PSI - Issue 13

Marko Katinić et al. / Procedia Structural Integrity 13 (2018) 2040 – 2047 Author name / Structural Integrity Procedia 00 (2018) 000–000

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Table 1. Technical data of the turbine No Name

Data

1. 2. 3. 4. 5. 6.

Type

Axial, impulse, condensing turbine

Rotation direction Number of stages The 1st critical speed The 2 nd critical speed Inlet steam condition - Pressure -

CCW

7

3300 rpm 9750 rpm

39,7 bar abs 395 °C 46,12 t/h 0,14 bar abs

Temperature

-

Flow

7. 8. 9.

Exhaust steam pressure

Outlet power

9895 kW

Operating speed range - Nominal - Maximum - Minimum

6190 rpm 6500 rpm 5260 rpm

10.

Rotor

Integral disk type

Fig. 2. Vibration trend plot on the exhaust end of the turbine

Existing computerized machinery management system had automatically collected and stored vibration data during this event. In order to identify source of vibration problem an analysis of the collected data was performed. Based on vibration analysis it was concluded that sudden change of vibration level had been caused by loss rotor blade and/or shroud band. Since the turbine operation with rotor blade failure could lead to catastrophic damage it was decided to put turbine out of operation. The turbine was shut down. During turbine shut down it was noted very high resonant vibration peak (above 200  m pp). This was yet evidence that the decision to stop the turbine operation was correct. When the turbine was shut down, the maintenance crew was ready to perform the repair. The turbine casing was opened in next two days. The visual inspection confirmed that two blades with related part of shroud band on the 5 th rotor wheel were missing (Fig. 3). The rotor was replaced with spare one. The unit was placed back in operation on 27 July 2009, after the repairs were completed. Vibration levels were low (15  m pp) and acceptable.