CONICET | Buscador de Institutos y Recursos Humanos

CO2 corrosion is a serious concern in oil & gas production industry. This phenomenon has a very complex nature due to the numerous variables involved (CO2 concentration, temperature, pH, flow condition, etc.). In addition, steel chemical composition and microstructure, can also affect corrosion rate. One of the most common methods employed to control CO2 corrosion is the use of low alloyed carbon steels combined with the use of corrosion inhibitors.A corrosion inhibitor has to interact with the surface to be protected, thus, its efficiency should be affected by the nature and morphology of corrosion products, which are dependent on steel metallurgy.Normally, inhibitors efficiency is tested on SAE1018 steel, but in most cases it is not representative of the actual steel that is used in the facilities construction. Moreover, for low Cr alloyed steels (0.5 -1%) a decrease in inhibitors efficiency related to this element has been reported [1-3], but there is not an explanation yet.The aim of the present work is to bring to light the effect of steel low Cr content on the efficiency of a commercial imidazoline based inhibitor for CO2 corrosion control. For this purpose, four C-Mn steels, with and without 1% Cr were tested in a deoxygenated 5% wt. NaCl solution, saturated with CO2 at 40 °C, pH 6. The inhibitor efficiency was studied by means of electrochemical measurements employing a.c. and d.c. techniques. Surface film characteristics were analyzed by means of SEM and EDX.The results obtained in this particular experimental system confirm the negative effect of low Cr content in the steel on the inhibitor efficiency. The inhibitor was very effective on Cr free steels, while 1% Cr steels were not fully protected and suffered localized corrosion. It is also shown for 1% Cr steel that microstructure plays an important role on inhibitor adsorption. Keywords: CO2 corrosion; corrosion inhibitor; carbon steel; chromium