Influence of FeCO₃ and FeSO₄ Layers on Corrosion in Sulfuric Acid Medium of Eutetoid Steels

This work addresses the corrosion resistance of Riser steels used in submarine pipelines for oil production, making it crucial to evaluate the variables related to corrosion in the marine environment. Three types of wires with spheroidized, lamellar and discontinuous cementite microstructure were tested in 0.1M H₂SO₄ with and without the use of CO₂, in addition to a different ambient temperature (80 °C). Thus, electrochemical tests, including OCP and linear potentiodynamic polarization, revealed the corrosion resistance of each material. The analysis of the polarization curves through Tafel extrapolation, obtained the current density, correlating with the potential of the sample in the medium, indicating the polarization resistance. The LC wires demonstrated greater resistance to corrosion (769.23; 2,544.79 and 4,790.87 Ω.cm²) compared to spheroidized cementite (502,40; 1,038.99 and 902.95 Ω.cm²) and, which, in turn, obtained lower resistance values in two of the solutions. The FeCO₃ and FeSO₄ salts were formed in different areas, including the most degraded ones identified by Raman spectroscopy.

Keywords:
Tensile armatures; H₂SO₄; CO₂; Corrosion; Raman spectroscopy; FeCO₃; FeSO₄