Corrosion inhibitive effect of organic dyestuffs towards API 5L X56 steel and its structural features evaluation

Abstract

This paper presents a report on the corrosion resistance behaviour of organic corrosion inhibitors like titan yellow (1) and hydroxyl naphthol blue (2) on API 5L X56 steel in 3.5% NaCl as a corrosive medium. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation methods were used in the investigation. The protective film-forming tendency of inhibitor 1 and 2 on steel surfaces was confirmed from scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The quantity of metallic iron dissolved in the corroding medium was validated through inductively coupled plasma–optical emission spectrometry. The adsorption behaviour of inhibitors 1 and 2 on steel surfaces in a corrosive environment follows the Langmuir isotherm. The electrochemical impedance spectroscopy and potentiodynamic polarisation results indicate that both 1 and 2 act as inhibitors in 3.5 wt.% NaCl solution. Further, an increase in the water contact angle as well as a decrease in iron content in the solution by inductively coupled plasma–optical emission spectrometry explains the corrosion resistance behaviour of the steel towards the protection of underground pipelines, and industrial equipment.