Flow Accelerated Corrosion of titanium alloys in water at 300 °C and 15 MPa
Abstract
Corrosion of titanium alloys in pressurized water at 300 °C, 15 MPa, pH300 °C = 7.2 follows a flow acceleration corrosion mechanism between 0 m.s-1 and 8 m.s-1. At low water velocity (0 m.s-1 or 10-3 m.s-1), the evacuation rate of titanium hydroxides away from the samples is low, the concentration of titanium hydroxides in the vicinity of the TiO2 layer is high, which limits the dissolution rate. The increase in the water velocity up to 8 m.s-1 increases both the corrosion rate (from ~1 µm/yr to ~10 µm/yr) and the fraction of oxidized titanium that is moved away from the samples (from ~0.3 to ~0.8). When titanium alloys are used in association with stainless steel, the increase of water velocity also accelerates the coverage of the TiO2 layer by FeTiO3 ilmenite crystallites, which protect the titanium alloys from further corrosion as long as the corresponding product of solubility is maintained in the water.