Corrosion of low carbon steel in buffered geofluid

• Main Authors: dela Rosa, Ma. Fatima S., Ong, Alvin S., Poon, Stafford H.
• Format: text
• Language: English
• Published: Animo Repository 2005
• Subjects: Mild steel—Corrosion; Buffer solutions; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/18685
• Institution: De La Salle University

The Philippines is the world's second largest producer of geothermal power next only to the United States of America and third behind Mexico in power generation. However, inspite of the huge sources of geothermal power, there are drilled geothermal wells that produced acidic geofluids. Because of this, geothermal industry incurs a huge financial loss due to plugging and abandoning of these acidic geothermal wells. In a recent study, a potential method for commercializing acidic geothermal well was developed by raising the pH to equal or greater than 3.5, pH levels considered to be non-corrosive for low carbon steels. In this study, the effectiveness of the buffer solution Beta-Chloro Propionic Acid - Sodium Beta-Chloro Propionate (BCPA-NaBCP) was tested to evaluate the rate of corrosion of low carbon steel in buffered acidic geofluid and non-buffered acidic geofluid. A design of experiment was used to decrease the number of experiments, to minimize the cost of chemicals and to be able to analyze the data statistically. There were five factors considered for buffered acidic geofluid (pH of buffer solution, concentration of buffer solution, time of immersion, temperature of solution, and velocity of solution in terms of pressure units) while there are only three factors for non-buffered acidic geofluid (time of immersion, temperature of solution and velocity of solution). Laboratory experiments showed that in buffered acidic geofluid, pH of buffer solution, time of immersion, and temperature of solution are linear with increasing corrosion rate as factors increases. It can be observed that pH is the most significant factor that affects corrosion. In non-buffered acidic geofluid, temperature of solution, time of immersion and velocity of solution are also linear and temperature is the most significant factor. In comparing buffered acidic geofluid and non-buffered acidic geofluid, it can be seen that temperature in buffered acidic geofluid is not that significant as compared to non-buffered acidic geofluid. This means that the effectiveness of the BCPA-NaBCP is independent of temperature. Time is not significant for both buffered and non-buffered acidic geofluid. Lastly, for buffered acidic geofluid, at low velocity, from 0 to 5 psia, it can be observed that the corrosion rate decreases but at 5 to 10 psia it resulted to increasing rate of corrosion, while it is linear for non-buffered acidic geofluid. In conclusion, the rate of corrosion for buffered acidic geofluid is significantly lower than non-buffered acidic geofluid. In fact, the corrosion rate of low carbon steel can be decreased by an average of 63% as compared to non-buffered acidic geofluid. Therefore, buffering of low carbon steel is an effective way of lowering the rate of corrosion.