Evaluation of the corrosion of UNS G10200 steel in aerated brines under hydrodynamic conditions Helmuth Sarmiento Klapper a, * , Dionisio Laverde b,1 , Custodio Vasquez b,1 a Otto von Guericke University Magdeburg, P.O. Box 4120, Magdeburg 39016, Germany b Universidad Industrial de Santander, P.O. Box 678, Bucaramanga, Colombia article info Article history: Received 14 April 2008 Accepted 20 June 2008 Available online 27 June 2008 Keywords: A. Low alloy steel B. Polarization B. EIS C. Oxygen reduction abstract The influence of the flow velocity and the temperature on the corrosion of UNS G10200 in aerated brines had been evaluated by means of electrochemical techniques at the RCE. Increasing the flow velocity and the temperature enhances the corrosion kinetic of the system and changes the corrosion mechanism. This behaviour was adduced to the presence of a mixed control on the corrosion process related with the formation and stabilization of corrosion product layers on the electrode surface. The correlations of Wranglen and Silverman for the mass transfer and the wall shear stresses respectively were validated at the RCE for this system. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The development and improvement of production technologies demand elevated temperatures, pressures, and high flow velocities at the industrial processes, which has important consequences in terms of the corrosion in the facilities and pipelines. In order to achieve a better comprehension of these complex corrosion phe- nomena, a challenge for the investigators has been simulate the ef- fect of such industrial conditions i.e. flow velocity, temperature and pressure affecting the corrosion rate. The hydrodynamic conditions that cause the internal corrosion of pipes are very difficult to simulate in a laboratory. Different de- vices: rotating electrodes, the flow loop, the rotated cage and the jet impingement, have been developed for this aim and can be used to reproduce specific operation conditions [1,2]. The simulation of fluid flow velocity effect on the corrosion rate in a laboratory de- vice is based on reproducing the sensitivity of the corrosion rate i.e. of the corrosion mechanism against the flow velocity. The Rotating Cylinder Electrode (RCE) allows this kind of simulations offering important advantages [3]. UNS G10200 steel is commonly used in pipelines and equip- ments of industrial facilities. On the other hand, brines are present frequently at most of the important industrial processes. These neutral solutions are usually aerated, being the dissolved oxygen the main oxidizing agent of the system. In order to obtain a better comprehension of the influence of the flow velocity and the tem- perature on the corrosion kinetic of this system an electrochemical study had been made at the RCE. In addition, some correlations for the mass transfer and the shear stress obtained at this device were validated. 2. Experimental The hydrodynamic simulations were carried out at a RCE EG & G PARC Model 636. The electrochemical measurements were per- formed using a classic arrangement of three electrodes. UNS G 10200 steel with the following typical chemical composition: 0.17–0.24% C, 0.3–0.6% Mn, 0.15–0.30% Si, max. 0.04% P, and max. 0.05% S, was used to produce the cylindrical electrodes (diameter: 1.2 cm, length 0.8 cm). The working electrodes were prepared before the beginning of the tests with emery paper (grit 240, 320, 400 and 600), degreased with ethanol, rinsed with dis- tilled water and then dried with air. In the arrangement a standard calomel electrode (SCE) was used like reference electrode and graphite electrodes like counter electrodes. Solutions of 3 wt.% NaCl (pH 6.4–6.6) were prepared for each test with analytic grade reagent and distilled water. The corrosion rate of the system was evaluated at different tem- peratures: 25 °C, 35 °C and 45 °C, and different electrode rotation rates: 500 rpm (31.4 cm/s), 1250 rpm (78.5 cm/s) and 2000 rpm (125.6 cm/s). The selection of these ranges were based on the con- ditions commonly observed at industrial facilities, as well as on the values of the Reynolds numbers (Re) allowing the validation of the existent hydrodynamic and mass transfer correlations for the RCE. The temperature was maintained constant during each test by means of a heating device, as well as registered and controlled 0010-938X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2008.06.022 * Corresponding author. Tel.: +49 391 6714566; fax: +49 391 6714505. E-mail address: helmuth.sarmiento@mb.uni-magdeburg.de (H.S. Klapper). 1 Fax: +57 7 6350540. Corrosion Science 50 (2008) 2718–2723 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci