Method for preventing corrosion of metal member

Abstract

Disclosed is a method for preventing corrosion of a metal member that is alternately brought into contact with a cooling water and a steam, the method being characterized in that a phosphorus compound and / or a zinc compound is added to the cooling water, and a corrosion prevention film forming substance is added to the steam. The phosphorus compound is at least one of hexametaphosphoric acid, tripolyphosphoric acid, orthophosphoric acid, phosphonobutane tricarboxylic acid, hydroxyethylidene diphosphonic acid (HEDP), and aminotrimethylphosphonic acid.

Description

Corrosion prevention method for metal components

[0001] The present invention relates to a method for preventing corrosion of metal members, and more particularly to a method for preventing corrosion of metal members of reactors, molding machines, and the like that are alternately in contact with steam and cooling water.

[0002] In order to inhibit corrosion of heat exchangers and piping made of carbon steel in open circulating cooling water systems, phosphorus compounds such as orthophosphates, hexametaphosphates, hydroxyethylidenephosphonates, and phosphonobutanetricarboxylates, zinc salts, dichromates, and the like, may be added to the cooling water alone or in combination (Patent Document 1).

[0003] When the above-mentioned corrosion inhibitor is added to cooling water to prevent corrosion of metal components such as a reactor that is alternately in contact with steam and cooling water, the cooling water is diluted with steam, reducing the concentration of the corrosion inhibitor, and therefore metal corrosion cannot be sufficiently suppressed.

[0004] Patent Document 1 discloses a method for inhibiting metal corrosion in an aqueous system by adding low concentrations of phosphate and zinc salt (each 1 mg / L or less) and an M alkalinity component to the aqueous system to achieve a Langelier index of 1.2 or more at 30°C. However, in a reactor or the like where steam and cooling water alternately come into contact, the cooling water is diluted by the steam, which reduces the concentration of the M alkalinity component, making it difficult to achieve sufficient corrosion prevention. Furthermore, when the reactor is heated by steam, the reactor temperature rises to a temperature that exceeds the specification temperature of the cooling water system corrosion inhibitor, making sufficient corrosion prevention impossible.

[0005] One method for inhibiting corrosion of carbon steel is to use a long-chain aliphatic amine, which is a type of film-forming substance (Patent Document 2). The mechanism of corrosion prevention using a long-chain aliphatic amine is that the long-chain aliphatic amine adsorbs to the metal surface via the amino group to form a dense monomolecular or multimolecular layer film, thereby preventing contact between the metal and water and inhibiting metal corrosion.

[0006] In corrosion prevention methods using long-chain aliphatic amines, unless the amine is continuously added to the aqueous system, the adsorbed coating peels off. Therefore, even if the corrosion prevention method using long-chain aliphatic amines is applied to metal components that are in alternate contact with cooling water and steam, it is not possible to obtain a sufficient corrosion prevention effect.

[0007] JP 2009-299161 A JP 2011-033301 A

[0008] Conventional corrosion prevention methods for metal components cannot adequately prevent corrosion of metal components that are in alternating contact with steam and cooling water, and as a result, corrosion products accumulate on the metal surface over long periods of use, impeding heat transfer, resulting in reduced production and longer reaction times. Periodic cleaning is also required.

[0009] An object of the present invention is to provide a method for preventing corrosion of metal members that can sufficiently prevent corrosion of metal members that are alternately in contact with steam and cooling water.

[0010] The corrosion protection method for metal components of the present invention is a method for protecting metal components that are alternately in contact with cooling water and steam, and is characterized by adding a phosphorus compound and / or a zinc compound to the cooling water and adding a corrosion-protective film-forming substance to the steam.

[0011] In one aspect of the present invention, the metal member is a steel reaction vessel or molding machine.

[0012] In one embodiment of the present invention, the phosphorus compound is at least one of hexametaphosphoric acid, tripolyphosphoric acid, orthophosphoric acid, phosphonobutanetricarboxylic acid, hydroxyethylidene diphosphonic acid (HEDP), and aminotrimethylphosphonic acid.

[0013] In one embodiment of the present invention, the corrosion protective film-forming substance is an anodic inhibitor.

[0014] In one embodiment of the present invention, the corrosion-protective film-forming substance is a polyamine represented by the following formula:

[0015] R １ -[NH-(CH ２ ) ｍ ] ｎ -NH ２ ...(1) (wherein, R １ represents a saturated or unsaturated hydrocarbon group having 10 to 22 carbon atoms, m is an integer of 1 to 8, and n is an integer of 1 to 7. When n is 2 or more, a plurality of NH—(CH ２ ) ｍ may be the same or different.)

[0016] In one embodiment of the present invention, a (meth)acrylic acid-based polymer is further added to the cooling water as a scale inhibitor.

[0017] In one embodiment of the present invention, the ratio A / B of the amount A of the scale inhibitor to the amount B of the corrosion-protective film-forming substance is set to 6 or less.

[0018] In the method for preventing corrosion of metal members of the present invention, a phosphorus compound and / or a zinc salt is added to the cooling water, and a corrosion-resistant film-forming substance such as a polyamine and / or a sarcosine is added to the steam.

[0019] This provides excellent corrosion protection for metal members that are alternately in contact with steam and cooling water, such as a reactor.

[0020] The corrosion protection method for metal members of the present invention is a method for protecting metal members that are alternately in contact with cooling water and steam, in which a phosphorus compound and / or a zinc compound is added to the cooling water and a corrosion-protective film-forming substance is added to the steam.

[0021] The metal member is preferably a steel member that alternately comes into contact with steam and cooling water, and examples thereof include a reactor and a heating / cooling molding machine. The metal member may be a carbon steel member, a stainless steel member, or the like. The steam temperature is preferably about 150 to 200°C, and the cooling water temperature is preferably about 10 to 40°C.

[0022] The phosphorus compound added to the cooling water is preferably phosphoric acid or a phosphate, and specific examples include inorganic phosphoric acid (orthophosphoric acid, polymeric phosphoric acid) and its salts, organic phosphoric acid and its salts or esters, and various phosphonic acids, which can be used alone or in combination of two or more. As the salt, sodium salts, potassium salts, etc. are preferred.

[0023] Suitable phosphoric acids and phosphates include hexametaphosphoric acid, tripolyphosphoric acid, orthophosphoric acid, phosphonobutanetricarboxylic acid (PBTC), hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylphosphonic acid, and salts thereof.

[0024] The amount of phosphorus compound added is PO ４The concentration is preferably about 2.0 to 12.0 mg / L, particularly about 5.0 to 7.0 mg / L.

[0025] Suitable zinc salts to be added to the cooling water include zinc chloride, zinc sulfate, zinc nitrate, zinc acetate, zinc malate, and zinc citrate, which may be used alone or in combination of two or more. The amount of zinc salt to be added is preferably about 0.5 to 5.0 mg / L, and more preferably about 1.0 to 3.0 mg / L.

[0026] The anticorrosion film forming substance is preferably added directly to steam, but may also be added to boiler water or the like.

[0027] As the anticorrosion film forming substance, an anodic inhibitor is preferred, specifically a polyamine or a sarcosine, and particularly a polyamine.

[0028] A preferred polyamine is represented by the following general formula (1):

[0029] R １ -[NH-(CH ２ ) ｍ ] ｎ -NH ２ ...(1) (wherein, R １ represents a saturated or unsaturated hydrocarbon group having 10 to 22 carbon atoms, m is an integer of 1 to 8, and n is an integer of 1 to 7. When n is 2 or more, a plurality of NH—(CH ２ ) ｍ may be the same or different.)

[0030] R １ The saturated or unsaturated hydrocarbon group of R may be linear, branched, or cyclic, and examples thereof include alkyl groups, alkenyl groups, alkadienyl groups, and alkynyl groups. However, preferred are linear alkyl groups and linear alkenyl groups. １ The number of carbon atoms is preferably 15 to 22.

[0031] m is an integer of 1 to 8, and from the viewpoint of corrosion inhibition, is preferably an integer of 2 to 6. (CH ２ ) ｍExamples of the group include a methylene group, an ethylene group (dimethylene group), a propylene group (trimethylene group), or a butylene group (tetramethylene group), with a propylene group being preferred.

[0032] Furthermore, n is preferably an integer of 1 to 3 from the viewpoint of corrosion inhibition.

[0033] Specific examples of such polyamines include dodecylaminomethyleneamine, dodecylaminodimethyleneamine, dodecylaminotrimethyleneamine (N-stearyl-1,3-propanediamine), tetradecyl, hexadecyl, and octadecyl compounds corresponding to these polyamines, octadecenylaminotrimethyleneamine, octadecenylaminodi-(trimethylamino)-trimethyleneamine, palmitylaminotrimethyleneamine, and the like, with N-oleyl-1,3-propanediamine (i.e., N-octadecenylpropane-3-diamine) being preferred because it is readily available with sufficient purity.

[0034] These polyamines may be dissolved in a solvent such as methanol, ethanol, or isopropanol and added to steam or boiler feed water, but it is preferable to make them into an aqueous emulsion and add this to steam or boiler feed water.

[0035] The polyamines may be used alone or in combination of two or more.

[0036] Furthermore, long-chain aliphatic amines such as octadecylamine and oleylamine may be used in combination within a range that does not cause clogging.

[0037] The polyamine is preferably present in an amount of 0.01 to 10 ppm, particularly 0.1 to 1 ppm, based on the amount of steam. If the amount of polyamine is less than this range, the polyamine's effects of suppressing the formation of a condensed water film and improving heating efficiency cannot be fully achieved, while if the amount is too much, sticky deposits may form in the system.

[0038] It should be noted that "ppm" refers to the weight ratio of polyamine to water corresponding to the amount of steam, and corresponds to "mg / L-water."

[0039] As the sarcosine, unsaturated and saturated C6 to C24 alkyl sarcosine, particularly oleyl sarcosine, tallow sarcosine and mixtures thereof can be used.

[0040] In the present invention, a scale inhibitor may be added to the cooling water. A (meth)acrylic acid-based polymer is suitable as the scale inhibitor. The (meth)acrylic acid-based polymer is preferably a copolymer containing (meth)acrylic acid and an unsaturated monomer having a sulfonic acid group, or a salt thereof. The polymer is preferably an AA / AMPS (acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer)-based polymer or an AA / HAPS (acrylic acid / hydroxyallyloxypropanesulfonic acid copolymer)-based polymer having a sulfonic group. The weight-average molecular weight is preferably 4,000 to 30,000, more preferably 5,000 to 20,000. The AA / AMPS ratio and AA / HAPS ratio (molar ratio of monomers) are both preferably 60 to 95:40 to 5, more preferably 75 to 90:25 to 10. It is preferable that the ratio A / B of the amount A (mg / L) of the scale inhibitor to the amount B (mg / L) of the anticorrosive film-forming substance be 6 or less.

[0041] In the present invention, a tracer substance of the scale inhibitor may further be added to the cooling water.

[0042] The method of the present invention is suitable for use when the temperature rise rate of the metal member is 10° C. / hour or more.

[0043] In the present invention, it is preferable to start the corrosion prevention method after removing rust from the metal member, which makes it easier to form a corrosion prevention film on the metal surface and improves the corrosion prevention effect.

[0044] In this case, after removing the rust and before starting the corrosion prevention method, a high concentration of phosphorus compound or zinc compound (for example, a total phosphorus concentration of 70 to 120 mg PO ) is added to the water that comes into contact with the metal member. ４ / L, zinc concentration 10 to 30 mg Zn / L) may be added. In this way, a strong anticorrosion film can be formed on the metal surface in advance, and a high anticorrosion effect is likely to be maintained for a long period of time. Furthermore, a corrosion-protective film may be formed in advance by adding the above-mentioned anticorrosion film-forming substance before starting the corrosion protection method.

[0045] The order of removing rust from the metal components before starting the corrosion prevention method, adding a high concentration phosphorus compound or zinc compound, and adding a corrosion-resistant film-forming substance may be reversed, or none of them may be performed at all.

[0046] In the present invention, the concentration of the corrosion-resistant coating-forming substance in the cooling water may be controlled proportionally to one or more of the temperature, electrical conductivity, pH, dispersant concentration, tracer substance concentration, and Langelier index of the cooling water in the heat exchanger through which the cooling water passes or at the outlet of the heat exchanger.

[0047] In the present invention, the calcium hardness of the cooling water in the heat exchanger may be calculated from the calcium hardness and electrical conductivity of the cooling tower make-up water and the electrical conductivity of the cooling water in the heat exchanger, and when the calcium hardness is a predetermined concentration or less (e.g., 30 mg / L or less), the concentration of the film-forming substance in the cooling water in the heat exchanger may be controlled to be a predetermined concentration or more (e.g., 0.1 mg / L or more). When the calcium hardness in the cooling water, which has a corrosion inhibitory effect, is low and the corrosion inhibitory effect is reduced, the corrosion inhibitory effect can be improved by increasing the concentration of the remaining film-forming substance.

[0048] In the present invention, a corrosion-resistant film-forming substance may be added to the cooling water in batches. By adding a film-forming substance to the cooling water in addition to the film-forming substance derived from steam and remaining therein, the corrosion prevention effect can be improved.

[0049] In the present invention, the film-forming substance may be added in batches to the cooling water in the piping immediately prior to the metal member immediately before the start of the temperature-raising step for the metal member.

[0050] Furthermore, in the present invention, when the piping in the system is made of carbon steel, the deposition of iron carried from the piping to the heat exchanger can be reduced, thereby reducing the inhibition of heat transfer in the heat exchanger.

[0051] [Corrosion Prevention Evaluation Tests 1 to 3 (Simulation of Examples)] <Experimental Conditions> <Preparation of Test Water 1> Pure water (30°C) was placed in a 1 L glass beaker, and calcium hardness and acid consumption (pH 4.8) were adjusted to 150 mg CaCO using a sodium bicarbonate solution and a calcium chloride solution, respectively. ３ / L. As a corrosion inhibitor, 6 mg PO ４ / L, zinc chloride was added as a zinc compound at 3 mg Zn / L, and an AA / AMPS polymer (monomer ratio 80:20, weight average molecular weight 20,000) was added as a scale inhibitor at 10 mg / L as solids (test water 1 in Table 1: cooling water).

[0052] <Preparation of Test Water 2> Test water (temperature 80°C) was prepared by diluting the same chemicals so that the concentration of each component was 1 / 5 (test water 2: steam system in Table 1). After adding the scale inhibitor, 0.3 mg / L of N-octadecenylpropane-1,3-diamine (OLDA) was added as a polyamine film-forming substance to test water 2.

[0053] <<Test Piece>> SPCC (50 mm x 30 mm x 1 mm) was used as a test piece.

[0054] <Test Procedure> The test piece was hung on a copper wire coated with vinyl chloride and immersed in the test water 1. Beaker 1 of test water 1 was placed in a thermostatic bath set at 30°C, and the water was stirred for 20 hours by rotating the stirring bar of a magnetic stirrer at 250 rpm.

[0055] Thereafter, the test piece was removed from beaker 1 and transferred to beaker 2 of test water 2 placed in a thermostatic bath set at 80°C, and stirred with a magnetic stirrer at 250 rpm for 5 hours.

[0056] After the test, the test specimen was removed from the beaker 2, and the corrosion products adhering to the surface of the test specimen were washed off with acid. The specimen was then dried and weighed. The corrosion weight loss was calculated from the difference between the dry weight of the test specimen after the test and the weight before the test. The results are shown in Table 2.

[0057] Test Examples 4 to 6 (simulating comparative examples) Tests were conducted in the same manner as Test Examples 1 to 3, except that the presence or absence and types of phosphorus compounds and zinc compounds in Test Waters 1 and 2, and the presence or absence of polyamine in Test Water 2 were as shown in Table 2, and corrosion weight loss was calculated. The results are shown in Table 2.

[0058]

[0059]

[0060] <Results and Discussion> As shown in Table 2, in Test Examples 1 to 3, in which a phosphorus compound, a zinc salt, and a polyamine were used in combination, sufficient corrosion inhibition effects were obtained even at low corrosion inhibitor concentrations and in high-temperature environments, and it can be seen that this can contribute to maintaining the heat transfer efficiency of heat exchangers and equipment maintenance.

[0061] [Test to evaluate the residual properties of a corrosion-protective film-forming substance when used in combination with a scale inhibitor] 1000 mL of pure water at room temperature was placed in a 1 L glass beaker, and 0.3 mg / L of N-octadecenylpropane-1,3-diamine (OLDA) was added as a corrosion-protective film-forming substance, and AA / AMPS polymer (monomer ratio 80:20, weight average molecular weight 20,000) was added as a scale inhibitor to the concentrations shown in Table 3. The mixture was stirred for 30 minutes to prepare test waters 1 to 6.

[0062] After each test water 1 to 6 was allowed to stand for 30 minutes, the residual OLDA concentration in the supernatant was measured. The OLDA concentration was analyzed by the Bengal Rose method described in Power Plant Chemistry 2015, 17(1). The results are shown in Table 3.

[0063]

[0064] <Results and Discussion> When OLDA and AA / AMPS polymer are used in combination, the OLDA and AA / AMPS polymer co-precipitate, reducing the OLDA concentration, as shown in Table 3. It was presumed that by setting the [AA / AMPS] / [OLDA] value to 6 or less, particularly 3 or less, the concentration of OLDA remaining in the cooling water increases, improving the corrosion prevention effect.

[0065] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-091035, filed on June 1, 2023, and is incorporated by reference in its entirety.

Claims

1. A method for preventing corrosion of metal components which are alternately in contact with cooling water and steam, comprising adding a phosphorus compound and / or a zinc compound to the cooling water and adding a substance which forms a corrosion-resistant film to the steam.

2. The method for preventing corrosion of metal parts according to claim 1, wherein the metal parts are steel reaction vessels or molding machines.

3. The method for preventing corrosion of metal components according to claim 1, wherein the phosphorus compound is at least one of hexametaphosphoric acid, tripolyphosphoric acid, orthophosphoric acid, phosphonobutanetricarboxylic acid, hydroxyethylidene diphosphonic acid (HEDP), and aminotrimethylphosphonic acid.

4. The method for protecting metal components from corrosion according to claim 1, characterized in that the anticorrosive film-forming substance is an anodic inhibitor.

5. The method for preventing corrosion of metal members according to claim 1, wherein the anticorrosive film-forming substance is a polyamine represented by the following formula: １ -[NH-(CH ２ ) ｍ ] ｎ -NH ２ ...(1) (wherein, R １ represents a saturated or unsaturated hydrocarbon group having 10 to 22 carbon atoms, m is an integer of 1 to 8, and n is an integer of 1 to 7. When n is 2 or more, a plurality of NH-(CH ２ ) ｍ may be the same or different.) 6. The method for preventing corrosion of metallic components according to claim 1, further comprising adding a phosphorus compound and a zinc compound to said cooling water.

7. Phosphorus compounds ４ 7. The method for preventing corrosion of a metal member according to claim 6, wherein 2.0 to 12.0 mg / L of zinc salt is added as the zinc compound, and 0.5 to 5.0 mg / L of zinc salt is added as the zinc compound.

8. The method for preventing corrosion of metal components according to any one of claims 1 to 7, further comprising adding a (meth)acrylic acid-based polymer as a scale inhibitor to the cooling water.

9. A method for protecting metal components from corrosion as set forth in claim 8, characterized in that the ratio A / B of the amount A of the scale inhibitor to the amount B of the anticorrosive film-forming substance is 6 or less.

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