JP2009299161A - Metal corrosion suppression method of water system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corrosion suppression method of metal exhibiting an excellent corrosion prevention effect without causing environmental pollution. <P>SOLUTION: The metal corrosion suppression method of a water system is characterized in that at least phosphate, zinc salt, and M alkalinity component are added to the water system, total phosphorus concentration and total zinc concentration respectively exceed 0 and ≤1 mg/L and the Langelier's index at 30°C is specified to ≥1.2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an aqueous metal corrosion suppression method. More specifically, the present invention relates to a water-based metal corrosion suppression method that does not cause environmental pollution.

  In water systems such as cooling water systems, various kinds of water treatment agents are added to suppress metal corrosion and scale.

  Among water treatment agents, heavy metal salts such as phosphates and zinc salts are used for the purpose of inhibiting metal corrosion. Phosphate is an environmental problem such as eutrophication of lakes and oceans. Cause it to cause. In addition, the use of heavy metal salts has been restricted due to recent stricter environmental regulations.

  However, the water treatment with a phosphate salt or the like and a chemical containing no zinc salt has a problem that the corrosion resistance of the metal is inferior and corrosion of the aqueous metal cannot be sufficiently suppressed.

In particular, when the calcium hardness is 100 mgCaCO ₃ / L or less, it is necessary to add a certain amount or more of phosphate or the like in order to obtain a sufficient metal anticorrosive effect (see Non-Patent Document 1).
Kurita Kogyo Handbook Editorial Committee, Pharmaceutical Handbook 3rd Edition, page 183.

  The main object of the present invention is to provide a method for inhibiting corrosion of a metal that exhibits an excellent anticorrosion effect without causing environmental pollution.

In order to solve the above-mentioned problems, the present invention is a water-based metal corrosion inhibiting method, wherein at least a phosphate, a zinc salt, and an M alkalinity component are added, and the total phosphorus concentration and the total zinc concentration are Provided is a water-based metal corrosion suppression method characterized in that each exceeds 0 and is 1 mg / L or less and the Langelia index is 1.2 or more. By adopting such a configuration, it is possible to obtain a sufficient metal anticorrosion effect while reducing the total phosphorus concentration and the total zinc concentration.
In the water-based metal corrosion inhibiting method according to the present invention, the M alkalinity component used is not particularly limited, but sodium hydroxide is preferably used. By using sodium hydroxide, the Langeria index can be increased with a small addition amount, which is advantageous in terms of cost.
Furthermore, in the water-based metal corrosion inhibiting method according to the present invention, the Langeria index is not particularly limited as long as it is 1.2 or more, but is preferably 1.3 to 2.0 or more.
The water-based metal corrosion inhibiting method according to the present invention can provide a sufficient metal anticorrosion effect even when the calcium hardness is 100 mgCaCO ₃ / L or less.
Moreover, the water system in which the water-based metal corrosion inhibiting method according to the present invention is used is not particularly limited, but is preferably used for an open circulation cooling water system.

  Here, terms used in the present invention will be described. The “M alkalinity component” refers to all alkali components dissolved in water, such as bicarbonate, carbonate, phosphate, hydroxide, and is also referred to as total alkalinity.

  The “Langeria index” is an index for determining the corrosiveness of water, and is represented by equation (1). The Langeria index used in the present invention is the value “LSI (30)” at 30 ° C., and the calculation formula is as shown in the following formula (1).

(Equation 1)
LSI (30) = log [Ca ²⁺ ] + log [A] + pH−11.79

LSI: Langeria index (saturation index)
pH: Actual pH value of water
log [Ca ²⁺ ]: Logarithm of calcium ion concentration
log [A]: Logarithm of total alkalinity

  ADVANTAGE OF THE INVENTION According to this invention, the corrosion inhibition method of the metal which exhibits the outstanding anticorrosion effect can be provided, without causing environmental pollution.

  Hereinafter, preferred embodiments for carrying out the present invention will be described. In addition, embodiment described below shows an example of typical embodiment of this invention, and, thereby, the range of this invention is not interpreted narrowly.

  In the water-based metal corrosion inhibiting method according to the present invention, at least a phosphate, a zinc salt, and an M alkalinity component are added, and the total phosphorus concentration and the total zinc concentration are each greater than 0 and less than 1 mg / L, and The Langellia index is 1.2 or more.

  In the aqueous metal corrosion inhibiting method according to the present invention, the type of phosphate added to the aqueous system is not particularly limited, and examples thereof include inorganic phosphoric acid (normal phosphoric acid, polymerized phosphoric acid) and salts thereof, organic phosphoric acid, Examples thereof include salts thereof, esters thereof, and various phosphonic acids. More specifically, hexametaphosphoric acid, tripolyphosphoric acid, orthophosphoric acid, phosphonobutanetricarboxylic acid, hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylphosphonic acid, etc. may be used alone or in combination of two or more. Can do.

  The total phosphorus concentration in the aqueous system is not particularly limited as long as it exceeds 0 and is 1 mg / L or less. According to the method of the present invention, even if the total phosphorus concentration is as low as 0 to 1 mg / L or less, a sufficient metal corrosion inhibiting effect can be obtained.

  In the aqueous metal corrosion inhibiting method according to the present invention, the kind of zinc salt added to the aqueous system is not particularly limited. For example, zinc chloride, zinc sulfate, zinc nitrate, zinc acetate, zinc malate, zinc citrate, etc. It can be used alone or in combination of two or more.

  The total zinc concentration in the aqueous system is not particularly limited as long as it exceeds 0 and is 1 mg / L or less. According to the method of the present invention, a sufficient metal corrosion inhibitory effect can be obtained even when the total zinc concentration is as low as 0 to 1 mg / L or less.

The kind of M alkali component used in the water-based metal corrosion inhibiting method according to the present invention is not particularly limited, and for example, alkali hydroxide salt, alkali bicarbonate, alkali carbonate, calcium salt and the like can be used.
Specific examples of the alkali hydroxide salt include sodium hydroxide and potassium hydroxide.
Specific examples of the alkali bicarbonate include sodium bicarbonate and potassium bicarbonate.
Specific examples of the alkali carbonate include sodium carbonate and potassium carbonate.
Specific examples of the calcium salt include calcium carbonate, calcium hydroxide, calcium chloride and the like.

Further, the concentration of the M alkalinity component is not particularly limited as long as it is added so that the water-based Langeria index is 1.2 or more, and can be appropriately set in consideration of the pH, calcium concentration, etc. of the water-based material. . By adding the M alkalinity component, corrosion of aqueous metals can be effectively suppressed even when phosphorus and zinc are at low concentrations.
In particular, conventionally, when the aqueous calcium hardness is low, a sufficient metal corrosion inhibitory effect cannot be obtained unless a relatively high concentration of phosphate and zinc salt is added. However, according to the method of the present invention, even when the aqueous calcium hardness is low, metal corrosion can be suppressed without increasing the concentration of phosphate and zinc salt.

  In the water-based metal corrosion inhibiting method according to the present invention, the water-based Langeria index is not particularly limited as long as it is 1.2 or more, but is preferably 1.3 to 2.0. By setting the Langeria index in the above range, corrosion of water-based metals can be effectively suppressed even if phosphorus and zinc are at low concentrations.

In the water-based metal corrosion suppression method according to the present invention, the water-based calcium hardness is not particularly limited, but conventionally, even under low calcium hardness conditions of 100 mg CaCO ₃ / L or less, which has been difficult to sufficiently suppress metal corrosion, Metal corrosion can be effectively suppressed.

  The water-based metal corrosion inhibiting method according to the present invention can be used for any water system, for example, a cooling water system such as an open circulation cooling water system and a sealed cooling water system.

  Furthermore, in the water-based metal corrosion inhibiting method according to the present invention, by using a water-soluble polymer or the like in the water system, the metal corrosion inhibiting effect is further improved, and supersaturated calcium carbonate, silica, calcium silicate, silicic acid Adhesion as a scale to a metal surface such as magnesium can be suppressed.

  The water-soluble polymer used is not particularly limited. For example, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-hydroxy-3-acryloxy-1 -Homopolymers, copolymers, etc., such as propanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, isoprenesulfonic acid and their salts. These water-soluble polymers can be used alone or in combination of two or more.

  Slime control agents such as hypochlorite, hypobromite, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one can be added. .

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to a following example.

  Using the bench scale cooling water system evaluation test apparatus shown in FIG. 1, an experiment for examining the corrosion inhibition effect of the following examples and comparative examples was conducted.

  In the bench scale cooling water system evaluation test apparatus shown in FIG. 1, the circulating cooling water is fed from the cooling tower 1 to the heat exchanger 3 through the circulation pipe 2 having the pump P 1, and the return water is returned to the cooling tower 1 through the pipe 4. It is. 5 is a supply water introduction pipe, 6 is an introduction pipe for an evaluation drug according to Examples and Comparative Examples, 7 is a cooling water quality adjusting agent tank, and 8 is a forced blow pipe, each having pumps P2 to P4. The heat exchanger 3 is a steam heating tube side water-flow heat exchanger provided with two carbon steel tubes having an outer diameter of 19 mm, a length of 1300 mm, and a thickness of 2.3 mm.

An evaluation test was conducted under the following operating conditions.
<Operating conditions>
Retained water volume: 350L
Flow rate: 0.3 m / sec Heat exchanger inlet water temperature: 30 ° C
Heat exchanger outlet water temperature: 50 ° C
Evaluation drug addition method: Continuously infused so that the retained concentration in cooling water is 60 mg / L using the evaluation drugs according to the following Examples and Comparative Examples

  Using a carbon steel test tube on which an initial anticorrosion film was formed with a commercially available initial treatment chemical, the above operation was performed for 14 days, and the corrosion inhibition effect was evaluated at the maximum depth of local corrosion that occurred in the heat exchanger tube. . After 14 days of operation, the test tube was removed from the heat exchanger. The test tube was pickled with hydrochloric acid containing inhibitor to remove corrosion products. The depth of local corrosion occurring on the test tube surface was measured with a depth gauge, and the maximum value was obtained.

<Evaluation method>
The initial treatment is phosphorous zinc initial treatment, Nogicho water (calcium hardness 50 mg CaCO ₃ / L), Cryroy P-320 (corrosion inhibitor made by Kurita Kogyo Co., Ltd.) 400 mg / L, Cry Royal P-652 (made by Kurita Kogyo Co., Ltd.) Anticorrosive agent) was performed by adding 200 mg / L. The initial treatment period was 1 day. Switching to the holding treated water, it was how to switch collectively holding process water adjusted in advance a predetermined water quality. The quality of the retained treated water was changed by adding an evaluation agent and changing the calcium hardness and the acid consumption (pH 4.8) silica concentration. For the purpose of adjusting calcium hardness, calcium chloride is used. For the purpose of adjusting acid consumption (pH 4.8), sodium hydrogen carbonate or sodium hydroxide is used. For adjusting the silica concentration, silicic acid No. 3 is used. Each was used. The water temperature was 30 ° C. at the heat exchanger inlet, the tube side water flow was 50 ° C. at the heat exchanger outlet, and the flow rate was 0.3 m / s. The retention treatment period was 14 days.
For slime control treatment, sodium hypochlorite was used, and continuous addition was performed so that the total residual chlorine was detected at 0.3 to 0.5 mg Cl ₂ / L.

<Evaluation drug A>
Dequest 2010 (Thermphos, 1-hydroxyethylidene 1,1-diphosphophosphoric acid) is 1 mg / L in terms of PO ₄ , 75% normal phosphoric acid is 2 mg / L in terms of PO ₄ , and zinc chloride is 1 mg / L in terms of zinc L, Aquaric GL-386 (manufactured by Nippon Shokubai Co., Ltd., acrylic acid polymer) was added to the test water so that the solid content was 5 mg / L.

<Evaluation drug B>
Bayhibit AM (manufactured by Bayer, 2-phosphono-1,2,4-butanetricarboxylic acid) is 0.2 mg / L in terms of PO4, 75% orthophosphoric acid is 5.8 mg / L in terms of PO4, and zinc chloride is zinc 3 mg / L in conversion, Dynaclin W-111 (manufactured by JSR Corporation, solid sodium salt of acrylic acid, 2-hydroxyethyl methacrylate, 2-methylbuta-1,3-diene-1-sulfonic acid copolymer) It added to test water so that it might become 5 mg / L in terms of minutes.

  Table 1 shows the evaluation conditions of each example and each comparative example.

  FIG. 2 shows the local corrosion depth in the conventional method for inhibiting metal corrosion. In order to obtain a sufficient anticorrosive effect, the total phosphorus concentration and the total zinc concentration must be increased, and a sufficient anticorrosive effect could not be obtained with a total phosphorus concentration of 1 mg / L and a total zinc concentration of 1 mg / L ( Comparative Examples 1 and 2)

  FIG. 3 shows the local corrosion depth when the amount of calcium chloride is changed and the Langeria coefficient LSI (30) is changed. When the LSI (30) was 1.4 or more, the local corrosion depth was 0.6 mm or less, and it was confirmed that a sufficient anticorrosive effect was obtained (see Example 1, Example 2, and Comparative Example 1).

  FIG. 4 shows the local corrosion depth under the low calcium hardness condition. Conversely, even in the case of low calcium hardness (50 mg / L), by setting the M alkalinity to 300 mg / L and making LSI (30) 1.2 or more, the local corrosion depth is 0.6 mm or less. It was confirmed that a sufficient anticorrosion effect was obtained (see Example 1 and Example 3).

  From the above, it is clear that the water-based metal corrosion inhibition method according to the present invention can provide a sufficient metal corrosion inhibition effect even when the total phosphorus concentration and the total zinc concentration are each greater than 0 and less than 1 mg / L. It was.

It is a conceptual diagram of a bench scale cooling water system evaluation test apparatus. It is a figure which shows the local corrosion depth in the conventional metal corrosion suppression method. It is a figure which shows the local corrosion depth at the time of changing the amount of calcium chloride and changing the Langeria coefficient LSI (30). It is a figure which shows the local corrosion depth in low calcium hardness conditions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cooling tower 2 Circulation piping 3 Heat exchanger 4 Piping 5 Supply water introduction piping 6 Evaluation chemical introduction piping 7 Water quality adjusting agent introduction piping 8 Forced blow piping P1, P2, P3, P4, P5 Pump

Claims (4)

An aqueous metal corrosion control method,
At least a phosphate, a zinc salt, and an M alkalinity component are added;
An aqueous metal corrosion inhibiting method, wherein the total phosphorus concentration and the total zinc concentration are each greater than 0 and less than 1 mg / L, and the Langelia index at 30 ° C. is 1.2 or more.   3. The water-based metal corrosion suppression method according to claim 1, wherein the Langeria index is 1.3 to 2.0. The water-based metal corrosion inhibiting method according to any one of claims 1 to 3, wherein the calcium hardness is 150 mgCaCO ₃ / L or less.   5. The method for inhibiting metal corrosion of an aqueous system according to claim 1, wherein the aqueous system is an open circulation cooling water system.