11265 New Method For Assessing Corrosion Under Iron Sulfide Deposits and CO2/H2S Conditions

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Product Number: 51300-11265-SG

ISBN: 2011 11265 CP

Author: C. M. Menendez, V. Jovancicevic, S. Ramachandran, M. Morton, D. Stegmann

Publication Date: 2011

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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). The UDC mechanism is dependent upon the local operating conditions, such as gas composition, conditions of fluid flow, and solid content of the fluids. In this work, a new monitoring method was developed to study the corrosion that occurs under a relatively thick layer of deposits. 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 localized corrosion monitoring and optical profiling was employed to evaluate the corrosion attack under the deposits. Optical profiling was found to be beneficial to quantify localized and general corrosion attack in the absence of electrochemical corrosion rate monitoring. It was determined that mackinawite precipitation from the bulk solution is the best method for reproducing localized corrosion morphology observed in the field. 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.

Keywords: Oilfield, under-deposit corrosion, iron sulfide deposits, sour conditions.