Turbine failures and startup questions
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The day before yesterday, our company’s entire facility lost power suddenly in the evening. A 12MW back-pressure steam turbine was not started until the next morning, during which it was turned 180 degrees every half hour. As soon as the load was applied, the vibration level reached 0.088 mm, and the temperature of the bearing shell at the coupling end reached 90 degrees. Emergency stop. After cooling the machine, it was found that there were some scratches on the bearing shell (i.e., the local contact points appeared shiny). Put into use after refinement. Due to an unknown cause of the malfunction, the engineer in charge requested that the low-speed spin-up time be extended during startup, but the operator believed this did not comply with the startup procedures, stating that the oil film on the bearing shells had not yet fully formed, which could be harmful to them. The engineers, however, believed that the formation of the oil film was unrelated to the rotational speed, and insisted on prolonging the low-speed spin-up process in order to eliminate thermal deformation of the rotor (this assumption has not been confirmed; it was a precautionary measure). I would like to ask everyone for advice: what is causing the malfunction of this device, and what are the procedures for turning it on? Why is it stipulated this way?
Wear of the bearing shells indicates that there was a problem with the oil supply to the bearings during the emergency stop. Is there an emergency oil pump, and was the shutdown carried out in accordance with regulations? Has the oil circulation functioned properly throughout? Excessive cooling of the shaft can cause it to deform; therefore, various parameters of the shaft should be checked during maintenance to determine whether they are within acceptable limits. Increasing the time spent at low speed helps to eliminate shaft deformation, but in my opinion the effect is limited. A long period of operation at low speed should not affect the oil film.
It was likely not caused by an emergency stop, but rather by shaft deformation resulting from a loss of oil supply to the bearings due to a power outage across the entire plant. Agreeing to increase the low-speed operation time to eliminate shaft deformation has little effect.
It could be caused by a power outage, but turbines normally come equipped with a high-level oil tank to provide oil lubrication during the unit’s coasting period. The vibration amplitude is extremely high; the rotor should be disassembled for inspection, and a dynamic balance check is necessary.
Testing began yesterday, but the critical speed was not reached. As the speed approached the critical value, the vibration level reached 0.16 mm, and the temperature of the shaft bearing at the coupling end rose sharply to 95 degrees. Due to these values exceeding the specified limits, the acceleration process was halted and the machine was shut down. Today, it was disassembled again, mainly to check the coaxiality of the turbine.
After several days of inspection, it was found that the rotor was bent; the maximum degree of deformation reached 0.20 mm. May I ask if this can be repaired? Which manufacturers can carry out such repairs? What is the approximate cost?