ИССЛЕДОВАНИЕ ВНУТРЕННЕЙ ПОВЕРХНОСТИ ТРУБОПРОВОДА СИСТЕМЫ НЕФТЕСБОРА СЕВЕРО-КРАСНОЯРСКОГО МЕСТОРОЖДЕНИЯ

Abstract

Background It is known that the presence in oil of a non-polar phase is an important factor of corrosion in heterogeneous media. Hydrocarbon phase, almost inert to metal at low temperatures, accumulates hydrogen sulfide in higher amounts, in comparison with the aqueous phase. This increases the potential aggressiveness of a heterogeneous system as a whole, and promotes diffusion of aggressive agents and maintenance of their high concentrations at the «metal - electrolyte» interface. This results in the intensive processes of electrochemical destruction and hydrogenation of the metal. Aims and Objectives To identify the causes of metal destruction along the lower generatrix of the internal surface of oil gathering pipeline in the Northern Krasnoyarsk field. To determine the corrosion rate of the base metal and metal in the bottom of the pit by plottig polarization curves. Methods Laboratory electrochemical corrosion tests were carried out using a held-down cell. Values of potential, corrosion current density and corrosion rate were measured using potentiostat. We used the three-electrode electrochemical system in which a sample cut from the pipeline spool was the working electrode and the platinum and silver chloride reference electrodes were supporting ones. Nitrogen purging of the medium was carried out. Polarization curves were recorded in potentiodynamic mode after two hours of the working electrode exposure to corrosive environment. The rate of corrosion was measured by means of potentiostat in compliance with the method of linear polarization resistance. Results Obtained polarization curves showed that the corrosion rate of base metal was 0.11 mm/year, and the rate of corrosion at the bottom of the pit was 3.45 mm/year. The authors suggest that the accelerated pitting of equipment could be caused by that the corrosion inhibitor could not get to the metal surface due to deposition of the heavy fraction of liquid hydrocarbons at low flow rates. Pilot tests demonstrated that the cleaning of pipelines from deposits and corrosion products, and subsequent inhibition resulted in a significant reduction of the pitting corrosion.