JPH11310890A - Microorganism corrosion preventing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To comprehensively and effectively prevent the corrosion of a metallic material under an underwater atmosphere, where microorganisms are present by impressing negative charge to the metallic material. SOLUTION: The corrosion of the metallic material is prevented preferably by impressing negative charge to the metallic material to inhibit the sticking of the microorganisms and to suppress the generation of a product by the action of the microorganisms. As the microorganisms capable of being suppressed in the action to prevent the corrosion of the metallic material, iron oxidizing bacteria, iron bacteria, sulfate reducing bacteria, sulfur oxidizing bacteria and the like are exemplified. Relating to the pipe line metallic material 1 handling cooling water, waste water, underground water, industrial water, seawater or the like, an electrode 3 made of high silicon iron, graphite, platinum or the like is disposed inside the pipe line metallic material 1 and is energized from a DC power source device 2 as an external power system to keep the potential of the pipe line metallic material negative. In a galvanic anode system, a galvanic anode 6 such as zinc, magnesium is disposed inside the pipe line metallic material 1 and is connected to the pipe line metallic material 1 and current is supplied through seawater 4 or the like by potential difference to keep the pipe line metallic material 1 negative.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention is widely used in natural environments,
Also, the present invention relates to a method for preventing corrosion of metallic materials used in equipment and facilities for handling cooling water, drainage, industrial water, groundwater, seawater, and the like. More specifically, in water containing microorganisms such as seawater and freshwater, and in soil containing moisture. The present invention relates to a method for preventing microbial corrosion of a metal material used in an underwater environment.

[0002]

2. Description of the Related Art In general, a water filling test is performed at the time of construction of pipes, towers, and the like that handle cooling water, drainage, groundwater, seawater, and the like. It has been reported that when drainage is performed after completion of the water filling test, corrosion that may be affected by microorganisms occurs. In addition, even after temporarily using pipes, tower tanks, and the like, corrosion is likely to occur in the stagnant water when operation is temporarily stopped.

[0003] As a metal material used for the pipes and towers, there is, for example, stainless steel, and pitting or crevice corrosion is a problem as a local corrosion suspected of being affected by microorganisms. As a method for preventing the microbial corrosion of stainless steel in the stagnant water before the start of use or at the time of stopping, completely dried or completely filled water, addition of a bactericide, and electrolytic protection are performed. Among such corrosion prevention methods, the invention of a corrosion prevention method relating to sterilization is disclosed in, for example, the following patent publications.

A. Japanese Patent Application Laid-Open No. 49-122834 discloses a "method of preventing pitting corrosion in the production of steel containers" in which caustic soda and chlorine are added to prevent pitting corrosion by iron bacteria in a water filling test in the production of steel containers. I have. b. JP-A-57-194260 and JP-A-58-1
In 1788 and JP-A-58-160697, it has been reported that, in an aqueous system to which nitrite is added as a corrosion inhibitor, conversion of nitrobacterium to nitric acid and the progress of corrosion are promoted by the addition of high-concentration nitrite or by the temperature. To increase the temperature to 40 ° C. or to prevent corrosion by a growth inhibitor.

C. In JP-A-3-288585,
It discloses a method of preventing corrosion due to slime generation in high COD cooling water by acid neutralization with an alkali agent, a corrosion suppression effect by phosphate ions and Zn ions, and prevention of slime generation by addition of hydrogen peroxide water. d. In Japanese Patent Application Laid-Open No. Hei 7-241556, corrosion caused by microorganisms in a cooling water system is prevented by reducing the number of viable bacteria to 1 × 10 ⁶ cells / ml or less by ultraviolet irradiation treatment or bacteriostatic agent addition. Corrosion prevention method "is disclosed. e. Japanese Patent Application Laid-Open No. 9-228080 discloses a "copper pitting prevention method" in which hydrogen peroxide is added at a low concentration to a heat storage water system or a closed water system to prevent copper pitting caused by microbial contamination.

[0006]

In the conventional method for preventing microbial corrosion, the purpose of the present invention is to stop the activity of the microorganism itself, and only to suppress the activity of the microorganism. Has been seriously affected by the occurrence of localized corrosion. That is, in the conventional method for preventing microbial corrosion which suppresses the activity of microorganisms by sterilization treatment or addition of a bacteriostatic agent, there are various means and effects depending on the type of microorganisms, and it cannot be said that this is a reliable and general-purpose method for preventing microbial corrosion. Further, since the chlorine resistance varies depending on the microorganism, there may be a case where the activity of the microorganism cannot be suppressed only by performing the sterilization treatment. In addition, there has been reported a case in which the addition of a corrosion inhibitor results in providing a nutrient source to microorganisms, thereby failing to achieve the purpose of preventing microbial corrosion.

As described above, various conventional methods for preventing microbial corrosion of metallic materials have been proposed. However, all of them have the above-mentioned problems, and thus universally and effectively prevent microbial corrosion. At present, there is no way to do this. On the other hand, the following report has been made on corrosion of stainless steel in an underwater environment where microorganisms are present. That is, a phenomenon called "nobleness" in which the corrosion potential becomes abnormally high occurs, and it is said that the increase in local corrosion susceptibility of stainless steel due to this "nobleness" phenomenon is the cause of the microbial corrosion of stainless steel. It has been reported that the phenomenon of "nobleness" of corrosion potential is caused by the action of microorganisms, but the mechanism has not been elucidated because there are many unknown points.

The inventor of the present invention has conducted extensive experiments and studies on the effects on the corrosion behavior of stainless steel by using iron oxidizing bacteria frequently detected from corrosion sites which are considered to be affected by microorganisms of stainless steel. As a result, the following findings were obtained. In other words, the "nobleness" of the corrosion potential is affected by changes in the environment caused by the activity of microorganisms, and specifically, by the activity of microorganisms, a product that acts as an oxidant is generated on the surface of the metal material. It has been found that it affects the occurrence of local corrosion of metallic materials.

Furthermore, the inventor of the present application has found that it is effective to apply a potential to the metal material to lower the potential in order to suppress the generation of products due to the above-mentioned microbial activity. . The method for preventing microbial corrosion of the present invention has been made based on the above findings. SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional methods for preventing microbial corrosion as described above, and provides a method capable of comprehensively and effectively preventing corrosion of metallic materials in an environment where microorganisms are present. It is intended to do so.

[0010]

According to the present invention, there is provided a method for preventing corrosion of a metal material in an underwater environment where microorganisms are present, wherein the method is applied to apply a negative potential to the metal material. Things. The present invention also provides a method for preventing corrosion of a metal material in an underwater environment in which microorganisms are present. In the method for preventing corrosion of a metal material, a negative potential is applied to the metal material to inhibit the adhesion of the microorganism and to the formation by the activity of the microorganism. The method employs a method of preventing microbial corrosion in which the generation of substances is suppressed to prevent corrosion of metal materials.

Microorganisms that can suppress the activity of the metal material using the method of the present invention and prevent corrosion of metallic materials due to the activity are not particularly limited as long as they exist in a real environment. , Iron bacteria, sulfate reducing bacteria, and sulfur oxidizing bacteria. As iron oxidizing bacteria,
For example, Thiobacillus ferrooxidans and the like, and as the iron bacteria, for example, Gallionella, Leptothrix, Sphaeroti
lus and the like, and sulfate-reducing bacteria include, for example, De.
sulfovibno spp.Desulfotomaculum spp. and the like,
As sulfur oxidizing bacteria, for example, Thiobacillus thiooxida
ns and the like. Such microorganisms may be present in the environment singly or in combination of two or more.

The environment is not particularly limited in the method for preventing microbial corrosion of the present invention as long as microorganisms can exist as described above. For example, pipes for handling cooling water, drainage, groundwater, industrial water, seawater, etc. It can be an underwater environment used for a water filling test before use such as a tower tank or the like, or a stagnant underwater environment when stopped. In order to reduce the potential of the metal material in such an environment, a method generally used for cathodic protection can be used. In other words, there is a method called an external power supply method in which a current is forcibly supplied to a protected object through an electrode provided in the environment from a DC power supply device, and a potential of the protected object is maintained at a set potential. Can be used.

Also, a method called a galvanic anode method, comprising a metal, for example, zinc, magnesium, aluminum or the like, which is installed in an environment in which the material to be protected is placed and whose corrosion potential is lower than that of the material to be protected. It is also possible to use a method in which the sacrificial anode is energized from the sacrificial anode to maintain the potential of the sacrificial body at a set potential. Examples of the metal material capable of preventing microbial corrosion by the method of the present invention include SUS30
And the like. However, the present invention is not limited to such stainless steels. Microbial corrosion of any metal material such as carbon steel and copper / copper alloy can be prevented by using the method of the present invention. .

In the method for preventing microbial corrosion according to the present invention, the potential of the metal material of the anticorrosion target is set to, for example, -400 mV vs. potential. S.
C. E. FIG. By maintaining a negative potential that is equal to or less than (saturated luster electrode reference), the adhesion of microorganisms to the surface of the metal material is suppressed, and the product of the activity of microorganisms is prevented from being generated on the surface of the metal material. Since "nobleness" of the corrosion potential of the metal material is suppressed, microbial corrosion can be effectively prevented.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to specific examples. The embodiment of the present invention exemplifies a case of preventing microbial corrosion of stainless steel (SUS304) by iron oxidizing bacteria by assuming water used for a water filling test or water used for cooling water as an environment where microorganisms are present. explain. First, in a Silverman 9K medium usually used for culturing iron oxidizing bacteria, Thiobacillus as iron oxidizing bacteria was used.
llus ferroxidans was cultured for 3 days. Next, one-tenth of the iron-oxidizing bacteria after culturing was added to a medium similar to a real environment that did not contain iron ions and had a low sulfate ion concentration, and 3
After acclimation for one day, iron oxidizing bacteria were collected from the culture using a centrifuge. The composition of each medium used here is summarized in Table 1 below.

[0016]

[Table 1]

As shown in Table 1, the medium similar to the real environment does not contain iron ions and has a sulfate ion concentration of 100 ppm.
Because it is lower than 20000 ppm of Silverman 9K medium,
The composition is close to the real environment, and can be assumed to be equivalent to the water used for the water filling test or the cooling water. further,
Three more glass cells containing 500 ml of the above-described real-environment approximate medium were prepared, and the above-mentioned iron-oxidizing bacteria were added to the first glass cell to obtain a sample S1, and the second glass cell was made to contain the above-described sample. A sample S2 was prepared by adding an iron-oxidizing bacterium and maintaining the potential of the test piece to be immersed by a method described later at a negative potential for a predetermined time. Samples S1 and S2 contained 1 × iron oxidizing bacteria per ml.
It contains about 10 ⁵ to 1 × 10 ⁷ cells. Also,
Sample S3 was prepared without adding iron-oxidizing bacteria to the third glass cell. Each sample S1 to S3 thus prepared
SUS304 stainless steel as a metal material sample was immersed in a test piece that was heat-treated at 650 ° C. for 2 hours, assuming that a Cr-deficient region was formed (sensitized) due to welding heat history.

Embodiment 1 FIG. 3 shows the configuration of a test apparatus according to an embodiment. In FIG.
D is a test device. G1, G2, and G3 are glass cells provided in the test apparatus D, and Ca and Kc are glass cells G1.
Glucose electrode and KCL used as reference electrodes
The solution, Ag is agar, Ba is agar bridge, and Bs is liquid bridge.
The agar bridge Ba and the liquid bridge Bs are glass cells G1, G, respectively.
2 and G2, G3. T is a test piece, L is a Luggin tube, and Eo is a counter electrode. These are immersed in a medium close to the real environment stored in the glass cell G3. M is a potentiometer for measuring an applied potential, and E is a constant voltage DC power supply. Then, three sets of the test apparatus D are prepared, and the solution in the glass cell G3 corresponds to the above three samples S1 to S3.

In the test apparatus D shown in FIG. 3, a constant voltage DC power supply E is connected to the test piece T immersed in the sample 2, and the electric potential is -400 mV vs. 400 V. S. C. E. FIG.
(Saturated luster electrode standard) and the circuit was opened after holding for 2 hours. Thereafter, the change with time of the corrosion potential of the test piece T immersed in each of the samples S1 to S3 was measured using a potentiometer M with the saturated gallbladder electrode shown in the figure as a reference electrode Es. The graph of FIG. 4 shows the change over time of the corrosion potential of the SUS304 test piece T immersed in each of the samples S1 to S3.

As shown in the graph of FIG. 4, when the iron-oxidizing bacteria were not added (sample S3), the corrosion potential of SUS304 was about -100 mV vs. SUS304. S. C. E. FIG. (Saturated luster electrode standard). On the other hand, when the iron-oxidizing bacteria were added and no negative potential was applied (sample S1), the corrosion potential of the test piece T of SUS304 was 25%.
0 mV vs. 0 mV. S. C. E. FIG. It is rising. From the increase in the corrosion potential, it is confirmed that the environment is such that microbial corrosion easily occurs due to the added iron-oxidizing bacteria.

On the other hand, by adding iron-oxidizing bacteria, the potential was lowered to -40.
0 mV vs. 0 mV. S. C. E. FIG. (Sample S2), the rise of the corrosion potential of the test piece T of SUS304 is delayed, and the reached corrosion potential is approximately 160 mV vs. 200 mV.
S. C. E. FIG. It is. Therefore, when the negative potential is not applied (Sample 1), the ultimate corrosion potential is 250 mV vs.
S. C. E. FIG. Compared to approximately 100 mV vs.
S. C. E. FIG. It is lower. This revealed that the application of the negative potential to the test piece T suppressed the "nobleness" of the potential by the microorganism. In this manner, by applying a negative potential to the metal material, microbial corrosion of the metal material can be effectively suppressed.

Second Embodiment Next, a second embodiment will be described. Five sets of test devices D were prepared in the same manner as in Example 1 described above, and iron-oxidizing bacteria cultured in the same manner as described above were added to each of the glass cells G3 containing 500 ml of the adjusted real ring approximate medium at a rate of 1 ml / ml. It is added so as to contain about × 10 ⁵ to 1 × 10 ⁷ cel / s. SUS30 was used as a test material for each sample S1 to S5.
Specimen T heat-treated at 650 ° C. for 2 hours is immersed in 4 steel, assuming that a Cr-deficient region is formed (sensitized) due to welding heat history. In the same manner as in Example 1 described above, a constant voltage DC power supply E is connected to each test piece T, and the potential is set to 0, -200, -400, -600, -800 mV while reading the potentiometer M.
vs. S. C. E. FIG. So that five samples S1
The circuit was opened after adjusting S5 to 5 steps and holding for 2 hours.

Thereafter, the change over time of the corrosion potential of the test piece T immersed in each of the samples S1 to S5 was measured using a potentiometer M with the saturated gallbladder electrode as a reference electrode Ca. The graph of FIG. 5 shows the change with time of the corrosion potential of the SUS304 test piece T immersed in each of the samples S1 to S5 at this time.
As shown in FIG. 5, the potential of the test piece T was set to -400 mV v
s. S. C. E. FIG. When the temperature is kept below, the rise of the corrosion potential is delayed. The ultimate corrosion potential is 200 mV v
s. S. C. E. FIG. Or less, and 250 mV vs. ultimate corrosion potential when no negative potential is applied. S. C. E. FIG. It is lower than. This indicates that the "nobleness" of the potential by the microorganism was suppressed. In this way, the metal material has a resistance of -400 mV vs. 400 mV. S. C. E. FIG. By applying the following negative potential, microbial corrosion of the metal material can be effectively suppressed.

Embodiments 1 and 2 Embodiments 1 and 2 of the present invention which have been developed into specific technologies based on the results of Examples 1 and 2 involving the above experiments and studies will be described below. . FIG. 1 is an explanatory diagram showing the configuration of Embodiment 1 of the present invention, and FIG. 2 is an explanatory diagram showing the configuration of Embodiment 2 of the present invention. FIG. 1 shows an external power supply system used for the above-described cathodic protection, and FIG. 2 shows a galvanic anode system.

1 and 2, reference numeral 1 denotes a pipe metal material;
Represents a DC power supply device, 3 represents an electrode, 4 represents cooling water or seawater stored in the pipe 1, and 5 represents the flow of current. Also,
Reference numeral 6 in FIG. 2 denotes a current carrying anode. FIG. 1 shows a configuration of a first embodiment in which a piping metal material 1 is applied to a negative potential by a DC power supply device 2 in a piping structure that handles cooling water, drainage, groundwater, seawater, industrial water, and the like 4. As shown in the external power supply system of FIG. 1, an insoluble electrode 3 made of high silicon iron, graphite, platinum or the like is provided in a pipe 1 for handling seawater 4 or the like, and electricity is supplied from a DC power supply 2 to the pipe metal material. 1
Is maintained at a negative potential.

As shown in FIG. 2, the galvanic anode system according to the second embodiment includes a galvanic anode 6 made of zinc, magnesium, aluminum or the like inside a pipe metal material 1 for handling seawater 4, for example.
Is connected to the pipe metal material 1, and the potential difference between the galvanic anode 6 and the pipe metal material 1 passes through the seawater 4 or the like, thereby forming the pipe metal material 1.
To maintain the pipe metal material 1 at a negative potential. The method of the present invention has been described with reference to an underwater environment such as seawater 4. However, the present invention is not limited to the underwater environment. For example, in all environments where microorganisms such as moist soil are present. Also, the use of the method of the present invention can effectively prevent microbial corrosion of metal materials.

[0027]

According to the present invention, a method for preventing corrosion of a metal material in an underwater environment where microorganisms are present, which employs a method for preventing corrosion of a metal material by applying a negative potential to the metal material. The present invention also provides a method for preventing corrosion of a metal material in an underwater environment in which microorganisms are present. In the method for preventing corrosion of a metal material, a negative potential is applied to the metal material to inhibit the adhesion of the microorganism and to the formation by the activity of the microorganism. A method of preventing microbial corrosion, which suppresses the generation of substances to prevent corrosion of metal materials, was adopted.

As described in detail above, according to the present invention, there is provided a method capable of preventing corrosion of a metallic material in an environment where microorganisms are present. As a result, not only the activity of microorganisms, but also the attachment of microorganisms to the surface of metal materials is suppressed, the generation of products due to the activity of microorganisms is suppressed, and factors that increase the corrosion potential of metal materials are removed. In addition, the corrosion of metal materials by microorganisms can be suppressed very effectively, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a configuration of a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a configuration of an experimental example of the test apparatus of the present invention.

FIG. 4 is a graph showing a change over time of a corrosion potential due to application of a potential.

FIG. 5 is a graph showing a change in corrosion potential with time according to another example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piping metal material 2 DC power supply 3 Electrode 4 Seawater etc. 5 Current 6 Galvanic anode Ag agar Ba Agar bridge Bs Liquid bridge Ca Reference electrode D Test equipment E Constant voltage DC power supply Eo Counter electrode G1, G2, G3 Glass cell Kc KCL solution L Luggin tube M Potentiometer S1 to S3 Sample S1 to S5 Sample T Specimen (protected body)

Claims (2)

[Claims] 1. A method for preventing corrosion of a metal material in an underwater environment in which microorganisms are present, wherein a negative potential is applied to the metal material. 2. A method for preventing corrosion of a metal material in an underwater environment where microorganisms are present, the method comprising the steps of: applying a negative potential to the metal material to inhibit adhesion of the microorganisms; A method for preventing microbial corrosion, characterized in that the generation of products by the above is suppressed to prevent corrosion of the metal material.