Method for preventing corrosion of metal member

Abstract

A method for preventing corrosion of a metal member in which cooling water and steam are alternately brought into contact with each other, said method being characterized in that a phosphorus compound and / or a zinc compound are added to the cooling water, and an anti-corrosion film-forming substance is added to the steam. The phosphorus compound is at least one of hexametaphosphoric acid, triphosphoric acid, orthophosphoric acid, phosphono butane tricarboxylic acid, HEDP (1-hydroxyethylidene-1, 1-diphosphonic acid) and amino trimethylphosphonic acid.

Description

Technical Field

[0001] This invention relates to a method for preventing corrosion of metal components, and in particular, to a method for preventing corrosion of metal components such as reaction vessels or molding machines that are in alternating contact with steam and cooling water. Background Technology

[0002] In order to suppress corrosion of carbon steel heat exchangers or piping in open circulating cooling water systems, phosphorus compounds such as orthophosphate, hexametaphosphate, hydroxyethyl phosphonate, and phosphonobutane tricarboxylate, as well as zinc salts or dichromates, are sometimes added to the cooling water alone or in combination (Patent Document 1).

[0003] To prevent corrosion of metal components such as reactors where steam and cooling water come into alternating contact, the addition of the corrosion inhibitor described above to the cooling water dilutes the water with steam, reducing the concentration of the corrosion inhibitor and thus failing to adequately suppress metal corrosion.

[0004] Patent Document 1 discloses a method for inhibiting metal corrosion by adding low concentrations of phosphate, zinc salt (each less than 1 mg / L), and total alkalinity to an aqueous system and setting the Langerile index at 30°C to 1.2 or higher. However, in reactors where steam and cooling water alternately come into contact, the concentration of the total alkalinity becomes low due to the dilution of the cooling water by steam, making it difficult to achieve sufficient corrosion protection. Furthermore, when the reactor is heated by steam, the temperature of the reactor increases, exceeding the standard temperature of the corrosion inhibitor in the cooling water system, thus failing to provide sufficient corrosion protection.

[0005] To inhibit the corrosion of carbon steel, there are also methods that use long-chain aliphatic amines as one of the film-forming substances (Patent Document 2). The corrosion protection mechanism of using long-chain aliphatic amines is that the long-chain aliphatic amines adsorb onto the surface of the metal via amino groups to form a dense monomolecular or multimolecular film, preventing the metal from contacting water, thereby inhibiting the corrosion of the metal.

[0006] In corrosion protection methods using long-chain aliphatic amines, the adsorbed coating will peel off if the amine is not added continuously to the water system. Therefore, even when applied to metal components where cooling water and steam alternately come into contact, the corrosion protection method using long-chain aliphatic amines cannot achieve sufficient corrosion protection.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2009-299161.

[0010] Patent Document 2: Japanese Patent Application Publication No. 2011-033301. Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Existing corrosion prevention methods for metal components cannot adequately suppress corrosion caused by alternating contact between steam and cooling water. Consequently, with prolonged use, corrosion products accumulate on the metal surface, hindering heat transfer and leading to reduced production or prolonged reaction times. Furthermore, regular cleaning is required.

[0013] The objective of this invention is to provide a corrosion protection method for metal components that can adequately prevent corrosion of metal components in alternating contact with steam and cooling water.

[0014] Methods for solving problems

[0015] The corrosion prevention method for metal components of the present invention is a corrosion prevention method for metal components in which cooling water and steam are in alternating contact, characterized in that phosphorus compounds and / or zinc compounds are added to the cooling water, and an anti-corrosion film forming substance is added to the steam.

[0016] In one aspect of the invention, the metal component is a steel reaction vessel or forming machine.

[0017] In one aspect of the invention, the phosphorus compound is at least one selected from hexametaphosphate, tripolyphosphate, orthophosphate, phosphonobutane tricarboxylic acid, hydroxyethylidene diphosphonic acid (HEDP), and aminotrimethylphosphonic acid.

[0018] In one aspect of the invention, the anti-corrosion film forming substance is an anodic corrosion inhibitor.

[0019] In one aspect of the invention, the anti-corrosion film forming substance is a polyamine represented by the following formula.

[0020] R1-[NH-(CH2) m ] n -NH2 (1)

[0021] (In the formula, R1 represents a saturated or unsaturated hydrocarbon group with 10 to 22 carbon atoms, m is an integer from 1 to 8, and n is an integer from 1 to 7. When n is 2 or more, it represents a complex number of NH-(CH2) groups.) m (Same or different)

[0022] In one aspect of the invention, a (meth)acrylic polymer is further added to the cooling water as an anti-scaling agent.

[0023] In one aspect of the invention, the ratio A / B of the amount of the anti-scaling agent A to the amount of the anti-corrosion film forming substance B is 6 or less.

[0024] The effects of the invention

[0025] In the corrosion prevention method for metal components of the present invention, phosphorus compounds and / or zinc salts are added to the cooling water, and anti-corrosion film-forming substances such as polyamines and / or sarcosines are added to the steam.

[0026] Therefore, it is possible to obtain excellent corrosion protection for metal components such as reaction vessels that are in alternating contact with steam and cooling water. Detailed Implementation

[0027] The corrosion prevention method for metal components of the present invention is a corrosion prevention method for metal components in which cooling water and steam are in alternating contact, wherein phosphorus compounds and / or zinc compounds are added to the cooling water, and an anti-corrosion film forming substance is added to the steam.

[0028] As for the metal components, steel components that are in alternating contact with steam and cooling water are preferred, such as reaction vessels and heating / cooling forming machines. The metal components can also be made of carbon steel, stainless steel, etc. The preferred steam temperature is approximately 150℃ to 200℃, and the preferred cooling water temperature is approximately 10℃ to 40℃.

[0029] As the phosphorus compound added to cooling water, phosphoric acid or phosphates are preferred. Specifically, examples include inorganic phosphoric acid (orthophosphoric acid, polyphosphoric acid) or its salts, organic phosphoric acid or its salts or esters, and various phosphonic acids, which can be used alone or in combination of two or more. As salts, sodium salts, potassium salts, etc., are preferred.

[0030] As phosphoric acid or phosphate, preferred options include hexametaphosphate, tripolyphosphate, orthophosphate, phosphonobutane tricarboxylic acid (PBTC), hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylphosphonic acid, or their salts.

[0031] The amount of phosphorus compound added, calculated as PO4, is preferably 2.0 mg / L to 12.0 mg / L, and particularly preferably about 5.0 mg / L to 7.0 mg / L.

[0032] The zinc salts added to the cooling water are preferably zinc chloride, zinc sulfate, zinc nitrate, zinc acetate, zinc malate, zinc citrate, etc., which can be used alone or in combination of two or more. The preferred amount of zinc salt added is 0.5 mg / L to 5.0 mg / L, and particularly preferably about 1.0 mg / L to 3.0 mg / L.

[0033] The preferred anti-corrosion film forming substance can be added directly to the steam, but it can also be added to boiler water, etc.

[0034] As a substance for forming an anti-corrosion film, anodic corrosion inhibitors are preferred, specifically polyamines or sarcosines, with polyamines being particularly preferred.

[0035] Preferred polyamines are substances represented by the following general formula (1).

[0036] R1-[NH-(CH2) m ] n -NH2 (1)

[0037] (In the formula, R1 represents a saturated or unsaturated hydrocarbon group with 10 to 22 carbon atoms, m is an integer from 1 to 8, and n is an integer from 1 to 7. When n is 2 or more, it represents a complex number of NH-(CH2) groups.) m (Same or different)

[0038] The saturated or unsaturated hydrocarbon group of R1 can be linear, branched, or cyclic, and can include alkyl, alkenyl, dienyl, alkynyl, etc., preferably linear alkyl or linear alkenyl, and the number of carbon atoms of R1 is preferably 15 to 22.

[0039] m is an integer from 1 to 8, and from the viewpoint of suppressing corrosion, it is preferably an integer from 2 to 6. (CH2) m The radical can be methylene, ethylene (dimethylene), propylene (trimethylene), butylene (tetramethylene), but propylene is preferred.

[0040] Furthermore, from the viewpoint of suppressing corrosion, n is preferably an integer from 1 to 3.

[0041] Specific examples of such polyamines include dodecylaminomethyleneamine, dodecylaminodimethylamine, dodecylaminotrimethyleneamine (N-stearoyl-1,3-propanediamine), or corresponding tetradecyl, hexadecyl, and octadecyl compounds, octadecenylaminotrimethyleneamine, octadecenylaminodi-(trimethylamino)-trimethyleneamine, palmitylaminotrimethyleneamine, etc., but N-oleoyl-1,3-propanediamine (i.e., N-octadecenylpropane-3-diamine) which can be readily obtained with sufficient purity is preferred.

[0042] These polyamines can be dissolved in solvents such as methanol, ethanol, and isopropanol and then added to steam or boiler water supply, but it is preferred to add them to steam or boiler water supply after they have been made into an aqueous emulsion.

[0043] Polyamines can be used alone or in combination with two or more.

[0044] Alternatively, long-chain aliphatic amines such as octadecylamine and oleylamine can be used within a range that does not cause blockage.

[0045] Preferably, the polyamine is present in a proportion of 0.01 ppm to 10 ppm, particularly 0.1 ppm to 1 ppm, relative to the amount of steam. If the amount of polyamine is too small compared to this range, the effect of inhibiting the formation of condensate film and improving heating efficiency based on polyamine cannot be sufficiently obtained; if it is too large, adhesive deposits may be generated in the system.

[0046] It should be noted that "ppm" refers to the weight ratio of polyamines to water corresponding to the amount of steam, which is equivalent to "mg / L - water".

[0047] As sarcosine derivatives, unsaturated and saturated C6-C24 alkyl sarcosines can be used, especially oleyl sarcosine, tallow sarcosine, and mixtures thereof.

[0048] In this invention, a scale inhibitor may also be added to the cooling water. As a scale inhibitor, a (meth)acrylic acid polymer is preferred. The (meth)acrylic acid polymer is preferably a copolymer or salt thereof comprising (meth)acrylic acid and an unsaturated monomer having a sulfonic acid group. This polymer is preferably an acrylic acid / 2-acrylamide-2-methylpropanesulfonic acid copolymer (AA / AMPS) or an acrylic acid / Hydroxyl allyloxypropanesulfonic acid copolymer (AA / HAPS). The weight-average molecular weight is preferably 4000–30000, more preferably 5000–20000. The AA / AMPS ratio and the AA / HAPS ratio (monomer molar ratio) are both preferably 60–95:40–5, more preferably 75–90:25–10. Furthermore, the ratio A / B of the amount of scale inhibitor A (mg / L) added to the amount of anti-corrosion film forming substance B (mg / L) is preferably 6 or less.

[0049] In this invention, a tracer substance for the anti-scaling agent may also be added to the cooling water.

[0050] Furthermore, the method of the present invention is preferably applied to cases where the heating rate of metal components is 10°C / hour or higher.

[0051] In this invention, it is preferable to begin the above-described anti-corrosion method after removing rust from the metal components. This facilitates the formation of an anti-corrosion film on the metal surface, thereby improving the anti-corrosion effect.

[0052] In this case, after rust removal and before starting the corrosion protection method, a high concentration of phosphorus or zinc compounds (e.g., total phosphoric acid concentration of 70 mgPO4 / L to 120 mgPO4 / L, zinc concentration of 10 mgZn / L to 30 mgZn / L) can be added to the water in contact with the metal components. This allows a strong anti-corrosion film to be formed on the metal surface in advance, easily maintaining a high anti-corrosion effect for a long time. Furthermore, an anti-corrosion film can also be formed in advance by adding the aforementioned anti-corrosion film-forming substances before starting the corrosion protection method.

[0053] Furthermore, the order in which the removal of rust from metal components, the addition of high-concentration phosphorus or zinc compounds, and the addition of anti-corrosion film-forming substances are performed before the start of the anti-corrosion method can be reversed, or they can be omitted individually.

[0054] In this invention, the concentration of the aforementioned anti-corrosion film-forming substance in the cooling water can also be controlled in proportion to any one or more of the following: temperature, conductivity, pH, dispersant concentration, tracer concentration, and Langerile index of the cooling water passing through the heat exchanger or at the heat exchanger outlet.

[0055] In this invention, the calcium hardness of the cooling water in the heat exchanger can also be calculated based on the calcium hardness and conductivity of the cooling tower makeup water, as well as the conductivity of the cooling water in the heat exchanger. When the calcium hardness is below a specified concentration (e.g., below 30 mg / L), it is controlled by ensuring that the concentration of the film-forming substance in the cooling water in the heat exchanger is above a specified concentration (e.g., above 0.1 mg / L). In cooling water, when the anti-corrosion effect is reduced due to low calcium hardness, the anti-corrosion effect can be improved by increasing the concentration of the residual film-forming substance.

[0056] In this invention, the anti-corrosion film-forming substance can also be added in batches to the cooling water. Adding the film-forming substance to the cooling water, in addition to the film-forming substance remaining due to steam, further enhances the anti-corrosion effect.

[0057] Alternatively, in this invention, the film-forming substance may be added in batches to the cooling water of the piping preceding the metal component just before the heating step of the metal component is about to begin.

[0058] Furthermore, in this invention, when the piping within the system is made of carbon steel, the accumulation of iron brought into the heat exchanger from the piping can be reduced, thereby reducing the heat transfer resistance of the heat exchanger.

[0059] Example

[0060] [Corrosion Resistance Evaluation Tests 1 to 3 (Simulated Examples)]

[0061] <Experimental Conditions>

[0062] <<Preparation of Experimental Water 1>>

[0063] Add pure water (30℃) to a 1 L glass beaker, and adjust the calcium hardness and acid consumption (pH 4.8) to 150 mg CaCO3 / L using sodium bicarbonate solution and calcium chloride solution. As a corrosion inhibitor, add 6 mg PO4 / L of the phosphorus compound from Table 2, 3 mg Zn / L of zinc chloride as a zinc compound, and add 10 mg / L of AA / AMPS polymer (monomer ratio 80:20, weight average molecular weight 20000) as a scale inhibitor in solid form (Test water 1 in Table 1: cooling water).

[0064] <<Preparation of Experimental Water 2>>

[0065] Test water (temperature 80°C) was prepared using the same reagents, with each component diluted to 1 / 5 concentration (Test Water 2 in Table 1: Steam System). For Test Water 2, after adding a scale inhibitor, 0.3 mg / L of a film-forming substance, namely N-octadecenyl propane-1,3-diamine (OLDA), was added as a polyamine.

[0066] <<Experimental Film>>

[0067] Cold-rolled steel plate (SPCC) (50 mm × 30 mm × 1 mm) was used as the test piece.

[0068] <<Experimental Procedure>>

[0069] The test piece was suspended on a copper wire coated with vinyl chloride and immersed in the test water 1. The beaker 1 of the test water 1 was placed in a constant temperature bath set at 30°C, and stirred for 20 hours by rotating the stir bar at 250 rpm using a magnetic stirrer.

[0070] Then, the test piece is removed from beaker 1 and transferred to beaker 2 containing test water 2 in a constant temperature bath set at 80°C. The mixture is stirred at 250 rpm for 5 hours using a magnetic stirrer.

[0071] After the experiment, the test piece was pulled out of beaker 2, and the corrosion products adhering to the surface of the test piece were rinsed off with acid. It was then dried, and its weight was measured. The corrosion loss was calculated based on the difference between the dried weight of the test piece after the experiment and its weight before the experiment. The results are shown in Table 2.

[0072] [Experimental Examples 4-6 (Simulated Comparative Examples)]

[0073] The presence and types of phosphorus and zinc compounds in test water 1 and test water 2, as well as the presence and absence of polyamines in test water 2, are set as described in Table 2. Otherwise, the tests were conducted in the same manner as in Test Examples 1 to 3, and the corrosion reduction was calculated. The results are shown in Table 2.

[0074] Table 1

[0075] Table 2

[0076] <Results, Investigation>

[0077] As shown in Table 2, it can be seen that in Test Examples 1 to 3, which use phosphorus compounds, zinc salts and polyamines in combination, sufficient corrosion inhibition effect can be obtained even under low corrosion inhibitor concentration and high temperature environment, which can help maintain the heat transfer efficiency of heat exchangers or equipment maintenance.

[0078] [Evaluation Test of Residue of Anti-corrosion Film-Forming Substances When Used in Concurrent Application with Anti-scaling Agents]

[0079] Add 1000 mL of room temperature pure water to a 1 L glass beaker, add 0.3 mg / L of N-octadecenylpropane-1,3-diamine (OLDA) as an anti-corrosion film forming substance, and add AA / AMPS polymer (monomer ratio 80:20, weight average molecular weight 20000) as a scale inhibitor to the concentration recorded in Table 3. Stir for 30 minutes to prepare test water 1 to test water 6.

[0080] After each test water sample (1-6) was allowed to stand for 30 minutes, the residual OLDA concentration in the supernatant was determined. The OLDA concentration was analyzed using the Bengal rose method described in Power Plant Chemistry 2015, 17(1). The results are shown in Table 3.

[0081] Table 3

[0082] <Results, Investigation>

[0083] As shown in Table 3, it is speculated that when OLDA and AA / AMPS polymers are used together, OLDA and AA / AMPS polymers co-precipitate, resulting in a decrease in OLDA concentration. By setting the [AA / AMPS] / [OLDA] value to below 6, especially below 3, the residual OLDA concentration in the cooling water is increased, thereby improving the corrosion protection effect.

[0084] Although the invention has been described in detail using specific methods, it will be apparent to those skilled in the art that various modifications can be made without departing from the intent and scope of the invention.

[0085] This application is based on Japanese Patent Application 2023-091035, filed on June 1, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A method for corrosion protection of metal components, wherein the corrosion protection method involves alternating contact between cooling water and steam, characterized in that, Add phosphorus and / or zinc compounds to the cooling water, and add anti-corrosion film-forming substances to the steam.

2. The corrosion protection method for metal components as described in claim 1, characterized in that, The metal component is a steel reaction vessel or forming machine.

3. The corrosion protection method for metal components as described in claim 1, wherein, The phosphorus compound is at least one of hexametaphosphate, tripolyphosphate, orthophosphate, phosphonobutane tricarboxylic acid, hydroxyethylidene diphosphonic acid (HEDP), and aminotrimethylphosphonic acid.

4. The corrosion protection method for metal components as described in claim 1, characterized in that, The anti-corrosion film forming substance is an anodic corrosion inhibitor.

5. The corrosion protection method for metal components as described in claim 1, characterized in that, The anti-corrosion film forming substance is a polyamine represented by the following formula. R1-[NH-(CH2) m ] n -NH2 (1) In the formula, R1 represents a saturated or unsaturated hydrocarbon group with 10 to 22 carbon atoms, m is an integer from 1 to 8, n is an integer from 1 to 7, and when n is 2 or more, it represents a complex number of NH-(CH2). m Same or different.

6. The corrosion protection method for metal components as described in claim 1, wherein, Phosphorus and zinc compounds are added to the cooling water.

7. The corrosion protection method for metal components as described in claim 6, wherein, Add P A phosphorus compound of 2.0 mg / L to 12.0 mg / L is added, along with a zinc salt of 0.5 mg / L to 5.0 mg / L as a zinc compound.

8. The corrosion protection method for metal components according to any one of claims 1 to 7, characterized in that, A (meth)acrylic polymer is further added to the cooling water as an anti-scaling agent.

9. The corrosion protection method for metal components as described in claim 8, characterized in that, The ratio of the amount of scale inhibitor A to the amount of anti-corrosion film forming substance B, A / B, is less than 6.

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