Preventive measures for main oil pump coupling failure

During maintenance, the inspection of the main oil pump coupling should be strengthened, especially when abnormal wear of the main oil pump thrust pads is found, attention should be paid. When the surface of the coupling is found to be worn, the coupling should be replaced in time and the cause should be found to avoid jamming during operation.
The following measures should be taken to ensure the operation of the main oil pump coupling:
1. Improve the installation accuracy
Improving the installation accuracy can reduce the circumferential deviation (shake) and end face deviation (scoop deviation) of the centerline of the main oil pump rotor relative to the centerline of the turbine rotor, thereby reducing the occurrence of jamming or friction in the gear coupling due to changes in the geometric position. possible. For the radial allowable deviation of the two shafts, in the case of no end face deviation, it can be > 1mm. But the output torque of the coupling will decrease with the increase of the included angle α and the radial deviation b. In the case of α=1°30′ and rated speed, the output torque is only about 15% of the rated torque, so the installation and alignment accuracy of the coupling rotor should be improved as much as possible.
The angle between the main oil pump rotor and the center line of the steam turbine rotor is not easy to measure in actual maintenance, and it is often replaced by measuring its end face deviation. Usually, when the main oil pump is centered, the end face deviation and circumferential deviation should be ≤ 0.03mm (high and low values ​​should be considered and reserved. height difference), the output power of the coupling is basically not affected at this time.
When finding the center in the cold state, the center line of the main oil pump rotor should be 0.20~0.25mm higher than the initial center line of the turbine.
l=Δt1·r·λ+h·λ·Δt2
In the formula: l is the height of the center of the main oil pump higher than the center of the steam turbine, mmΔt1 is the temperature difference between the cold state and the hot state of the steam turbine rotor, °C; r is the radius of the journal at the No. 1 bearing shell of the turbine, mm; λ is the thermal expansion of the metal Coefficient, mm/(mm °C); h is the height from the front box of the steam turbine to the No. 1. bearing pad pocket, mm; Δt2 is the temperature difference between the cold state and the hot state at the No. 1 bearing pad of the steam turbine front box, °C.
2. Improve the lubrication conditions of the coupling
The main oil pump of the steam turbine is lubricated by turbine oil. According to the installation experience, most of the coupling lubricating oil is taken from the lubricating oil pipe. During the maintenance, it was found that because the oil pipe is relatively thin, the oil pipe often needs to be bent during the maintenance and disassembly, and the bending part has a certain throttling for the lubricating oil. If there is debris accumulated in the pipeline to block the pipe, there is a danger of breaking the lubricating oil. During the on-site maintenance, many times it was found that the coupling failed to lubricate. For the hydraulically regulated system, the front tank oil borrows a lot, and the oil pipe is easy to bend. It must be paid attention to during maintenance, and the pipe diameter of the main pipe section of the oil pipe should be increased from time to time to reduce the throttling loss in the pipeline, which can also improve the The pressure of the oil, such as the pressure oil from the outlet of the main oil pump, is throttled and then led to the coupling.
3. Eliminate the jamming of the sliding pin system
The jamming of the sliding pin system is an important reason for the change of the elevation and lateral position of the main oil pump rotor. In the actual maintenance, due to the large number of connecting pipelines in the front box, especially the vertical pin is located in the lower part of the front box, it is necessary to lift the front box to deal with it. , and the defects in this part are not easy to detect, so the maintenance of the sliding pin system of the front box is often ignored during maintenance. In fact, ensuring the good expansion of the initial group is also a measure to maintain the economic operation of the unit. In 2004, the No. 5 unit of a power plant had a load swing caused by the elevation change of the main oil pump caused by the lift of the front box. Therefore, we must pay attention to the inspection of the sliding pin system during maintenance.
In order to eliminate the jamming of the sliding pin system, the surface finish of the sliding pin can be improved, the wear-resistant material can be used, or an appropriate lubricant such as graphite or molybdenum disulfide can be applied. At the same time, attention should be paid to the cleaning around the front box to prevent foreign objects from entering the sliding pin gap.
4. Ensure the hardness of the tooth surface of the coupling
The tooth surface hardness of the inner and outer gear rings of the gear coupling should reach 45~50HRC/40~45HRC in the case of quenching, and >500HV in the case of nitriding, and the layer depth should not be less than 0.5mm; it is worth noting that some couplings are The hardness of the tooth surface of the coupling is insufficient when it leaves the factory, so when the tooth surface of the coupling is found to be worn, it is necessary to check whether the hardness meets the requirements, and at the same time, the hardness should be checked when the coupling is replaced.