Impedance distribution at the interface of the API steel X65 in marine environment

Steel pipelines used for injection systems containing seawater for secondary oil extraction show corrosion caused by bacterial consortia, species in solution and aggressive ions. In this work an experiment capable of reproducing the steel–seawater system is designed to study impedance distribution of the film formed at the steel–seawater interface. From experimental data we proposed a mathematical approach describing the impedance distribution of steel API X65 exposed to the marine environment by means of 2D transmission line model (TLM). The formation of two layers (inner and outer layer) at the metal surface originated by bacterial consortia, calcareous deposits (outer layer) and/or corrosion products (inner layer) influenced physical heterogeneities that favor corrosion at some active sites. The interfacial response of the metal-layers-electrolyte obtained by applying electrochemical impedance spectroscopy (EIS) shows active dissolution and diffusion phenomena, this last controlling the process when the oxygen present in the solution diffuses through the film formed after immersion of the metallic structure into the seawater electrolyte. A deterministic model is proposed based on TLM model and impedance distribution of the time-dependent evolution of this interface that describes film growth and dissolution, based on impedance experimental data and SEM analysis we conclude that the interface is formed with two layers (inner and outer).