Behaviour of Carbon Steel in the Presence of Hydrocarbon and a Pyridinic Compound

The electrochemical behaviour of a pyridinic compound, as corrosion inhibitor, on a system of AISI 1018 carbon steel in a synthetic corrosive medium (brine type NACE 1D196), in the absence and presence of hydrocarbon (kerosene), was investigated in this work. Electrochemical techniques used were polarisation curves and electrochemical impedance spectroscopy. In the polarization curves, it is observed that the presence of the corrosion inhibitor in the system affects both the anodic and the cathodic branches, showing that currents obtained are lower with the presence of the inhibitor. On the other hand, the inhibitor efficiency decreases with the presence of hydrocarbon in the system evaluated. Electrochemical impedance spectroscopy shows that steel has great activity in the system studied being more noticeable at low frequencies and in the presence of hydrocarbon. This shows the interaction of ions present in the solution with metal, favoured by the presence of hydrocarbon. The analysis with x-ray Photoelectron Spectroscopy (XPS) showed that the presence of hydrocarbon in the system allows the deposition of several Cl-crystals on the metal surface. Also, there is an increase in Ca, Mg and C with a strong signal of iron, suggesting the presence of iron carbonate and iron hydroxides.