TW202028535A - Method for inhibiting corrosion of metal member of cooling water system - Google Patents

Abstract

A method for inhibiting corrosion of a metal member of a cooling water system, which comprises: a step (1) wherein one or more compounds (A) selected from among tartaric acid and tartaric acid salts are added into the cooling water system, thereby being brought into contact with the metal member; and a step (2) wherein one or more compounds (B) selected from among zinc and zinc salts are added into the cooling water system after the step (1), thereby being brought into contact with the metal member.

Description

Anti-corrosion method for metal components of cooling water system

The invention relates to an anticorrosion method for metal components of a cooling water system, which forms an anticorrosion film on the surface of a metal component that is in contact with the cooling water in the cooling water system.

In order to indirectly cool various fluids in air-conditioning equipment such as buildings and local facilities, and plants, water-cooled heat exchangers are used. Metals such as carbon steel or stainless steel are generally used for various components such as heat exchangers and piping around them in such cooling water systems. If these metal members are always or intermittently in contact with cooling water, they are likely to corrode due to dissolved oxygen in the water. If metal components such as piping are reduced in thickness 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 anti-corrosion method for such a metal member, for example, Patent Document 1 proposes to form a strong anti-corrosion film on the surface of the metal member by using phosphoric acid-based and zinc-based corrosion inhibitors in the basic treatment at the start of the cooling water system . [Prior Art Literature] [Patent Literature]

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

[The problem to be solved by the invention] However, in recent years, due to increasing concern for environmental protection or strengthening of drainage restrictions, it is required to reduce the content of phosphorus and the like in drainage. It is difficult for machinery and equipment without drainage treatment equipment to meet this requirement, and sometimes the use of phosphoric acid and zinc corrosion inhibitors has to be discontinued. In addition, the phosphoric acid-based corrosion inhibitor forms the corrosion protection film by depositing the film, so a long time of about 4 days is required in the basic treatment. Therefore, it is also desired to shorten the basic processing period.

Therefore, an anti-corrosion method that can obtain an excellent anti-corrosion effect in a shorter time without using a phosphoric acid-based anti-corrosion agent is sought.

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

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

That is, the present invention provides the following [1] to [8]. [1] An anti-corrosion method for metal components of a cooling water system, comprising: step (1), adding one or more compounds (A) selected from the group consisting of tartaric acid and tartrate to the cooling water system to contact the metal components; and (2) After the step (1), one or more compounds (B) selected from zinc and zinc salts are added to the cooling water system to contact the metal member. [2] The method for preventing corrosion of metal components of a cooling water system as described in [1], wherein, in the step (1), 30 mg per tartaric acid conversion amount is added to the cooling water system. The compound (A) at a concentration of L to 100 mg/L. [3] The method for preventing corrosion of metal components of a cooling water system as described in [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 a metal member of a cooling water system according to any one of [1] to [3], wherein, in the step (1), the metal member and the compound ( A) The contact time is 20 hours to 30 hours. [5] The method for preventing corrosion of metal components of a cooling water system according to any one of [1] to [4], wherein, in the step (2), adding to the cooling water system 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 a metal member of a cooling water system according to any one of [1] to [5], wherein, in the step (2), the metal member and the compound ( B) The contact time is 20 hours to 30 hours. [7] The method for preventing corrosion of metal components of 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 of a 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.

[Effects of the invention] According to the present invention, without using a phosphoric acid-based corrosion inhibitor, it is possible to impart an excellent corrosion protection effect to the surface of the metal member of the cooling water system in a shorter processing time. Therefore, the anti-corrosion method of the present invention can help maintain the cooling capacity of the cooling water system while coping with environmental protection.

Hereinafter, the present invention will be described in detail.

The method for preventing corrosion of metal components of a cooling water system of the present invention includes: step (1), adding one or more compounds (A) selected from the group consisting of tartaric acid and tartrate to the cooling water system to contact the metal component; and step (2) ), after the step (1), add one or more compounds (B) selected from zinc and zinc salts to the cooling water system to make contact with the metal member. In this way, in the corrosion prevention method of the present invention, after using the tartaric acid compound (A) as the corrosion inhibitor, the zinc compound (B) is used. The tartaric acid-based compound has an effect of suppressing an anode reaction in the surface of the metal member. Moreover, the zinc-based compound has an effect of suppressing the cathode reaction in the surface of the metal member. According to the anti-corrosion method of the present invention, an excellent anti-corrosion effect can be imparted to the metal member due to the synergistic effect of the two.

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

In the cooling water system, the present invention can be applied in any state such as startup or stable operation, and is particularly preferably applied to basic processing at startup such as initial startup or re-operation. When the cooling water system is started, there are a lot 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 of 3 to 10 times that of the stable operation to perform the corrosion protection treatment to obtain sufficient corrosion protection effect. . The anti-corrosion treatment at the start of this cooling water system is called basic treatment, and sometimes called initial treatment. The anti-corrosion method of the present invention can volatilize an excellent anti-corrosion effect in such basic treatment.

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

(Metal components) The metal member is a metal member constituting a part of the cooling water system that is in contact with cooling water. As the metal member, for example, the target is a metal part in a heat exchanger, a refrigerator, various pipes, and valves. The metal to which the present invention is applied is preferably an iron-based metal. For example, in carbon steel pipes (STB pipes) for boilers/heat exchangers, etc., an excellent anti-corrosion effect can be obtained.

(step 1)) In the corrosion prevention method of the present invention, first, one or more compounds (A) selected from the group consisting of tartaric acid and tartrate are added to the cooling water system to make contact with the metal member.

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

In addition, although the details of the mechanism by which the compound (A) can obtain the anti-corrosion effect are not clear, it is estimated as follows. Tartrate ions generated from the compound (A) are bonded to calcium ions present in the cooling water, and an adsorption film mainly composed of calcium salts that are hardly soluble in water is formed on the surface of the metal member. In addition, the compound (A) reacts with the iron component of the metal member, thereby forming an adsorption film by iron (II) tartrate. It is believed that this kind of adsorption film (anti-corrosion film) prevents direct contact between the metal components and the corrosion factors contained in the cooling water system such as dissolved oxygen, chloride ions, and sulfate ions, thereby reducing the size of the metal components. The rate of corrosion in the surface.

Tartaric acid is either L-body, D-body, meso or racemate (racemate). The tartrate refers to a tartrate ion (anion) formed by ionizing tartaric acid from one or more hydrogen atoms selected from the hydrogen atoms of the two hydroxyl groups and the hydrogen atoms of the two carboxyl groups in the tartaric acid molecule and the cation derived from alkali. A compound formed by ionic bonding. 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, from the viewpoint of a good anticorrosive effect, easy availability, etc., sodium tartrate, potassium tartrate, and sodium potassium tartrate are preferred. The compound (A) may be used alone or in combination of two or more kinds.

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 concentration above 30 mg/L, a good anti-corrosion effect can be obtained. Moreover, if it is 100 mg/L or less, it is possible to suppress the corrosion of the metal member caused by the chelation of tartrate ions.

The pH of the cooling water system in step (1) is preferably 6.0-8.0, more preferably 6.0-7.5, and still more preferably 6.5-7.5. By setting the pH to 6.0 or more, acid corrosion of the metal member can be suppressed. Furthermore, by making the pH 8.0 or less, tartaric acid ions react with metal ions (for example, iron ions) eluted from the surface of the metal member, so that a corrosion protection film is easily formed. In addition, the pH in the present invention is a value measured by a glass electrode method in accordance with Japanese Industrial Standards (JIS) Z 8802:2011. According to the water quality of the cooling water system, it is possible to select and use any one of tartaric acid and tartrate as the compound (A) so that the pH is within the above range. Moreover, the said pH can be adjusted using general pH adjusters, such as sulfuric acid, sodium hydroxide, 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, the improvement of the anti-corrosion effect over time cannot be expected, so from the viewpoint of the anti-corrosion effect, it is preferably 30 hours or less. In addition, the contact time corresponds to the water passing time when cooling water is passed through the cooling water system. Moreover, in the case of a circulating cooling water system, it can also be regarded as the circulation time of cooling water. In order for the compound (A) to spread over the surface of the metal member at a uniform concentration, the cooling water system is preferably in a water-passing state, and from the viewpoint of efficiency, it is preferably circulated.

In the case of applying the anti-corrosion 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, no high-temperature fluid to be cooled by the cooling water is introduced to the contact surface with the cooling water system. The state heated by the high-temperature fluid, that is, the non-heat transfer state. The specific temperature in the state where no heat load is applied is preferably 10°C to 40°C, more preferably 15°C to 35°C, and still more preferably 20°C to 30°C. By setting the temperature within the above-mentioned range, evaporation in the cooling water system is suppressed, so that the concentration of the compound (A) is easily maintained 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 maintained at a constant level. 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 in the middle of the step, it is preferable to add the compound (A) to achieve The concentration range. In addition, when the concentration of the compound (A) rises due to evaporation in the cooling water system in the middle of the step, it is also possible to supplement water 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. Examples of zinc salts include zinc chloride and zinc sulfate. The compound (B) may be used alone or in combination of two or more. As described above, after the metal member is treated with the compound (A) that has the effect of suppressing the anode reaction on the surface, the compound (B) is further treated with the compound (B) that has the effect of suppressing the cathode reaction. The time-based anti-corrosion treatment imparts an excellent anti-corrosion effect to the metal component due to the cooperative effect of the two compounds. In addition, when the compound (A) and the compound (B) are added at the same time, the tartrate ion acts as a dispersant for the zinc ion, thereby failing to obtain a good anticorrosive effect.

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, especially 3 mg/L～10 mg/L. If the concentration is within the above range, a good anti-corrosion effect can be obtained. However, if the concentration becomes higher, scale is likely to adhere to the metal member. Therefore, as the upper limit, it is preferably 50 mg/L or less, more preferably 30 mg/L or less, and still more preferably 20 mg/L. Less than L, particularly 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, the improvement of the anti-corrosion effect over time cannot be expected, so from the viewpoint of the anti-corrosion effect, it is preferably 30 hours or less. In addition, the contact time has the same meaning as the contact time for the compound (A). In order for the compound (B) to spread over the surface of the metal member at a uniform concentration, the cooling water system is preferably in a water-passing state, and from the viewpoint of efficiency, it is preferably circulated.

In the case of applying the anti-corrosion method of the present invention to the basic treatment, step (2) is also the same as the step (1), preferably performed in a state where no thermal load is applied to the cooling water system. From the viewpoint that it is easy to maintain the concentration of the compound (B) at a constant level, the specific temperature is also the same as in step (1).

From the viewpoint that a uniform anti-corrosion effect can be obtained on the surface of the metal member, the concentration of the compound (B) in the cooling water system is preferably maintained at a constant level. 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 realize the concentration range. In addition, when the concentration of the compound (B) rises due to evaporation in the cooling water system in the middle of the step, it is also possible to supplement water for dilution.

When the cooling water system is in a water-passing state, the water-passing speed, that is, the flow rate of the cooling water system, is not particularly limited. For example, when the anti-corrosion method of the present invention is applied to basic treatment, the cooling water system is stable The flow velocity during operation is usually 0.3 m/s to 1.0 m/s. On the other hand, even at the same or low speed, specifically even 0.2 m/s to 0.5 m/s, according to the corrosion prevention method of the present invention, It can also obtain a good anti-corrosion effect.

When the corrosion prevention method of the present invention is applied to the basic treatment, after completing the steps (1) and (2) as the basic treatment, stable operation is started. At this time, during the steady operation, the compound (A) and/or the compound (B) may be contained in the cooling water system. In the cooling water system, well-known water treatment agents such as slime inhibitors, dirt inhibitors, and other corrosion inhibitors can be added for 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, the water used in the following tests was tap water (pH 7.0, calcium hardness 40 mgCaCO ₃ /L, ionic silica concentration 20 mgSiO ₂ /L) in Nogi Town, Shimotsuga County, Tochigi Prefecture.

[Test 1] Evaluation of corrosion reduction (Example 1) A test piece of SPCC (cold rolled steel sheet) with a thickness of 30 mm × 50 mm and a thickness of 1 mm was immersed in nitric acid with a concentration of 20% by mass for 30 seconds, and then immersed in sulfuric acid with a concentration of 10% by mass for 60 seconds. Perform etching treatment. After washing this test piece with water, it was dried, and the weight before the test (W1) was measured. Put water in a 1 L beaker and add sodium tartrate with a concentration of 50 mg/L (tartaric acid conversion amount) to obtain a test solution adjusted to pH 7.5. After immersing the test piece in the test solution for 24 hours with a rotating corrosion test device (manufactured by Xinhe Chemical Co., Ltd.; test solution temperature 30°C, test piece rotation speed 150 rpm), add it to the test solution Zinc chloride with a concentration of 5 mg/L (zinc conversion amount), and then continue to soak for 24 hours. This test solution was replaced with water, and after further immersion for 24 hours, the test piece was lifted, dried, and the weight after the test (W2) was measured. The value (W1-W2) obtained by subtracting the weight (W2) after the test from the weight before the test (W1) was calculated as the amount of corrosion reduction.

(Comparative example 1) In Example 1, zinc chloride was not added, and after being immersed in a test solution of sodium tartrate aqueous solution for 48 hours, the test solution was replaced with water, except that the amount of corrosion reduction was determined in the same manner as in Example 1. .

(Comparative example 2) In Example 1, after immersing for 48 hours in a test solution containing an aqueous solution of sodium tartrate and zinc chloride added at the same time from the beginning, the test solution was replaced with water, except that it was performed in the same manner as in Example 1. Find the amount of corrosion reduction.

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

[Table 1] Table 1 Sodium tartrate [mg/L] (converted amount of tartaric acid) Zinc chloride [mg/L] (converted amount of zinc) 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 seen that when zinc chloride is added to sodium tartrate later (Example 1), the amount of corrosion reduction is small, and it can be said that a good corrosion protection film is formed. In addition, it is believed that when zinc chloride and sodium tartrate are added at the same time (Comparative Example 2), tartrate ions act as a dispersant for zinc ions, compared to the case where only sodium tartrate is added (without zinc chloride) In the case (Comparative Example 1), it is more difficult to form an anti-corrosion film, so the amount of corrosion reduction increases.

[Test 2] Simulate real machine test In the heat exchanger test device of the cooling water system as shown in Fig. 1, the tube 2 (STB340 (carbon steel pipe for heat exchanger), outer diameter 19 mm, Thickness 2.3 mm, length 1350 mm, 2 pieces), after the basic treatment of the following examples and comparative examples, stable operation was performed, and the maximum pitting corrosion depth and dirt adhesion speed were evaluated. The heat exchanger 1 is connected to the cooling tower 3, and the 500 L water storage tank 4 at the lower part of the cooling tower 3 is supplied with cold water added with a predetermined chemical by the water supply pump P1. The cold water circulates in the tube 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 the cold water circulating in the tube 2 and discharged as drain 11. Due to the heat exchange with the steam 10, the cold water is heated to become warm water, is sent to the cooling tower 3, and is dispersed to the filling material 5. Air is sucked into the cooling tower 3 from the side periphery of the cooling tower 3 and exhausted by an upper fan 6. To the cold water in the water storage tank 4, the water treatment chemical is added from the chemical tank 7 through the chemical injection pump P2. The concentration and water quality of the water treatment agent in the cold water in the water storage tank 4 are managed by the electrical conductivity automatic management device 8 ("kuriauto (registered trademark) C-505", manufactured by Kurita Industrial Co., Ltd.) , It is also possible to link the medicament injection pump P2 with the blow pump P3 for proper discharge. Furthermore, supplemental water 20 can be added as needed.

[Test 2-1] Confirmation of the influence of the addition amount of zinc chloride (Example 2) The basic treatment of the tube 2 was performed as follows. In storage tank 4, store synthetic water (calcium hardness 100 mgCaCO ₃ /L, total hardness 150 mgCaCO ₃ /L, acid consumption 30 mgCaCO ₃ /L), and add sodium tartrate with a concentration of 50 mg/L (tartaric acid conversion amount), Adjust to pH 7.5. Open the circulation valve V2, and pass the water to a test tube A in tube 2 at a flow rate of 5.3 L/min (flow rate 0.5 m/s). In addition, the flow rate is measured with a flow meter 9 near the inlet of the heat exchanger 2 (hereinafter, the same). After 24 hours, zinc chloride with a concentration of 2 mg/L (amount of zinc conversion) was added to the water, and the test tube A was continuously maintained at the flow rate (flow velocity) 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 (zinc conversion amount), 10 mg/L (zinc conversion amount), 30 mg/L (zinc conversion amount), 0 mg/L Except for L (not added), the basic treatment of tube 2 was performed in the same manner as in Example 2.

(Reference example 1) The basic treatment of tube 2 is carried out in this way. In the water storage tank 4, the same synthetic water as in Example 2 was stored, and sodium hexametaphosphate (sodium hexametaphosphate) with a concentration of 100 mg/L (converted to phosphoric acid) and chlorine with a concentration of 20 mg/L (converted to zinc) were added at the same time. Zinc, 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 velocity) as in Example 2 for 4 days.

[Water flow test (1)] After the basic treatment of each of the examples, comparative examples and reference examples, synthetic water (pH 8.5-8.7, calcium hardness 450 mgCaCO ₃ /L-500 mgCaCO) was prepared in the water storage tank 4 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 (zinc conversion the amount)). Then, the synthetic water was injected with a chemical agent so that the maleic acid-based polymer and zinc could maintain the above concentration range, and sodium hypochlorite was used as a slime control agent so that the total residual chlorine concentration became 0.1 mg/L ~0.2 mg/L to inject the agent. Start the operation of the device, and run water through the test tube A at a flow rate of 0.5 m/s. It is controlled so that the inlet water temperature (cold water) of the water supplied to the heat exchanger 1 becomes 30 degreeC, and the outlet water temperature (warm water) becomes 40 degreeC. On the 14th day of operation, the water flow test was ended.

After the water flow test is over, remove the test tube A. The test tube A was cut every 200 mm in length and divided into half to produce an evaluation tube. The maximum depth of pitting corrosion and the dirt adhesion speed were determined as follows to evaluate the basic treatment methods of the respective Examples, Comparative Examples, and Reference Examples.

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

･The dirt adhesion speed is for each evaluation tube, and the adhesion on the inner surface of the tube is collected and dried to measure the quality. Regarding the deposits as dirt, the amount of dirt deposits [mg/(cm ² ･month)] in 1 cm ² of the surface area of the inner surface of the pipe for each evaluation tube was calculated. The maximum value of the dirt adhesion amounts calculated for all the evaluation tubes is defined as the dirt adhesion speed. It can be said that the smaller the dirt adhesion speed, the better the dirt adhesion inhibiting effect.

These evaluation results are shown in Table 2 below.

[Table 2] Table 2 Sodium tartrate [mg/L] (converted amount of tartaric acid) Zinc chloride [mg/L] (converted amount of zinc) 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] (Converted in phosphoric acid) 100 20 (add at the same time, 4 days) 0.02 8.8

According to the results shown in Table 2, it was confirmed that the basic treatment of tube 2, after adding sodium tartrate, and adding zinc chloride (Example 2 to Example 5), compared with the conventional phosphoric acid corrosion inhibitor 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 corrosion inhibitor is small, a shorter treatment time can still obtain a high corrosion protection effect. In addition, it was confirmed that, compared to the conventional method in combination with sodium phosphate (Reference Example 1), by combining with sodium tartrate, it was confirmed that the addition concentration of zinc chloride could be suppressed to a predetermined amount (Example 2 and Examples) 3), it will be excellent in the effect of inhibiting dirt adhesion. In addition, it is considered that if the concentration of zinc chloride added becomes higher (Example 4 and Example 5), zinc ions will become a fouling-causing substance, and therefore the fouling adhesion speed will increase.

[Test 2-2] Confirmation of the influence of flow rate (Example 6, Example 7, Comparative Example 4, and Reference Example 2) In Example 3, Example 5, Comparative Example 3, and Reference Example 1, instead of passing water to the test tube A, another test tube B in the tube 2 was set to flow 3.2 L/min (flow rate 0.3 m/ s) Passing water, 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 Basic treatment of tube 2.

〔Water test (2)〕 After the basic treatments of the respective Examples, Comparative Examples, and Reference Examples were performed, the same water passing test as the water passing test (1) of Test 2-1 was performed. Regarding the water passing test (2) in this experiment 2-2, in the water passing test (1), instead of passing water to the test tube A, the test tube B was passed at a flow rate of 0.3 m/s. Except for the water, it was performed in the same manner as the water passing test (1).

After the water-passing test, the test tube B was removed, and the maximum pitting corrosion depth and dirt adhesion speed were determined in the same manner as the evaluation method in the test 2-1. For the respective examples, comparative examples and reference The basic treatment method of the case is evaluated. In Table 3 below, these evaluation results are shown.

[Table 3] Table 3 Velocity [m/s] Sodium tartrate [mg/L] (converted amount of tartaric acid) Zinc chloride [mg/L] (converted amount of zinc) 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] (Converted in phosphoric acid) 100 20 (add at the same time, 4 days) 0.02 8.8 Reference example 2 0.3 0.01 4.1

According to 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), a situation with a flow velocity of 0.5 m/s can be obtained ( Example 3 and Example 5) have the same high anti-corrosion effect.

1: Multi-tube heat exchanger (heat exchanger) 2: tube 3: cooling tower 4: Water storage tank 5: Filling material 6: Exhaust fan 7: Pharmacy tank 8: Automatic conductivity management device 9: Flow meter 10: Steam 11: Drain water 20: Make-up water P1: water pump P2: Medicine injection pump P3: Discharge pump V1: Temperature adjustment valve V2: Circulation valve

Fig. 1 is a schematic diagram showing the outline of a heat exchanger test device of a cooling water system in an embodiment.

1: Multi-tube heat exchanger

2: tube

3: cooling tower

4: Water storage tank

5: Filling material

6: Exhaust fan

7: Pharmacy tank

8: Automatic conductivity management device

9: Flow meter

10: Steam

11: Drain water

20: Make-up water

P1: water pump

P2: Medicine injection pump

P3: Discharge pump

V1: Temperature adjustment valve

V2: Circulation valve

Claims (8)

An anti-corrosion method for metal components of a cooling water system has: Step (1), adding more than one compound (A) selected from tartaric acid and tartrate to the cooling water system to make it contact with the metal member; and Step (2), after the step (1), add one or more compounds (B) selected from zinc and zinc salts to the cooling water system to make contact with the metal member. The method for preventing corrosion of metal components of a cooling water system according to the first item of the scope of patent application, wherein, in the step (1), 30 mg/L in terms of tartaric acid conversion amount is added to the cooling water system. The compound (A) at a concentration of 100 mg/L. The method for preventing corrosion of metal components of a cooling water system as described in item 1 or item 2 of the scope of patent application, wherein the pH of the cooling water system in the step (1) is 6.0 to 8.0. The method for preventing corrosion of metal components of a cooling water system according to any one of items 1 to 3 of the scope of patent application, wherein, in the step (1), the metal component and the compound (A) The contact time is 20 hours to 30 hours. The method for preventing corrosion of metal components of a cooling water system as described in any one of items 1 to 4 of the scope of the patent application, wherein, in the step (2), zinc is added to the cooling water system The conversion amount is the compound (B) at a concentration of 1 mg/L to 50 mg/L. The method for preventing corrosion of metal components of a cooling water system according to any one of items 1 to 5 of the scope of patent application, wherein, in the step (2), the metal component and the compound (B) The contact time is 20 hours to 30 hours. According to any one of items 1 to 6 of the scope of patent application, the method for preventing corrosion of metal components of a cooling water system, wherein the cooling water system is a circulating cooling water system. The method for preventing corrosion of metal components of a cooling water system as described in any one of items 1 to 7 of the scope of the patent application, wherein the step (1) and the step (2) are performed in the cooling water system In the basic processing.

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