Effect of carbon dioxide and temperature on passive film parametersof superduplex stainless steel

Emandro Vieira Da Costa,Ricardo Pereira Nogueira,Thiago José Mesquita,Ivan Napoleão Bastos,Ariane Ferreira

doi:10.1590/s1516-14392013005000088

Emandro Vieira Da Costa, Ricardo Pereira Nogueira + Show 3 more

Open Access

https://doi.org/10.1590/s1516-14392013005000088

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Abstract

Superduplex stainless steel has been frequently employed in new sites of Brazilian Pre-Salt. In these environments, chloride concentration, temperature and carbon dioxide are normally present in higher levels than those at sea water at room temperature. In these conditions, it is expected that the passive films of stainless steel also show modifications. To better understand such modifications, samples of superduplex stainless steel UNS S32750 were submitted to electrochemical impedance measurements in brine media, at two temperatures and under presence/absence of carbon dioxide. The electrochemical impedance results were initially tested using the Kramers-Kronig transform and subsequently fitted by equivalent circuit employing constant phase elements - CPE. Moreover, to quantify the effect of each factor (temperature, chloride, carbon dioxide and microstructure) on the equivalent circuit, their parameters were tested applying statistical analysis. Significant effect of carbon dioxide and temperature was found on related parameters of passive film for heat-treated samples.

Highlights

Commercial companies face challenging situations when exploiting oil and gas in offshore fields whose access is difficult and the environment may be extremely aggressive
Another aggressive factor is the presence of carbon dioxide that promotes the pH reduction due to the H2CO3 formation[1] and it well-known to be a major problem in corrosion behavior of iron based alloys[2,3,4,5,6]
The results of KK analysis suggested that the electrochemical impedance spectroscopy (EIS) experiments obeyed the four necessary conditions to validate the electrochemical impedance measurements since the associated errors were acceptable

Summary

Introduction

Commercial companies face challenging situations when exploiting oil and gas in offshore fields whose access is difficult and the environment may be extremely aggressive. Hydrocarbon sources existing on Brazilian Pre-Salt, for example, present temperature and salinity, besides harmful gas, in which the use of ordinary carbon steels become unfeasible since the corrosion effect is intensified by the local conditions. Another aggressive factor is the presence of carbon dioxide that promotes the pH reduction due to the H2CO3 formation[1] and it well-known to be a major problem in corrosion behavior of iron based alloys[2,3,4,5,6]. The heat-treatments used during the production of equipments may cause the precipitations of deleterious intermetallic components like sigma phase, making the steel more susceptible to localized corrosion[2]

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