The effect of environmental parameters on the electrochemical corrosion of X100 steel in NS4 simulated soil solution is investigated. The parameters examined were pH (4.7-9), purging gas (5% carbon dioxide (CO2)/95% nitrogen (N2), 100% carbon dioxide, and 100% nitrogen), solution temperature (25, 40, and 55 °C), bicarbonate (HCO3-) concentration, chloride (Cl[-]), and sulfate (SO4[2-]). Overall, corrosion rates of the specimens decreased with pH. EIS results reveal three varying surface interactions occurring on the steel based on the environmental conditions. Acidic solutions with a pH below 6 induce impedance responses representing the absence of any adsorptive and/or diffusive effects outside the capacitive double-layer. Near-neutral solutions introduce a capacitive adsorption region at the steel surface whose dominance increases with solution temperature and decreases with chloride and/or sulfate additions. Further increase in pH into the alkaline region brings about mass-transfer controlled behavior which, in parallel with adsorption effects, controls the corrosion rate of the steel. Chloride and/or sulfate additions of any amount eliminate this diffusion behavior completely and are found to impede charge transfer at OCP or during free corrosion.Sufficient bicarbonate was critical for the passivation of the steel. Higher chloride/sulfate content prevented stable passivation. Impedance results reveal the involvement of adsorption and parallel adsorption-diffusion in near-neutral and mildly alkaline conditions, respectively.
Electrochemical behavior of API-X100 pipeline steel in NS4, near-neutral, and mildly alkaline pH simulated soil solutions
Elektrochemisches Verhalten des Rohrstahles API-X100 in NS4, nahezu neutralen und schwach alkalischen künstlichen Erdbodenlösungen
Corrosion Science ; 82 ; 45-57
2014
13 Seiten, 13 Bilder, 5 Tabellen, 39 Quellen
Aufsatz (Zeitschrift)
Englisch
Rohrstahl , Pipeline , unterirdische Rohrleitung , Erde (Boden) , neutrales pH-Milieu , alkalische Lösung , pH-Einfluss , Temperatureinfluss , Hydrogencarbonat , Chlorid , Konzentrationseinfluss , Korrosionsgeschwindigkeit , Korrosionspotenzial , Passivierung , elektrochemische Impedanzspektrometrie , Kohlendioxid , Polarisationskurve , Gasatmosphäre , Korrosionsmechanismus
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