Thank you so much.yawadu,
The limiting factor is L.O. Bearing Header temperature. The temperature should not exceed 175 deg F--if at all possible.
The purpose of turning gear is to keep the axial compressor shaft from warping (bowing) when the turbine has been tripped from load or shut down when the rotor is warm (hot). L.O. flow to the bearings is also required to keep the bearing material from deforming because of excessive heat from the the shaft.
High L.O. Bearing Header temperature is dangerous because the oil vapours in the bearing cavities can be ignited by the high temperatures in the bearing cavities, resulting in a fire or explosion. BUT, it is desirable to try to keep the shaft turning as long as possible even if there is no cooling water because of cooling water pump issues. Just watch the L.O. Bearing Header temperature, and if it gets too close to 175 deg F, then you need to decide if it's going to continue to increase and how quickly and if so then you need to take appropriate action by taking the unit off turning gear and then waiting about 24 hours before trying to re-start th unit or even put it back on turning gear. It's not catastrophic if the unit can't stay on turning gear for the proper amount of time; it's just incovenient to have to wait so long before putting it back on turning gear or attempting to re-start it;. Patience is the key!!!
Hope this helps!!!
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by Seth Price
by Seth Price