JPS6254090A - Device for electrically preventing corrosion of embedded metallic body - Google Patents

Abstract

PURPOSE:To prevent the corrosion of the embedded metallic body at low cost by using a secondary cell-contg. transfer circuit and transferring the electrical protection by the external electric power source system using a solar cell as the power source to the electrical protection by a galvanic anode system in accordance with the quantity of solar radiation and always passing a necessary anticorrosive current through the embedded metallic body. CONSTITUTION:The electromotive force generated in a solar cell is passed from the positive terminal through the anode 3 for the external electric power source, the earth, an embedded metallic body 5 and a negative terminal and a closed circuit is formed Besides, the electromotive force generated between a galvanic anode 4 and the embedded metallic body 5 is passed from the galvanic anode 4 through the earth and the embedded metallic body 5 and a closed circuit is formed. When the solar radiation is avilable in the daytime, a transistor 8 is in the nonconducting state, a relay 7 is not energized, the solar cell 1 is connected to the embedded metallic body 5, and the electromotive force generated in the solar cell 1 is conducted as the anticorrosive current and simultaneously charged in a secondary cell 9 in a transfer circuit 2. When the output voltage of the solar cell 1 is decreased at night or the like, the transistor 8 is conducted, the relay 7 is energized, the terminals are transferred so that the galvanic anode 4 is connected to the embedded metallic body 5 and the anticorrosive current is conducted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to petroleum, petrochemical, chemical products,
This relates to cathodic protection equipment for embedded metal objects such as gas and water supplies.

[Conventional technology]

When underground metal objects such as water pipes, gas pipes, and oil pipes are located near electric railway rails, leakage current flows from the rails, flows out again, and is damaged by electrolytic corrosion when it returns to the rails.

In addition, a local or large electromotive force is generated due to the potential difference on the surface of the buried metal body due to the difference in specific resistivity of the soil at the buried location, and current flows from the buried metal body toward the ground, causing electrolytic corrosion. The receiver is at risk of corrosion. As a method for protecting buried metal bodies from such dangers, cathodic protection methods such as a galvanic anode method and an external power supply method are generally known.

In the galvanic anode method, a galvanic anode using a material with a strong ionization tendency, such as magnesium, is buried near the buried metal body, or a low-grounding body with a current comparable to this galvanic anode is buried. At the same time, these and the buried metal body are electrically connected, and the electromotive force generated between them causes an anti-corrosion current to flow in a closed circuit from the current anode to the earth and the buried metal body, thereby preventing corrosion of the buried metal body. It is something to do. This method is
Although it has the advantages of being easy to construct, requiring no period control, and being economical as it can be applied to places where power supply is not available or small-scale projects, it has the advantage of being economical. Because it wears out, it needs to be replaced at regular intervals.Since the effective voltage is constant, the current generated in high-resistance soil is small and may not be suitable for practical use.Magnesium is an expensive metal, so it is generated. It has drawbacks such as high current cost and a significant reduction in the generated current due to conductor resistance.

On the other hand, in the external power supply method, a suitable external DC power source such as a battery is connected between the buried metal body buried underground and the electrode to supply a sufficient value of anti-corrosion current to the buried metal body. This method has the advantages of being able to freely adjust the voltage or current, responding to changes in corrosion conditions, and if the anode is sufficiently insoluble, it can be applied semi-permanently, reducing costs. The operation is more complicated than the galvanic anode method, and a certain amount of monitoring and management is required after installation.
It has drawbacks such as high initial cost and constant power supply.

Recently, an external power supply system using solar cells has also been proposed. One is to use a solar cell in combination with a battery, and switch the power supply so that anti-corrosion current flows from the pond during the day and from the battery at night, and the other uses solar cells alone to prevent corrosion. It is designed to allow current to flow through it.

[Problem that the invention seeks to solve]

By the way, in pipelines that are regulated as transfer stations under the Fire Service Act, the average value of potential to the ground is stipulated to be 1850 mV or less based on copper sulfate electrodes.

The above-mentioned external power supply system that uses solar cells in combination with a battery can pass the above criteria and reduce the burden on the battery by the amount of solar cells.
Due to the drawbacks of the external power supply method mentioned above, the scale of the entire system increases.

On the other hand, an external power source system using only solar cells has a problem in that the above standards cannot be completely maintained.

FIG. 4 is a diagram showing changes in the ground potential of a buried metal body when only a solar cell is used as an external power source. According to the inventors' previous experiments, when an anti-corrosion current is applied only by the solar cell, the potential to the ground during the period when no solar cell secondary electromotive force is obtained, that is, during the period when the anti-corrosion current is interrupted, is the same as that of the buried metal body. It has been found that there are significant differences in terms of corrosion protection depending on the difference. This is due to the difference in the coating of the buried metal body.

For example, in the case of deteriorated coatings or bare tubes, polarization occurs around them while the anticorrosion current is flowing, and even after the anticorrosion current is interrupted, it takes some time (depolarization time) for depolarization. For this reason, a considerable ground potential can be maintained during nighttime only, as shown by the solid line in FIG. Therefore, if the power supply capacity, daytime corrosion protection current, etc. are set so that the lowest ground potential during this period can be maintained at the value required for corrosion protection (-fish head vA), corrosion protection using solar cells alone becomes possible.

However, in buried metal objects with a high level of coating such as polyethylene lining, little polarization occurs around them while the anticorrosion current is flowing, so the quaternary
As shown by the dotted line in the figure, the potential returns to the natural potential immediately after the anticorrosion current is interrupted. Although the natural potential varies depending on the soil, it is approximately -500 mV to -600 mV, so it is impossible to maintain the potential required for corrosion protection according to the above standards.

The present invention is based on the above considerations, and uses solar cells to provide corrosion protection with a simple configuration and low cost even for buried metal bodies with high-level coatings such as polyethylene lining. The object of the present invention is to provide a cathodic protection device for a buried metal body that can maintain a suitable ground potential.

[Means for solving problems]

For this purpose, the cathodic protection device for a buried metal body of the present invention connects the cathode (negative) electrode of the solar cell and the galvanic anode buried underground to the buried metal body through the switching means, and Connect the positive (positive) pole to an electrode buried underground, detect the voltage generated by the solar cell, and switch from the negative (negative) pole of the solar cell to the galvanic anode on the condition that the generated voltage is lower than a predetermined value. The device is characterized in that the connection of the switching means is switched.

[Effect]

In the electrolytic protection device for buried metal bodies of the present invention, when a predetermined electromotive force can be obtained by the solar cell, a corrosion protection current is passed by an external power supply method using the solar cell, and when the predetermined electromotive force cannot be obtained by the solar cell. In some cases, an anti-corrosion current is passed using the galvanic anode method, so there is no need for an auxiliary power source such as a battery as a backup for the solar cell, and the consumption of the galvanic anode is also reduced by the amount of anti-corrosion current flowing through the solar cell. .

〔Example〕

Examples will be described below with reference to the drawings.

Fig. 1 is a diagram showing one embodiment of the electrolytic protection device for buried metal bodies according to the present invention, and Fig. 2 is a specific configuration example of a switching circuit applied to the electrolytic protection device for buried metal bodies according to the present invention. FIG. 3 is a time chart for explaining the operation of the switching circuit shown in FIG. 2.

In Fig. 1, 1 is a solar cell, 2 is a switching circuit, and 3 is a solar cell.
is an anode for external power supply, 4 is a galvanic anode, 5 is a buried metal body, 6
is a comparator, 7 is a relay, 8 is a transistor, 9 is a secondary battery, D1 to D3 are diodes, R1 to R7 are resistors, and VR is an adjustment resistor.

The buried metal body 5 is a metal body such as a gas pipe or an oil transport pipe buried in the ground. The external power supply anode 3 is connected to the buried metal body 5
The current anode 4 is an anode for an external power supply system made of iron, graphite, platinum, etc. buried near the buried metal body 5, and the current anode 4 is an anode for an external power source such as iron, graphite, platinum, etc. buried near the buried metal body 5. It is an anode made of a large substance.

The specific configuration example of the switching circuit 2 will be described later, but
As shown in FIG. 2, a rechargeable secondary battery 9 such as a Nisocad battery is built in, and a comparator 6 compares the output voltage of the secondary battery 9 with the output voltage of the solar cell 1 to control a relay 7. The relay 7 is used to switch between connecting the solar cell 1 to the buried metal body 5 or connecting the galvanic anode 4 to the buried metal body 5.

Therefore, when the switching circuit 2 connects the solar cell 1 to the buried metal body 5 as shown in the figure, the circuit using the external power supply method described above, that is, the electromotive force generated by the solar cell 1 is used to The structure is such that a forward anticorrosive current flows through a closed circuit from the terminal to the external power supply anode 3, the ground, the buried metal body 5, and the negative terminal. On the other hand, when the switching circuit 2 connects the current anode 4 to the buried metal body 5, it is configured to cause a corrosion protection current in the forward direction to flow due to the electromotive force generated between the current current anode 4 and the buried metal body 5. are doing.

Next, a specific example of the configuration of the switching circuit 2 will be explained. The switching circuit 2 connects the solar cell 1 and the secondary battery 9 via the diode DI as shown in FIG.
The example voltage is passed through a voltage divider circuit consisting of resistors R1 and R2,
Further, the voltage on the secondary battery 9 side is inputted to the comparator 6 through a voltage dividing circuit made up of resistors R3 and R4. The output of the comparator 6 compares the two input voltages, and becomes a high level when the output voltage of the solar cell 1 is low, and becomes a low level when the output voltage of the solar cell 1 becomes higher than the output voltage of the secondary battery. Therefore, as shown in FIG. 3, when there is solar radiation during the day, the transistor 8 is in a non-conducting state and the relay 7 is not energized. is connected to the buried metal body 5, and the electromotive force generated by the solar cell 1 is used to flow an anticorrosive current and charge the secondary battery 9. Then, when the output voltage of the solar cell 1 becomes low due to nighttime or cloudy weather, the transistor 8 ventilates and energizes the relay 7, thereby switching the contact so as to connect the current anode 4 to the buried metal body 5. Note that this chattering in the on/off operation can be prevented by providing an offset using the adjustment resistor VR, but since the output voltage of the solar cell rises sharply with a small amount of solar radiation, the on/off level of relay 7 It is also possible to prevent chattering by setting low. Also, the switching voltage value is determined by the resistance R
It can be adjusted by changing the voltage dividing ratio of the voltage dividing circuit made up of R1 and R2 and the voltage dividing circuit made up of resistors R3 and R4. The present invention can be modified in various other ways and is not limited to the above embodiments.

In this way, the secondary battery 9 is charged when the amount of solar radiation is high, and the secondary battery 9 is charged when the amount of solar radiation is low, such as in the morning, evening, and on cloudy days.
The switching circuit 2 is operated using the current anode to connect the current anode 4 to the buried metal body 5, and the anticorrosive current is passed through the current anode, so the secondary battery 9 can be used semi-permanently. Therefore, similar to the galvanic anode method, a nearly maintenance-free device can be provided.

Furthermore, the amount of expensive galvanic anodes such as magnesium Mg required, for example, was 100 kg in the 2020 design, but can be reduced to about 50 kg according to the present invention.

[Effects of the Invention] As is clear from the above description, according to the present invention, a switching circuit with a built-in secondary battery is provided to provide cathodic protection and flow control using an external power source system using a solar cell as a power source according to the amount of solar radiation. Since the system switches between cathodic protection using the electrode anode method and constantly supplies the necessary corrosion protection current, it is possible to maintain a sufficient corrosion protection potential even in buried metal objects with high-level coatings such as polyethylene lining. can. Moreover, since the time for cathodic protection using the galvanic anode method is shortened, it is possible to reduce the cost of the galvanic anode, and
Since the external power source relies only on solar cells, overall costs can be reduced and maintenance can be facilitated.

[Brief explanation of drawings]

Fig. 1 is a diagram showing one embodiment of the electrolytic protection device for buried metal bodies according to the present invention, and Fig. 2 is a specific configuration example of a switching circuit applied to the electrolytic protection device for buried metal bodies according to the present invention. Fig. 3 is a time chart to explain the operation of the switching circuit shown in Fig. 2, and Fig. 4 shows the change in ground potential of the buried metal body when only the solar cell is used as an external power source. It is a diagram. DESCRIPTION OF SYMBOLS 1... Solar cell, 2... Switching circuit, 3... Anode for external power supply, 4... Current anode, 5... Buried metal body, 6... Comparator, 7... Relay , 8...Transistor, 9...Secondary battery, D1-D3...Diode, R1-R7...Resistor, VR...Adjustment resistor.

Claims (3)

[Claims] (1) An electrolytic protection device for a buried metal body that prevents corrosion by passing an anticorrosion current to a buried metal body such as a metal pipe buried underground, and which connects the buried metal body to the shade of a solar cell through a switching means.
In addition to connecting the negative) electrode and the galvanic anode buried underground,
Connect the anode (positive) pole of the solar cell to an electrode buried underground,
Embedded metal characterized in that the connection of the switching means is switched from the cathode (negative) electrode of the solar cell to the current anode on the condition that the generated voltage of the solar cell is detected and the generated voltage becomes lower than a predetermined value. Body cathodic protection device. (2) The cathodic protection device for a buried metal body according to claim 1, characterized in that the switching means is provided with an auxiliary power source. (3) The switching means connects the cathode (negative) electrode of the solar cell to the buried metal body on the condition that the voltage generated by the solar cell exceeds a first predetermined value, and the voltage drops below a second predetermined value. 2. The cathodic protection device for a buried metal body according to claim 1, wherein the galvanic anode is connected to the buried metal body under the condition that: