JP2005345116A - Buried pipe inspecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform the diagnosis of a deterioration on the basis of a unfied standard by the correction of the frequency spectrum corresponding to the buried depth of a buried pipe even if the burying depth of the buried pipe is different when impact elastic wave tests are successively performed with respect to the respective mutually connected pipe bodies of the buried pipe and the frequency spectra of received waves in the respective tests are analyzed/determined to perform the diagnosis of the deterioration of the embedded pipe. <P>SOLUTION: An elastic wave is inputted from an impactor A to the predetermined inner surface place of the buried pipe, the propagated elastic wave is received at a pipe inner surface place separated from the input place at a predetermined interval by a vibration sensor B, the intensity value of the frequency spectrum of the received wave is corrected by the preliminarily calculated correction factor to the depth of the buried pipe to calculate the frequency spectrum to the reference burying depth of the received wave and the frequency spectrum is analyzed to diagnose the deterioration of the buried pipe. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 hitting, a frequency spectrum of a waveform received by a vibrator in contact with the object to be inspected, and analysis and determination of the frequency spectrum is performed. 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)

JP 2004-028976 A Minagi, Kamada, Nozaki, Funabashi, Basic research on deterioration diagnosis method of concrete sewer pipes by elastic wave, Concrete engineering annual papers, 2002, VOL24, No1, p1539-1544

The basic configuration of this diagnostic system will be described as follows.
In FIG. 17A, 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. 18 (b) shows a type 1 of a JIS A 5303B type concrete 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. 18 shows a frequency spectrum obtained by fast Fourier transforming 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. 19, 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 elastic wave in the buried pipe, the buried soil also becomes a propagation field of the elastic wave. In this case, at the normal embedment depth, the characteristics (1) to (3) are not substantially affected by the embedment depth, and exist in the buried pipe regardless of the presence of the earth covering just above the pipe. It has been confirmed that defects such as cracks can be diagnosed by analyzing the frequency spectrum of the received elastic wave.

However, when the soil covering depth reaches 2 m, it becomes difficult to ignore the influence of the soil covering.
Therefore, the concrete fume pipe and the sand covered with sand were regarded as elastic bodies, models were created, and elastic waves were actually input to this model, and the time calendar response waveform was obtained by FEM analysis at the actual receiving position. However, in the model, it is difficult to simulate the boundary between the concrete fume pipe and the soil covering sand to an actual state, and it is difficult to accurately grasp the relationship between the buried depth and the received wave frequency spectrum.
However, in the present inventor, since the compression state of the earth and sand between the buried pipe and the earth covering affects the above-described received wave frequency spectrum, the spectrum intensity of the received wave frequency spectrum is determined based on a certain compressed state. It was found that if the correction factor was calculated, pipe defects could be judged on the same basis, even if the burial depth was different, by eliminating the influence of the burial depth.

The object of the present invention is to perform a shock elastic wave test sequentially on each pipe body connected to each other in the buried pipe line, analyze and judge the frequency spectrum of the received wave in each test, Even if the embedment depth is different, deterioration diagnosis can be performed based on a unified standard by correcting the frequency spectrum corresponding to the embedment depth.

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, and a propagating elastic wave is received at a tube inner surface portion spaced from the input portion by a predetermined distance. The frequency spectrum intensity is corrected with the correction coefficient for the pipe embedment depth obtained in advance, the frequency spectrum for the reference embedment depth of the received wave is obtained, and this frequency spectrum is analyzed to diagnose deterioration of the buried pipe. Features.

Even if the embedment depth of the buried pipe to be inspected is different for each tubular body, the received wave frequency spectrum obtained for each tubular body is the reference wave (for example, embedment depth 0.5 m). The frequency spectrum can be corrected, and the deterioration diagnosis of the buried pipe can be performed without being affected by the depth of the buried pipe.

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 B and the hammer A may be in contact with water, acidic water, or basic water, it is preferable that the vibration sensor B or the hammer A is made of 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.
For the input duration of 100 to 150 μs, the vibration receiving time is set to 0 to 800 × 10 μs,
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 the received wave information.

In the present invention, even if there is a difference in the embedding depth of the defective tube, 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 crest values are only substantially different, and the ratio of the differences is substantially equal to that of the healthy pipe. Therefore, the relationship between the pipe embedment depth and the crest value of the received wave frequency spectrum is determined in advance for the healthy pipe. In this case, it is based on the fact that the frequency spectrum at the reference embedment depth (usually 0.5 m) can be obtained by correcting the spectral intensity of the frequency spectrum of the received wave of the tube having a certain embedment depth.
This fact is that when the elastic wave is input to the buried pipe, a part of the input elastic wave propagates in the earth and sand around the pipe, and the higher the degree of compression of the earth and sand around the pipe, the more elastic the sand and sand. As the wave propagation ratio increases, it can be estimated that the deeper the pipe embedment depth, the greater the amount of elastic wave leakage into the soil and the lower the intensity of the received elastic wave. There is a certain relationship between the frequency spectrum of the received elastic wave and the frequency spectrum of the received elastic wave. From this relationship, the frequency spectrum of the received elastic wave at the pipe embedment depth can be corrected to the received elastic wave frequency spectrum at the reference embedded depth.

First, the basic items are verified.
(A) Setting of embedding conditions Samples used in the experiment are 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
2 is used, and a sound pipe sample is disposed on a sand of 200 mm thickness as shown in FIG. 2 (a), and a sand of 300mm thickness as shown in FIG. 2 (b). The earth pressure state where the embedding depth is 0.5 m, 1.0 m, 1.5 m, and 2.0 m (the earth pressure on the outer surface of the pipe is 0.5 m, 1.0 m, 1.5 m, 2 m (Same pressure as earth pressure when buried in 0m)
In order to simulate the above, as shown in FIG. 3C, a required number of steel plates m were placed through a wood plate spacer c. The weight of the steel plate used is 5 kN / sheet, and the specific gravity of the earth and sand used is 1
Table 1 shows the total weight (number of steel plates) of 7.8 kN / m 3 for setting a predetermined embedding depth.
It was as follows.

(B) Calculation of correction formula for pipe embedment depth of received wave in healthy pipe This correction formula was calculated as follows.
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.
For each sample in which the embedding depth is set to 0.5 m, 1.0 m, 1.5 m, or 2.0 m by placing a steel plate, the inspection robot is introduced into the sample (receiving vibration from the impact hammer impact location) The distance to the location was 1950 mm), and the shock elastic wave test was performed to record the waveform of the received wave. FIG. 4 (a) shows the waveform of the received wave in a sample corresponding to an embedding depth of 0.5 mm.
The received waveform for each embedding depth is converted into an absolute value ((B) in FIG. 4 is a waveform obtained by converting the absolute value of the waveform shown in (A) in FIG. 4), and is integrated over a time interval of 0 to 700 × 10 μs. And
Ratio of integral value y = (integrated value of received wave at buried depth xm) / (integrated value of received wave at buried depth of 0.5 m)
Is calculated and shown in FIG.
[Formula 2] y = −0.28x + 1.14
Got.
The ratio y of the integral value is (the energy of the received wave at the embedment depth xm) / (the embedment depth 0.5 m).
The energy of the received wave at
Similarly, the frequency spectrum of the received wave of each sample with different embedment depth is obtained ((b) in FIG. 5 shows the frequency spectrum of the received wave of the sample corresponding to the embedded depth of 0.5 m, and (b) in FIG. Indicates the frequency spectrum of the received wave of the sample corresponding to the embedding depth of 2.0 m), frequency 0 to 10 k
Integrate over the interval of Hz,
Ratio of integral value y = (integrated value of received wave frequency spectrum at buried depth xm) / (integrated value of received wave frequency spectrum at buried depth of 0.5 m)
As a result, the same formula as [Formula 2] was obtained.
From this correction formula, the correction coefficient for the buried depth changed in units of 0.5 m is as follows.

(C) Correlation between the correction formula y and the received wave frequency spectrum of the defective tube body It was confirmed that there was a correlation as follows.
As a defective tube sample, the fume tube was dropped as shown in FIG. 6 and a crack in the circumferential direction was placed in the center of the tube with a width of 0.15 mm (average value at five equally spaced circumferential points). used.
Even if the embedment depth of the defective pipe sample is made different by placing the steel plate, the spectral intensity (crest value) of the received wave frequency spectrum of the defective pipe is corrected by the correction equation y as follows. A frequency spectrum substantially equal to the received wave frequency spectrum at the embedment depth (embedment depth 0/5 m with the correction coefficient 1) can be obtained.
The left side of FIG. 7 (a) shows the received wave frequency spectrum at a depth of 0.5 m of the defective tube, and the right side shows the corrected received wave frequency spectrum corrected by the correction coefficient 1 based on the correction formula. Show.
The left side of (b) in FIG. 7 shows the received wave frequency spectrum when the defective pipe is embedded at a depth of 2.0 m, and the right side is the corrected received wave frequency corrected by the correction coefficient 1.72 based on the correction equation. The spectrum is shown.

(A) in FIG. 8 shows the ratio between the maximum peak value and the maximum heak value before correction of the received wave frequency spectrum for the healthy sample having an embedding depth of 0.5 m and 2.0 m and the circumferential crack sample described above. (B) in FIG. 8 shows the ratio between the maximum peak value and the maximum heak value after correction of the received wave frequency spectrum for the healthy sample having the embedment depth of 0.5 m and 2.0 m and the above-described circumferential crack sample, respectively. It is clear that the maximum peak values are almost the same by the correction even when the embedment depth is different, and that the deterioration diagnosis by the maximum peak value can be performed by the same standard by the correction even if the embedment depth is different.
Further, from the comparison of the received wave frequency spectrum in the cases (a) and (b) of FIG. 5 having different embedment depths or (b) and (b) of FIG. 7 having different embedment depths, the maximum peak value frequency ( It is clear that the natural vibration frequency) and the number of peaks are substantially unchanged.

Therefore, even if the embedment depth of the tube is different, 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 buried depth and the wave height is determined for a healthy pipe, defects with different buried depths can be obtained. The reference embedding depth (usually 0.5m) by correcting the spectral intensity of the frequency spectrum of the tube's received wave
The frequency spectrum at can be obtained.

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. 3B, this inspection robot can be folded in the middle so that it can be smoothly inserted into a right angle space from the manhole to the pipeline.

で求めることができ、図９において、ＴＶカメラ３または検査ロボット１に傾斜計６を
取付け、その信号をパソコン５に入力して受振波周波数スペクトルの埋設深さに対する補
正を行い得るようにしてもよい。 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 can be used as shown in FIG. 9 and the flow 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. 9, 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 pipe. 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.
The embedment depth H of each tube can be the embedment depth at the tube center point position, for example, FIG.
The inclination angle θm (m = 1, 2,...) Of each tube shown in FIG.

In FIG. 9, an inclinometer 6 is attached to the TV camera 3 or the inspection robot 1, and the signal is input to the personal computer 5 so that the embedded depth of the received wave frequency spectrum can be corrected. Good.

In order to perform the deterioration diagnosis of the buried pipe, in FIG. 9, 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 received. It saves in the personal computer 5, The input elastic wave is Fourier-transformed with a fast Fourier transform software, and a frequency spectrum is calculated | required. The embedment depth x (m) is measured by the inclinometer 6, the correction coefficient is calculated by the above equation 2, the embedment depth is corrected, and the corrected frequency spectrum is obtained.
This corrected frequency spectrum is analyzed to obtain the number of peaks having a maximum peak spectral intensity value of 40% or more. If the number of peaks is 2 or less (see (b) in FIG. 12), it is diagnosed that there is an axial crack. If the number of peaks is 3 or more (see (c) in FIG. 12, (d) in FIG. 12), 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. 12), the maximum peak intensity value is significantly reduced (see (c) of FIG. 12), and it is diagnosed that there is a crack in the circumferential direction. A small one (see FIG. 12D) can be diagnosed as a decrease in tube thickness.

The correction formula for the above-described embedding depth varies depending on the type of earth and sand. Therefore, in the same manner as the calculation formula for the sandy soil described above, a correction formula is also calculated for gravelly soil and viscous soil,
It is preferable to deal with soil quality.

Since the amount of water in the pipe attenuates the propagation elastic wave and brings about 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 basic equation of the vibration waveform [Equation 1],
It makes a difference in its frequency spectrum.
Thus, draining the test 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 improving the diagnostic accuracy. In the above embodiment, as shown in FIG. In addition,
The section existing in the inspection pipeline section is stopped with an airbag G or the like, the inspection section is drained, and the inspection water amount is 0%.

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 the natural vibration frequency and the number of peaks of the received wave frequency spectrum are hardly changed, and the intensity of the spectrum (the peak value). ).
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.

We will verify this fact.
(A) Calculation of correction formula for pipe water volume of received wave in healthy pipe This correction formula was calculated as follows.
The water level in the pipe of a healthy pipe sample with a reference embedding depth (0.5 m) is 0%, 10%, 30%, 50
%, A shock elastic wave test was performed for each water level, and the waveform of the received wave was recorded. (A) in FIG.
Indicates 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. 13 is a waveform obtained by converting the absolute value of the waveform shown in (b) in FIG. 13), 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 3] 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 ((b) in FIG.
The frequency spectrum of the received wave at 0% is shown, and (b) in FIG. 14 shows the frequency spectrum of the received wave at the water level of 50%).
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 3] 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 a defective tube body, the fume tube is dropped as shown in FIG. 6 and a circumferential crack is formed at the center of the tube body with a width of 0.15 mm (average value at five equally spaced circumferential points). We used what we put.
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 side of FIG. 15 (a) shows the received wave frequency spectrum when the in-pipe water level of the defective pipe body is 20%, and the right side figure shows the corrected received wave frequency spectrum corrected by the correction coefficient 1.11 based on the correction formula. Is shown.
The left side of (b) in FIG. 15 shows the received wave frequency spectrum when the in-pipe water level of the defective pipe body is 50%, and the right side shows the corrected received wave frequency spectrum corrected by the correction coefficient 1.33 based on the correction formula. Is shown.
The maximum peak value of the received wave frequency spectrum after correction shown in the left side of FIG.
5 together with the maximum peak value of the received frequency spectrum after correction shown in the left diagram of (b) 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 according to another embodiment of the buried pipe inspection method according to the present invention, for example, the flow shown in FIG. 16 can be followed.
First, for each tube of the buried pipeline, in addition to the inclinometer, the water level meter is attached to the inspection robot, and the shock elastic wave test is performed using the inspection robot while the amount of water remains in the pipe.
The input elastic wave received by the vibration sensor is stored in a personal computer, and the input elastic wave is Fourier-transformed by fast Fourier transform software to obtain the transfer function of the frequency spectrum. Embedding depth H (
m) is measured, the pipe water level x (%) is measured, the correction coefficient is calculated by the above formulas 2 and 3, the correction to the buried depth and the pipe water level is performed, and the corrected frequency spectrum Find the transfer function of.
The transfer function of this corrected frequency spectrum is analyzed, and the spectrum intensity value of the maximum peak is 4
The number of peaks of 0% or more is obtained. If the number of peaks is 2 or less, it is diagnosed that there is an axial crack. If the number of peaks is 3 or more, the intensity value of the maximum peak is analyzed and obtained in advance. If the maximum peak intensity value is significantly reduced compared to the frequency spectrum transfer function of a healthy tube, it is diagnosed that there is a circumferential crack, and if the decrease in the maximum peak intensity value is small, the tube thickness is reduced. Can be diagnosed.

It is drawing used in order to show the shock elastic wave method used in this invention. It is drawing for showing the sample used in order to obtain | require the embedment depth correction | amendment formula used in this invention. 1 is a view showing an inspection robot used in the present invention. It is drawing for showing the process of calculating | requiring the embedment depth correction coefficient used in this invention. It is drawing which shows the frequency spectrum in different embedding depth for calculating | requiring the embedding depth correction coefficient same as the above from the frequency spectrum of a receiving 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 embedment depth correction coefficient. It is drawing which shows the frequency spectrum of the defect pipe body in the different embedment depth used in order to confirm the correlation with the defect pipe body of the said embedment depth correction coefficient. It is a graph which shows ratio of the maximum peak value of the receiving wave frequency spectrum before correction | amendment with respect to the embedment depth of a healthy product and a defective product. It is drawing used in order to show the Example of the inspection method of the buried pipeline which concerns on this invention. It is drawing which shows the flowchart of an Example same as the above. It is drawing which shows the method for measuring the embedding depth of the tubular body in an Example same as the above. It is drawing which shows the various modes 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 process of calculating | requiring an in-pipe water level correction coefficient in another Example of this 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 received wave frequency spectrum of the defective pipe body in 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 drawing which shows the flowchart of another Example same as the above. It is drawing which shows the input wave used in order to show the waveform of the received wave 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.

Explanation of symbols

A Impact tool B Vibration sensor 1 Inspection robot p Tube 6 Inclinometer

Claims (1)

An elastic wave is input to a predetermined inner surface portion of the buried pipe, a propagation elastic wave is received at the inner surface portion of the pipe spaced from the input portion, and the intensity of the frequency spectrum of the received wave is obtained in advance. A method for inspecting a buried pipe, characterized in that a frequency spectrum with respect to a reference burying depth of the received wave is obtained by correcting with a correction coefficient for the depth, and the deterioration of the buried pipe is diagnosed by analyzing the frequency spectrum.

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