[en] A loop operating under power reactor feedwater conditions is used to determine chemistry and flow effects in flow-accelerated corrosion (FAC) at 140 C in neutral and ammoniated water. Electrochemical corrosion potential (ECP) and corrosion rate are measured on-line; mechanisms are indicated through surface analyses. In this paper the results of several experiments are presented. In neutral water, FAC was mass transfer controlled, correlated to surface fluid shear stress and stifled at oxygen concentrations of about 40 μg . kg^-1. Chromium in the steel reduced FAC significantly. Corroded surfaces were covered with thin magnetite films and some developed typical ''scalloped'' textures related to oxide structures of underlying metal grains. In ammoniated water, pH_25C 9.15-9.35, FAC was halved, not clearly mass transfer controlled, and extremely sensitive to oxygen. It was stifled at 1-2 μg . kg^-1, apparently by a ''front'' of protective haematite-based oxide moving downstream as magnetite was progressively oxidised. The subsequent resumption of FAC when oxygen levels were reduced occurred at the upstream ends of probes. (orig.)