The pitting corrosion behavior of the austenitic stainless steel in aqueous chloride solution was investigated using electrochemical technique. Corrosion potential (Ecorr) measurement, potentiodynamic experiments, potential-hold experiments in the passive range, and microscopic examination were used for the evaluation of corrosion characteristics. The experimental parameters were chloride ion concentration, immersion time and anodic-hold potential. Ecorr measurements along with microscopic examinations suggest that in or above 3.5 % NaCl at pH 2 pitting took place on the surface in absence of applied potential after 6 hour immersion. The potentiodynamic experiment reveals that Ecorr and pitting potential (Epit) decreased and current density in the passive region increased with the increase of chloride ion concentrations. A linear relationship between Epit and chloride ion concentrations was found in this investigation. The analysis of the results suggests that six chloride ions are involved for the dissolution of iron ion in the pitting corrosion process of austenitic stainless steel
Corrosion inhibition of mild steel by sodium nitrite in simulated cooling water (SCW) containing chloride ion was investigated. Electrochemical techniques such as corrosion potential (E corr ) measurement and potentiodynamic sweep experiments were used. The experimental parameters were concentration of the inhibitor, pH of the aqueous media and soaking time. Nitrite inhibited mild steel corrosion in near neutral and alkaline (pH 6 and above) SCW and accelerated corrosion in acidic media (pH 4 and below). Inhibition activity increased with the increase of nitrite concentration up to 500 ppm, and afterwards remained more or less constant at pH 6 and above. In stagnant SCW, maximum corrosion inhibition was observed at pH 8 for all concentration of NaNO 2 . Inhibition action of NaNO 2 was found to increase with the increase of soaking time up to 24 hours, and afterwards it remained more or less constant at all nitrite concentrations at and above pH 6. Based on the experimental results, mechanisms of action of NaNO 2 on mild steel corrosion inhibition in SCW have been proposed.
Top-of-the-line corrosion (TLC) is a concern for subsea wet-gas transportation pipelines operating in a stratified flow regime. The insufficient volume of electrolyte at the top of the line combined with the low electrical conductivity of the condensed liquid has confined the majority of TLC studies to the weight loss method which only provides integrated corrosion rate over long period of exposure. The instantaneous monitoring of TLC rates using electrochemical methods is still a challenge for researchers and in the field. To overcome this limitation, this study presents a novel TLC monitoring cell capable of measuring in situ corrosion rates of carbon steel under condensing condition by electrochemical methods such as linear polarization resistance, electrochemical impedance spectroscopy, and electrochemical frequency modulation. The data presented in this paper have been conducted over 5 d at varying condensation rates to evaluate the feasibility and accuracy of the methods applied. In addition, TLC rates have also been measured by weight loss and monitored in situ by measuring the iron concentration in the condensed liquids in order to compare these results with electrochemical methods. Both the electrochemical and non-electrochemical methods provide comparable results, which validates the design and efficacy of the probe. Therefore, the probe appears to be a promising tool for further investigation into the TLC process and its inhibition.
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