Abstract
The initiation and inhibition of the localized pitting corrosion on the C-steel surface in oilfield produced water are investigated by pitting corrosion current measurements. The current-time curves are characterized by the appearance of an induction period, tau followed by a rapid rise in the pitting corrosion current till reaches the limiting value, IL, due to propagation of pitting corrosion. The IL value reaches 5.0 mu A cm(-2) in 99% diluted oilfield-produced water and 260 mu A cm(-2) in pure oilfield-produced water. The presence of HPO4-2, WO4-2, and MoO4-2 anions suppresses the initiated current by elongation of the induction time, tau. Such anions acted as inhibitors towards the pitting corrosion of the C-steel. The inhibition efficiency, eta, of the studied inhibitors increases in the following order: Na2WO4 < Na2MoO4 < Na2HPO4. The inhibition mechanism is assumed to take place through an adsorption process obeying Langmuir's model. The thermodynamic parameters for the adsorption process K-ads and Delta G degrees(ads) are calculated and discussed.