Susceptibility to Stress Corrosion Cracking for Low-Carbon Steel Welds in Carbonate-Bicarbonate Solution

Corrosion Engineering, Science and Technology

2014

This research evaluates the passivation process, in relation to the anodic and cathodic reactions, in deoxygenated solutions of different bicarbonate concentrations. Two types of API-X100 steel microstructures were examined. They are similar to near fusion heat affected zones (HAZs) which were produced by special thermal cycles. By monitoring the open circuit potentials, the passivation process exhibited electrochemical signs that it forms faster with higher bicarbonate concentration. During cyclic voltammetry, bicarbonate in concentrations less than 0?1M impedes the passivation, by catalysing the anodic dissolution. In higher concentrations, bicarbonate seemed more protective in facilitating the development of thicker passive films, from an electrochemical perspective that encourages corresponding physicochemical investigations in the future. The transpassivation seemed to depend more on the chemistry of the passive film than on the formation of FeCO 3 . Cooling down the HAZs at high rates could make them more corrosion resistant, but probably of less protective corrosion products.

Section: Experimental Test Materialsmentioning

confidence: 99%

Effect of bicarbonate concentration on corrosion of high strength steel

Corrosion Engineering, Science and Technology

2014

“…The results of our slow‐scan potentiodynamic tests show, however, that the HAZ microstructures, which are similar to theirs, distinctly, from each other, reacted during dissolution and passivation. In some studies, like that for instance reported by Mitsui et al and by others, the significance of the dilute bicarbonate–carbonate solutions with the reactions, and with the cathodic currents did not particularly receive an interest. With regard to the experimental techniques, the potentiostatic polarization and electrochemical impedance spectroscopy are not currently widely applied in the field of HAZ corrosion.…”

Section: Introductionmentioning

confidence: 91%

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

Icre

2013

Materials & Corrosion

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.

“…Rather, the electrochemical investigations were carried out in mildly alkaline solutions synthesized from bicarbonate and carbonate, or only from bicarbonate . Moreover, the emphasis was mostly on synergistic effects, such as these associated with high stresses and cracking susceptibility, without addressing the electrochemical phenomena that govern the early stages of the corrosion reactions . In many of the previous studies on HAZ corrosion, the test HAZs were produced by regular heat treatments, compromising the microstructural specificity and electrochemical significance of the HAZs in the field.…”

Section: Introductionmentioning

confidence: 99%

“…[17,18] Moreover, the emphasis was mostly on synergistic effects, such as these associated with high stresses and cracking susceptibility, without addressing the electrochemical phenomena that govern the early stages of the corrosion reactions. [19][20][21][22] In many of the previous studies on HAZ corrosion, the test HAZs were produced by regular heat treatments, compromising the microstructural specificity and electrochemical significance of the HAZs in the field. That is due to the fact that during regular heat treatments the resulting microstructures could not be exposed to the thermal conditions of a real welding process.…”

Section: Introductionmentioning

confidence: 99%

Re‐examining the influence of chloride ions on electrochemical CO₂ corrosion of pipeline steels—corrosion of the heat‐affected zones (HAZs) of API‐X100 steel

2015

Can J Chem Eng

This research investigates the corrosion characteristics of simulated heat‐affected zones (HAZs) of API X‐100 pipeline steels in CO2‐saturated brines of different chloride concentrations. It links the significances of the HAZ microstructure and chloride concentration to the corrosion kinetics and corrosion products. The ferritic HAZs dissolve at almost two times the rate of acicular ferritic and bainitic HAZs. This paper shows that the samples corrode at rates increasing with the chloride concentration to a maximum rate, at a low chloride concentration, beyond which the corrosion rates decrease with increased chloride concentrations. For the base steel, for instance, the corrosion current densities increased from 8.5 μA/cm2 in 0.02 mol/L to the maximum 22 μA/cm2 in 0.07 mol/L before they decreased to 10 μA/cm2 in 0.1 mol/L. The corrosion products showed an increase with the chloride concentration, from almost 1‐3 μm to 25‐35 μm in 0.02 and 0.85 mol/L solutions, respectively.