Effect of particle impingement on electrochemical properties of stainless steel in a jet flow

Abstract

The objective of this research was to discuss the effects of physical impingement on the corrosion resistance of super 13Cr stainless steel in a solid-liquid jet flow. Data from standard laboratory tests including open-circuit potential (OCP), polarization potential, current and surface morphology was obtained. In addition, the passivation process at a changing flow velocity and after particle impacts were discussed using a point-defect model (PDM). The experimental results showed that particle impacts affect not only the electrochemical parameters but also the apparent structure of a sample, thus weakening the surface corrosion resistance of stainless steel. An uninterrupted particle impact damages loose passive films, decreases the electric potential and increases the current density. When the change in the potential reaches a stable state, the metal potential is gradually increased due to the influence of passivation; the passivation rate is the most significant at the beginning of the passivation and at a low flow velocity. Keywords: solid-liquid two-phase flow, electrochemical property, passive film, repassivation Predmet raziskave je bil raziskati vplive fizikalnih trkov na odpornost proti koroziji super nerjavnega jekla 13 Cr v toku me{a-nice kapljevine in trdne faze. Avtorji so podatke zbrali s pomo~jo standardnih laboratorijskih testov, kot so: potencial v odprtem tokokrogu (OCP; angl.: open-circuit potential), povr{inska morfologija, polarizacijski potencial in tok. Dodatno so uporabili model to~kovnih napak (PDM; angl.: Point Defect Model) za razlago procesa pasivacije v spreminjajo~ih se pogojih hitrosti pretoka medija po trkanju delcev na povr{ino vzorca. Rezultati preizkusov so pokazali, da trki delcev ne vplivajo samo na elektrokemi~ne procese temve~tudi na navidezno strukturo vzorca in s tem se slabi protikorozijska odpornost nerjavnega jekla. Neprekinjeno mesebojno trkanje (udarjanje oz. zadevanje) delcev po{koduje pasivni film in tako zmanj{a elektri~ni potencial ter pove~a gostoto toka. Ko sprememba potenciala dose`e neko stabilno vrednost, potencial kovine postopno naraste zaradi vpliva pasivacije in hitrost pasivacije je najbolj pomemben faktor na za~etku pasivacije pri majhni hitrosti pretoka. Klju~ne besede: dvofazni tok kapljevina-trdno, elektrokemijske lastnosti, pasivni film, repasivacija