JP5194916B2 - Method for preventing deterioration and corrosion of steel materials - Google Patents

Description

  The present invention relates to a coating film deterioration and corrosion prevention method for a steel material whose surface is partially or entirely covered with an epoxy resin.

  In 2001, the US FHWA (The US Federal Highway Administration) reported the results of a survey of costs related to metal corrosion (Non-patent Document 1). According to the report, metal corrosion losses amount to $ 276 billion annually in the United States, accounting for 3.1% of gross domestic product (GDP). Also, in the US gas industry, the cost of corrosion of pipelines reaches $ 13.4 billion annually, of which about $ 2 billion (about 15%) is reported to be due to microbial corrosion (Non-patent literature) 2). In Japan, the cost of our anti-corrosion measures in 1997 was 3.9 trillion yen, based on a survey by the Corrosion Cost Research Committee led by the Corrosion and Corrosion Protection Association and the Japan Anticorrosion Technology Association. It is reported that it corresponds to 0.8% of (GDP) (Non-patent Document 3). As described above, the amount of damage caused by corrosion is enormous, and preventing this is an important issue for Japan, which has few resources.

  As a countermeasure against corrosion of steel materials, a method of preventing corrosion of steel materials by blocking between the steel material surface and the surrounding environment with a coating film and electrically insulating is widely put into practical use. As the coating material for the coating used for anticorrosion, there are epoxy resin, urethane resin, phenol resin, fluororesin and the like. In a petroleum environment, hydrogen sulfide, carbon dioxide gas, chlorine ions, etc. are mixed in a severe corrosive environment, and epoxy resin is mainly used as a paint. Epoxy resin paints are superior to other resin paints in terms of water resistance, chemical resistance, adhesion to the base material, wear resistance, impact resistance, etc., and are very often used as anticorrosion coatings. It has been. Among epoxy resins, in particular, tar epoxy resins are used as anticorrosion coatings in harsh corrosive environments for steel materials such as petroleum environments and seawater environments. Tar epoxy contains tar containing a large amount of aromatic ring compounds and is considered to be difficult to be decomposed, and since it has excellent properties to electrically shield steel materials from the external environment, tar epoxy resins are Most widely used for anticorrosion coatings.

  However, anti-corrosion of steel materials by coating film prevents the deterioration and peeling of the coating film because the steel material will be directly exposed to the external environment when the coating film deteriorates and peels, and the anti-corrosion action cannot be exhibited. That is extremely important.

  As a method for preventing the deterioration of the coating film, in the case of a resin whose coating film component is an organic substance, a resin that does not easily deteriorate in consideration of water resistance, chemical resistance, abrasion resistance, impact resistance, ultraviolet resistance, etc. It is necessary to select. Generally, epoxy resins are widely used for anticorrosion coatings because they are less likely to deteriorate than other resins such as urethane resins and phenol resins.

  Moreover, as a method for preventing the peeling of the coating film, for example, in order to improve the adhesion of the coating film to the base material, the peeling is prevented by using an undercoat paint called a primer. .

  In addition, when a steel material whose surface is coated with a paint film, such as a line pipe, is catalyzed, there is a phenomenon called cathodic detachment in which the paint film peels off if there is a defect in the paint film. Are known.

Report FHWA-RD-01-156, September 2001. National Energy Technology Laboratory, DE-FC26-01NT41158 Corrosion costs in Japan (Corrosion and Corrosion Protection Association, Japan Rust Prevention Technology Association) (1997)

  As described above, epoxy resins have been widely used as coatings for preventing corrosion of steel materials in severe corrosive environments such as petroleum environments. However, there are the following problems in preventing the corrosion of steel materials by the epoxy resin coating.

  First of all, not only epoxy resin but also one of the issues that apply to the entire coating film, if the coating film has a defective part, the base steel material is exposed, so the problem of unexpected severe corrosion at the coating film defective part There is. Film defects are caused by physical contact with the coating film, coating film scratches due to collisions, deformation of steel materials, temperature changes, deterioration of the coating film in corrosive environments, etc. It is not easy to detect. Therefore, when the steel material is anticorrosive with the coating film, there is a problem that unexpected corrosion of the steel material occurs.

  In order to prevent the deterioration of the coating film, there is a problem that costs are required for the maintenance of the coating film such as periodic inspection and top coating. At present, the cause of the deterioration mechanism of the coating film is hardly known.

  Furthermore, the tar epoxy resin contains a large amount of polycyclic aromatic compounds harmful to the contained tar, and the use of a large amount of the tar epoxy resin should be avoided from the viewpoint of environmental impact. Moreover, also about epoxy resins other than a tar epoxy resin, after using as a coating film, there also exists a subject used as an environmental impact factor as a waste material. It is preferable that the coating film be used in as small a quantity as possible from the viewpoints of cost and environmental load.

  When the present inventors coexist with methanogenic bacteria and sulfate-reducing bacteria, not only severe corrosion of the steel material occurs in the coating film defect portion of the epoxy resin such as tar epoxy, but also deterioration of the coating film itself occurs. It has been found that a phenomenon occurs in which the coating film peels and falls off. As the coating film deteriorates and peels off and drops off, not only the coating film defects, but also the steel material under the coating film corrodes vigorously due to the corrosive action caused by the coexistence of methane-producing bacteria and sulfate-reducing bacteria. I found out.

  In the conventional prevention of coating film deterioration, water resistance, chemical resistance, abrasion resistance, impact resistance, UV resistance, etc. are taken into consideration, and these are excellent epoxy resins having a property that is not easily deteriorated, particularly tar epoxy resins. Has been used.

  In addition, there are methods for preventing the peeling of the coating film, such as the use of a primer that enhances the adhesion to the base material.

  However, none of these methods are intended for coating film deterioration or peeling due to microbial action, or corrosion of steel materials.

  In the present invention, in the environment where the surface of the steel material in which a part or the whole of the surface is covered with an epoxy resin coating is in contact with a water-containing liquid containing both methanogens and sulfate-reducing bacteria, the quality of the liquid By providing control, it is possible to provide an effective prevention method against coating film deterioration and steel corrosion caused by coexistence of methanogens and sulfate-reducing bacteria.

As a result of diligent studies to solve the above-mentioned problems, methane generation is achieved by managing the water quality of the liquid that comes into contact with the surface of the steel material covered with an epoxy resin coating over part or all of the surface as follows. The present inventors have succeeded in establishing a method for preventing coating film deterioration and steel corrosion due to the coexistence of bacteria and sulfate-reducing bacteria, thereby completing the present invention. The gist of the present invention is the following (1) to ( 6 ).
(1) The steel material when the surface of the steel material, which is partially or entirely covered with an epoxy resin coating, is in contact with a water-containing liquid containing both methanogens and sulfate-reducing bacteria. A coating film deterioration prevention and corrosion prevention method of
In the water-containing liquid in contact with the surface,
(1) The dissolved oxygen concentration is 1 mg / L or more.
(2) The oxidation-reduction potential is -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or more.
(3) The pH is set to 9.5 or more and 12 or less,
(4) The chloride ion concentration is 0 mg / L or more and 10 mg / L or less.
(5) The bicarbonate ion concentration is 0 mg / L or more and 10 mg / L or less.
(6) When the temperature is higher than 15 ° C and lower than 50 ° C, the temperature is set to 0 ° C to 15 ° C or 50 ° C to 70 ° C.
One or two or more means selected from the group of (1) to (6) are performed, and a method for preventing coating film deterioration and corrosion of a steel material is provided.
(2) In advance, measure at least one of dissolved oxygen concentration, redox potential, pH, chlorine ion concentration, bicarbonate ion concentration, temperature of the water-containing liquid,
(1) When the dissolved oxygen concentration is in the range of less than 1 mg / L, the dissolved oxygen concentration is 1 mg / L or more.
(2) When the oxidation-reduction potential is in the range of less than -100 mV (saturated potassium chloride / silver silver chloride electrode standard), the oxidation-reduction potential is set to -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or more.
(3) When the pH is in the range of less than 9.5, the pH is set to 9.5 or more and 12 or less.
(4) When the chlorine ion concentration is in the range of more than 10 mg / L, the chlorine ion concentration is 0 mg / L or more and 10 mg / L or less.
(5) When the bicarbonate ion concentration is in the range of more than 10 mg / L, the bicarbonate ion concentration is 0 mg / L or more and 10 mg / L or less.
(6) When the temperature is in the range of more than 15 ° C and less than 50 ° C, the temperature is set to 0 ° C to 15 ° C or 50 ° C to 70 ° C.
(1) A method for preventing deterioration and corrosion prevention of a steel material, comprising executing one or more means selected from the group (1) to (6).
(3) The method for preventing coating film deterioration and corrosion of the steel material according to (1) or (2), wherein the epoxy resin is a tar epoxy resin.
( 4 ) Any one of (1) to (3), wherein the methanogen is Methanococcus (Methanococcalae), Methanococcus mariparidis belonging to the family Methanococceae Methods for preventing coating material deterioration and corrosion of steel materials.
( 5 ) The Methanococcus (Methanococcales) Methanococceae family Methanococcus maripaldis is a microorganism identified by the accession number NITE BP-252 ( four ) For preventing deterioration and corrosion of steel materials.
( 6 ) The iron or steel material according to any one of (1) to (5 ), wherein the sulfate-reducing bacterium is a microorganism belonging to the family Desulfobibrionales> Desulfobibrionaceae Coating film prevention and corrosion prevention methods.

  According to the present invention, in an environment in which the surface of a steel material whose surface is partially or entirely covered with an epoxy resin coating is in contact with a water-containing liquid containing both methanogens and sulfate-reducing bacteria, the quality of the liquid It is possible to prevent coating film deterioration and corrosion of steel materials caused by the coexistence of methanogens and sulfate-reducing bacteria.

  First, steel materials targeted by the present invention will be described.

  In the present invention, the steel material means pure iron, carbon steel, and alloy steel containing iron as a main component. An alloy steel is also called a low alloy steel if the total amount of alloy elements other than iron and carbon is 5 mass% or less, a medium alloy steel if it is 5 to 10 mass%, or a high alloy steel if it is 10 mass% or more. Examples of alloy steel include hot tool steel, cold tool steel, high speed tool steel, heat resistant steel, high tensile steel, martensitic stainless steel, silicon steel, chrome steel, chrome molybdenum steel, nickel chrome steel, There are nickel chrome molybdenum steel and manganese molybdenum steel.

  The steel material that is the subject of the present invention is one in which part or all of the surface of the steel material is covered with an epoxy resin. In particular, when the present invention is applied to a steel material covered with a tar epoxy resin that is widely spread among epoxy resins, the effect is remarkable.

  Next, a description will be given of a water-containing liquid in contact with a steel material in which part or all of the surface is covered with an epoxy resin. This water-containing liquid means not only water and aqueous solutions, but also all liquids containing water. For example, in oil-related facilities, seawater, oil well irrigation, and crude oil containing emulsion water are also target water-containing liquids. If the steel material whose surface is covered with an epoxy coating film is immersed in this water-containing liquid, or if the steel tube has an inner surface whose surface is covered with an epoxy resin, the water-containing liquid is Even when it is contained, it is an aspect of a water-containing liquid in contact with a steel material in which a part or all of the surface targeted by the present invention is covered with a coating film.

The present invention provides an anticorrosion method for coexisting methanogens and sulfate-reducing bacteria. Therefore, a description will be given of methanogens and sulfate-reducing bacteria that exist in a water-containing liquid in contact with a steel material whose surface is partly or entirely covered with a coating film and may cause corrosion.
First, regarding methanogens, methanogens are representative anaerobic microorganisms that live in any anaerobic environment along with sulfate-reducing bacteria. Of these, the cause of corrosion of steel materials in particular is that iron is used as an electron donor, and carbon dioxide or dissolved carbon dioxide, carbonic acid, hydrogencarbonate ions, carbonate ions and their salts are carbon. It is a methanogen that can be used as a source.

As a simple method for confirming the presence of corrosive methanogens in a water-containing liquid in contact with a steel material whose surface is partly or entirely covered with a coating film, for example, the following method is available. A part of the water-containing liquid in contact with the steel material part or all of the surface of which is covered with a coating is collected, and in addition to the iron carbonate medium shown in Table 1, a gas mixture of nitrogen and carbon dioxide ( Under anaerobic conditions filled with N ₂ (80%) + CO ₂ (20%)), if iron corrosion occurs, or if methane is detected in the gas phase, the corrosive methanogenic bacteria will become liquid It can be confirmed that it is included. In addition, the method using the medium shown in Table 1 is merely an example, and in this other method, iron is used as an electron donor, and dissolved carbon dioxide or carbonic acid, hydrogencarbonate ion, carbonate ion, and salts thereof are used. Of course, it does not matter if a methanogenic bacterium that can be cultured using any of them as a carbon source is confirmed.

  In this case, the meaning of iron as an electron donor means that, in addition to the case where iron itself is used as an electron donor for methanogens, hydrogen atoms and hydrogen molecules generated in the cathode reaction when iron corrodes are converted into electrons. This includes cases where methanogens are used as donors. In this way, the presence of iron corrosive methanogens can be confirmed. In addition to the above, as a method for confirming the methanogen, for example, a method such as PCR (Polymerase Chain Reaction) or FISH (Fluorescence in situ hybridization) using a characteristic base sequence of DNA or RNA possessed by the methanogen It is also possible to confirm the existence.

  Examples of methanogens that corrode steel materials include methanogens belonging to the family Methanococcales> Methanococceae. In particular, Methanococcus maripaludis, which is a methanogen belonging to the family Methanococcasae, has a strong corrosiveness to steel materials.

Methanococcus malparidis KA1 strain (Methanococcus maripaludis KA1) and Methanococcus maripaldisis OS7 strain (Methanococcus maripaldisis OS7) identified by the accession number NITE BP-252 Is isolated) is a strong corrosive steel material .

  As for sulfate-reducing bacteria, sulfate-reducing bacteria produce hydrogen sulfide ions or sulfide ions by a sulfate reduction reaction. When hydrogen sulfide ions or sulfide ions are generated by sulfate-reducing bacteria, the redox potential of the liquid decreases and the dissolved oxygen concentration also decreases. Therefore, when sulfate-reducing bacteria coexist with methanogens, a suitable environment is formed for methanogens of anaerobic microorganisms that prefer a low redox potential, and the corrosion of steel materials by methanogens is promoted.

  A sulfate-reducing bacterium coexisting with a methane-producing bacterium produces hydrogen sulfide ions or sulfide ions by a sulfate reduction reaction. Therefore, any sulfate-reducing bacterium may be used. However, corrosion by methanogens in the presence of sulfate-reducing bacteria, which has the property that iron can be used as an electron donor, and dissolved carbon dioxide, hydrogen carbonate ions, carbonate ions and any of these salts as carbon sources. Becomes more intense.

  Examples of sulfate reduction having such properties include sulfate-reducing bacteria belonging to the family of Desulfobibrionales, Desulfobibrionaceae. In particular, the MIC5-15 strain (isolated from the NEDO project “Investigation on environmental safety measures of petroleum using microorganisms”) belonging to the family of Desulfobrionionae, Desulfovibrioaceae is isolated from methane-producing bacteria. Coexistence with steel causes severe corrosion of steel materials. Of course, other sulfate-reducing bacteria may be used.

  As a method for confirming the presence of sulfate-reducing bacteria in a liquid in contact with a steel material whose surface is partly or entirely covered with a coating film, for example, using sulfate ions as a substrate, and using sulfate-reducing bacteria under anaerobic conditions The presence can be confirmed by detecting hydrogen sulfide ions and sulfide ions generated by sulfate reduction reaction. In addition, for example, using a characteristic base sequence of DNA or RNA possessed by sulfate-reducing bacteria, it is also possible to confirm the presence by a method such as PCR (Polymerase Chain Reaction) or FISH (Fluorescence in situ hybridization). is there.

  In addition, although it is about the state where a methanogen and a sulfate reducing bacterium coexist, it means that both a methanogen and a sulfate reduction exist in the same water-containing liquid. When methanogens and sulfate-reducing bacteria coexist, it is the methanogen that is the main cause of corrosion. This can be seen from the fact that the main component of the corrosion product in the case where the methanogen and the sulfate-reducing bacterium coexist is iron carbonate, similar to the corrosion caused by the methanogen alone. Iron sulfide, which is a corrosion product of sulfate-reducing bacteria, is slightly detected compared to iron carbonate. Therefore, it is important to suppress the corrosive action of a methanogen that has a strong corrosive action even when it is alone due to the coexistence of the methanogen and sulfate-reducing bacteria.

  Examples of environments where methanogens and sulfate-reducing bacteria coexist include water and sludge accumulated in the lower part of oil tanks, water and sludge accumulated in the lower part of cargo oil pipes, sea bottom mud, and nearby anoxic oxygen There is an environment such as seawater and sludge accumulated in the lower part of the ballast tank that stores seawater and ship's seawater.

  Next, in the present invention, the properties of the water-containing liquid in contact with the steel material whose surface is partially or entirely covered with a coating film will be described.

  In crude oil and the like, brine water, which is an emulsion-like water contained in crude oil, often contains high-concentration chlorine ions, like seawater. In addition, many oil well environments have high concentrations of carbon dioxide. Further, in a tank or the like for storing crude oil, combustion exhaust gas containing a high concentration of carbon dioxide is often used as an inert gas for explosion prevention. Furthermore, in crude oil obtained by seawater injection, not only high-concentration chlorine ions but also sulfate ions are contained in the brine contained in the crude oil as an emulsion.

  The present inventors have found that a methanogen alone causes carbonic acid corrosion, but when the methanogen and sulfate-reducing bacteria coexist, a more severe carbonic acid corrosion occurs. The pH of seawater and brine is about pH 7 to 8, which is a neutral pH suitable for the habitat of methanogens and sulfate-reducing bacteria. Furthermore, the water present in the form of an emulsion in crude oil has a higher specific gravity than the oil, so that when the crude oil or petroleum is left standing, the water accumulates below. Such water has a thick layer of crude oil or oil at the top, and oxygen is consumed by microorganisms that break down the organic matter of crude oil and petroleum. It is considered that the anaerobic condition is almost absent. Carbon dioxide is supplied not only from oil well environment contained in crude oil but also from decomposition of organic matter by microorganisms as well as inert gas.

  Therefore, when the bottom of a tank, a cargo oil pipe, or the like is made of a steel material, the chlorine ion concentration is high in an anaerobic environment with almost no oxygen, and in some cases, the sulfate ion concentration is high. It must exist in contact with steel materials under the presence of carbon dioxide, and it must be equipped with conditions that are severely subject to carbonic corrosion due to the coexistence of iron-causing methanogens or iron-causing methanogens and sulfate-reducing bacteria. Become.

  Therefore, even for tanks and cargo pipes used for crude oil and oil storage, etc., iron corrosion can be controlled by adjusting the properties of water existing in contact with the surface of the steel material that accumulates under the oil layer as follows. It is possible to prevent coating film deterioration and corrosion of iron and steel materials due to methane-forming bacteria and sulfate-reducing bacteria.

  In addition, it is about the measurement of the water quality of emulsion water contained in crude oil etc., but by collecting the crude oil etc. containing emulsion water, the water is collected below the oil layer of crude oil using the difference in specific gravity. In addition, water can be collected by centrifugation. The water collected in this way can be used for water quality measurement.

  (1) By setting the dissolved oxygen concentration of the liquid to 1 mg / L or more, it becomes possible to suppress the action of methanogenic bacteria and sulfate reducing bacteria that degrade the coating film and corrode the steel material. When the dissolved oxygen concentration is less than 1 mg / L, the action of methanogens and sulfate-reducing bacteria, which are anaerobic microorganisms, is activated. Therefore, by setting the dissolved oxygen concentration of the liquid to 1 mg / L or more, both prevention of coating film deterioration and prevention of corrosion of the steel material can be achieved. As a method of setting the dissolved oxygen concentration of the liquid to 1 mg / L or more, specifically, for example, a method of increasing the dissolved oxygen concentration by aeration of the liquid with air or oxygen gas, There are methods such as a method of increasing the dissolved oxygen concentration by adding water having an increased dissolved oxygen concentration to the liquid, and a method of increasing the dissolved oxygen concentration by adding an oxygen generator such as hydrogen peroxide to the liquid.

  Moreover, as a measuring method of the dissolved oxygen concentration of the liquid, there is a measuring method using an oxygen electrode.

  There is no particular upper limit on the dissolved oxygen concentration of the liquid. This is because, if the dissolved oxygen concentration is 1 mg / L or more, it is possible to suppress the action of methanogenic bacteria and sulfate reducing bacteria at any dissolved oxygen concentration. However, the higher the dissolved oxygen concentration, the more disadvantageous in terms of cost, such as the need to aerate more air and oxygen. Although an upper limit is not specifically limited, It is desirable to set it as below saturated oxygen concentration. For example, since the saturated dissolved oxygen concentration of water at 20 ° C. is about 9 mg / L, the upper limit is a low-cost dissolved oxygen concentration of 1 mg / L or more and 9 mg / L or less by air aeration or the like.

  (2) In addition, the redox potential of the liquid water is -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or more, so that an environment with a low redox potential is preferred. It is possible to suppress the deterioration of the coating film and the corrosive action of the steel material. When the oxidation-reduction potential is less than −100 mV (saturated potassium chloride / silver-silver chloride electrode standard), the oxidation-reduction potential is lowered by sulfides produced by sulfate-reducing bacteria, and methanogenic and sulfate-reducing bacteria are preferred. There is a possibility of redox potential. Therefore, by setting the redox potential of the liquid water to -100 mV (saturated potassium chloride / silver-silver chloride electrode standard) or more, coating film deterioration and steel corrosion due to coexistence of methanogen and sulfate-reducing bacteria are prevented. It becomes possible to do. As a specific method for setting the oxidation-reduction potential to -100 mV (saturated potassium chloride / silver-silver chloride electrode standard) or more, for example, a method of raising the oxidation-reduction potential by aeration of the liquid with air or oxygen gas, There are methods such as a method of increasing the oxidation-reduction potential by adding an oxidizing agent such as nitric acid or hydrogen peroxide to the liquid.

  As a method for measuring the oxidation-reduction potential of the liquid, there is a method of measuring the oxidation-reduction potential measurement using a gold electrode or a platinum electrode. In the present invention, the oxidation-reduction potential is described as a potential value when a saturated potassium chloride-silver chloride electrode is used as a reference electrode. However, when the reference electrode is different, it is of course a converted oxidation-reduction potential value.

  There is no particular upper limit on the redox potential of the liquid. This is because, if the redox potential is -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or higher, it is possible to suppress the action of methanogenic and sulfate reducing bacteria at any redox potential. . However, the higher the redox potential, the more disadvantageous in terms of cost, such as aeration of air and oxygen, or the addition of more oxidizing agent. The upper limit of the redox potential in water is the oxygen generation potential. Since the oxygen generation potential is about +1400 mV (saturated potassium chloride / silver silver chloride electrode standard), the upper limit of the oxidation-reduction potential is +1400 mV (saturated potassium chloride / silver silver chloride electrode standard). Since the potential is disadvantageous in terms of cost, it is disadvantageous in terms of cost to raise the redox potential excessively.

  (3) Also, by controlling the pH of the liquid water quality to 9.5 or more and 12 or less, the growth of methanogens and sulfate-reducing bacteria can be suppressed, and the coating film deterioration and the corrosive action of the steel material can be suppressed. Is possible. When the pH is less than 5, it becomes acidic, so that the cathode reaction for generating hydrogen molecules from hydrogen ions is promoted, and the pH conditions are such that iron corrosion is promoted without depending on the action of microorganisms. When the pH is 5 or more and less than 9.5, both the methanogenic bacteria and the sulfate-reducing bacteria are likely to grow, which may promote coating film deterioration and corrosion of the steel material. Therefore, the pH of the water quality of the liquid is desirably 9.5 or higher.

  On the other hand, when the pH exceeds 12, iron forms a complex and is easily dissolved. Moreover, it is not preferable to increase the pH excessively because the cost of the alkali chemicals is also increased. Therefore, the pH is preferably 9.5 or more and 12 or less.

  As a specific method for adjusting the pH to 9.5 or more and 12 or less, water in a corrosive environment such as brine contained in seawater or petroleum generally has a pH of less than 9.5. There is a method of increasing pH by adding water containing an alkali agent such as sodium, calcium hydroxide or magnesium hydroxide.

  In addition, as a measuring method of the pH of the liquid, there are a method of directly measuring pH with a pH electrode, a method of measuring pH by colorimetry using a pH test paper, and the like.

  (4) Further, by setting the chlorine ion concentration of the water quality of the liquid to 0 mg / L or more and 10 mg / L or less, in the corrosion of steel materials due to the coexistence of methane-producing bacteria or methane-producing bacteria and sulfate-reducing bacteria, By suppressing the inflow and concentration of chlorine ions to the corrosion site that promotes anode dissolution, it is possible to suppress both coating film deterioration and corrosion of the steel material. In particular, seawater has a chlorine ion concentration of about 19000 mg / L, and the chlorine ion concentration of brine contained in crude oil and the like is also very high. Corrosion by methanogens or methane bacteria and sulfate-reducing bacteria is promoted at high chloride ion concentrations, like seawater and brine, so reducing the chloride ion concentration of the liquid is extremely important for corrosion protection. .

  As for the lower limit of the chlorine ion concentration, the lower the chlorine ion concentration is, the more effective it can be to suppress the corrosion because the chlorine ions can be prevented from concentrating at the bottom of the corrosion hole where corrosion progresses. Therefore, the chlorine ion concentration is preferably 0 mg / L or more and 10 mg / L or less.

  As a specific method for reducing the chlorine ion concentration of the liquid to 10 mg / L or less, for example, the chlorine ion concentration of the liquid is reduced by adding fresh water having no chlorine ion or low chlorine ion concentration to the liquid. There are methods such as a method of lowering, a method of adding an anion exchange resin to the liquid and removing chlorine ions to lower the chlorine ion concentration.

  In addition, it is about the measuring method of the chlorine ion concentration of the said liquid, For example, using the method which samples the said liquid and measures the density | concentration of chlorine ion by the ion chromatography method, and the sensor which measures a chlorine ion concentration There are methods such as a method for measuring the concentration of chlorine ions in the liquid.

  (5) Further, by setting the hydrogen carbonate ion concentration of the liquid to 0 mg / L or more and 10 mg / L or less, it is possible to suppress the growth of methanogens using these as carbon sources, and the methanogens and sulfates It is possible to prevent both the deterioration of the coating film due to the coexistence of reducing bacteria and the corrosion of the steel material. The iron corrosive methanogen that is the subject of the present invention grows particularly well in the range of pH 6 to 9.

  The methanogen uses carbon dioxide as a carbon source and electron acceptor. More precisely, the methanogen uses dissolved carbon dioxide dissolved in water. Dissolved carbon dioxide takes a chemical form such as carbonic acid, hydrogen carbonate ion, or carbonate ion depending on pH. Corrosion due to methanogens becomes a problem in the pH range where methanogens grow well. That is, corrosion by methanogenic bacteria becomes a problem at pH 6 or more and pH 9 or less. In this pH range, dissolved carbon dioxide exists mainly as bicarbonate ions. Although a method for measuring the total carbonic acid concentration has been reported as the total concentration of dissolved carbon dioxide, that is, the concentration of dissolved carbon dioxide gas, carbonic acid, hydrogencarbonate ions, and carbonate ions, the measuring method is not easy.

  Therefore, in the present invention, in order to prevent carbonic acid corrosion, focusing on the concentration of bicarbonate ion, which is a major chemical form of dissolved carbon dioxide in the pH range where corrosion by methanogens occurs and which can be measured easily. The conditions of were set. As a method for measuring the concentration of hydrogen carbonate ions, for example, there is a method shown in JIS.K0101.25.2.

  As a specific method for setting the bicarbonate ion concentration to 10 mg / L or less, for example, an inert gas that does not contain carbon dioxide and does not act on corrosion or coating film deterioration, such as nitrogen gas, is used. A method of reducing the hydrogen carbonate ion concentration of the liquid by adding a calcium hydroxide to the liquid and immobilizing the hydrogen carbonate ions as calcium carbonate There are methods.

  As a method for measuring the bicarbonate ion concentration of the liquid, for example, there is a method of measuring the bicarbonate ion concentration of the liquid by sampling the liquid and using the method shown in the JIS K0101.25.2. is there.

  As for the lower limit of bicarbonate ions, the lower the bicarbonate ion concentration, the more difficult it is to use bicarbonate ions as a carbon source or as an electron acceptor for methanogens. It is possible to suppress. Moreover, the production | generation of the iron carbonate which is a corrosion product can also be suppressed. Therefore, the bicarbonate ion concentration is preferably 0 mg / L or more and 10 mg / L or less.

  (6) In addition, the temperature of the liquid is 0 ° C. or higher and 15 ° C. or lower, or 50 ° C. or higher and 70 ° C. or lower, so that both the growth of methanogens and sulfate-reducing bacteria is suppressed. It is possible to suppress both corrosion of materials. When the temperature is higher than 15 ° C and lower than 50 ° C, the temperature is suitable for the growth of iron-corrosive methanogens and sulfate-reducing bacteria. Therefore, by setting the temperature to 15 ° C. or lower or 50 ° C. or higher, it is possible to suppress the growth of iron corrosive methanogens and sulfate-reducing bacteria.

  Further, at a high temperature exceeding 70 ° C., there is a limit to the heat resistance of the coating film for an epoxy coating film such as a tar epoxy coating film, and there is a risk of partial decomposition. Moreover, since abiotic carbonic acid corrosion tends to occur when the temperature exceeds 70 ° C., it is necessary to pay attention to a portion of the steel material not covered with the coating film. Moreover, if it is less than 0 degreeC, there exists a possibility that water may freeze. Therefore, the temperature of the liquid is preferably 0 ° C. or higher and 15 ° C. or lower, or 50 ° C. or higher and 70 ° C. or lower.

  As a specific method for setting the temperature of the liquid to 0 ° C. or higher and 15 ° C. or lower or 50 ° C. or higher and 70 ° C. or lower, for example, a heating device or a cooling device is inserted into the liquid to set the temperature of the liquid to a target value. There are a method, a method of adding water having different temperatures to the liquid, and setting the temperature of the liquid to a target value.

  As a method for measuring the temperature of the liquid, there are a method of measuring a temperature by putting a thermometer in the liquid, a method of measuring a temperature by putting a thermocouple in the liquid, and the like.

  In addition, prior to the execution of the coating film deterioration prevention and corrosion prevention methods, at least one of the dissolved oxygen concentration, redox potential, pH, chlorine ion concentration, bicarbonate ion concentration, and temperature of the water-containing liquid is required. When the dissolved oxygen concentration is in the range of less than 1 mg / L, the dissolved oxygen concentration is set to 1 mg / L or more and the redox potential is less than −100 mV (saturated potassium chloride / silver silver chloride electrode standard). When it is in the range, the oxidation-reduction potential is set to -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or more, and when the pH is in the range of less than 9.5, the pH is set to 9.5 or more and 12 or less. When the ion concentration is in the range of more than 10 mg / L, the chlorine ion concentration is from 0 mg / L to 10 mg / L, and when the bicarbonate ion concentration is in the range of more than 10 mg / L, The concentration is 0 mg / L or more and 10 mg / L or less, or the temperature is 0 ° C. or more and 15 ° C. or less or 50 ° C. or more and 70 ° C. or less when the temperature is in the range of more than 15 ° C. and less than 50 ° C. It is preferable to execute 1 type (s) or 2 or more types.

  The reason for this is that if any of the conditions is already within the conditions for preventing coating deterioration and corrosion, it may not be necessary to take countermeasures, and multiple or all of the above conditions may be measured in advance. For example, among the conditions, by operating with priority the one closest to the coating film deterioration prevention and corrosion prevention conditions, it is possible to respond quickly and inexpensively.

  In addition, it is about the case where it is going to adjust the water quality of the emulsion-like water contained in crude oil etc. For example, in the case of a tank for storing crude oil etc. or a steel pipe to be transported, the emulsion originally contained in the crude oil at the bottom Brine or the like having a high chlorine ion concentration derived from water-like water accumulates below the oil reservoir and corrodes the steel material under the action of methanogens and sulfate-reducing bacteria that live in the water. Therefore, the water quality of the liquid in contact with the surface of the steel material can be adjusted to the water quality of the present invention by, for example, newly adding water to these bottom parts, adding a chemical, aerating the bottom part with air, etc. It becomes possible.

  As a method for measuring the water quality of the emulsion water contained in the crude oil, for example, the crude oil containing the emulsion water is collected and left to stand or centrifuged, so that the emulsion water is added to the lower part of the oil layer. Can be collected. When the water quality item is directly measured with an electrode or a sensor, this water may be used as it is for measurement of each water quality item. It is also possible to collect this water using a pipette or the like and use it for measuring each water quality item.

  In addition, among the conditions of dissolved oxygen concentration, redox potential, pH, chlorine ion concentration, bicarbonate ion concentration, and temperature of the water-containing liquid in contact with the steel material covered with a coating film, part or all of the surface described above If any one or more of these can be satisfied, it is possible to suppress coating film deterioration and corrosion of the steel material due to coexisting methanogens and sulfate-reducing bacteria.

  However, more preferably, the methanogenic and sulfate-reducing bacteria are used so as to satisfy a plurality of conditions among the dissolved oxygen concentration, redox potential, pH, chloride ion concentration, bicarbonate ion concentration, and temperature. It is desirable to adjust the water quality of the water-containing liquid contained together. For example, the chlorine ion concentration of brine or seawater is a high concentration exceeding 10,000 mg / L. If a very small amount of brackish water or seawater is in contact with the bottom surface of the steel material at the bottom of the crude oil or petroleum layer, dilute with a large amount of fresh water to reduce the chlorine ion concentration to 10 mg / L or less. It is possible to lower it.

  However, when the amount of brine or seawater is large, it is necessary to dilute with a very large amount of fresh water, and it is feasible to reduce the chlorine ion concentration to 10 mg / L or less, but more water is used in crude oil and oil. Can be a factor that degrades the properties of crude oil and petroleum. In such a case, the pH of water in contact with the surface of the steel material is set to 9.5 or more and 12 or less, for example, by satisfying another condition other than the chlorine ion concentration shown in the present invention, the methanogen It is possible to prevent coating film deterioration and corrosion of steel materials by sulfate-reducing bacteria.

  As described above, both the methanogenic and sulfate-reducing bacteria are used so as to satisfy multiple conditions among the dissolved oxygen concentration, redox potential, pH, chloride ion concentration, bicarbonate ion concentration, and temperature. Although it is more desirable to adjust the water quality of the contained water-containing liquid, pH, bicarbonate ion concentration, and chloride ion concentration are particularly effective in preventing coating film deterioration and corrosion. However, the bicarbonate ion concentration has an effect of dissolving carbon dioxide in the air in water.

  For example, it is reported that the bicarbonate ion concentration in river water in Japan is about 30 mg / L, and even if diluted with river water, the bicarbonate ion concentration is adjusted to 0 mg / L or more and 10 mg / L or less. It is difficult. In addition, there is an effect that carbon dioxide is discharged and dissolved in water when microorganisms breathe oxygen near the surface of the steel material. Thus, there is a problem that it is difficult to adjust to a desired bicarbonate ion concentration. Therefore, by satisfying the conditions of pH and chloride ion concentration, the pH of the liquid is 9.5 or more and 12 or less, and the chloride ion concentration is 0 mg / L or more and 10 mg / L or less. It is possible to prevent coating film deterioration and corrosion of steel materials due to the bacteria and sulfate-reducing bacteria.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the technical scope of the present invention is not limited to these examples.
{Example 1} Evaluation of influence of dissolved oxygen concentration Artificial seawater having the composition shown in Table 1 was used as a corrosion test solution. A corrosion test solution which was filtered through a 0.2 μm pore size filter and sterilized by filtration was prepared. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS Is added to fill the container, and the dissolved oxygen concentration of the artificial seawater is reduced to 0.1, 0. 0 by degassing with N ₂ : CO ₂ = 4: 1 gas. 5, 1, 1.5, 2 mg / L. The test piece of FIG. 1 is a surface coated with a tar epoxy resin, including the side surface and the back surface, except that a non-coating portion is provided in a circular region having a diameter of 2 mm on the surface of a pure iron plate. A culture solution of methanogen and sulfate-reducing bacteria that can be cultured using iron as an electron donor and bicarbonate ions as a carbon source, each cultured in a culture solution having the composition shown in Table 2, was added in an amount of 0.5 mL. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL. A corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks in a sealed state so that no gas phase remained above the artificial seawater. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in FIG. The dissolved oxygen concentration was 1 mg / L or more, and iron corrosion was suppressed. Moreover, the surface of the test piece was observed, and the presence or absence of exposure of pure iron by peeling of the coating film was shown in Table 3. Corresponding to the state of corrosion of iron, when the dissolved oxygen concentration was less than 1 mg / L, the exposure of pure iron was observed by peeling of the coating film. However, when the dissolved oxygen concentration was 1 mg / L or more, peeling of the coating film was observed. No exposure of pure iron was observed.

{Example 2} Evaluation of influence of oxidation-reduction potential Artificial seawater having the composition shown in Table 1 was filtered through a filter having a pore size of 0.2 μm to prepare a corrosion test solution sterilized by filtration. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS Add artificial water that has been sterilized by filtration to fill the container, and oxidize this artificial seawater by degassing with N ₂ : CO ₂ = 4: 1 gas and adding sodium sulfide as a reducing agent. The reduction potential was -300, -200, -100, 0, +100 mV (saturated potassium chloride / silver silver chloride electrode standard).

A culture solution of methanogen and sulfate-reducing bacteria that can be cultured using iron as an electron donor and bicarbonate ions as a carbon source, each cultured in a culture solution having the composition shown in Table 2, was added in an amount of 0.5 mL. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL. A corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks in a sealed state so that no gas phase remained above the artificial seawater. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in FIG. When the oxidation-reduction potential was -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or more, corrosion of iron was suppressed. Moreover, the surface of the test piece was observed, and the presence or absence of exposure of pure iron by peeling of the coating film was shown in Table 4. Corresponding to the state of iron corrosion, when the redox potential is less than -100 mV (saturated potassium chloride / silver silver chloride electrode standard), the exposure of pure iron was observed by peeling of the coating film, but the dissolved oxygen concentration was Above -100 mV (saturated potassium chloride / silver silver chloride electrode standard), no exposure of pure iron due to peeling of the coating film was observed.

  The redox potential is often linked with the dissolved oxygen concentration, but may not always be linked. For example, even if there is no dissolved oxygen, if an oxidizing agent such as nitrate ion is present, the oxidation-reduction potential shows a high value. Therefore, in the present invention, the oxidation-reduction potential is also defined with respect to the coating film deterioration and the corrosion prevention method.

{Example 3} Evaluation of influence of pH Based on artificial seawater having the composition shown in Table 5, the pH was 5, 6, 7, 8, 9, 9.5, using diluted hydrochloric acid and diluted sodium hydroxide solution. Ten artificial seawaters were prepared. Artificial seawater with different pH was prepared by filtration through a 0.2 μm pore size filter and sterilized by filtration. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS 20 mL of artificial seawater with different pH and sterilized by filtration is added, degassed with N ₂ : CO ₂ = 4: 1 gas, and diluted hydrochloric acid and diluted sodium hydroxide solution are used to adjust the pH. Was adjusted to the set value, and the dissolved oxygen concentration was less than 0.1 mg / L, confirming that anaerobic conditions were achieved. The upper space in the container was filled with N ₂ : CO ₂ = 4: 1 gas and sealed.

A culture solution of methanogen and sulfate-reducing bacteria that can be cultured using iron as an electron donor and bicarbonate ions as a carbon source, each cultured in a culture solution having the composition shown in Table 2, was added in an amount of 0.5 mL. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL. The corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in FIG. When the pH was 9.5 or higher, iron corrosion was suppressed. Further, the surface of the test piece was observed, and the presence or absence of exposure of pure iron due to peeling of the coating film was shown in Table 6. Corresponding to the state of corrosion of iron, when the pH was less than 9.5, the exposure of pure iron was observed by peeling of the coating film. However, when the pH was 9.5 or more, the pure iron due to peeling of the coating film was observed. No exposure was observed.

  Usually, when used as artificial seawater, it is adjusted to pH 8.2 with NaOH aqueous solution and adjusted to 1 L with pure water.

{Example 4} Evaluation of Influence of Chlorine Ion Concentration Artificial seawater having the composition shown in Table 5 was prepared by changing the concentration of sodium chloride, and the chloride ion concentration was 1, 10, 50, 100, 500, 1000, 5000, 10,000. A corrosion test solution of 20000 mg / L was prepared. Corrosion test solutions with different chlorine ion concentrations prepared by filtration through a 0.2 μm pore size filter and sterilized by filtration were prepared. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS 20 mL of corrosion test solution with different chloride ion concentrations added, and degassed with N ₂ : CO ₂ = 4: 1 gas, so that the dissolved oxygen concentration becomes less than 0.1 mg / L, I confirmed that it became an anaerobic condition. The upper space in the container was filled with N ₂ : CO ₂ = 4: 1 gas and sealed.

A culture solution of methanogen and sulfate-reducing bacteria that can be cultured using iron as an electron donor and bicarbonate ions as a carbon source, each cultured in a culture solution having the composition shown in Table 2, was added in an amount of 0.5 mL. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL. The corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in FIG. When the chlorine ion concentration was 10 mg / L or less, corrosion of iron was suppressed. Moreover, the surface of the test piece was observed, and the presence or absence of exposure of pure iron by peeling of the coating film was shown in Table 7. Corresponding to the state of iron corrosion, exposure of pure iron due to peeling of the coating film was not observed at a chlorine ion concentration of 10 mg / L or less.

{Example 5} Evaluation of influence of hydrogen carbonate ion concentration Artificial seawater having the composition of Table 5 was prepared by changing the concentration of sodium hydrogen carbonate, and the hydrogen carbonate ion concentration was 0, 5, 10, 50, 100, 500 mg / A corrosion test solution of L was prepared. Corrosion test solutions with different bicarbonate ion concentrations were prepared by filtration through a 0.2 μm pore size filter and sterilization by filtration. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS A corrosion test solution with different hydrogen carbonate ion concentrations sterilized by filtration was degassed with N ₂ gas, and it was confirmed that the dissolved oxygen concentration was less than 0.1 mg / L and anaerobic conditions were achieved. The container was filled with the test solution and sealed. A culture solution of methanogen and sulfate-reducing bacteria that can be cultured using iron as an electron donor and bicarbonate ions as a carbon source, each cultured in a culture solution having the composition shown in Table 2, was added in an amount of 0.5 mL. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL. The corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in FIG. When the bicarbonate ion concentration was less than 10 mg / L, corrosion of iron was suppressed. Moreover, the surface of the test piece was observed, and Table 8 shows whether or not pure iron was exposed due to peeling of the coating film. Corresponding to the state of iron corrosion, exposure of pure iron due to peeling of the coating film was not observed at a bicarbonate ion concentration of 10 mg / L or less.

{Example 6} Evaluation of temperature influence Artificial seawater having the composition shown in Table 1 was prepared. Artificial seawater filtered and sterilized by filtration with a 0.2 μm pore size filter was prepared. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS Was added, 20 mL of filter-sterilized artificial seawater was added, and degassed with N ₂ : CO ₂ = 4: 1 gas, resulting in an anaerobic condition with a dissolved oxygen concentration of less than 0.1 mg / L. It was confirmed. The upper space in the container was filled with N ₂ : CO ₂ = 4: 1 gas and sealed.

A culture solution of methanogen and sulfate-reducing bacteria that can be cultured using iron as an electron donor and bicarbonate ions as a carbon source, each cultured in a culture solution having the composition shown in Table 2, was added in an amount of 0.5 mL. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL. Corrosion tests were conducted by standing at temperatures of 10, 15, 20, 25, 30, 35, 40, 50, and 60 ° C. for 2 weeks. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in FIG. When the temperature was 15 ° C. or lower or 50 ° C. or higher, corrosion of iron was suppressed. Moreover, the surface of the test piece was observed, and Table 9 shows whether or not pure iron was exposed due to peeling of the coating film. Corresponding to the state of corrosion of iron, exposure of pure iron due to peeling of the coating film was not observed at temperatures of 15 ° C. or lower and 50 ° C. or higher.

{Example 7} Corrosion test using crude oil Artificial seawater having a pH of 7, 9, 9.5 and 10 using diluted hydrochloric acid and diluted sodium hydroxide solution based on the artificial seawater having the composition shown in Table 5 Adjusted. Artificial seawater with different pH was prepared by filtration through a 0.2 μm pore size filter and sterilized by filtration.

A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS Add 10 mL of artificial seawater with different pH, deaerate with N ₂ : CO ₂ = 4: 1 gas, and use diluted hydrochloric acid and diluted sodium hydroxide solution to adjust the pH. It adjusted to the said setting value, and it was confirmed that the dissolved oxygen concentration became less than 0.1 mg / L and it became anaerobic conditions. Further, N ₂ was added the crude 10mL: CO ₂ = 4: 1 after the artificial seawater and crude oil were mixed and stirred by the gas, the upper space in the container N _2: CO ₂ = 4: satisfies 1 gas, sealed did. The corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks.

After a two-week corrosion test, a portion of the artificial seawater collected in the lower part of the oil reservoir is collected and added to the iron carbonate medium in Table 1 and the gas phase contains N ₂ : CO ₂ = 4: 1 gas. Corrosion of iron occurred under anaerobic conditions filled with methane, and methane was detected in the gas phase. Therefore, it was confirmed that the artificial seawater contained methanogens that cause corrosion. Moreover, since iron sulfide was generated, it was confirmed that sulfate-reducing bacteria were also contained in this artificial seawater.

  Since artificial seawater was prepared by filter sterilization, these methanogens and sulfate-reducing bacteria may be derived from emulsion water contained in crude oil.

  Moreover, in order to investigate the state of corrosion, the iron concentration of this artificial seawater was measured.

  The measurement result of iron concentration is shown in FIG. When the pH was 9.5 or higher, iron corrosion was suppressed. Further, the surface of the test piece was observed, and Table 10 shows whether pure iron was exposed due to peeling of the coating film. Corresponding to the state of corrosion of iron, when the pH was less than 9.5, the exposure of pure iron was observed by peeling of the coating film. However, when the pH was 9.5 or more, the pure iron due to peeling of the coating film was observed. No exposure was observed.

{Example 8} Prevention of coating film deterioration and corrosion by combination conditions of pH and chloride ion concentration Artificial seawater having the composition shown in Table 5 was prepared by changing the pH and sodium chloride concentrations, and the pH was 8, 9, 9 Corrosion test solutions having a concentration of 0.5, 10, and a chloride ion concentration of 0, 10, 100, 1000 mg / L were prepared. Corrosion test solutions with different pH and chloride ion concentration prepared by filtration through a 0.2 μm pore size filter and sterilized by filtration were prepared. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS 20 mL of corrosion test solutions with different pH and chloride ion concentration added, and degassed with N ₂ : CO ₂ = 4: 1 gas, and the dissolved oxygen concentration is less than 0.1 mg / L It was confirmed that it became an anaerobic condition. The upper space in the container was filled with N ₂ : CO ₂ = 4: 1 gas and sealed.

A culture solution of methanogen and sulfate-reducing bacteria that can be cultured using iron as an electron donor and bicarbonate ions as a carbon source, each cultured in a culture solution having the composition shown in Table 2, was added in an amount of 0.5 mL. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL. The corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in Table 11. When the pH was 9.5 or more and the chlorine ion concentration was 10 mg / L or less, corrosion of iron was more reliably suppressed. Moreover, the surface of the test piece was observed, and Table 12 shows whether or not pure iron was exposed due to peeling of the coating film. Corresponding to the state of iron corrosion, exposure of pure iron due to peeling of the coating film was not observed when the pH was 9.5 or more and the chlorine ion concentration was 10 mg / L or less.

{Example 9} Evaluation of corrosion effect by methanogenic bacteria alone and sulfate-reducing bacteria alone Artificial seawater having the composition shown in Table 1 was used as a corrosion test solution. A corrosion test solution which was filtered through a 0.2 μm pore size filter and sterilized by filtration was prepared. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a tar-epoxy resin coating film having defects in the coating film as shown in FIG. 1 at the bottom of a glass container with a volume of 50 mL for GC-MS Is added to fill the container, and the dissolved oxygen concentration of this artificial seawater is less than 0.1 mg / L by degassing with N ₂ : CO ₂ = 4: 1 gas. I made it. Methane-producing bacteria that can be cultured using iron as an electron donor and hydrogen carbonate ions as a carbon source, and sulfate-reducing bacteria in the culture solution cultured in the culture solution having the composition shown in Table 2 coexisting with methanogens and sulfate-reducing bacteria In the case of making methanogen alone, 0.5 mL was added for each of sulfate-reducing bacteria alone. The initial concentrations of the methanogen and sulfate-reducing bacteria were 1 × 10 ⁶ cells / mL, respectively. A corrosion test was carried out by allowing to stand at 37 ° C. for 2 weeks in a sealed state so that no gas phase remained above the artificial seawater. As a control, a corrosion test was also performed for the sterile case. Two weeks later, the iron concentration in the corrosion test solution was measured.

  The results are shown in FIG. In the case of sulfate-reducing bacteria alone and aseptic, iron corrosion hardly occurred. In addition, Table 13 shows the observation results of the presence or absence of peeling of the coating film. Only when the methanogen and sulfate-reducing bacteria coexist, the exposure of pure iron due to peeling of the coating film was observed. FIG. 10 shows the state of the coating film after the corrosion test when the methanogen and the sulfate-reducing bacterium coexist, when the methanogen alone, when the sulfate-reducing bacterium is alone, or when it is sterile. Shows the photograph.

{Example 10}
In a glass container with a capacity of 50 mL, under conditions where 20 mL of crude oil is present in the upper layer and 20 mL of seawater is present in the lower layer, the lower layer seawater is cultured with a culture solution having the composition shown in Table 2, and iron is used as the electron donor, and bicarbonate ions are used as the carbon source. As a culture solution of methanogen and sulfate-reducing bacteria that can be cultured as 0.5 mL each. The initial concentrations of the methanogen and sulfate-reducing bacteria were both 1 × 10 ⁶ cells / mL.

  The dissolved oxygen concentration of this lower layer seawater is 0.05 mg / L, the oxidation-reduction potential is -150 mV (saturated potassium chloride silver-silver chloride electrode standard), the pH is 8, the chlorine ion concentration is 19000 mg / L, and the bicarbonate ion concentration is 1800 mg. / L, temperature was 30 ° C.

As shown in FIG. 1, a pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a coating film of a tar epoxy resin having a defect in the coating film is placed on the bottom of the glass container in the lower seawater. The glass container was sealed in a state where N ₂ : CO ₂ = 4: 1 gas was filled in the upper gas phase, and the corrosion test was carried out by allowing to stand at 30 ° C. for 2 weeks. Two weeks later, the iron concentration of the lower seawater was measured and the state of the coating film was observed.

On the other hand, in the same manner as in the above test, a culture solution of methanogen and sulfate-reducing bacteria that can be cultured using lower layer seawater with the culture solution of Table 2 and iron as an electron donor and hydrogen carbonate ion as a carbon source. The added lower seawater has a dissolved oxygen concentration of 0.05 mg / L, a redox potential of -150 mV (saturated potassium chloride, silver and silver chloride electrode standard), a pH of 8, a chloride ion concentration of 19000 mg / L, and a bicarbonate ion concentration of After confirming that the temperature is 1800 mg / L and the temperature is 30 ° C., the aqueous film of filter sterilized sodium hydroxide is added to the lower layer seawater, so that the coating film is applied to the lower layer seawater having a pH of 9.5. A pure iron test piece (10 × 10 × 1 mm) whose surface is covered with a coating film of a tar epoxy resin having a defective portion is placed, and the upper gas phase is filled with N ₂ : CO ₂ = 4: 1 gas In the state of glass And sealed and carried out corrosion tests to stand for 2 weeks at 30 ° C.. Two weeks later, the iron concentration of the lower seawater was measured and the properties of the coating film were observed.

  The measurement result of the iron concentration of the lower seawater is shown in FIG. 11, and the observation result of the coating film properties is shown in Table 14. By changing the pH of the lower seawater containing both methanogenic and sulfate-reducing bacteria from 8 to 9.5, both iron corrosion and coating film deterioration could be suppressed.

It is a figure of the pure iron test piece which has a coating-film defect. It is a figure showing the influence of the dissolved oxygen concentration on the iron corrosion by a methanogen and a sulfate reducing bacterium. It is a figure showing the influence of the oxidation reduction potential which acts on the iron corrosion by a methanogenic bacterium and a sulfate reducing bacterium. It is a figure showing the influence of pH which acts on the iron corrosion by a methanogen and a sulfate reduction bacterium. It is a figure showing the influence of the chloride ion density | concentration on the iron corrosion by a methanogen and a sulfate reduction bacterium. It is a figure showing the influence of bicarbonate ion concentration on iron corrosion by methanogenic bacteria and sulfate-reducing bacteria. It is a figure showing the influence of the temperature which acts on the iron corrosion by a methanogen and a sulfate reducing bacterium. It is a figure showing the influence of pH which acts on the iron corrosion by crude oil. It is a figure showing the comparison of iron corrosion in the case of aseptic, sulfate-reducing bacteria alone, methanogen alone, and coexistence of methanogens and sulfate-reducing bacteria. It is the photograph which observed the state of the coating film after a corrosion test about methanogenic bacteria and a sulfate reducing bacterium coexisting, a methanogenic bacterium alone, a sulfate reducing bacterium alone, and aseptic. It is a figure which shows the measurement result of the iron concentration in lower layer seawater by the corrosion test at the time of changing pH of lower layer seawater.

Claims (6)

A coating film of the steel material when the surface of the steel material, which is partially or entirely covered with an epoxy resin coating, is in contact with a water-containing liquid containing both methanogens and sulfate-reducing bacteria A method for preventing deterioration and corrosion,
In the water-containing liquid in contact with the surface,
(1) The dissolved oxygen concentration is 1 mg / L or more.
(2) The oxidation-reduction potential is -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or more.
(3) The pH is set to 9.5 or more and 12 or less,
(4) The chloride ion concentration is 0 mg / L or more and 10 mg / L or less.
(5) The bicarbonate ion concentration is 0 mg / L or more and 10 mg / L or less.
(6) When the temperature is higher than 15 ° C and lower than 50 ° C, the temperature is set to 0 ° C to 15 ° C or 50 ° C to 70 ° C.
One or two or more means selected from the group of (1) to (6) are performed, and a method for preventing coating film deterioration and corrosion of a steel material is provided. In advance, measure the dissolved oxygen concentration, redox potential, pH, chloride ion concentration, bicarbonate ion concentration, temperature of the water-containing liquid,
(1) When the dissolved oxygen concentration is in the range of less than 1 mg / L, the dissolved oxygen concentration is 1 mg / L or more.
(2) When the oxidation-reduction potential is in the range of less than -100 mV (saturated potassium chloride / silver silver chloride electrode standard), the oxidation-reduction potential is set to -100 mV (saturated potassium chloride / silver silver chloride electrode standard) or more.
(3) When the pH is in the range of less than 9.5, the pH is set to 9.5 or more and 12 or less.
(4) When the chlorine ion concentration is in the range of more than 10 mg / L, the chlorine ion concentration is 0 mg / L or more and 10 mg / L or less.
(5) When the bicarbonate ion concentration is in the range of more than 10 mg / L, the bicarbonate ion concentration is 0 mg / L or more and 10 mg / L or less.
(6) When the temperature is in the range of more than 15 ° C and less than 50 ° C, the temperature is set to 0 ° C to 15 ° C or 50 ° C to 70 ° C.
The coating material deterioration prevention and corrosion prevention method of a steel material according to claim 1, wherein one or two or more means selected from the group (1) to (6) are executed.   The said epoxy resin is a tar epoxy resin, The coating-film deterioration prevention and corrosion prevention method of the steel material of Claim 1 or 2 characterized by the above-mentioned. The steel according to any one of claims 1 to 3, wherein the methanogenic bacterium is Methanococcus mariparudis belonging to the family Methanococcalae (Methanococceae). Methods for preventing coating film deterioration and corrosion of materials. 5. The microorganism according to claim 4 , wherein the Methanococcus (Methanococcalae) Methanococcusae family Methanococcus mariparudis is a microorganism identified by the accession number NITE BP-252. Methods for preventing coating material deterioration and corrosion of steel materials. The steel material coating according to any one of claims 1 to 5 , wherein the sulfate-reducing bacterium is a microorganism belonging to the family of Desulfobibrionales (Desulfobrionionaceae). Method to prevent film deterioration and corrosion.