Oxidation of steel T91 in flowing lead–bismuth eutectic (LBE) at 550 °C

This paper reports results of exposure experiments with martensitic steel T91 for 1200, 2998 and 5016 h in the CORRIDA loop. Owing to initial problems with the enrichment of oxygen in the circulating LBE, the conditions with respect to the oxygen activity (expressed as the activity of lead oxide, aPbO) varied significantly. At 550 °C, oxidation is the only mode of material degradation for T91 in flowing LBE (2 m/s) when the oxygen activity corresponds to 10−4 ⩽ aPbO ⩽ 10−2. The mean oxidation rate in the course of the first 1200 h approximates 0.13 mm/year. Lower oxygen activity in the LBE (10−6 ⩽ aPbO ⩽ 10−4) may be beneficial with respect to the oxidation rate, but undershooting a certain value around the threshold for Fe3O4 stability (aPbO = 10−5.2) poses the risk of liquid–metal attack accompanied by high local material consumption. The composition and structure of the oxide scales on the surface of T91 are analysed and a mechanism for scale growth initiating from oxide nuclei of various compositions is proposed.