Inspection Based Corrosion Rate Mapping for Remaining Strength and Remaining Life of Two-Phase Geothermal Steel Piping

Abstract

Geothermal as green energy has many advantages for power generation due to cleanness, zero waste, and renewable. However, during the operational period, corrosion and scaling in two-phase geothermal steel piping are two main challenges that can cause leaks, reduce flow performance, and reduce safety. Therefore, the two-phase geothermal steel piping remaining strength and life analysis are conducted to manage its integrity. This paper presents a case study on the corrosion rate mapping, excessive corrosion, and scaling for a two-phase flow line in Well Pad B, one of the geothermal production facilities in Unit 1 Dieng, PT Geo Dipa Energi. The data used for this assessment refer to the results of the wall thickness inspection; meanwhile, the data used for scaling and corrosion analysis refer to field observation results. The results of the remaining strength calculation, using both ASME B31G Original and Modified methods, indicate that the remaining strength of all tested points was deemed acceptable in 2020. The remaining life calculation, based on API 579, reveals that the longest remaining life is 9.08 years and the shortest is 0.83 years in the long-term scenario. In the short-term scenario, the longest remaining life is 57.29 years and the shortest is 11.01 years. The corrosion rate is classified as Class I, based on the total key species, with a predictive corrosion rate value > 1.3 mm/year or 51.1 mpy (poor level). In the long-term scenario, the highest corrosion rate recorded is 258.7 mpy (unacceptable level), while the lowest is 39 mpy (fair level). In the short-term scenario, the highest corrosion rate observed is 23 mpy (fair level), and the lowest is 9 mpy (good level). Furthermore, based on the calculation of the Ryznar Stability Index, the fluid has the potential to generate heavy scale, with an RSI value of 4.1.