A bench-top supercritical water reactor was constructed for the purposes of conducting
corrosion and fouling experiments. The reactor’s austenitic 316 stainless steel tubing was
exposed to ammoniacal ammonium sulfate solution under supercritical water oxidation
conditions to a maximum temperature of 500°C at 3600 PSI. Despite an initial pH of 10 at
25°C, the oxidizing ammoniacal solution led to severe alloy degradation within less than 40
minutes of exposure. Corrosion rates are estimated to be on the order of 140 to 560 mm.yr-1.
The reactor tubing was sectioned and the corrosion morphology and oxide composition was
analyzed. Homogeneous oxide films which were formed at lower temperatures appeared to
thin between 350 and 400°C. A bi-layered inner chromium and outer iron oxide formed at
temperatures between 110 and 310°C. At temperatures above 400°C the oxide appeared to
be mostly chromium oxide. The results of the morphological analysis were compared to
effluent analyses.
Key words: Corrosion, Supercritical Water Oxidation, Stainless Steel, Alloy 316, Ammonia,
Sulfate