Abstract
This study aims to evaluate which of the materials currently available on the market could overcome the problem of corrosion and withstand highly aggressive conditions in the exploitation of geothermal resources in volcanic environments. Our investigations were triggered by the conditions on Lahendong geothermal field (North Sulawesi, Indonesia): well LHD-23 presents one of the greatest challenges due to its capacity of producing > 20 MWe of energy from a single well and in the same time having very low pH (2 - 3) and relatively high chloride (1,500 mg/L) and sulphate (1,600 mg/L) concentration. Three different steel grades (low-alloyed steel UNS G41300, stainless steel UNS S31603 and high-alloyed stainless steel UNS N08031) were selected, and their corrosion behavior was evaluated by means of short-term electrochemical methods (potentiodynamic polarization) and long-term exposure tests (up to 6 months). The research was carried out in the laboratory under stagnant conditions in the artificial LHD-23 geothermal brine (1,500 mg/L chlorides, 1,600 mg/L sulphates, pH 2) at 100 °C (100 kPa) and 175 °C (900 kPa), simulating the conditions present at the site.
Considering the selected alloys’ corrosion behavior at 100 °C, stainless steel UNS S31603 could represent an option to be used in the designed geothermal application due to its excellent performance in terms of corrosion resistance, compared to alloy UNS G41300, and lower cost, compared to alloy UNS N08031. Controversially, at 175 °C, due to the relatively low and within the acceptable limits corrosion rates of UNS G41300, low-alloyed steels could be employed as a constructional material for the geothermal power plant in stagnant highly acidic environments, as long as the wall thickness of the material vs. corrosion rate is taken into account.
