JPS5827683A - Corrosion-prevention of metallic device or apparatus - Google Patents

Abstract

PURPOSE:To inhibit corrosion of a metallic device or apparatus, while eliminating or suppressing the activity of metal-corrosion microbes in water with a simplified means, by irradiating the water, in which the metal-corrosive microbes grow, accommodated in the metallic device or apparatus with gamma-rays. CONSTITUTION:A sealed gamma-ray source part 6 is provided at the down stream side of a circulating pump 2 but at the upper stream side of a cooler 3, and a Co- 60 ray source entirely covered with plastics is arranged in the gamma-ray source part 6. As cooling water, desalinated water prepared by passing river water through an ion-exchange resin column is used. Sodium nitrite is added to the water so that initial nitrite ion concentration will be at 2,000ppm. By irradiation with gamma-rays from the sealed gamma-ray source part 6, the activity of nitrobacterium can be esily eliminated or suppressed, so that corrosion of a metallic device or apparatus can be inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing corrosion of metal equipment and devices that use water in which metal-corrosive microorganisms can grow.

Equipment that comes into contact with water, such as cooling equipment and water pumps,
There are many types of devices, a typical example of which is a recirculating water cooling device.

Carbon steel is usually used as the constituent material of these devices and devices, and in many cases nitrite is used as an oxidizing agent to prevent corrosion of carbon steel by water bodies (・.

For water, use river water, ground water, or tap water as is.
Alternatively, it is common to use so-called demineralized water that has been passed through an ion exchange resin.

However, the water used in these applications contains iron) (cutilia (bacteria that live by obtaining energy by oxidizing iron in water) and microorganisms that have the ability to oxidize nitrite ions into nitrate ions (hereinafter referred to as microorganisms). Nitrono (referred to as Cutilia) force exists, which corrodes the metals that are the constituent materials, especially carbon steel, and in severe cases causes stress corrosion cracking.

Conventionally, as a countermeasure for this problem, in the case of a recirculating water type device, a method of replacing most or all of the water used and/or a method of adding sodium azide as a disinfectant have been adopted.

However, the former method has drawbacks such as consuming a large amount of water and requiring the plant operation in which the device is used to be stopped while replacing the water. In addition, the latter method has the disadvantage that sodium azide is gradually consumed and the water must be constantly analyzed and monitored to maintain the appropriate concentration. ) If a large amount of IJum is added, if nitrite is used as a corrosion inhibitor, sodium azide is a reducing agent, so it will react with the nitrite ion, which is an oxidizing agent, and both will be It also has the disadvantage that it loses its effectiveness and instead accelerates corrosion.

The object of the present invention is to eliminate the drawbacks of the prior art described above, eliminate or suppress the activity of metal-corrosive microorganisms, and thereby improve the convenience of metal equipment and equipment in which these microorganisms grow and use effluent. To provide a corrosion prevention method.

That is, to summarize the present invention, the present invention is characterized in that, in metal equipment and devices that use water in which metal-corrosive microorganisms grow, the used water is irradiated with gamma rays.
Concerning methods for preventing corrosion of metal equipment and devices.

The present invention discloses that the corrosion of carbon steel materials in equipment and devices that use water with nitrite added as a corrosion inhibitor is caused by nitrate ions produced by nitro bacteria in the water, and that the activity of nitro bacteria is reduced by γ-ray irradiation. As a result of further research and discovering that it can be easily eliminated or suppressed,
The present invention was completed by confirming that metal-corrosive microorganisms that generally grow in water can be easily eliminated or suppressed by γ-ray irradiation.

It was also confirmed that when nitrite is used as a corrosion inhibitor, the anticorrosive effect of nitrite ions is not impaired and only the activity of microorganisms can be controlled.

The bactericidal effect of radiation is generally known, but
α rays and β rays are easily shielded and are not particularly suitable for controlling microorganisms in water, which is the object of the present invention, and γ rays are preferred.

The γ-ray source may be either a sealed type or an unsealed type, but in general, a sealed type source is preferable in consideration of the treatment of water discharged outside the system.

The nuclide used and the irradiation dose vary depending on the case. In other words, depending on the amount of water, circulation amount, water temperature, number of microorganisms, etc.
The required irradiation dose is different.

Therefore, when implementing such methods, it is necessary to individually determine the nuclide and irradiation dose suitable for the equipment and equipment. However, in general, the radiation dose required to kill microorganisms is
It is said to be 105 to 2X106 reps. However, in the case of living tissue, the above level is required since the level is >1R, but in the present invention, it is sufficient that the microorganisms have ceased activity, so generally, the level is 10 to 100R. It is enough. In addition, there are various types of nuclides as gamma ray sources, but Co-60, which has a half-life of 5.2 years, is optimal from the viewpoint of easy availability and long-term use.

Therefore, Co-60 is 13.2 R/hr++ m
Since the radiation dose is 1 mci, it is sufficient to use a radiation source of about 1 mci compared to the above-mentioned irradiation dose, as long as time passes, but when considering the near dead weight, it is preferable to use a radiation source of about 1 mci. .

Note that gamma rays do not have the effect of activating other substances, so there is no need to worry about radioactive contamination.

However, H2O generated by partial decomposition of water by γ rays
It is fully inferred that 2 and radicals act to control microorganisms in the case of the present invention.

Furthermore, since nitrobacteria at least cease to be active at temperatures above 7IoC, there is no need to consider corrosion caused by nitrobacteria in equipment and devices that use water at a temperature of 40'C or above. Furthermore, nitrobacteria cease to be active even if the nitrite ion concentration exceeds 500 ppm, but normally in recirculating water cooling systems, nitrite is added in the form of nitrite ions at a concentration of 50 to 2001) pm. , corrosion occurs.

Copper sulfate is also considered as a disinfectant, but in iron-containing equipment, it is not preferred from the viewpoint of corrosion protection due to its ionization tendency.

It is clear that the use of other chemicals such as disinfectants is not preferable from the viewpoint of wastewater treatment.

As mentioned above, a typical example that uses water is a recirculating water type cooling device, so the present invention will be specifically explained below using this as an example.

FIG. 1 of the accompanying drawings is a schematic diagram of a conventionally known recirculating water type cooling device.

This device is composed of an object to be cooled 1, a circulation pump 2 that circulates cooling water, a cooler 3 that removes heat from the cooling water to the outside of the system, and piping 5 that connects these.
The cooling water passes through the object to be cooled 1, the circulation pump 2 and the cooler 6, and returns to the object to be cooled 1 again for circulation. Because it is often the case that a portion of the cooling water is intentionally removed from the system for investigation or for leakage of cooling water from a seal in the system, it is usually necessary to replenish cooling water to compensate for the amount of waste inside the system. The system is equipped with a surge tank 4 for the purpose of cooling, and is connected to a circulation system via piping.

In contrast, FIG. 2 is a schematic system diagram of a recirculating water type cooling device shown as one embodiment of the present invention.

1 to 5 are the same as in FIG. 1, and 6 indicates a sealed gamma-ray source section.

As will be explained in detail later, Figure 3 shows time (days) (horizontal axis) and concentration (ppm) (vertical axis) to represent changes over time in the concentration of nitrite ions and nitrate ions in the water used. It is a graph showing the relationship.

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to this.

Example The apparatus shown in FIG. 2 was used.

That is, in this case, the sealed gamma ray source section 6 is installed downstream of the circulation pump 2 and upstream of the cooler B. Sealing γ
Co-60(
A 1 mCi) source was placed. Desalinated water obtained by passing river water through an ion exchange resin tower was used as the cooling water, and sodium nitrite was added so that the nitrite ion concentration was 200 ppm initially. The circulation volume is 7 m3/hour. The temperature of the circulating cooling water is 65° C. upstream of the cooler 3 and 30° C. downstream.

First, cooling water was circulated without putting a radiation source into the sealed radiation source section 6, and a portion of the cooling water was extracted to examine changes over time in the concentrations of nitrite ions and nitrate ions in the cooling water. After confirming that nitrite ions are definitely reduced and nitrate ions are increased, the above-mentioned Co-60 sealed radiation source is attached to the sealed radiation source section 6, and the subsequent nitrite ion and nitrate ion concentrations in the cooling water are measured. We further investigated changes over time. The results are shown in Figure 6. Nitrite ions in the cooling water began to decrease slowly at first, but after the second day, they decreased rapidly.

The nitrate ion concentration increased slowly at first and then rapidly, corresponding to the case of nitrite ion.

When the sealed radiation source was attached to the sealed radiation source unit 6 after 5 days from the start of the experiment, that is, at the point of arrow A in Fig. 5, the rate of decrease in nitrite ion concentration and increase in nitrate ion concentration became gradual.8 After the first day, the concentrations of both ions became constant. The results of this example show that γ-ray irradiation is effective in eliminating the activity of nitrobacteria.

In addition, the same results were obtained even when a part of FIG. 2 was changed and a sealed radiation source was attached to the surge tank 4.

It was confirmed that the activities of other metal-corrosive microorganisms could be stopped in the same way.

Therefore, the effect of the method of the present invention is more remarkable than that of the conventional method, taking into consideration the wastewater treatment.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventionally known recirculating water type cooling device. FIG. 2 is a schematic diagram of a recirculating water type cooling device that is one embodiment of the present invention. FIG. 6 is a graph showing the relationship between time and concentration of nitrite ions and nitrate ions in the water used. 1: Cooled object, 2: Circulation pump, 6: Cooler, 4: Surge tank, 5: Piping, 6: Sealed γ-ray source Patent applicant Hiroshi Moto, representative of Hitachi, Ltd. Figure 1 Figure 2 Figure 3: Inside the temple (Japanese)

Claims (1)

[Scope of Claims] 1. Metal equipment and equipment that use water in which metal-corrosive microorganisms can grow, characterized in that the used water is irradiated with r-rays. Corrosion prevention method. 2. The method for preventing corrosion of metal equipment and devices according to claim 1, characterized in that Go-60 is used as the γ-ray source. 3. A method for preventing corrosion of metal equipment and equipment according to claim 1, characterized in that the gamma ray source is a sealed radiation source. 4. The method for preventing corrosion of metal equipment and equipment according to any one of claims 1 to 3, wherein the water used is water to which nitrite is added as a corrosion inhibitor.