Creep damage assessment of a 50 MW steam turbine shaft

Abstract

This paper reported the evaluation of a 50 MW steam turbine shaft that has exceeded the designed lifetime (30 years). The inspection of turbine is a mandatory for safety and continued reliable operation. The shaft was made of nickel-chromium-molybdenum alloy steel. The turbine operated in the range temperature of 500-600 °C, and creep was considered to be a major damage mechanism. The remaining life assessment of the turbine shaft was also conducted using replication technique. The replica samples were taken from 125 position distributed along the turbine shaft. The microstructural analysa of replicas showed that creep had occurred, which was indicated by the cavities formation at the grain boundaries. After evaluation and assessment, it can be concluded that the turbine shaft still can be used however it needs to be re-inspected within 6 months.