Development of Controlled Hydrodynamic Techniques for Corrosion Testing

A systematic study was carried out to investigate the effect of hydrodynamic variables, such as flow rate and geometry, on the corrosion of 90/10 Cu-Ni alloy in 1 M sodium chloride solution at 25°C under the air-saturated condition. Three hydrodynamic geometries were investigated: a flow-through pipe system, an annular flow system, and a rotating cylinder system. Flow rates spanned the range from laminar flow to highly turbulent conditions, and all hydrodynamic conditions were characterized in terms of Reynolds and Schmidt numbers. Corrosion rates have been measured using small amplitude cyclic voltammetry (SACV), electrochemical impedance spectroscopy, and the direct weight loss method. Good agreement was obtained between SACV and electrochemical impedance techniques for measuring the polarization resistance, and the calculated weight losses were in reasonable agreement with the directly measured values. The corrosion rate measured in all three hydrodynamic systems was independent of the geometry involved when plotted as a function of mass transfer coefficient on a log-log scale. This implies that transfer of corrosion data from one hydrodynamic system to another can be achieved based on the mass transfer coefficient. The advantage of using the rotating cylinder system for the simulation of fluid velocity effects on materials degradation is also discussed.