The method of protecting steel against corrosion in aqueous environments

 

(57) Abstract:

The invention relates to corrosion protection and can be used to protect equipment from steel under the action of aggressive media that are close to neutral. The developed method is the introduction working in the aquatic environment complex inhibitor whose components have the following concentrations in the environment, g/DM3: sodium nitrite 50 - 100, water-soluble urea-formaldehyde resin (brand KF-W, GOST-14231-88) 10 - 20; orthophosphoric acid, 10 - 20. The way to protect steel from corrosion, has a high protective characteristics, relatively low concentrations of reagents, which are low-toxic substances and have a lesser impact on the environment. At these concentrations the observed corrosion rate was less than 0.005 mm/year, a protective effect is greater than 95%. 2 C.p. f-crystals, 1 table.

The invention relates to the field of corrosion protection and can be used for protection of parts and equipment in water circulation systems of various types. In particular, it can be used for corrosion protection of heat networks in the summer (Parking mode), to protect stations in the calibration of instrumentation and gozdarstva aggressive environment (water) [1]. In addition to stabilization, de-aeration, water desalination, which, as a rule, expensive and labor-intensive, widespread methods based on the use of corrosion inhibitors. As inhibitors used individual inorganic and organic compounds or composition of several substances [2]. Among inorganic inhibitors widespread found chromates (bichromate), wolframate, molybdates, vanadates, alkaline metals and zinc [2]. Despite the high efficiency in a neutral environment, these inhibitors are toxic and expensive reagents. In addition, in the presence of chlorine ions, they can cause pitting corrosion [4, S. 293]. It is also known the use of polyphosphates and hypophosphate sodium. However, such inhibitors are ineffective in terms of Parking corrosion [1, S. 49] and their concentration should be maintained at a sufficiently high that a specific level, because at low concentrations they cause harmful manifestations of pitting corrosion, and at too high concentrations may even encourage corrosion [1, 50 C.].

Phosphoric acid in an individual state is used for phosphating, as the inhibitor is not applied. N is Noah acid and zinc salts [5]. However, this method requires high acid concentration (up to 100 mg/DM3), which in low concentration of zinc ions cause severe corrosion.

It is also known the use of sodium nitrite as a one-component corrosion inhibitor, and in the composition of the inhibitor compositions [2, 112 S. and more]. However, in these cases, the sodium nitrite is used in high enough concentrations, because if its lack of hard runs pitting corrosion. For example, for the protection of steel in neutral water containing Na2SO4(0,1 N), the required concentration of NaNO2more than 10 g/DM3[4, S. 295]. In idle modes of heat transfer equipment requires the same concentration of sodium nitrite [1, S. 77].

Water-soluble polymers are also used as corrosion inhibitors, and, as a rule, the composition of the inhibitor compositions. For example, certain water-soluble phenol-formaldehyde resin in combination with salts of zinc or polyphosphates [6]. However, this method requires a high concentration of expensive inhibitor is a phenol-formaldehyde resin-based resorcinol or salicylic acid.

Closest to the proposed tehnicheskie in the aquatic environment inhibitory composition based on sodium nitrite and diamine [7] (prototype). To implement this method for the protection of steel equipment vagocirculatory system introduce the following quantities of reagents:

sodium nitrite 1 - 10 g/DM3;

hexamethylenediamine were 0.01 to 1 g/DM3.

The disadvantages of the prototype method:

1. The high cost of reagents and their high concentration in the working environment.

2. High toxicity diamine.

3. This composition does not protect against pitting corrosion at lower concentrations of sodium nitrite.

4. Hexamethylenediamine were one of the most difficult and expensive reagents.

The purpose of the invention is development of a method of protecting steel against corrosion in aqueous media with high protective performance, using available low-toxic reagents having a relatively low concentration.

This goal is achieved by introducing working in the aquatic environment inhibitor composition, the components which have the following concentrations in the environment:

sodium nitrite 50 - 100 g/DM3;

water-soluble urea-formaldehyde resin (brand KF-W, GOST-14231-88) 10 - 20 g/DM3;

phosphoric acid 10 - 20 g/DM3.

Significant excellent is my urea-formaldehyde resin, in the presence of minor amounts of phosphoric acid gives a high protective effect. When used, the concentration of sodium nitrite is considerably lower (3 to 100 times) than the commonly used concentration.

As water-soluble urea-formaldehyde resin used resin brand KF-W GOST-14231-88. In the used concentrations of the resin gives a stable aqueous solutions.

The advantages of the proposed method are the following:

1. All three components of the inhibiting compositions are available and relatively cheap reagents.

2. The offered chemicals are toxic and are widely used in other areas.

3. Concentrations of reagents and therefore their costs are lower than typically used for nitrite and phosphoric acid.

4. The decrease in the concentration of the reactants below the recommended limits does not entail a sharp increase in corrosion rate.

Implementation of the proposed method of protecting steel against corrosion in aqueous environments carried out in the laboratory using the gravimetric method, recommended for Parking modes [8]. Samples of the Article. 20 cylindricus, in which you have entered inhibitory components of the composition at a concentration indicated in the table for each example. The concentration of KF-W obtained using the commodity form, containing 64% of the polymer. Phosphoric acid and sodium nitrite are used as reagents brand "chemically pure".

The samples were completely immersed in water, mixing is not used.

As a working environment used tap water with a total dissolved solids 150 - 230 mg/DM3. The solutions after the introduction of the inhibitor compositions had a pH of 6.3 and 7.5. The duration of the experiment 100 hours At the table presents data on the corrosion protection of the proposed method.

As can be seen from the table, the proposed method of protection against corrosion by introducing inhibitory composition provides effective protection of steel samples ( 100%). The increase in the concentration of the components above these limits does not give a significant increase in the protective effect and impractical from the point of view of consumption of reagents. The decrease in concentrations below the proposed levels reduces the protective effect.

Sources of information

1. P. A. Akol'zin. The prevention of corrosion of equipment technical water and talona, 1968.

3. I. L. Rosenfeld. Corrosion inhibitors.- M.: Khimiya, 1977.

4. Protection against corrosion, aging and biodegradation of machinery, equipment and structures. Reference book/ Ed. by A. A. Gerasimenko. T. 2.- M: Engineering. 1987.

5. Pat. USA 4018701, 1977 (P. H. Ralston, B. P. Boffard).

6. Pat. USA 4014814, 1977 (D. C. Zecher).

7. Centuries of Flowers and other corrosion Inhibition of metals systems recirculating water. Chemical and pharmaceutical journal, 1994, No. 5, S. 50 (prototype).

8. P. A. Akol'zin. Control corrosion of boilers.- M.: Energoatomizdat. 1994, c. 115.

1. The method of protecting steel against corrosion in aqueous environments, including the introduction in aggressive environment inhibitory composition based on sodium nitrite and nitrogen-containing organic compounds, characterized in that as the nitrogen-containing compounds using water-soluble urea-formaldehyde resin, and optionally in the environment enter phosphoric acid.

2. The method according to p. 1, characterized in that the components of the inhibiting composition is administered in the following concentrations, g/DM3:

Sodium nitrite - 50 - 100

Water-soluble urea-formaldehyde resin (brand KF-W, GOST-14231-88) - 10 - 20

Phosphoric acid - 1 is used by the resin grade KF-J.

 

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