In part two of this two-part series, we further explore the comprehensive mechanistic CO2 corrosion model developed in part one by examining how the changing hydrodynamics influence the system at various bulk pHs. Parametric studies are conducted over the model over an extensive range of fluid velocities, pipe diameters, and bulk pH values. Contour plots are produced showing the variation in key outputs, including the boundary layer properties, corrosion rate, surface pH, and surface saturation ratio with respect to iron carbonate (FeCO3).
Changes to the behavior of the system were found to be strongly correlated with the thickness of the boundary layer, determined by the Reynolds number in the bulk flow and the diameter of the pipe. Thinning of the boundary layer was found to result in greater rates of species transport through the boundary layer, accelerating the mass-transport limited surface reactions and reducing the deviation between the bulk and surface concentrations. Hydrodynamic influences were found to be consistent across varying bulk pH conditions, indicating a separation of the effect of flow conditions from the fluid chemistry. The observed trends are discussed in detail in relation to the real-world behavior of fluid flow to improve the understanding of the connection between hydrodynamics and the corrosion process.
It is well known that the hydrodynamics of fluid flow directly influences the corrosion process, as shown in various experiments utilizing rotating electrodes1, 2 and flow loops3-6 to measure corrosion within turbulent flow. However, when fluid is flowing through a pipe, there is a phenomenon known as the ‘no-slip condition’ which causes the velocity of the fluid to tend to zero as it reaches the wall.7 For straight pipe flow, this follows the ‘universal law of the wall’ (Figure 1) which separates flow into 3 domains: fully turbulent flow, the buffer layer, and the viscous sublayer (also known as the boundary layer) which is the being modelled here.
