AC Induced Corrosion of Carbon Steel in 3.5wt% NaCl Electrolyte

Abstract

This paper deals with alternating current (AC) corrosion of low alloy carbon steel in 3.5 wt% NaCl electrolyte. Accelerated corrosion rates have been reported when exposed to AC and the corrosion mechanism is not well understood. Electrical heating of subsea pipelines, applied to avoid hydrate formation and waxing of multiphase hydrocarbon well streams has made this topic increasingly relevant in recent years. To study the effect of AC on corrosion rates, weight loss experiments under a wide range of experimental conditions were performed. Results show that AC strongly influence corrosion kinetics of the system studied. Once AC is applied, a drop in corrosion potential and the formation of a passive iron oxide surface layer is observed. This layer is porous and believed to be the result of a rapid surface alkalization. Pitting corrosion is observed for all applied AC densities at open circuit. Weight loss- and LPR measurements conform well and the use of this technique in the presence of AC is on this basis considered valid. Corrosion rates increase as applied level of AC is increased and an approximately linear relationship has been established between iAC and icorr.