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DESIGN AND APPLICATION OF CORROSION PROTECTION
ON STORAGE TANK TOPS
Prof. Efim Ya. Lyublinski and Dr. Donald A. Kubik
Northern Technologies International Corporation
23205 Mercantile Rd., Beachwood, OH 44122 USA
6°° COTEQ Conferência sobre Tecnologia de Equipamentos
22°° CONBRASCORR – Congresso Brasileiro de Corrosão
Salvador – Bahia
19 a 21 de Agosto de 2002
As informações e opiniões contidas nesse trabalho são de exclusiva responsabilidade do autor.
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ABSTRACT
This presentation will describe new corrosion protection technologies designed to protect
the tops of oil and water storage tanks. New devices which deliver volatile corrosion
inhibitors directly to the tops of storage tanks have been created. These technologies are
highly efficient and provide a significant extension of storage tank service life. Critical
concentrations are presented which make corrosion prevention possible in different
atmospheric and gaseous environments.
Keywords : mild steel, oil, gas, atmosphere, water, corrosion, volatile inhibitor,
protection, storage tank.
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1 - INTRODUCTION
Corrosion inhibitors can be efficiently employed to inhibit the corrosion of steel in the
tops of oil and water storage tanks. The tops of the storage tanks have different corrosion
activities depending on environmental conditions (Figure 1). Corrosion rates can change
from 0.03 to 0.70 mm/year depending on the gaseous compositions, their concentrations,
temperature, humidity, duration and frequency of their influence. The pitting corrosion
rate can increase to 20 mm/year and higher [1-6,12]. Obviously, reliable and efficient
corrosion protection systems are necessary. These structures use [2, 4-11] coatings in
some cases, but the service life is low (5-10 years, for example) and repair is difficult.
The most progressive corrosion protection method for the tops of tanks utilize volatile
corrosion inhibitors (VCI). Different VCI compounds and compositions can be used for
corrosion protection in the tops of oil and water storage tanks, however, application
conditions in storage tanks are unpredictable and it is thus impossible to deal with the
myriad of potential problems using a single corrosion inhibiting technology. Until now,
VCI’s have not been commonly employed to protect the tops of storage tanks. We have
created new devices and methods for delivering VCI to the tops of storage tanks only
when the atmosphere and/or gases begin to influence the empty surface.
This paper describes a special system for delivering VCI to the empty volume at the top
of the storage tank, which provides efficient corrosion protection.
2 - EXPERIMENTAL
The specimens (50x20x1 mm) were produced from strips of mild steel containing, in
mass percent: 0.11 C, 0.94 Si, and 0.71 Mn. The y were sand blasted, degreased in
alcohol, cleaned by water flushing and dried in a stream of air or at room temperature in a
desiccator.
The corrosive medium (gases) were created in chambers and they had the following
typical compositions:
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SO2 – 25 mg/m3 , CO2 –100 mg/m3 , H2 S –50 mg/m3 , Cl- - 2.0 g/m2 xh, RH (relatively
humidity) - 95 – 100%, Temperature – +55o C.
The inhibitors tested were several different mixtures of VCI, including: amines,
imidazolines, triazoles, sulfonates, etc. [1-7, 11, 12]. The vapor pressure of VCI
investigated varied between 10-4 and 10 Pa. The corrosion rate (CR) was determined by
measuring weight loss.
3 – RESULTS AND DISCUSSION
Table 1 shows the corrosion rate (and VCI efficiency) of mild steel in different media –
atmosphere and gases. The maximum CR occurs rarely and on less than 5% of the top
surface. The maximum corrosion rate is very dangerous. This is the well-known
honeycomb corrosion seen on the tops of crude oil tanks. Prevention is not difficult, and
in any case, the prevention of average and maximum corrosion rates is possible at the
same time. That is why the avarage corrosion rates are also of concern.
VCI are highly efficient in atmosphere and gases (Table 1). In the case where the
concentration of inhibitors equals the vapor pressure the efficiency is 70-90%. But it is
necessary to define the optimal inhibitor concentration in all cases. By decreasing the
VCI concentration the corrosion increases and in some cases the rate can be higher than
without the inhibitor. Normally, after some time, pitting corrosion will start. We have
created the method, which ensures that the VCI concentration is maintained constant
independent of the empty volume above the liquid level.
4 – CONCLUSIONS
1.
Devices and technology have been created to deliver VCI to the top of storage
tanks.
2.
It is possible to choose several existing compounds to supply VCI in
atmosphere and gases.
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3.
Based on our experiments, we could find the best combination of VCI
compounds to provide the highest efficiency of corrosion protection.
REFERENCES
1. W. von Baeckman, W. Schwenk, and W. Prinz, Handbook of Cathodic Corrosion
Protection (Houston, Gulf Publishing Company, 1997), p. 290
2. D.A. Kubik and E.Y. Lyublinski, Creation and Application of Volatile Inhibitors:
(NACE, Corrosion 2001), paper 01189
3. Y.I. Kuznetsov, and E.Y. Lyublinski, Inhibitors for Corrosion Protection by
Storage and Transportation of Oil (Moscow, Russia, VNIIONG, 1980), p. 27, 43,
50
4. Y I. Kuznetsov, Organic Inhibitors of Corrosion of Metals ( Kluwer Academic
Publishers), 1996
5. I.M. Parker, Inhibition of Tanks and Other Structures: Corrosion Inhibitors,
(NACE, Houston, 1981), p.98
6. P.R. Roberge, Handbook of Corrosion Engineering (New York, McGraw-Hill,
2000), p. 13, 55, 833, 863
7. I.L. Rosenfeld, Corrosion Inhibitors (Moskow, Chimia, 1977)
8. M.A. Quraishi, J.Rawat, and M.Ajmal: Corrosion 10 (1999), p. 919
9. P.F. Anto, Materials Performance 39,3(2000), p.70
10. X.G.Zhang, Corrosion 55,8(1999), p. 787
11. R.W.Revie, Ulig’s Corrosion Handbook (New York, Jonh Wiley & Sons, INC,
2000), p.305, 521, 529, 561, 1061,1089
12. P.A. Vinogradov, Preservation of Mashinary Items (Leningrad, Mashinostroenie,
1986), p. 128
13. Reviews on Corrosion Inhibitor Science and Technology (Houston, NACE,
1993), p. II-1-1 – II-5-1
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TABLE 1
Examples of Corrosion Rate of Mild Steel and Efficiency of VCI
in the Top of Storage Tanks, Containers, Reservoirs
Type of
Tanks
Corrosion Media
Corrosion Rate (mm/year)
Average
Drinking
Water
Seawater
Industrial
Aqueous
Waste
Crude Oil
Light Oil
Atmosphere (A)
(A) + VCI
Atmosphere
(A) + VCI
Gases (G)
0.04
0.009
0.05
0.01
0.200
Pitting
(Maximum)
0.200
0.300
1.500
(G) + VCI
0.03
-
75-90
Gases
(G) + VCI
Gases
(G) + VCI
0.200
0.05
0.120
0.03
30.00
0.400
-
70-90
70-90
Atmosphere
+ Gas
Atmosphere
+ Gas
Crude
Oil
Light Oil
Sediment
Aqueous
Solution
A
Efficiency of
VCI (%)
60 - 80
70-85
-
Atmosphere
+ Gas
Atmosphere
Light Oil
Water
Sediment
Aqueous
Solution
B
C
FIGURE 1. Typical storage tanks
D
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P1
3
P0
P1>P 0
1
4
2
Figure 2. Typical scheme delivering VCI's in to the
top of storage tanks
1 - Steel Tank 2 - Crude or Light Oil
3 - Atmosphere + Gas 4 - Devices with VCI