Life Extension Experience with GT blades made of Nickel Based Superalloys

Blades made of Nickel based superalloys are used in gas turbines due to their high temperature stability and excellent stress rupture properties. High temperature service for a long duration leads to various types of service induced microstructural damages in Nickel based superalloys. These damages in turn may lead to failure of the blades. Timely in-service evaluation and proper rejuvenation process are important for the successful reuse of these blades in the turbines. The in-service evaluation includes microstructural evaluation and stress rupture testing of specimen extracted from service exposed blade. Rejuvenation of service damaged Nickel based superalloy blades restores their microstructure and properties to as much close as to their virgin condition and allows the blades to be reused. Over the years, Sulzer has successfully rejuvenated numerous sets of gas turbine blades made of different Nickel Based-Superalloys.

This presentation will discuss some interesting observations Sulzer had during the actual metallurgical evaluation of service exposed Nickel based blades and the subsequent rejuvenation. Similarly, it will discuss some lessons and limitations on using stress rupture test to evaluate the serviced exposed rejuvenated condition of Nickel based alloys. Despite these issues and limitations, rejuvenation of service exposed Nickel based blades has been successful as Sulzer’s historical rejuvenation data corresponding to blades made of Inconel 738LC, GTD 111 and Udimet 500 shows.