Service for Steam Turbine SST-100
General Information
- Description
The SST-100 is a single-casing multi-stage steam turbine, providing geared drive to 1,500 and 1,800 rpm generators and packaged in a base frame-mounted design.
For SST-100 steam turbines, Siemens feature a major portfolio of service solutions and products to help optimize efficient plant operation.
This service can include:
- Performance Maintenance
- Performance Enhancement
- Service Programs
- Product-Related Services
- Training and Consulting
Our Portfolio (3)
Seal Strips in Rotor
- Background
- Improvements
- Benefits
In steam turbine construction no-contact seals, i.e labyrinth seals, are used between the rotor and stationary bushings or guide blade carriers.
The goal is to attain clearances as small as possible in the interests of minimizing steam leakage.
However, the clearances must be adequately dimensioned to prevent closing of the gaps and rubbing as a result of thermal phenomena.
To keep the heat generated by friction low if rubbing occurs, seal strips which are 0.3 mm thick may be used. Seal strips used in some older turbines may be caulked into the stationary bushings (Fig. 1).
In the event of pronounced rubbing, the rotor body may (Fig. 2)
- experience pronounced localized heating in the rubbing zones
- turn blue and expand locally
- undergo plastic deformation after the deformation limit of the material is exceeded.
After cooling, this plastic deformation can result in permanent bowing of the rotor, which may render further operation impossible due to high vibrations.
Metallographic examinations of rotors with evidence of pronounced rubbing have shown:
- impermissibly high hardness values
- high internal tensile stresses
- changes in microstructure.
Rotors with pronounced signs of rubbing may require complex stress relief annealing at approx. 600°C and extensive reworking – with no guarantee that the efforts will be successful and even if successful, there may be some restricted thermal stability.
Siemens has a design available, which inserts the strips in the rotor and using bushings with a labyrinth profile (Fig. 1 + 3).
Benefits can include:
- Radial bridging of the gap can help mitigate the risk of a permanent bowing of the rotor due to seal strip rubbing damage, because, as designed, there is no direct contact between the stationary parts and the rotor body.
- If rubbing-related damage does occur, it may be possible that only the seal strips in the rotor and the bushings may need to be replaced.
- It can help avoid the need for a complex stress-relief annealing of the rotor to reduce the internal stress inequilibrium if rubbing occurs.