JPH0253515B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to petroleum, petrochemical,
This relates to cathodic protection equipment for buried metal bodies such as chemical products, 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 based on the difference in resistivity of the soil at the buried location, and current flows from the buried metal body toward the ground, causing electrolytic corrosion. exposed to the risk of corrosion. As a way to protect buried metal objects from such dangers,
Generally, cathodic protection methods such as galvanic anode method and external power supply method are 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
It is easy to construct and requires no management for a certain period of time.
Although it has the advantage of being economical and can be applied to places where power cannot be obtained or small-scale items, etc., on the other hand, the galvanic anode is consumed as the current flows out.
It needs to be replaced at regular intervals.Since the effective voltage is constant, the generated current may be low in high-resistance soil and may not be suitable for practical use.Magnesium is an expensive metal, so the cost of generated current is high. The generated current is significantly reduced due to conductor resistance.
It has the following disadvantages.

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, being able to respond to changes in corrosion conditions, being semi-permanent if the anode is sufficiently insoluble, and reducing costs. It has disadvantages such as being more complicated to operate than the galvanic anode method, requiring a certain amount of monitoring and management after installation, high initial cost, and requiring constant power supply.

Furthermore, recently, an external power supply method using solar cells has 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 solar cell during the day and from the battery at night. It was designed to flow.

[Problem that the invention seeks to solve]

By the way, in pipelines that are regulated as transfer handling facilities under the Fire Service Act, the average value of potential to the ground is stipulated to be -850 mV or less based on copper sulfate electrode standards.

The above-mentioned external power supply system that uses solar cells in combination with a battery passes the above criteria and can reduce the burden on the battery by the amount of solar cells, but the drawbacks of the external power supply system mentioned earlier are that the entire system becomes large-scale.
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 through the solar cells, the potential to the ground during the period when no electromotive force is obtained in the solar cells, that is, during the period when the anti-corrosion current is interrupted, is lower than that of the buried metal body. It has been found that there are large 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 prevention current, etc. are set so that the lowest ground potential during this period can be maintained at the value required for corrosion prevention (dotted chain line), corrosion prevention using solar cells alone becomes possible.

However, in buried metal objects with a high level coating such as polyethylene lining, there is almost no polarization around the object while the anti-corrosion current is flowing, so the anti-corrosion current is interrupted as shown by the dotted line in Figure 4. After that, it immediately returns to its natural potential. The natural potential varies depending on the soil, but is approximately -500
Since the voltage is about mV to -600 mV, it is impossible to maintain the potential required for corrosion protection according to the above standards.

The present invention is based on the above invention, and includes:
Even for buried metal bodies with high-level coatings such as polyethylene lining, we can use solar cells, have a simple configuration, and maintain the ground potential necessary for corrosion protection at low cost. The purpose is to provide a cathodic protection device.

[Means for solving problems]

For this purpose, the electrolytic protection device for a buried metal body of the present invention includes a solar cell, a galvanic anode buried in the ground, an electrode connected to the anode of the solar cell buried in the ground, and a cathode of the solar cell in the buried metal body. The switching means connects the cathode of the solar cell to the buried metal body on condition that the voltage generated by the solar cell exceeds a first predetermined value, and connects the cathode of the solar cell to the buried metal body, and This feature is characterized in that the galvanic anode is switched to be connected to the buried metal body on the condition that the current has decreased below a predetermined value.

[Effect]

In the electrolytic protection device for buried metal bodies of the present invention, when a predetermined electromotive force can be obtained from the solar cell, a corrosion protection current is applied by an external power source method using the solar cell,
If the specified electromotive force cannot be obtained from the solar cell, an anti-corrosion current is applied using the galvanic anode method, so there is no need for an auxiliary power source such as a battery to back up the solar cell, and the consumption of the galvanic anode is reduced. The amount also decreases due to the anti-corrosion current flowing through the solar cells.

〔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, 3 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
9 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. Anode 3 for external power supply,
It 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 made of magnesium, aluminum, zinc, etc. buried near the buried metal body 5. The anode is made of a substance with a high ionization tendency, such as The switching circuit 2 has a built-in rechargeable secondary battery 9 such as a rechargeable NiCd battery, as shown in FIG. 2, although a specific example of its configuration will be described later. The relay 7 is controlled by comparing the output voltage of the solar cell 1 with the output voltage of the solar cell 1 by a comparator 6, and the relay 7 connects the solar cell 1 to the buried metal body 5 or connects the galvanic anode 4 to the buried metal body 5. It is used to switch between

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. The structure is such that a forward anticorrosive current flows through a closed circuit from the positive terminal to the external power supply anode 3, the ground, the buried metal body 5, and the negative terminal. On the contrary, the switching circuit 2 is connected to the current anode 4.
When connected to the buried metal body 5, the electromotive force generated between the current anode 4 and the buried metal body 5 causes forward corrosion protection in the closed circuit from the current current anode 4 to the earth and the buried metal body 5. It is configured to allow current to flow.

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 a diode D1 as shown in FIG. 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, so that the contact point causes the solar cell to be activated as shown in FIG. 1 is connected to the buried metal body 5, and the electromotive force generated by the solar cell 1 is used to flow an anticorrosion 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 conducts and energizes the relay 7, thereby switching the contact so that the current anode 4 is connected to the buried metal body 5. . Note that this chatter 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 operation of relay 7 can be prevented. -Chattering can also be prevented by setting the level low. Further, the switching voltage value can be adjusted by changing the voltage dividing ratio of the voltage dividing circuit including the resistors R1 and R2 and the voltage dividing circuit including the 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 when the amount of solar radiation is low, such as in the morning, evening, or on cloudy days, the secondary battery 9 is used to operate the switching circuit 2 to connect the current anode 4. Since it is connected to the buried metal body 5 and a corrosion protection current is passed through the galvanic anode, the secondary battery 9 can be used semi-permanently. Therefore, like the galvanic anode method, it is possible to provide an almost maintenance-free device. Furthermore, the amount of expensive galvanic anodes such as magnesium Mg required, for example, which was 100 kg in the 20-year design, can be reduced to about 50 kg according to the present invention.

〔Effect 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, and electric corrosion protection is achieved by an external power source system using a solar cell as a power source according to the amount of solar radiation, and electrical protection is provided by a galvanic anode system. Since the necessary corrosion protection current is constantly supplied by switching between corrosion protection and corrosion protection, even buried metal bodies with high-level coatings such as polyethylene lining can be maintained at a sufficient corrosion protection potential. Moreover, since the time for cathodic protection using the galvanic anode method is shortened, the cost of the galvanic anode can be reduced, and since the external power source relies only on solar cells, the overall cost can be reduced as well. Maintenance can be made easier.

[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. 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 (1)

[Claims] 1. A cathodic protection device for buried metal bodies, which prevents corrosion of buried metal bodies by passing an anti-corrosion current through buried metal bodies such as metal pipes buried underground, and is used for solar cells, galvanic anodes buried underground, underground metal bodies, etc. An electrode connected to the anode of the solar cell buried therein, and a switching means for switching and connecting the cathode and galvanic anode of the solar cell to the buried metal body, and the switching means is configured to adjust the voltage generated by the solar cell to a first predetermined value. The cathode of the solar cell is connected to the buried metal body on the condition that the value exceeds a second predetermined value, and the anode of the solar cell is switched to be connected to the buried metal body on the condition that the value falls below a second predetermined value. Cathodic protection equipment for buried metal objects.