Evaluation of Zn Sacrificial Anodes Performance to Protect Carbon Steel in the Presence of Crude Oil and Produced Water

Abstract The present work evaluated the performance of zinc anodes, new and used samples already exposed to oil, presenting an adherent deposit layer, in three different media to simulate environments where protection systems from oil storage tanks are exposed: (i) produced water, (ii) crude oil, and (iii) a mixture of 10%v/v crude oil and 90%v/v produced water after intense agitation for 24 hours. The anode performances were evaluated through open circuit potentials (OCP) of zinc anodes throughout 30 days, zero resistance ammeter (ZRA) for the galvanic pair (zinc/X65 steel) and potentiodynamic polarizations. Results did not point out significant differences between the new and used anodes, as they provided relatively high current densities, despite the existence of scales on the surface of the aged one. Regarding medium evaluation, it was confirmed by ZRA analysis that samples immersed in crude oil could not be protected, if required, because ionic current could not flow through such a resistive material, yielding current densities below -10-9 A/cm2. On the other hand, within high salinity it produced current densities higher than 1.5x10-5A/cm2 even in the mixture between produced water and oil, indicating that the protection efficiency is highly dependent on the instantaneous condition the galvanic pair is immersed in.