Investigation of Non-Ionic Polymer as a Suitable Inhibitor in Protecting Carbon Steel from the Aggressive Corrosion of Acidic Simulated Geothermal Brine

Abstract

The use of inhibitors is considered to be one of the most economical and practical corrosion technology solutions. However, this technology is still underutilized in Southern Negros Geothermal Field. This is mainly due to the complexity of the geothermal brine which makes it difficult to find a compatible inhibitor available in the market. A good geothermal corrosion inhibitor should be able to control the corrosion rate at the acceptable level without causing any significant change to the brine chemistry that could lead to unwanted mineral scaling. Other factors that need to be considered in selection of inhibitors are thermal stability, good solubility even at high ionic concentrations, and a wide pH range. For this study, we used a nonionic water-soluble polymer reported to be a good cathodic inhibitor and at the same time can promote silica layer formation. Despite the abundance of silica in geothermal brine, it is not easily deposited in low pH conditions since it is present in solution as silicic acid, which is very soluble in the brine and tends to be well dissolved in solutions. If the polymer can promote silica deposition, it could act not only as a corrosion inhibitor but can also add as an additional barrier from the corrosive species present in the brine. Various characterization techniques such as Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transform-Infrared ( FT-IR) were done to determine inhibition mechanism of the polymer to carbon steel immersed in simulated acidic geothermal brine. The anti-corrosion property of the inhibitor was further tested using the weight loss method, Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization scan (PPS), and open-circuit potential measurements (OCP). The mechanism of corrosion inhibition action of the polymeric inhibitor is proposed based on the results of the analysis made throughout the course of the study.