We examined the fouling and corrosion that took place when 316 stainless steel and pure iron wires were electrically heated to 540-680�C in a liquid bath of the atmospheric bottoms fraction of a crude oil.  The foulant was determined to be heterogeneous, with a thick macro-scale outer layer of pitch, covering a micro-scale sheath of coke, which was in turn both covering and interspersed with a micro-scale layer of iron sulfide.  This foulant was observed to delaminate from the wire surface, presumably both due to the generation of growth stresses and due to 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 micro-scale 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.

Corrosion-fouling of 316 stainless steel and pure iron by hot oil

245th National Meeting (2013)

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