Abstract
Crude oil composition is highly variable and complex. Its components can be broken down into four different classes by solubility characteristics such as: saturates, aromatics, resins, and asphaltenes. Within each class are myriad of chemical compounds, and many have the potential to interact with the pipeline wall to confer protection from corrosion. In this work the focus is on saturates, with the the n-paraffins chosen as being most relevant for the purposes of the present study. A representative pure model compound for the n-paraffins used in the experiments is eicosane (C20H42). A mixture of eicosane and a clear, inert model oil was prepared with a range of paraffin concentrations (0 – 50% eicosane). The chemical properties of the mixture were measured, including the Wax Appearance Temperature (WAT), density, viscosity and interfacial tension. The CO2 corrosion rate for carbon steel was measured both below and above the WAT, using the linear polarization resistance (LPR) technique. The protectiveness of the long-chain paraffin layer was challenged by inducing flow (hydrodynamic shear stress) and by increasing temperature. The eicosane successfully conferred corrosion retardation at temperatures below the WAT; however, this protection did not withstand the effect of shear stress or increased temperature. Further analysis by using sessile drop contact angle measurements using a goniometer revealed that the protectiveness by the eicosane is related to changes in the wettability of the surface. The hydrophobicity of the steel surface increased as the concentration of the paraffins in the synthetic paraffin-oil mixture was increased.
