Vibration problems of steam turbines.
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Our plant has a compressor driven by a turbine. Recently, the turbine has been experiencing increased vibration in its radial bearings. Through the DCS system, it was observed that between 9 a.m. and 2 p.m. every day, the readings from all four vibration sensors increased simultaneously, rising from a normal level of 12 to 39; these readings returned to normal after 2 p.m. This phenomenon has occurred for 4 consecutive days. I wonder if anyone else is facing the same issue? What problem caused it? How was it solved?
Vibration problems are quite complex; they are usually caused by imbalance issues. If there is a problem with the rotor, it can only be disassembled for inspection. Usually, if it can be maintained, it should be maintained as much as possible; if maintenance becomes impossible, then it has to be dismantled. As for possible problems with the bearings, most of them are caused by dynamic imbalance. But there are also issues with the oil quality, which need to be addressed one by one. For reference.
The circulating water has been checked and shows no issues, and the lubricating oil has also been inspected and analyzed. When vibration increased, the oil temperature rose by 4°C; it’s unlikely that the problem lies with the lubricating oil.
If the lubricant temperature is too high, its viscosity decreases, which can cause excessive vibration; though your case seems a bit exaggerated
The periodic variation in vibration may be caused by carbonization of the lubricating oil at the shaft journal where the oil seal is located; when the layer of carbon buildup reaches a certain thickness, it rubs against the shaft, resulting in vibration. Once this carbon layer falls off, the vibration decreases~~~~~~~~~~~ However, it is also necessary to consider and analyze the following information: 1. Do the GAP voltage, phase, frequency components, and waveform also change as the vibration varies? 2. Whether process parameters such as lubricating oil temperature, bearing shell temperature, steam temperature and pressure (including the inlet strainer), and the negative pressure of the extraction pump have changed (the exhaust volume from the on-site gas seal release pipe can also be used for monitoring)~~~~~
What was said on the fifth floor might also be true; vibrations can occur as a result of carbon buildup in the gas seals and oil seals, which is caused by lubricant leakage combined with high temperatures. High vibration due to carbon buildup during repeated cycles is not something to worry about; be sure to check the oil seals and air seals during maintenance. It is particularly important to note that the time periods with high vibration levels, as described by the poster, correspond to the times of day when the temperature is highest. In light of this, the oil film should be suspected as the cause; it would be advisable to examine the vibration monitoring data or to reduce the temperature of the lubricating oil during these periods in order to observe any changes in the turbine’s vibration levels.