JPH06158364A - Corrosion inhibiting method for metal in water system - Google Patents

Abstract

PURPOSE:To effectively prevent the corrosion of a metal in a water system without inducing the problem of environmental contamination or the like. CONSTITUTION:A corrosive ion containing water of the water system is brought into contact with an anion exchanger carrying an anticorrosive anion and a low molecular weight polymer is added into the water system. By allowing the corrosive ion in water such as Cl<->, SO4<2-> to be brought into contact with the anion exchanger carrying the aniticorrosive anion such as HCO3<->, OH<-> to ion exchange, the corrosive ion conc. in water is decreased and the corrosiveness of the water system is suppressed. A anticorrosive film is formed HCO3<-> or the like eluted by ion exchanging and Ca<2+> or the like originated from the water system on the surface of the metal by the film forming accelerating action of the low molecular weight polymer and the corrosion of the metal is more certainly inhibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of inhibiting corrosion of a water-based metal, and more particularly to mild steel, stainless steel,
The present invention relates to a method for effectively suppressing corrosion of metals such as copper and copper alloys.

[0002]

2. Description of the Prior Art Mild steel, stainless steel, copper, copper alloys, etc. are used as base materials for various equipment and pipes used in open water, closed circulation cooling water system, heat storage water system, closed cold / hot water system and other fresh water systems. There is. These substrates are immersed used in freshwater, chloride ions carried over from makeup water (Cl ^-),
Corrosion due to sulfate ions (SO ₄ ^2- ) etc. causes pitting corrosion. Therefore, a corrosion inhibitor is used in order to suppress the corrosion of the metal material in contact with such a fresh water system.

Conventionally, as corrosion inhibitors for metals (including alloys) such as mild steel, stainless steel, copper or copper alloys in a fresh water system, chromates, molybdates, nitrites, phosphates and phosphonic acids are used. Salts, zinc salts, benzotriazole, tolyltriazole, mercaptobenzothiazole and the like have been used.

Further, there has been proposed a method of treating an aqueous system with an OH type anion exchange resin having chromium ions or zinc ions adsorbed as an anticorrosion agent and eluting the anticorrosion agent into water to prevent corrosion (Japanese Patent Publication No. 48-39704). Issue).

Furthermore, a method has been proposed in which the circulating cooling water is passed through a desalting tower consisting of an H-type strong acid cation exchange resin and an OH-type weakly basic anion exchange resin to prevent the concentration of salts in the cooling water. (Japanese Patent Laid-Open No. 48-13936).

[0006]

When the fresh water containing the above-mentioned conventional corrosion inhibitor is released to the outside of the system, it may cause environmental pollution. Also, in the method described in JP-B-48-39704, there is concern that the eluted chromium and zinc ions may affect the environment.

Therefore, there is a demand for the development of a corrosion inhibiting method which has little influence on the environment.

Further, the method described in JP-A-48-13936 is intended to remove not only anions in water but also components such as calcium ions which are involved in anticorrosion.

The present invention has been made in view of the above conventional circumstances, and is a method for effectively inhibiting corrosion of a water-based metal without causing problems such as environmental pollution and the like. The purpose is to provide.

[0010]

A method of inhibiting corrosion of a water-based metal according to the present invention is a method of inhibiting corrosion of a water-based metal, which comprises anion exchange carrying corrosive ion-containing water of the water-based anticorrosion anion. It is characterized in that a low molecular weight polymer is added to the water system while contacting with the body.

In the present invention, the anticorrosive anion is an anion which can be dissolved in water by ion exchange and can form an anticorrosive film by reacting with a dissolved cation even if it does not exhibit anticorrosive property. Point to.

The present invention will be described in detail below.

[0013] In the method of the present invention, Cl as an object to be processed aqueous ^-, water containing corrosive ions SO ₄ ^2-like,
A low molecular weight polymer is added together with the anion exchange resin supporting anticorrosive anions such as OH ⁻ and HCO ₃ ⁻ and anion exchanger such as zeolite for ion exchange.

As a result, corrosive ions such as Cl ⁻ and SO ₄ ^{2− in} water are ion-exchanged with anticorrosive anions such as OH ⁻ and HCO ₃ ⁻ , the content thereof is reduced, and the corrosiveness is reduced. It

Further, by adding a low-molecular weight polymer, a uniform anticorrosion of anticorrosion anions such as OH ⁻ and HCO ₃ ⁻ dissolved in water by the above-mentioned ion exchange and anticorrosion components such as Ca ²⁺ and SiO ₂ derived from an aqueous system. A film is effectively formed on the metal surface,
Corrosion is suppressed even more reliably.

There is no particular limitation on the method of contacting the water-based water containing corrosive ions with the anion exchanger carrying the anticorrosion anion. For example, anion exchange resin carrying the anticorrosion anion, specifically HCO _{3 type} Make-up water or circulating water may be brought into water contact with a packed tower filled with an anion exchange resin. The water flow conditions and the like in this case are appropriately determined according to the water quality and the like of the water system to be treated.

On the other hand, the low molecular weight polymer has a molecular weight of 500 to 100,000, particularly 1000 to 20,000.
Water-soluble polymer to a certain extent, specifically, maleic acid-isobutylene copolymer, polyacrylic acid, partial hydrolyzate of polyacrylamide, acrylic acid-allyloxy-2-
Hydroxypropanesulfonic acid copolymer, acrylic acid-
Hydroxyethyl methacrylic acid copolymer, acrylamide and allyl sulfonic acid copolymer, acrylic acid-maleic acid copolymer, acrylic acid-styrene copolymer, acrylic acid-styrene sulfonic acid copolymer, polymaleic acid, polystyrene sulfonic acid Examples thereof include known low molecular weight polymers such as acrylic acid-itaconic acid copolymer, polyitaconic acid, acrylic acid-acrylonitrile copolymer, acrylic acid-vinyl sulfonic acid copolymer, and methyl vinyl ether-maleic acid copolymer.

The addition amount of such a low molecular weight polymer varies depending on the water quality of the water to be treated, but in the usual case, it is added in an amount of 0.1 to 500 mg / l to the water to be treated.

The addition timing of the low molecular weight polymer is not particularly limited, but in the usual case, it is preferably after the treatment with the anion exchanger.

The method of the present invention as described above is extremely effective in inhibiting corrosion of water-based metals, such as fresh water-based metals, containing Cl ⁻ and SO ₄ ²⁻ as corrosive ions.

As described above, according to the present invention, the anticorrosion treatment of hydrogen can be achieved without causing environmental problems by the above-mentioned constitution. However, if necessary, inorganic phosphate (orthophosphate or polymerized phosphate) can be used. Salts), organic phosphates, phosphonic acids, zinc, nickel salts, tungstates, molybdates, nitrites, borates, silicates, oxycarboxylates, benzotriazole, mercaptobenzothiazole, and other anticorrosive agents Alternatively, scale inhibitors such as lignin derivatives, tannic acids, and polysaccharides such as tempun may be used in combination.

[0022]

[Action] Cl ^-, water corrosive ions SO ₄ ^2-like H
By contacting with an anion exchanger carrying an anticorrosive anion such as CO ₃ ⁻ or OH ⁻ to carry out ion exchange, the concentration of corrosive ions in water is reduced and the corrosiveness of the water system is mitigated.

Further, due to the film formation-promoting action of the low molecular weight polymer, HCO ₃ ⁻ etc. eluted by ion exchange and Ca ²⁺ etc. derived from the water system form an anticorrosion film on the metal surface, so that metal corrosion is more reliable. Suppressed to.

[0024] That is, a corrosive anions Cl ^- Reducing of mild steel and stainless steel, copper, on an effective pitting inhibition such as brass, effective prevention of the frequently occurring stress corrosion cracking in stainless steel and brass Becomes

Further, the reduction of SO ₄ ²⁻ prevents the formation of basic copper sulfate, which causes pitting corrosion, with respect to copper and brass, and suppresses corrosion.

On the other hand, Ca ²⁺ and HCO which are anticorrosive ions
₃ ^- is CaCO on the metal surface in the presence of low molecular weight polymer.
Corrosion is suppressed by forming a uniform precipitate film of ₃ and preventing the diffusion of dissolved oxygen which is a factor promoting corrosion.

SiO _{2 in} water has the function of changing the rust of mild steel to a sticky property and suppressing corrosion.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 Preparation of test water 1 liter of a strongly basic anion exchange resin "Levacit M500" was packed in an acrylic column having an inner diameter of 38 mm and a length of 1000 mm, and regenerated with a 5% NaHCO ₃ aqueous solution to generate HC.
It was made O _{3 type} and washed with water. The HCO _{3 type} anion exchange resin tower was subjected to anion exchange treatment by passing water of artificial water A, B, and C having the water quality shown in Table 1 at a flow rate of 50 liters / hr. Liquids a ', b', and c'shown in water quality were obtained.

[0030]

[Table 1]

Separately, 12 mg / l of maleic anhydride-isobutylene copolymer "Isoban KPS-3" having a molecular weight of about 15,000 was added as a water-soluble low-molecular weight polymer. , C liquid were subjected to anion exchange treatment in the same manner as described above, and the water quality A'solution, B'solution and C'solution shown in Table 2 were obtained.

[0032]

[Table 2]

Corrosion test Insert a vinyl chloride rotary shaft with a mild steel test piece at the tip into a glass beaker of 1 liter containing test water, and use a rotary corrosion tester to rotate in test water. The test was conducted.

The test temperature was 50 ° C., the test water amount was 1 liter, the test period was 4 days, and the rotation speed of the rotary shaft was 180 rpm.
p. m. And A test piece having a surface area of 31 cm ² made of SPCC material was polished with No. 400 emery polishing paper, degreased, and used for the test. Table 3 shows the test results (corrosion weight loss, corrosion rate).

[0035]

[Table 3]

From the above results, the following is clear.
That is, in particular, by comparing the results of the corrosion tests of the liquid a and the liquid a ′, the corrosiveness is remarkably reduced by the anion exchange treatment of fresh water.

In addition, since CaCO ₃ is precipitated in water in the b'solution and the c'solution obtained by anion-exchange of the b-solution and the c-solution having a relatively high hardness, the anion-exchange treatment does not exhibit the corrosion inhibiting effect. The precipitation of CaCO ₃ is c as shown in Table 1.
Calcium hardness of liquid'b 'is 144,26
It is obvious from the fact that it should be 0 mg / l, but 28,12 mg / l. That is, these b'solution, c
Since the M alkalinity is increased by the anion exchange treatment in the liquid ', the condition is that CaCO ₃ is likely to precipitate.

However, even in such a liquid having high hardness, a water-soluble low-molecular weight polymer is added, and CaCO in water is added.
_When controlling so as to prevent precipitation of ₃ , B liquid, C
As is clear from the comparison of the corrosion test results of the liquid, the B'solution, and the C'solution, CaCO ₃ is effectively deposited as a uniform film on the surface of the mild steel test piece, and the anticorrosion effect is significantly enhanced.

From the above, it is clear that by exchanging corrosive ions in water with anticorrosive anions and adding a low molecular weight polymer, it is possible to reliably suppress metal corrosion regardless of hardness in water. is there.

[0040]

As described in detail above, according to the method of inhibiting corrosion of a metal in the water system of the present invention, the corrosive ions in the water system are reduced by anion exchange, and at the same time, the anticorrosive ions eluted by the anion exchange and water-derived By effectively utilizing the anticorrosive ions, a uniform anticorrosive film is efficiently deposited and formed on the metal surface by the film formation promoting action of the low molecular weight polymer, so that metal corrosion can be ensured without adversely affecting the environment. It is possible to prevent it.

Claims (1)

[Claims] 1. A method for inhibiting corrosion of a water-based metal, which comprises contacting the water-based water containing corrosive ions with an anion exchanger carrying an anticorrosive anion, and adding a low molecular weight polymer to the water-based system. A method for inhibiting corrosion of a water-based metal, which is characterized by the above.