  We investigate calcium carbonate scale formation at high Reynolds numbers in
a large pipe rig facility. The calcium carbonate solution is produced from the
injection, at a T-joint inlet, of pH-stabilized sodium carbonate and calcium
chloride aqueous solutions. A scanning electron microscopy analysis of the
deposited mass along the pipe indicates that after an initial transient regime
of ion-by-ion crystal growth, calcium carbonate scale is dominated by
particulate deposition. While limescale formation in regions that are closer to
the pipe's entrance can be described as the heterogeneous surface nucleation of
calcium and carbonate ions driven by turbulent diffusion, we rely upon
turbophoresis phenomenology to devise a peculiarly simple kinetic model of
deposition at farther downstream regions. Letting $\Phi$ and $R$ be the flow
rate and the pipe's radius, respectively, the mass deposition rates per unit
time and unit area are predicted to scale as $\Phi^\alpha / R^\beta$ (for
certain modeled values of the $\alpha$ and $\beta$ parameters) with suggestive
support from our experiments.
