Corrosion prevention methods for copper alloy piping

Abstract

In one embodiment, a novel method is provided that can prevent corrosion of copper alloy piping in contact with seawater. [Solution] In one embodiment, this disclosure relates to a method for preventing corrosion of copper alloy piping in contact with seawater, comprising adding iron ions or an iron ion supplying compound to the seawater, and adding monochloramine to the seawater.

Description

[Technical Field]

[0001] This disclosure relates to a method for preventing corrosion of copper alloy piping that comes into contact with seawater. [Background technology]

[0002] Heat exchangers and condensers in nuclear and thermal power plants, as well as oil refineries, are fitted with thin tubes (cooling tubes) through which cooling water flows. The standard material used for these tubes is a copper alloy with seawater corrosion resistance (e.g., aluminum brass tubes). It has become clear that the excellent corrosion resistance of aluminum brass tubes is primarily due to the iron hydroxide film formed on their surface by injecting iron ions into seawater. Therefore, iron ion implantation is generally applied as a corrosion prevention method for aluminum brass tubes. However, with iron ion implantation as a corrosion prevention method, there were cases where it was not sufficiently effective depending on the water quality, or corrosion occurred relatively quickly if it came into contact with contaminated seawater before the protective film was formed.

[0003] In piping used in seawater cooling systems, not only corrosion but also damage caused by the attachment of marine organisms is a problem. Therefore, in the process of conducting research to prevent both corrosion and the attachment of marine organisms in aluminum brass pipes, the applicant attempted to use iron ions and hydrogen peroxide in combination. When iron ions and hydrogen peroxide were added continuously for 24 hours, the effect of suppressing the attachment of marine organisms was confirmed, but hydrogen peroxide inhibited the formation of a corrosion-preventive film (iron hydroxide film) on the inner surface of the aluminum brass pipe by iron ions, resulting in pitting corrosion. To solve this problem, the applicant has proposed a method in which iron ions are supplied continuously while hydrogen peroxide is added intermittently (Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-28479 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In one aspect, this disclosure provides a novel method for preventing corrosion of copper alloy piping in contact with seawater. [Means for solving the problem]

[0006] This disclosure relates, in one embodiment, to a method for preventing corrosion of copper alloy piping in contact with seawater, comprising adding iron ions or an iron ion-supplying compound to the seawater and adding monochloramine to the seawater. [Effects of the Invention]

[0007] According to this disclosure, in one embodiment, corrosion of copper alloy piping in contact with seawater can be prevented. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the model waterway used in the example. [Figure 2] Figure 2 is a schematic diagram showing the model waterway used in the example. [Modes for carrying out the invention]

[0009] In the course of their research to provide a new method for preventing corrosion of copper alloy piping in contact with seawater, the inventors discovered that using iron ions in combination with monochloramine can improve the corrosion-preventive effect of iron ions on copper alloy piping.

[0010] This disclosure relates, in one embodiment, to a method for preventing corrosion of copper alloy piping in contact with seawater. The method of this disclosure includes adding iron ions or an iron ion supplying compound to the seawater, and adding monochloramine to the seawater. In one or more embodiments, the method of this disclosure may include passing seawater to which iron ions or an iron ion supplying compound has been added through the copper alloy piping, and passing seawater to which monochloramine has been added through the copper alloy piping.

[0011] In this disclosure, “copper alloy piping” means piping in which a copper alloy is used and / or piping made of a copper alloy. In one or more embodiments, copper alloys in this disclosure include brass (an alloy of copper and zinc) and cupronickel (an alloy of copper and nickel). In one or more embodiments, brass may further contain aluminum, lead, and tin. Examples of copper alloys include, but are not limited to, C4430 Admiralty brass (condenser brass) as described in JIS H3300-2018, aluminum brass (condenser brass) such as C6870, C6871, and C6872 as described in JIS H3300-2018, and cupronickel or cupronickel for condensers such as C7060, C7100, C7150, and C7164 as described in JIS H3300-2018.

[0012] In this disclosure, examples of copper alloy piping to be protected against corrosion include, in one or more embodiments, thin tubes (cooling tubes) through which cooling water flows in heat exchangers and condensers. Examples of heat exchangers and condensers in one or more embodiments include heat exchangers and condensers installed in nuclear power plants, thermal power plants, oil refineries, and petrochemical plants.

[0013] [Iron ions or iron ion-supplying compounds] The method disclosed herein includes adding iron ions or an iron ion supply compound to seawater that comes into contact with copper alloy piping.

[0014] The "iron ion supply compound" in the present disclosure refers to an iron salt containing iron ions as constituent ions. In one or more embodiments, examples of the iron ion supply compound include a ferrous ion supply compound and a ferric ion supply compound, and a ferrous ion supply compound that is soluble in seawater and can form divalent iron ions in seawater is preferred. In one or more embodiments, examples of the iron ion supply compound include ferrous sulfate, ferrous chloride, ammonium ferrous sulfate, and the like. In one or more embodiments, the iron ion supply compound may be used alone or in combination of two or more kinds.

[0015] In one or more embodiments, the method of the present disclosure includes adding iron ions or an iron ion supply compound for 14 to 24 hours per day such that the concentration of the iron ions in the seawater is 0.005 mg / L to 0.05 mg / L. Here, for example, adding iron ions or an iron ion supply compound for 14 hours per day means that, in one or more embodiments, the total time for adding iron ions or an iron ion supply compound to reach the above-mentioned predetermined concentration is 14 hours per day. The addition concentration of the iron ions or the iron ion supply compound can be appropriately determined according to the iron ion addition time per day. When adding iron ions or an iron ion supply compound for 14 to 24 hours per day, the addition concentration is, in one or more embodiments, 0.005 mg / L to 0.04 mg / L or 0.01 mg / L to 0.03 mg / L as the iron ions in the seawater. In one or more embodiments, the method of the present disclosure includes passing seawater containing 0.005 mg / L to 0.05 mg / L of iron ions through a copper alloy pipe for 24 hours. In one or more embodiments, the method of the present disclosure includes passing seawater containing 0.005 mg / L to 0.04 mg / L or 0.01 mg / L to 0.03 mg / L of iron ions through a copper alloy pipe for 24 hours.

[0016] In one or more embodiments, the addition of iron ions or an iron ion supply compound may be continuous addition for 24 hours per day or intermittent addition for less than 24 hours. When the iron ions or the iron ion supply compound are intermittently added for less than 24 hours, in one or more embodiments, the addition of the iron ions or the iron ion supply compound may be performed separately from the addition of monochloramine (during a time period when monochloramine is not added or alternately with the addition of monochloramine), or at the timing of switching the addition, the addition of the iron ions or the iron ion supply compound and the addition of monochloramine may partially overlap.

[0017] In one or more embodiments, the addition of iron ions or an iron ion supply compound may be 14 to 24 hours per day, or 30 minutes to 3 hours per day, or 1 to 3 hours per day, or 30 minutes to 2 hours per day.

[0018] In one or more embodiments, the method of the present disclosure includes adding an iron ion or an iron ion supply compound for 30 minutes to 3 hours per day such that the concentration of the iron ion in the seawater is 0.5 mg / L to 1 mg / L. In one or more embodiments, the method of the present disclosure includes passing seawater containing 0.5 mg / L to 1 mg / L of iron ions through a copper alloy pipe for 30 minutes to 3 hours per day.

[0019] In one or more embodiments, the method of the present disclosure includes adding an iron ion or an iron ion supply compound to seawater such that the average daily addition amount of the iron ion or the iron ion supply compound to the seawater is 0.1 mg / L to 1.5 mg / L as the iron ion. In one or more embodiments, the average daily addition amount of the iron ion or the iron ion supply compound to the seawater is 0.3 mg / L to 1.4 mg / L, 0.5 mg / L to 1.2 mg / L, or 0.5 mg / L to 1 mg / L as the iron ion. In this disclosure, "average daily addition amount" refers to the total concentration of iron ions added (supplied) to seawater in one day (24 hours). The average daily addition amount can be calculated by multiplying the addition concentration by the addition time.

[0020] In one or more embodiments, iron ions or iron ion-supplying compounds can be added to seawater in the form of an aqueous solution. In other embodiments, iron ions produced by electrolysis or iron ions naturally generated by placing iron scraps or the like in the aqueous system can be used.

[0021] [Monochrome] The method disclosed herein includes adding monochloramine to seawater that comes into contact with copper alloy piping.

[0022] In this disclosure, "monochloramine" refers to a compound represented by NH2Cl (a compound in which one of the hydrogen atoms of ammonia is replaced with a chlorine atom). Monochloramine is OCl - +NH4 + → Produced by reactions such as NH2Cl + H2O

[0023] The method of the present disclosure, in one or more embodiments, includes adding monochloramine to seawater in contact with copper alloy piping such that the total residual chlorine concentration is 0.001 mg / L to 1 mg / L. The concentration of monochloramine to be added can be appropriately determined according to the daily monochloramine addition time. In one or more embodiments, the concentration of monochloramine to be added is 0.002 mg / L to 0.7 mg / L, 0.01 mg / L to 0.5 mg / L, 0.02 mg / L to 0.4 mg / L, or 0.03 mg / L to 0.3 mg / L as the total residual chlorine concentration in seawater. The method of the present disclosure, in one or more embodiments, includes passing seawater containing monochloramine having a total residual chlorine concentration of 0.001 mg / L to 1 mg / L through copper alloy piping. The method of the present disclosure, in one or more embodiments, includes passing seawater containing monochloramine having a total residual chlorine concentration of 0.002 mg / L to 0.7 mg / L, 0.01 mg / L to 0.5 mg / L, 0.02 mg / L to 0.4 mg / L, or 0.03 mg / L to 0.3 mg / L through copper alloy piping.

[0024] In this disclosure, "total residual chlorine concentration" refers to the sum of the residual free chlorine concentration and the residual bound chlorine concentration. The total residual chlorine concentration, residual free chlorine concentration, and residual bound chlorine concentration in seawater can be measured by the diethyl-p-phenylenediamine (DPD) method in one or more embodiments. In this disclosure, the residual free chlorine concentration refers to the residual free chlorine concentration measured by the DPD method, specifically the chlorine concentration measurement result (mg-Cl2 / L) after 30 seconds using the DPD(Free) reagent, which is a reagent for measuring free chlorine. In this disclosure, the residual bound chlorine concentration refers to the value obtained by subtracting the chlorine concentration measurement result (mg-Cl2 / L) after 30 seconds using the DPD(Free) reagent, which is a reagent for measuring free chlorine, from the chlorine concentration measurement result (mg-Cl2 / L) after 120 seconds using the DPD(Total) reagent, which is a reagent for measuring total chlorine. Therefore, the total residual chlorine concentration in this disclosure can also be said to be the chlorine concentration measurement result (mg-Cl2 / L) after 120 seconds using the DPD(Total) reagent, which is a reagent for measuring total chlorine.

[0025] In one or more embodiments, monochloramine can be added to seawater using a pre-prepared monochloramine solution. Alternatively, in one or more embodiments, monochloramine may be generated in seawater by adding a hypochlorite compound and an ammonium compound to seawater.

[0026] A monochloramine solution can be prepared in one or more embodiments by mixing a hypochlorite compound and an ammonium compound. Examples of hypochlorite compounds in one or more embodiments include sodium hypochlorite, potassium hypochlorite, and calcium hypochlorite. Examples of ammonium compounds in one or more embodiments include ammonium sulfate, ammonium bromide, ammonium chloride, ammonium sulfamate, ammonium bromide, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium nitrate. These may be used individually or in combination of two or more. The molar ratio of the hypochlorite compound to the ammonium compound is, in one or more embodiments, 1:1 to 1:2, 1:1.1 to 1:2, 1:1.2 to 1:2, 1:1.2 to 1:1.6, 1:1.2 to 1:1.5, or 1:1.2 to 1:1.4, as the molar ratio of total residual chlorine to nitrogen. Monochloramine solutions can be prepared in one or more embodiments by methods described in Japanese Patent No. 4914146, Japanese Unexamined Patent Publication No. 2017-119245, and Japanese Unexamined Patent Publication No. 2017-53054, etc.

[0027] In one or more embodiments, the monochloramine solution may be prepared by mixing aqueous solutions of 5% to 15% by mass of sodium hypochlorite and ammonium sulfate, with the solutions being appropriately diluted.

[0028] In one or more embodiments, a high-concentration monochloramine solution may be used for the addition of monochloramine. The concentration of the monochloramine solution is not particularly limited, but in one or more embodiments, the total residual chlorine concentration is 400 mg / L to 8000 mg / L, 700 mg / L to 7000 mg / L, or 800 mg / L to 6000 mg / L.

[0029] In one or more embodiments, the addition of monochloramine may be continuous for 24 hours per day, or intermittent for less than 24 hours per day. In one or more embodiments, the addition of monochloramine may be carried out for 14 to 24 hours per day. In one or more embodiments, the addition of monochloramine may be carried out for 24 hours per day, or for 16 to 23 hours or 18 to 22 hours per day. Here, for example, adding monochloramine for 14 hours per day means that in one or more embodiments, the total time spent adding monochloramine to achieve the predetermined concentration described above is 14 hours per day.

[0030] In one or more embodiments, iron ions or iron ion-supplying compounds and monochloramine may be added simultaneously, their addition times may not overlap, or their addition times may overlap partially or completely.

[0031] In one or more embodiments, the method of this disclosure may include alternating the addition of iron ions or an iron ion-supplying compound with the addition of monochloramine. In one or more embodiments, the method of the present disclosure may include adding monochloramine for 14 to 21 hours per day and adding iron ions or an iron ion-supplying compound for 1 to 3 hours per day. In other embodiments, the method of the present disclosure may include adding monochloramine continuously for 14 to 21 hours per day, followed by the continuous addition of iron ions or an iron ion-supplying compound for 1 to 3 hours per day, or adding iron ions or an iron ion-supplying compound continuously for 1 to 3 hours per day, followed by the continuous addition of monochloramine for 14 to 21 hours per day.

[0032] In one or more embodiments, the method of the present disclosure may include refraining from adding monochloramine and iron ions or iron ion-supplying compounds to seawater for 1 to 3 hours per day. In one or more embodiments, the method of the present disclosure may include passing seawater that does not contain monochloramine and iron ions or iron ion-supplying compounds through copper alloy piping for 1 to 3 hours per day.

[0033] The method of the present disclosure may, in one or more embodiments, further include the addition of hydrogen peroxide to the seawater in contact with the copper alloy piping, or it may not include the addition of hydrogen peroxide.

[0034] In one or more embodiments, the method of this disclosure may include adding hydrogen peroxide to seawater so that the concentration of hydrogen peroxide in seawater is 0.1 mg / L to 2 mg / L. In one or more embodiments, the concentration of hydrogen peroxide is 0.12 mg / L to 1.5 mg / L, 0.14 mg / L to 1 mg / L, or 0.15 mg / L to 0.5 mg / L.

[0035] In one or more embodiments, hydrogen peroxide may be added continuously for 24 hours per day, or intermittently for less than 24 hours per day. In one or more embodiments, hydrogen peroxide is added for 14 to 24 hours per day.

[0036] In one or more embodiments, the time periods for adding hydrogen peroxide and adding monochloramine preferably overlap in part or in whole, and in one or more embodiments, the addition of hydrogen peroxide is preferably performed simultaneously with the addition of monochloramine.

[0037] In one or more embodiments, the method of the present disclosure may include adding monochloramine and hydrogen peroxide to seawater in such a ratio of total residual chlorine to hydrogen peroxide concentration (total residual chlorine concentration (mg / L): hydrogen peroxide concentration (mg / L)) as 1:1 to 10, 1:1.5 to 7, or 1:2 to 5. In one or more embodiments, the method of this disclosure may include adding hydrogen peroxide to seawater such that the concentration of hydrogen peroxide added to seawater is 1 or more, 1.5 or more, 2 or more, 2.5 or more, or 3 or more times the concentration of monochloramine added to seawater (total residual chlorine concentration).

[0038] The addition of iron ions or iron ion-supplying compounds and monochloramine (and hydrogen peroxide if necessary) may, in one or more embodiments, be performed continuously every day in order to obtain a simple and stable corrosion-preventive effect, or, in some cases, intermittently as necessary depending on the condition of the inner surface of the copper alloy pipe (for example, it may be added every other day or as a spot addition).

[0039] The locations where iron ions, monochloramine, and hydrogen peroxide are added are not particularly limited as long as they are upstream of the location where the corrosion prevention effect on copper alloy piping is to be obtained. In one or more embodiments, examples include piping or water conduits attached to a heat exchanger or condenser, the inlet of a heat exchanger, or the inlet of a condenser. The locations where iron ions or iron ion supply compounds and monochloramine solutions are added may be the same or different in one or more embodiments. If the locations where iron ions or iron ion supply compounds and monochloramine solutions are added are different, the location where monochloramine is added may be upstream of the location where iron ions or iron ion supply compounds are added. In one or more embodiments, the addition site may be one or more locations.

[0040] The concentrations of iron ions, monochloramine, and hydrogen peroxide can be measured by known methods.

[0041] This disclosure further relates to one or more embodiments described below. [1] A method for preventing corrosion of copper alloy piping that comes into contact with seawater, Adding iron ions or iron ion-supplying compounds to the aforementioned seawater, A method comprising adding monochloramine to the aforementioned seawater. [2] The method according to [1], further comprising adding hydrogen peroxide to the seawater. [3] The method according to [1] or [2], comprising adding monochloramine to the seawater such that the total residual chlorine concentration is 0.001 mg / L to 1 mg / L. [4] The addition of monochloramine is carried out over a period of 14 to 24 hours per day, according to any one of the methods described in [1] to [3]. [5] The method according to any one of [1] to [4], comprising adding the iron ions or iron ion supply compound for 14 to 24 hours per day such that the concentration of iron ions in the seawater is 0.005 mg / L to 0.05 mg / L. [6] The method according to any one of [1] to [4], comprising adding the iron ions or iron ion supply compound to the seawater for 30 minutes to 3 hours per day so that the concentration of iron ions in the seawater is 0.5 mg / L to 1 mg / L. [7] The method according to any one of [1] to [6], comprising adding the iron ions or iron ion supply compound such that the average daily concentration of iron ions in the seawater is 0.1 mg / L to 1.5 mg / L. [8] The method according to any one of [1] to [7], comprising alternating the addition of the iron ions or iron ion supply compound with the addition of the monochloramine. [9] per day, Add monochloramine for 14 to 21 hours, and Add iron ions or iron ion-supplying compounds for 1 to 3 hours. The method described in any of [1] to [8], including performing the actions in this order or in reverse order. [Examples]

[0042] [Fe 2+ [Method for measuring ion concentration] Fe 2+ The ion concentration was measured using the phenanthroline spectrophotometric method described in JIS K0102 "Testing Methods for Industrial Wastewater". [Method for measuring total residual chlorine concentration] The total residual chlorine concentration was measured using the diethyl-p-phenylenediamine (DPD) colorimetric method described in JIS K0101 "Test Methods for Industrial Water". [Method for measuring hydrogen peroxide concentration] The hydrogen peroxide concentration was measured using an enzyme-based 4-aminoantipyrine colorimetric method.

[0043] [Evaluation test using a model waterway 1] A model waterway test apparatus, as shown in Figure 1, was set up at a certain location in Wakayama Prefecture, and tests were conducted. Unfiltered seawater (pH 8), pumped up using a submersible pump, was fed into four separate waterways (test sections) at a flow rate of 1 m³. 3 The system was run in a single pass mode at / h for 28 days (April to May 2024). Inside each waterway, an aluminum brass tube C6871 (inner diameter 16.6 mm x length 100 mm x thickness 1.2 mm, surface area 5212.4 mm²) is used to verify the corrosion protection effect of the copper alloy tubes. 2 A tube with a flow velocity of 128.4 cm / s was inserted. The flow velocity of the tube was calculated from the seawater flow rate of the waterway and the cross-sectional area of ​​the aluminum brass tube. The chemicals listed in Table 1 were added to each waterway to the concentrations in the seawater and the daily addition time shown in Table 1 (Example 1, Comparative Examples 1-2, and Blank). [Monochrome] A high-concentration monochloramine solution was prepared by appropriately diluting commercially available 12% sodium hypochlorite solution and ammonium sulfate aqueous solutions, respectively, using a metering pump, and mixing them in a tube before the chemical addition point. This solution was then added to the preceding aluminum brass tube to achieve the concentration (total residual chlorine concentration) in seawater and the daily addition time shown in Table 1. 〔chlorine〕 Chlorine was added to the upstream section of an aluminum brass tube by supplying an aqueous solution of a commercially available 12% sodium hypochlorite solution, which had been appropriately diluted, using a metering pump, so that the concentration in the seawater (free residual chlorine concentration) and the daily addition time shown in Table 1 were achieved. [Fe 2+ ion〕 Fe2+ The ions were added by feeding a solution prepared by appropriately diluting commercially available ferrous sulfate with an aqueous sulfuric acid solution using a metering pump, to a position in front of the aluminum brass tube and after the addition points of monochloramine and chlorine, so as to achieve the concentrations in seawater shown in Table 1 and the addition time per day.

[0044] 〔Confirmation of corrosion prevention effect〕 Before the test, the dry weight W0 (g) of the aluminum brass tube was measured. After the test, the tube removed from the water channel was immersed in 10% sulfuric acid for 5 minutes, and the dry weight W1 (g) after pickling was measured. The weight loss W2 (g) of the tube was calculated by the following formula. Weight loss of the tube W2 = W0 - W1 Comparative Example 1 (Fe 2+ When the weight loss (W2 Comparative Example 1) of the tube in the case of adding only ions was taken as 100%, the ratio (weight loss ratio) of the weight loss (W2 each test section) of the tube in each test section was calculated from the following formula, and the results are shown in Table 1 below. Weight loss ratio of the tube in each test section with respect to Comparative Example 1 (%) = W2 each test section / W2 Comparative Example 1 × 100

Table 1

[0045] In Example 1 where iron ions and monochloramine were added, the corrosion prevention effect of the aluminum brass tube was improved compared to the case of adding only iron ions (Comparative Example 1) and the combined use of iron ions and chlorine (Comparative Example 2).

[0046] [Evaluation test 2 using a model water channel] A model water channel test apparatus shown in Figure 2 was installed at a certain location in Wakayama Prefecture, and the same test as in Example 1 was conducted. Unfiltered seawater (pH 8) pumped up using an underwater pump was passed through a water channel (test section) branched into 8 systems at a flow rate of 1 m 3 / h for 82 days (from July to October 2024) in a once-through manner. The chemicals listed in Table 2 were added to each waterway to the concentrations in the seawater and the daily addition time shown in Table 2 (Examples 2-4, Comparative Examples 3-4, Reference Examples 1-2, and Blank). Specifically, in Examples 2 and 4, Fe 2+ After continuously adding ions for 2 hours, only seawater was passed through for 1 hour (no chemicals added), then monochloramine was continuously added for 20 hours, and then only seawater was passed through for 1 hour (no chemicals added), and this process was repeated. In Example 3, the procedure was the same as in Examples 2 and 4, except that hydrogen peroxide was added continuously for 20 hours along with monochloramine. In Comparative Example 3, Fe 2+ Ions were added continuously for two hours, and for the remaining time, only seawater was passed through. Comparative Example 4 was carried out in the same manner as in Examples 2 and 4, except that chlorine was added continuously for 20 hours instead of monochloramine. In Reference Examples 1 and 2, chlorine or monochloramine was added continuously for 20 hours, and seawater alone was passed through for the remaining time. [Fe 2+ Ions, chlorine, monochloramine] Fe 2+ The addition of ions, chlorine, and monochloramine was carried out in the same manner as in evaluation test 1 using a model waterway. 〔hydrogen peroxide〕 Hydrogen peroxide was added to the front of an aluminum brass tube by supplying an aqueous solution of a commercially available 35% hydrogen peroxide solution, which had been appropriately diluted, using a metering pump, so that the concentration in the seawater and the daily addition time shown in Table 2 were achieved.

[0047] [Confirmation of corrosion protection effect] Comparative Example 3 (Fe) is used as Comparative Example 1 for W2 in Evaluation Test 1. 2+ Except for using the reduced wall weight of the tube with only ions added (W2 Comparative Example 3), the weight reduction percentage (%) was calculated using the same method as in Evaluation Test 1. The results are shown in Table 2 below. [Table 2]

[0048] In Examples 2-4, where iron ions were added alternately with monochloramine or monochloramine and hydrogen peroxide, the corrosion protection effect on aluminum brass pipes was improved compared to iron ions alone (Comparative Example 3) and iron ions and chlorine in combination (Comparative Example 4). In particular, the corrosion protection effect was further improved by using monochloramine and hydrogen peroxide in combination (Example 3).

Claims

1. A method for preventing corrosion of copper alloy pipes that come into contact with seawater, Adding iron ions or iron ion-supplying compounds to the aforementioned seawater, A method comprising adding monochloramine to the aforementioned seawater.

2. The method according to claim 1, further comprising adding hydrogen peroxide to the seawater.

3. The method according to claim 1, further comprising adding the monochloramine such that the total residual chlorine concentration in the seawater is between 0.001 mg / L and 1 mg / L.

4. The method according to claim 1, wherein the addition of monochloramine is carried out for 14 to 24 hours per day.

5. The method according to claim 1, further comprising adding the iron ions or iron ion supply compound for 14 to 24 hours per day such that the concentration of iron ions in the seawater is 0.005 mg / L to 0.05 mg / L.

6. The method according to claim 1, further comprising adding the iron ions or iron ion supply compound to the seawater for 30 minutes to 3 hours per day so that the concentration of iron ions in the seawater is 0.5 mg / L to 1 mg / L.

7. The method according to claim 1, further comprising adding the iron ions or iron ion supply compound such that the average daily concentration of iron ions in the seawater is 0.1 mg / L to 1.5 mg / L.

8. The method according to claim 1, comprising alternating between adding the iron ions or iron ion supplying compound and adding the monochloramine.

9. Per day, Add monochloramine for 14 to 21 hours, and Add iron ions or iron ion-supplying compounds for 1 to 3 hours. The method according to claim 1, including performing the actions in this order or in the reverse order.

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