Paraffins are one of the most common components in crude oil. Paraffin wax can generate corrosion inhibition by wax formation on the internal surface of the pipeline, reducing the corrosion. Furthermore, paraffin wax is believed to have effects on wettability of steel as well as the interfacial tension of oil and water, with consequent positive effect on the internal pipeline corrosion.
The objective of the study is to experimentally investigate the effect of paraffins on CO2 corrosion rate, wettability and interfacial tension in an oil-water system. Furthermore, the goal was to develop a thermodynamic model to predict the wax appearance temperature (WAT) theoretically.
The corrosion inhibition measurements, contact angle measurements and interfacial tension measurements were conducted at two different temperatures, 30°C (above the WAT) and 5°C (below the WAT), using a synthetic paraffin-oil mixture which is composed of LVT200 and a laboratory grade n-paraffin called Eicosane [CH3(CH2)18CH3] at different concentration, ranging from 0 to 50 wt%. A model for predicting wax precipitation was proposed by applying thermodynamic principles, mass balances and computational methods.
It is found that paraffins produce significant corrosion inhibition at temperatures below the WAT. Paraffins change the wettability of steel surface from being hydrophilic to hydrophobic when the temperature is below the WAT. A new thermodynamic model for predicting wax precipitation was proposed and agrees rather well with experimental results for synthetic normal paraffin oils.