The Effect of Time on the Formation & Growth of Passive Layer on Carbon Steel A516 Gr. 70 in Sour Water

A proposed method for protecting carbon steel and hence reducing iron release in an aqueous solution saturated with H2S is presented in this paper. The method is based on forming a stable and resistant sulfide layer (pyrite, FeS2, or pyrrhotite, Fe(1-x)S, phase or a mixture of both) on the carbon steel surface. The study on the formation of the sulfide layer was carried out considering the effects of exposure time and surface status of the steel samples under conditions of static solution saturated with H2S. The sample weight was measured and the chemical composition of the sulfide layer produced was analyzed using the XRD (X-ray diffraction). The crystalline structure was identified by SEM (Scanning Electron Microscope) and EDAX analysis. The results showed that after a 12-day exposure time at a pressure of 15.7 bars and temperature of 130 oC, a passive layer including the pyrite phase was formed on various samples. In addition, the acid citric washed samples enjoyed a more coherence and layer thickness as compared other samples that had a different surface condition.