Geothermal sources are found to be the most aggressive natural environments for construction materials in terms of corrosion. This study was focused on investigating the suitability of stainless steel UNS S31603 in volcanic areas of geothermal sites Sibayak and Lahendong (Indonesia). Influence of different factors (temperatures up to 175 degrees C, chloride content up to 1500 mg/L and pH down to 2) was assessed to determine a "safe operating window" of a power plant and assure the system integrity. Investigations were performed by means of electrochemical methods and long-term exposure tests. (C) 2014 Elsevier Ltd. All rights reserved.