REPAIR OF A TURBINE ROTOR FOR 1050℉ SERVICE BY INSERTING A ROTOR SECTION WITH WELD BUILD-UP

摘要

This paper presents the long term repair of a cross compound General Electric turbine rotor designed for main steam conditions of 3500 psig and 1050℉ with double reheat to 1050℉. After 32 years of service, the first stage buckets of the second reheat turbine lifted at the root due to creep deformation of the rotor wheel dovetail.The repair strategy chosen involved cutting out the creep damaged section of the rotor and inserting a new rotor section. That section included all the areas that operate above 750℉. including the first four rows of buckets. A forging large enough to replace the front section of the rotor could not be procured in time to complete the repair within the scheduled outage, so a smaller forging was built-up with weld metal to achieve the required wheel diameters and meet the outage deadline. Weld build-up was used for the gland seal, the inlet packing area, and the wheel for each of the four rows of buckets. The new rotor section was inserted by two joining welds. This repair is unique because it included weld build-up of the first stage wheel, which operates at 1050℉. The majority of rotor welding experience is on areas that operate at significantly lower temperatures. Also, this repair included weld build-up of a forging to achieve the required diameters.The proposed joining weld locations were changed after the insurance carrier stated that the proposed welds might not withstand the steady state and transient stresses because they were in high temperature and high stress areas.To further improve the life of the welds in the high temperature area, a cooling steam modification was installed.