Passivation of HAZs of API‐X100 pipeline steel in bicarbonate‐carbonate solutions at 298 K

Abstract

This research explores electrochemical correlations between heat‐affected zones (HAZs), produced by Gleeble© thermal simulation cycles, and their passivation behavior in bicarbonate–carbonate solutions. The investigations were carried out in comparison with the base API‐X100 steel in naturally aerated 0.5 g/L chloride solutions, containing a matrix of bicarbonate and carbonate concentrations at 298 K. The slow 0.05 mV/s potentiodynamic scans revealed that the passivation onsets earlier in proportion with the bicarbonate concentrations, possessing accordingly greater immunity against chloride ions on HAZs cooled at 10 and 60 K/s from 1223 K peak temperature. The HAZs cooled at 10 K/s, particularly in concentrated carbonate solutions, showed the most stable passivation, and the HAZs cooled at 60 K/s showed the lowest cathodic activity regardless of the chemical conditions. −0.1 V, versus saturated calomel electrode, potentiostatic currents and the open‐circuit potentials decreased and increased, respectively, with the carbonate concentration, confirming with the main potentiodynamic polarization results, and a corresponding passivation behavior of the HAZs, regardless of a bicarbonate–carbonate condition, was relatively similar. In contrary to the 60 K/s HAZs, the 10 K/s HAZs showed evidence of growing passive films with time and high charge‐transfer resistance, as measured by the EIS tests.

Effect of bicarbonate concentration on corrosion of high strength steel

“…3, were monitored for 20 000 s to analyse the significance of the bicarbonate concentration with the interfacial interactions and passivation. In de-oxygenated solutions, bicarbonate, besides water and hydroxyl, drives both the anodic and cathodic reactions without interference from oxygen, 11 carbonate, 28 or H 2 CO 3 . 29 During free immersion, bicarbonate adsorbs onto the surface and raises the local alkalinity (the concentrations of hydroxyl which is of direct anodic roles).…”

Modeling Corrosion Reactions of Steel in a Dilute Carbonate Solution

“…The cyclic voltammetry started at À1.1 V versus SCE, during which water was reduced under charge-transfer control (Eq 2) ( Ref 1,8,10), producing hydrogen and hydroxyl ions, as depicted in Fig. 2.…”

“…It might not have fully consolidated some of the mechanistic details that are until today being investigated, but it provides a visual guide that helps better understand the corrosion reactions and the significance of the properties and reactivity of the corrosion products. The test samples are made of API-X100, a new-generation pipeline steel, whose electrochemical significance and behavior were explained and examined previously ( Ref 1,8,10,[20][21][22].…”

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

“…Most studies on the corrosion behavior of the carbon steel in NaHCO 3 solution saturated with CO 2 have reported that the carbon steel is passive in NaHCO 3 solution; however, no consensus on passivation mechanism has been reached. Therefore, in the present study, a thin wire specimen with a small working area was used.…”