Vagapov_subbed.qxp 27/3/09 03:54 Page 68
Corrosion Inhibitors for the Protection of Oil Production Equipment
Figure 2: Dependence of the Corrosion Rate of Low-carbon Steel in
Hydrophobic inhibitors cannot protect steel equipment in the
3% NaCl Solution on the Concentration of H
2
S and the Protection
absence of mixing.
4
Effect of Inhibitor in this Medium
Corrosion Inhibition of Reserve Tubes
1.8
Corrosion rate
100
1.6
Protection effect
The inner surface of the reserve tubes required for the repair of
1.4
80
equipment and pipelines should be protected from atmospheric
1.2
corrosion even when closed. Oxygen in the air and condensated
1
60
moisture cause formation of rust on the metal surface. Under such
0.8
40
conditions, the inner surface of tubes can be effectively protected
0.6
Protection effect (%)
Corrosion rate (mm/year) 0.4
30
against atmospheric corrosion by volatile corrosion inhibitors. Unlike
0.2 traditional inhibitors, volatile inhibitors have high volatility and can
0.0 0
12 20 65 240
spontaneously adsorb onto a surface from a vapour–gas phase and
Concentration of H
easily penetrate into various slots and gaps.
2
S
Figure 3: Corrosion Rate of Low-carbon Steel in Drilling Fluids and the
Electrolyte that Can Be Used for Its Preparation
The surface electrolyte corresponding to this relationship can be
separated into the pure inhibitor and an azeotropic solution of the
3.0 volatile corrosion inhibitor. Since the concentration of the volatile
2.5
corrosion inhibitor (C
inh
) in the azeotropic (C
az
) solution is greater
than the protective concentration (C
pr
) of the volatile corrosion
2.0
inhibitor, it is evident that corrosion is impossible. Volatile
1.5
corrosion inhibitors forming an azeotropic mixture with water can
1.0
protect metals under any heat-exchanger condition if C
inh
> C
az
>
Corrosion rate (mm/year)
C
pr
. Using this principle of vapour-phase protection against
0.5
corrosion, one can create volatile corrosion inhibitors for conditions
0.0
of intense moisture condensation at a metal. The results of a
8% NaCI 14% NaCI
10%
24% NaCI
25% 50%
75% Drilling
CHCOOK CHCOOK
CHCOOK CHCOOK
fluids
corrosion test using the volatile corrosion inhibitor IFkhAN-8, which
Corrosion medium
support this principle, are shown in Table 2.
5
Table 2: Results of Corrosion Tests of the Volatile Corrosion
Inhibitor IFKhAN-8
Corrosion Inhibition of H
2
S-containing Motor Oil
Motor oil used at the compressor stations that press the
VCI and Protection Visual Examination Results
Conditions Effect (%)
hydrocarbons transmitted by pipelines can be saturated by H
2
S. Such
Water (10g) 0 Corrosion over 70–100%
motor oil is corrosively aggressive to metal. The addition of inhibitors
of the surface area
can protect steel surfaces from H
6% IFKhAN-8 (10g) (no 96.3 Pitting on the lateral faces
2
S corrosion. The use of corrosion
pre-treatment with the VCI vapour) of the specimen
inhibitors prevents corrosion in H
2
S-containing motor oil.
10% IFKhAN-8 (10g) (no 99.8 A few pits on the lateral faces
pre-treatment with the VCI vapour) of the specimen
Conclusions
14% IFKhAN-8 (10g) (no 100 Complete protection
pre-treatment with the VCI vapour)
Different kinds of inhibitor can be used to protect steel equipment
and pipelines from corrosion by the many corrosive media used in oil
IFKhAN-8 (1.6g) + 100 Complete protection
production. However, in many cases the implementation of
H
2
O (10g)
accumulated experience and its formal transfer from one deposit to
VCI = volatile corrosion inhibitor.
another is ineffective. It is necessary to select the optimum protective
measures, including inhibitors, in each particular case. In summary:
of steel in the solution used for the preparation of drilling fluids is
more than 2.5mm/year (see Figure 3). The corrosion rate in drilling • the corrosive activity of produced hydrocarbons and the
fluids is also high (1–1.5mm/year). In these corrosively aggressive protective properties of inhibitors depend on the mineralisation
media, effective corrosion inhibitors will be those that include and the H
2
S content of stratal water;
derivatives of phosphonic acid or synergetic mixtures. • it is difficult to find effective corrosion inhibitors for steel in
media with high mineralisation levels both with and without low
Corrosion Inhibition of Equipment Under Conservation H
2
S content;
Sometimes oil production equipment is found under conservation. • volatile corrosion inhibitors can be used to protect the inside
Stratal water and acidic gases (CO
2
and H
2
S) have a corrosive effect surface of reserve tubes from atmospheric corrosion; and
on metal equipment even under static conditions (see Figure 1). In • corrosion inhibitors can protect the steel equipment found under
these static conditions, water-soluble compounds should be used conservation or that comes into contact with H
2
S-containing
that dissolve in water and reach and adsorb on the steel surface. motor oil. ■
1. Rozenfeld IL, Frolova LV, Brusnikina VM, Soviet Scientific 3. Vagapov RK, Protection of metals, 2008;7:31. 5. Kuznetsov YuI, Vagapov RK, Getmanskiy MD, Technology
Reviews, Section B, Chemistry Reviews, 1987;8:115. 4. Kuznetsov YuI, Vagapov RK, Frolova LV, European congress conference: Advance technologies in the oil and gas field service
2. Vagapov RK, Protection of metals, 2007;7:39. on corrosion EUROCORR 2008, September 2008, UK. market in GIS Asia Pacific countries, December 2008, China.
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EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 1
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