The effect of aerobic corrosion on anaerobically-formed sulfide layers on carbon steel in dilute near-neutral pH saline solutions

The aerobic corrosion of pipeline steel was investigated in an aqueous sulfide solution by monitoring the corrosion potential and periodically measuring the polarization resistance. The properties and composition of the corrosion product deposits formed were determined using scanning electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy. The establishment of aerobic conditions leads to corrosion and (oxyhydr)oxide deposition beneath the anaerobically-formed mackinawite film originally present on the steel surface. This leads to blistering and spalling of the sulfide film. Chemical conversion of the mackinawite to Fe(III) (oxyhydr)oxides also occurs but is a relatively slow reaction.