This paper reports findings from an investigation into the effect of flow rate and organic inhibitor on the
material performance, film thickness and hardness of protective scales formed on X65 carbon steel
surface in a rotating cylinder electrode (RCE) system. The experiments were conducted at a
temperature of 70 °C, pH of 5.9 and 4.5 g/cm.s2 wall shear stress (tw) using both uninhibited and
inhibited Forties brine with 25 ppm of inhibitor saturated with carbon dioxide (CO2) containing 0.1%
HST60 PSA silica sand, which can be described as semi-spherical with sharp edges. Weight gain/loss
was measured for: as-received X65 specimens and specimens before and after removing corrosion
scales in both uninhibited and inhibited systems. In addition, the hardness of the surface specimens
and scales was measured using a nano-indenter. This was supported by post-test analysis of samples
using scanning electron microscopy (SEM), focus ion beam SEM (FIBSEM), energy dispersive X-ray
spectroscopy (EDX) to assess the nature, the thickness, the elemental composition and the possible
salts forming these protective films. It was found that the weight loss of as-received surfaces was
reduced by more than 43% when 25 ppm of inhibitor was introduced. Nevertheless, inhibitor was found
not to be effective in reducing weight loss of pre-scaled surfaces.
Key words: inhibitor, hardness, iron carbonate, CO2 and sand.