Assessment of Corrosion Under Iron Sulfide Deposits and CO₂/H₂S Conditions

The presence of surface deposits, such as sand, iron sulfide, or organic solids, in oil and gas production systems can lead to premature failure of fluid-handling equipment. When corrosion occurs under solid deposition, the process of corrosion is often referred to as under-deposit corrosion (UDC). Iron sulfide deposits obtained from various sources were characterized with respect to their particle size, crystalline structure, and surface composition using particle size analysis, x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). Autoclave testing in conjunction with optical profiling was used to evaluate the corrosion attack under the deposits. It was found that when lab-synthesized or in situ-precipitated mackinawite was deposited on a metal surface, significant general and localized corrosion was observed. This finding is important since it can explain localized corrosion observed in sour gas systems where iron sulfide is deposited.