V84.2 Inner Casing Refurbishment and Upgrade Modification
The inner casing on a V84.2 gas turbine is a large fabricated assembly which takes the hot gases from the two combustion chambers and turns it to the first stage turbine vanes. The casing is fabricated from Inconel 617 plate, with steel radiation liners to direct and control cooling air flow over the casing. The casing exhibits in-service deterioration typical of combustion components from a gas turbine, including distortion, oxidation, cracking, fretting wear at fixation/interface points, and rusting of the steel components. The most significant in-service defect typically found on the inner casing is a large circumferential crack in the cylindrical section approximately 5-1/2” upstream of the first stage turbine vanes, with axial cracks emanating from the circumferential crack. Removal of the inner casing for repairs requires removal and unstacking of the rotor, so this defect was causing operators to pull rotors prematurely.
Eta Technologies offers an engineered redesign of the inner casing to eliminate this cracking and to significantly extend the life of the components. Finite element modeling shows an order of magnitude reduction in stresses that cause this cracking. Refurbishment and upgrade of an inner casing by Eta Technologies includes the following features:
- Full solution heat treatment of the IN617 material to restore material properties
- Replacement of the cylindrical barrel with a new flange location and new flange design.
- Material upgrade on the cylindrical barrel to Haynes 230
- Modification of the steel radiation liners on the cylindrical section to redirect cooling air flow away from the flange location in the cylinder
- Modification of the steel radiation liners on the forward panels of the inner casing to extend perimeter standoffs
- Welding of radiation liner spacer disks to their pins to prevent fretting wear by loose spacer disks
- Thermal barrier coating of the entire inside of the casing
- Chrome carbide wear-resistant coating on interface points to reduce fretting wear
- New dogbone seal rings manufactured from Hastelloy-X
Additionally, upgrade to the new fixation arrangement with a new inlet bowl ring (and required casing finger ring) and conversion of the pin bosses to sliding keyways has been performed on multiple casings.
Eta Technologies principals have overseen the successful repair and upgrade of more than 30 inner casings for the V-machines!