Laboratory Study of a Steam Turbine Rotor Weld Repair

Abstract

In 1986, a large utility discovered a crack in its IP/LP steam turbine rotor and weld repair was chosen as the most cost-effective alternative. The repair consisted of severing the rotor between the 12th and 13th stages and welding a new forging, replacing the 9th and 12th stages, to the remaining original rotor. A test rotor was prepared from the scrapped rotor section using procedures similar to the actual rotor repair. The test rotor was subjected to a mechanical and metallurgical test program to determine the properties of the material in the weld-repaired area. Testing included: nondestructive examination of the rotor bore, chemical analysis of the rotor material, metallographic examination, hardness, tensile, rotating beam fatigue, fracture appearance transition temperature, J-integral fracture toughness, and stress rupture testing. In addition, boresonic inspection records were compared to the destructive examination of the scrapped section of the rotor and four disk sections from the original rotor were tested for evidence of a temper embrittlement gradient.