2 vibration monitoring system 3 monitoring process, results and analysis 3. 1 Test process When the compressor unit is in normal operation state, measure the effective value and spectrum of the vibration velocity in the horizontal, vertical and axial directions of each bearing seat of the unit housing; measure the peak value of the vibration displacement of the motor anchor bolt and the adjacent foundation; Measure the amplitude, peak value and spectrum of the vibration signal output of the buffer output interface of each channel of the compressor group online vibration monitoring table. 3. 2 test data 3. 3 test results and assessment No obvious faults and problems were found in motors, couplings, III-IV rotors and bearings, pipes, foundations and other related components. 3. 4 Fault and vibration cause analysis Through the test and analysis of the unit, the following reasons for the vibration of the unit can be excluded: poor alignment; weak foundation; loose ground angle bolt; gas disturbance such as surge, rotation and detachment; oil film whirl; excitation. Judging from the current data only, the exciting force of the vibration mainly comes from the imbalance of the rotor mass and the poor meshing of the gears. Natural gas compressors tend to cause fouling on the impeller and cause imbalance. Analysis of the vibration data shows that the imbalance of the I to II rotors is large, and the imbalance of the III to IV rotors is small. The quality of the gear is usually large, so the gear with poor meshing will produce a large vibration, which will affect the whole unit. If the gear meshing condition of the compressor is improved, the vibration amplitude of each point of the unit will be greatly reduced compared with the current one. In addition to the above two main exciting forces, there are other factors affecting vibration, which are listed below. (1) After analyzing the various vibration spectra of the I-II rotors, it is found that there is a certain degree of disagreement between the two supporting bearings, which will make the rotor support directions on the two supporting bearings inconsistent, thus making the rotor The oscillation is generated. It can be seen from the two-dimensional and three-dimensional holographic spectrum of the rotor vibration that the vibration phases of the measuring points in the same direction at both ends of the I-II rotor shaft are almost 180° different, and the rotors swing up and down in different directions when the rotor is in operation. The center line of rotation is composed of a large waist and a thin waist in the middle; while the vibration phase of the measuring point in the same direction at both ends of the normal rotor should be nearly uniform, the center line of rotation surrounds the cylinder, and the vibration of the III-IV rotor is normal. type. The dissimilarity of the two supporting bearings can also cause the center line of rotation of the I-II rotor to be non-parallel to the center line of the large gear shaft, thereby affecting the meshing of the gears. (2) In the vibration spectrum collected on the motor, gear box, I-IV class volute and bearing housing, the power frequency components of the I-II rotor are found, and the amplitude also has considerable advantages. It shows that the energy of the I-II rotor vibration is relatively large, which has a considerable impact on the whole unit. If the vibration of the I-II rotor is greatly reduced, the vibration of the whole unit will be greatly reduced. (3) The horizontal and vertical support stiffness of the I-II rotor is different, and the vertical rigidity is weak, so that the vibration amplitude in the vertical direction is higher than the horizontal direction. If the support rigidity in the vertical direction can be enhanced, it is advantageous to reduce the vibration. (4) The vibration spectrum collected on the gearbox housing presents a typical form of poor gear meshing failure. In addition to having a high power frequency peak, a large number of peaks appear near the frequency of 800 to 1500 Hz. This is not the meshing frequency of the gear, and may be the natural frequency of a component such as a rotor or a casing. Similar vibrations can cause severe erosion of the toothed engagement surfaces, and in a few cases the support bearings of the gear shaft are also severely damaged. If the vibration amplitude of this part of the frequency can be reduced, the vibration amplitude of each point of the gearbox will be greatly reduced. (5) The blade of the compressor impeller will cause serious imbalance of the rotor. Improper design of the impeller runner will cause the fluid to generate exciting force in the volute. For example, a large number of peaks near the frequency of 800 to 1 000 Hz may be impeller blades or inlets. The passing frequency of the guide vanes, if there is a problem with the impeller, will cause many types of vibration, so the design calculation and processing quality of the impeller should be strictly required. 4 recommended treatment plan (1) Firstly, the imbalance of each rotor should be reduced. It is recommended to make dynamic balance for the large gear rotor, I~II and III~IV rotors. The balance accuracy grade should not be lower than G2. (2) Secondly, it must be ensured that the gears mesh well when the unit is running. The following improvements are recommended. 1 Improve the quality of maintenance and improve the meshing conditions of the gears. Due to the unstable factors of the quality of the inspection and the uncontrollable factors such as the deformation of the casing, the non-parallel or center-to-center distance of the rotation centerlines of the two gear shafts may be incorrect, thereby affecting the meshing of the gears. During the standby group inspection, the concentricity of the support bearing and the center distance between the two rotors, the static and dynamic contact area data of the gear can be measured. If the above data does not meet the requirements of the maintenance plan, an adjustment plan should be proposed based on these data. 2 Improve the lubrication condition of the gear meshing. The feasible solutions are: increase the amount of lubricating oil in the gear meshing part to prevent local high temperature in the gear meshing; enhance the anti-wear ability of the lubricating oil to improve the bearing capacity of the lubricating oil at the meshing part, and wear anti-wear Hydraulic oil L-HM46 or extreme pressure turbine oil for this purpose. (3) At present, there is no accurate conclusion about the I-II rotor shimmy and the large frequency peaks of 800～1 500 Hz. The compressor manufacturer should also calculate the full dynamic characteristics of the compressor rotor and other components. Determine the cause of the problem. (4) It is recommended to develop and strictly implement a set of special vibration standards and operating procedures for this unit, and use various testing methods (vibration monitoring, oil monitoring, etc.) to regularly monitor and analyze the operating status of the unit. When the relevant indicators exceed certain standards (refer to SHO 103 and API-613), stop the maintenance as soon as possible to ensure safe operation of the unit without failure. Of course, it is difficult to comprehensively find out the cause of the vibration of the unit and propose a perfect solution through a short-time vibration monitoring. It is necessary to thoroughly solve the vibration problem, carry out detailed observation and inspection of the unit, and summarize the vibration law of the unit. In order to finally reduce and eliminate vibration, technical transformation and adjustment are carried out in a targeted manner. In the vibration signal, the phase is very important information. Combined with the phase analysis, more problems can be found, but no phase is measured in this test.
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Vibration measurement and discrimination for compression facility groups
1 equipment overview and phenomenon