Analysis of the galvanostatic polarization method for determining reliable pitting potentials on stainless steels in crevice-free conditions

S. Frangini, N. De Cristofaro

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Abstract

In this paper the potential of the galvanostatic polarization technique as accelerated method for determining the characteristic pit potentials on stainless steels in crevice-free conditions is examined. Measurement of the potential change as a function of time shows a maximum that agrees with the nucleation pit potential. Thereafter, a stationary potential is reached corresponding to the protection potential against pit. Possible limitations of this kind of measurements have been remedied by refinements in the test procedure and conditions. The state of the surface oxide film and the applied anodic current are two basic parameters that must be well defined because they govern the pitting susceptibility. It has been found that with applied anodic currents in the range 40-200 μA/cm2and with prior electrode exposures to solution between 30 and 60 min it is possible to obtain results in excellent agreement with the conventional potentiodynamic tests with the advantage of smaller data scattering and absence of crevice at electrode/holder interfaces. These effects are the result of the rapid pitting stimulated in the galvanostatic method. This implies a short duration of the experiment thus also favouring the elimination of the time-dependent crevice, which notoriously contributes to the poor reproducibility of pit potentiodynamic potentials. A detailed series of experiments have been conducted on several stainless steels and in different test conditions to validate the accuracy of the galvanostatic polarization method. © 2003 Elsevier Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)2769 - 2786
Number of pages18
JournalCorrosion Science
Volume45
Issue number12
DOIs
Publication statusPublished - 2003

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All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Science(all)

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