JPS59100273A - Prevention of electrolytic corrosion and contamination in sea water environment - Google Patents

Abstract

PURPOSE:To prevent sticking of ocean living things on an object to be prevented of corrosion and contamination and the corrosion thereof at a low cost with ease by connecting the cathode of a DC power source device to said object and connecting the anode thereof to a lead-silver alloy electrode inserted in the sea water. CONSTITUTION:An electrolytic cell 1 is interposed in the mid-way of a steel pipe 2 for feeding and discharging sea water. A copper electrode 3 consisting of pure copper and a lead-silver alloy electrode 4 contg. about 1.0-4.5wt% silver are inserted therein. The cathode of a D.C power source device 5 is connected to a steel pipe 2 which is an object to be prevented of corrosion and contamination and the anode thereof is connected to the electrode 3 and the electrode 4. Then, copper ion and lead ion elute from the anode side and act cooperatively to prevent sticking of ocean living things on the inside peripheral surface of the pipe 2 by a sterilization effect. The potential difference between the cathode and anode of the local cell generated on the inside peripheral surface of the pipe 2 is annihilated whereby corrosion prevention is effected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for preventing marine organisms from adhering to anti-corrosion and anti-fouling objects such as steel pipes for conveying and discharging seawater in a seawater environment, and also for preventing corrosion thereof. Regarding.

In equipment that utilizes seawater, such as ships, thermal power plants, nuclear power plants, wave power plants, and temperature difference power plants, steel pipes for transmitting and discharging seawater are likely to be corroded by seawater. In addition, marine organisms adhere to and breed on steel pipes for conveying and discharging seawater, causing problems such as reduced flow rates and blockages. In order to solve this problem, conventional anti-corrosion methods include the use of anti-corrosion materials, coating anti-corrosion methods using paints or adhesion, and electrolytic anti-corrosion methods. However, corrosion-resistant materials are expensive;
In the anticorrosion coating method, the coating must be recoated every one or two years, which is time consuming and increases costs. Furthermore, in the cathodic protection method, when only a copper electrode is used as an anode, excessive copper dissolves, causing pollution problems, and the formation of copper chloride accelerates corrosion of copper pipes for conveying and discharging seawater.

On the other hand, when only a lead-silver alloy electrode is used as the anode, an insoluble oxide film is formed on the electrode surface, which reduces the dissolution of lead ions necessary for sterilizing action.

Conventional antifouling methods include injecting sodium hypochlorite, which is produced by electrolyzing seawater, and applying paint containing cuprous oxide or organic tin poisons. has been done. In the method of injecting sodium hypochlorite, excessive use accelerates corrosion of seawater conveyance and drainage steel pipes. On the other hand, in the method of applying paint containing poisonous substances,
It has to be reapplied every one or two years, which is time-consuming and increases costs.

Therefore, the present invention provides an electrolytic anti-corrosion and anti-fouling method in a seawater environment that solves these problems, and is characterized by connecting the cathode of a DC power supply to the anti-corrosion and anti-fouling body that is in contact with seawater. Then, insert a copper electrode and a lead-silver alloy electrode into seawater, connect the anode of a DC power supply to the copper electrode and the lead-silver alloy electrode, and collect copper ions from the copper electrode and the lead-silver alloy electrode. Lead ions are dissolved in seawater to make the seawater an environment unsuitable for the survival of marine organisms, and at the same time eliminate the potential difference between the cathode and anode of the local battery that occurs on the surface of the corrosion-protected antifouling body, resulting in excessive corrosion. According to this method, since two anodes are used, the current value of the anode can be lower than that of the conventional method.

Therefore, excessive dissolution of copper ions from the copper electrode can be suppressed, and generation of chlorine gas from the lead-silver alloy electrode can be suppressed. In addition, the dissolved amount of copper ions, which have a bactericidal effect, is reduced, but since lead ions, which also have a bactericidal effect, are dissolved, the combination of these two prevents marine organisms from adhering to the corrosion-protected and antifouling body. It is something that can be done.

Furthermore, it is possible to prevent corrosion by eliminating the potential difference between the cathode and the anode of the local battery that occurs on the surface of the anti-corrosion and anti-fouling body.

Hereinafter, one embodiment of the present invention will be described based on FIG. 1.
(1) is an electrolytic cell interposed in the middle of the seawater conveyance and drainage steel pipe (2), (3) is a copper electrode made of pure copper inserted into the seawater in electrolytic cell (1), and (4) is the same. A lead-silver alloy electrode containing 2.5% by weight of silver is inserted into the seawater in the electrolytic cell (1), and (5) is a DC power supply, the cathode of which is a steel pipe (2
), and its anode is connected to a copper electrode (3) and a lead-silver alloy electrode (4), respectively. Note that lead-silver alloy electrodes form a dense oxide film at a current density of 0.6 A/dm2 or higher, so they do not elute much even if the current density is changed, and the usable current density is higher than that of other Pb alloys. Wider. And the silver content is 1.0-4.5% by weight
That's fine. If the silver content is less than 1%, when electricity is applied to the anode, the adhesion of the oxide film is poor and the elution rate of lead increases.
．． This is because if it exceeds 5%, the dissolution rate of lead will not be improved.

In the above configuration, when the DC power supply (5) is operated, copper ions are released from the copper electrode (3) and the lead-silver alloy electrode (
The lead ions from 4) are dissolved to prevent marine organisms (for example, barnacles) from adhering to the inner circumferential surface of the steel pipe (2) by a bactericidal action. It also prevents corrosion by eliminating the potential difference between the cathode and anode of the local battery that occurs on the inner peripheral surface of the steel pipe (2).

Next, the effects of this embodiment will be explained based on a specific example shown in FIG. In the figure, (6) is a seawater pump, (2
1) to (27) are steel pipes, and (7) to (11) are flowmeters.

In addition, in order to change the flow chain, (7), (8), (10), and (1)
In 1), the pipe diameters are different. For comparison, the steel pipe (9) in the center is one in which seawater is passed directly through the electrolytic cell (1) without passing through it. The current of the copper electrode was set so that the electrolytic copper ion concentration in seawater was 0.002 ppm.

Table 1 shows the results obtained using this seawater piping system.

In this case, for comparison, a case where an aluminum electrode was used instead of the lead-silver alloy electrode (4) is also shown. As is clear from Table 1, the electrolytic conditions and antifouling effect when copper electrode (3) and aluminum electrode are used together are as shown in the fourth column for the period from September to November. Current value 0
．． 2A, and a slight amount of biofouling was observed under the conditions of aluminum electrode current value 0.15A, but in column 1 and column 2,
As shown in the column, no biofouling was observed under the conditions of a current value of 0.4 A for the copper electrode (3) and a current value of 0.3 A for the aluminum electrode. However, under the same conditions from April to August, some biofouling was observed as shown in columns 6 and 7. On the other hand, in the case of the copper electrode (3) and the lead-silver alloy electrode (4), no biofouling was observed even under the same conditions as above, as shown in columns 9 and 10. This biofouling prevention effect is due to steel pipes (21)
(27) remained the same for bare steel and tar-epoxy coated steel.

Next, Fig. 3 shows the results of investigating the anticorrosion effect. (a) in the same figure shows the natural state, and (b) in the same figure shows the copper electrode (
3) shows the case where a current of 0.4 A was passed through the lead-silver alloy, and the case where a current of 0.3 A was passed through the lead-silver alloy. As shown in (a), if the steel pipe (2) is left in its natural state, there is a potential difference between the cathode and anode of the local battery that occurs on the inner peripheral surface of the steel pipe (2), and corrosion progresses. On the other hand, in the case of (b), the potential of the inner circumferential surface of the steel pipe (2) is in the completely anti-corrosion range after a few days, and the potential difference between the cathode and anode of the local battery has almost disappeared, preventing corrosion. It almost never occurs.

In other words, in its natural state, bare steel loses 0.450 mm per year.
While corrosion progresses, it was confirmed that when electric current was applied as described above, corrosion only progressed by about 0.025 mm per year. (Table 2).

As described above, according to the method for electrolytic corrosion protection and antifouling in a seawater environment of the present invention, since two anodes are used, the current value of each anode can be lower than that of the conventional method. Therefore, excessive dissolution of copper ions from the copper electrode can be suppressed, and generation of chlorine gas from the lead-silver alloy electrode can be suppressed. In addition, the amount of dissolved copper ions, which have a bactericidal effect, is reduced, but lead ions, which also have a bactericidal effect, are dissolved, so the combination of the two prevents marine organisms from adhering to the corrosion-protected and antifouling body. It is possible. Furthermore, it is possible to prevent corrosion by eliminating the potential difference between the cathode and the anode of the local battery that occurs on the surface of the anti-corrosion and anti-fouling body.

[Brief explanation of drawings]

FIG. 1 is a schematic front view showing an embodiment of the present invention, FIG. 2 is a piping diagram for confirming the anti-corrosion and anti-fouling effect, and FIG. 3 is a graph showing the anti-corrosion effect. (1)... Electrolytic cell, (2) (21) to (27)...
Steel pipe for seawater conveyance and drainage (corrosion-proof and antifouling body), (3)...Copper battery case, (4)...Lead-silver alloy electrode, (5)...DC power supply unit■

Claims (1)

[Claims] 1. Connect the cathode of the DC power supply to the anti-corrosion and antifouling body that is in contact with seawater, insert a copper electrode and a lead-silver alloy electrode into the seawater, and connect the anode of the DC power supply to the copper electrode and lead-silver alloy electrode. Dissolve copper ions from the copper electrode and lead ions from the lead-silver alloy electrode into the seawater, making the seawater an unsuitable environment for marine organisms to live in, and at the same time, dissolving the copper ions from the copper electrode and the lead ions from the lead-silver alloy electrode. An electrolytic anti-corrosion and anti-fouling method in a seawater environment characterized by preventing corrosion by eliminating the potential difference between the cathode and the anode of a local battery.