Condition Monitoring Reporting - Case Study
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1. Bearing Inner Race Damage

Machine component: Bucket Elevator Tail Pulley
Fault diagnosed: Bearing damage
Severity: Severe  
Analyst Comments: Both bearings are showing elevated bearing noise, stronger in the LHS (when you stand facing the belt that's going up). Refer to Figure 1.
Spectrum Plot(s):
Recommendations: We recommend changing out the LHS bearing as soon as con-venient. Ensure sufficient lubrication for the LHS bearing before changing out.
Feedbacks: Feedback from the client confirmed the bearing damage due to water ingress.


2. Bearing Looseness/Wear

Machine component: Boiler Feedwater Pump #2 Motor
Fault diagnosed: Bearing damage
Severity: Critical  
Analyst Comments: The motor shows another significant increase in running speed harmonics and subhar-monics, which indicates bearing looseness. The sharp increasing trend has been observed for four surveys, and the condition is deteriorating fast in recent two surveys.
Spectrum Plot(s):

Recommendations: Again, we recommend checking bearing clearances and changing out the bearing as soon as possible.
Feedbacks: Motor and pump were decoupled to check the alignment condition. While trying to re-align the motor and pump, the motor drive end bearing was found to have excessive clearances. Onsite alignment could not be done. The motor was sent to repair and new bearings were fitted in. Catastrophic failure was prevented.

3. Poor Bearing Lubrication

Machine component: SF305 Scrubber Fan
Fault diagnosed: Poor Bearing Lubrication
Severity: Severe  
Analyst Comments: Fan drive end bearing has elevated friction level with impacting at 255 Hz, which may be inner race defect. The non-drive bearing also shows 201 Hz harmonics in the peakvue, early signs of a bearing race defect.
Spectrum Plot(s):
Recommendations: Grease both bearings.
Feedbacks: The high acceleration level seen on 22/06 and 15/07/11 dropped significantly after greasing the fan bearings on 20/07/2011. The feedback email from the customer is shown below.


4. Fan Blade Distortion/Damage

Machine component: Blaster Drying Oven Fan
Fault diagnosed: Imbalance, Fan Blade Damage
Severity: Severe  
Analyst Comments: The fan bearings are showing strong running speed vibration at 24.5 Hz in all three directions, strong at the non-drive end bearing. This may be caused by imbalance of the overhung fan due to excessive dust build-up, blade distortion or damage. The maximum overall vibration level, 10.28 mm/sec, was re-corded from the non-drive end bearing axial direction. The stronger run speed vibration may also indicate belt pulley misalignment or pulley runout or bent shaft. The fan also has a series of running speed harmonics and asymmetric pattern in the time waveform, which indicate bearing looseness. The drive end bearing is showing low frequency vibration at 3.6 Hz. The source for this component is unknown, but suspected to be belt induced. There are no apparent indications of bearing race defects.
Spectrum Plot(s):
Recommendations: Grease both bearings.
Feedbacks: Inspecting fan blades for signs of excessive dust build-up, distortion or damage. Checking fan bearing for excessive clearances and looseness. Checking fan drive pulley for dust build-up and wear.

5. Structural Loosenss

Machine component: Odour Control Fan B - Fan
Fault diagnosed: Structural Loosenss or Imbalance
Severity: Critical  
Analyst Comments: The fan bearings are showing a significant increase in running speed vibration indicative of imbalance or structural looseness. Increased bearing looseness also noted. Vibration level reached 27 mm/sec in the axial direction at fan drive end bearing.

Increased shock pulse readings for both bearings (DE 52/34, NDE 62/21).

Temperature: NDE: 52 degrees DE: 43 degrees Celsius.

Spectrum Plot(s):
Recommendations: We recommend checking the fan bearing and foundation condition, hold down bolt tension IMMEDIATELY. Also, inspect fan blades for excessive dust build up as soon as possible.
Feedbacks: Unfortunately, there was not a happy ending with this case. The client did open the fan housing and inspected the impeller, but didnít notice any problems and chose to continue running the fan due to production requirements. The fan failed 25 days after the VA survey and was beyond repair.