Repairing and Rejuvenation of Turbine Blades
Gas turbine blades suffer different types of damage in service, such as foreign object damage (FOD), high strain low cycle fatigue (LCF), high cycle fatigue (HCF), creep, oxidation, etc. These failure mechanisms can bring damages on surface of the parts like coating removal, pits and cracks, and or affects the blades internally like micro-structure degeneration or creation of creep void.
Hot section blades are among the most expensive parts in gas turbines. It is possible to repair and extent its life time by using specific process. This process has several main steps:
- Preliminary Visual inspection and record
- Cleaning
- Visually inspection
- Dimensional control and record
- Coating strip
- NDT test
- Mark all defects to be repaired
- Blending surface
- Fluorescent penetrant inspect blended areas
- Welding (or laser welding) for repairing defects or welding for building up if required
- Apply coating
- Visually inspect coating
- Controlling micro-structure and designing heat treatment cycle
- Heat treatment to restore the original metallurgical and mechanical properties
- Apply topcoat if required
- Visually inspect coating.
- Visually inspect cooling holes and record
- NDT test
- Checking micro-structure
- Perform final inspection