Characterizing and exploring the mechanism of formation of corrosion scales by reusing advanced-softened, silica-rich, oilfield-produced water (ASOW) in a steam-injection boiler: Characterizing and exploring the formation mechanism of corrosion scale

BACKGROUND: Corrosion scales, which very strongly affect the thermal efficiency and security of boilers, are formed on the furnace tubes of the radiant section during the process of reusing advanced-softened, silica-rich, oilfield-produced water (ASOW) as boiler feedwater in oilfields. To evaluate the reuse and to explore the composition and formation of corrosion scales a 16-month pilot-scale test was conducted. RESULTS: The silicon content and total hardness in the boiler feedwater were 238.93 mg L-1 and 0.031 mg L-1, respectively. Morphology and compositions of the corrosion scales were determined by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). These were measured both during the early stage of steam injection (ESSI) and the later stage of steam injection (LSSI). Iron oxides (Fe3O4, Fe2O3) were the main crystalline phases identified in the ESSI, while Acmite (NaFeSi2O6) was the primary crystalline phase in the LSSI. Based on the results, formation of the main corrosion scales are explained. CONCLUSION: It can be concluded that NaFeSi2O6 is the reaction product of Fe2O3, H2SiO3 (gas), and Na2CO3 in the saturated steam. These results can offer an important reference for reusing the ASOW as feedwater and for reducing the corrosion scales in steam-injection boiler. (C) 2016 Society of Chemical Industry