A turbo generator unit at Al-Khobar power and desalination plant (7 years old) was unable to start due to high vibration. Vibration trend increasing was noticed in the beginning of 2006 and inflated in 2007 due to unbalance which came to acceptable limits after rotor low speed balancing. Fortunately, this inspection prevented a complete damage of turbine due to detached of casing’s top pressure sensor’s sleeve which was digging into nozzle box body and created a big hole and was few millimeters from the rotor. Site repair was done for the nozzle box as per OEM procedure and sensor was omitted since it is not related to control system. In addition, both journal bearings were getting discoloration and pitting in left side due to selected operation mode of steam admission (partial arc mode) which shifting axis of rotation to left side by 30 μm and increases vibration reading compare to full arc mode. Also, another unit found with similar problems which seems to be a design issue. So an assessment study was done to evaluate the design.

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