JPH07128272A - Method for monitoring degree of damage of covered steel pipe, and device therefor - Google Patents

Abstract

PURPOSE:To provide a method for regularly monitoring the degree of damage of a covered steel pipe with ease and high precision and a device therefor. CONSTITUTION:Current and potential value measuring devices 11, 12 for measuring current value and potential value are set at a certain interval along the line of a covered steel pipe 1, the current value and potential value of a signal current carried from a standard point to the pipe 1 are measured between two points, respectively, and the damage resistance between the two points is determined from these values, and the degree of damage of the coat and the damage position are judged from the magnitude of the damage resistance by a computer 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and 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 it is damaged by contact with other buried objects, workpieces, stones in the soil, etc., or if the coating is damaged due to natural deterioration, etc. there is a possibility. Therefore, it is important for security to constantly monitor the coating damage location of the coated steel pipe and its extent.

As a technique for evaluating a coating damage portion of a coated steel pipe buried in soil and its degree, a. Coating resistance measurement method, b. Coating film damage area search method, c. In-tube current measurement method, d. The direct method pipe locator can be used.

FIG. 8 shows the method a. In this method, an alternating current signal or a pulsed direct current signal is passed through the grounding resistance R from the through electrode to the coated steel pipe as an energizing current, and an energizing current i and an alternating potential E (in the case of a direct current signal, a potential change amount). ) Is obtained from the equation (1).

[0005]

[Equation 1]

When the length of the coated steel pipe buried in the soil to be measured is short, the ground resistance can be converted into a coating resistance, which is effective for evaluating the deterioration of the coating. However, if the coated steel pipe to be measured has a long electrical continuity, the applied current does not reach the far-off point in the above method. Since it is not the value of the total extension of the steel pipe but the apparent ground resistance of the unidentified portion of the coated steel pipe, it cannot be converted into the coating film resistance, and the deterioration of the coating or the like cannot be accurately evaluated.

The method of b includes a needle electrode method, a Pearson method, a coating film defect detection device and the like. These methods detect the position and size of a coating film defect from the potential difference on the ground surface. However, they cannot be used for constant monitoring because of the nature of exploration on the road.

The method c) is to detect a damaged portion from the distribution of the in-pipe current of the coated steel pipe. However, when the coated steel pipe is provided with a corrosion preventive facility such as a drainage device and a galvanic anode, it is necessary to evaluate while eliminating changes in these resistances. Further, it is not accurate to evaluate the degree of damage only from the current value.

The method of d is to detect the contact position between the covered steel pipe and another buried object by using a pipe locator that searches the position of the buried pipe. However, this method is difficult to detect coating film defects and cannot be used for constant monitoring because it has the property of exploring on the road.

[0010]

In the conventional method, in order to detect the coating damaged portion of the coated steel pipe, there is no choice but to search from the ground surface directly above the coated steel pipe or to evaluate from the in-pipe current. . However, the method of evaluating from the in-tube current requires a skilled technique and has low accuracy. In addition, a field survey was required at the location where the coated steel pipe was buried, and simultaneous monitoring at multiple locations was difficult as well as constant monitoring.

It is an object of the present invention to provide a method and apparatus for monitoring the degree of damage to a coated steel pipe which does not require any skill and is capable of constantly monitoring at a plurality of locations with high accuracy.

[0012]

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

1. One point of the covered steel pipe to be monitored is used as a reference point, a constant signal current is applied to the coated steel pipe from this reference point, and the current value and the potential value measured at two points of the covered steel pipe at appropriate intervals are 2 A method of monitoring the degree of damage of a coated steel pipe by determining the damage resistance between points and judging that there is no damage when this damage resistance value is larger than a specified value and judging that there is damage when it is smaller.

2. An energization power supply device for supplying a signal current to the covered steel pipe to be monitored, a current / potential value measuring device for measuring a current value and a potential value flowing between two points of the coated steel pipe, the current / potential value A transmitting device for transmitting a current value and a potential value measured by a measuring device, a receiving device for receiving a signal of the current value and the potential value transmitted from the transmitting device, and a current value received by the receiving device A computer which calculates the damage resistance in the section from the potential value, judges that there is no damage when the value of this damage resistance is larger than a predetermined value, and judges that there is damage when it is smaller. Damager monitoring device for coated steel pipes.

[0015]

When a fixed signal current is applied to the coated steel pipe from this point, a current / potential value can be measured by a current / potential measuring device installed at two points. The electric current value and the electric potential value are transmitted from the transmitting device to the receiving device on the computer side by cable or wireless, and the computer
The damage resistance between the two points is calculated based on the current value and the electric 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 it is smaller than that, it is determined that there is damage.

In this way, a large number of sections are provided along the pipeline of the coated steel pipe, and the damage resistance is calculated for each section, so that damage within a specific section can be found promptly and appropriate measures can be taken. It becomes possible to take

[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, each point at which the coated steel pipe 1 is appropriately spaced based on the point 0 is defined as a point 1, a point 2, ..., A point x, and a point x + 1 from the side closer to the point 0.

FIG. 2 shows facilities installed at a point 0 and other points (for example, a point x and a point x + 1) in the figure. The through electrode 2 is installed at the point 0, and the current-carrying lead wire 3 attached to the coated steel pipe 1 and the current-carrying electrode 2 lead wire 4 are set up on the ground surface. The potential measuring electrode 5 is installed at each point, and the potential measuring lead wire 6 attached to the coated steel pipe 1 and the lead wire 7 of the potential measuring electrode 5 are set up on the ground surface. In addition, at each point of the coated steel pipe 1, the in-tube current measurement lead wires 8 and 9 attached to two points of the coated steel pipe 1 at certain intervals (distances that do not reach the neighboring points) are set up. deep.

The energization lead wire 3 and the lead wire 4 of the energization electrode 2 are used for the energization power source 10, and the potential measurement lead wire 6 and the lead wire 7 of the potential measurement electrode 5 are used for the potential measurement device 1.
First, 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-pipe current measuring device 12 are connected to the transmitting device 13, and the potential data and the in-pipe current data are transmitted to the computer 15 via the transmitting device 13 and the receiving device 14. In addition,
Here, in-tube current measurement uses the voltage drop method,
Alternatively, a method of measuring a current flowing through a lead wire connecting both sides of the insulating joint or a method using a clip-on ammeter can be used.

Monitoring of the coating damage is performed by the following procedure. Hereinafter, a case in which damage occurs between the point x and the point x + 1 will be described using an example in which an AC signal is used as the energizing current.

The ground resistance between the point x and the point x + 1 is measured by measuring the AC potentials E (x) and E (x + 1) of the coated steel pipe 1 at the point x and the point x + 1 which are both ends of the range.
And the in-tube alternating current i flowing through the coated steel tube 1
While measuring (x) and i (x + 1), an AC signal or the like is applied to the coated steel pipe 1 at the point 0 from the through electrode 2 using the energizing power supply 10. Point x
And the point x + 1 between the ground resistance R (x ~
x + 1) is calculated as shown in Expression (2).

[0022]

[Equation 2]

Here, between the point x and the point + 1, when contact of another grounding resistance Rd (x to x + 1) with another buried object or a machine tool or a corresponding coating defect is generated, Rd ( x to x + 1) and R (x to x + 1) and the ground resistance RO (x to x in the steady state between the point x and the point +1)
x + 1) has the relationship of Expression (3). Below, Rd (x
~ X + 1) is the damage resistance between point x and point x + 1.

[0024]

[Equation 3]

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

[0026]

[Equation 4]

Accordingly, the AC potential and the AC current in the tube at each point are continuously measured and transmitted to the host computer 15 by the transmitter / receivers 13 and 14, and the data are synchronized between the points by the above equation while synchronizing the data. Seeking Rd,
By constantly monitoring this, it is possible to detect, in real time, the contact with another embedded object or the work piece, or the generation of a coating covering defect corresponding to this, and the degree thereof.

Experimental Example A test conducted using a test pipe buried in soil will be described below. 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 50 A.

An AC signal having a frequency of 220 Hz is applied to a lead wire attached to a point 0 (one end of the test pipe) and a through electrode (using a Mg anode) installed in the vicinity of the lead wire, and a potential measuring electrode installed in the same vicinity as the pipe. Amplitude of (Zn electrode) is 5 Vrm
Electricity was applied using a through electrode so that s was obtained.

The AC potential at the point 1 which is 2 m from the point 0 is the AC voltage between the lead wire attached to the test pipe at the point 1 and the potential measuring electrode (Zn electrode) installed in the vicinity thereof. It measured using the measuring device. Also, point 1
The in-tube AC current was measured by measuring the AC voltage between the lead wires attached to the test pipe at a point 1 m away from the point 1 on the point 0 side and a point 1 m away from the point 1 on the point 2 side. It was measured using a device and converted into an in-tube alternating current i to obtain it.

The AC potential at the point 2 which is 6 m from the point 0 is the AC voltage between the lead wire attached to the test pipe at the point 2 and the potential measuring electrode (Zn electrode) installed in the vicinity thereof. It measured using the measuring device. Also, point 2
The in-tube AC current in the tube is the AC voltage between the lead wires attached to the test pipe at the point 1 m away from the point 2 on the side of the point 1 and the point 1 m away from the point 1 on the side opposite to the point 1. The current was measured using a current measuring device and converted into an in-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 of 242 Ω at 220 Hz installed in the vicinity of the lead wire are electrically connected to each other. Let

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 calculated values thereof. Dotted lines in FIGS. 6 and 7 show values obtained from the actual measurement values of the ground resistance of the simulated damage electrode. In addition, the measurement time is 50 seconds, of which 10 to 10 seconds of about 20 to 30 seconds.
Simulated damage was given in a second.

The following changes are observed when simulated damage is given.

The in-tube AC current i at the point 1 increases, but the in-tube AC current i at the point 2 does not change.

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

From this result, the ground resistance R between the point 1 and the point 2 is calculated to be 10,000 Ω or more when there is no damage, whereas it is approximately 300 Ω when damaged, which is almost the same as the measured value. I understand. Further, when the damage resistance Rd is calculated, it is 10000Ω or more when there is no damage, while it is about 300Ω when damage is given, which is almost equal to the measured value. From the above, it is clear that the present invention can accurately detect and detect damage.

[0039]

As described above, according to the present invention, a current / potential measuring device is installed along a pipeline of a coated steel pipe at regular intervals, and a section is obtained from the current value and the potential value of the current supplied from the reference point. Since the damage resistance is obtained for each of them and the damage degree and the damage section (position) are specified by the damage resistance, the following effects can be obtained.

A. Accurate determination of damage degree.

B. Since it can be applied even for long distances, it is extremely effective for constant monitoring of the degree of coating damage on main 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 work.

[Brief description of 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 illustration of ground resistance

FIG. 7 is an explanatory diagram of damage resistance.

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

[Explanation of symbols]

 1 coated steel pipe 2 through electrode 3 lead wire for energization 4 lead wire 5 electrode for electric potential measurement 6 lead wire for electric potential measurement 7 lead wire 8.9 lead wire for measuring electric current in pipe 10 power supply for electric current 11 electric potential measuring device 12 electric current measuring device in pipe 13 transmitter 14 receiver 15 computer

Claims (3)

[Claims] 1. A current value measured at two points of the coated steel pipe at appropriate intervals by setting one point of the coated steel pipe to be monitored as a reference point, applying a constant signal current to the coated steel pipe from this reference point. Also, the damage resistance between two locations is calculated from the potential value, and if this damage resistance value is larger than a specified value, it is judged as no damage, and if it is smaller, it is judged as damaged. How to monitor. 2. An energization power supply device for supplying a signal current to a coated steel pipe to be monitored, a current / potential value measuring device for measuring a current value and a potential value flowing between two points of the coated steel pipe, A transmitting device for transmitting a current value and a potential value measured by the current / potential value measuring device, a receiving device for receiving a signal of the current value and the potential value transmitted from the transmitting device, the receiving device A computer that calculates the damage resistance within the section from the received current value and potential value, and judges that there is no damage when this damage resistance value is larger than a specified value, and judges that there is damage when it is smaller. A coated steel pipe damage degree monitoring device consisting of. 3. The damage level monitoring method and apparatus for a coated steel pipe according to claim 1, wherein an alternating current is used as the signal current.