Electrochemical behavior of metallic materials exposed to wastewater effluent

Purpose In this paper, the effects of electro-flocculation of the wastewater obtained from oil refinery distillation unit on the corrosion of three carbon steels and cupronickel alloy were analyzed by electrochemical methods. Design/methodology/approach Samples of each metallic material were individually exposed to wastewater effluent at 0 rpm, 2000 rpm, 20°C, 35°C and 45°C. The metallic materials were exposed to wastewater and evaluated by impedance spectroscopy, polarization curves, scanning electron microcopy and X-ray diffraction (XRD) patterns, before and after the electro-flocculation. Findings 1018 and X52 steels showed higher corrosion resistance in wastewater before and after electro-flocculation at 0 rpm and 35°C, while cupronickel alloy passed to passive and to active state or re-passive process, respectively, after electro-flocculation, at 2000 rpm and 45°C. XRD patterns and electrochemical testing on X80 steel revealed that before electro-flocculation, localized corrosion effect was performed, while after electro-flocculation predominated the general corrosion with evidence of iron sulfides. Practical implications Low carbon steels, such as API steels, as well as cupronickel alloy can be attacked by wastewater, causing serious corrosive problems in refineries equipment and pipelines. The electro-flocculation is a good tool with real application for metallic materials in similar wastewater environments. Originality/value The electro-flocculation of the wastewater is a really important electrochemical treatment for the corrosion control of the refineries equipment and pipelines. It can diminish aggressiveness of corrosive species and semi-protective thin films of iron sulfides might form on metal surface.