Protective Efficiency of the Oil Composition Coatings Against Carbon Steel Atmospheric Corrosion in the SO2 Presence

The protective properties of the compositions on base of the industrial oil or transformic one and oilsoluble inhibitor IFHAN 29-A (the product of the catalytic interaction between tall oil production waste and higher aliphatic amines) have been studied with respect to carbon steel in the atmosphere containing 0.1 – 10 vol.% SO₂ at the different humidity (70 – 100%) and room temperature.

IFHAN 29-A shows the thickening ability with respect to  industrial and transformic oils in the 293 – 353K temperature range. It allows to deposit the oil coating films of 20 ± 5 μm thickness on the metal surface. These films provide a protection of carbon steel against atmospheric corrosion in the presence of SO₂.  A growth of the inhibitor concentration in the oil composition film results a sharp increase of the protective efficiency in the presence of SO₂ in comparison with the conditions without  SO₂. The oil nature doesn’t practically influence on the qualitative and quantitative character of the dependences. Protective efficience of the oil compositions reaches 80%.

Kinetics of the cathodic and anodic processes on steel has been investigated in the 0.5 M NaCl solutions in the presence of SO₂. A growth of the SO₂ volume concentration in the air phase increases the cathodic limiting diffusion current density  in the absence of the protective oil composition film on the electrode surface, but does not practically influnce in the presence of the coating. A dependence of the anodic ionisation rate on the SO₂ concentration in the presence of the protective oil composition film has an unmonotonous character.

      The observed results are discussed with taking into account an interaction between SO₂ and water leading to a formation of the SO₂^.H₂O hydrate and the [SO₂]/[H₂SO₃]  correlation equal to 20 in the aqueous solution.