Erosion-corrosion in a pipe system often ocurs at fittings, valves and weld beads where flow separation and reattachment yield high turbulence intensity. Thus identifying their correlations would be the first step towards resolving the erosion-corrosion problems associated with industrial applications. In an earlier work, we proposed that a rotating cylinder with surface roughness (two backward-facing steps periodically mounted on a circular cylinder) be an economical and tractable tool which can generate extreme flow conditionsfor erosion corrosion study. The aim of this paper is to elucidate the flow characteristics associated with this particular configuration. The numerical result shows that a region of intense turbulence intensity and high wall-shear stress fluctuation is formed along the cylinder surface in the recirculating region downstream of the step, where high mass-transfer capacity is also experimentally observed. Since corrosion is mass transfer controlled, our finding sheds light on the direction of future corrosion research.