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Query: "keywords" (repassivation) .

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1.
Activation and repassivation of stainless steels in artificial brines as a function of pH
Emir Mujanović, Bojan Zajec, Tadeja Kosec, Andraž Legat, Stefan Hönig, Gerald Zehethofer, Gregor Mori, 2019, original scientific article

Abstract: When planning oil wells with stainless steel components, two possible reasons for depassivation have to be considered-chemical depassivation caused by acidizing jobs and mechanical depassivation caused by various tools and hard particles. The study explores conditions causing chemical activation of investigated steels and circumstances under which repassivation occurs after activation. The main focus of the study is to determine, how quickly various steels can repassivate under different conditions and to find pH values where repassivation will occur after depassivation. The investigated steels were ferritic (martensitic or bainitic) in the cases of 13Cr, 13Cr6Ni2Mo, and 17Cr4Ni2Mo, austenitic in the case of 17Cr12Ni2Mo, and duplex (austenitic and ferritic) in the case of 22Cr5Ni3Mo. Potentiodynamic experiments were employed to obtain electrochemical properties of investigated steels, followed by immersion tests to find ultimate conditions, where the steels still retain their passivity. After obtaining this information, scratch tests were performed to study the repassivation kinetics. It was found that repassivation times are similar for nearly all investigated steels independent of their chemical composition and microstructure.
Keywords: stainless steels, activation, repassivation
Published in DiRROS: 21.11.2023; Views: 259; Downloads: 125
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2.
Modelling the electrochemical transients during repassivation under open-circuit conditions in a neutral solution
Bojan Zajec, Tadeja Kosec, Andraž Legat, 2022, original scientific article

Abstract: The responses of the current and the coupled potential to rapid depassivation have been studied on a three-electrode system under open-circuit conditions. Passivated AISI 304 stainless steel in low- and high-conductivity solutions of NaSO has been depassivated with a single, rapid scratch over the small fraction of surface of the working electrode (WE). Single- and dual-WE configurations have been implemented. Once the surface is scratched, the current and potential transients exhibit a delayed maximum and minimum, respectively, in contrast to the outcome of more common potentiostatic scratching experiments. A simple model based on the equivalent circuit has been developed to predict the observed transients and provides clear relations between the features of the transient and the parameters of the electrolyte and the electrodes. The interfacial capacitance of the electrodes’ passive surfaces proves crucial for the shapes of the observed potential and current transients. It is shown that this capacitance temporarily provides the majority of the charge for repassivation under open-circuit conditions. Possible sources of specific discrepancies between the model and the measured transients are indicated.
Keywords: repassivation, open circuit conditions, transient, modelling, interfacial capacitance
Published in DiRROS: 21.06.2023; Views: 341; Downloads: 155
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