Fitness for Service Assessment of Geothermal Steam Turbines

Abstract

Geothermal rotors operate in severe operating conditions with aggressive steam and carryover of particulates into the steam path. Operational campaigns of 4 years or more are typically followed by inspection and condition assessment to identify any degradation that may require decision making for repair or component replacement actions to return the asset to service as quickly as possible. The paper will look at the steps and processes involved in completing a fitness for service assessment of a geothermal rotor exhibiting degradation. A case study will be reviewed and discussed covering a single flow rotor which developed erosion damage (throttling) to the crest of the last stage disc fir tree. The objective of the assessment in this instance was to determine the remaining safe operating life of the rotor to enable a planned repair strategy to be proposed and implemented.