JP3737203B2 - Method and apparatus for detecting coating damage in buried pipeline - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to coating damage detection for buried pipelines for detecting the occurrence of damage to coatings for protecting metal pipelines buried over long distances from corrosion by heavy machinery for civil engineering work, etc. It relates to a method and an apparatus.
[0002]
[Prior art]
Conventionally, metal pipelines buried in the ground for transporting city gas and the like have been coated to prevent corrosion. The coating is made of an electrically insulating synthetic resin and covers the metal tube main body of the conduit constituting the metal pipeline to prevent surface corrosion due to moisture in the soil.
[0003]
Although it is used for a long time after the pipeline is buried, ground excavation work may be performed near the buried site. For example, when heavy excavating machines such as excavator backhoes or excavator drill augers collide, the pipeline coating is susceptible to damage. If the coating is damaged, it will need to be repaired urgently as the conduit will corrode and cause leakage of city gas and the like. For this reason, it is necessary to apply a great deal of effort for damage detection, such as running a vehicle that monitors whether excavation work is being performed in the vicinity of the buried pipeline and constantly patroling it. Moreover, it is very difficult to determine whether the coating is damaged from the appearance.
[0004]
FIG. 7 shows a typical prior art for detecting damage to the coating of a conduit in a buried pipeline. (A) shows a basic configuration for detection, and (b) shows an example of a detection state. The conduit 1 is provided with a connection terminal 3 for supplying an AC signal for damage detection from the signal generator 2. The signal generator 2 generates an AC signal between the connection terminal 3 and the ground electrode 4 for connection to the surrounding soil. An electrically insulating coating is interposed between the metal pipe body of the conduit 1 and the surrounding soil. When an AC signal is applied, the coating acts as a capacitor, and a displacement current is applied during the coating. Flows. When the excavating heavy machine damages the coating, the insulation resistance between the metal tube main body of the conduit 1 and the surrounding soil is lowered, and the current flows easily. As shown in FIG. The surface potential of the 1 metal main tube also varies. Therefore, it is possible to detect damage to the coating by detecting fluctuations in the surface potential of the metal pipe body and fluctuations in the conduit current flowing in the metal pipe body. Prior art to which such a basic concept is applied is also disclosed in, for example, Japanese Patent Laid-Open No. 7-128189 by the present applicant.
[0005]
[Problems to be solved by the invention]
As shown in FIG. 7 (a), when the output of the signal generator 2 is directly connected to the conduit 1, when the output impedance of the signal generator 2 is small, the surface potential of the tube body of the conduit 1 at the connection terminal 3 portion is obtained. The tube potential hardly changes as shown in FIG. Even if the coating is damaged at time t1, a slight potential drop is observed due to the slight output impedance of the signal generator 2 and the impedance of the connection lead wire from the signal generator 2 to the connection terminal 3. Only.
[0006]
The AC signal current flowing in the pipeline 1 of the pipeline buried in the ground is disturbed by noise components generated by such an external environment when there are electric railways, factories, substations, etc. in the vicinity of the pipeline buried location. In spite of this, there is a possibility that the coating is not damaged, but it is erroneously determined that the damage has occurred, or cannot be detected even though the damage has occurred. In particular, when damage occurs in the coating at a long distance from the signal generator 2, it is very difficult to detect the damage.
[0007]
Although the idea of combining the current and potential and comparing them as resistance values is also disclosed in, for example, Japanese Patent Laid-Open No. 7-128272, it is difficult to avoid erroneous detection of fluctuations due to noise.
[0008]
An object of the present invention is to provide a coating pipeline damage detection method and apparatus that can improve the sensitivity of signal detection with a simple configuration and prevent false detection due to noise.
[0009]
[Means for Solving the Problems]
The present invention is a method for supplying an AC signal to a metal pipeline buried in the ground and detecting the presence or absence of damage to the coating from the change in surface potential of the metal pipeline,
Supply of AC signals to the metallic pipelines, are performed by the state of connecting the coil in series between the signal generator and the pipeline, the inductance value of the coil, depending on the value of the frequency and voltage of the AC signal A method for detecting a coating damage in an embedded pipeline, characterized by being selected .
According to the present invention, when supplying an AC signal to a metal pipeline buried in the ground, a coil is connected in series, and the inductance value of the coil is selected according to the frequency and voltage value of the AC signal. is performed by, raising the signal detection sensitivity for detecting the change in impedance between the soil around occurring during damage paint-covering metal pipeline, it is easily detected from the surface potential of the metal pipeline Can do.
[0010]
Furthermore, the present invention is an apparatus for supplying an alternating current signal to a metal pipeline buried in the ground, and detecting the occurrence of coating damage from the change in surface potential of the metal pipeline,
A coating damage detection apparatus for an embedded pipeline, comprising a coil connected in series to a supply path from an AC signal output side to a metal pipeline.
According to the present invention, since an AC signal is supplied from the output side to the metal pipeline via the coil, it is possible to easily detect an impedance change due to damage to the coating of the metal pipeline from a change in the surface potential. Can do. Even in the case of performing anticorrosion for preventing corrosion of a metal pipeline, it is possible to efficiently detect damage by increasing the signal detection sensitivity without affecting the anticorrosion current.
[0011]
The present invention is a plurality of positions which are set at intervals along the metal pipeline, measures the signal current and the surface potential through a metal pipe line,
Surface potential changes occur simultaneously at all measurement points, and the coating current is damaged when the signal current increases at one measurement point along the metal pipeline and the signal current decreases at the other measurement point. Generation | occurrence | production is detected and it judges that it is noise when a signal current changes to the same direction in all the measurement locations.
According to the present invention, when the signal current and the surface potential flowing through the metal pipeline are measured at a plurality of locations at intervals along the metal pipeline, the surface potential is measured at all measurement locations when the coating is damaged. At the same time, the signal current increases between the point where the AC signal is supplied and the point where the damage occurs, and the signal current decreases on the side away from the point where the signal is supplied. Since changes due to noise occur in the same way at all measurement locations with respect to signal current, it is determined whether noise or coating damage is detected based on whether the direction of change in signal current is the same at all measurement locations. can do.
[0012]
The present invention is a terminal point of the metal pipeline, while selectively absorb only the current of the AC signal,
It is characterized by detecting damage to the coating.
According to the present invention, only the current of the AC signal is selectively absorbed at the end point of the metal pipeline, so even if the distance from the AC signal supply position to the end point becomes long, a sufficient signal current is supplied to the pipeline. It can be made to flow along, and the detection sensitivity with respect to damage of a coating can be improved.
[0013]
The present invention is a plurality of positions which are set at intervals along the metal pipeline, a signal current and a surface potential through a metal pipe line, each frequency corresponding to the distance from the AC signal supply point Select and measure,
The present invention is characterized in that the presence or absence of occurrence of damage to the coating is detected based on the measurement result.
According to the present invention, AC signals having a plurality of frequencies are superimposed and supplied to a metal pipeline buried in the ground. The surface potential is more attenuated by the distance from the supply point as the frequency of the AC signal is higher, but the signal current is less attenuated by the distance as the frequency is lower. Therefore, it is possible to reliably detect damage by selecting a frequency according to the distance at the detection point and selecting a low frequency for the surface potential and a high frequency for the signal current at a point far from the supply point of the AC signal, for example.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic configuration of an embodiment of the present invention in (a), (b) shows a state of damage detection, and (c) shows a cross-sectional configuration of a conduit as a target of damage detection. . As shown to (a), the output from the signal generator 12 which generate | occur | produces the alternating current signal for damage detection is supplied via the connection terminal 13 to the conduit | pipe 11 of a buried pipeline. The signal generator 12 supplies an AC signal between the connection terminal 13 and the ground electrode 14 for electrical connection to the soil. The potential based on the surrounding soil at the connection terminal 13 can be measured as the tube potential shown in FIG. The conduit 11 has a cross-sectional configuration as shown in (c), and the surface of the pipe body 15 is covered with a coating 16 made of an electrically insulating synthetic resin around the pipe body 15 made of metal such as steel. Protects against corrosion. The coating 16 interposed between the tube main body 15 and the surrounding soil acts as a capacitor, and a displacement current corresponding to an AC signal current flows. As shown at time t2 in (b), the tube potential decreases.
[0015]
In the present embodiment, a coil 17 is connected in series between the signal generator 12 and the connection terminal 13 in order to more reliably detect a decrease in tube potential. The inductance value of the coil 17 is appropriately selected according to the frequency and voltage values of the signal generated from the signal generator 12. For example, the frequency of alternating current given as a signal is 15 Hz, and the inductance is about 40 mH. This inductance value has an impedance of about 4Ω at a frequency of 15 Hz. When the coating device 16 is damaged, the impedance between the damaged point and the ground varies depending on the type of heavy equipment and the level of damage, and is about 100 to 200Ω .
[0016]
FIG. 2 shows an overall configuration of a comprehensive coating damage detection system provided along a pipeline by a conduit 11 for supplying city gas buried in the ground. The length of the conduit 11 is 100 km or more, and an AC signal from the signal generator 12 is supplied near the middle thereof. Current sensors 18 and 19 are installed on both sides of the connection terminal 13 in the axial direction of the conduit 11. The current sensors 18 and 19 are current transformers abbreviated as CT, for example, and can detect a signal current flowing in the conduit 11. A damage detection device 20 is also installed in an intermediate portion of the conduit 11 where the signal generation device 12 is provided. The damage detection device 20 includes a potential detection means 21 for detecting the surface potential of the conduit 11 from the connection terminal 13 and a current detection means 22 and 23 for detecting a signal current flowing through the conduit 11 via the current sensors 18 and 19. including. The detection outputs from the potential detection means 21 and the current detection means 22 and 23 are given to the damage determination means 24, and the coating 16 shown in FIG. 1 is damaged by combining the potential detection result and the current detection result. It is determined whether or not. The central damage detection device 20 further includes a section specifying means 25 for specifying a section where damage has occurred and a communication processing means 26 for performing data communication with other damage detection apparatuses as will be described later. included.
[0017]
A plurality of damage detection devices 30 and 40 are installed at intervals along the axial direction of the pipeline 11 of the pipeline. Each damage detection device 30, 40 includes potential detection means 31, 41 and current detection means 32, 42 similar to the potential detection means 21 and current detection means 22, 23 of the central damage detection device 20, respectively. The potential detection means 31 and 41 are connected to connection terminals 33 and 43 provided in the conduit 11, and detect the surface potential of the conduit 11 at that portion. Each damage detection device 30, 40 also includes damage determination means 34, 44 and communication processing means 36, 46 similar to the damage determination means 24 and communication processing means 26 of the damage detection device 20. The current detection means 31 and 41 detect the signal current flowing through the conduit 11 via the current sensors 38 and 48, respectively.
[0018]
The central damage detection device 20 and a plurality of damage detection devices 30, 40 provided along the conduit 11 are connected via communication lines 51, 52, 53, 54 so that data communication is possible. When the damage determination means 24 detects that the coating has been damaged, the section identification means 25 of the central damage detection apparatus 20 detects another damage detection apparatus 30 via the communication processing means 26, 36, 46. , 40, it is checked whether the same damage detection with potential change is performed. When the potential detection means 21, 31, 41 of each damage detection device 20, 30, 40 detects the same potential change at the same time, the change in current detected by the plurality of damage detection devices 20, 30, 40 is From the position where the specific damage detection device 20, 30, 40 is provided, according to whether or not there is a change in which, for example, current increases on one side of the conduit 11 in the axial direction and current decreases on the other side. Then, it is determined whether or not the coating coating 16 is damaged.
[0019]
3 and 4 show the results of potential and current detection experiments in the case where the damage detection devices 30 and 40 are installed on the downstream side and the upstream side with respect to the connection point of the signal generation device 12 from the damage occurrence point to the coating. Shown on the top and bottom, respectively. The scale on the vertical axis indicates the relative values of potential and current. In this case, damage to the coating is given in a simulated manner at time points (1), (2), (3), (3), (4), (5), and (6). As shown in FIGS. 3 and 4, the effect of noise fluctuations on the potential is generally smaller than the noise influence on current fluctuations. Due to the occurrence of damage, the potential decreases similarly on the downstream side and the upstream side of the damage point. On the downstream side away from the signal generator 12 that is the signal source, the detected current value is small, so in FIG. 3, the change in current is displayed four times that in FIG. On the downstream side, a large amount of signal current flows out into the soil at the damage point, so the signal current decreases. On the upstream side of the damaged point, a larger amount of current flows into the soil at the damaged point. As shown by changes at times other than (1) to (6), the potential also changes due to noise, but the change in potential due to noise is not accompanied by a change in current.
[0020]
FIG. 5 shows a configuration for preventing the occurrence of false detection due to noise by increasing the signal current and the conduit current when the length of the conduit 11 is increased as another embodiment of the present invention. (A) shows the basic configuration of the present embodiment, and (b) shows the configuration of the embodiment shown in FIGS. 1 and 2 for comparison. In order to increase the signal current 60a and the conduit currents 61a and 62a of the present embodiment more than the signal current 60b and the conduit currents 61b and 62b shown in (b), the soil currents 63a and 64a flowing in the soil are also the soil current 63b. , 64b. For this reason, signal current absorbers 65 and 66 are provided near both ends of the conduit 11 to selectively absorb the signal current by matching the frequency and phase with the AC signal generated from the signal generator 12. As a result, the conduit currents 61a and 62a sufficient to overcome the noise current can be passed even at the end of the remote pipeline, and the damage detection performance can be improved. If the conduit currents 61a and 62a can be increased in this way, the S / N ratio for detection against noise is improved, and the occurrence of false alarms due to false detection of coating damage and the situation where damage detection is impossible are avoided. be able to.
[0021]
FIG. 6 shows another embodiment of the present invention in which an AC signal is supplied to the conduit 11 from the signal generator 12 shown in FIG. 1 at a plurality of frequencies, and potential measurement and current measurement are simultaneously performed at different frequencies. This shows the effect of improving damage detection sensitivity. For example, the three frequencies f1, f2, and f3 are 15 Hz, 100 Hz, and 200 Hz. As shown in (a), the potential measured by the potential measurement is more attenuated by the distance as the frequency is higher. Therefore, when the distance from the signal source is increased, the lower the frequency, the smaller the potential can be measured. it can. On the other hand, as shown in (b), the measured current value has a smaller attenuation due to distance as the frequency is higher, so that the measured current value becomes larger as the distance from the signal source increases. Thus, when the frequency has a relationship of f1 <f2 <f3, the measurement at a point far from the signal source can be reliably performed by measuring the current of a signal having a low frequency and measuring the current of a signal having a high frequency. Damage detection is possible.
[0022]
The signal current detection devices 65 and 66 can be realized by, for example, an LC resonance circuit or an AC constant current circuit having a frequency synchronization function by feedback control. Although the increase in the signal current is possible even if the amplitude of the AC signal generated by the signal generator 12 is increased, when the amplitude of the AC voltage increases, the potential of the surface of the conduit 11 becomes higher than the soil at the positive peak. From the viewpoint of anticorrosion, which may be on the positive side and the surface potential of the conduit 11 needs to be kept more negative than the soil, the increase in amplitude is limited.
[0023]
【The invention's effect】
As described above, according to the present invention, there is a risk of erroneous detection due to noise simply by connecting a coil having an inductance corresponding to the frequency and voltage of the AC signal in series to the supply path to the metal pipeline of the AC signal. As a result, the change in the surface potential of the metal pipeline can be detected more reliably, and the sensitivity of signal detection for detecting the occurrence of damage to the coating can be improved with a simple configuration.
[0024]
Furthermore, according to the present invention, by simply connecting the coil in series with the supply path from the output side of the AC signal to the metal pipeline, false detection due to noise is reduced, and coating is performed from changes in the surface potential of the metal pipeline. It is possible to improve the signal detection sensitivity for detecting whether or not the covering is damaged.
[0025]
Furthermore, according to the present invention, it is possible to easily determine whether the coating is damaged or noise from the change in the surface potential of the metal pipeline at a plurality of measurement points and the direction of the change in the signal current. Even in a noisy environment, it is possible to detect damage to the coating with high sensitivity.
[0026]
Furthermore, according to the present invention, the signal current flowing through the pipeline can be increased efficiently, so that even if the pipeline is buried over a long distance, false detection due to noise is prevented and damage to the coating is detected. Can be performed with high sensitivity.
[0027]
Furthermore, according to the present invention, a plurality of frequencies are superimposed on an alternating current signal and supplied to the buried pipeline. Therefore, the frequency is selected according to the distance between the signal supply point and the measurement point, and erroneous detection due to noise is less likely to occur. Thus, the sensitivity of coating coating damage detection can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration according to an embodiment of the present invention, a time chart showing an example of a detection result, and a cross-sectional view perpendicular to an axis showing a configuration of a conduit 11 to be detected.
FIG. 2 is a block diagram showing a schematic configuration of a comprehensive coating damage detection system to which the embodiment of FIG. 1 is applied.
FIG. 3 is a time chart showing an example of a detection result by the system of FIG. 2;
4 is a time chart showing an example of a detection result by the system of FIG.
FIG. 5 is a block diagram showing a basic configuration of another embodiment of the present invention.
FIG. 6 is a graph showing potential and current measurement results according to still another embodiment of the present invention.
FIG. 7 is a block diagram showing a basic configuration for detecting coating damage according to a typical prior art, and a time chart showing an example of a detection state thereof.
[Explanation of symbols]
11 Conduit 12 Signal generator 13, 33, 43 Connection terminal 14 Ground electrode 15 Tube body 16 Coating 17 Coil 18, 19, 38, 48 Current sensor 20, 30, 40 Damage detection device 21, 31, 41 Potential detection means 22, 23, 32, 42 Current detection means 24, 34, 44 Damage determination means 25 Section identification means 26, 36, 46 Communication processing means 51-54 Communication lines 65, 66 Signal current absorber

Claims (5)

An AC signal is supplied to a metal pipeline buried in the ground, and the presence or absence of damage to the coating is detected from a change in the surface potential of the metal pipeline,
Supply of AC signals to the metallic pipelines, are performed by the state of connecting the coil in series between the signal generator and the pipeline, the inductance value of the coil, depending on the value of the frequency and voltage of the AC signal A method for detecting a coating damage in an embedded pipeline, wherein the method is selected. An apparatus for supplying an alternating current signal to a metal pipeline buried in the ground and detecting the occurrence of damage to the coating from the change in surface potential of the metal pipeline,
A coating damage detection apparatus for an embedded pipeline, comprising a coil connected in series to a supply path from an AC signal output side to a metal pipeline. At a plurality of positions which are set at intervals along the metal pipeline, it measures the signal current and the surface potential through a metal pipe line,
Surface potential changes occur simultaneously at all measurement points, and the coating current is damaged when the signal current increases at one measurement point along the metal pipeline and the signal current decreases at the other measurement point. 2. The method for detecting a coating damage in an embedded pipeline according to claim 1 , wherein occurrence is detected and it is determined that noise occurs when the signal current changes in the same direction at all measurement points. At the end point of the metal pipeline, while selectively absorb only the current of the AC signal,
The damage detection method for an embedded pipeline according to claim 1, wherein damage detection for the coating is performed. Measurement wherein at a plurality of points which are set at intervals along the metal pipeline, a signal current and a surface potential through a metal pipe line, to select each frequency corresponds to the distance from the AC signal supply point And
2. The coating damage detection method for an embedded pipeline according to claim 1 , wherein presence or absence of occurrence of damage to the coating is detected based on a measurement result.

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