There are several chemical plants along the river Rhine that use river water as coolant in once through-systems. Microbially Influenced Corrosion (MIC) failures occur on stainless steel pipes and also in heat exchanger tubes coming in contact with this cooling water. This paper presents results of failure analysis of three case histories suspected to be caused by MIC. Afterwards several important corrosion engineering aspects are presented and discussed with respect to practical observations. Finally, a summary of the case histories and also some practical recommendations for MIC prevention in water handling units are given. Keywords: Microbially Influenced Corrosion, process water, pitting, heat tints, deposits, scaling, anion-selective precipitates, crevice corrosion, electrochemistry