Polyvinyl pyrrolidone as a green corrosion inhibitor for carbon steel in alkaline solutions containing NaCl

Purpose - The purpose of this paper is to study the corrosion inhibition of carbon steel (CS) using a "green" inhibitor, polyvinyl pyrrolidone (PVP), in an aerated, alkaline medium containing 0.1M NaCl (blank) at pH 9 and pH 10. The effects of some additives, such as KI and untreated Saudi clay (UC) were investigated. Design/methodology/approach - Weight loss method, surface studies, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation were applied. Findings - The inhibition efficiencies of blank solutions with 1000 ppm PVP ranged from 66-78% for weight loss results and from 23-66% for the electrochemical tests. The EIS results indicated that the adsorption of PVP led to the formation of a protective film on the metal/solution interface. Tafel results indicated that PVP is a mixed-type inhibitor. The addition of KI to PVP and the blank solution significantly increased inhibition efficiency, while the addition of UC reduced the inhibition efficiency. Adding KI resulted in a high surface-area coverage ranging from about 91% after one hour to about 81% after 45 hours. The adsorption mechanism was fitted with a Langmuir isotherm. Research limitations/implications - This is a static study, whereas in oil drilling there is a dynamic system; however the findings may apply to both systems. Practical implications - Carbon steel is used in alkaline and neutral media in the petroleum industry. The effect of KI additives was examined. Social implications - The paper shows how it may be possible to reduce the cost of repair of equipment and lower the environmental impact of corrosion. Originality/value - There are few studies which investigate the combining effect of polymer and KI in alkaline medium containing NaCl.