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Nickel alloys are broadly used in upstream oil and gas applications as a result of an advantageous set of properties including high mechanical strength accompanied by good ductility and toughness, ...

The use of electrochemical noise (EN) measurements for the investigation and monitoring of corrosion has allowed many interesting advances in the corrosion science in recent years. A special advantage of EN measurements includes the possibility to detect and study the early stages of localized corrosion. Nevertheless, the understanding of the electrochemical information included in the EN signal is actually very limited. The role of the cathodic process on the EN signals remains uncertain and has not been sufficiently investigated to date. Thus, an accurate understanding of the influence of the cathodic process on the EN signal is still lacking. On the basis of different kinetics of the oxygen reduction it was established that the anodic amplitude of transients arising from pitting corrosion on stainless steel can be decreased by the corresponding electron consumption of the cathodic process. Therefore, the stronger the electron consumption, the weaker the anodic amplitude of the EN signal becomes. EN signals arising from pitting corrosion on stainless steel can be measured because the cathodic process is inhibited by the passive layer. This was confirmed by means of EN measurements under cathodic polarisation. Since the cathodic process plays a decisive role on the form of transients arising from pitting corrosion, its influence must be considered in the evaluation and interpretation of the EN signals.

Oxygen reduction occurring at the passive layer is probably the most important cathodic reaction involved in corrosion processes on stainless steel. Furthermore, the influence of the surface state on the oxygen reduction reaction is a key point for the understanding of the mechanism of localized corrosion on stainless steel. In this study, electrochemical noise measurements under cathodic polarization were carried out to obtain new information about this influence. It has been confirmed that the surface state of stainless steel plays a very important role in the kinetic of this cathodic reaction. Oxygen reduction kinetics was significantly reduced on passivated surfaces and improved on pre-reduced and ground surfaces. In addition, electrochemical current noise measurements allowed to differentiate between the electrochemical activity produced by the oxygen reduction reaction and that due to the reduction of the passive layer, in direct dependence on the characteristics of the different surface states investigated.

The influence of the flow velocity and the temperature on the corrosion of UNS G10200 in aerated brines had been evaluated by means of electrochemical techniques at the RCE. Increasing the flow velocity and the temperature enhances the corrosion kinetic of the system and changes the corrosion mechanism. This behaviour was adduced to the presence of a mixed control on the corrosion process related with the formation and stabilization of corrosion product layers on the electrode surface. The correlations of Wranglen and Silverman for the mass transfer and the wall shear stresses respectively were validated at the RCE for this system.