Abstract
Water treatment systems used to recycle produced water and/or make-up water for the production of steam used in the SAGD and CSS processes have noted failures associated with erosion-corrosion, under deposit corrosion, and fouling/scaling. Oil sands operators employ corrosion monitoring tools, chemical treatment, and/or material selection to resolve integrity related issues. However, the unpredictable occurrences of serious corrosion issues related to the complex and constantly changing water chemistries make it difficult to choose the appropriate preventative and mitigation strategies. This is further complicated by the effects of operating conditions; such as temperature, pressure, and flow geometry. This paper presents the corrosivity of model/simulated produced and make-up (brackish) water to UNS G10180 carbon steel. Rotating cylinder electrode methodology was used to determine the general corrosion rates using linear polarization resistance technique.
The corrosion rate in the model brackish water system was low for the investigated environmental conditions. However, as the pH of the systems was reduced from 8 to 6, the corrosion rate became high (0.8 mm/yr). Similarly, dissolved oxygen (DO) ingress was found to increase the general corrosion rate. However, only DO = 8,000 ppb led to localized (pitting) corrosion (0.6 mm/yr). Contrary to model brackish water corrosivity, oxygen ingress as low as 120 ppb triggered localized corrosion in the simulated produced water system.
Introduction
Background
Water treatment systems used to recycle produced water and/or make-up water for the production of steam used in the SAGD and CSS processes have noted failures associated with erosion-corrosion, under deposit corrosion, and fouling/scaling. The corrosion control/ prevention strategies highly depend on the environmental conditions of the system, i.e. water chemistries and operating conditions. The approach to resolve the aforementioned integrity issues may involve improved monitoring capabilities, the use of corrosion control chemicals, and/or alternate materials. Oftentimes, the unpredictable occurrences of serious corrosion issues due to complex water chemistry make it difficult to choose the appropriate preventative and mitigation measures. This is further complicated by the effects of operating conditions; such as temperature, pressure, and flow dynamics on the equilibrium concentrations of the different corrosion influencing chemical species. Considering that the water chemistries are continually changing, it is beneficial to establish operating envelopes for the different chemical components and determine the effect of operating parameters such as flow velocity (wall shear stress), pressure, and temperature. Furthermore, a better understanding of the interactive effects of dissolved ions and gases in produced water is a necessary precursor for an effective integrity management program.
