JP2014091843A - Corrosion prevention method for heat exchanger narrow pipe made of copper alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion prevention method for a heat exchanger narrow pipe made of a copper alloy, which has a high effect for preventing corrosion of the heat exchanger narrow pipe made of the copper alloy.SOLUTION: The corrosion prevention method for the heat exchanger narrow pipe made of the copper alloy which is in contact with the water includes adding an oxidizing agent having higher oxidation ability than that of oxygen and/or iron salt to the water. Oxidation-reduction potential of the water or natural electrode potential of the copper alloy is measured, and the amount of the oxidizing agent and/or the iron salt to be added is preferably controlled based on the measurement result. The oxidizing agent to be used includes chlorine, sodium hypochlorite, chlorine dioxide and hydrogen peroxide.

Description

  The present invention relates to an anticorrosion method for copper alloy heat exchanger capillaries, and more particularly to a cooling pipe into which cooling water is introduced, in particular, a heat exchanger cooling pipe installed in a power plant, an oil refinery plant, and a petrochemical plant. The present invention relates to a method suitable for preventing corrosion.

  Tube-type heat exchangers installed in power plants, oil refining plants, and petrochemical plants are equipped with thin tubes (cooling tubes) through which cooling water circulates, and between high-temperature gases and liquids and cooling water. Heat exchange takes place at. In this case, the water taken from the river, the sea, etc. is used for the cooling water passing through the narrow tube.

Water taken from rivers, seas, etc. may contain sulfide ions (S ²⁻ ), which causes corrosion of copper alloy heat exchanger tubes. That is, if sulfide water is contained in the water flowing through the narrow tube, a copper sulfide (CuS) film is formed on the inner surface of the thin tube by the reaction of copper and sulfide ions, and this copper sulfide film is formed from the inner surface of the thin tube. The base material of the thin tube is corroded by peeling or potential difference between the copper sulfide film and copper. In particular, in eutrophied closed waters, the concentration of sulfide ions in the water is increased by bacteria that produce sulfide ions from sulfate ions in the water (sulfate ion-reducing bacteria (SRB)). In this case, the local corrosion of the tubule proceeds significantly.

  In order to prevent the corrosion of the narrow tube, it is effective to form an iron oxide film (iron hydroxide film) on the inner surface of the narrow tube in advance. However, if the cooling water contains a high concentration of sulfide ions or a low concentration even over a long period of time, the iron oxide film is reduced to iron sulfide and the anticorrosion performance of the oxide film. Decreases.

  Patent Document 1 describes a method of preventing corrosion of a cooling pipe by reducing or removing sulfide ions in the water by sending air into the water taken as cooling water. However, the oxidation of sulfide ions is not sufficient only by oxidation with oxygen in the air, and the corrosion prevention effect is not sufficient.

JP2002-4071

  An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for preventing corrosion of a copper alloy heat exchanger capillary having a high corrosion prevention effect on the copper alloy heat exchanger capillary.

  The anticorrosion method for copper alloy heat exchanger capillaries according to the present invention is an anticorrosion method for copper alloy heat exchanger capillaries in contact with water. It is characterized by adding.

  As the oxidizing agent, at least one of chlorine, sodium hypochlorite, chlorine dioxide, hydrogen peroxide, chloramine, bromamine, bromide, permanganate, ferrate, and ozone is suitable.

  As the iron salt, at least one of ferrous sulfate, ferric sulfate, ferrous chloride, and ferric chloride is suitable.

  In the present invention, it is preferable to measure the redox potential of water or the natural electrode potential of the copper alloy, and to control the addition amount of the oxidizing agent and / or iron salt based on the measurement result.

  In the anticorrosion method for copper alloy heat exchanger capillaries according to the present invention, when an oxidizing agent is added to water, the oxidizing power of this oxidizing agent is stronger than that of oxygen, so that sulfide ions in water are efficiently oxidized to sulfate ions. The formation of a sulfide film on the inner surface of the copper alloy heat exchanger capillary is prevented, and corrosion of the copper alloy heat exchanger capillary is prevented.

  In the present invention, when an iron salt is added to water, sulfide ions react with iron ions to form iron sulfide. For this reason, it is prevented that the oxide film on the inner surface of the copper alloy heat exchanger capillary is reduced to iron sulfide, and the corrosion resistance of the oxide film is prevented from being lowered.

  In the method of the present invention, chemical addition control based on the oxidation-reduction potential of seawater or the like or the natural electrode potential of a copper alloy can prevent excessive addition or insufficient addition of chemicals.

It is explanatory drawing of embodiment. It is a graph which shows an experimental result. It is a graph which shows an experimental result.

  In the present invention, the heat exchanger capillaries made of copper alloy that are subject to corrosion prevention include tube heat exchanger capillaries installed in power plants, petroleum refining plants, and petrochemical plants.

  Examples of the copper alloy of the copper alloy heat exchanger capillary tube include brass for condensers such as C4430, C6870, C6871, and C6872 described in JIS H3300-2012 and white copper for condensers such as C7060, C7100, C7150, and C7164. However, it is not limited to this. Examples of the water that contacts the copper alloy heat exchanger capillary include seawater, lake water, river water (hereinafter sometimes referred to as seawater), and the like.

  The oxidizing agent added to this water includes chlorine (liquid chlorine or electrolytic chlorine), sodium hypochlorite, chlorine dioxide, hydrogen peroxide, chloramine, bromamine, bromide, permanganate, ferrate, and At least one kind of ozone is preferable, and sodium hypochlorite and hydrogen peroxide are particularly preferable.

  As the iron salt to be added to water, ferrous sulfate or ferrous chloride is suitable, but ferric sulfate, ferric chloride and the like can also be used.

  Only one or both of the oxidizing agent and the iron salt may be added. When adding an oxidizing agent to seawater or the like, the redox potential of seawater or the natural electrode potential of the copper alloy is measured, and this measured potential is in contact with the seawater or the like where the copper alloy heat exchanger capillary is clean. It is preferable to add so as to be equal to or higher than the potential at that time. When adding an iron salt, measure the redox potential of seawater or the natural electrode potential of the copper alloy, and add an iron salt equivalent to or greater than the sulfide concentration estimated from this measured value. Is preferred.

  In order to evaluate the corrosion resistance of copper alloy heat exchanger capillaries by adding oxidizer and / or iron salt, a temporary water flow test device installed near the heat exchanger in the downstream area from the chemical injection point By measuring the self-potential and polarization resistance of the attached test capillary manually or automatically, and removing the test capillary after water has passed for a certain period of time, and analyzing the amount of corrosion, the amount of deposits and deposit components It is preferable to evaluate.

  Thus, when an oxidizing agent is added to seawater or the like, the oxidation of sulfide ions to sulfate ions is promoted, the arrival of sulfide ions to the downstream copper alloy heat exchanger capillary is reduced, and the sulfide film Formation is prevented.

  When iron salt is added to seawater or the like, sulfide ions dissolved in seawater or the like react with iron ions to become iron sulfide. Thereby, it is prevented that the iron oxide film on the surface of the copper alloy heat exchanger capillary is reduced to iron sulfide, and corrosion of the capillary is prevented.

  FIG. 1 is a flowchart for explaining an example of the method of the present invention. The taken seawater flows from the pipe 1 to the heat exchanger 2 and is discharged from the water outlet. A chemical (oxidant or iron salt) in the chemical tank 3 is added to the pipe 1 by the chemical injection device 4. A part of the seawater is separated from the pipe 1 to the detection pipe 5, the redox potential and / or the natural electrode potential of the copper alloy is measured, and drug injection is performed based on this measurement result. Further, a part of the seawater is collected into the pipe 7 immediately before the heat exchanger 2 and is passed through the evaluation unit 8. The evaluation section 8 is provided with a test tube made of the same material as the copper alloy heat exchanger thin tube of the heat exchanger 2. Pass seawater through this test tube, measure the potential and observe the corrosion status, and evaluate the corrosion prevention effect.

  The detection unit 6 measures the redox potential of seawater or the natural electrode potential of copper alloy, and when the potential is confirmed to be reduced, it is determined that sulfide ions have flowed from the sea area, and the chemical injection device 4 Is activated.

  When the oxidizing agent is added, injection is performed until the redox potential or the natural electrode potential of the copper alloy shows a potential equal to or higher than the potential in the clean seawater before the flow of sulfide ions.

  When adding an iron salt, add an amount of iron salt equivalent to or higher than the sulfide ion concentration estimated from the potential or analyzed by analysis of seawater (for example, 1 to 10 times the equivalent). To do.

  The increase / decrease and the suppression effect of the chemical injection amount are confirmed manually or automatically by measuring the transition of the natural potential and polarization resistance value of the test tube installed in the evaluation unit 8. Also, periodically measure the amount of corrosion, amount of deposits, and deposit components of the test tube to evaluate the drug injection effect.

  Hereinafter, experimental examples for showing the effects of the present invention will be described.

  In the following examples, a test piece with an iron oxide film (hereinafter sometimes referred to as an iron film forming tube) prepared by cutting a drawn tube of an aluminum brass tube used in an actual heat exchanger, and this test. A pickling test piece (hereinafter sometimes referred to as a pickling tube) in which the piece was washed with hydrochloric acid to remove the iron oxide film was used.

  As simulated seawater, artificial seawater (Aquamarine for metal corrosion test manufactured by Yasu Pharmaceutical Co., Ltd.) (Experiment 1) or sodium sulfide nonahydrate was dissolved in this artificial seawater as sulfide ions to 100 mg / L. The ones (Experiments 2-6) were used.

In Experiments 1 and 2, no chemicals (oxidant or iron salt) were added to the simulated seawater.
In Experiments 3 and 4, sodium hypochlorite or hydrogen peroxide was added to simulated seawater so that the redox potential was 200 mV or higher.
In Experiments 5 and 6, ferrous sulfate was added to the simulated seawater so that the iron ion was 100 mg / L (Experiment 5) or 1000 mg / L (Experiment 6).

  The test piece was immersed in each simulated seawater (0.5 L, 25 ° C.) for 24 hours, and the redox potential of the simulated seawater and the natural electrode potential of the test piece were measured. The results are shown in FIG.

  After 24 hours, each test piece was pulled up from each simulated seawater, washed with the above-mentioned artificial seawater to which no chemical was added, and polarized according to the Ohm's law from the current density when negatively polarized with a potentiostat at −100 mV. The resistance value was determined. The results are shown in FIG.

  Compared to the results of Experiments 1 and 2 in Fig. 2, in Experiment 2, the redox potential and natural electrode potential are lower than those in Experiment 1 in which no sulfide ions are added, and the presence of sulfide ions. It can be seen that can be confirmed by the potential.

  In Experiments 3 and 4 in which an oxidizing agent was added, the natural electrode potential was higher than that in Experiment 2. Therefore, it was recognized that sulfide ions were oxidized by the oxidizing agent.

  As shown in FIG. 3, in Experiment 3 and Experiment 4 in which an oxidizing agent was added, a decrease in polarization resistance value was suppressed in both the pickling tube and the iron film forming tube as compared with Experiment 2. Comparing Experiments 5 and 6 with addition of iron ions with Experiment 2 without addition, the pickling tube had almost no effect of suppressing polarization resistance, but the iron film forming tube had an effect of suppressing a decrease in polarization resistance value. Admitted.

  The sulfide film was black, but when the appearance of each test piece was observed, no black deposit was observed except in Experiment 2, and the addition of an oxidizing agent or iron salt suppressed the formation of the sulfide film. It was recognized that

DESCRIPTION OF SYMBOLS 1 Piping 2 Heat exchanger 3 Chemical tank 4 Chemical injection apparatus 6 Detection part 8 Evaluation part

Claims (4)

  In the anticorrosion method for a copper alloy heat exchanger capillary in contact with water, an oxidizing agent having a higher oxidizing power than oxygen and / or an iron salt is added to the water. Anticorrosion method.   2. The oxidant according to claim 1, wherein the oxidizing agent is at least one of chlorine, sodium hypochlorite, chlorine dioxide, hydrogen peroxide, chloramine, bromamine, bromide, permanganate, ferrate, and ozone. A corrosion prevention method for copper alloy heat exchanger capillaries.   The method of claim 1, wherein the iron salt is at least one of ferrous sulfate, ferric sulfate, ferrous chloride, and ferric chloride. .   In any one of Claims 1 thru | or 3, it measures the oxidation-reduction potential of water or the natural electrode potential of the said copper alloy, and controls the addition amount of an oxidizing agent and / or an iron salt based on this measurement result. A corrosion prevention method for copper alloy heat exchanger capillaries.

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