JPH0293083A - Method for preventing corrosion of inner surface of copper alloy pipe - Google Patents

Abstract

PURPOSE:To form an iron coating film effective for preventing corrosion on the inner surface of a copper or copper alloy pipe by passing the seawater contg. chlorine and mixed with an iron ion soln. and a reducing agent soln. through the pipe, and further injecting the reducing agent soln. into the seawater on the upstream side of the iron ion soln. CONSTITUTION:The Cl2 for preventing the deposition of marine organisms is injected into seawater 2 at its intake 1. The seawater 2 is passed through the copper or copper alloy pipe 5 by a seawater pump 3 through a seawater conduit 4 as cooling water. A ferrous sulfate soln. 7 is injected into the seawater 2 by a fixed delivery pump 8, and the soln. 11 of a reducing agent such as sodium sulfite is injected by a fixed delivery pump 12. In this case, the injection point 14b for the reducing agent soln. 11 is set on the upstream side of the injection point 14a for the ferrous sulfate soln. 7 of the conduit 4. As a result, the Cl2 in the seawater 2 is converted to Cl<->, hence the oxidation of the iron ion is prevented, and the iron coating film effective for preventing corrosion is formed on the inner surface of the pipe 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for preventing corrosion of copper or copper alloys, and more specifically, to a seawater heat exchanger, condenser, etc. for ships, chemical plants, power plants, etc. This invention relates to a method for preventing corrosion of the inner surface of copper or copper alloy tubes.

[Conventional technology]

Currently, corrosion prevention measures for copper alloy pipes in seawater heat exchangers and condensers in various plants are carried out by injecting small amounts of iron ions into cooling seawater. A method of injecting a ferrous sulfate solution and a method of injecting a solution in which a ferrous sulfate coexisted with a ferrous sulfate solution proposed by the present inventors (Japanese Patent Application No. 61-29159)
No. 6). The latter suppresses rapid colloidalization of iron ions and controls the amount of iron coating deposited. Corrosion prevention by iron ion implantation is due to the fact that ferrous ions (Fe) injected into seawater turn into oxide and colloid states and form an iron coating on the inner surface of the tube.

[Problem to be solved by the invention]

Normally, in plants that use seawater as cooling water, chlorine is always injected into the seawater intake to prevent problems caused by marine organisms adhering to the seawater intake pipes and various equipment. Since chlorine is both a sterilizing agent and an oxidizing agent, the presence of chlorine in seawater promotes the oxidation and colloidalization of the injected ferrous ions, significantly inhibiting the formation of iron coatings.

Depending on the plant, seawater is often supplied to multiple condensers and heat exchangers from the same seawater intake, and since chlorine is injected into the intake, only the equipment that is injected with iron ions is chlorinated. Unable to stop injection.

Figure 6 shows the distribution of the amount of ridges deposited on the inner surface of a 60m copper alloy pipe when iron ions were implanted in the presence of chlorine using the testing apparatus shown in Figure 5. In addition, patent application No. 61-29159
Even in the method described in No. 6, the presence of chlorine promotes the oxidation of iron ions and at the same time oxidizes p-boxylate ions, making it impossible to suppress colloid formation and significantly inhibiting the formation of iron coatings.

Injection conditions (1) Injection concentration and number of days of injection Fe''+ was taken as tOppm, and injection was carried out for two consecutive days.

■ Copper alloy pipe diameter and seawater flow rate in the pipe Pipe diameter = 26φ, seawater flow rate in the pipe: 2 m / sec ■
Injection of ferrous sulfate solution In FIG. 5, seawater 02 pumped into a seawater tank 01 was supplied to a copper alloy pipe 05 via a vinyl chloride Y pipe 04 using a seawater pump 03. In order to inject iron ions, the ferrous sulfate solution 07 in the ferrous sulfate solution tank 06 is injected into the end of the vinyl chloride/L/pipe 04 using the pump 08 through the vinyl hose 09. A shows the amount of ridge adhesion when no chlorine is injected, solid line B shows the amount of ridge adhesion when 0.2 ppm of chlorine is injected, and solid line C shows the amount of ridge adhesion when 6 ppm of chlorine is injected, but the presence of chlorine significantly worsens iron adhesion. I understand. Further, the adhesion state was not good as it was wrinkled.

[Purpose of the invention]

The present invention aims to provide a corrosion prevention method for forming an iron coating on the inner surface of a copper alloy pipe that is effective for corrosion prevention even when chlorine is present in seawater.

[Means to achieve the purpose]

As mentioned above, it is impossible to stop the injection of chlorine into seawater. For this reason, as a result of intensive research on means to eliminate chlorine in seawater, we found that sodium sulfite, sodium thiosulfate, sodium bisulfite, oxalic acid, hydrazino,
It was confirmed that chlorine, an oxidizing agent, could be eliminated by injecting a reducing agent such as hydroxylamine or boron hydride salt.

The present invention has been completed based on this knowledge.

That is, the present invention provides a method for preventing corrosion of the inner surface of a copper or copper alloy pipe by injecting an iron ion solution and a reducing agent solution into seawater. This is a corrosion prevention method for the inner surface of a copper or copper alloy pipe, characterized by setting the corrosion prevention method on the upstream side of a copper or copper alloy pipe.

[Effect]

Chlorine (CI4) is a reducing agent, such as sodium sulfite (N
a25O3) means sodium thiosulfate (Na
zSsOm) reacts as shown in the second equation, becomes chlorine ion (CZ-), and loses its function as a sterilizing agent and oxidizing agent.

CI4+H20+Na*SO3 + 2- -2Ct+2H+2Na +SO4 1st formula % formula % -8CA +2Na +10H+2SO4 2nd formula In this case, cyclochlorine can be eliminated by injecting a reducing agent into the seawater.

Figures 3 and 4 show that the degree of residual chlorine is a 5 ppm (
Chlorine concentration from the injection point when a constant amount of sodium sulfite (NalSO3) and sodium thiosulfate (Na2S20B) are injected into seawater different from ○ mark) and 11.25 ppm (', iJ mark) under the following conditions. This shows the attenuation curve of .

Test conditions (a) Seawater flow tube used - 25+wφ bis M-space (b) Seawater flow velocity in vinyl hose - 1-2 m
/5ec (56m"/Hr) (c) Sea water temperature -1-23~24°C (d) Reducing agent injection ■NuzSO1---10ras Na25O1/17
Inject the liquid at a rate of approximately 10cc/min.

■Na2S103---10rasNa! 5203/ solution was injected at approximately 10 CC/min.

By injecting a reducing agent as shown in FIGS. 5 and 4, chlorine in seawater can be eliminated.

〔Example〕

FIG. 1 is a diagram showing the flow of a corrosion prevention method for the inner surface of a copper alloy tube in a one-shot embodiment of the present invention.

In FIG. 1, 1 is a seawater intake port, and seawater 2 pumped up by a seawater pump 3 is supplied to copper alloy pipes 5 of condensers, heat exchangers, etc. through a seawater conductor R4. 6 is a ferrous sulfate solution tank, 7 is a ferrous sulfate solution, 8 is a metering pump, and 9 is a rubber hose, vinyl hose, vinyl chloride/vinyl chloride solution, etc. for injecting the ferrous sulfate solution 7 into the seawater pipe 14.
l/tube. 10 is a reducing agent solution tank, and 11 is a reducing agent solution such as a solution of sodium sulfite, sodium thiosulfate, etc. 12 is a metering pump for injecting the reducing agent solution 11 into the seawater conduit 4; 13 is, for example, a rubber hose, a vinyl hose, or a vinyl chloride IV pipe;
The injection point 14a is connected to an injection point 14b provided on the upstream side of the seawater conduit 4.

In such a system, the third
As shown in the figure and FIG. 4, chlorine in seawater can be eliminated. In this case, the injection amount of the reducing agent solution 11 changes depending on the chlorine concentration in the seawater 2, the distance between the injection point 14a of the ferrous sulfate solution 7 and the injection point 14a of the reducing agent solution 11, or the flow rate of the seawater 2. However, reducing agent solution 1
The concentration of 1 can be easily controlled by the discharge sewing of the constant voltage pump 12.

After confirming that the chlorine in the seawater 2 has been eliminated by the injection of the reducing agent solution 7 at the injection point 14a of the ferrous sulfate solution 7,
The ferrous sulfate solution 7 is injected from the injection point 14a using the constant pump 8. At the injection point 14a of the ferrous sulfate solution 7, the chlorine in the seawater 2 has been eliminated, so an iron coating with excellent corrosion resistance can be formed on the inner surface of the copper alloy tube 5 without being affected by chlorine. can.

FIG. 2 shows the distribution of the amount of iron on the inner surface of the copper alloy tube 5 when the method of the present invention was used under the following conditions.

■Copper alloy tube shape---26mmφ
25±1°C■ Sulfur 1 dredged - Ferrous injection concentration 1--1,2pp
masFe''■Reducing agent solution---Na weight 80°■Reducing agent solution injection concentration---2.0 ppmasNa3
sO3■ Reducing agent solution injection point 20m upstream of the ferrous sulfate solution injection point.

■Number of days for simulated iron treatment --- 5 days ■Concentration of chlorine in seawater --- [125 ppm Figure 2 also shows the amount of simulated iron without injecting the reducing agent solution. It can be seen that the formation of the iron coating is significantly improved by the injection.

〔Effect of the invention〕

It is extremely effective as a corrosion prevention measure for condensers and heat exchangers in Plan F, which cannot stop the injection of chlorine into seawater, and improves the reliability of the equipment.

[Brief explanation of drawings]

FIG. 1 is a flow diagram showing one example of the method of the present invention, and FIG. 2 is a graph showing the distribution of the amount of iron coating when sodium sulfite is injected as a third embodiment of the present invention. Figure 3 is a graph showing the attenuation of the chlorine concentration in seawater when sodium sulfite is injected, Figure 4 is a graph showing the attenuation of the chlorine concentration in seawater when sodium thiomtate is injected, and Figure 5 is a graph showing the attenuation of the chlorine concentration in seawater when sodium thiomtate is injected. The figure shows 11. of the conventional method. FIG. 6, which is a flowchart showing one aspect of V formation, is a graph showing the distribution of iron deposits according to the conventional method.

Claims (1)

[Claims] In a method for preventing corrosion of the inner surface of a copper or copper alloy pipe by injecting an iron ion solution and a reducing agent solution into seawater, the injection point of the reducing agent solution is placed upstream of the injection point of the iron ion solution in the flow of seawater. A method for preventing corrosion on the inner surface of a copper or copper alloy pipe.