210
PROTECTING STEELS AGAINST CORROSION AND THE FORMATION OF
MINERAL SALT DEPOSITS
A. M. Mamatov, Sh. P. Nurullaev, N. Ernazarova,
Tashkent Institute of Chemical Technology,
Abstract
: The paper studies the physicochemical properties of import-substituted and
export-oriented nitrogen, amine and phosphorus new composite inhibitors for corrosion protection
of steels as well as scaling obtained from local raw materials and industrial wastes. Inhibiting
properties of corrosion and mineral salt deposit accumulation in acid and hydrogen sulfide
environments have been determined. It was found that the efficiency of the inhibition process with
the use of composite inhibitors in acidic and hydrogen sulfide environments obeys the Langmuir
law. The values of activation energy of the adsorption process in these media and thermodynamic
values
(
∆
H,
∆
S,
∆
G).
Keywords:
inhibition, thermodynamics, corrosion of steels, inhibitor, protective
mechanism, activation energy, Gibbs energy, corrosion rate, hydrogen sulfide
.
Introduction.
Globally, corrosion protection of steel is one of the most important
scientific, technical and economic problems. Because in industrially developed countries losses
from corrosion of metals makeup from 2 to 4% of gross national product [1-3]. In the Republic of
Uzbekistan, industrial scale as a result of research works has achieved significant results in
studying the effect of inhibitors on corrosion of metal equipment, creation and implementation of
new import-substituting, export-oriented, competitive inhibitors meeting the requirements of
international standards, providing high efficiency even at low concentrations, safe in the
application of new universal corrosion inhibitors. In this relation, the most effective neutral and
weakly alkaline media inhibitors are nitrogen, amine, and oxygen-containing organic compounds
[4-6], as well as organophosphorus zinc acids which effectively prevent corrosion and mineral salt
deposits on equipment surfaces.
Materials and methods of research.
The object of the study is multi-component
composite inhibitors created on the basis of nitrogen, amine and phosphorus-containing substances
and the subject of the study includes the study of general patterns of inhibitor application
mechanisms for anticorrosion protection and against the mineral salt build-up of steel samples
using modern methods of physical and chemical analysis. Materials for research were the samples in
the form of metal plates made of steel St.3 and St.12. Influence of nitrogen and phosphate-containing
inhibitors on steel St.3 and St.12 corrosion rate was investigated by the gravimetric method in the
model environment and using 5-10
-3
mol/l solution of H
2
SO
4
(background). In addition,
experiments were conducted in 1-3% aqueous solution of NaCI, NaOH and 1-3% aqueous solution
of Na
2
S in the presence of H
2
S. The duration of the tests was 48 and 760 hours. The inhibitors are a
transparent liquid mass, well soluble in aqueous and acidic media. No independent phase
formation was observed during storage.
Results and their discussion.
Experimental data on the dependence of the inhibition
process on concentration and temperature on the degree of corrosion protection of steel samples of
St.3 and 12 grades 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 processing waste have the protection degree at 25°C 88.5-94.4%, and at
40÷50°C this index is in the range 89.0÷99.7%. If the process temperature goes up to 70°C, the
degree of anti-corrosion protection begins to decrease slightly up to values of 99.3÷90.4%.
Using the gravimetric method based on time, temperature, inhibitor concentration and other
indices it has been determined that during the process in aqueous, acidic and neutral medium, at
increasing inhibitor concentration from 0.1% to 1.0% the index of corrosion protection is equal to
96.2%÷99.8%. The corrosion protection rate of imported inhibitors of the Nalco brand in our
Republic is 87.6% at the temperature of 80°С. It is known that inhibition of acid corrosion of metals
by organic compounds is caused mainly by surface shielding and activation factor (an increase of
activation energy of corrosion process in the presence of inhibitors in relation to background). To
211
calculate activation energy, we plotted
lgK-1/T
(Fig. 1). Studies on corrosion of St.3 and St.12 in
acidic solutions in the presence of inhibitors containing amino- and phosphate groups showed their
high efficiency.
Fig.1. Dependence of lgK on the inverse temperature of the corrosion process of steels St.3
and St.12:
1 - Background; 2 - Sinh -1.0 mol/l; 3 - Sinh -1.25 mol/l; 4 - Sinh -2.5 mol/l; 5 - Sing -5.0
mol/l; 6 - Sinh -10.0 mol/l.
The best inhibitor of corrosion of St.3 in the studied conditions recognized, in a series of
alkylamines, phosphate-diethylmethacrylate, apparently because of the large number of radicals in
its molecule and their size, so that the required protective concentration of this inhibiting system is
minimal, in comparison with the other studied amines. From the IgK-1/T dependence plot with the
value of the slope tangent, the effective activation energy was calculated (E
act
=2,3Rtg
𝛼
). The
value of E
act
was found to be 28.5÷47 kJ/mol. The
Eact,
∆
H and
∆
𝐒
of multicomponent
composite inhibitors containing nitrogen, amine and phosphorus in a strong acid medium have
been determined. The results are given in table 1.
Table 1
Thermodynamic values for corrosion in 3% Na2 S solution media involving 3%
H2 SO4 and H2 S (T=298K; Sing =1.0%)
Alloy sample
Background
inhibition
Eact,
kJ/mol
∆
Н,
Dj/mo
l
∆
𝐒
,
Dj/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
involvement 3%
Na
2
S
37,48
38,25
69,75
St. 12
59,56
-70,04
39,51
The results give a good explanation for the Langmuir isotherm about the high degree of
filling of the metal surface directly proportional to the dependence of the adsorption process with
the concentration of nitrogen, amine and phosphorus- containing composite inhibitors. In addition,
the dissolution rate (K) of metal samples depends on the content of inhibitors and even if the
inhibitor is of low concentration the degree of corrosion resistance will be 96-99.6%. At the
introduction of composite inhibitor in the medium of 3% H
2
SO
4
solution in the temperature range
298÷343K the values of Gibbs energy ∆G
ads
change from -48.24 kJ/mol
-1
to -42.52 kJ/mol
-1
. The
correlation of process temperature along the direction of Langmuir adsorption isotherm in alkaline-
saline aggressive media for steel samples of St.3 and St.12 grades at temperature intervals
298÷343K with nitrogen, amine and phosphorus-containing inhibitors had different degrees of
anticorrosive protection of metal samples. At the same time, increasing the processing time from
212
240 to 360 hours increases the degree of corrosion protection to 92.9÷96.7%. This indicates that
multiple phases exist on the metal surface and that they do not dissolve simultaneously. Under
conditions of H
2
S solution background, indices of corrosion rate of steel sample St.3 during 3-4
hours are approximately the same and it proves that corrosion process in aggressive media occurs at
high speed. When inhibitor concentration increases from 0,001 to 1% the protection efficiency of
the inhibitor used increases from 92.3% to 99.2% respectively. This change is also observed at
temperatures of 313, 323 and 343K.
Composite corrosion inhibitors involving zinc oxide, glycerine, caustic soda, sodium
hydroxide and the cube residue of methyl ethyl ammonium reagents based on oxyethylene
phosphonic acid, A composite inhibitor was tested on equipment and pipelines of Shurtan gas
chemical complex for corrosion resistance, including prevention of mineral salts formation by
comparing performance of
Option and Nalco
inhibitors supplied from abroad
.
The results of the
tests at SHCC are shown in Table 2.
Table 2
Corrosion protection performance of nitrogen, amine and phosphorus inhibitors
Inhibitor compositions
Corrosion inhibition
efficiency, %
Efficiency from 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
Option brand
comparison inhibitor
96,6
90,1
Conclusion.
The results of the research showed the prospects of using nitrogen, amine and
phosphorus-containing inhibitors derived from local raw materials and industrial wastes of the
Republic of Uzbekistan. The optimum concentrations of inhibitors for the protection of metals
against corrosion and prevention of the formation of mineral deposits in acid and hydrogen sulfide
environments have been established. It is shown that the coating speed of composite inhibitors on
the steel sample surface (St. 3 and St. 12) passes in one plane and is realized by the Langmuir law
with the formation of layer preventing metal corrosion and activation energy in these media of
steel St. 3 and St. 12 with inhibitors application is determined. On the basis of the calculated
thermodynamic functions (∆H, ∆S, ∆G) it is found that the Gibbs energy has a negative value (∆G
eff
).
In order to import substitution of inhibitors the mechanisms and indicators of inhibition of metal
corrosion process as well as prevention of formation of mineral salt deposits in acid, hydrogen
sulfide, alkaline-saline and water aggressive media have been studied and optimal concentrations
of multicomponent inhibitors for different media have been established.
The composite inhibitors are used to increase the inhibition efficiency of mineral salt
accumulation by 2-6% and increase the corrosion protection of metals to 98.4%.
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SUYULTIRILGAN GAZLARNI SAQLASH MASALALARINI O'RGANISH
Xudoyberdiyev F. I., Sobirov M.
Toshkent kimyo-texnologiya instituti
Hozirgi vaqtda suyultirilgan tabiiy gaz global uglevodorod bozorida tobora muhim rol
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suyultirilgan tabiiy gazni etkazib berish uchun gaz quvurlari tizimini, shu jumladan borish qiyin
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keladi. Ikkinchidan, suyultirilgan tabiiy gaz quvur liniyasiga nisbatan yuqori sifat bilan tavsiflanadi.
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Suyultirilgan tabiiy gazni suyultirish, berish va qabul qilish uchun yuqori texnologiyali
komplekslarning ajralmas qismi bu katta hajmli er usti izotermik tanklardir. Suyultirilgan tabiiy
gazning katta hajmli rezervuarlari katta hajmdagi yong'in va portlash xavfi bo'lgan mahsulotning
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bu suyuqlik qatlamlarini bug' hosil bo'lishi bilan keskin o'z-o'zidan aralashishiga va suyultirilgan
