JP2006038597A - Inspection method for buried pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely inspect discrimination among deterioration phenomena in a buried pipe such as a buried pipe and a ceramic pipe constituting a sewer pipe line, an agricultural water pipe line or the like. <P>SOLUTION: In this method of inspecting a deterioration condition in the buried pipe, from its pipe inside, a propagation wave is measured by carrying out an impact elastic wave test, a frequency spectrum is analyzed as to the propagation wave, and at least a spectral area value of the first frequency section (for example, 0.5-4kHz) of the frequency spectrum, and a spectral area value of the second frequency section (for example, 0.5-10kHz) are evaluated to determine the discrimination of the deterioration conditions in the buried pipe. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a buried pipe inspection method for inspecting a deterioration state of a buried pipe.

  In sewage pipes and agricultural water pipes, accidents such as depressions and water leakage are increasing due to corrosive wear and breakage of buried pipes over time. For this reason, appropriate repair and renewal based on the appropriate deterioration degree diagnosis and the survey results are desired.

  In the diagnosis survey of sewage pipelines and agricultural water pipelines, in general, in order to determine the order of repair and reconstruction work 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.

  For this reason, conventionally, a method is generally used in which an appearance inspection is performed using visual observation or a TV camera, and a physical property is investigated by removing the core if necessary. However, with such a method, only visible deterioration can be detected, and deterioration on the outer periphery and inside of the pipe is overlooked, and it is difficult to appropriately and quantitatively grasp the deterioration phenomenon. In addition, in order to collect quantitative data, it is necessary to remove a large amount of cores, and there is a disadvantage that the strength of the sewage pipe and the agricultural water pipe is impaired and work is troublesome.

On the other hand, application of inspection methods performed on concrete structures is also considered. For example, a system for predicting crack width and depth using elastic waves has been proposed (see, for example, Patent Document 1). However, according to this inspection system, since the elastic wave amplitude value or the decrease in the elastic wave count number (the count number of the amplitude greater than or equal to the predetermined value) is used, the influence of the surrounding situation where the buried pipe is buried is used. There is a problem that the inspection accuracy is poor.
JP-A-10-142200

  The present invention has been made to solve the above-described problems, and it is possible to distinguish the deterioration phenomenon of buried pipes that construct sewage pipes and agricultural water pipes without being affected by the buried environment. An object of the present invention is to provide an embedded pipe inspection method capable of inspecting with accuracy.

  The method for inspecting a buried pipe according to the present invention is a method for inspecting the deterioration state of a buried pipe from the inside of the pipe, performing a shock elastic wave test to measure a propagation wave of the examination target pipe, and calculating a frequency spectrum for the propagation wave. Analysis is performed, and the distinction of the deterioration phenomenon is determined from at least the spectrum area value of the first frequency section and the spectrum area value of the second frequency section of the frequency spectrum.

  In the buried pipe inspection method of the present invention, as a method of setting a frequency section for calculating a spectrum area value, for example, a propagation wave is measured by performing a shock elastic wave test on each of a plurality of types of test tubes having different states. Then, analyze the frequency spectrum for each propagation wave, integrate each frequency spectrum for each fixed minute frequency interval, and sequentially integrate the integrated values to obtain the integrated integrated value. A method of determining a frequency at a point where the value greatly changes and setting a frequency section for obtaining the spectrum area value can be mentioned.

  In the buried pipe inspection method of the present invention, the frequency section for obtaining the spectrum area value is a first frequency section starting point of 0 to 2.5 kHz, an ending point of 3 to 5.5 kHz, and a second frequency section starting point of the frequency section. It is preferable that it is the frequency section which is the same value as the first frequency section and satisfies the range where the end point is 7 to 10 kHz.

  Hereinafter, the present invention will be described in detail.

  First, the applicant conducted a shock elastic wave test on a tubular body such as a reinforced concrete pipe, measured the propagation wave of the tubular body, analyzed the frequency spectrum of the propagation wave, and determined the deterioration state of the tubular body from the frequency spectrum. We propose a technique to determine

  In the present invention, the frequency spectrum obtained by such a shock elastic wave test is integrated for each fixed minute frequency section, and the integrated values are sequentially integrated to obtain an integrated integrated value (spectrum area value). In addition, as shown in the graph of FIG. 10, there are points at which the integrated integrated value changes greatly, and the phenomenon in which the change point appears is “Axial crack in tubular body”, “Circumferential crack”, and “Tube meat” It has been found that this is related to “thickness reduction”.

  In the present invention, using such a phenomenon, as described above, the shock elastic wave test is performed to measure the propagation wave of the inspection target tube, the frequency spectrum is analyzed for the propagation wave, and the frequency spectrum is analyzed. By evaluating the spectrum area value of the first frequency section (for example, 0.5 to 4 kHz) and the spectrum area value of the second frequency section (for example, 0.5 to 10 kHz) in FIG. It is characterized by specifying whether it is “sound”, “axial crack”, “circumferential crack”, “axial + circumferential crack” or “reduced tube thickness”.

  Next, in the present invention, a method for setting a frequency section used when obtaining a spectrum area will be described.

  First, as multiple types of test tubes with different states (degraded states), “sound tube”, “axial crack introduction tube”, “circumferential crack introduction tube”, “axial direction + circumferential crack introduction tube”, “tube” “Thickness reduction tubes” are prepared, and each of these test tubes is subjected to a shock elastic wave test to measure a propagation wave, and a frequency spectrum is analyzed for each of the propagation waves.

  Next, with respect to the frequency spectrum of each tubular body, integration is performed for each fixed minute frequency section (for example, 0.5 kHz), and the integrated values are sequentially integrated to obtain an integrated integrated value. When the integrated integral value of each tubular body obtained in this way is plotted on a graph using the frequency as a parameter, the result shown in the graph of FIG. 10 is obtained. Note that the graph of FIG. 10 is a graph obtained by modeling the result of a shock elastic wave test performed on samples S1 to S5 described later.

  Considering the graph of FIG. 10, first, the integrated integrated value of each tubular body up to the frequency section F1 including the point at which the integrated integrated value of the “axial crack introducing pipe” changes greatly is the first group with a large integrated integrated value. ("Sound pipe", "Pipe thickness reducing pipe", "Axial crack introduction pipe") and the second group with small integral integrated values ("Circumferential crack introduction pipe", "Axial + circumferential crack introduction pipe") ) Divided into two groups. In the first group, the integrated integral value is larger in the “thickness-reduced pipe” than in the “sound pipe” because the lower frequency component is more in the thinner pipe thickness.

  Further examination shows that the frequency interval F2 includes a point at which the integrated integrated value of the “tube thickness reducing pipe” greatly changes (decreases) and a point at which the integrated integrated value of the “circumferential crack introduction pipe” greatly changes (increases). The integrated value up to is slightly greater for the “sound pipe” than for the “thickness reduction pipe”, and the “axial crack introduction pipe” for the “sound pipe” and “thickness reduction pipe” Becomes smaller. Further, the “circumferential crack introduction pipe” is larger than the “axial direction + circumferential crack introduction pipe”.

  From the above, the frequency section F1 including the point where the integrated integrated value of the “axial crack introducing pipe” greatly changes is defined as the first frequency section, and the integration of the “pipe thickness reducing pipe” and the “circumferential crack introducing pipe” is integrated. The distinction of the deterioration phenomenon can be determined by setting the frequency section F2 including the point at which the integrated value greatly changes as the second frequency section.

  Specifically, with “sound pipe” as a reference, the integrated integrated value (spectrum area) of the first frequency section is “large” when it is larger than “sound pipe”, and “middle” when the same or a little smaller "Small" when the case is extremely small, and "Large" when the integral integrated value (spectrum area) of the second frequency interval is the same or slightly smaller than the "sound tube" Is “medium” and extremely small is “small”, it is possible to determine the distinction of the deterioration phenomenon under the determination conditions shown in Table 2 described later.

  The frequency section for obtaining the spectrum area value is not limited to the two sections of the first frequency section and the second frequency section described above, and three or more frequency sections may be set.

  Here, examples of the buried pipe to which the inspection method of the present invention is applied include a concrete pipe, a reinforced concrete pipe, a ceramic pipe, a metal pipe, a resin pipe, or an FRPM pipe (composite pipe of mortar and FRP). Examples of the cross-sectional shape of the buried pipe include a circular shape, an oval shape, a rectangular shape, and a horseshoe shape.

  According to the buried pipe inspection method of the present invention, a shock wave test is performed to measure the propagation wave of the pipe to be inspected, the frequency spectrum of the propagation wave is analyzed, and the spectrum of at least the first frequency section of the frequency spectrum. Since the area value and the spectrum area value of the second frequency section are evaluated and the deterioration state of the buried pipe is inspected, the amplitude value of the elastic wave and the decrease in the elastic wave count number (count number of amplitudes greater than or equal to the predetermined value) Compared to the inspection method to be used, it is less affected by the surrounding situation of the buried pipe, and the deterioration phenomenon can be accurately distinguished.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Embodiment 1>
In this embodiment, the shock elastic wave test is performed as follows.

[input method]
As the input device, a hammer, a steel ball, or an impact hammer such as an impulse hammer can be used. In particular, as an input device, in order to reflect input information at the time of analysis, it is desirable to perform striking with a constant force using a striking tool that can measure input information as numerical data, such as a Schmitt hammer, a spring, a piston, or the like . Further, for example, a method of driving a hammer, a steel ball, or the like with a constant force using a Schmitt hammer, a spring, a piston, or the like, or a method of dropping the steel ball or the like from a certain height is desirable.

[Reception method]
As the receiver, an acceleration sensor, an AE sensor, a vibration sensor, or the like can be used. As a method for setting the receiver, the receiver may be fixed with a tape, an adhesive, or the like, or may be crimped using a hand or a holding jig.

  Since these input devices and receiving devices may come into contact with water, acidic water, or basic water, it is desirable that the input device and the receiving device be formed of a material having excellent corrosion resistance such as stainless steel.

[Measurement method]
An elastic wave is input to the inner surface of the tube with an impulse hammer or the like. On the other hand, a propagation wave propagated through the tube is measured by a receiver set in the tube, and a waveform is stored by a recording device (measurement of received data). It is desirable that the incident position and the receiver position be separated from each other by 1/4 or more of the tube length of the inspection target tube. This is because changes in the vibration phenomenon of the entire tube due to deterioration such as cracks are easily captured. Further, it is desirable that the incident position and the receiving position are installed so that the relative positions are the same.

[analysis method]
For the input and reception data measured at the measurement position, a frequency spectrum in consideration of the relationship between the input (striking side) and the output (receiving side) is drawn. In this frequency spectrum distribution, a spectrum area value in the first frequency section (0.5 to 4 kHz) and a spectrum area value in the second frequency section (0.5 to 10 kHz) are obtained. When this analysis method is adopted, it is necessary to digitize the impact force (input information) of the impulse hammer.

  Here, the frequency spectrum considering the relationship between the input and the output is, for example, the input Fourier spectrum A (f), the output Fourier spectrum B (f), and the transfer function (frequency response function) H (f ), It is represented by the relationship of H (f) = B (f) / A (f), and this H (f) is drawn as the distribution of the frequency spectrum here.

<Example 1>
Specific examples of the present invention will be described.

[Sample preparation]
The following samples were prepared using a concrete fume pipe (product made from Nippon Hume Pipe) having a nominal diameter of 250 mm (pipe length: 2 m) based on JIS A 5372 B type 1 standard.
Sample S1: Untreated tube (tube thickness: average 28 mm). The tube thickness was measured with calipers at 10 points on each end near the end surface of the tube, for a total of 20 points.
Sample S2: Axial crack introduction tube Using a load tester capable of applying a linear load to the sample, four cracks (crack width = 0.15 mm) were generated in the axial direction (see FIG. 1). . In addition, the number of cracks visually confirmed the number of cracks generated on the inner surface and outer surface at one end surface.
Sample S3: Circumferential crack introduction tube A crack having a crack width of 1.3 mm introduced by the introduction method shown in FIG. 2 (see FIG. 3). Note that the crack width was measured by enlarging with a magnifier with a scale on the outer periphery of the pipe (average value of 5 points).
Sample S4: Axial direction + circumferential crack introduction tube After introducing an axial crack by the same method as sample S2, a circumferential crack was introduced by the same method as sample S3 (see FIG. 4).
Sample S5: Reduced tube thickness tube By special molding, the outer diameter is the same as that of the untreated tube, and the inner diameter is increased so that the average tube thickness is 13 mm (see FIG. 5). The tube thickness was measured with calipers at 10 points on each end near the end surface of the tube, for a total of 20 points.

  A list of samples is shown in Table 1 below.

［入射及び受信位置］
入射装置と受信装置を図６に示す位置に配置して弾性波の入射及び伝播波の受信を行った。

[Incoming and receiving position]
The incident device and the receiving device were arranged at the positions shown in FIG. 6 to receive the elastic wave and receive the propagation wave.

[Used equipment]
Incident device: Impulse hammer Receiver: Vibration sensor GH-313A (manufactured by Keyence) was used by screwing a cylindrical object having a diameter of 10 mm and a height of 15 mm.

Receiver amplifier: Keyence GA-245
Data logger (recording device): NR-2000 manufactured by Keyence
[Measurement conditions]
Assuming an actual pipeline, measurement was performed in a state where the above-described samples S1 to S5 were embedded under the conditions shown in FIG.

[Data analysis]
The input Fourier spectrum A (f) is obtained from the impact force of the incident device (impulse hammer), and the output Fourier spectrum B (f) is obtained from the waveform data of the propagation wave received and recorded by the receiver, and the input Fourier spectrum is obtained. Using the spectrum A (f) and the output Fourier spectrum B (f), the transfer function (frequency response function) H (f) (H (f) = B (f) / A (f) between the input and the output ) And a frequency spectrum in consideration of the relationship between the input and the output was drawn for each of the samples S1 to S5.

  Among these samples, the distribution graph of the frequency spectrum of sample S1 (untreated tube (healthy tube)) is shown in FIG. Further, with respect to the frequency spectrum of the sample S1, an integral value (spectrum area value) for each minute frequency interval (0.5 kHz) is calculated, and the integral integration value obtained by sequentially integrating the integration values is used as a parameter on the graph. When plotted, a graph as shown in FIG. 9 is obtained. Further, the integrated integrated value of the frequency spectrum is obtained for the samples S2 to S5 by the same method, and a graph of the frequency-integrated integrated value is created. The integrated integrated values of all the samples S1 to S5 are put on the same graph. If it represents, the tendency as shown in FIG. 10 will appear. Since the details have been described above, the description thereof is omitted here. In addition, the graph of FIG. 10 has modeled and shown the change of the integral integration value of each sample S1-S5.

  In this embodiment, the spectrum area value of the first frequency interval 0.5 to 4 kHz and the spectrum area value of the second frequency interval 0.5 to 10 kHz are calculated for the frequency spectra of the samples S1 to S5. The results are shown in FIGS. 11 and 12, respectively.

  Next, the spectrum area value in the first frequency interval 0.5 to 4 kHz is evaluated (hereinafter referred to as the first evaluation). Specifically, with reference to “no-treatment pipe (healthy pipe)”, the spectrum area value is “large” when the spectrum area value is larger than “no-treatment pipe”, “medium” when the spectrum area value is the same or slightly smaller, and extremely The small case is evaluated as “small”. The evaluation results are shown in Table 2 below.

  Further, the spectrum area value of the second frequency section 0.5 to 10 kHz is evaluated. Specifically, with reference to “no treatment pipe (healthy pipe)”, the spectrum area value is “large” when the spectrum area value is the same or slightly smaller than “no treatment pipe”, “medium” when the spectrum area is small, An extremely small case is evaluated as “small” (hereinafter referred to as a second evaluation). The evaluation results are shown in Table 2 below.

以上の表２の結果から、サンプルＳ１〜Ｓ５の劣化現象の区別を特定することできる。すなわち、上記第１の評価が「中」で第２の評価が「中」である場合、劣化現象の区別が「軸方向クラック」であると特定することができる。また、第１の評価が「小」で第２の評価が「中」である場合は劣化現象の区別が「周方向クラック」、第１の評価が「小」で第２の評価が「小」である場合は劣化現象の区別が「軸方向＋周方向クラック」、第１の評価が「大」で第２の評価が「大」である場合は劣化現象の区別が「管肉厚減少」であると特定することができる。なお、基準となる「無処理管（健全管）」の場合は、第１の評価が「中」で第２の評価が「大」となる。

From the results in Table 2 above, it is possible to specify the distinction between the deterioration phenomena of the samples S1 to S5. That is, when the first evaluation is “medium” and the second evaluation is “medium”, the deterioration phenomenon can be identified as “axial crack”. Further, when the first evaluation is “small” and the second evaluation is “medium”, the deterioration phenomenon is distinguished from “circumferential crack”, the first evaluation is “small”, and the second evaluation is “small”. ”Is“ Axial + circumferential crack ”, the first evaluation is“ Large ”, and the second evaluation is“ Large ”, the deterioration phenomenon is“ Tube thickness reduction ”. Can be specified. In addition, in the case of the standard “non-treated pipe (sound pipe)”, the first evaluation is “medium” and the second evaluation is “large”.

  Therefore, a shock elastic wave test is performed on an untreated tube (test tube) in advance, and the spectrum area value of the first frequency section 0.5 to 4 kHz and the spectrum area value of the second frequency section 0.5 to 10 kHz are Is calculated and recorded, and each of the above-described frequency sections of 0.5 to 4 kHz and 0.5 to 10 kHz is obtained from the frequency spectrum obtained by performing the shock elastic wave test on the inspection target pipe (buried pipe). The spectrum area value is obtained, and the magnitude of the actually measured spectrum area value is determined based on the previously recorded spectrum area value (the spectrum area value of the reference non-processed tube). It is possible to specify the distinction of the deterioration phenomenon of the inspection target pipe.

  In addition, the threshold value for determining “large”, “medium”, and “small”, which are judgment criteria in the first and second evaluations described above, is performed by performing a shock elastic wave test on each of the samples S1 to S5 in advance. A graph as shown in FIG. 10 may be created and obtained based on the graph.

  In the above embodiment, the first frequency section for obtaining the spectrum area is 0.5 to 4 kHz and the second frequency section is 0.5 to 10 kHz. However, the present invention is not limited to this, and the first frequency section The start point of 0 to 2.5 kHz, the end point is 3 to 5.5 kHz, the start point of the second frequency interval is the same value as the first frequency interval, and the frequency interval satisfying the range where the end point is 7 to 10 kHz The present invention can be implemented.

  Further, the frequency section for obtaining the spectrum area value is not limited to the two sections of the first frequency section and the second frequency section described above, and three or more frequency sections may be set.

  In the inspection method of the present invention, when determining the order of repair and reconstruction work and the construction method for buried pipes such as sewage pipes and agricultural water pipes, it is determined whether or not the deterioration phenomenon is distinguished between the element areas constituting the survey basin. Can be used effectively.

It is a schematic diagram of an axial crack introducing tube. It is a figure which shows typically the introduction method of the circumferential crack employ | adopted in the Example of this invention. It is a schematic diagram of the circumferential crack introduction pipe. It is a schematic diagram of an axial direction + circumferential crack introduction pipe. It is a schematic diagram of a pipe thickness reduction pipe. It is a figure which shows arrangement | positioning of the measurement apparatus to a sample. It is a figure which shows typically the sample embedding conditions of the Example of this invention. It is a distribution graph of the frequency spectrum of an untreated pipe (healthy pipe). It is a graph which shows the integral integration value of the frequency spectrum of FIG. It is a graph which shows the integral integration value of the frequency spectrum of the multiple types of tubular body from which a state differs. It is a figure which shows the result of the Example of this invention, and is a graph which shows the spectrum area value in the frequency area of 0.5-4 kHz of each sample. It is a figure which shows the result of the Example of this invention, and is a graph which shows the spectrum area value in the frequency area of 0.5-10 kHz of each sample.

Explanation of symbols

S1-S5 Sample of buried pipe

Claims (3)

  A method of inspecting a deterioration state of a buried pipe from the inside of the pipe, performing a shock elastic wave test to measure a propagation wave of the pipe to be inspected, analyzing a frequency spectrum of the propagation wave, and at least a first of the frequency spectrum. A method for inspecting a buried pipe, wherein a distinction of a deterioration phenomenon is determined from a spectrum area value in a frequency section and a spectrum area value in a second frequency section.   2. The buried pipe inspection method according to claim 1, wherein a plurality of types of test tubes having different states are subjected to shock elastic wave tests to measure the propagation waves, the frequency spectrum of each of the propagation waves is analyzed, and each frequency is analyzed. The spectrum is integrated for each fixed minute frequency interval, and the integrated values are sequentially integrated to obtain an integrated integrated value. The frequency of the point at which the integrated integrated value greatly changes is determined, and the spectrum area value is determined. A method for inspecting a buried pipe, characterized in that a frequency section for obtaining the frequency is set. 2. The buried pipe inspection method according to claim 1, wherein the first frequency section has a start point of 0 to 2.5 kHz, an end point of 3 to 5.5 kHz, and the second frequency section has a start point that is the same value as the first frequency section. A method for inspecting a buried pipe, which is a frequency section satisfying a range in which an end point is 7 to 10 kHz.

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