Abstract

The oil and gas industry has a severe problem with chemical corrosion and microbial contamination of pipelines and infrastructure. The main source of the chemical corrosion is the water that used in digging the crude oil from the ground. It is estimated that the water content in the extracted oil can reach up to 30% in the pipeline. The principal factor in the corrosion of carbon steel in crude oil pipelines is the presence of water.

The objective of this work is to identify the corrosion products of the carbon steel pipelines and elucidate the mechanisms and the rate of their formation at various temperatures. The observed corrosion rates increase in three distinct modes dominated by the formation of different corrosion products: lepidocrocite below 35 °C, corrosion-inhibiting goethite and hematite between 35 °C and 45 °C, and magnetite at temperatures greater than 45 °C. The XPS data shows that at 25 °C the concentration of OH− species appears to be higher than the concentration of O2− species in the corrosion products formed. However, all temperatures above 25 °C showed higher concentrations of O2- species with the highest ratio values at 65 °C (O-2/OH− = 1.17) and 75 °C (O-2/OH− = 1.03). Based on the electrochemical results, this work shows that the corrosion is anodically controlled (charge-transfer controlled) at 25 ˚C-45 oC, and the cathodic reaction is diffusion controlled. Since both the anodic and cathodic reactions are activation and diffusion controlled, it is concluded that the corrosion process of this system is mixed controlled. This work also shows that as the flow rate of the electrolyte increases, the observed measured activation energy for the overall corrosion processes increases.

Finally, this study also shows while the corrosion rate of carbon steel in a mixture of (70% vol. crude oil /30% vol. seawater) decreases, on the contrary, the pitting corrosion increases, due to the adsorption of the nitrogen and oxygen-containing compounds on the metal surface, and the establishing of localized concentrated Cl− ions, respectively.