Steam Turbine Water Induction

Identification of water induction is critical to averting costly steam turbine repairs and downtime. Recent AEGIS evaluations of steam turbine generators have highlighted concerns about the effectiveness of using operational data for identifying water induction. Operator training and attention, as well as the optimization of alarm configuration, can avert water induction events. 

Water induction has been a contributing factor in numerous uncontained overspeed and blade liberation events. More typically, water induction causes rotor or shell cracks and/or rotor and shell deformation, all of which would require extensive repairs and downtime. If it occurs during start-up, online time could be delayed by several hours. Additionally, over time, routinely occurring water induction events will open seal/packing clearances, negatively affecting unit thermal performance.

Water induction can be identified by monitoring the following parameters:

• Matched or paired upper and lower shell metal temperatures: Per ASME TDP-1-2013, a difference of greater than 50°F indicates the presence of water and is often configured with a delta T alarm. Under normal conditions, the difference should be less than 10°F.
  

• Steam temperatures: During start-up evolutions, rapid changes in steam temperatures, such as a negative step change or dip, indicates water has entered the steam path.  

• Attemperator spray control valve position and flow indication: Water should not be entering the steam path when the attemperator spray control valve is closed.
  

• Rotor position: Abnormal changes in rotor position could indicate a water induction event has occurred. 

These parameters can be monitored by operators and are suitable for alarm configuration in remote monitoring centers and local controls.

An AEGIS white paper on water induction prevention is available at AEGISlink.com. If you would like further information about steam turbine water induction, please contact Tim Maker by e-mail.

AEGIS Loss Control continuously monitors emerging risks and technologies, hosting frequent webinars covering recent issues and trends in generator technology, operation, maintenance and repair practices at power generating facilities. Click here to learn more about our upcoming safety programs. 

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