JP6589959B2 - Corrosion prevention method - Google Patents

Description

  The present invention relates to a corrosion prevention method for suppressing corrosion by forming an anticorrosive film on the surface of a metal member in contact with a cooling water system, particularly an iron-based metal member such as carbon steel.

Metal members provided in an open circulating cooling water system, such as heat exchangers, reaction kettles and piping made of carbon steel, copper, or copper alloys, are generally corroded by contact with cooling water. Corrosion protection treatment is applied.
For example, phosphorous compounds such as orthophosphate, hexametaphosphate, hydroxyethylidene phosphonate, phosphonobutane tricarboxylate are added to the cooling water system to suppress corrosion of carbon steel heat exchangers, reaction kettles and piping. It has been added. A heavy metal salt such as zinc salt or dichromate may be added alone or in combination.
However, the anticorrosion treatment in which such a phosphorus compound or zinc salt is added may contaminate water quality and seriously affect the environment.

  On the other hand, the following patent documents 1 to 3 propose methods for improving the anticorrosion effect by adjusting water quality components without depending on phosphorus compounds and zinc salts as treatment methods with reduced environmental load.

In Patent Document 1, in an open circulation cooling water system, the water quality is adjusted so that the Langelia index is 1.5 or more and the product of silica concentration and calcium hardness is 2000 or more, and a copolymer of maleic acid and isobutylene is prepared. A method for inhibiting corrosion of a metal to be added is disclosed.
In Patent Document 2, a maleic acid polymer A and a maleic acid monomer are added to an aqueous system in which the Langellia index is 1.5 or more and the product of silica concentration and calcium hardness is 2000 or more. And a method for inhibiting corrosion of a metal in which a copolymer B of a nonionic monoethylenically unsaturated monomer is added at a specific ratio.
In Patent Document 3, a phosphate, a zinc salt, and an M alkalinity component are added, the total phosphoric acid concentration and the total zinc concentration are each 1 mg / L or less, and the Langeria index at 30 ° C. is 1.2 or more. An aqueous metal corrosion suppression method is disclosed.

  However, all of the methods of Patent Documents 1 to 3 require that a large amount of chemicals be added in order to keep the calcium hardness, the silica concentration, and the Langeria index constant in water quality with low calcium hardness.

  As another method for suppressing corrosion, there is a method using a film-forming amine, and this method is mainly applied to metal corrosion suppression in a boiler water system. The mechanism of corrosion protection by film-forming amines is to prevent contact between metal and water by forming film-forming amines adsorbing on the metal surface via amino groups to form a dense monomolecular or multi-layer film. In other words, metal corrosion is suppressed (Non-Patent Document 1).

Japanese Patent Publication No. 4-33868 Japanese Patent Laid-Open No. 2007-119835 JP 2009-299161 A

Corrosion Center News No. 054 (August 2010) Water treatment technology (1) “Corrosion and corrosion protection of boilers and peripheral equipment” Fumio Kawamura

  As described above, the anticorrosion treatment in which a phosphorus compound or zinc salt is added may contaminate water quality and seriously affect the environment. On the other hand, when adjusting the water quality without using these substances to improve the anticorrosion effect, it is necessary to add a large amount of chemicals in order to exert the anticorrosion effect especially in the cooling water system having a low calcium hardness. Not right.

  The method of forming an anticorrosive film on the surface of a metal using a film-forming amine is that the required amount of film-forming amine is basically proportional to the surface area of the metal, and the film-forming amine is required once the anticorrosion film is formed. Since the amount is small enough, the cost of chemicals can be reduced. It was difficult.

  The present invention is a corrosion prevention method for suppressing corrosion of a metal member in contact with a cooling water system by forming an anticorrosion film with a film-forming amine without using chemicals that cause environmental burden such as phosphorus compounds and zinc salts. It is an object of the present invention to provide a corrosion prevention method capable of significantly reducing the amount of chemical added for the purpose.

As a result of intensive studies to solve the above problems, the present inventors have been unable to form an anticorrosion film with a film-forming amine alone in the anticorrosion treatment with a film-forming amine, but to form an anticorrosion film and maintain the anticorrosion effect. Has found that it requires an M alkalinity component. Further, as a result of further investigation on the anticorrosion treatment using the combination of the film-forming amine and the M alkalinity component, the M alkalinity of the cooling water system and further the pH are set to predetermined conditions only at the initial treatment for starting the treatment with the film-forming amine. In this way, it was found that the anticorrosion effect can be maintained by adding no chemical or adding a very small amount of chemical during the subsequent holding treatment.
In the corrosion prevention method by forming the anticorrosive film with the film-forming amine according to the present invention, the anticorrosion effect can be obtained by forming the anti-corrosion film if the M alkalinity and the film-forming amine concentration are higher than the predetermined value. And an inexpensive anticorrosion treatment becomes possible. In particular, in the cooling water system, M alkalinity derived from makeup water is concentrated. Therefore, in order to adjust the M alkalinity for the formation of the anticorrosive film, the M alkalinity component that is insufficient only in the initial stage before concentration is increased You just have to put it in. Therefore, after that, it is usually only necessary to add a film-forming amine as a drug.

  The present invention has been achieved based on such findings, and the gist thereof is as follows.

[1] A corrosion prevention method for suppressing corrosion of a metal member by forming a corrosion prevention film on the surface of a metal member in contact with the cooling water system by coexisting a film-forming amine and an M alkalinity component in the cooling water system,
A method for preventing corrosion, comprising using a neutralizing amine as the M alkalinity component and adjusting the M alkalinity of the cooling water system during initial treatment for forming the anticorrosion film to 90 mg / L as CaCO ₃ or more.

[2] The method for preventing corrosion according to [1], wherein the pH of the cooling water system during the initial treatment is set to 9.5 or more.

[3] A corrosion prevention method for suppressing corrosion of the metal member by forming a corrosion prevention film on the surface of the metal member in contact with the cooling water system by coexisting a film-forming amine and an M alkalinity component in the cooling water system,
An inorganic alkali is used as the M alkalinity component, and the M alkalinity of the cooling water system during initial treatment for forming the anticorrosion film is adjusted to 120 mg / L as CaCO ₃ or more, and the pH is adjusted to 9.5 or more. How to prevent corrosion.

[4] In any one of [1] to [3], at least 10 mg / L of the film-forming amine is added to the cooling water system during the initial treatment, and then the film-forming amine concentration of the cooling water system during the initial treatment Is maintained at a concentration exceeding 0.1 mg / L.

[5] In any one of [1] to [4], the M alkalinity of the cooling water system is 30 mg / L as CaCO ₃ or more in the holding treatment for holding the formed anticorrosion coating after the initial treatment. A corrosion prevention method characterized in that the concentration of the reactive amine is maintained at 0.1 mg / L or more.

According to the present invention, it is possible to obtain a high anticorrosion effect by forming an anticorrosion film without using an agent that causes environmental burden such as a phosphorus compound or a zinc salt using a film-forming amine and an M alkalinity component. According to the present invention, it is necessary to add a chemical for adjusting the water quality during the initial treatment until the formation of the anticorrosive film, but it is necessary to add a chemical for adjusting the water quality during the retention treatment after the anticorrosive film is formed. The anticorrosion effect can be maintained with no or a small amount of drug added.
For this reason, according to the present invention, it is possible to stably obtain a high anticorrosive effect for a long period of time by economical treatment that reduces the environmental load and suppresses the drug cost.

  Hereinafter, embodiments of the corrosion prevention method of the present invention will be described in detail.

In the corrosion prevention method of the present invention, a corrosion-resistant film is formed by inhibiting the corrosion of a metal member by forming a corrosion-resistant film on the surface of the metal member in contact with the cooling water system by coexisting a film-forming amine and an M alkalinity component in the cooling water system. When neutralizing amine is used as the M alkalinity component during the initial treatment to form the water, the M alkalinity of the cooling water system is adjusted to 90 mg / L as CaCO ₃ or more, and the inorganic alkali is used as the M alkalinity component Adjusts the M alkalinity of the cooling water system to 120 mg / L as CaCO ₃ or more and the pH to 9.5 or more.

<Initial processing / holding processing>
In the present invention, the initial treatment refers to a treatment for forming an anticorrosive film on the entire surface of the metal member in contact with the cooling water system in the cooling water system to be treated with a film-forming amine.
Here, the entire surface of the metal member means a pipe, a heat exchanger, a reaction kettle, or the like.
In addition, the initial treatment is a treatment in which the M alkalinity is sufficiently increased using a neutralizing amine or an inorganic alkali, and an anticorrosive film is formed on the entire surface of the metal member by adding a high concentration film-forming amine. That is.

  The holding process is a process for holding (maintaining) the anticorrosive film formed on the entire surface of the metal member in the cooling water system after the initial process.

<Water quality adjustment>
In the present invention, by adjusting the water quality of the cooling water system during the initial treatment, a stable anticorrosive film is efficiently formed on the surface of the metal member in contact with the cooling water system.

Sufficient M alkalinity is required at the initial treatment for forming the anticorrosive film, and when the neutralizing amine described later is used as the M alkalinity component, the M alkalinity of the cooling water system is 90 mg / L as CaCO ₃ or more, The water quality is adjusted so that the pH is preferably 9.5 or higher. Normally, when neutralizing amine is added so that the M alkalinity of the cooling water system is 90 mg / L as CaCO ₃ or more, the pH is 9.5 or more, so there is no need to add an alkali agent separately. .
On the other hand, when the inorganic alkali described later is used as the M alkalinity component, the water quality is adjusted so that the M alkalinity of the cooling water system is 120 mg / L as CaCO ₃ or more and the pH is 9.5 or more. In this case, the M alkalinity component is adjusted to 120 mg / L as CaCO ₃ or higher with the carbonate and bicarbonate described later, and the pH is adjusted to 9.5 or higher with alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. It is preferable to do.

In this case, the water quality is adjusted so that the M alkalinity of the cooling water system is 120 mg / L as CaCO ₃ or more and the pH is 9.5 or more.

  When a neutralizing amine is used as the M alkalinity component, generally, a necessary amount of neutralizing amine is added to the cooling water system together with the film-forming amine to adjust the M alkalinity.

When an inorganic alkali is used as the M alkalinity component, the M alkalinity in the makeup water such as sodium bicarbonate, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide and the like can be used. When these M alkalinity components are contained in the replenishing water of the cooling water system, an insufficient amount of inorganic alkali for making the water quality of M alkalinity 120 mg / L as CaCO ₃ or more and pH 9.5 or more may be added.

  When either neutralizing amine or inorganic alkali is used as the M alkalinity component, the film-forming amine is preferably added at a cooling water-based film-forming amine concentration of 10 mg / L or more. By adding a film-forming amine, an anticorrosion film is formed on the surface of the metal member, so that the concentration of the cooling-water-based film-forming amine is reduced. Thus, it is preferable to maintain the film-forming amine concentration. Accordingly, when the consumption of the film-forming amine is severe, an additional film-forming amine is added as necessary.

At the time of such a holding treatment after the initial treatment, the already formed anticorrosion film can be stabilized by maintaining the water quality of M alkalinity 30 mg / L as CaCO ₃ or more and film-forming amine concentration 0.1 mg / L or more. The anticorrosion effect can be maintained by maintaining the above.
At the time of this holding treatment, the M alkalinity tends to increase due to the concentration of the cooling water system, and therefore it is usually unnecessary to add an M alkalinity component. Further, the concentration of the film-forming amine can be normally maintained at 1 mg / L or more without additional addition. However, when the film-forming amine concentration tends to decrease, a necessary amount of the film-forming amine is appropriately added.

  As described above, according to the present invention, the anticorrosion effect can be maintained only by adding a necessary amount of drug at the initial processing, and without adding any drug at the time of the subsequent holding process, or by adding a very small amount of drug. Can do.

  In the description of the water quality adjustment, the film-forming amine concentration and the M alkalinity are only the lower limit, and the upper limit is not particularly limited. The lower the concentration, the lower the anticorrosion effect, and the higher the concentration, the better the anticorrosion effect. In order to increase the M alkalinity and film-forming amine concentration, the amount of drug added increases, and the drug cost increases. Therefore, the upper limit of the M alkalinity and film-forming amine concentration is determined appropriately in accordance with the anticorrosive effect and the drug cost. Is done. In addition, about pH at the time of a holding | maintenance process, it is preferable to set it as 10 or less from viewpoints, such as safety | security of a working environment, chemical | medical agent cost, and copper anticorrosion.

<Cooling water system>
In the present invention, the cooling water system to be treated may be a closed circulating cooling water system or an open circulating cooling water system. The cooling water system water is not particularly limited, such as pure water, soft water, and industrial water. In any cooling water system, in order to make up for the amount lost by blowing or splashing water, and the amount consumed by re-forming the destroyed film, additional chemicals are added to achieve the above water quality.

  In addition, although there is no restriction | limiting in particular about water quality other than M alkalinity component, pH, and film-forming amine density | concentration of the cooling water system made into a process target, It is preferable that it is the water quality generally employ | adopted with cooling water.

<Metal member>
In the present invention, there is no particular limitation on the metal member to be protected against corrosion, and it may be an iron-based metal member such as carbon steel or a copper-based metal member. Therefore, the present invention is effective in inhibiting corrosion of ferrous metal members such as carbon steel.

<Film-forming amine>
A film-forming amine is an amine capable of forming a corrosion-resistant film on a metal surface. The film-forming amine used in the present invention is not particularly limited, and any film-forming amine that is usually used for boiler water-based anticorrosion treatment or the like can be suitably used. As the general film-forming amine, one type or two or more types such as long-chain aliphatic amines (aliphatic amines and diamines) are used.

  Of these, long-chain aliphatic amines are particularly preferable from the viewpoint of the corrosion inhibition effect. The long chain aliphatic group of the long chain aliphatic amine has preferably 10 to 22 carbon atoms, particularly preferably 12 to 20 carbon atoms. When this carbon number is less than 10, it is difficult to form a film on the metal member, and the corrosion inhibiting function may be insufficient. Conversely, those having more than 22 carbon atoms tend to be inferior in handleability during drug injection.

  The long chain aliphatic group constituting the long chain aliphatic amine may contain an unsaturated bond. In the amino group constituting the long-chain aliphatic amine, the hydrogen portion may be appropriately substituted with a hydrocarbon group such as a methyl group or an ethyl group. Further, the long chain aliphatic amine may be a fatty acid salt. In this case, examples of the fatty acid constituting the fatty acid salt include oleic acid, lauric acid, and stearic acid.

  Among the long-chain aliphatic amines, preferred are saturated aliphatic amines such as dodecylamine, tridecylamine, tetradecylamine, heptadecylamine, hexadecylamine, octadecylamine, nonadecylamine, eicosylamine, docosylamine and the like. , Oleylamine, ricinoleylamine, linoleylamine, unsaturated aliphatic amines such as linoleylamine, mixed amines such as coconut oil amine and hardened tallow amine. Moreover, it has a long chain aliphatic group in an amino group such as N-oleyl-1,3-diaminopropane, N-tallow-1,3-diaminopropane, N-coco-1,3-diaminopropane, and the like. Good. Further, it may be an alkylene oxide adduct such as N-tallow-1,3-diaminopropane-ethylene oxide adduct.

  Since these film-forming amines are hardly soluble in water, they may be used by dissolving in a solvent, or may be used by being dispersed as an emulsion in water.

<M alkalinity component>
The M alkalinity component used in the present invention may be an inorganic alkali or an organic alkali neutralizing amine (an amine capable of neutralizing an acid component).

Examples of the inorganic alkali include carbonates such as sodium carbonate (Na ₂ CO ₃ ) and potassium carbonate (K ₂ CO ₃ ), bicarbonates such as sodium bicarbonate (NaHCO ₃ ) and potassium bicarbonate (KHCO ₃ ), water Examples include alkali metal hydroxides such as sodium oxide (NaOH) and potassium hydroxide (KOH), and one or more calcium compounds such as calcium hydroxide (Ca (OH) ₂ ). For the adjustment, it is preferable to adjust the pH by using carbonates and bicarbonates together with these weak alkaline compounds and, if necessary, strong alkaline compounds such as sodium hydroxide and potassium hydroxide.

  As neutralizing amines, dimethylaminoethanol (DMEA), diethylethanolamine (DEEA), monoisopropanolamine (MIPA), monoethanolamine (MEA), cyclohexylamine (CHA), morpholine (MOR), methoxypropylamine 1 type (s) or 2 or more types, such as (MOPA) and 2-amino-2-methyl-1-propanol (AMP), can be used.

  As described above, an inorganic alkali and a neutralizing amine may be used in combination.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
In the following examples and comparative examples, the corrosion test was performed in the following procedure using a rotary corrosion test apparatus that corrodes the test piece by immersing and rotating the test piece in test water. The unit of the corrosion rate was mdd (mg / dm ² / day), and 10 mdd or less was judged as a sufficient anticorrosion effect.

[Corrosion test procedure]
(1) 1.0 L of pure water was put into a 1 L beaker.
(2) 5 ml of an aqueous sodium chloride solution (chloride ion concentration: 0.1 wt%) and 5 ml of an aqueous sodium sulfate solution (sulfate ion: 0.1 wt%) were added to the beaker of (1). Further, as an M alkalinity component, an aqueous solution of sodium bicarbonate (NaHCO ₃ ) (M alkalinity 5%), a dimethylaminoethanol (DMEA) solution (M alkalinity 5%), or a monoisopropanolamine (MIPA) solution (M alkalinity) 5%) was added in a predetermined amount (however, it was not added in Comparative Examples 9 and 10). Further, 10 mg / L of N-oleyl-1,3-diaminopropane was added as a film-forming amine (however, it was not added in Comparative Examples 7, 8, and 10). Each component was added while always mixing the water in the beaker with a stirring bar.
When changing the pH in the same M alkalinity solution was adjusted to be M alkalinity set by sodium bicarbonate (NaHCO ₃₎ solution and the pH was adjusted by addition of sodium hydroxide solution.
(3) The beaker created in (2) was placed in a constant temperature water bath at 50 ° C.
(4) A mild steel test piece (50 mm × 30 mm × 1 mm) was attached to the support rod and immersed in the test water in the beaker of (3).
(5) The test was started by rotating the support rod of (4) at a rotation speed of 145 rpm.
(6) After the test for 7 days, the test piece was taken out and the corrosion rate was calculated from the corrosion weight loss.

[Examples 1-7, Comparative Examples 1-10]
In Examples 1 to 7 and Comparative Examples 1 to 10, among the corrosion test procedures, in the step (3), the M alkalinity component shown in Table 1 was added so as to have the M alkalinity shown in Table 1, A sodium hydroxide solution was added as necessary to adjust the initial pH shown in Table 1.
Table 1 shows the corrosion rates determined in each example.

As is apparent from Table 1, even when a film-forming amine is added, in Comparative Examples 1 to 6 and 9 where the initial M alkalinity and the initial pH do not satisfy the conditions of the present invention, a sufficient corrosion inhibitory effect cannot be obtained. . In Comparative Examples 7, 8, and 10 in which no film-forming amine is added, an anticorrosion film cannot be formed, and thus a corrosion inhibiting effect cannot be obtained. On the other hand, in Examples 1 to 7 in which the film-forming amine is added and the water quality during the initial treatment is adjusted to the specified range of the present invention, the corrosion of the metal member can be effectively suppressed.
In each of the above examples, since the corrosion test was performed in the beaker, the M alkalinity of the test water in the beaker for 7 days was almost unchanged after the step (3). The concentration of N-oleyl-1,3-diaminopropane after the day test was reduced to about 1 mg / L.
In addition, after the initial treatment, the test water was replaced and the test including the holding treatment was performed. The same test was continued for 5 days with M alkalinity of the test water of 30 to 150 mg / L as CaCO ₃ and pH of 8 to 9, but the corrosion rate was 10 mdd or less in any of the examples. The sustained effect was confirmed.

Claims (5)

A corrosion prevention method for suppressing corrosion of the metal member by forming a corrosion prevention film on the surface of the metal member in contact with the cooling water system by coexisting a film-forming amine and an M alkalinity component in the cooling water system,
Using a neutralizing amine as the M alkalinity component,
Adding 10 mg / L or more of the film-forming amine to the cooling water system during the initial treatment for forming the anticorrosion film, and adjusting the M alkalinity of the cooling water system during the initial treatment to 90 mg / L as CaCO ₃ or more. Corrosion prevention method characterized by   2. The corrosion prevention method according to claim 1, wherein the pH of the cooling water system during the initial treatment is set to 9.5 or more. A corrosion prevention method for suppressing corrosion of the metal member by forming a corrosion prevention film on the surface of the metal member in contact with the cooling water system by coexisting a film-forming amine and an M alkalinity component in the cooling water system,
An inorganic alkali is used as the M alkalinity component,
10 mg / L or more of the film-forming amine is added to the cooling water system during the initial treatment for forming the anticorrosion film, and the M alkalinity of the cooling water system during the initial treatment is 120 mg / L as CaCO ₃ or more, and the pH is 9 Corrosion prevention method characterized by adjusting to 5 or more.   4. The film-forming amine is added to the cooling water system at 10 mg / L or more during the initial treatment according to claim 1, and then the film-forming amine concentration of the cooling water system during the initial treatment is set to 0. A corrosion prevention method characterized by maintaining a concentration exceeding 1 mg / L. 5. The M alkalinity of the cooling water system is 30 mg / L as CaCO ₃ or more and the film-forming amine concentration in the holding treatment for holding the formed anticorrosion film after the initial treatment according to claim 1. Is maintained at 0.1 mg / L or more.