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In the article “Corrosion-Fouling of 316 Stainless Steel and Pure Iron by Hot Oil,” the authors investigate how high-temperature crude oil environments affect 316 stainless steel and pure iron surfaces. Wires of both metals were electrically heated to 540–680 °C in a bath of the atmospheric bottoms fraction of crude oil to simulate conditions relevant to heat exchange and refinery equipment. The researchers found that the foulant forming on these surfaces was a complex, heterogeneous mixture: a thick outer layer of pitch overlies a coke sheath interspersed with iron sulfide. This deposit tended to delaminate, driven by stresses from growth and gas bubble evolution during the fouling process.
Unexpectedly, significant underlying corrosion of the metal surfaces was observed beneath the fouling layer. On the 316 stainless steel, a microscale chromium oxide layer was present between the foulant and the metal, which likely slowed metal dissolution. In contrast, the pure iron samples showed much greater corrosion since no protective oxide layer formed. The authors propose that there is a synergistic relationship between macroscopic fouling and microscopic corrosion: iron reacts with sulfur in the oil to form iron sulfide, which contributes to both the buildup of thick foulant and enhanced corrosion.
In the article “Sulfide Promoted Chronic Fouling in a Refinery: A Broad Phenomenon Spanning a Range of Heat Transfer Surfaces and Oil Types,” the authors examine how fouling develops on different refinery heat-transfer surfaces in the presence of sulfur-rich crude oils. Using advanced characterization tools (TEM, SEM, FIB, XRD), they exposed three representative alloys—carbon steel, a 9Cr–1Mo steel (P91), and a 347 stainless steel—to two crude oil blends at elevated surface and oil temperatures to mimic refinery preheater conditions. Across all materials tested, fouling begins with sulfidic corrosion of the metal surface, which then catalyzes organic coke formation and the buildup of complex fouling layers; this points to a mechanistic link between corrosion and subsequent organic deposition
Unexpected trends emerged: carbon steel, traditionally less corrosion-resistant, actually accumulated somewhat less fouling early on than the P91 alloy, likely because its poorly adherent sulfide layer tended to spall off, effectively “self-cleaning” the surface. 347 stainless steel, though more resistant to sulfidic attack, still developed a thin Fe–Cr–Mn inner sulfide and thicker Fe-rich outer sulfide, showing that even high-alloy materials are not immune under these conditions. The study also observed that fouling rates decreased in repeated tests on the same oil batch, which the authors attribute to the depletion of reactive sulfur species needed to sustain sulfide formation
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