JP3451348B2 - Method for detecting paint film damage on buried coated steel pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating film damage detection method for a buried coating steel pipe, which detects a coating film damage position of a coating steel pipe buried in the ground in a non-contact manner from the ground surface.

[0002]

2. Description of the Related Art As a method for detecting a coating film damage (defect) of a coated steel pipe buried in the ground in a non-contact manner from the ground surface, for example, an alternating current is applied between the coated steel pipe and a grounding electrode in the ground. There is a method called the potential method that measures the damage position by applying a voltage, passing a current through the steel pipe, and measuring the potential distribution generated on the ground surface by the current flowing into the ground from the coating damage. is there. In coating film damage detection by the actual potential method,
A terminal for cathodic protection provided on the buried coated steel pipe and M
Using a positive electrode (ground electrode), a low frequency sine wave signal is applied between the buried coated steel pipe and the ground electrode in the ground to flow a low frequency alternating current. Then, two electrodes with a constant interval are arranged on the ground surface along the coated steel pipe, and the two electrodes are scanned along the buried coated steel pipe, and the two electrodes are used to separate the two electrodes. The potential difference signals are sequentially detected and the signals are detected to measure the intensity and phase of the potential difference distribution. Then, the potential difference distribution generated by the current flowing out from the damage of the buried coating steel pipe is detected from the change pattern of the potential difference distribution on the ground surface, and the damage position is estimated.

[0003]

In the conventional coating film damage detecting method for a buried coating steel pipe, as described above, the two electrodes are scanned along the buried coating steel pipe and the two electrodes are scanned. The potential difference distribution generated by the current flowing out from the damage of the buried coated steel pipe is detected from the change pattern of the potential difference on the ground surface detected by the electrode of No. 1, and the damage position is estimated.
The potential distribution on the ground surface, which is generated by the outflow current from the damage of the coating, is a local distribution in which the position immediately above the damage is maximum and decreases as the distance from the damage increases. When the steel pipe has multiple damages, the influence of the potential distribution generated by the current flowing out from the largest damage of the multiple damages becomes dominant, and the potential distribution generated by the smaller damage should be detected. Is difficult.

In actual detection of coating film damage,
Although it is possible to detect damage over a range of several Km by a signal applied from one point of the buried coating steel pipe,
When there is a plurality of damages in the range of several kilometers of the steel pipe, a steady current flows in the pipe axial direction along the steel pipe due to the outflow current from each damaged portion. If two electrodes are placed on an arbitrary ground surface along the buried coating steel pipe, the potential difference due to the steady-state current is detected, so if there is slight damage to the coating. However, it is difficult to detect minute changes in the potential distribution due to the damage, and it is difficult to detect minute damage.

The present invention has been made in order to solve the above-mentioned problems, and suppresses the influence of other damages and makes it possible to detect minute damages to the steel pipes for the buried coating. An object of the present invention is to provide a coating film damage detection method for a steel pipe.

[0006]

(1) A coating film damage detection method for a buried coating steel pipe according to an aspect of the present invention is a random signal or a signal between a buried coating steel pipe and a grounding electrode in the ground. pseudo
A low-frequency AC voltage related to a random signal is applied, and the potential difference between two points is detected and correlated by two electrodes arranged along the direction orthogonal to the pipe axis direction of the buried coated steel pipe.
By performing the treatment and changing its position, the potential difference distribution on the ground surface in the direction orthogonal to the pipe axis direction of the buried coating steel pipe is obtained, and the buried coating is calculated based on the potential difference distribution on the ground surface. Detects the damaged position of the covered steel pipe.

In the coating film damage detection method according to one aspect of the present invention, a low-frequency AC voltage relating to a random signal or a pseudo-random signal is applied between one point of a buried coated steel pipe and a grounding electrode in the ground. Then, an alternating current is caused to flow into the buried coated steel pipe. When the coating of the steel pipe is damaged and the steel pipe itself and the ground are in contact with each other, a part of the electric current flowing through the steel pipe flows into the ground, and a potential is generated by the current flowing out from the damaged portion. The potential distribution on the ground surface is a local potential distribution in which the position immediately above the damage is the maximum, and the position is directly above the damage and decreases as the distance from the damage increases. If there is a single damage to the coated steel pipe, the potential distribution around the damaged site is 1
Only those produced by the current from one damage,
The distribution is even in each direction centered on the damage. However, when there are multiple damages to the coating, a potential distribution is generated by the current flowing out from each damage according to the damage size, so the potential at any position is a combination of multiple potential distributions. Therefore, unlike the case of a single damage, the potential distribution on the upper part of the damage is not uniform due to the influence of the potential distribution caused by other damages.

Here, for example, when two electrodes with a constant interval are arranged on the ground surface and the potential difference between the two electrodes is measured, it is generated by the outflow current from the installation position of each electrode and the damage of the coated steel pipe. A potential difference determined by the potential distribution can be obtained.

In the conventional coating film damage detection method, two electrodes are arranged in the pipe axis direction of a buried coated steel pipe and the potential difference between two points in the pipe axis direction is measured. When the damage is single, as shown in FIG. 9A, the potential difference between the two electrodes is determined by the position of each electrode and the uniform potential distribution centering on the damage generated by the single damage. When scanning is performed in the tube axis direction, the potential difference becomes 0 at a position equidistant from the damaged position of the two electrodes, and at other positions, a potential difference of + or − is caused by a difference in distance from the damaged position of the two electrodes. Since it is measured, the damage position is estimated from the change in the potential difference depending on the position.

As shown in FIG. 9B, when there are a plurality of damages 4, there is a damage with a large loss small area (contact area with the ground) especially at a position adjacent to the target damage. In this case, the potential difference detected by the two electrodes installed in the tube axis direction is affected by the potential distribution generated by the adjacent damage, and there is a + or − potential difference in the tube axis direction. If the target damage is small,
As shown in (C), the change in the potential difference due to the target damage becomes relatively small, which makes detection difficult.

In the coating film damage detection method for a buried coated steel pipe according to the present invention, the ground surface is formed by two electrodes arranged at regular intervals on the ground surface in a direction orthogonal to the pipe axis of the steel pipe. Measure the potential difference. As shown in FIG. 10 (A), in the case of a single damage, if the electrodes are scanned on a line which is orthogonal to the tube axis and passes through the damage position, the potential difference distribution similar to that in the case where the electrodes are arranged in the tube axis direction is obtained. Is obtained. In addition, FIG.
As shown in (B), when there are a plurality of damages 4 and there is a damage with a large damage area adjacent to each other, there is a potential distribution due to the damages adjacent to each other, but the two electrodes are orthogonal to the tube axis. Since they are arranged in the same direction, the distance between each electrode and the adjacent damage can be considered to be the same, and the potential difference due to the potential distribution generated by the adjacent damage between the two electrodes is not observed. On the other hand, for the target damage, the potential difference signal according to the difference in the distance between the two electrodes and the damage is measured as in the case of the single damage, and as a result, the influence of other damage is suppressed. It becomes possible to easily detect the potential difference due to minute damage and to know its position.

(2) A coating film damage detection method for a buried coating steel pipe according to another aspect of the present invention relates to a random signal or a pseudo-random signal between the buried coating steel pipe and a grounding electrode in the ground. br /> With respect to an arbitrary position of the buried coated steel pipe, by applying a low frequency AC voltage, the positions of two electrodes at regular intervals arranged in the pipe axis direction or in the direction orthogonal to the pipe axis are changed to arbitrary positions. To a mesh shape with a constant interval around the center, and at each position of the electrode changed to the mesh shape, between the two points of the pipe axis direction of the embedded coating-covered steel pipe or the direction orthogonal to the pipe axis direction. A potential difference is detected and a correlation process is performed, and a damaged position of the buried coated steel pipe is detected based on a potential difference distribution on the ground surface around an arbitrary position obtained by the correlated potential signal .

In the method for investigating coating film damage of a buried coated steel pipe according to another aspect of the present invention, the positions of two electrodes arranged at regular intervals in the pipe axis direction or in the direction orthogonal to the pipe axis are set to arbitrary positions. Since the distribution of the potential difference on the ground surface is obtained by changing to a mesh shape with a fixed interval in the center, the potential difference between the electrodes at each measurement point can be obtained, and the relative position of each electrode and the relative result in an arbitrary range can be determined from the measurement results. It is possible to obtain a different potential difference distribution, and the damage position can be obtained from the change in the potential difference distribution due to the influence of the potential distribution generated by minute damage from the change in the potential difference distribution.

(3) A coating film damage detection method for a buried coating steel pipe according to another aspect of the present invention relates to a random signal or a pseudo-random signal between the buried coating steel pipe and a grounding electrode in the ground. An alternating voltage of low frequency is applied, a first electrode is arranged at an arbitrary position with respect to an arbitrary position of the buried coating steel pipe, and a second electrode is arranged on a circumference at a constant distance with the electrode as a center. Arranging the electrodes and changing the position of the second electrode on the circumference,
Based on the potential difference distribution on the ground surface centered on an arbitrary position obtained from the potential difference signal subjected to the correlation processing by detecting the potential difference between the two points at each position of the electrode To detect the damaged position of the buried coated steel pipe.

In a coating film damage detection method for a buried coating steel pipe according to another aspect of the present invention, a first electrode is arranged at an arbitrary position, and a second electrode is arranged on a circumference at a constant distance with the electrode as a center. Place the electrode of, and change the position on the circumference of the second electrode,
Since the potential difference distribution on the ground surface is obtained by the first and second electrodes, it becomes possible to know the relative potential difference distribution at any position from the potential difference at each point on the circumference, and in particular, there are multiple damages. In this case, the influence of the potential distribution generated by the adjacent damage can be minimized, and the change in the potential generated by minute damage can be efficiently measured. Detection can be performed.

(4) A coating film damage detection method for a buried coating steel pipe according to another aspect of the present invention relates to a random signal or a pseudo-random signal between the buried coating steel pipe and a grounding electrode in the ground. br /> A low-frequency AC voltage is applied, a plurality of electrodes are arranged at regular intervals in a direction orthogonal to the pipe axis direction of the buried coated steel pipe, and the plurality of electrodes are arranged in the pipe axial direction of the buried coated steel pipe. To detect the potential difference between multiple points and perform correlation processing.
First, the damaged position of the buried coated steel pipe is detected based on the potential difference distribution on the ground surface in the direction orthogonal to the pipe axis direction of the buried coated steel pipe obtained from the correlated potential difference signal .

In the coating film damage inspection method for a buried coating steel pipe according to another aspect of the present invention, two or more electrodes are arranged at regular intervals in a direction orthogonal to the pipe axis direction of the filling coating steel pipe. Therefore, the potential difference measured between each electrode suppresses the influence of the potential distribution generated by adjacent (distanced) damages even when there are multiple damages, and the local potential generated by damages existing at a short distance. Since it is determined by the distribution, the electrodes are scanned in the direction of the pipe axis of the buried coated steel pipe, and the change in the potential difference distribution between the electrodes is determined to efficiently determine the change in the local potential distribution generated by damage, It is possible to detect the damaged position of the buried coating steel pipe.

(5) A method for detecting coating film damage of a buried coating steel pipe according to another aspect of the present invention is the same as the above-mentioned detection methods (1) to (4). An alternating voltage applied to a random signal or a pseudo-random signal is used as an alternating voltage applied between the reference signal extracted from the alternating voltage and the detection signal of the potential difference between the electrodes. Then, the peak value is used as a representative value of the potential difference between the two points to obtain the potential difference distribution. (6) A coating film damage detection method for a buried coating steel pipe according to another aspect of the present invention is the method for detecting a coating film damage of a buried coating steel pipe between a buried coating steel pipe and a grounding electrode in the ground according to the above detection methods. As the AC voltage applied to the, using an AC voltage according to a pseudo-random signal, and perform a correlation process between the reference signal of the same pattern as the AC voltage, and the detection signal of the potential difference between the electrodes, The potential difference distribution is obtained using the peak value as a representative value of the potential difference between the two points.

In a coating film damage detection method for a buried coating steel pipe according to another aspect of the present invention, correlation processing is performed using a random signal or a pseudo-random signal as an AC signal applied to the buried coating pipe. As a result, the noise component is removed and the S / N is improved. Therefore, it is possible to detect the coating film damage position of the buried coating steel pipe with high sensitivity, accuracy and reliability.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1A and 1B are a configuration of an apparatus to which a coating film damage detection method for a buried coating steel pipe according to a first embodiment of the present invention is applied and an operation waveform diagram thereof. In FIG. 1 (A), 1 and 2 are electrodes moving on the surface of the earth, 3 is a buried coating steel pipe, 4 is a damage to the buried coating steel pipe 3, 5 is a detection device, 6 is a cable, 7 is A power feeding device, 8 is a terminal, and 9 is a ground electrode.

In the present embodiment, a low frequency (440 Hz) AC voltage is applied from the power supply device 7 between the terminal 8 and the ground electrode 9 of the buried coated steel pipe 3 to generate an alternating current to the buried coated steel pipe 3. Allow current to flow. The current flowing into the buried coated steel pipe 3 is determined by the amplitude of the AC voltage applied between the terminal 8 and the ground electrode 9 and the resistance between the terminal 8 and the ground electrode 9 (ground resistance of the steel pipe to the ground). It depends on the environment in which the coated steel pipe 3 is buried. When the buried coating steel pipe 3 is damaged 4, a part of the current flowing through the buried coating steel pipe 3 flows out into the ground through the damage 4, so that the current value flowing through the buried coating steel pipe 3 is fed. Although it will decrease according to the distance from the point, in the normal damage detection test, the current value becomes 1 to 2 A so that the current value at a level capable of damage detection can be maintained over a range of several km. The power is supplied from the terminal 8.

The current value flowing out from the damage 4 is also determined by the ground voltage value of the buried coating steel pipe 3 at the damaged position, the damage and the contact resistance with the ground, and is generally proportional to the damaged area. Then, on the ground surface above the damage 4, a potential distribution is generated by the current flowing out from the damage. The potential distribution on the ground surface is determined by the current value flowing out from the damage, the depth of damage, and the electrical characteristics of the ground, and is proportional to the damage area as well as the current. Further, since the alternating current is flowing in the buried coating steel pipe 3, the potential distribution generated on the ground surface also fluctuates at the same frequency as the current frequency.

The electrodes 1 and 2 arranged in the direction orthogonal to the tube axis direction on the ground surface are connected to a detection device 5 via a cable 6, and an AC signal corresponding to the potential difference between the electrodes 1 and 2 is detected by the detection device 5. To enter. Here, as the electrodes 1 and 2, conductive rubber is used to improve the adhesion to the road surface, and the conductive rubber is arranged at intervals of 1 m. Further, to reduce the contact resistance with the road surface, water is sprayed on the road surface. I do. As the electrodes 1 and 2, any one having conductivity can be used,
Depending on the condition of the ground surface, it is also possible to use a metal rod that is directly inserted into the ground as an electrode.In that case, the electrode and the soil surface are brought into direct contact with each other to provide a stable signal. It is also possible to detect.

The detector 5 detects the AC signal detected by the electrodes 1 and 2 and measures the intensity and phase thereof. In the present embodiment, when the positions of the electrodes 1 and 2 are changed in the direction orthogonal to the tube axis in the vicinity of the position of the damage 4 and changes in the intensity and phase of the detected potential difference signal are observed, the electrodes 1 and 2 are observed.
The potential difference distribution changes depending on the position of, and as shown in FIG. 1 (B), the potential difference becomes 0 when the electrodes 1 and 2 are equidistant from the damage (the buried coated steel pipe), and the potential difference at the front and rear positions. The result is that the signal is inverted, confirming that the damage 4 is present. Further, when the positions of the electrodes 1 and 2 in the tube axis direction for scanning are changed, the pattern of change in the potential difference is the same and the intensity changes as a whole. Here, when the maximum potential difference is detected, it is determined that the damage 4 exists on the scanning line, and the exact position of the damage on the tube axis can be known.

It is also confirmed that the same change pattern of the potential difference is measured in the detection test when there is a large damage at the adjacent position. Here, similarly to the conventional detection test, when the electrodes are arranged in the tube axis direction and the positions of the electrodes are changed in the tube axis direction and the orthogonal direction, almost the same potential difference signal is produced regardless of the electrode positions. Detected, no change observed. This is because the potential difference signal detected by the electrode is mainly due to the potential distribution generated by the outflow current from the adjacent large damage. Therefore, it is difficult to detect damage and specify the position, and it is confirmed that the detection by the electrodes arranged in the orthogonal direction is effective.

Embodiment 2. FIG. 2 is a configuration diagram of an apparatus to which the coating film damage detection method for a buried coating steel pipe according to Embodiment 2 of the present invention is applied. In the present embodiment, the electrodes 1 and 2 are arranged in a direction orthogonal to the tube axis direction, and the positions of the electrodes 1 and 2 are changed respectively in the direction orthogonal to the tube axis direction and the tube axis direction to form a matrix. And arrange them in the shape of a circle to obtain the potential difference distribution. Regarding this matrix arrangement, the electrodes 1 and 2 may be arranged in the tube axis direction, and the positions of the electrodes 1 and 2 may be changed in the tube axis direction and the direction orthogonal to the tube axis direction, respectively. Here, the electrode interval is set to 0.5 m, and the position of the electrode is changed at intervals of 0.5 m, which is equal to the electrode interval, in the tube axis direction and the orthogonal direction for measurement. Each measurement signal is 0.5
Since the potential difference is shown at m intervals, it is possible to obtain a relative potential distribution from each measurement result.

From the measurement result at the position without damage,
It is estimated that there is a uniform potential distribution that changes monotonically (increases or decreases) in the tube axis direction and has little change in the orthogonal direction. This is considered to be the potential distribution generated by the current flowing out from multiple damages existing in the buried coated steel pipe, and it is considered that it exists at any position along the coated steel pipe regardless of the damage. To be

From the measurement results around the damaged position,
There is a potential distribution that changes locally compared to the undamaged position. Particularly, in the vicinity of the damaged position, the potential distribution changes in the direction orthogonal to the tube axis, and from this result, the damage is detected and the position is specified. According to this method, it is possible to detect a subtle change in the potential distribution due to minute damage, and it is possible to detect a damaged position with high sensitivity with respect to the conventional detection test.

Embodiment 3. FIG. 3 is a configuration diagram of an apparatus to which a coating film damage detection method for a buried coating steel pipe according to a third embodiment of the present invention is applied. In the present embodiment, the electrode 1 is installed at an arbitrary position on the pipe axis of the buried coating steel pipe 3 on the ground surface, and the electrode 2
Is placed on the circumference of the electrode 1 at a constant distance from the center, and the position of the electrode 2 is changed to measure the potential difference between the electrodes 1 and 2. In this embodiment, the distance between the electrodes 1 and 2 was set to 1 m for measurement. The potential difference signal measured in the position where there is no damage is due to the potential distribution generated by the current flowing out from a plurality of damages existing in the buried coating steel pipe 3, and ideally the pipe It is considered that the axial direction becomes maximum and the orthogonal direction becomes minimum (0). Actually, the potential distribution differs from the ideal potential distribution due to the positional relationship of damage existing on the steel pipe, the electrical condition in the ground at the measurement position, etc., but according to the present embodiment, the potential distribution at any position can be grasped. be able to. Further, in the measurement at the damaged position, the influence of other damages can be suppressed by finely changing the position on the circumference of the electrode 2, and the potential difference signal due to the local potential distribution can be efficiently measured.

Embodiment 4. FIG. 4 is a configuration diagram of an apparatus to which the coating film damage detection method for a buried coating steel pipe according to Embodiment 4 of the present invention is applied. In this embodiment, three electrodes 1, 2,
10 was arranged in the direction orthogonal to the tube axis, and the electrode 2 was arranged on the tube axis. The electrodes 1 and 2 and the electrodes 2 and 10 were arranged so as to be equidistant (1 m). . The potential difference signal detected between the electrodes 1 and 2 and between the electrodes 2 and 10 is input to the detection device 5, and the respective signal strengths and phases are measured.

When the electrodes 1, 2 and 10 are simultaneously scanned in the tube axis direction, the change in the potential in the orthogonal direction is small in both the electrodes 1 and 2 and between the electrodes 2 and 10 at a position where there is no damage, and therefore the measurement is performed. The intensity of the potential difference signal is small and changes little. When scanning the electrodes 1, 2 and 10 and approaching the damaged position,
The measured potential difference signal gradually increases, and the potential difference signal gradually decreases when passing through the damaged position. At this time, the electrodes 1,
The signal strength of the potential difference signal between the two electrodes and the potential difference signal between the electrodes 2 and 10 are almost the same, but the phases thereof are inverted, which is caused by the local potential change due to the outflow current from the damage of the buried coating steel pipe. Is determined.

Here, even if the intensity of the potential difference signal measured between the electrodes 1 and 2 and the electrodes 2 and 10 varies, if the phases are the same, it is not caused by the damage but the electrical potential of the ground. Since it is determined that the damage is due to other factors such as a change in properties, only the damage can be accurately detected.

Although the method of using three electrodes has been described in the present embodiment, by increasing the number of electrodes and the number of combinations between the electrodes, it is possible to detect a minute change in the potential and detect a minute damage. It is also possible to do so.

Embodiment 5. FIG. 5 is a configuration diagram of an apparatus to which a coating film damage detection method for a buried coating steel pipe according to a fifth embodiment of the present invention is applied. In the present embodiment, the AC voltage applied from the power feeding device 7 between the terminal 8 and the ground electrode 9 is M
This is an example using a series signal, and the arrangements and scans of the electrodes 1 and 2 and the like described in the first to fourth embodiments are applied, and here, the processing of the M series signal will be mainly described.

The power supply device 7 is composed of an M-sequence signal generator 21 and a power amplifier 22. The detection device 5 is composed of an M-sequence reference signal generator 23 and a correlation processing unit 24. The M-sequence signal can be generated by a shift register having a feedback loop as shown in FIG. The code length obtained by the seven-stage shift register 25 shown in FIG. 6 is 2 ⁷ −1 = 12.
7

FIG. 7 is a diagram showing an example of the signal waveform of the M-sequence signal and its autocorrelation signal waveform. In FIG. 7, the horizontal axis represents time, the vertical axis represents signal magnitude, and τa is the cycle of the clock given to the shift register.

Since the M-sequence signal is a pseudo-random signal having a periodicity and has a periodicity of a code length 127 here, when the autocorrelation is taken, the peaks shown in FIG. To have. From this, it can be seen that when the cross-correlation with other signals is taken, only the signal whose pattern matches the M-sequence signal has the cross-correlation value having a high peak value. In the present embodiment, this property is utilized to reduce the noise signal.

In FIG. 5, the M-sequence signal from the M-sequence signal generator 21 is amplified by the power amplifier 22 and applied as a voltage between the buried coating steel pipe 3 and the ground electrode 9.
In this state, the positions of the electrodes 1 and 2 are changed as shown in the above-described first to fourth embodiments, and the electrodes 1 and 2 detect the potential of the ground with which they are in contact. The detection device 5 takes in these potential differences. M-series reference signal generator 2 of detection device 5
Although 3 is electrically independent of the M-sequence signal generator 21, it is configured to generate an M-sequence signal having the same pulse pattern.

The correlation processing section 24 of the detection device 5 performs a cross-correlation operation between the reference signal from the M-series reference signal generator 23 and the potential difference signal (detection signal) between the electrodes 1 and 2. That is, when the detection signal is f (t) and the reference signal is g (t), the cross-correlation calculation result is shown as follows.

[0040]

[Equation 1] Here, T is a repetition period.

Since the detection signal f (t) contains an M-system signal component and the reference signal g (t) is an M-sequence signal having the same pattern as this, the cross-correlation calculation result has the same cycle as the reference signal. It has a peak value. FIG. 8 shows an example of the cross-correlation calculation result. In FIG. 8, the horizontal axis represents τ in equation (1) and the vertical axis represents Φfg (τ) in equation (1). By detecting this peak value and using it as the representative value of the detection signal, it is possible to detect the potential difference with high accuracy while suppressing the noise signal. And
By performing processing using this representative value, the damaged position of the coating film can be reliably detected with high accuracy.

Since this processing method suppresses the noise component in the potential difference detection, it is possible to perform detection with high accuracy and high sensitivity. A conventionally known circuit may be used to perform this processing method. For example, a circuit that detects the point where the potential difference crosses zero, a method that sets a threshold value for the potential difference, and a circuit that detects the point that crosses zero after the absolute value of the potential difference exceeds this threshold, and the positive potential difference indicates the maximum value. There is a method using a circuit that detects the midpoint between the point and the point where the negative potential difference shows the maximum value.

In the above embodiment, an example using the M-sequence signal has been described, but a random signal can be used as the AC voltage to be applied. In that case, a random signal is extracted from the applied AC voltage and used as a reference signal.

[0044]

As described above, according to the present invention, the potential difference in the orthogonal direction can be measured by the two electrodes arranged in the orthogonal direction to the pipe axis of the buried coating steel pipe installed on the ground surface. Therefore, the influence of the potential distribution generated by the outflow current from other damage existing at the adjacent position is reduced,
Minute damage can be detected. In addition, it is possible to estimate the potential distribution by measuring the potential difference distribution centered on an arbitrary position, and it is possible to detect minute damage to the buried coated steel pipe from the change in the potential distribution. Furthermore, by performing correlation processing using a random signal or a pseudo-random signal as an AC voltage applied to the embedded coating film pipe, noise components are removed and S / N is improved. It is possible to detect the coating film damage position on the steel pipe with high sensitivity, high accuracy, and certainty.

[Brief description of drawings]

FIG. 1 is a configuration diagram and an operation explanatory diagram of an apparatus to which a coating film damage position detecting method for a buried coating steel pipe according to a first embodiment of the present invention is applied.

FIG. 2 is a configuration diagram of an apparatus to which a coating film damage position detecting method for a buried coating steel pipe according to a second embodiment of the present invention is applied.

FIG. 3 is a configuration diagram of an apparatus to which a coating film damage position detection method for a buried coating steel pipe according to a third embodiment of the present invention is applied.

FIG. 4 is a configuration diagram of an apparatus to which a coating film damage position detecting method for a buried coating steel pipe according to a fourth embodiment of the present invention is applied.

FIG. 5 is a configuration diagram of an apparatus to which a coating film damage position detection method for a buried coating steel pipe according to a fifth embodiment of the present invention is applied.

FIG. 6 is a diagram showing an example of an M-sequence signal generation shift register.

FIG. 7 is a diagram showing an example of an M-sequence signal waveform and its autocorrelation signal waveform.

8 is a diagram showing an example of a correlation waveform between a reference signal and a detection signal according to the embodiment of FIG.

FIG. 9 is an explanatory diagram for explaining the operation of the conventional method.

FIG. 10 is an explanatory diagram for explaining the operation of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuji Chiba 88 Ono-cho, Tsurumi-ku, Yokohama, Kanagawa Nihon Steel Pipe Works Co., Ltd. (56) Reference JP-A-63-205555 (JP, A) JP-A 10-239267 (JP, A) JP-A-63-191049 (JP, A) Actually developed 58-119755 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 27/00 -27/24

Claims (6)

(57) [Claims] 1. Between the buried coated steel pipe and the ground electrode in the ground
A low-frequency AC voltage related to a random signal or a pseudo-random signal is applied, and the potential difference between two points is detected by two electrodes arranged along the direction orthogonal to the pipe axis direction of the buried coated steel pipe. Correlation processing is performed and the position is changed to obtain the potential difference distribution on the ground surface in the direction orthogonal to the pipe axis direction of the buried coated steel pipe, and based on the potential difference distribution on the ground surface. A method for detecting coating film damage in a buried coated steel pipe, which comprises detecting a damaged position of the buried coated steel pipe. 2. Between the buried coated steel pipe and the ground electrode in the ground
Applying a low-frequency AC voltage related to a random signal or a pseudo-random signal, with respect to any position of the buried coated steel pipe,
The positions of two electrodes arranged at regular intervals in the tube axis direction or in the direction orthogonal to the tube axis are changed to a mesh shape at constant intervals around an arbitrary position, and each of the electrodes changed to the mesh shape. At the position, the phase difference is detected by detecting the potential difference between the two points of the buried coated steel pipe in the pipe axis direction or in the direction orthogonal to the pipe axis direction.
Of the buried coated steel pipe, which is characterized in that the damaged position of the buried coated steel pipe is detected based on the potential difference distribution on the ground surface around an arbitrary position obtained by the correlation processing and the correlated potential difference signal . Coating film damage detection method. 3. Between the buried coating steel pipe and the ground electrode in the ground
Applying a low-frequency AC voltage related to a random signal or a pseudo-random signal, with respect to any position of the buried coated steel pipe,
The first electrode is arranged at an arbitrary position, the second electrode is arranged on the circumference of a constant distance with respect to the electrode, and the position on the circumference of the second electrode is changed to And the correlation processing by detecting the potential difference between the two points at each position of the second electrode.
And the coating position of the buried coated steel pipe characterized by detecting the damaged position of the buried coated steel pipe based on the potential difference distribution on the ground surface centered on an arbitrary position obtained by the correlated potential difference signal. Membrane damage detection method. 4. Between the buried coating steel pipe and the ground electrode in the ground
A low-frequency AC voltage related to a random signal or a pseudo-random signal is applied, and a plurality of electrodes are arranged at regular intervals in the direction orthogonal to the pipe axis direction of the embedded coating steel pipe, and the multiple electrodes are embedded coating. Scan the steel pipe in the pipe axis direction, detect the potential differences between multiple points , and perform correlation processing.
The embedded coating is characterized by detecting the damage position of the embedded coating steel pipe based on the potential difference distribution on the ground surface in the direction orthogonal to the pipe axis direction of the embedded coating steel pipe obtained by the calculated potential difference signal. Method for detecting coating film damage on steel pipes. 5. A reference signal extracted from the AC voltage,
The potential difference distribution is obtained by performing a correlation process with a detection signal of the potential difference between the electrodes and using the peak value as a representative value of the potential difference between the two points. Method for detecting coating film damage of buried coating steel pipe. 6. Using an AC voltage according to the pseudo-random signal as the AC voltage, and performs the reference signal of the AC voltage and the same pattern, the correlation process between the detection signal of the potential difference between the electrodes, The potential difference distribution is obtained by using the peak value as a representative value of the potential difference between the two points, and the coating film damage detection method for a buried coated steel pipe according to any one of claims 1 to 4, wherein: