Abstract
Aiming to simulate the external corrosion of pipelines, the first stages of the inclusion attack and nucleation of pits were studied by AFM on the API 5LX56 steel in pure 10mM Na2SO4 solution and with additions of HA or FA, both extracted from a Brazilian peat soil. For this, selected inclusions were first marked with micro indentations, viewed in the SEM in the backscattering mode and chemically mapped with EDS. Pit formation was then investigated by scanning Kelvin probe force microscopy (SKPFM). The SKPFM evidenced that HA added to sulfate solutions promotes the fast dissolution of the sulfides of complex inclusions, resulting in pit nucleation, while FA additions slow this attack, acting as a natural corrosion inhibitor.