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A power generation company in Victoria experienced multiple undetected failures in their coal pulverising mills due to a rapid failure mode. The site strategy for monitoring the coal pulverises was time-based inspections and whilst this had detected and prevented some failures in the past, it hadn’t caught them all.

Initially the client’s solution to this issue was to increase the frequency of the vibration analysis survey to weekly to provide earlier detection. Whilst the vibration data collection and analysis method are well-proven at detecting faults like these, the rapid deterioration of the fault meant that they still occurred between surveys.

The installation of the Waites Wireless Condition Monitoring (CM) hardware offered the desired increased data collection, with data collection also now occurring when the condition monitoring team was off-site. This provided the ability to trend for change at a very high level of resolution and ultimately detected this failure mode reliably and early. 

Following the implementation of the Waites Wireless CM hardware a developing failure was detected. Early detection allowed for a controlled shutdown of the machine avoiding secondary damage and interruptions to production. On this occasion, monitoring and detection were all performed ‘after-hours’ and without the condition monitoring team being on site.

Figure 1. Coal Mill
HISTORY:

The system was deployed across the coal pulverising mills in an attempt to provide early detection of bearing faults to avoid production interruptions and secondary damage due to the rapid deterioration of the failure mode.

Historically due to a rapid failure mode, when the bearing failed on these mills the failure would occur quickly, unnoticed and there would be additional secondary damage to bearing housings, shafts and gears causing repairs to cost significantly more than simple bearing replacement.

One morning, the Waites Wireless system detected a change in the vibration levels and triggered the release of notification to the offsite condition monitoring team.  The team was able to review the notification, evaluate the data and determine a particular mill had developed a bearing defect. 

The condition monitoring team continued to monitor the bearing fault over the course of a few days and once the fault became more advanced, the team notified the operational team allowing another mill to be brought online while the mill with the advanced fault was shut down without any interruption to production or secondary damage.

IN REVIEW:

The week prior to the failure, the spectral data developed subtle peaks in the FFTs at very low amplitudes. These peaks were low in amplitude and remained stable for a period of time. 

Waites FFT Data with the envelope alarm overlayed.
Figure 2. FFT Data with the envelope alarm overlayed

 

After a short period of time, the peaks slowly grew in amplitude and became more defined.  The FFT data showed a well-defined fault developed just below the alarm threshold the day before the functional failure.

 

Figure 3 - Fault increasing approaching the envelope alarm
Figure 3. Fault increasing approaching the envelope alarm

 

Later that day the fault deteriorated to a point and the amplitudes breach the alarm triggering an email notification to be sent out to the maintenance teams.  This alarm triggered a review, and the decision was made to run it until the morning when the day shift maintenance team was available.

 

Waites FFT levels breaching the envelope alarm.
Figure 4. FFT levels breaching the envelope alarm

 

By the next morning, the mill showed a large change in the acceleration readings indicating the mill was at the end of its useful life.  These vibration and fault frequencies were confirmed, and the mill was shut down for replacement.

 

Waites later stage of the bearing fault.
Figure 5. Later stage of the bearing fault.

 

The velocity readings were steady, however, once the bearing raceways started to deteriorate, the amplitude levels rapidly increased, particularly in the last few hours of operation.

 

Figure 6 - Velocity trend increasing.
Figure 6 - Velocity trend increasing
Figure 7. Inner race damage
Figure 7 - Outer race damage.
Figure 8. Outer race damage
CONCLUSION

Implementation of the Waites Wireless online CM system provided near-continuous, high-resolution data of the mill condition.  The improved condition monitoring data allowed early detection of the rapidly developing mill bearing failure mode, that had previously been missed.  The early detection and early notification allowed the operations team to remove the mill from production prior to any secondary damage significantly reducing the repair cost of the mill.

The end-repair only cost a few thousand dollars for the bearings and seals, however, if this had run to failure the secondary damage would have been substantial showing a potential saving of over $30,000 protecting the shafts, gear set, and potentially the housing.

Please reach out to your local GVS Reliability Products representative for more information on how to easily monitor your own vibrating screens (and other rotating equipment) with the Waites Wireless condition monitoring hardware.

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Let us show you how Waites Full-Service Condition Monitoring can be a game changer for your business.  Contact GVS Reliability Products today for a consultation and start your journey towards smarter, less unscheduled downtime and more efficient operations.
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