JPH1112771A - Aqueous corrosion inhibitor and corrosion preventive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aq. corrosion inhibitor which is capable of effectively preventing the corrosion of steel products, etc., by low- and middle concd. water without eutrophication of lakes and ponds by not incorporating a phosphorus compd., incorporating a specific ratio of a molybdic acid compd. and further incorporating a zinc compd. and high-polymer electrolyte therein into the corrosion preventive material. SOLUTION: This aq. corrosion inhibitor has substantially 0 ratio of the phosphorus compd., such as orthophosphate, contains >=1 wt.%, more preferably about 2 to 20% (in terms of MoO4 ) molybdic acid compd., such as sodium orthomolybdate, contains the zinc compd., such as zinc sulfate, preferably at 0.05 to 0.5 part for each 1 pt.wt. of the molybdic acid compd. and further contains the high-polymer electrolyte. The inhibitor is effective in preventing the corrosion of the steel products, such as piping, by the low and middle concd. water of <=200 mg/l in calcium hardness and does not give rise to a heat transfer fault. An azole compd. is further preferably added to this corrosion inhibitor if the inhibitor is used for copper. The aq. corrosion inhibitor is preferably used at a holding concn. of 20 to 200 mg/l.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based anticorrosion agent, and more particularly to a water-based anticorrosion agent for preventing corrosion of a metal member and a method for preventing corrosion.

[0002]

2. Description of the Related Art In the steel industry, chemical plants and the like, cooling water is widely used for cooling equipment. In such a cooling water system, the piping is often formed of mild steel, and the heat exchanger is formed of copper or the like. How to prevent corrosion of metal pipes and heat exchangers is one of the problems with cooling water systems. Hardness components such as calcium are usually present in the cooling water used in the cooling water system, but some of the water evaporates due to cooling. It is not unusual for calcium to be concentrated to 250 mg / liter or more. Water containing a large amount of a hardness component generally does not easily corrode metals, so that corrosion prevention can be achieved by concentrating cooling water and increasing the concentration of the hardness component. In such a system, the failure of the cooling water system can be prevented by adding only the polymer for scale prevention.

[0003] However, in the case of an industrial cooling tower having a high heat load or a replenishing water for the cooling water, when the chloride water, the sulfate ion, the silica, the organic matter or the like which causes a large amount of corrosion or scale adhesion is contained, the cooling water is used. Cannot be concentrated too much. In such a cooling water system, the hardness component is generally 250.
mg / liter or less, and is highly corrosive to metals, especially mild steel. Therefore, in the past, anticorrosion was attempted by always adding an anticorrosive containing a specific phosphorus compound to cooling water and forming a precipitate film, which is mainly composed of calcium phosphate or the like, on the surface of mild steel.

[0004]

The cooling water system circulates water while partially evaporating the water. If the evaporation proceeds and the calcium ion concentration is concentrated to a considerably high concentration, such water is discharged by blowing. Phosphorus compounds in the cooling water are discharged together with the blow water and flow into lakes and marshes, leading to enrichment. As described above, the conventional cooling water-based anticorrosive containing a phosphoric acid compound has a problem that it can enrich lakes and marshes. Further, the phosphate compound easily adheres to the high temperature part of the cooling device as a scale. If the phosphate compound adheres to the high-temperature portion, it may also cause the inhibition of heat transfer. Conventional cooling water-based anticorrosives containing a phosphoric acid compound also have such a problem.

[0005] Other anticorrosives include those containing a molybdate compound as a main component and those containing a zinc compound as a main component. However, in order to obtain a sufficient anticorrosion effect, when the molybdate compound is the main component, 200 mg
It was necessary to maintain the concentration at a high concentration of 1 / liter or more, and the cost was high, which was not practical. In addition, those containing a zinc compound as a main component have a limited applicable water quality range, and it has been difficult to obtain a long-term stable anticorrosion effect due to precipitation of hydroxide.

Accordingly, the present invention provides a low- and low-calcium hardness of 200 mg / liter or less without enriching the lake.
A water-based anticorrosive agent that can effectively prevent corrosion of steel pipes, etc. due to concentrated water, and also has the excellent effect of preventing heat transfer from occurring at high temperatures, especially in cooling water systems. An object of the present invention is to provide a water-based anticorrosive agent and an anticorrosion method to be exhibited.

[0007]

That is, the object of the present invention is achieved by the following constitutions. (1) A water-based anticorrosive, wherein the proportion of a phosphorus compound is substantially zero, the molybdate compound is contained in an amount of 1 wt% or more, and a zinc compound and a polymer electrolyte are further contained. (2) The aqueous anticorrosive according to the above (1), wherein the zinc compound is blended in a ratio of 0.05 to 0.5 part by weight with respect to 1 part by weight of the molybdate compound. (3) The aqueous anticorrosive according to the above (1) or (2), further comprising an azole compound. (4) The aqueous corrosion inhibitor according to the above (3), wherein the azole compound is benzotriazole or tolyltriazole.

(5) The aqueous anticorrosive described in (1) is added to 20
A water-based anticorrosion method characterized by being used at a retention concentration of 200 mg / liter. (6) A water-based anticorrosion method characterized in that the ratio of the phosphoric acid compound is substantially zero, the water containing the molybdic acid compound is 0.2 to 60 ppm, and the water containing the zinc compound and the polymer electrolyte is circulated. .

The above-mentioned water-based anticorrosive agent and anticorrosion method do not contain a phosphoric acid compound which is a component of the conventional anticorrosive agent, but have a synergistic effect of a molybdate compound and a zinc compound to prevent corrosion of mild steel pipe materials and the like. Prevention. An aqueous anticorrosive and an anticorrosion method preferably used in a cooling water system are preferred.
The weight percent of the molybdate compound is obtained by conversion as MoO _4. In addition, the weight percent of the zinc compound is calculated as Zn alone.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited thereto. In the aqueous anticorrosive of the present invention, the ratio of the phosphoric acid compound is substantially zero.
The phosphate compound specifically refers to orthophosphate, polyphosphate, phosphonate, and a phosphorus-containing polymer. Conventionally, these have been considered as essential components for preventing corrosion due to low / medium concentrated cooling water having a calcium hardness of about 20 to 200 mg / liter. Substantially zero means that no phosphate compound is contained. Also, it does not cause scale in the high temperature part of the cooling device, and it can be evaluated that it does not actually cause eutrophication even if discharged to lakes and marshes,
It also refers to the case where almost no phosphate compound is contained.

Phosphoric acid compounds are practically scarcely contained, but instead molybdate compounds. The molybdate compound specifically includes orthomolybdate, paramolybdate, metamolybdate, and the like. Examples of the metal salt in this case include a sodium salt, a potassium salt, and an ammonium salt. Among them, sodium orthomolybdate particularly contains a zinc compound together with the most preferred molybdate compound. Specific examples of the zinc compound include zinc sulfate, zinc chloride, zinc acetate, sodium zincate, potassium zincate and the like. Among them, zinc sulfate is most preferable.

In addition to the molybdate compound and the like, a polymer electrolyte is further contained as an auxiliary. The polymer electrolyte is specifically an acrylic acid copolymer and its metal salt,
Maleic acid copolymers and metal salts thereof, sulfonic acid copolymers and metal salts thereof, polyethylene glycol and esters thereof, and the like can be given. The action of such a polymer electrolyte prevents zinc precipitation and enhances the anticorrosion effect, and at the same time, prevents the adhesion of scale and corrosion products, keeps the metal surface clean, helps the formation of anticorrosion films, and promotes secondary corrosion. To prevent

In addition to the polymer electrolyte, an azole compound serving as an anticorrosive for copper may be further added. Such azole compounds include, for example, benzotriazole, tritriazole, aminotriazole and the like. In addition, organic acids such as sulfamic acid and citric acid may be added.

The above components are mixed, for example, in the following ratio. That is, the mixing ratio of the molybdic acid compound is 1 to 30% by weight, preferably 2 to 2% by weight based on the total weight of the anticorrosive.
0% by weight is desirable. If the compounding ratio is less than 1% by weight, a sufficient anticorrosive effect cannot be expected, which is not preferable. 3
If the amount exceeds 0% by weight, the stability of the drug is impaired, and the cost is increased. Most preferred is 2 to 20% by weight. When it is in this range, both the anticorrosion effect and the stability are increased, which is preferable. The compounding ratio of the zinc compound is 0.0 to 1 part by weight of the molybdate compound.
5 to 0.5 parts by weight is preferred. The total weight is preferably 1 to 5% by weight, and if it is less than 1% by weight, a sufficient anticorrosive effect cannot be obtained.
If the content is more than 10% by weight, not only the stability of the drug is impaired, but also when zinc is used after being diluted in a cooling water system, it causes zinc to be scaled. The mixing ratio of the polymer electrolyte is preferably 1 to 50% by weight based on the total weight. If it exceeds 50% by weight, gelation may occur and the effect may be impaired. Other azoles are desirably 10% by weight or less.

Such an aqueous anticorrosive is stabilized by adding a chelating raw material, for example, a polymer electrolyte, to sodium hydroxide dissolved in zinc sulfate, and further adding other raw materials. To manufacture. In order to prevent the precipitation of zinc hydroxide, the pH should be maintained at 11 or more during the production, particularly when adding an acidic raw material. Since the stability may be impaired by heat generation, the liquid temperature is preferably kept at 40 ° C. or lower. The above anticorrosive is, for example, in an aqueous system,
It is recommended to dilute to a retention concentration of 20 to 200 mg / liter before use. That is, the molybdate compound is preferably used in an aqueous system so as to be maintained at a concentration of 0.2 to 60 ppm.

More specifically, for example, it may be used in the following cooling water system cooling device. FIG. 1 is an example of a cooling device for managing cooling water. This cooling device has a heat exchanger 1 for absorbing waste heat such as a chemical reaction tank (not shown) for performing an exothermic reaction and the like. In this heat exchanger 1,
A cooling pipe extends from a bottom water tank 2 for temporarily storing cooling water, and communicates with a refrigerant inlet via a pump 3. A refrigerant outlet of the heat exchanger 1 communicates with a cooling tower 5 having a blower 4 through a high-temperature pipe. Cooled water from this cooling tower 5,
It is supplied to the bottom water tank 2 located immediately below. The bottom tank 2
An injection tube with a pump extends from the dosing tank 6 again.

The above-mentioned anticorrosive agent is previously charged in the form of an aqueous solution into the chemical injection tank 6. The above anticorrosive may be used by diluting it to a concentration range of usually 20 to 200 mg / liter in an aqueous system. If the concentration of the above-mentioned anticorrosive in the bottom water tank 2 does not satisfy a concentration sufficient for the anticorrosion of the cooling device, that is, does not satisfy 20 mg / liter, the anticorrosive is supplied from the chemical injection tank 6. Bottom water tank 2, heat exchanger 1,
Cooling water is circulated between the bottom water tanks 2. The blower 4 is driven, and waste heat sent from a chemical reaction tank (not shown) or the like is absorbed in the cooling water by the heat exchanger 1. If the concentration of the anticorrosive component in the bottom water tank 2 rises while circulating the cooling water, make-up water is supplied from the water supply pipe 8 to bring the anticorrosive component to a preferable concentration. Further, when the quality of the cooling water is deteriorated or when the amount of the cooling water is increased, the blow pipe 7 branching from the high temperature pipe.
, A part of the water is discharged, the bottom water tank 2 is replenished with fresh water from a water supply device, and if necessary, an anticorrosive is replenished by the chemical injection tank 6 to bring the anticorrosive component to a preferred concentration.

[0018]

EXAMPLES Examples will be described below, but the present invention is not limited to these contents. [Examples 1 to 13] [Comparative Examples 1 to 11] [Reference Example 1,
2] Aqueous corrosion inhibitors were prepared at the ratios shown in Tables 1 and 2, and the corrosion rates of mild steel and copper were measured by the mass subtraction method shown in the Industrial Water Corrosion Test Method (JIS-K0100). That is, a disk on which the test piece was fixed was put into the test water and stirred at a constant speed for 5 days. After 5 days, the test piece was taken out, rust-removed, and the weight was measured. The corrosion rate was determined from the difference from the weight of the test piece measured before the start of the test.

Test conditions Sample water: pH 7.5, calcium hardness 150 mg / liter (CaCO ₃ equivalent) Water temperature: 40 ° C. Stirring: 60 rpm Test period: 5 days Drug concentration: Diluted to a concentration of 100 mg / liter. Use 2 liter beaker. The results are shown in Table 1 and FIG. In the table, m of mdd is mg, d
Represents dm ² , and d represents day (day). Azole represents benzotriazole and zinc represents a zinc compound.

[0020]

[Table 1]

[0021]

[Table 2]

Further, the relationship between the chemical concentration and the corrosion rate of mild steel was examined for the anticorrosive provided in Example 6, and compared with a conventional anticorrosive containing phosphoric acid. FIG. 3 shows a comparative graph. The phosphoric acid concentration of the conventional anticorrosive was 5 wt%, and was 1% as in the example.
The sample was diluted to 00 mg / liter and used for the test. As can be seen from Table 1, the mild steel corrosion rate can be effectively suppressed by the synergistic effect of sodium molybdate and zinc sulfate. Further, as can be seen from FIG. 2, the anticorrosive of the present invention contains 10% by weight of sodium molybdate and 1% by weight of zinc sulfate.
Is most effective in suppressing the mild steel corrosion rate. Even if sodium molybdate and zinc sulfate are further added, the anticorrosion effect does not increase significantly.

[0023]

Industrial Applicability The aqueous anticorrosive agent and the anticorrosive method of the present invention have a phosphoric acid compound ratio of substantially zero, contain a molybdate compound at 1 wt% or more, and further contain a zinc compound and a polymer electrolyte. So that they do not enrich the lakes. Fully prevent eutrophication of rivers and lakes. It effectively prevents corrosion of piping steel materials and the like by low / medium concentrated water having a calcium hardness of 200 mg / liter or less. Since it does not contain a phosphoric acid compound, there is no scale adhered to the high-temperature part of the cooling system, and the excellent effect of preventing heat transfer at the high-temperature part when used in the cooling water system is also exhibited. I do.

[Brief description of the drawings]

FIG. 1 is an example of a cooling device for managing cooling water.

FIG. 2 is a graph showing the relationship between the content of a molybdate compound, the content of a zinc compound, and the corrosion rate of mild steel.

FIG. 3 is a graph comparing the corrosion rate of mild steel between the corrosion inhibitor of Example 6 and a conventional phosphorus-based anticorrosive.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat exchanger 2 Bottom water tank 3 Pump 4 Blower 5 Cooling tower 6 Chemical injection tank 7 Blow pipe 8 Water supply pipe

Claims (6)

[Claims] 1. A water-based anticorrosive, wherein the ratio of a phosphorus compound is substantially zero, a molybdate compound is contained in an amount of 1 wt% or more, and a zinc compound and a polymer electrolyte are further contained. 2. The aqueous anticorrosive according to claim 1, wherein the zinc compound is blended in a ratio of 0.05 to 0.5 part by weight with respect to 1 part by weight of the molybdate compound. 3. The aqueous anticorrosive according to claim 1, further comprising an azole compound. 4. The aqueous anticorrosive according to claim 3, wherein the azole compound is benzotriazole or tolyltriazole. 5. The water-based anticorrosive according to claim 1, wherein the water-based anticorrosive is 20 to 2 times.
A water-based anticorrosion method characterized by being used at a retention concentration of 00 mg / liter. 6. The method according to claim 1, wherein the ratio of the phosphoric acid compound is substantially zero, the molybdate compound is contained in an amount of 0.2 to 60 ppm,
A water-based anticorrosion method, further comprising circulating water containing a zinc compound and a polymer electrolyte.