We examined the fouling and corrosion that took place when 316 stainless steel and pure iron wires were electrically heated to 540À680°C in a liquid bath of the atmospheric bottoms fraction of a crude oil. The foulant was determined to be heterogeneous, with a thick macroscale outer layer of pitch, covering a microscale sheath of coke, which was in turn both covering and interspersed with a microscale layer of iron sulfide. This foulant was observed to delaminate from the wire surface, presumably as a result of both the generation of growth stresses and the action of gas bubbles that were evolved during the fouling process. Unexpectedly but conclusively, we observed that the underlying wire surface was heavily corroded. In the case of the stainless steel, we observed a microscale chromium oxide layer that separated the foulant from the underlying metal. This layer presumably reduced the rate of metal dissolution. The degree of corrosion was much higher in the pure iron samples, where such a layer did not exist. Our hypothesis is that there is a synergy between the measured macroscopic fouling and the underlying microscopic corrosion, where the iron from the wire reacts with the sulfur in the oil to build up the thick sulfide.

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In this study, we examine the link between stability of asphaltenes at ambient conditions with fouling at the conditions of a delayed coker furnace, with heat-transfer surfaces above 450 °C. The atmospheric bottom fraction of a crude oil was blended with an aliphatic diluent in different ratios; the S values were measured; and then fouling rates were measured on electrically heated stainless-steel 316 wires in an autoclave reactor. As expected, the less stable the blend, the greater the rate and extent of fouling. The most severe fouling occurred with the unstable asphaltenes. Scanning electron microscopy (SEM) imaging of the foulant illustrates very different textures, with the structure becoming more porous with lower stability. Under crosspolarized light, the coke shows the presence of mesophase in the foulant layer. These data suggest a correlation between the fouling rate at high-temperature furnace conditions and the stability index of the crude oil.

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