Addition of halides (KCl, KBr and KI) to corrosion inhibitor systems is intended to enhance their inhibition efficiency due to the synergetic effect. Halides ions have been proven to be good corrosion inhibitor intensifiers in acidic or basic media and for both steel and aluminum. The halides ions themselves act as corrosion inhibitors. This paper sheds lights on some limitations of halides ions (Cl and Br) in HCl acid solutions for low carbon steel. The inhibition performance of halides ions as a function of temperature, soaking time and acid concentration was investigated using the gravimetric method. A synthesized diamine corrosion inhibitor was used in this study and the synergetic effect with halides ions was investigated. The testing conditions included HCl acid concentrations of 15 and 28 wt%, soaking time of 1, 2, 4 and 6 hours, and temperatures of 60 and 80 and 104°C.

The results revealed that the synergetic effect of Cl and Br ions failed at high temperature/acid concentration/soaking time and tended to induce more corrosion. In contrast, iodide ions maintained good intensifying properties with the synthesized diamine corrosion inhibitor at all examined conditions. The value of the synergism parameter was found to be greater than unity for iodide ions at all examined conditions and varied from 1 to less than 1 for Cl and Br ions depending on test conditions. The morphology of the corroded surface, examined employing stereomicroscopy, indicated that the corrosion attack occurred over the surfaces of all exposed low carbon steel with varying degree of severity. The most sever attack was observed in coupons exposed to inhibited 28 wt% HCl acid in the presence of Cl and Br ions. In contrast, the corrosion attack in the case of coupons exposed to inhibited HCl acid in presence and absence of iodide ions is less severe.

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