Abstract

Background: Pipeline steels such as the API 5L X80 grade can be subjected to corrosion in contact with either acidic or alkaline sour brines. The surfaces oxides formed in each case can have a protective or non-protective character against corrosion. This behavior is not understood and gives rise to conflicting reports in the literature. The aim of the present work was to investigate the electrochemical response of anodic films formed by cyclic voltammetry on the surface of the API 5L X80 pipeline steel.

Methods: The anodic films were formed by cyclic voltammetry under different pH conditions and switching potentials. The corrosion behavior was assessed using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis.

Results: Mott-Schottky analysis revealed that the doping densities were higher for the films formed in the acidic solution whereas those formed in the alkaline solution were less defective. SEM micrographs suggest the formation of a defective and porous surface as the switching potential becomes more positive.

Conclusion: The poorest protective properties are associated with films formed under high switching potentials and low pH.

Keywords: Cyclic voltammetry, electrochemical impedance spectroscopy, Mott-Schottky plots, anodic films, API 5L X80 pipeline steel.

Graphical Abstract