Independent life extension of a steam turbine rotor

In 1995, an independent technical approach was taken to determine the remaining life of a utility power cooperative`s HP-IP steam turbine rotor, which had been recommended for retirement by the Original Equipment Manufacturer (OEM). The approach consisted of a series of tasks, including special boreside nondestructive examinations, material analysis, statistical validation of inspection system performance, and finite element stress analysis. The information obtained from these tasks was used to calculate the theoretical remaining life of the rotor. Based on predicted use, the independent inspection and analysis of the rotor indicated a remaining useful life of over 100 years. Based on this conclusion, and upon acceptance of the insuring agency, the rotor was returned to service with minimal additional testing or machining of the rotor bore. Continued use of the rotor saved this small utility several million dollars in terms of the replacement cost of the rotor and potential lost power production. The tasks described in this paper could extend the life of other similar rotors that have reached their OEM recommended retirement age.