Investigation of the performance of some corrosion inhibitors in aerated acid solutions

Corrosion tests on commercial carbon steel pipe in aerated 0.1N HCl solution under static and flow conditions with rotational speed range of 400–1400 rpm and temperature range 35 – 60ºC were curried out by weight loss techniques. Experiments were carried out in absence and presence of several inhibitors: thiourea, ethylene diamine, diethanol amine and formaldehyde as adsorption type inhibitors in concentration range 400 – 2000 ppm using rotating cylinder electrode technique.The experimental results showed that corrosion rate in the absence and presence of inhibitors increased with increasing temperature of the
corrosive solution and the rotational speed and decreased with increasing the inhibitor concentrations for the whole range of temperature and rotational speed. It was also found that order of corrosion inhibitors according to their inhibition efficiency was as follows: thiourea > ethylene diamine > diethanol amine > formaldehyde. The maximum inhibition efficiency obtained was for thiourea about 77.59% and the minimum inhibition efficiency for formaldehyde which is 37.12%. Also the results revealed that increasing temperature and Reynolds number (or rotational speed) lead to increase the oxygen transport from the bulk solution to the metal surface, i.e. increase in the value of (i₀₂) but it was observed that increasing Re have no clear effect on hydrogen evolution current (i_H2 ).Arrhenius plots were performed in presence of thiourea at various Reynold numbers, concentrations, and the three temperatures of 35, 45, and 60ºC led to different values of activation energies.