Identifying phases in protective scale formed during high temperature corrosion

Identification of the layout of phases produced on silicon-containing steel exposed to heavy cuts of crude oil during high temperature refining service provides an indication of the inherent passivation available from the overall system and is a gauge of long term reliability. By characterizing the corrosion scale on a pipe corroding at negligible rates, we have identified the phases and their layout needed for adequate passivation, namely an appreciable content of the iron sulphide phase troilite in the bulk of the scale coupled with a compact and continuous layer of magnetite between the sulphide layer and the steel.