Understanding how various factors interact and affect materials performance and the kinetics of surface scaling process is essential in order to design scaling tests that minimize experimental variations and best simulate actual service conditions in a given environment. Major studies on scale has been based on thermodynamic considerations in the bulk while the few kinetic studies on surface have been off line and in static condition that did not give a real understanding of the real process. In studies carried out in closed system the saturation ratio will decrease with time as a result of reduction in ionic species with precipitation and the conclusion regarding faster kinetics promoting more scale in the bulk cannot be made for longer periods of time. The previous study on the newly developed once through in-situ flow rig has shown that surface scaling is not always a result of pre precipitated crystals in the bulk in contrast to popular assumption thereby necessitating further assessment of the mechanisms and kinetics of surface scaling.In this study the kinetics and mechanisms of CaCO3 growth are evaluated at different SR with and without inhibitors using 2ppm of PPCA. Brines with different saturation ratios (SR) 10 15 25 45 and 60 at 250C were tested. The residence time from mixing point to sample was shorter than the induction time for bulk precipitation and as a result there are no crystals in the bulk solution as the flow passes the sample. Also brine with SR = 70 having bulk particles was also tested. The rig is a once through flow system where saturation was always kept constant. The dynamic condition of changing between SR and inhibitors were also tested to simulate conditions in oil field where saturation and inhibitor concentration may change. The results showed that surface nucleation depends on the number as well as the quality of active nucleation sites a factor influenced by change in SR while the growth rate and mechanisms of surface and bulk are affected differently with inhibitors addition.