JP3169754B2 - Method and apparatus for monitoring damage degree of 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 method and an apparatus for quantitatively evaluating the degree of coating damage of a coated steel pipe buried in soil.

[0002]

2. Description of the Related Art The steel surface of a coated steel pipe buried in soil is
The coating is insulated from the soil and prevents the progress of corrosion. However, the steel surface of the coated steel pipe will come into contact with the soil if the coating is damaged due to contact with other buried objects, workpieces, stones in the soil, or natural deterioration, etc., and will be corroded. there is a possibility. Therefore, it is important for security to constantly monitor the location and degree of the coating damage of the coated steel pipe.

Techniques for evaluating the location and extent of coating damage on a coated steel pipe buried in soil include the following: Coating resistance measurement, b. Paint damage detection method, c. Tube current measurement method, d. There is a method using a direct method pipe locator.

FIG. 8 shows the method (a). In this method, an alternating current signal or a pulsed direct current signal is applied to the coated steel pipe as a conducting current from the through electrode to the coated steel pipe, and the conducting current i and the alternating potential E (in the case of a direct current signal, the potential change amount). ) To (1).

[0005]

(Equation 1)

When the length of the coated steel pipe buried in the soil to be measured is short, the grounding resistance can be converted into the coating resistance, which is effective for evaluating the deterioration of the coating. However, in the case where the length of electrical conduction in the coated steel pipe to be measured is long, since the applied current does not reach a distant portion in the above method, the measured ground resistance is Since it is not the value of the total length of the steel pipe but the apparent ground resistance of an unspecified portion of the coated steel pipe, it cannot be converted to the coating film resistance, and accurate evaluation of deterioration of the coating cannot be performed.

The method (b) includes a needle electrode method, a Pearson method, and a coating film defect detecting device. These methods detect the position and size of a coating defect from the potential difference on the ground surface. However, since they are of the nature of exploring on roads, they cannot be used for constant monitoring.

The method (c) detects a damaged portion from the distribution of current in the coated steel pipe. However, when the coated steel pipe is provided with anti-corrosion equipment such as a drainage device and a galvanic anode, it is necessary to evaluate the resistance while eliminating the change in resistance. Evaluating the degree of damage only from the current value has low accuracy.

The method d detects a contact position between the coated steel pipe and another buried object using a pipe locator for searching a position of the buried pipe. However, this method cannot be used for constant monitoring because it is difficult to detect a coating film defect and also has a nature of exploring on a road.

[0010]

In the conventional method, the only way to detect the coating damage portion of the coated steel pipe is to search from the ground surface immediately above the coated steel pipe or to evaluate from the current in the pipe. . However, the method of evaluating from the in-tube current requires a skilled technique and has low accuracy. In addition, it was necessary to conduct an on-site survey at the place where the coated steel pipe was buried, and it was difficult to monitor not only constantly but also simultaneously at multiple places.

An object of the present invention is to provide a method and an apparatus for monitoring the degree of damage of a coated steel pipe which can be constantly monitored at a plurality of locations with high accuracy without requiring a skilled technique.

[0012]

Means for monitoring the damage degree of a coated steel pipe according to the present invention and the structure of the apparatus are as follows.

1. One point of the coated steel pipe to be monitored is defined as a reference point. From this reference point, a constant signal current is applied to the coated steel pipe, and the current value and the potential value measured at two places at appropriate intervals of the coated steel pipe are used as two points. A method of monitoring the damage degree of a coated steel pipe in which damage resistance between portions is determined, and when the damage resistance value is larger than a predetermined value, it is determined that there is no damage. 2. 2. The device according to the above 1, wherein an alternating current is used as a signal
A method for monitoring the degree of damage to steel-clad pipes.

[0014] 3. Signal current to the monitored coated steel pipe
An energizing power supply for energizing, and a plurality of
Installed in a place and measures the current value and potential value at each place
Current / potential value measuring apparatus for measuring current / potential value
Transmitter for transmitting the current and potential values measured by the
Signal of current value and potential value transmitted from the transmitting device
Receiving device for receiving the power,
The current / potential value measuring device is installed from the current value and the potential value.
Calculate the damage resistance in the section between
If the value is larger than a certain value, it is determined that there is no damage
If it is small, it is determined that the computer is damaged,
Damage monitoring system for coated steel pipes. 4. 4. The damage monitoring device for a coated steel pipe according to the above item 3, wherein an alternating current is used as the signal current .

[0015]

When a reference point is determined and a constant signal current is applied to the coated steel pipe from the reference point, the current and potential values can be measured by the current / potential measuring devices installed at the two points. The current value and the potential value are transmitted from the transmitting device to the receiving device on the computer side by cable or wirelessly.
Damage resistance between two points is determined based on the current value and the potential value transmitted from the point. If the damage resistance is larger than a certain value, it is determined that there is no damage, and if the damage resistance is smaller, it is determined that there is damage.

In this way, a number of sections are provided along the pipeline of the coated steel pipe, and damage resistance is determined for each section. Can be taken.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a coated steel pipe buried in soil. Here, points at appropriate intervals of the coated steel pipe 1 based on the point 0 are referred to as a point 1, a point 2,..., A point x, and a point x + 1 from a point closer to the point 0.

FIG. 2 shows equipment to be installed at point 0 and other points (for example, point x and point x + 1) in the figure. At the point 0, the through electrode 2 is installed, and the lead wire 3 for current supply and the lead wire 4 of the electrode 2 for current supply attached to the coated steel pipe 1 are raised on the ground surface. At each point, a potential measuring electrode 5 is installed, and a potential measuring lead wire 6 attached to the coated steel pipe 1 and a lead wire 7 of the potential measuring electrode 5 are raised on the ground surface. In addition, at each point of the coated steel pipe 1, lead wires 8 and 9 for in-pipe current measurement attached to two places of the coated steel pipe 1 at a certain interval (a distance that does not reach the adjacent point) are set up. deep.

The power supply lead wire 3 and the lead wire 4 of the power supply electrode 2 are connected to a power supply 10 for power supply, and the lead wire 6 for potential measurement and the lead wire 7 of the electrode 5 for potential control are connected to the potential measurement device 1.
1, the in-tube current measuring leads 8 and 9 are connected to the in-tube current measuring device 12, respectively. The potential measuring device 11 and the in-tube current measuring device 12 are connected to the transmitting device 13, and the potential data and the in-tube current data are transmitted to the computer 15 via the transmitting device 13 and the receiving device 14. In addition,
Here, the in-tube current measurement uses the voltage drop method,
In addition, a method of measuring a current flowing through a lead wire connecting both sides of the insulating joint and a method using a clip-on ammeter are also possible.

The monitoring of coating damage is performed in the following procedure. Hereinafter, a case where damage has occurred between the point x and the point x + 1 will be described using an example in which an AC signal is used as a conduction current.

The measurement of the ground resistance between the point x and the point x + 1 is performed by measuring the AC potentials E (x) and E (x + 1) of the coated steel pipe 1 at the points x and x + 1 at both ends of the range.
And the alternating current i in the pipe flowing through the coated steel pipe 1
The measurement is performed by applying an AC signal or the like from the through electrode 2 to the coated steel pipe 1 at the point 0 using the power supply 10 for electricity while measuring (x) and i (x + 1). Point x
And the ground resistance R (x to x) of the coated steel pipe 1 between the point x + 1 and
x + 1) is obtained as in equation (2).

[0022]

(Equation 2)

Here, between the point x and the point +1, when a contact between the ground resistance Rd (x to x + 1) and a buried object or a machine tool, or the generation of a coating defect corresponding thereto occurs, Rd ( x to x + 1), R (x to x + 1), and the ground resistance RO (x to x) in the steady state between the points x and +1.
x + 1) has the relationship of equation (3). Hereinafter, Rd (x
To x + 1) is the damage resistance between the point x and the point x + 1.

[0024]

(Equation 3)

When equation (3) is solved for Rd (x to x + 1), equation (4) is obtained.

[0026]

(Equation 4)

Therefore, the continuous measurement of the AC potential and the AC current in each tube at each point is performed, and the measured data is transmitted to the host computer 15 by the transmission / reception devices 13 and 14, and the data is synchronized with each other by the above equation while synchronizing the data. Finding Rd,
By constantly monitoring this, it is possible to detect, in real time, the contact of another buried object or a workpiece or the generation of a coating and covering defect corresponding thereto, and the degree of the detection.

Experimental Example Hereinafter, a test performed using a test pipe buried in soil will be described. FIG. 3 shows an outline of the test equipment. The test pipe is a polyethylene-coated steel pipe (JIS G 3469) having a length of 8 m and a nominal diameter of 50A.

An AC signal having a frequency of 220 Hz is applied to a lead wire attached at a point 0 (one end of a test pipe) and a through electrode (using a Mg anode) installed near the lead wire, and a potential measurement electrode installed near the pipe. (Zn electrode) amplitude is 5Vrm
The current was passed using the through-electrode so that s was reached.

The AC potential at the point 1, which is 2 m from the point 0, is obtained by calculating the AC voltage between the lead wire attached to the test pipe at the point 1 and the potential measurement electrode (Zn electrode) installed near the lead. It measured using the measuring device. In addition, point 1
The AC current in the pipe was measured by measuring the AC voltage between the lead wires attached to the test pipe at a point 1 m away from point 1 to point 0 and at a point 1 m away from point 1 to point 2. It was measured using a device and converted to the tube alternating current i.

The AC potential at the point 2 which is 6 m from the point 0 is obtained by calculating the AC voltage between the lead wire attached to the test pipe at the point 2 and the potential measuring electrode (Zn electrode) installed near the lead. It measured using the measuring device. In addition, point 2
The AC voltage in the pipe at the point 1 m away from point 2 to point 1 and the point 1 m away from point 1 on the opposite side of point 1 is the AC voltage between the lead wires attached to the test pipes. It was measured using a current measuring device, and was obtained by converting it into a tube alternating current.

As the simulated damage, the lead wire attached to the test pipe at a position 4 m from the point 0 and the simulated damage electrode having a ground resistance at 220 Hz of 242 Ω installed in the vicinity of the lead wire were brought into an electrically conductive state. I let it.

Each measuring device is connected to a computer,
The transmitted data was processed by a computer.

The measurement and calculation results are shown in FIGS. FIG. 4 shows the AC current i in the tube, and FIG. 5 shows the AC potential E. FIG. 6 shows the ground resistance R between the points 1 and 2, and FIG. 7 shows the damage resistance Rd in the same range, and the respective calculated values. The dotted lines in FIGS. 6 and 7 show values obtained from the measured values of the ground resistance of the simulated damage electrode. The measurement time was 50 seconds, of which 10 to 20 to 30 seconds.
Simulated damage in seconds.

When the simulated damage is caused, the following changes are observed.

In-pipe AC current i at point 1 increases, but in-pipe AC current i at point 2 does not change.

The AC potential E at point 1 and point 2 is
Both decrease.

From these results, the ground resistance R between the point 1 and the point 2 is found to be 10000Ω or more when there is no damage, whereas it becomes about 300Ω when damaged, which is almost equal to the measured value. You can see that. Further, when the damage resistance Rd is obtained, the value is 10,000Ω or more when there is no damage, and it is about 300Ω when the damage is given, which is almost equal to the actually measured value. From the above, it is apparent that the present invention can accurately detect damage and its degree.

[0039]

As described above, according to the present invention, the current / potential measuring device is installed at every fixed section along the pipe of the coated steel pipe, and the current / potential value of the current supplied from the reference point is set based on the current / potential value. Since the damage resistance is determined for each case and the damage degree and the damage section (position) are specified by this, the following effects are obtained.

A. The degree of damage can be accurately determined.

B. Since it can be applied to long distances, it is extremely effective for constantly monitoring the degree of coating damage on trunk lines such as gas and oil.

C. Since the degree of damage can be immediately determined using a computer, no experience or skill is required for the determination operation.

[Brief description of the drawings]

FIG. 1 is a conceptual explanatory diagram of a monitoring method according to the present invention.

FIG. 2 is an explanatory diagram of a monitoring device and a monitoring method according to the present invention.

FIG. 3 is an explanatory diagram of an experimental example.

FIG. 4 is an explanatory diagram of an alternating current in a tube.

FIG. 5 is an explanatory diagram of an AC potential.

FIG. 6 is an explanatory diagram of a ground resistance.

FIG. 7 is an explanatory diagram of damage resistance.

FIG. 8 is an explanatory view of a conventional method for measuring coating film resistance.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 coated steel pipe 2 through electrode 3 conducting lead 4 lead 5 potential measuring electrode 6 potential measuring lead 7 lead 8.9 lead current measuring lead 10 power supply 11 potential measuring device 12 tube current measuring device 13 transmitting device 14 receiving device 15 computer

Claims (4)

(57) [Claims] A reference point is defined as one point of a coated steel pipe to be monitored, a constant signal current is applied to the coated steel pipe from this reference point, and a current value measured at two places at appropriate intervals of the coated steel pipe. The damage resistance between two locations is determined from the potential value and the damage resistance value is determined to be no damage if the damage resistance value is larger than a predetermined value, and the damage degree of the coated steel pipe is determined to be damaged if the damage resistance value is smaller than a predetermined value. How to monitor. 2. An alternating current is used as a signal current.
2. The method for monitoring the degree of damage of a coated steel pipe according to item 1. 3. A signal current is passed to a coated steel pipe to be monitored.
Power supply device for supplying electricity , installed at a plurality of locations of the coated steel pipe, the current value at each location
And current and potential measuring apparatus for measuring a potential value, the current value measured by the current-potential measuring apparatus and the potential value
For transmitting current and potential signals transmitted from the transmitting device.
A receiving device for transmitting the current and the potential from the current value and the potential value received by the receiving device.
Damage resistance in the section between the locations where the potentiometers are installed
Is calculated, and the value of the damage resistance is larger than a predetermined value.
If not, it is judged that there is no damage.
And a computer for determining the degree of damage of the coated steel pipe. 4. An alternating current is used as a signal current.
4. The damage monitoring device for a coated steel pipe according to 3 .