Vibration Survey & Analysis Report Area: 332 Cooling Water System Equipment Description: Cooling Tower Fan A Equipment ID: 332-00-CT001A Equipment design: Motor: 1485 rpm, AC induction motor, 4-pole, 50Hz, antifriction bearings Power Transmission: Motor Flexible Spacer Coupling Gearbox Reducer Fan Flexible Spool Spacer Coupling (Spacer length: 154 ±1, Spacer Material: Plastic) Gearbox Reuction Ratio: 12.8 Fan Blades: 12, Fan rpm : 116 Scope of job: To analyze the cause of high vibration and abnormal noise Analyzer: PRUFTECHNIK VibXpert, Offline vibration analyzer, 2-channel. Coupling Alignment Tool PRUFTECHNIK Optalign Smart, Coupling laser alignment tool. Personnel: Ateeq M Farooqi : Graduate Mechanical Engineer & Professional Trainer, Mobius CAT-II certified vibration analyst with 7 years of hands-on experience. Muhammad Shahbaz Khan: Graduate Mechanical Engineer, Mobius CAT-II certified vibration analyst with 7 years of hands-on experience. 01 Condition Monitoring Technician. Igor Ponomaryov : Mechanical Foreman with 10+ years of experience.
Activities done: 1- On load vibration measurement. 2- Decouple motor. 3- Tight motor grouting bolts. 4- Lube oil sample collection. 5- Motor solo run and vibration measurement. 6- Coupling alignment attempt with coupling laser alignment tool. FFT/TWF/Acc. Env. analysis on machine bearings (casing vibration) along with onsite physical observations, measurements taken in velocity mm/s, rms with offline system. Onsite observation: - Excessive Noise - Loose grouting bolts - Excessive misalignment - Slot under motor is insufficient to make the necessary alignment correction. - Laser beam intersects the casing, and due to severe misalignment the laser beam moves out of the detector lens. Severity Level: High Symptoms: - Excited peak at 12x of motor in velocity spectrum with side bands - A minor peak at 100 Hz (2xLf) - Vibration amplitude dropped while solo run, but still 100Hz and 12 th order is still present. - Multiple harmonics of 36x with sidebands of 100 Hz (2xLf). - Vibration increased suddenly, it wasn t a gradual increase (increasing trend) Explanation: - The loose bolts which were observed in the motor foundation were not the reason of high vibration as they were loose from the first time, and they are loose on B & C, If the vibration is due to loose bolts it was supposed to be high since first startup, and it should be high in fan B & C as they have loose bolts as well. (1x peak is not excited as well) - Similar case is with misalignment, that the vibration didn t increased gradually as this is an inherent misalignment, hence if it is a misalignment vibration it was supposed to be there from long time or increasing with time. (1x, 2x & 3x are not excited) - 12x excited peak belongs to motor or rotor bars or gear meshing, but gears are not designed in a way that they may have even number of teeth, the number of teeth in gear are always an odd number else they would cause hunting problem. - 12x peak didn t disappeared in motor solo run, amplitude dropped as the load was removed. - Existence of 100Hz (2xLf) side bands reflects an electric fault.
Lube Oil: The lube oil sample was sent to the laboratory for oil analysis but we were informed that due to their equipment limitation they can t check the kinetic viscosity of this oil, furthermore they can t provide the particle count of the oil contents. (I.e. the ppm of Fe, Si, Zn etc) As per manual the gearbox oil should be replaced first time after 500 hours, but not replaced yet now. Misalignment: The coupling gap with Vernier Caliper at 12:00, 03:00, 06:00 and 09:00 position was checked between i- Gearbox - Spool spacer coupling hubs ii- Motor Spool spacer coupling hubs The results are as following Gearbox Spool (Coupling gaps) 12:00 position 17.0 mm 03:00 position 14.6 mm 06:00 position 11.6 mm 09:00 position 20.1 mm Spool Motor (Coupling gaps) 12:00 position 18.1 mm 03:00 position 19.9 mm 06:00 position 18.3 mm 09:00 position 17.7 mm Spacer length: 3970 mm Distance between motor feet: 875 mm (Measurements taken by Mechanical Foreman) Acceptable Misalignment: Conclusion: Parallel Offset : 0.2mm, Angular : 0.05 mm/mm 1- The loose bots needed to be tightened (tightening done) 2- Firstly the coupling needs to be aligned roughly with dial indicator later with laser alignment tool for preciseness. (Refer to limitation provided below) 3- Precise lube oil analysis can t be done due to Lab limitation hence preferred to replace oil as per OEM instruction (already it s over utilized) 4- Motor needs to be checked and rectified for rotor related faults. 5- Foundation bolts tightening and alignment verification and correction for Fan B & C is also recommended after success in this equipment. Limitation: - The misalignment is so severe that it will require too much motor horizontal movement while the space/slot in the base isn t sufficient. ( It is expected that even if the slot will
be increased even the space will be insufficient for alignment, probably it would require to modify the base) - The laser alignment can t be used at the moment because while rotation the laser beam will move out of the detector lens. - The laser beam will intersects at the casing wall and doesn t reach the detector lens. The hole diameter of the casing (plastic fan shell) needs to be increased to let the laser reach the detector.
Relevant data: Overall Values (On load) Motor NDE Vertical Velocity Motor NDE Horizontal Velocity Motor NDE Acceleration env Motor DE Vertical Velocity Motor DE Horizontal Velocity Motor DE Acceleration env Motor DE Axial Velocity 1.88 mm/s rms 4.54 mm/s rms 0.134 ge rms 2.83 mm/s rms 4.08 mm/s rms 0.079 ge rms 3.28 mm/s rms Overall Values (Off-load) Motor NDE Vertical Velocity Motor NDE Horizontal Velocity Motor NDE Acceleration env Motor DE Vertical Velocity Motor DE Horizontal Velocity Motor DE Acceleration env Motor DE Axial Velocity 0.14 mm/s rms 0.25 mm/s rms 0.055 ge rms 0.19 mm/s rms 0.17 mm/s rms 0.037 ge rms 0.27 mm/s rms
Reference Data: Motor NDE Horizontal Velocity Trend Sudden increase in vibration Motor NDE Horizontal Velocity (Onload) 12 th Order
Motor NDE Horizontal Velocity (offload) 100Hz (2xLf) 12 th order (3 rd harmonic of 2xLf) Acceleration Spectrum Motor DE Horizontal (Offload) 36 th order with harmonics and sidebands
Motor NDE Horizontal Acceleration (offload) 100Hz (2x Lf) Side bands