Effect of the addition of CO2 in synthetic seawater,
simulating deep waters, on the pitting corrosion behaviour
of stainless steels
N. A. Mariano1, E. C. T. Ramos1, D. H. C. Marinho1, S. R. F. Batista2; M.A. Tommaselli3, M.
M. Melo4
1
Universidade Federal de Alfenas, Campus de Poços de Caldas, MG, Brazil
2
Instituto Federal de Educação, Ciência e Tecnologia, São Luiz, MA, Brazil
3
Universidade Federal da Grande Dourados, Dourados, MS, Brasil
4
Universidade Federal de Itajubá, Itajubá, MG, Brazil
Nonconventional martensitic stainless steels have been increasingly employed in the
production and installation of oil drilling equipment, thanks to their good combination of
mechanical properties and corrosion resistance in aqueous solutions containing ion chlorides
[1-4]. The present work involved a study of the pitting corrosion of ASTM A487 Gr CA-6NM
steel in synthetic seawater containing chloride concentrations of 20000 and 80000 ppm, at
temperatures of 5, 25, 60, and 80°C, and in the conditions of aerated and CO2-saturated
solutions. Table 1 indicates the values obtained for the pitting potential. Note that the
potential decreased as the chloride concentration and temperature increased, although the
influence of CO2 was more complex. This stainless steel showed the highest pitting corrosion
resistance in CO2-saturated solution containing 20000ppm of chloride at 25oC. The pitting
potential decreased linearly as the temperature increased. At low temperatures (T=0°C), the
pitting potential underwent the same alterations it did at other temperatures, in both solutions,
and the pitting potential reduction rate was found to be independent of the chloride ion
concentration or of the presence CO2.
Keywords: Pitting, Stainless Steel, Corrosion, CO2, Seawater.
Table 1- Pitting potential (Ep) values obtained the potentiodynamic curves
Ep (mV) x SCE
[Cl-]
5°C
25°C
60°C
80°C
(ppm)
CO2
CO2
CO2
CO2
Aerated
Aerated
Aerated
Aerated
saturated
saturated
saturated
saturated
20000
-21
58
-64
-70
-85
-89
-89
-96
80000
-38
-76
-88
-110
-93
-105
-115
-200
References
[1] P. D. Bilmes, et al., Materials Characterization, 46, 285 (2001).
[2] M.P. Ryan, et al., Nature, 415, 770 (2002).
[3] Z. Szklarska-Smialowska, Corrosion Science, 44, 1143 (2002).
[4] N. Anselmo, J. E. May, N. A. Mariano, P. A. Nascente, S.E. Kuri, Materials Science and
Engineering A-Structural Materials Properties Microstructure and Processing, 5, 20 (2006).
[email protected]
Rua: Célio Barbosa da Silva, 274-Santa Paula – São Carlos-SP - CEP 13564-060.