Abstract
The rotating cage (RC) has been widely used for evaluating the performance of corrosion inhibitors in CO2 and H2S containing systems at high temperatures and pressures, under flow conditions. The RC methodology has several practical advantages for assessing uniform and localized corrosion, and has shown to be a more stringent test than others typically used, since some inhibitors (at a given concentration) loose effectiveness beyond a critical flow intensity.
Wall shear stress (WSS), which could be related to mass-transfer coefficient, is typically used to establish the appropriate RC velocity for simulating a field condition (e.g., pipe flow). The empirical equation included in ASTM G170-06 is commonly used for calculating the WSS of RC under homogeneous flow. However, it has been shown using Computational Fluid Dynamic (CFD) calculations and experimental measurement that the WSS can vary significantly with the RC geometry and the location on each of the coupons mounted in the RC. This paper presents preliminary CFD and experimental results from a systematic study designed to show how the above mentioned empirical RC equation correlates with the average or maximum WSS on the rotating coupons, at different conditions.
