MD1615Z - Process for corrosion protection of steel in water - Google Patents

Abstract

The invention relates to the field of protection of metals against corrosion in water and can be used to inhibit corrosion in closed systems of steel pipelines. According to the invention, the process of protecting steel from corrosion in water consists in the separate or combined introduction into the aqueous medium, which is in contact with steel surfaces, of adipic acid and α-ketoglutaric acid, respectively in concentrations of 0.025...0.75 g/L and 0.05...0.75 g/L. The technical result of the invention consists in reducing the corrosion rate by up to 40 times.

Description

The invention relates to the field of metal protection against corrosion in water and can be used for inhibiting corrosion in closed steel pipeline systems.

Natural or technological water, which contains active chlorine and sulfate ions, is a relatively aggressive environment, in which steel corrosion occurs at high speeds. Thus, in the aqueduct waters of the Chisinau municipality, which contain, mg/l: Ca2+ - 42.5; Mg2+ - 19.5; HCO3- - 97.6; SO4 2- - 203.7; CI- - 56.7 and a total salt content of 0.457 g/L, the steel corrosion rate after 8 hours of testing is high, reaching 21 g/m2·day. With increasing exposure time, the corrosion rate decreases, for example, to 12 g/m2·day at 24 hours, 6.6 g/m2·day at 72 hours and 4.0 g/m2·day at 240 hours of testing, due to the formation of an oxide-hydroxide film of corrosion products and calcite CaCO3 on the corroded surface. SO4 2- ions cause general, fairly uniform corrosion. However, cracks may form on the inner surface of the pipes due to the presence of active chlorine ions in the water, which in some cases can be pierced, which can cause damage. In addition, iron during ionization, migrating into the water, accumulates in it and worsens the water quality [1].

The use of hydrazine H2N-NH2 as a corrosion inhibitor is known [2], the action of which is based on the binding of oxygen dissolved in water and, therefore, the reduction of the corrosive activity of water: N2H4 + O2 → 2H2O + N2.

However, the known inhibitor has significant disadvantages. First of all, the action of hydrazine manifests itself either at sufficiently high temperatures (80...100°C), or upon additional administration of certain catalysts, for example, cobalt, copper or manganese.

Secondly, hydrazine is toxic, working with it requires a lot of caution, protection. All this greatly complicates the operation of closed water systems.

In addition to hydrazine, its derivatives, especially hydrazides and hydrazones, are also known as inhibitors. For example, the use of adipic acid dihydrazide as an inhibitor of steel corrosion in water, introduced into the aqueous medium in concentrations of 0.05...1.0 g/L [3], is known. At an inhibitor concentration of 0.25 g/L and a contact time of the steel surface with the aqueous medium of 24 hours, the braking coefficient is equal to 31.6.

The disadvantage of using this inhibitor is its relatively high cost and, in addition, a significant variation in the inhibitor action is observed depending on the duration of contact with the steel surface. For example, at a concentration of 0.5 g/L the braking coefficient varies in the range of 6.2...4.6, passing through the aforementioned maximum.

It is known to use as a corrosion inhibitor a derivative of α-ketoglutaric acid, namely α-ketoglutaric acid aminoguanizone, at a concentration of 0.05...1.0 g/L [4]. The protection process using this inhibitor ensures a reduction in steel corrosion in water by 3.6...8.8 times, depending on the concentration of the inhibitor and the duration of contact of the aqueous medium with the steel surfaces.

The disadvantage of using this inhibitor is its high cost compared to α-ketoglutaric acid and in addition, a significant variation of the inhibitor action is observed depending on the duration of contact with the steel surface. For example, at a concentration of 0.5 g/L and contact duration of 8, 24, 72 and 240 hours the braking coefficient is equal to 5.0, 6.9, 8.3 and 4.4, respectively.

The use of aliphatic dicarboxylic acids as inhibitors for aqueous media is also disclosed. For example, adipic, pimelic, suberic acid, etc., taken in a mixture with polyamidoamines, have been proposed as inhibitors [5]. The disadvantage of these inhibitors is that the second component - polyamidoamines - is a less accessible preparation, which is obtained by condensation of fatty polymeric acids with alkylpolyamines.

As the closest solution (proximal analogue) for the claimed invention, the work [6] can be indicated, in which adipic acid is used alone as a corrosion inhibitor introduced into the aqueous medium in the concentration range of 0.025...0.75 g/L. The protection process using this inhibitor in a concentration of 0.05 g/L ensures a reduction in steel corrosion in water by 7.8 and 6 times, respectively at 8 and 24 hours of contact with the steel surface. At adipic acid concentration of 0.1 g/L and a contact time of 24 hours, a reduction in steel corrosion by 5.5 times is observed.

The disadvantage of this process using adipic acid as an inhibitor is that the reduction in corrosion losses is not significant.

The problem solved by the invention consists in developing a process that ensures a significant reduction in corrosion losses in closed steel pipe systems through which water circulates, in which adipic acid is used in combination with another dicarboxylic acid, without other auxiliary substances.

The problem is solved by the process of protecting steel from corrosion in water, which consists of the combined or successive introduction into the aqueous medium, which is in contact with the steel surfaces, of adipic acid and α-ketoglutaric acid, respectively in concentrations of 0.025...0.75 g/L and 0.05...0.75 g/L.

The technical result of the claimed invention presents a significant reduction in corrosion losses up to 40 times following the synergistic action of two dicarboxylic acids in combined use.

The advantages of the invention consist in the fact that in the proposed process for protecting steel from corrosion in water a combination of two cheap and accessible components is used, which act synergistically. As a result, corrosion losses are significantly reduced compared to when each component is used separately.

Adipic acid is a representative of the class of saturated dicarboxylic acids, used to obtain polymers:

.

Adipic acid is obtained in large quantities as a starting product or semi-product for the synthesis of polyamide resins and fibers (https://en.wikipedia.org/wiki/Adipic_acid).

α-Ketoglutaric acid is an important derivative of glutaric acid (НООС-(CH2)3-СООН), it is also a key intermediate in the Krebs cycle, it is used in medicine, pharmaceuticals. Unlike glutaric acid, it contains a ketone group in position 2 of the chain:

Other names for α-ketoglutaric acid: 2-oxopentanedioic acid or 2-oxoketoglutaric acid (https://en.wikipedia.org/wiki/Alpha-Ketoglutaric_acid). The compound has a molecular mass of 146.098 g/mol and is soluble in water (10g/100 mL at 25oC).

Embodiment of the invention

Corrosion tests of steel samples (Ст. 3) with a size of 50×25×3 mm were carried out at a complete immersion in the solution at the same depth and with air access. The initial roughness of the samples was performed by grinding. Corrosion losses were recorded gravimetrically. The effect of the inhibitor action was quantitatively determined by the corrosion rate K, g/m2·day, and by the value of the braking coefficient γ = k/k1, where k1 and k - the corrosion rate of the metal, in the presence of the inhibitor and in the absence of the latter, respectively. This coefficient indicates how many times the corrosion rate is reduced as a result of the inhibitor action.

The influence of the inhibitor concentration, its separate components, and the testing time on the corrosion rate K, as well as the braking coefficient γ, are presented in tables 1-3.

Table 1

Influence of adipic acid concentration on the parameters of the corrosion process in water

of steel St. 3

Inhibitor concentration, g/L Test time, τ, hours Corrosion rate, k, g/m2·day Braking coefficient, γ 0.025 8 24 72 240 3.4 2.3 1.6 1.0 6.2 5.2 4.1 4.0 0.05 8 24 72 240 2.7 2.0 1.4 0.9 7.8 6.0 4.7 4.4 0.1 8 24 72 240 4.0 2.2 1.5 1.0 5.2 5.5 4.4 4.0 0.25 8 24 72 240 4.1 2.3 1.2 0.6 5.1 5.3 5.5 6.7 0.5 8 24 72 240 5.6 3.3 2.1 1.2 3.7 3.6 3.1 3.4 0.75 8 24 72 240 5.8 3.5 2.3 1.4 3.6 3.2 2.9 2.9

From the data in Table 1 it is observed that the corrosion protection effect is achieved when using adipic acid in concentrations of 0.025...0.5 g/L. Thus, when the inhibitor concentration is 0.05 g/L and the test duration is 8 and 24 hours, the corrosion losses, expressed by the braking coefficient, are reduced by 7.8 and 6.0 times respectively. At an inhibitor concentration of 0.1 g/L and a test duration of 24 hours, the corrosion losses are reduced by 5.5 times, and at a concentration of 0.25 g/L and a test duration of 72 hours, the corrosion losses are reduced by 5.3 times.

It is worth noting that the difference in the braking coefficient values is not large, depending on the duration of the tests. This fact indicates the homogeneity of corrosion inhibition over time.

The amount of inhibitor introduced into the corrosive medium plays a crucial role. The lower limit is 0.025 g/L, because at lower concentrations of inhibitor in the corrosive medium the corrosion losses are insignificantly reduced.

The upper limit of the inhibitor concentration is 0.75 g/L, because with a further increase in the inhibitor concentration, corrosion losses increase insignificantly, but on the other hand, the costs related to the inhibitor increase.

The corrosion inhibitor activity of α-ketoglutaric acid, when used alone, is shown in Table 2.

Table 2

Influence of α-ketoglutaric acid concentration on process parameters

of steel corrosion in water St. 3

Inhibitor concentration, g/L Test time, τ, hours Corrosion rate, k, g/m2·day Braking coefficient, γ 0.0 8 24 72 240 21.0 12.0 6.6 4.0 - - - - 0.05 8 24 72 240 5.5 2.5 1.3 0.9 3.8 4.8 5.0 4.3 0.1 8 24 72 240 3.0 1.9 0.9 0.93 5.8 6.2 7.4 4.3 0.25 8 24 72 240 3.9 1.9 0.94 0.8 5.4 6.4 7.0 5.2 0. 5 8 24 72 240 2.8 2.8 1.8 1.9 7.4 4.3 3.6 2.6 0.75 8 24 72 240 4.5 3.0 1.1 0.8 4.7 4.0 6.0 5.0

The presented data show that the maximum effect of corrosion reduction is achieved at a concentration of 0.0...0.75 g/L of α-ketoglutaric acid. For example, at an inhibitor concentration of 0.1 g/L and a test duration of 24 and 72 hours, corrosion losses are reduced by 6.2 and 7.4 times, respectively. At an inhibitor concentration of 0.25 g/L and in the same time intervals, corrosion losses are reduced by 6.4 and 7.0 times, respectively.

The concentration of the inhibitor used in the corrosion medium plays a decisive role. The lower limit of the concentration is 0.05 g/L, at which the values of the braking coefficient do not exceed 5.0 because at a lower inhibitor content the corrosion losses decrease insignificantly. The upper limit of the inhibitor concentration can be considered 0.75 g/L, with a further increase in the inhibitor concentration the corrosion losses decrease very little, at the same time the costs for the inhibitor increase.

It was found that the combined use of inhibitors in the process manifests a synergistic effect, which allows to significantly reduce corrosion losses and with a small time lag compared to the closest analogue (see table 3).

Table 3

Influence of adding α-ketoglutaric acid to aqueous adipic acid solution on the parameters of the steel corrosion process in water St. 3

Adipic acid concentration, g/L α-ketoglutaric acid concentration, g/L Test time, τ, hours Corrosion rate, k, g/m2·day Braking coefficient, γ 0 0 8 24 72 240 21.0 12.0 6.6 4.0 - - - - 0.025 0.05 8 24 72 240 3.23 2.0 1.22 0.89 6.5 6.0 5.4 4.5 0.1 8 24 72 240 2.96 1.76 1.14 0.784 7.1 6.82 5.8 5.1 0.25 8 24 72 240 2.84 1.69 0.78 0.63 7.4 7.1 8.46 6.35 0.5 8 24 72 240 2.69 1.62 0.74 0.59 7.8 7.4 8.92 6.78 0.75 8 24 72 240 2.59 1.40 0.88 0.556 8.1 8.57 7.5 7.2 0.05 0.05 8 24 72 240 2.02 1.08 0.56 0.308 10.4 11.1 11.8 13.0 0.1 8 24 72 240 1.71 0.94 0.47 0.263 12.3 12.76 14.04 15.2 0.25 8 24 72 240 1.37 0.70 0.35 0.206 15.33 17.14 18.86 19.42 0.5 8 24 72 240 1.08 0.4 0.2 0.105 19.44 30.0 33.0 38.1 0.75 8 24 72 240 1.38 0.4 0.21 0.107 15.2 30.0 31.43 37.4 0.1 0.05 8 24 72 240 1.78 0.99 0.51 0.30 11.8 12.12 12.94 13.33 0.1 8 24 72 240 1.49 0.78 0.41 0.238 14.1 15.38 16.1 16.8 0.25 8 24 72 240 1.35 0.75 0.39 0.223 15.55 16.0 16.92 17.94 0.5 8 24 72 240 1.03 0.57 0.27 0.153 20.39 21.05 24.44 26.14 0.75 8 24 72 240 1.05 0.58 0.28 0.159 20.0 20.69 23.57 25.15 0.25 0.05 8 24 72 240 1.69 0.9 0.42 0.25 12.42 13.33 15.71 16.0 0.1 8 24 72 240 1.27 0.69 0.36 0.2 16.54 17.4 18.33 20.0 0.25 8 24 72 240 1.21 0.66 0.35 0.186 17.36 18.2 18.86 21.5 0.5 8 24 72 240 0.97 0.51 0.25 0.147 21.65 23.53 26.4 27.21 0.75 8 24 72 240 0.98 0.53 0.26 0.151 21.43 22.64 25.4 26.5 0.5 0.05 8 24 72 240 1.59 0.83 0.4 0.225 13.2 14.45 16.5 17.78 0.1 8 24 72 240 1.16 0.62 0.33 0.18 18.1 19.35 20.0 22.22 0.25 8 24 72 240 0.864 0.43 0.244 0.145 24.3 25.0 27.05 27.6 0.5 8 24 72 240 0.61 0.33 0.18 0.10 34.43 36.36 36.67 40.0 0.75 8 24 72 240 0.63 0.34 0.183 0.102 33.33 35.3 36.07 39.22 0.75 0.05 8 24 72 240 1.62 0.84 0.42 0.23 12.96 14.3 15.71 17.4 0.1 8 24 72 240 1.17 0.63 0.333 0.185 17.95 19.05 19.82 21.62 0.25 8 24 72 240 0.87 0.48 0.247 0.148 24.14 25.0 26.72 27.03 0.5 8 24 72 240 0.614 0.335 0.179 0.10 34.2 35.82 36.87 40.0 0.75 8 24 72 240 0.636 0.342 0.184 0.104 33.0 35.1 35.87 38.46

The obtained data show that the claimed process is much more effective than the closest analogue or than the use of each component separately, due to the manifestation of a synergistic effect when interacting with the components in combination. For example, at a concentration of both components of 0.5 g/L and a test duration of 240 hours, corrosion losses are reduced by 40 times. It should also be noted that when using the claimed process, the braking coefficient γ increases with the test duration, while in the closest process an opposite trend is observed, which reduces the effectiveness of the latter when used in extended steel pipeline systems.

Adipic acid and α-ketoglutaric acid can be introduced into the aqueous medium, which contacts the steel surfaces possibly subject to corrosion, either combined (in the form of a mixture with a certain mass ratio), or separately, i.e. successively and in any order. The mentioned acids can also be introduced in the preliminary preparation of an aqueous solution, which will subsequently be used as an aqueous medium, for example, for closed systems with steel surfaces, the quantities of the mentioned acids being taken based on the volume of the aqueous medium and their effective concentrations in this medium, respectively 0.025...0.75 g/L and 0.05...0.75 g/L.

In conclusion, an efficient, accessible and quite ecological process is proposed for protecting steel from corrosion in water, which allows reducing corrosion losses up to 40 times.

1. Parshutin V. V., Sholtoyan N. S., Sidelnikova S. P., Volodina G. Ф. Ингибирование бороглюконатом калция корозии углеродистой стали Ст. 3 in water. I. Corrosion in the conditions of natural aeration and forced convection. Electronic processing of materials, 1999, №5, p. 42-56

2. Rosenfeld I. L. Corrosion inhibitors. M., 1977, p. 249-252

3. MD 359 Y 2011.04.30

4. MD 4310 B1 2014.11.30

5. JPS 5779180 A 1982.05.18

6. V. Lozan, V. Parshutin, N. Sholtoyan, A. Kovali, N. Chernysheva. Adipic acid - carbon steel corrosion inhibitor in natural water. Physical Methods in Coordination and Supramolecular Chemistry, Chisinau, Moldova, October 8-9, 2015, p. 117

Claims (1)

Process for protecting steel from corrosion in water, which consists of the combined or successive introduction into the aqueous medium, which is in contact with the steel surfaces, of adipic acid and α-ketoglutaric acid, respectively in concentrations of 0.025...0.75 g/L and 0.05...0.75 g/L.