Abstract
The corrosion behavior of oilfield used L245N standard steel was tested in simulated oilfield solution by dynamic high-temperature autoclave. The corrosion products were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Electrochemical impedance spectroscopy (EIS) respectively. In addition, the corrosion rates and surface morphological characteristics of the steels after different exposure times were studied. The results showed that the corrosion rate decreased sharply and then increased with time in the high salinity flow solution, which was related to the formation of corrosion scale and the remaining cementite within it. At the beginning of the exposure time, the formed corrosion scale became thicker, resulting in a significant decrease of the corrosion rate. While with increasing time, on the one hand, the increased remaining cementite within corrosion scale facilitated the corrosion by the galvanic corrosion between the remaining cementite and the ferrite within the metal. On the other hand, the protective effect of corrosion scale formed on the remaining cementite skeleton declined due to the formation of large amounts of FexCa1−xCO3, which also promoted the corrosion rate of the steels, both these ways contributed to a slow increase of corrosion rate.
Highlights
20# carbon steel has been widely used as the oilfield pipeline material
Other reports found that pitting corrosion was not observed at any salt concentration, and that the corrosion rate decreased with increasing salt concentrations [11]
The oil content affected the corrosion of carbon steel, because the existence of oil phase was beneficial to the cathodic partial to promote the corrosion process [12]
Summary
20# carbon steel has been widely used as the oilfield pipeline material. The designed service life of these oilfield pipelines should be 5–8 years. The high oilfield brine caused perforation by serious corrosion of the carbon steel [4]. Other reports found that pitting corrosion was not observed at any salt concentration, and that the corrosion rate decreased with increasing salt concentrations [11]. The loose corrosion scale formed by the effect of Ca2+ ions decreased the protective effect and increased the corrosion rate [15,16]. The effect of Fe3C on the corrosion process of carbon steel has been studied. The effect of Ca2+ ions and the remaining cementite on the corrosion mechanism in the flow environment is not fully understood. The present work aims to investigate the corrosion behavior of carbon steel in simulated flow oilfield water. The corrosion scale and metal surface morphology evolution were evaluated by SEM, XRD, EIS and a white light interferometer
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