125
PHYSICO-CHEMICAL PROPERTIES OF CORROSION INHIBITION OF St.3 AND St.12
AND THE FORMATION OF MINERAL SALT DEPOSITS.
A.M. Mamatov, рrofessor Sh. P. Nurullayev, senior lecturer, PhD
A.K. Oserbaeva, associate professor J.S.Kayumov
Tashkent Institute of Chemical Technology.
Currently, the Republic of Uzbekistan deservedly pays attention to the introduction of
inhibitors to protect equipment from corrosion and scaling in production. The use of inhibitors
allows several times to increase the service life of expensive equipment. In this regard, the most
effective inhibitors of neutral and slightly alkaline media are nitrogen, amine and oxygen-
containing organic compounds [1-3] as well as zinc organophosphonic acids, which effectively
prevent corrosion and deposits of mineral salts on the surface of equipment.
The republic's demand for such types of inhibitors is more than 5.0 thousand tons per year.
Due to the lack of production of these products in the republic, they have recently been brought
from other foreign countries for a fee [4]. Therefore, the development of new import -substituting,
export-oriented inhibitors of corrosion and mineral salt deposition based on local raw materials and
production wastes, and the study of their physicochemical, as well as inhibitory properties, is a very
urgent task. Results and its discussion. Experimental data on the study of the polarity curves of
inhibitors, their relationship from concentration and temperature to the degree of anti-corrosion
protection of a sample of steel grades St.3 and St.12 in the presence of inhibitors and without them
showed that the applied composite inhibitors synthesized on the basis of nitrogen, amine and
phosphorus-containing local raw materials and production wastes have a degree of protection at
25
0
С 88.5÷94.4%, and at 40÷50
0
С this indicator will be in the range of 89.0÷99.7%. If the process
temperature rises to 70
0
C, then the degree of anti-corrosion protection begins to decrease somewhat
to the interval, values of 99.3÷90.4% of polarization. With the introduction of nitrogen-, amine- and
phosphorus-containing inhibitors into the solution, the value of the electrode potential changes in a
positive direction, which indicates a slowdown in the anodic reaction. This state indicates that a thin
protective film is formed on the metal surface, consisting of such protective substances as nitrogen,
amide and phosphate, which are part of the introduced inhibitors. With a change in the corrosion
potential, the value of the corrosion current simultaneously changes, which indicates the effect of
the inhibitor on the corrosion process of the metal by a mixed mechanism. Samples of metals (St.3
and St.12) were placed in various aggressive acidic hydrogen sulfide media in order to protect
against corrosion, and the inhibition properties of amines, which contain various radicals and
monomers, were studied.
Gravimetric method for time, temperature, inhibitor concentration and other indicators
found that when the process is carried out in aqueous, acidic and neutral environments, the
corrosion rate of the metal alloy grades St.3 and St.12 at a temperature of 25÷70
0
C for 360 and 720
hours for inhibitors with solutions of 0.1% concentration, the degree of anticorrosion protection was
equal to 95.8÷99.6%. With an increase in the concentration of inhibitors from 0.1% to 1.0%, the
corrosion protection index will be equal to 96.2÷99.8%. The degree of anti-corrosion protection of
the Nalco brand inhibitor imported into our Republic is 87.6% at a temperature of 80
0
C. Based on
the calculated data, the thermodynamic properties in the phases of acid, hydrogen sulfide solutions
and the dependence of inhibition on temperature with the participation of inhibitors in the process
of metal corrosion were established. At the same time, an increase in temperature has very little
effect on the corrosion process, so with an increase in temperature, the adsorption of the metal
surface remains almost unchanged. It was found that an increase in the concentration of inhibitors
in both cases affects the effectiveness of corrosion inhibition. In all aggressive media studied,
inhibitors have an energetic effect on completely filled surfaces. To calculate the activity (E
act
), a
graph of the dependence of IgK -1/T was drawn, and the energy of effective activity (E
act
) was
calculated using the tangent of the slope (E
act
=2.3
*
R
*
). It was found that with an increase in
the temperature of the corrosion process, the energy efficiency index is equal to 28.5÷47 kJ/mol.
126
Established indicators of E
act
, H and
multicomponent compo-site inhibitors containing
nitrogen, amide and phosphorus, in environments of strong acids are given in table -1.
Table 1
Thermodynamic values of corrosion in 3% Na
2
S solutions with 3% H
2
SO
4
and H
2
S metal
sample St. 3
Metal sample
Inhibition
background
E
act,
kJ/mole
N, J/mol
St. 3
3%
H
2
SO
4
39.88
37.48
70.49
St. 12
76.54
-41.82
48.64
St. 3
H
2
S with 3%
Na
2
S
37.48
38.25
69.75
St. 12
59.56
-70.04
39.51
From the results obtained, it was found that in the process of corrosion of the metal sample
St.3 under conditions with inhibitors placed and not placed in an acidic environment, the indicators
E
act
and H were almost close to each other. The results obtained provide a good explanation for
the fact that, according to the Langmuir isotherm, a high degree of filling of the metal surface is
directly proportional to the dependence of the adsorption process with the concentration of nitrogen,
amine, and phosphorus-containing composite inhibitors. Also, that the rate of dissolution (K) of
metal samples depends on the content of inhibitors and, even if the inhibitor is at a low
concentration, the anti- corrosion will be 96-99.6%. When a composite inhibitor is introduced into
the medium of a 3% H
2
SO
4
solution of a steel sample St.3 St.12, the change in G
ads
in the
temperature range 298÷343K from -48.24 kJ/mole
-1
to -42.52 kJ/mole
-1
on the effect of different
kind of adsorption on the surface of the steel sample St.3 St.12 this inhibitor is adsorbed as a result
of physical and chemical sorption. The thermodynamic properties of the metal surface adsorption
process in the alkaline-salty medium of the composite inhibitor were calculated (Table 2), and the
Langmuir adsorption isotherms of the composite inhibitor in the alkaline-salty medium were also
studied. The relationship between the process temperature along the directions of the Langmuir
adsorption isotherm in alkaline-salty aggressive media was found out. Steel samples St.3 and St.12
that is at different temperatures (between 298÷343K) nitrogen, amine and phosphorus-containing
inhibitor has a different degree of anti-corrosion protection of metal samples.
Table 2
Thermodynamic values of surface adsorption of metal samples in a 3% NaOH + 3% NaCl
solution of a composite inhibitor St.3
Temperature, K
K
ads
mole
-1
G
ads
, kJ/mole
H
ads
, J/mole
S
ads
, J/mole
*
K
298
7.4* 10
5
-50.94
-79.25
97.54
313
7.8* 10
5
-49.58
-79.56
96.98
323
5.4* 10
5
-48.86
-78.49
96.31
343
3.2* 10
5
-46.78
-78.80
96.44
Synthesized composite corrosion inhibitors with the participation of zinc oxide, glycerin,
caustic soda, sodium hydroxide and the bottom residue of methyl ethyl ammonium reagents based
on hydroxyethylidene diphosphonic acid, the composite inhibitor was tested on the equipment and
127
pipelines of the Shurtan gas chemical complex for anti-corrosion , including prevention formation
of deposits of mineral salts, comparing the performance of inhibitors brands " Option " and Nalco,
supplied from abroad. Based on the results of the tests, it was found that the applied composite
inhibitor reduces the formation of deposits of mineral salts, and also, in comparison with the
inhibitor used in industry, reduces corrosion to 4.8÷7.6%.
Table 3
Indicators of the degree of protection against corrosion of nitrogen, amino phosphorus-
containing inhibitors
Compositions of inhibitors
Corrosion inhibition
efficiency, %
Efficiency from the formation
of mineral salts, %
1
97.8
94.8
2
96.8
95.2
3
98.4
97.7
4
93.3
92.5
5
91.5
88.6
Inhibitor brand "Option"
96.6
90.1
Conclusion.
On the basis of the conducted studies, the prospects for the use of nitrogen,
amine and phosphorus-containing inhibitors based on local raw materials and industrial wastes of
the republic are shown. Optimal concentrations of inhibitors have been established to protect metals
from corrosion and prevent the formation of deposits of mineral fields in acidic and hydrogen
sulfide media. It is shown that the rate of coating on the surface of a steel sample (St.3 and St.12) of
composite inhibitors passes in the same plane and is realized according to the Langmuir law with
the formation of a layer that prevents corrosion of the metal, and the activation energy in these
media of steels St.3 and St. is determined. 12 with the use of inhibitors. Based on the
thermodynamic functions ( H, S, G) it is found that the Gibbs energy has a high negative value
( G
ads
). The applied composite inhibitors increase the efficiency of inhibiting the accumulation of
mineral salts by 2-6% and increase the degree of protection of metals against corrosion up to 98.4%.
Literature
1. Х.И.Кадиров, С.М.Турабджанов. Ингибиторы коррозии и солеотложения; синтез,
технология и свойства. Т., 2019. – 150 стр.
2. Х.И.Кадиров, У.Азаматов, С.М.Турабжанов. Новые композиции ингибиторов
коррозии и солеотложения. Журнал «Композиционные материалы», №2, 2015, стр. 53-57.
3. Michael L. Walker. Pat, 8933000. Corrosion inhibitor for acid stimulation sustems, 2010.
P. 13.01.2015.
4. М.А.Медведева. Коррозия и защита оборудования при переработке нефти и газа. Нефт и
газ РГУ нефти и газа. М. – 312 стр.
