Corrosion rates under charge-conservation conditions.

Laboratory and numerical corrosion experiments impose an electric potential on the metal surface, differing from natural corrosion conditions, where corrosion typically occurs in the absence of external current sources. In this work, we present a new computational model that enables predicting corrosion under charge-conservation conditions. The metal potential, an output of the model, is allowed to change, capturing how the corrosion and cathodic reactions must produce/consume electrons at the same rates, as in natural conditions. Finite element simulations are performed over a large range of concentrations and geometric parameters. The results highlight the notable influence of the charge-conservation assumption and pioneeringly quantify corrosion rates under realistic conditions. They further show: (i) the strong coupling between the corrosion rate and the hydrogen and oxygen evolution reactions, (ii) under which circumstances corrosion pits acidify, and (iii) when corrosion is able to become self-sustained lacking oxygen. • A numerical model for corrosion in absence of external current sources is presented. • The model requires corrosion currents to be counteracted by cathodic reactions. • We simulate pencil-electrodes under varying geometric and environmental conditions. • We show strong influence of available oxygen and external surface area on corrosion. • Oxygen is required to develop acidic pits, but pits can sustain corrosion lacking oxygen. [ABSTRACT FROM AUTHOR]