RU2848794C1 - Composition for inhibiting metal corrosion - Google Patents

Abstract

FIELD: protection of metals from corrosion.

SUBSTANCE: protection of steel against corrosion in mineralised aqueous environments containing oxygen. The invention can be used to protect equipment and pipelines in the oil industry against corrosion. The composition for inhibiting metal corrosion contains components in the following proportions, wt.%: orthophosphoric acid 26.0-61.0, paraform 7.0-14.8, formaldehyde condensation product with monoethanolamine 6.2-29.2, solvent 2.8-53.0.

EFFECT: high degree of corrosion protection – 78.6-96.2% and a reduction in the corrosion rate of steel at an effective dosage of the claimed inhibitor of 50-200 mg/l.

2 cl, 2 tbl

Description

The invention relates to the field of protecting metals from corrosion, in particular protecting steel from corrosion in mineralized aqueous environments containing oxygen, and can be used in protecting equipment and pipelines from corrosion in the oil industry.

There are known methods of protecting steel from corrosion in oxygen-containing environments using inhibitors based on phosphoric acid derivatives and various amines: VFIKS-82 inhibitor, consisting of the reaction product of orthophosphoric acid with urea (TU 38-4-0262-86. Introduced on 15.02.1986. 12 p.); Amphicor corrosion inhibitor, consisting of an ammonium salt of alkyl phosphorous acid (TU 39-12966038-004-95. Introduced on 12.03.1995. 12 p.); Alpan inhibitor, which is an ammonium salt of alkyl phosphorous and phosphoric acids (TU 39-12966038-006-97. Introduced on 17.02.1997. 14 p.); corrosion inhibitor-bactericide SNPKh-1004, which is a 70% solution of N-alkylmethylammonium O-methylphosphite in isopropanol (TU 39 - 12966038-005-94. Introduced on 13.04.1994, 13 p.); inhibitor C-2H, which is wastewater from a coke-chemical plant with the addition of sodium polyphosphate (10%) and potassium ferricyanide (TU 14-253-8-79. Introduced on 18.02.1980. 12 p.).

However, these inhibitors do not have high protection efficiency in oxygen-containing environments.

The closest analogue in structure and effectiveness is the inhibitor IKB-4AFM, which is a product of the interaction of orthophosphoric acid with aminophenol (TU 38.401-66-58-90. Introduced 15.03.90).

The disadvantage of this inhibitor is its low efficiency in oxygen-containing environments.

The objective of the stated technical solution is to increase the effectiveness of steel protection in oxygen-containing mineralized aqueous environments.

The claimed technical solution proposes a composition for protecting steel from oxygen corrosion, containing orthophosphoric acid, paraformaldehyde and an amine component, which is a product of the condensation of formaldehyde with monoethanolamine, obtained in the presence of a catalyst - nickel acetylacetonate, %.

Orthophosphoric acid 26.0-61.0 Paraform 7.0-14.8 Formaldehyde condensation product with monoethanolamine 6.2-29.2 Solvent (water + alcohol) 2.8-53.0

A composition of a given concentration was obtained by dissolving concentrated orthophosphoric acid in a solvent and sequentially adding calculated amounts of paraformaldehyde and the condensation products of monoethanolamine with formalin. The condensation products of monoethanolamine with formaldehyde were obtained at room temperature in the presence of a catalyst (0.1 wt. % nickel acetylacetonate).

where n is 5-6.

The solvent consisted of a mixture of water and one of the alcohols (ethyl or isopropyl or ethylene glycol) in a volume ratio of 1:1.

Tests of the protective action of compositions 1-5 and the prototype as a steel corrosion inhibitor in oxygen-containing environments were carried out in laboratory conditions using the gravimetric method in accordance with OST 39-099-79 "Corrosion Inhibitors. Method for Assessing the Efficiency of the Protective Action of Corrosion Inhibitors in Oilfield Wastewater", VNIISPTneft, 1980. The working environments were the following model wastewater (MWW) composition, g/l: NaCl - 111.5; CaCl ₂ ⋅6Н ₂ О - 10.8; CaSO ₄ ⋅2Н ₂ О - 0.3; MgCl ₂ ⋅6Н ₂ О - 17.00. The oxygen content was 10 mg/l. Plates of steel grade St-3 (GOST 380-2005) were used as witness samples.

The essence of the declared technical solution is confirmed by examples of specific implementation.

Example 1. Obtaining composition No. 1

26.0 g of concentrated phosphoric acid was diluted with 53.0 g of solvent (a mixture of water and ethyl alcohol), and 14.8 g of paraformaldehyde and 2.2 g of the condensation product of monoethanolamine with formalin were added sequentially. The resulting mixture was stirred until completely dissolved at room temperature. Composition No. 1 with a density of 1.1 g/cm ³ was formed.

Examples of preparation of other compositions are given in Table 1.

Table 1. Examples of preparation of corrosion inhibitor compositions

Composition number Orthophosphoric acid, mass % Paraform, mass % Condensation products of monoethanolamine with formalin, mass % Solvent*, mass % 1 26.0 14.8 6.2 53.0 2 35.0 14.0 11.9 39.1 3 44.5 11.4 17.9 26.2 4 53.0 9.7 23.5 13.8 5 61.0 7.0 29.2 2.8 * compositions 1 and 2 use ethyl alcohol, 3 and 4 use isopropyl alcohol, and 5 uses ethylene glycol

Example 2. Testing the effectiveness of the protective action of composition No. 1

Degreased and dried to a constant weight, steel samples were placed in the working environment for 6 hours at 20°C, with and without the addition of Composition No. 1 at a concentration of 200 mg/L. After the holding time, the samples were thoroughly rinsed under running water, immersed in an alkali solution for 5-10 minutes, rinsed again under running water, and dried to a constant weight. The samples were then weighed to the nearest 0.0002 g.

The corrosion rate (ρ), the degree of protection of steel from corrosion (Z) were determined in accordance with formulas (1) and (2).

where m ₁ is the mass of the original sample, g;

m ₂ - mass of the sample after the experiment, g;

S – sample area, ^m2 ;

t - test time, h.

where ρ ₁ is the corrosion rate in an environment without inhibitor, g/ ^m2 h;

ρ ₂ - corrosion rate in an inhibited environment, g/m ² h.

The corrosion rate was 0.033 g/m2 ^h , the degree of corrosion protection was 96.2%.

The results of other tests are shown in Table 2.

Table 2. Test results of compositions No. 1-5 as an inhibitor of oxygen corrosion of steel

Composition number Dosage, mg/l Corrosion rate, g/ ^m2 h Degree of protection, % Control - 0.87 - Prototype 200 0.46 47.1 100 0.465 46.5 50 0.469 46.1 1 300 0.032 96.3 200 0.033 96.2 100 0.0365 95.8 50 0.04 95.4 30 0.085 90.2 2 300 0.053 93.9 200 0.055 93.7 100 0.060 93.1 50 0.064 92.6 30 0.092 89.4 3 300 0.072 91.7 200 0.073 91.6 100 0.077 91.1 50 0.080 90.8 30 0106 87.8 4 300 0.086 90.0 200 0.087 90.0 100 0.092 88.4 50 0.096 89.0 30 0.120 86.2 5 300 0.184 78.9 200 0.186 78.6 100 0.215 75.3 50 0.230 73.6 30 0.300 65.5

The test results presented in Table 2 demonstrate the high effectiveness of the proposed steel corrosion inhibitor in oxygen-containing environments. Maximum effectiveness is achieved at inhibitor concentrations of 50-200 mg/L. Increasing the inhibitor concentration above 200 mg/L does not significantly alter the degree of protection, while decreasing the concentration below 50 mg/L significantly reduces the degree of protection. For the prototype, at a concentration of 200 mg/L, the corrosion rate is 0.46 g/ ^m² h, and the degree of protection is 47.1%.

The advantages of the proposed steel corrosion inhibitor compared to the prototype are as follows:

1. High degree of corrosion protection of compositions No. 1-5 (78.6-96.2%) compared to the prototype (47.1%).

2. Reduction in the rate of steel corrosion in the presence of compositions No. 1-5 by 9.77-25.76 times, and in the presence of the prototype - 1.85 times.

3. Effective dosages of the proposed inhibitor are 50-200 mg/l (protection level 78.6-96.2%), and in the prototype, even at dosages of 200 mg/l, the protection level does not exceed 47.1%.

The obtained results allow us to conclude that the proposed composition is highly effective for protecting steel from corrosion in oxygen-containing environments, which can find application in the oil industry.

Claims (3)

1. A composition for inhibiting corrosion of metals containing orthophosphoric acid and a solvent, characterized in that it contains paraformaldehyde and an amine component, which is a condensation product of formaldehyde with monoethanolamine, in a ratio of components, wt.%: orthophosphoric acid 26.0-61.0 paraform 7.0-14.8 formaldehyde condensation product with monoethanolamine 6.2-29.2 solvent 2.8-53.0 2. The composition according to claim 1, characterized in that it contains a water-alcohol solution as a solvent.