Comparison of Rotating Cylinder and Loop Methods for Testing CO2 corrosion inhibitors
S.Nesic, G. T. Solvi and S. Skjerve

A study was carried out to investigate the effect of various hydrodynamic parameters on the corrosion rate of low carbon steel in CO2 environments in the presence of inhibitors. Two different flow geometries, rotating cylinder and pipe flow, were situated simultaneously in the same electrolyte within a glass loop. Comparisons were also carried out at room temperature, pH 4 -6, partial pressure of CO2 1 bar, and velocity 0 - 13 m s -1. the hydrodynamic conditions studied cover the range from stagnant to highly turbulent flow.The corrosion process was monitored using polarisation resistance, potentiodynamic sweep and electro chemical impedance. Comparison of the two flow geometries was carried out in terms of the hydrodynamics, mass transfer rates, CO2 corrosion rates, and corrosion mechanisms.The mesured mass transfer rates were found to agree well with previously published correlations for the rotating and straight pipe flow. In the case of CO2 corrosion without inhibitors, it was possible to achieve good agreement between corrosion rates in the two flow geometries by ensuring the same water chemistry and mass transfer conditions.This conclusion is valid for the case when no protective corrosion product or scale is present. With inhibitors present, the performance of both amine and iniadazoline based inhibitors measured using the rotating cylinder was identical to that in the straight pipe flow geaometry. The performance of the inhibitors was not significantly affected by flowrate in the range 2 - 10 m s-1(corresponding to shear stresses of 13 and 222 Pa respectively).

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