Depassivation and Repassivation of Stainless Steels

Emir Mujanović

Research output: ThesisDoctoral Thesis

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Abstract

In oil and gas production, deep wells producing highly aggressive media are often completed with highly alloyed corrosion resistant alloys (CRAs, mainly steels). These CRAs have excellent corrosion properties due to the formation of a passive layer of chromium, iron and molybdenum oxides and hydroxides. During acidizing jobs, when a plugged well is re-opened, and during sand production at high flow velocities, localized or uniform depassivation can occur and yield high corrosion rates of used CRAs. In the present work the resistance of passive layers of various stainless steels was investigated alongside the conditions and kinetics of when these layers are rebuilt. Methods applied consisted of: potentiodynamic experiments, immersion tests, scratch tests and variable pH flow experiments. Results revealed that, with the exception of those with very low alloys, all stainless steels showed repassivation after acidizing when the pH level increased above 3. Repassivation occurs within 100 s to a certain (sufficient) extent, although the passive layer is not completely rebuilt within this period.
Translated title of the contributionEntpassivierung und Repassivierung chemisch beständiger Stähle
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Mori, Gregor Karl, Assessor A (internal)
  • Legat, Andraz, Assessor B (external), External person
Publication statusPublished - 2020

Bibliographical note

no embargo

Keywords

  • Stainless steel
  • Depassivation
  • Repassivation
  • Scratch test
  • Mechanical depassivation
  • Chemical depassivation

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