Effect of Sulfide on Carbon Steel Corrosion in Anaerobic Near-Neutral pH Saline Solutions

Abstract

Severe corrosion damage may occur when gas transmission pipelines are exposed, at disbonded coating locations, to trapped waters containing sulfide. This scenario has been investigated in long-term anaerobic experiments in which corrosion was followed by measurement of corrosion potentials and relative corrosion rates obtained from linear polarization resistance measurements. The properties and composition of the corrosion product deposits formed were determined using scanning electron microscopy, energy-dispersive x-ray analysis, and Raman spectroscopy. Under anaerobic conditions, corrosion rates were lower for freshly polished steel than for precorroded carbon steel exposed to sulfide, suggesting pre-oxidization of the steel surface prevents passivation in the presence of sulfide. Under these last conditions, a non-protective layer of mackinawite forms on the surface and magnetite/maghemite are chemically converted to sulfide and sulfur, leading to a slow increase in corrosion rate.