TWI786339B - Anti-corrosion method for metal components of cooling water system - Google Patents

Abstract

A method for preventing corrosion of metal components in a cooling water system, comprising: step (1), adding more than one compound (A) selected from tartaric acid and tartrates into the cooling water system to make it contact with the metal components; and step (2) , after the step (1), adding at least one compound (B) selected from zinc and zinc salts into the cooling water system to make it contact with the metal member.

Description

Anti-corrosion method for metal components of cooling water system

The present invention relates to a method for preventing corrosion of metal components in a cooling water system by forming an anti-corrosion film on the surface of a metal component that forms a portion in contact with cooling water in the cooling water system.

A water-cooled heat exchanger is used for indirect cooling of various fluids in air-conditioning equipment such as buildings and regional facilities, and mechanical equipment (plants). Metals such as carbon steel and stainless steel are generally used for various members such as heat exchangers and piping around them in such cooling water systems. If these metal components are always or intermittently in contact with cooling water, they are easily corroded by dissolved oxygen in the water. If the thickness of metal components such as piping is reduced or pitted due to corrosion, it may cause damage to equipment or contamination of products in machinery and equipment, which may cause serious accidents.

As an anticorrosion method for such metal members, for example, Patent Document 1 proposes to form a strong anticorrosion film on the surface of the metal member by using phosphoric acid and zinc-based corrosion inhibitors in the basic treatment at the start-up of the cooling water system. . [Prior art literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2011-202243

[Problem to be Solved by the Invention] However, in recent years, due to increased interest in environmental protection and stricter regulations on drainage, it has been required to reduce the content of phosphorus and the like in wastewater. It is difficult for machinery and equipment not equipped with wastewater treatment equipment to meet such requirements, and the use of phosphoric acid-based and zinc-based corrosion inhibitors may have to be discontinued. In addition, since the phosphoric acid-based anticorrosion agent forms an anticorrosion film by depositing a film, it takes a long time of about 4 days for the basic treatment. Therefore, shortening of the base processing period is also desired.

Therefore, a corrosion protection method capable of obtaining an excellent corrosion protection effect in a shorter period of time without using a phosphoric acid-based corrosion inhibitor has been sought.

The present invention is made to solve the above problems, and an object of the present invention is to provide a metal member of a cooling water system that can provide an excellent anti-corrosion effect on the surface of a metal member of a cooling water system in a shorter treatment time without using a phosphoric acid-based corrosion inhibitor. anti-corrosion method.

[Means to solve the problem] The present invention is based on the following discovery: by using tartaric acid-based compounds and further applying zinc-based compounds, a good anti-corrosion effect can be brought to the metal components of the cooling water system.

That is, the present invention provides the following [1] to [8]. [1] A method for preventing corrosion of metal components in a cooling water system, comprising: step (1), adding one or more compounds (A) selected from tartaric acid and tartrates to the cooling water system to contact the metal components; and (2) After the step (1), adding at least one compound (B) selected from zinc and zinc salts into the cooling water system to make it contact with the metal member. [2] The method for preventing corrosion of metal components in the cooling water system according to [1], wherein, in the step (1), adding 30 mg/ The compound (A) at a concentration of L to 100 mg/L. [3] The method for preventing corrosion of metal components in a cooling water system according to [1] or [2], wherein the pH of the cooling water system in the step (1) is 6.0 to 8.0. [4] The method for preventing corrosion of metal components of a cooling water system according to any one of [1] to [3], wherein, in the step (1), the metal component and the compound ( The contact time of A) is 20 hours - 30 hours. [5] The method for preventing corrosion of metal components of the cooling water system according to any one of [1] to [4], wherein, in the step (2), adding The compound (B) at a concentration of 1 mg/L to 50 mg/L in terms of zinc conversion. [6] The method for preventing corrosion of metal components of a cooling water system according to any one of [1] to [5], wherein, in the step (2), the metal component and the compound ( The contact time of B) is 20 hours - 30 hours. [7] The method for preventing corrosion of metal components in a cooling water system according to any one of [1] to [6], wherein the cooling water system is a circulating cooling water system. [8] The method for preventing corrosion of metal components in the cooling water system according to any one of [1] to [7], wherein the steps (1) and (2) are performed in the cooling water system in the basic processing.

[Effect of the invention] According to the present invention, an excellent anticorrosion effect can be imparted to the surface of a metal member in a cooling water system in a shorter treatment time without using a phosphoric acid-based anticorrosion agent. Therefore, the anti-corrosion method of the present invention can contribute to the maintenance of the cooling capacity of the cooling water system while dealing with environmental protection.

Hereinafter, the present invention will be described in detail.

The anti-corrosion method of the metal components of the cooling water system of the present invention has: step (1), adding more than one compound (A) selected from tartaric acid and tartrate in the cooling water system to make it contact with the metal components; and step (2) ), after the step (1), adding at least one compound (B) selected from zinc and zinc salts into the cooling water system to make it contact with the metal member. Thus, in the anticorrosion method of this invention, after using a tartaric acid type compound (A) as an anticorrosion agent, a zinc type compound (B) is used. The tartaric acid-based compound has an effect of suppressing anodic reaction in the surface of the metal member. Furthermore, the zinc-based compound has an effect of suppressing a cathodic reaction in the surface of the metal member. According to the anticorrosion method of the present invention, an excellent anticorrosion effect can be imparted to the metal member due to the synergistic effect of both.

(cooling water system) The cooling water system in the present invention refers to a system through which cooling water is passed for operation of heat exchangers in air-conditioning equipment such as buildings and regional facilities, and mechanical equipment. The cooling water system can be any one of cross-flow type, open circulation type or closed circulation type. The invention can exert excellent anti-corrosion effect in the circulating cooling water system, especially in the open circulating cooling water system.

In the cooling water system, the present invention can be applied in any state such as start-up or steady operation, and is particularly preferably applied to basic treatment at start-up such as initial start-up or re-operation. When the cooling water system is started, there are likely to be a large amount of corrosion products in the system, and it is easy to consume the corrosion inhibitor. Therefore, the corrosion inhibitor is usually added at a concentration 3 to 10 times that of the stable operation, and anti-corrosion treatment is performed to obtain sufficient anti-corrosion effects. . The anti-corrosion treatment at the start-up of this kind of cooling water system is called basic treatment, and sometimes called initial treatment. The anti-corrosion method of the present invention can volatilize excellent anti-corrosion effects in such basic treatment.

As long as the cooling water system is of general cooling water system water quality, the anti-corrosion effect brought by the anti-corrosion method of the present invention can be fully exerted. Preferable pH is 6.0-8.0, more preferably 6.0-7.5, still more preferably 6.5-7.5. Moreover, the preferred calcium hardness is 30 mgCaCO ₃ /L-150 mgCaCO ₃ /L, more preferably 30 mgCaCO ₃ /L-120 mgCaCO ₃ /L, and still more preferably 30 mgCaCO ₃ /L-100 mgCaCO ₃ /L. Moreover, the preferred concentration of ionic silicon dioxide is 5 mgSiO ₂ /L to 35 mgSiO ₂ /L, more preferably 10 mgSiO ₂ /L to 30 mgSiO ₂ /L, further preferably 15 mgSiO ₂ /L to 25 mgSiO ₂ /L.

(metal components) The metal member is a metal member constituting a portion of the cooling water system that is in contact with cooling water. Examples of the metal member include metal parts in heat exchangers, refrigerators, various piping, valves, and the like. As the metal to which the present invention is applied, iron-based metals are preferred. For example, in carbon steel pipes (STB pipes) for boilers and heat exchangers, an excellent anti-corrosion effect can be obtained.

(step 1)) In the anticorrosion method of the present invention, first, one or more compounds (A) selected from tartaric acid and tartrates are added to the cooling water system and brought into contact with the metal member.

Compound (A) is a tartaric acid-based compound, that is, a compound selected from tartaric acid and tartrate salts. The tartaric acid-based compound is considered to impart an anti-corrosion effect to the metal member by adsorbing the hydroxyl group in the molecule to form an adsorption film on the surface of the metal member. Compared with the anti-corrosion film formed by the phosphoric acid-based anti-corrosion agent, that is, the precipitation film, this adsorption film has a faster film formation speed and can shorten the anti-corrosion treatment time.

In addition, although the details of the mechanism by which the anticorrosion effect is obtained by the compound (A) are not clear, it is estimated as follows. The tartrate ions generated from the compound (A) bond to the calcium ions present in the cooling water to form an adsorption film mainly composed of a poorly water-soluble calcium salt on the surface of the metal member. Furthermore, the compound (A) reacts with the iron component of the metal member, whereby an adsorption film can also be formed by the iron (II) tartrate. It is considered that this adsorption film (anti-corrosion film) prevents the metal member from being in direct contact with the corrosion factors contained in the cooling water system, such as dissolved oxygen or chloride ions, sulfuric acid ions, etc., thereby reducing the corrosion resistance of the metal member. Corrosion rate in the surface.

Tartaric acid does not matter whether it is L body, D body, meso body, or racemate (racemate). Described tartrate refers to the tartaric acid ion (anion) that is selected from the hydrogen atom of two hydroxyl groups and the hydrogen atom of two carboxyl groups in the tartaric acid molecule from the ionization of tartrate ion (anion) and the cation derived from the alkali. Compounds made of ionic bonds. Examples of the cation include alkali metal ions, alkaline earth metal ions, magnesium ions, zinc ions, aluminum ions, iron ions (II), and ammonium ions. Specific examples of the tartrate include sodium hydrogen tartrate, potassium hydrogen tartrate, lithium tartrate, sodium tartrate, potassium tartrate, potassium sodium tartrate, calcium tartrate, iron (II) tartrate, zinc tartrate, ammonium tartrate, and the like. Among these, sodium tartrate, potassium tartrate, and sodium potassium tartrate are preferable from the viewpoint of a good anticorrosion effect, easy availability, and the like. Compound (A) may be used alone or in combination of two or more.

Compound (A) is preferably added to the cooling water system at a concentration of 30 mg/L-100 mg/L in terms of tartaric acid conversion, more preferably 40 mg/L-90 mg/L, and more preferably 50 mg /L～70 mg/L. By making the above-mentioned concentration 30 mg/L or more, a good anti-corrosion effect can be obtained. Moreover, when it is 100 mg/L or less, corrosion of the metal member due to chelation of tartrate ions can be suppressed.

The pH of the cooling water system in step (1) is preferably from 6.0 to 8.0, more preferably from 6.0 to 7.5, and still more preferably from 6.5 to 7.5. By setting the pH to 6.0 or higher, acid corrosion of the metal member can be suppressed. And by making the said pH into 8.0 or less, tartrate ions react with the metal ion (for example, iron ion) eluted from the surface of the said metal member, and it becomes easy to form an anticorrosion film. In addition, the pH in this invention is a value measured by the glass electrode method based on Japanese Industrial Standards (Japanese Industrial Standards, JIS) Z 8802:2011. Depending on the water quality of the cooling water system, either one of tartaric acid and a tartrate salt can be selected and used as the compound (A) so that the pH falls within the above-mentioned range. Moreover, the said pH can be adjusted using general pH adjusters, such as sulfuric acid, sodium hydroxide, and potassium hydroxide, for example.

The contact time between the metal member and the compound (A) is preferably 20 hours to 30 hours, more preferably 20 hours to 28 hours, and still more preferably 20 hours to 24 hours. If the contact time is more than 20 hours, a good anti-corrosion effect can be obtained. Moreover, when it exceeds 30 hours, improvement with time of an anticorrosion effect cannot be expected, Therefore From a viewpoint of an anticorrosion effect, it is preferable that it is 30 hours or less. In addition, the contact time is equivalent to the water passing time when the cooling water is passed through the cooling water system. Furthermore, in the case of a circulating cooling water system, it can also be regarded as the circulation time of cooling water. In order to make the compound (A) spread over the surface of the metal member at a uniform concentration, the cooling water system is preferably in a water-flowing state, and is preferably circulated from the viewpoint of efficiency.

When applying the anticorrosion method of the present invention to basic treatment, step (1) is preferably performed in a state where no thermal load is applied to the cooling water system. The "state without thermal load" mentioned in this manual refers to the state before stable operation, that is, the high-temperature fluid to be cooled by the cooling water is not introduced into the contact surface with the cooling water system, and the cooling water is not used. The state heated by the high-temperature fluid, that is, the non-heat transfer state. The specific temperature in a state where no heat load is applied is preferably from 10°C to 40°C, more preferably from 15°C to 35°C, and still more preferably from 20°C to 30°C. When the temperature is within the above range, evaporation in the cooling water system is suppressed, and it becomes easy to maintain the concentration of the compound (A) constant.

From the viewpoint of obtaining a uniform anti-corrosion effect on the surface of the metal member, the concentration of the compound (A) in the cooling water system is preferably kept constant. In the middle of the step, when the concentration of the compound (A) decreases due to the significant consumption of the compound (A) due to the adhesion of corrosion products existing in the cooling water system, etc., it is preferable to add the compound (A) to achieve the concentration range. Furthermore, when the concentration of the compound (A) increases due to evaporation in the cooling water system or the like in the middle of the process, water may be supplied for dilution.

(step (2)) After step (1), one or more compounds (B) selected from zinc and zinc salts are added to the cooling water system to make contact with the metal member.

Compound (B) is a zinc-based compound, that is, a compound selected from zinc and zinc salts. As a zinc salt, zinc chloride, zinc sulfate, etc. are mentioned, for example. The compound (B) may be used alone or in combination of two or more. As described above, after treating the metal member with the compound (A) having the effect of suppressing the anodic reaction on the surface, and then treating the metal member with the compound (B) having the effect of suppressing the cathodic reaction, it can be shortened. Time-based anti-corrosion treatment, through the synergistic effect of the two compounds, imparts an excellent anti-corrosion effect to the metal member. In addition, when the compound (A) and the compound (B) are added simultaneously, tartrate ions function as a dispersant for zinc ions, whereby a favorable anticorrosion effect cannot be obtained.

Compound (B) is preferably added to the cooling water system at a concentration of 1 mg/L-50 mg/L in terms of zinc conversion, more preferably 2 mg/L-30 mg/L, and more preferably 3 mg /L～20 mg/L, preferably 3 mg/L～10 mg/L. If it is a concentration within the above range, a good anti-corrosion effect can be obtained. However, if the concentration becomes high, scale will easily adhere to the metal member, so as the upper limit, it is preferably 50 mg/L or less, more preferably 30 mg/L or less, and even more preferably 20 mg/L. L or less, preferably less than 10 mg/L.

The contact time between the metal member and the compound (B) is preferably 20 hours to 30 hours, more preferably 20 hours to 28 hours, and still more preferably 20 hours to 24 hours. If the contact time is more than 20 hours, a good anti-corrosion effect can be obtained. Moreover, when it exceeds 30 hours, improvement with time of an anticorrosion effect cannot be expected, Therefore From a viewpoint of an anticorrosion effect, it is preferable that it is 30 hours or less. In addition, the said contact time has the same meaning as the contact time with respect to the said compound (A). In order to make the compound (B) spread over the surface of the metal member at a uniform concentration, the cooling water system is preferably in a water-passing state, and is preferably circulated from the viewpoint of efficiency.

When applying the anticorrosion method of the present invention to basic treatment, step (2) is preferably performed in a state where no thermal load is applied to the cooling water system, as in the above step (1). The specific temperature is also the same as that in the step (1) from the viewpoint that it is easy to keep the concentration of the compound (B) constant.

From the viewpoint of obtaining a uniform anti-corrosion effect on the surface of the metal member, the concentration of the compound (B) in the cooling water system is preferably kept constant. When the concentration of the compound (B) decreases due to significant consumption of the compound (B) in the middle of the step, it is preferable to add the compound (B) to achieve the concentration range. Furthermore, when the concentration of the compound (B) increases due to evaporation in the cooling water system or the like in the middle of the process, water may be supplied for dilution.

In the case where the cooling water system is in a water-through state, the water-through speed of the cooling water system, that is, the flow rate, is not particularly limited. For example, when the anti-corrosion method of the present invention is applied to basic treatment, the stability of the cooling water system The flow velocity during operation is usually 0.3 m/s to 1.0 m/s, but even if it is the same or at a low velocity, specifically, even if it is 0.2 m/s to 0.5 m/s, according to the corrosion prevention method of the present invention, Good anti-corrosion effect can also be obtained.

When applying the anticorrosion method of the present invention to the basic treatment, the steady operation is started after the steps (1) and (2) as the basic treatment are completed. In this case, the compound (A) and/or the compound (B) may be contained in the cooling water system during the stable operation. In the cooling water system, well-known water treatment chemicals such as slime inhibitors, fouling inhibitors, and other corrosion inhibitors can be added to perform stable operation. Example

Hereinafter, the present invention will be described in more detail, but the present invention is not limited by the following examples. In addition, water used in each of the following tests was tap water in Nogi Town, Shimotsuga-gun, Tochigi Prefecture (pH 7.0, calcium hardness 40 mgCaCO ₃ /L, ionic silica concentration 20 mgSiO ₂ /L).

[Test 1] Evaluation of corrosion reduction (Example 1) A 30 mm x 50 mm, 1 mm thick SPCC (cold-rolled steel sheet) test piece was immersed in nitric acid with a concentration of 20 mass % for 30 seconds, and then immersed in sulfuric acid with a concentration of 10 mass % for 60 seconds. Perform etching treatment. After this test piece was washed with water, it was dried, and the weight before the test (W1) was measured. Water was placed in a 1 L beaker, and sodium tartrate at a concentration of 50 mg/L (in terms of tartaric acid) was added to obtain a test solution whose pH was adjusted to 7.5. After immersing the test piece in the test solution for 24 hours by means of a rotary corrosion test device (manufactured by Shinwa Chemical Co., Ltd.; test solution temperature 30°C, test piece rotation speed 150 rpm), add Concentration of 5 mg/L (zinc equivalent) of zinc chloride, and then continue to immerse for 24 hours. After replacing this test solution with water and further immersing it for 24 hours, the test piece was pulled up, dried, and the weight after the test (W2) was measured. The value (W1-W2) obtained by subtracting the weight after the test (W2) from the weight before the test (W1) was determined as the amount of corrosion reduction.

(comparative example 1) In Example 1, zinc chloride was not added, and after 48 hours of immersion in the test solution of sodium tartrate aqueous solution, the test solution was replaced with water, and the amount of corrosion reduction was obtained in the same manner as in Example 1. .

(comparative example 2) In Example 1, after 48 hours of immersion in the test solution to which the aqueous solution of sodium tartrate and zinc chloride was added at the same time from the beginning, the test solution was replaced with water, and in the same manner as in Example 1 Calculate the corrosion reduction.

The results of Test 1 are shown in Table 1 below.

[Table 1] Table 1 Sodium tartrate [mg/L] (converted to tartaric acid) Zinc chloride [mg/L] (Zinc conversion amount) Corrosion reduction [mg] Example 1 50 5 (added after 24 hours) 4.7 Comparative example 1 50 - 8.0 Comparative example 2 50 5 (add at the same time) 12.6

From the results shown in Table 1, it can be said that when zinc chloride was added to sodium tartrate later (Example 1), the amount of corrosion reduction was small and a good anticorrosion film was formed. In addition, it is considered that when zinc chloride and sodium tartrate were added together (comparative example 2), tartrate ions functioned as a dispersant for zinc ions, and compared with the case where only sodium tartrate was added (no zinc chloride was added), In the case (Comparative Example 1), the formation of the anti-corrosion film is more difficult, so the amount of corrosion reduction increases.

[Test 2] Simulated real machine test In the heat exchanger test device of the cooling water system shown in Figure 1, for the tube (tube) 2 (STB340 (carbon steel pipe for heat exchanger) in the multi-tube heat exchanger 1, the outer diameter is 19 mm, Thickness 2.3 mm, length 1350 mm, 2), after the basic treatment of the following examples and comparative examples, the stable operation was carried out, and the maximum pitting depth and dirt adhesion speed were evaluated. The heat exchanger 1 is connected to the cooling tower 3, and cold water to which a predetermined chemical is added is supplied from the 500 L water storage tank 4 at the lower part of the cooling tower 3 through the water supply pump P1. The cold water circulates in the tubes 2 in the heat exchanger 1 . To the outside of the tube 2 in the heat exchanger 1, steam (heat source) 10 is supplied via a temperature adjustment valve V1. The steam is cooled by cold water flowing through the pipe 2 and discharged as drain 11 . The cold water is heated by heat exchange with the steam 10 to become warm water, sent to the cooling tower 3 , and sprayed to the filling material 5 . Air is sucked into the cooling tower 3 from the side peripheral portion of the cooling tower 3 and exhausted by an exhaust fan (fan) 6 at the top.

To the cold water in the water storage tank 4, water treatment chemicals are added from the chemical tank 7 through the chemical injection pump P2. The concentration and water quality of the water treatment chemicals in the cold water in the water storage tank 4 are managed by an automatic conductivity management device 8 ("Kuriauto (registered trademark) C-505", manufactured by Kurita Industrial Co., Ltd.) , It is also possible to make the chemical injection pump P2 and the discharge pump (blow pump) P3 interlock to perform proper discharge. Also, make-up water 20 may be added as needed.

[Test 2-1] Confirmation of the influence of the addition amount of zinc chloride

(Example 2)

Base treatment of tube 2 was performed as follows. Store synthetic water (calcium hardness 100mgCaCO ₃ /L, total hardness 150mgCaCO ₃ /L, acid consumption 30mgCaCO ₃ /L) in the water storage tank 4, add sodium tartrate with a concentration of 50mg/L (tartaric acid conversion amount), adjust to pH 7.5 . Open the valve V2 for circulation, and pass this water to a test tube A in the tube 2 at a flow rate of 5.3 L/min (flow rate 0.5 m/s). In addition, the flow rate was measured with the flowmeter 9 near the inlet of the heat exchanger 1 (it shall be the same hereafter).

After 24 hours, add zinc chloride with a concentration of 2mg/L (zinc conversion amount) to this water, and continue to maintain the flow rate (flow rate) to pass water to the test tube A for 24 hours.

(Example 3 to Example 5 and Comparative Example 3) In Example 2, the concentration of zinc chloride added later was changed to 5 mg/L (converted amount of zinc), 10 mg/L (converted amount of zinc), 30 mg/L (converted amount of zinc), 0 mg/L Except for L (not added), the base treatment of the tube 2 was carried out in the same manner as in Example 2.

(reference example 1) Base treatment of tube 2 is carried out in this way. The same synthetic water as in Example 2 was stored in the water storage tank 4, and sodium hexametaphosphate (sodium hexametaphosphate) with a concentration of 100 mg/L (converted amount of phosphoric acid) and chlorine with a concentration of 20 mg/L (converted amount of zinc) were added at the same time. Zinc chloride, adjusted to pH 7.5. The circulation valve V2 was opened, and the water was passed through the test tube A at the same flow rate (flow rate) as in Example 2 for 4 days.

[Water flow test (1)] After performing the basic treatment of each of the examples, comparative examples, and reference examples, synthetic water (pH 8.5 to 8.7, calcium hardness 450 mgCaCO ₃ /L to 500 mgCaCO ₃ /L, acid consumption 130 mgCaCO ₃ /L～170 mgCaCO ₃ /L, maleic acid polymer 10 mgsolid/L～15 mgsolid/L, zinc chloride 1.8 mg/L～2.2 mg/L (converted to zinc quantity)). Then, into the synthetic water, the maleic acid-based polymer and zinc were injected into the above-mentioned concentration range, and sodium hypochlorite was added as the slime control agent so that the total residual chlorine concentration became 0.1 mg/L. ～0.2 mg/L to inject the drug. Start the operation of the device, pass water into the test tube A at a flow rate of 0.5 m/s, and perform the operation. Control was performed so that the inlet water temperature (cold water) of the water supplied to the heat exchanger 1 was 30°C, and the outlet water temperature (warm water) was 40°C. On the 14th day of operation, the water flow test was completed.

After the water test is over, remove the test tube A. The test tube A was cut at intervals of 200 mm in length and divided in half to prepare tubes for evaluation. The maximum pitting depth and the scale deposition rate were obtained as follows, and the basic treatment methods of the above-mentioned examples, comparative examples, and reference examples were evaluated.

･Maximum pitting depth For each tube for evaluation, the inner surface of the tube was visually observed, and the pitting depth was measured with a dial gauge. The maximum value among the pitting depths measured for all the tubes for evaluation was set as the maximum pitting depth. The maximum pitting depth is an index of the anti-corrosion effect, and it can be said that the smaller the value, the better the anti-corrosion effect.

･Fouling adhesion speed For each evaluation tube, the deposits on the inner surface of the tube were recovered and dried to measure the mass. The deposits were regarded as dirt, and for each tube for evaluation, the amount of dirt deposited on average for one month [mg/(cm ² ･month)] in a surface area of 1 cm ² on the inner surface of the tube was calculated. The maximum value among the amounts of stain deposition calculated for all the tubes for evaluation was defined as the stain deposition rate. It can be said that the smaller the value of the dirt adhesion rate, the more excellent the dirt adhesion inhibiting effect.

These evaluation results are shown in Table 2 below.

[Table 2] Table 2 Sodium tartrate [mg/L] (converted to tartaric acid) Zinc chloride [mg/L] (Zinc equivalent) Maximum pitting depth [mm] Dirt adhesion speed [mg/(cm ² ･month)] Example 2 50 2 0.02 2.0 Example 3 50 5 0.02 3.8 Example 4 50 10 0.01 9.1 Example 5 50 30 0.01 15.4 Comparative example 3 50 - 0.18 2.9 Reference example 1 Sodium hexametaphosphate [mg/L] (phosphoric acid conversion) 100 20 (add at the same time, 4 days) 0.02 8.8

From the results shown in Table 2, it was confirmed that by adding zinc chloride (Example 2 to Example 5) after adding sodium tartrate in the basic treatment of pipe 2, it was confirmed that the phosphoric acid-based anticorrosion agent used in the past Compared with the case where zinc chloride is used in combination (Reference Example 1), even if the addition amount of sodium tartrate and zinc chloride, that is, the addition amount of the anti-corrosion agent is small, a high anti-corrosion effect can be obtained in a shorter treatment time. Furthermore, it was confirmed that, compared with the conventional method of using sodium phosphate in combination (Reference Example 1), by using it in combination with sodium tartrate, it is only necessary to suppress the addition concentration of zinc chloride to a predetermined amount (Example 2 and Example 3), it is excellent in the aspect of the effect of suppressing the adhesion of dirt. In addition, it is considered that when the added concentration of zinc chloride becomes higher (Example 4 and Example 5), zinc ions become the substance causing the fouling, and thus the fouling rate increases.

[Test 2-2] Confirmation of the influence of the flow rate (Example 6, Example 7, Comparative Example 4 and Reference Example 2) In embodiment 3, embodiment 5, comparative example 3 and reference example 1, instead of passing water to test tube A, be set to flow 3.2 L/min (flow velocity 0.3 m/min) to another test tube B in tube 2 s) Water flow was carried out, except that, in the same manner as in Example 3, Example 5, Comparative Example 3, and Reference Example 1, respectively, as Example 6, Example 7, Comparative Example 4, and Reference Example 2. Tube 2 base treatment.

[Water test (2)] After performing the basic treatment of each of the Examples, Comparative Examples, and Reference Examples, a water-passing test similar to the water-passing test (1) of the above-mentioned Test 2-1 was performed. Regarding the water passage test (2) in this test 2-2, in the water passage test (1), instead of passing water to the test pipe A, it is set to pass water to the test pipe B at a flow rate of 0.3 m/s. Water was performed in the same manner as the above-mentioned water passage test (1) except for that.

After the water test was over, the test tube B was removed, and in the same manner as the evaluation method in the test 2-1, the maximum pitting depth and dirt adhesion speed were obtained. For the various embodiments, comparative examples and reference Case-based methods are evaluated. These evaluation results are shown in Table 3 below.

[Table 3] Table 3 Velocity [m/s] Sodium tartrate [mg/L] (converted to tartaric acid) Zinc chloride [mg/L] (Zinc conversion amount) Maximum pitting depth [mm] Dirt adhesion speed [mg/(cm ² ･month)] Example 3 0.5 50 5 0.02 3.8 Example 6 0.3 0.02 3.6 Example 5 0.5 50 30 0.01 15.4 Example 7 0.3 0.01 20.5 Comparative example 3 0.5 50 - 0.18 2.9 Comparative example 4 0.3 0.17 12.5 Reference example 1 0.5 Sodium hexametaphosphate [mg/L] (phosphoric acid conversion) 100 20 (add at the same time, 4 days) 0.02 8.8 Reference example 2 0.3 0.01 4.1

From the results shown in Table 3, it was confirmed that even in the case of low flow velocity (0.3 m/s) (Example 6 and Example 7), the same flow rate as that of the flow velocity of 0.5 m/s ( Example 3 and Example 5) have the same high anti-corrosion effect.

1: Multi-tubular heat exchanger (heat exchanger) 2: tube 3: cooling tower 4: Water storage tank 5: Filling material 6:Exhaust fan 7: potion tank 8: Conductivity automatic management device 9: Flow meter 10: steam 11: discharge water 20: Supply water P1: water pump P2: Pharmacy Injection Pump P3: discharge pump V1: temperature adjustment valve V2: Valve for circulation

FIG. 1 is a schematic diagram showing an outline of a heat exchanger test device for a cooling water system in an example.

1: Multi-tube heat exchanger

2: tube

3: cooling tower

4: Water storage tank

5: Filling material

6:Exhaust fan

7: potion tank

8: Conductivity automatic management device

9: Flow meter

10: steam

11: discharge water

20: Supply water

P1: water pump

P2: Pharmacy Injection Pump

P3: discharge pump

V1: temperature adjustment valve

V2: Valve for circulation

Claims (8)

A method for preventing corrosion of metal components in a cooling water system, comprising: step (1), adding more than one compound (A) selected from tartaric acid and tartrates to the cooling water system to make it contact with the metal components; and step (2) , after the step (1), adding one or more compounds (B) selected from zinc and zinc salts to the cooling water system to make it contact with the metal member. The anti-corrosion method of the metal components of the cooling water system as described in item 1 of the scope of patent application, wherein, in the step (1), in the cooling water system, add 30mg/L~100mg in conversion amount of tartaric acid /L concentration of the compound (A). The method for preventing corrosion of metal components in a cooling water system as described in item 1 or item 2 of the scope of the patent application, wherein the pH of the cooling water system in the step (1) is 6.0-8.0. The anti-corrosion method of the metal component of the cooling water system as described in item 1 or item 2 of the patent scope, wherein, in the step (1), the contact time between the metal component and the compound (A) is 20 hours to 30 hours. The anti-corrosion method of the metal components of the cooling water system as described in item 1 or item 2 of the scope of application, wherein, in the step (2), 1 mg is added to the cooling water system in terms of zinc conversion The compound (B) of the concentration of /L～50mg/L. The anti-corrosion method of the metal components of the cooling water system as described in item 1 or item 2 of the scope of the patent application, wherein, in the step (2), the metal components and The contact time of the compound (B) is 20 hours to 30 hours. The anticorrosion method for metal components of a cooling water system as described in item 1 or item 2 of the scope of the patent application, wherein the cooling water system is a circulating cooling water system. The anti-corrosion method of the metal components of the cooling water system as described in item 1 or item 2 of the patent scope, wherein, the step (1) and the step (2) are in the basic treatment of the cooling water system conduct.

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