CORROSION OF CARBON STEEL IN ACIDIC SALT SOLUTIONS UNDER FLOW CONDITIONS

 Corrosion of carbon steel in acid (HCl) - salt (Na_²SO₄) solutions under flow conditions was investigated for a range of rotation velocity, 0 – 2000 rpm, and temperature, 32oC- 52oC, by using rotating cylinder electrode (RCE).The corrosion rate was determined by using both weight loss method and electrochemical polarization technique. Different acid and salt concentrations were used from range 0.01 M to 0.4 M for salt and 0.5 % to 5 % (v/v) for acid with different oxygen concentrations provided by pumping air through the corrosive solution. Indole and cetyl trimethyl ammonium bromides (CTAB)inhibitors were used in concentrations of 2.74×10^-3  M for CTAB and 1.7×10^-3  to 3.4×10^-3  M for indole. The effects of time (or corrosion product formation), and oxygen concentration through air bubbling in the solutions were also
investigated.The results showed that increasing the rotational velocity leads to an increase in the corrosion rate for all solutions investigated. Also, the corrosion rate in salt solutions had unstable trend with salt concentrations and temperature. In acid solutions, increasing the temperature and acid concentrations leads to an increase in the corrosion rate. Generally, the corrosion rate that represented by limiting current density decreased with time depending on rotational velocity and temperature. It was found that, adding air bubbles (i.e. by using air pump) leads to a considerable increase in the corrosion rates depending on rotational velocity,temperature, and time. High effect of oxygen concentration was noted in cases of acid solutions and in case of high rotational velocity.Using statistical analysis (STATISTICA version 5.0), empirical correlations for the corrosion rate as a function of the velocity, temperature, concentrations,and time were obtained and discussed. Indole and CTAB showed very good inhibition efficiency in most conditions investigated with the former exhibited better inhibition efficiency arriving up to 88 % at low rotational velocities decreasing with flow velocity increase.In addition, indole inhibitor reveals excellent inhibition efficiency for high temperatures, while in CTAB solution increasing the temperature leads to decrease the inhibition efficiency.