Temperature and condensation rate driven formation and stability of iron sulfide films in sour top of the line corrosion of X-65 pipeline steel

• K.A. Mohammed

Oil and Gas Department, College of Engineering, University of Thi-Qar, 64001, Iraq

Abstract: This study replicates realistic sour environments to explore how variations in gas temperature and water condensation rate (WCR) influence top of the line corrosion (TLC) of low alloy X-65 steel, as both are dependent on it. Experiments were conducted using a 10-liter stirred stainless steel autoclave specifically designed for TLC tests. The system operated at a total pressure of 3 MPa, with H₂S partial pressure maintained at 0.25 MPa. TLC rates were measured, and corrosion features were examined through weight loss analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results show that increased gas and steel surface temperatures promote the formation of compact iron sulfide (FeS) scales, improving corrosion resistance and minimizing TLC rates. Under most test conditions, Mackinawite-type sulfide layers formed consistently on the top parts of the samples. However, no substantial impact of water condensation on TLC was observed. These findings provide a valuable understanding of the protective behavior of FeS scales and provide a guide for optimizing operating conditions to mitigate TLC in field applications.

Keywords: gas temperature, steel temperature, water condensation rate, sour environment, top of the line corrosion

Int. J. Corros. Scale Inhib., 2025, 14, no. 3, 1347-1361
doi: 10.17675/2305-6894-2025-14-3-17

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