RU2082714C1 - Inhibitor of corrosion-mechanical decomposition of low-alloy steel - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: invention relates to metal protection from corrosion in hydrogen sulfide-containing mineralized media with inhibitors. Compound 5-methyl-5-acetyl-1,3-dioxane is proposed to use as an inhibitor of corrosion-mechanical decomposition of low-alloy steel. Protection degree of 5-methyl-5-acetyl-1,3-dioxane is 99%. EFFECT: enhanced effectiveness of metal protection. 3 tbl

Description

 The invention relates to the protection of metals from corrosion-mechanical destruction (CMR) in hydrogen sulfide-containing mineralized environments.

Among the closest to the intended purpose inhibitors (analogue), recently protected by RF patents, it is known, for example, the use of trialkylbenzylmethylammonium chloride or fluoride, or iodide, additionally containing octidecylamine, quinoline or its derivatives as an inhibitor of hydrogen sulfide corrosion and hydrogenation of steel. [one]
The claimed inhibitor is similar in composition (prototype) to a corrosion inhibitor of iron, steel, iron alloys and nickel in HCl solutions, which consists of 1-ethynylcyclohexanol + dioxane. The ratio of the components is 1: 1. [2]
The disadvantage of the prototype is the impossibility of its use in conditions of hydrogen sulfide corrosion and corrosion-mechanical destruction of steel.

 The objective of the invention is to develop a highly effective inhibitor of the CMR of low alloy steels during transportation of hydrogen sulfide-associated gas and oil condensate.

 The objective is achieved in that 5-methyl-5-acetyl-1,3-dioxane is used as an inhibitor of KMP of low alloy steels. This compound has never been used before.

Данных об использовании 5-метил-5-ацетил-1,3-диоксана в качестве ингибитора КМР низколегированных сталей в известных науке и технике решениях нет.The method of producing 5-methyl-5-acetyl-1,3-dioxane consists in the interaction of methyl ethyl ketone and trioxane in chloroform medium in the presence of sulfuric acid under heating and vigorous stirring, followed by processing the resulting mixture after it is cooled with water and then sodium bicarbonate and isolation of the target product known methods [3]

There are no data on the use of 5-methyl-5-acetyl-1,3-dioxane as an inhibitor of KMP of low alloy steels in solutions known to science and technology.

 Studies to determine the inhibitory effectiveness of the compounds were carried out on samples of 17G1S steel, which is currently widely used in the construction of gas and oil pipelines.

As a model corrosion steel (KS), NACE medium was used, simulating in its composition (5% NaCl + 0.5% CH ₃ COOH + 3.4 g / l H ₂ S) moistened hydrogen sulfide-containing natural and associated petroleum gases.

 The protective effect against CMR of low alloy steels was determined in accordance with RD 39-0147103-324-88 "Methodology for determining the degree of protection of steel by inhibitors against corrosion and mechanical damage in hydrogen sulfide-containing mineralized media."

The effectiveness of protection against general corrosion (OK) was evaluated by polarization curves as follows:
By extrapolating the tafel sections of the anodic and cathodic polarization curves to the value of the corrosion potential, we obtained the value of the corrosion current in a hydrogen sulfide corrosive medium (CS). Comparing the course of the polarization curves in the inhibited and non-inhibited CS, we obtain the values of the corrosion currents in the inhibited (i) and non-inhibited (i ₀ ) CS.

The degree of protection against OK is determined by the formula:
Z (i ₀ -i) / i ₀ • 100%
The measurement data are given in table. 1, with each value obtained as the arithmetic mean of five experiments. Values of corrosion currents were estimated by polarization curves as follows:
By extrapolating the tafel sections of the anodic and cathodic polarization curves to the value of the corrosion potential, the value of the corrosion current in a hydrogen sulfide corrosion medium (CS) was obtained. Comparing the course of the polarization curves in the inhibited and non-inhibited CS, we obtain the values of the corrosion currents in the inhibited (i) and non-inhibited (i ₀ ) CS.

The degree of protection against OK is determined by the formula:
Z (i ₀ -i / i ₀ • 100%
Further, according to GOST 1493-83 (sample type N 4, size 7), samples of steel 17G1S are tested on an MP-8V tensile testing machine in air, in a NACE model medium and in a model medium with the addition of an inhibitor. To test the samples in the COP, a special corrosion-proof sealed cell was used. The deformation rate of the samples is 7.2 • 10 ^-8 m / s, this speed is chosen in order to increase the contact of steel with the COP. Then, the coefficient of influence of the CS medium on the relative narrowing of the samples at rupture ψ is determined. The parameter j most fully reflects the ductility margin of steel, which sharply decreases when it corrodes in hydrogen sulfide-containing media, that is, it is an indicator of CP of the main cause of CMR.

 In the table. 2 shows the results of tests by definition and CS, and each value is obtained as the arithmetic average of five parallel experiments.

где ψ_в относительное сужение образцов на воздухе;
ψ_N относительное сужение образцов в КС.Coefficient of influence of CS on j

where ψ _{is the} relative narrowing of the samples in air;
ψ _{N is the} relative narrowing of the samples in the CS.

где ψ_N+H относительное сужение образцов в КС при добавлении ингибитора. Степень защиты от СР определяют по формуле:

При степени защиты от СР более 90% переходят к следующему этапу - испытаниям на коррозионную усталость.Similarly, the coefficient of influence of CS when adding an inhibitor is calculated:

where ψ _{N + H is the} relative narrowing of the samples in the CS with the addition of an inhibitor. The degree of protection against CP is determined by the formula:

With a degree of protection against SR more than 90%, they proceed to the next stage - corrosion fatigue tests.

 The protective effect against corrosion fatigue (KU), i.e. the destruction of the total cyclic alternating stress that occurs when low-alloy steel is exposed to gas and oil pipelines due to the influence of the operational factor, is determined as follows: on a special fatigue machine, flat specimens of 17G1S steel are subjected to cantilever bending with an elastic-plastic span strain 2ε = 0.74% at a loading frequency of 0.6 Hz, which corresponds to the actual operating conditions.

 Loading is carried out in air, as well as in a special sealed overhead cell in the COP and in the COP with the addition of an inhibitor. In this case, the number of cycles to complete destruction is determined.

 In the table. Figure 3 shows the results of these measurements, with each measurement obtained as the arithmetic mean of five parallel experiments.

где N_b число циклов до разрушения на воздухе;
N_N число циклов до разрушения в КС;
N_N+H число циклов до разрушения в КС при добавлении ингибитора.The coefficient of influence of KS on the fatigue life of low alloy steel in KS without an inhibitor and in its presence is determined by the formula:

where N _{b the} number of cycles to failure in air;
N _{N the} number of cycles to failure in the COP;
N _{N + H the} number of cycles to failure in the COP with the addition of an inhibitor.

Из таблиц видно, что предлагаемый игибитор 5- метил-5-ацетил-1,3-диоксан обладает высокой степенью защиты как от общей коррозии, так и от сероводородного растрескивания и коррозионнной усталости стали в примененной коррозионной среде. Использование предлагаемого ингибитора позволит защищать оборудование не только от общей коррозии, но и от коррозионно-механического разрушения.The degree of protection against KU is calculated by the formula:

From the tables it can be seen that the proposed 5-methyl-5-acetyl-1,3-dioxane inhibitor has a high degree of protection both from general corrosion and from hydrogen sulfide cracking and corrosion fatigue of steel in the applied corrosive medium. The use of the proposed inhibitor will protect the equipment not only from general corrosion, but also from mechanical corrosion.

Claims (1)

 The use of 5-methyl-5-acetyl-1,3-dioxane as an inhibitor of the corrosion-mechanical destruction of low alloy steels.

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