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Low Alloy X100 Pipeline Steel Corrosion and Passivation Behavior in Bicarbonate-Based Solutions of pH 6.7 to 8.9 with Groundwater Anions: An Electrochemical Study

“…Rather, this behavior likely indicates iron(II,III/II)oxide (Fe 3 O 4 /c-Fe 2 O 3 ) presence, previously shown to be unaffected by the presence of HCO 3 À /CO 3 2À as long as E remains in the passive region, since the oxidation current is practically independent of [HCO 3 À /CO 3 2À ]. [44] Corrosion product between E bd1 and E bd2 loses some but not all of its protective strength, suggesting formation of a more porous or less protective product/pseudomorph is occurring at these particular potentials. Superimposing the upper boundary of the Fe 2 O 3 dominance region from the Fe-H-C-O Pourbaix system [38] to Figure 9 further supports the impression that Fe 3 O 4 /c-Fe 2 O 3 formation in alkaline media is happening around E bd1 .…”

“…In Figures 6(a) and (b), decreasing i p values in this region with increasing [NaHCO 3 ] indicates the gradually enhancing protectiveness of FeCO 3 at higher anodic potentials, [40,44] plotted vs pH in Figure 8(a). The potential difference (DE) parameter, between the most anodic passive layer development potential (E p1 or E p2 ) and the earliest breakdown potential (E bd1 ), is plotted vs pH in Figure 8(b).…”

Passivation of X65 steel in NaHCO3 solution saturated with CO2 using thin wire specimens

“…The dissolution and passivation mechanisms in NaHCO 3 systems have been studied by many scholars. Simard et al investigated FeHCO 3 + as a dissolution product of bicarbonate and concluded that FeCO 3 precipitation is governed by localized FeHCO 3 + . Castro et al reported that Fe(OH) 2 forms before FeCO 3 in an inner underlying layer, leading to multilayered passivation.…”

Influence of alloying on the passive behaviour of steels in bicarbonate medium

“…The pitting corrosion of these types of steel has been studied in 0.1 M KCl solution [6,7], in which they do not show an anodic passive film region before pitting commences, as evidenced by the polarization curves. The bicarbonate passivating medium has been used by Brossard et al to study the electrochemical behaviour of 1024 mild steel [8]; its localised corrosion was studied by adding chloride to bicarbonate and phosphate passivating media [9,10]. Cheng et al [11,12] also used bicarbonate solution with and without chloride to study metastable pit formation in A516 carbon steel, as well as in chromate/bicarbonate mixtures [13].…”

“…Simard et al [8] showed that this film is not affected by the presence of HCO À 3 /CO 2À 3 as long as the applied potential remains in the passive region, since the oxidation current is practically independent of the HCO À 3 /CO 2À 3 concentration although other studies showed that this is pH and temperature dependent [25]. Pit nucleation and passivation of carbon steel [12,26] has also been assessed.…”