Abstract
Repassivation behaviour of the passive film formed on lean duplex stainless steel UNS S32101 and austenitic stainless steel UNS S30403 in a CO2-saturated oilfield environment has been studied. The native passive film on the alloys was thinned/removed by stepping the potential of the alloy to ﹣850 mV/Ag/AgCl for 30 minutes. Potentiostatic measurements were then taken at potentials of ﹣200, ﹣100, 0, 100 and 200 mV versus Ag/AgCl. Results show that the passive film repassivates at potentials of ﹣200 and ﹣100 mV and 0 mV for both alloys at 50°C. The current density however continues to rise for potentials of 100 and 200 mV. This shows that both alloys are susceptible to pitting at potentials above 100 mV at the test temperature of 50°C.
Highlights
The behavior of stainless steels in aqueous solution has been widely studied
1) The passive film formed on both UNS S32101 and UNS S30403 after an initial cathodic stripping repassivates at potentials of −200 mV, −100 mV and 0 mV at 50 ̊C. This is shown by the continuous steady anodic current decrease for both alloys at these test potentials
2) The passive film formed on both UNS S32101 and UNS S30403 does not repassivate at potentials of 100 mV and 200 mV the test temperature of 50 ̊C
Summary
The behavior of stainless steels in aqueous solution has been widely studied. It is widely agreed that the alloying elements help in the formation of the protective passive film [1] [2]. This film is stable, invisible, thin durable and extremely adherent and self-repairing. The stability of the film depends on the nature of the corroding metal and ions present in the solution [3]. In order to prevent corrosion, it is important that stainless steels have stable passive film with rapid passivation in severe environments [4]. It is believed that the stability of passive film and
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