JPS609594B2 - Electrolytic protection method for buried metal objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cathodic protection of buried metal bodies, particularly buried aluminum tubes, using an external power source.

Normally, in the cathodic protection method for buried metal bodies using an external power supply method, the electrodes are arranged as shown in Fig. 1 by connecting a plurality of electrodes 1 in parallel and forming an electrode group along the buried metal body 2 to be protected. By installing and connecting the electrode 1 to the DC power supply device 3 as an anode and the buried metal body 2 as a cathode, and supplying power,
A method of suppressing corrosion of a buried metal body is carried out by setting the ground potential of the buried metal body below the corrosion protection potential.

Since the electrodes are usually placed at intervals of several tens of meters to several hundred meters, the ground potential of the buried metal body is low near the electrodes and high between them, as shown in Figure 2. be.

Therefore, if the DC power supply device is controlled to keep the ground potential of the buried metal body between the exposed electrode and the electrode, where the ground potential of the buried metal body is highest, at least below the anti-corrosion potential, the ground potential of the buried metal body near the electrode will be indicates a potential that is considerably lower than the corrosion protection potential required to prevent corrosion of buried metal bodies.

Conventionally, cathodic protection methods for buried metal objects using external power sources have been used. Although it has been successfully applied to the corrosion protection of steel pipes and lead-coated pipes, the following disadvantages arise when applying this type of cathodic protection method using an external power source to the corrosion protection of buried aluminum pipes. In other words, unlike iron and lead, aluminum is an amphoteric metal that is easily attacked by acids and alkali, so the cathodic protection method shown in Figure 1 is applied to buried aluminum pipes, and the electrode When an anticorrosive current is passed through the aluminum tube as a cathode, if the ground potential of the aluminum tube near the electrode drops too much, the surface of the aluminum tube, which is the cathode, becomes highly alkaline and the surface of the aluminum tube near the electrode becomes corroded. It had the disadvantage of being Normally, to prevent corrosion of buried aluminum pipes, when an anti-corrosion current is applied to the buried aluminum pipes, the mine potential of the buried aluminum pipes must change to a negative value of at least 15 V compared to when no anti-corrosion current is applied; It is also said that it is necessary that the corrosion protection potential does not exceed 1.200y based on a saturated sulfuric acid steel electrode.

The ground potential of a buried aluminum pipe in soil is approximately 10.600V to -0.700V, although it varies depending on the nature of the soil and the material of the aluminum pipe. Therefore, in order to prevent a buried aluminum pipe from corrosion, it is necessary to The ground potential of the aluminum tube must be controlled within a narrow corrosion protection potential range of -0.850V to 1.200V.

In the conventional electrode placement method using the cathodic protection method shown in Figure 1, the pipe-to-ground potential is controlled to a narrow range of -0.850V to -1.200V over the entire buried aluminum pipe. Because it is very difficult to
It has traditionally been considered difficult to apply cathodic protection methods using an external power source to protect aluminum pipes.

SUMMARY OF THE INVENTION An object of the present invention is to improve the shortcomings of the conventional method and to provide a cathodic protection method using an external power source that provides a stable electric potential to suppress corrosion to a buried aluminum pipe.

That is, a linear electrode and a third metal body having a lower potential than the buried aluminum tube are installed along the buried aluminum tube, for example in parallel and close to each other, and the buried aluminum tube is used as a cathode, the electrode is an anode, and a third metal body is installed, for example, in parallel and close to each other. By using the metal body No. 3 as a reference electrode and detecting the direction of the current flowing between the buried aluminum pipe and the third metal body to drive the DC power supply, a stable anti-corrosion potential can be achieved over the entire route of the buried aluminum pipe. This made it possible to give
Next, the present invention will be explained based on the drawings.

FIG. 3 is a principle diagram of the method for cathodic protection of a buried metal body according to the present invention, in which 12 is a buried aluminum pipe for the purpose of corrosion protection, and 11 is a linear line installed parallel to and close to the buried aluminum pipe 12. electrode, 14 is the buried aluminum pipe 1
15 is a detection device that detects the direction of the current flowing between the buried aluminum pipe 12 and the third metal body 14; 13 is a detection device that detects the direction of the current flowing between the buried aluminum pipe 12 and the third metal body 14; It is a controlled DC power supply.

The detection device 15 determines the direction of the current between points A and B in FIG. 3 based on the polarity of points A and B. If the current flow is from B to A, the voltage will increase, and if the current is from A to B, the detection device 15 will determine the direction of the current between points A and B in FIG. Voltage drop, A
If no current flows between points B, it has a function of sending a signal instructing voltage maintenance to a control circuit (not shown) of the DC power supply 13 to automatically control the DC power supply.
In FIG. 3, the electrode 11 is connected to the (10) poles of the DC power supply device
, (-) electrically connects the buried aluminum tube 12 to the buried aluminum tube 12 and a third electrode that has a lower potential than the buried aluminum tube 12 and can serve as a sacrificial anode for the buried aluminum tube. Device 1 for detecting metal body 14
5, the buried aluminum pipe 12 connects to the third
The buried aluminum tube 12 serves as a cathode and the third metal body 14 serves as an anode, forming a battery using soil as an electrolyte. Current flows towards 0. In other words, current flows from B to A, and point A has negative polarity.
Since point B shows positive polarity, a voltage increase signal is output from the detection device 15 to the DC power supply device 13. When the DC power supply device is activated by the signal from the detection device 15, the electrode 11 (10)
pole, buried aluminum pipe 12 and third metal body 14
A circuit is formed in which is (one) pole. As the potential difference between the two poles increases, the current value between B → A decreases, and when the potential of the buried aluminum pipe reaches the corrosion protection potential, the current value between points A and B becomes 0, and the control of the DC power supply 0 device 13 A circuit works to maintain a constant potential. When the potential of the buried aluminum pipe falls below the potential of the third metal body 14, a current flows in the opposite direction from A to B', and point A becomes (ten) poles and point B becomes (one) pole, so the control circuit Since the DC power supply device 13 is activated and controlled so that no current flows between points A and B, the buried aluminum pipe 12 is always maintained at a stable anti-corrosion potential. Next, specific examples of the present invention will be described.

Embodiment FIG. 4 shows a configuration diagram of an embodiment of the cathodic protection device for buried metal bodies according to the present invention.

In order to prevent corrosion of the underground part 180 of an aluminum alloy pipe whose surface is coated with epoxy powder, a linear insoluble electrode 21 and a zinc wire 24 are buried parallel to the buried pipe 22. The zinc wire 24 is connected via the detection device 25, and the buried pipe 22 is connected to the DC power supply 23 having a built-in control circuit that works with the detection device 25, with the buried pipe 22 as the (one) pole and the insoluble electrode 21 as the (ten) poles. Electrolytic protection was applied using an external power supply method. In FIG. 4, 26 is a grounding battery used for safety grounding of the buried pipe. At this time, the open circuit potential of the buried pipe measured using the sulfuric acid steel saturation electrode as the reference electrode was -0.6
45V, the open circuit potential of the zinc wire was -1.156V.

Further, the closed circuit potential of the buried pipe and the zinc wire in a state where the DC power supply circuit was not connected was -0.988V, and the total current generated by the zinc was 23 plates A. Next, while activating the aforementioned cathodic protection device and supplying power from the DC power supply device 23 according to the signal from the detection device 25, the pipe-to-ground potential of the buried pipe 22 was measured every 10 times using a saturated sulfuric acid steel electrode. As shown in Figure 5, -0.930V to -1 over the entire area of the buried pipe.
．． A stable corrosion protection potential of 0.070V was obtained. Note that the types of the buried metal body to be protected from corrosion, the electrode, and the third metal body are of course not limited to those of the above embodiments, and the relative arrangement method and optimal distance of these can be determined as appropriate. That's true.

As shown above, in the electrolytic protection method for buried metal bodies according to the present invention, it is extremely easy to control the anticorrosion potential in the electrolytic protection method using an external power supply method, and it is possible to provide a stable anticorrosion potential to the buried aluminum pipe. It is possible and
Effective corrosion protection can be achieved.

It is expected that the use of aluminum pipes instead of steel pipes will increase in the future in the fields of electrical equipment, telephone cables, power cables, etc., and the technical and industrial value of the present invention is extremely large.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the principle of the conventional cathodic protection method using an external power supply method, Figure 2 is a diagram showing the position of mines on buried pipes when the secondary cathode protection method is implemented, and Figure 3 is the main figure. A principle diagram of the cathodic protection method using an external power source according to the invention, FIG. 4 is a block diagram showing an embodiment of the cathodic protection method according to the invention, and FIG. FIG. 3 is a diagram showing the tube-to-ground potential. In the figure, 22 is a buried pipe, 23 is a DC power supply device, 25 is a detection device, and 26 is a ground battery. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. An electrode and a third metal body having a potential lower than that of the buried metal body are installed in the vicinity of the buried metal body made of aluminum or an aluminum alloy structure to extend along the buried metal body. and electrically connect the buried metal body to a DC power supply device with the buried metal body as a cathode and the electrode as an anode, and to follow the direction of the current flowing between the buried metal body and the third metal body detected by the electrode. A method for cathodic protection of a buried metal object, characterized in that the DC power supply device is driven in response.