Generally, the temperature of lubricating oil for regular equipment can be above 25 degrees, while that for steam turbines needs to be above 38 degrees. Why is that?

Not necessarily; different grades of turbine oil have different viscosities. Model 32# can start operating at 20 degrees, while model 46# requires 30 degrees to start. During operation, 32# is between 25 degrees and 40 degrees. 46# operates at 35~45 degrees during runtime.

There are two nouns: bearing self-excited vibration and oil film oscillation, which is related to oil temperature. From my experience, not only steam turbines but also high-speed centrifugal machines can experience oil film oscillation. The vibrations caused by oil film oscillation can be very severe; I’ve seen a centrifugal air compressor whose vibration level increased from 20 UM to 400–500 UM due to oil film oscillation. Oil temperature is a very important factor in this regard. A decrease in oil temperature leads to an increase in oil viscosity, and higher viscosity reduces the stability of the bearing shells. An excessively low inlet oil temperature increases the likelihood of self-excited vibration in the bearing shells; oil film oscillations caused by low oil temperatures are common in practice, especially during startup in winter. A simple measure to eliminate oil film oscillation is to increase the oil temperature at the inlet of the bearing bush. However, excessively high oil temperatures accelerate the deterioration of the oil quality, and as the temperature of the bearing bush babbitt rises, the margin for safe operation of the bearing bush decreases; therefore, this temperature must be controlled based on the specific conditions of the equipment in use.