a) shows the received wave frequency spectrum when the in-pipe water level of the defective pipe body is 20%, and the right view shows the corrected received wave frequency spectrum corrected by the correction coefficient 1.11 based on the correction equation. Is shown.
7B shows the received wave frequency spectrum when the in-pipe water level of the defective pipe body is 50%, and the right figure shows the corrected received wave frequency spectrum corrected by the correction coefficient 1.33 based on the correction equation. Is shown.
Both the maximum peak value of the corrected received wave frequency spectrum shown in the left diagram of FIG. 7A and the maximum peak value of the corrected received wave frequency spectrum shown in the left diagram of FIG. 4, the maximum peak value frequency (natural vibration frequency) and the number of peaks substantially match.

Therefore, even if there is water in the defective pipe, the defect information such as the natural vibration frequency of the received wave and the number of peaks of the frequency spectrum of the received wave is substantially unchanged, and the peak value of the received wave is substantially unchanged. The ratio of the difference is substantially equal to that of a healthy pipe. Therefore, if the relationship between the amount of water in the pipe and the peak value of the received wave is obtained for the healthy pipe, the defective pipe where the amount of water exists is obtained. The frequency spectrum at the reference water amount (usually 0% water amount) can be obtained by correcting the spectral intensity of the frequency spectrum of the body vibration wave.
The reason for this is that the ratio of the correction coefficient described above, that is, the (integrated value of the received wave frequency spectrum of the sample at the water level x%) / (the integrated value of the received wave frequency spectrum of the sample at the 0% water level) is (water level). is the ratio of the received wave energy at x%) to the received wave energy at 0% water level,
It is estimated that the energy of the elastic wave output is released into the pipe water in proportion to the water level in the pipe, and the energy of the received wave is reduced by this amount.

In order to perform the deterioration diagnosis of the buried pipe by the buried pipe inspection method according to the present invention, it is preferable to use the inspection robot shown in FIG. As shown in FIG. 2B, this inspection robot can be folded in the middle, and can be smoothly inserted into a right angle space from the manhole to the pipe line.

In order to perform the deterioration diagnosis of the buried pipe by the buried pipe inspection method according to the present invention, for example, the inspection robot 1 shown in FIG. In this case, if the shock elastic wave test of one tube is performed, the inspection apparatus is transferred to the next tube, but if the depression is severe, it is determined that the deterioration is severe without performing the shock elastic wave test.
In FIG. 8, 3 indicates a TV camera, and the degree of depression is monitored by the TV camera, and the inspection apparatus is shifted while monitoring the inner surface of the pipeline. Reference numeral 4 denotes a control unit, and c denotes a personal computer or TV camera monitor for inputting operation signals, data recording, and fast Fourier transform. T
The water level meter 5 may be attached to the V camera 3 or the inspection robot 1, and the signal may be input to a personal computer so that the amount of water in the pipe in the received wave frequency spectrum can be corrected.

In order to diagnose the deterioration of the buried pipe, first, an impact elastic wave test is performed on each pipe body of the buried pipe using the inspection robot 1, and the input elastic wave received by the vibration sensor B is stored in a personal computer. ,
The input elastic wave is Fourier transformed by fast Fourier transform software to obtain a frequency spectrum. The water level x (%) in the pipe is measured by the water level meter 5, the correction coefficient is calculated by the above-described equation 2, the correction by the pipe water level is performed, and the corrected frequency spectrum is obtained.
This corrected frequency spectrum is analyzed to obtain the number of peaks having a spectrum intensity value of 40% or more of the maximum peak. If the number of peaks is 2 or less (see (b) in FIG. 10), the presence of an axial crack is diagnosed. If the number of peaks is 3 or more (see (c) in FIG. 10, (d) in FIG. 10), the intensity spectrum of the maximum peak is analyzed and the frequency spectrum of the healthy tube obtained in advance [FIG. (See (b) of FIG. 10), the maximum peak intensity value is significantly reduced (see (c) of FIG. 10), and it is diagnosed that there is a crack in the circumferential direction. A small one (see FIG. 10D) can be diagnosed as a decrease in tube thickness.

It is drawing used in order to show the shock elastic wave method used in this invention. It is drawing which shows the inspection robot used in this invention. It is drawing for showing the sample used in order to obtain | require a water level correction coefficient in this invention. 3 is a diagram illustrating a process of obtaining a water level correction coefficient in the present invention. It is drawing which shows the frequency spectrum in a different water level for calculating | requiring a water level correction coefficient same as the above from the frequency spectrum of a received wave. It is drawing which shows the defective pipe sample used in order to confirm the correlation with the defective pipe body of the said water level correction coefficient. It is drawing which shows the received wave frequency spectrum of the defective pipe body of a different water level used in order to confirm the correlation with the defective pipe body of the said water level correction coefficient. It is a drawing used to show an embodiment of the inspection method of the buried pipeline according to the present invention, It is drawing which shows the flowchart of an Example same as the above. It is drawing which shows each kind type of the received wave frequency spectrum used as the reference | standard which performs the defect determination in an Example same as the above. It is drawing which shows the input wave used in order to demonstrate the received wave function in a shock elastic wave method. It is drawing which shows the received wave and its frequency spectrum by a shock elastic wave method. It is drawing which shows the flowchart of the inspection method of the conventional buried pipe. It is drawing which shows the working state of the inspection method of the conventional buried pipe.

Explanation of symbols

A Hammer B Vibration sensor p Tube 1 Inspection robot 5 Water level gauge

Claims (1)

An elastic wave is input to a predetermined inner surface portion of the buried pipe in a state where the amount of water is present in the tube. corrected by the correction factor for the pipe water level obtained in advance the intensity values of the frequency spectrum of the geophone wave calculated frequency spectrum with respect to a reference level of the geophone wave, performing the deterioration diagnosis of the buried pipe by analyzing the frequency spectrum An inspection method for buried pipes.

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