Corrosion-Induced H₂S Leakage Risk Assessment in a Separator: A Case Study of a Steam-Dominated Geothermal Power Plant

Abstract

The steam separators at Units 2 and 3 of the steam-dominated geothermal plant are exposed to hydrogen sulfide (H₂S) gas, which can cause corrosion and potential hazardous gas leaks. This study aims to assess the risk of H₂S leakage due to corrosion in a carbon steel horizontal pressure vessel-type separator that has been in operation for more than 35 years. The method used consisted of two stages: (1) visual inspection data analysis and ultrasonic (UT) wall thickness measurements to detect thinning and surface defects, and (2) risk analysis using Failure Mode and Effects Analysis (FMEA) and Fault Tree Analysis (FTA), based on expert survey inputs. Results showed the presence of uniform corrosion and localized pitting, with a minimum thickness of 5.5 mm. The highest Risk Priority Number (RPN) of 270 occurred in internal casing corrosion. The FTA identified the main causes to include long-term exposure to corrosive fluids, inadequate surface protection, and aging equipment. The novelty of this study lies in the combined approach of empirical inspection data and FMEA-FTA integrated analysis to proactively assess the risk of leakage in old geothermal separators, a topic that is still rarely researched in Indonesia. This study emphasizes the importance of regular inspections, the use of corrosionresistant materials, and improved monitoring systems to mitigate the risk of H₂S leakage and ensure the safety of geothermal plant operations.