Inhibition of pitting corrosion of C-steel in oilfield-produced water using some purine derivatives

The pitting corrosion current of C-steel in 50% diluted oilfield-produced water devoid of and containing various amounts of some purine inhibitors, 9H-purine-2,6-diamine, Inh I, 9H-purin-6-amine, Inh II, and 2-amino-1H-purin-6(9H)-one, Inh III was followed under natural corrosion conditions. In the inhibitor-free solution, the pitting corrosion current starts to initiate after an induction period, tau which extends to similar to 40 min and propagates to reach a steady-state current, I-S. In the presence of an inhibitor, the induction period increases with a decrease in the I-S values that depends on the inhibitor type, concentration, and temperature. The surface coverage, theta, and the inhibition efficiency, eta, were found to depend on the inhibitor type and its concentration, and decreased with temperature. The inhibition mechanism is supposed to occur through an adsorption process obeying Langmuir's model. The scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize and analyze the elements of the C-steel surface. Some thermodynamic parameters of the adsorption process such as K-ads and Delta G degrees(ads) are calculated and discussed.