Corrosion inhibition assessment on API 5L X70 steel by preussomerin G immersed in saline and saline acetic

The spirodioxynaphthalene preussomerin G, obtained from the fungus Pyrenochaetopsis sp. T1-41 (Plesosporales), was evaluated as a corrosion inhibitor in API 5L X70 steel samples. According to the electrochemical impedance spectroscopy and polarization curves analysis, the natural product showed good corrosion inhibition properties under static conditions in two corrosive media. The maximum efficiency (η = 91%) was obtained in the NaCl 3% medium with a 5-ppm inhibitor concentration. In the NaCl 5% w/v-glacial acetic acid 0.5% v/v medium, the charge transfer resistance value decreased, and the inhibition efficiency was 75%. In addition, the polarization curves show that preussomerin G behaves as an anodic inhibitor in the saline medium but presents mixed (anodic/cathodic) characteristics in the saline-acetic medium. Moreover, the thermodynamic analysis indicates that preussomerin G is adsorbed onto the steel surface via chemisorption, according to the Langmuir isotherm. According to a dispersion-corrected density functional theory study, at the BPW91-D2/6-311++G(2d,2p) level, ether and carbonyl groups bond with the metal surface. Finally, the surface analysis by scanning electron microscopy shows that the corrosion in API 5L X70 steel decreased in the presence preussomerin G.HighlightsPreussomerin G showed good corrosion inhibition properties under static conditions in two corrosive media.The adsorption of preussomerin G onto the steel surface via chemisorption obeys the Langmuir isotherm.Ether and carbonyl groups are responsible of the chemisorption of preussomerin G onto the metal surface.Preussomerin G provides an almost inert protective cover, towards nucleophilic and electrophilic attacks, to the metal surface.