Electrochemical methods of determining corrosion rate of low carbon steel in a buffered and non-buffered acidic geofluid

• Main Authors: Leyesa, Marikris D., Moraleda, Charisse Mayen P., Palustre, Ray Michael P.
• Format: text
• Language: English
• Published: Animo Repository 2006
• Subjects: Electrochemistry; Electrochemical analysis; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/7180
• Institution: De La Salle University

Two electrochemical methods of linear polarization and Tafel extrapolation were used in this research to measure the corrosion rare of low carbon steel in a buffered and non-buffered acidic geothermal fluid (geofluid). An EG&G Potentiostat/Galvanostat Model 273A and a corrosion cell kit were used. The solution of geofluid and the buffer (β-Chloro-Propionic Acid-Sodium-β-Propionate) served as the test fluid in the corrosion cell. The operating parameters were: pH of the acidic geofluid at 2.0. 2.5 and 3.0 pH of the buffer at 4.0, 4.5 and 5.0 concentration of the buffer at 0.15, 0.2 and 0.25 M current applied at 1 mA, 10 mA and 100 mA and time at which the current passed through the working electrode at 3.0 min, 3.5 min and 4.0 min. The corrosion rate in milli-inches per year or mils per year (mpy) was measured by the use of the 352/252 Softcor II Corrosion Measurement and Analysis Software. The outcome of this study also support and strengthen the claims of previous researches on the effectiveness of the buffer, β-Chloro-Propionic Acid-Sodium-β-Chloro-Propionate in lowering the corrosion rate of low carbon steel in an acidic geofluid. Based from the analyses of the graphs, the corrosion rate of low carbon steel in a buffered acidic geofluid is significantly lower compared to that of a non-buffered acidic geofluid. The results show that buffering the acidic geofluid to a pH of 4 to 5 decreases the corrosion rate of low carbon steel by 45%. The experimental runs confirmed that the corrosion rate of low carbon steel in a non-buffered acidic geofluid has a higher range of 2.12 to 11.45 mpy. However, in a buffered acidic geofluid, the buffered acidic geofluid, the corrosion rate is precise and almost of the same range of 1.61 to 6.19 mpy for both linear polarization and Tafel extrapolation. Furthermore, comparing the results obtained using linear polarization and Tafel extrapolation in a buffered acidic geofluid, the measured corrosion rates are 1.657 to 5.386 for linear polarization and 1.61 to 6.19 for Tafel extrapolation. This shows that the measured corrosion rates were almost of the same range regardless of the electrochemical method used. Moreover, it was observed that the corrosion rate obtained using Tafel extrapolation for a 0.15 to 0.25M buffer concentration and a buffer pH of 4.0 to 5.0 is almost constant. Therefore, using a pH buffer of 4.0 and a buffer concentration of 0.15M is a recommended combination due to economic reasons.