DETERMINING STEAM TURBINE INSPECTION INTERVALS

Steam turbine maintenance intervals have been extended from the Original Equipment Manufacturers' (OEM) recommended intervals over the last 20 years. Inspections in which the casing is completely opened have been pushed to 10 years or longer on units with OEM recommended intervals of 5 to 6 years. This has been made possible because of additional data monitoring and in place inspection techniques which allow the internal condition of the unit to be assessed without opening the casing. Risk-based computer modeling and analysis techniques have allowed us to predict safe extended component inspection intervals using fracture mechanics. This paper gives a systematic approach to determining the condition of a steam turbine based on past history and current measured parameters. It provides a discussion of the effects of changes to components and how to determine and rank risk factors. Also discussed are results of inspections of machines which have been opened after extended intervals.