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If the pump goes into failure mode during the weekend, the duty operator receives a failed alert message and immediately switches over to a backup pump. Under normal circumstances, maintenance can do little but go out and remove the pump that was shut down. But with access to all the data on conditions leading up to the failure, including the original baseline measurements for that pump and trend data for the previous 30 days, the vibration analyst can conduct a post-mortem examination to determine what needs to be done to fix the machine and possibly how to prevent such problems in other similar pumps on-site.

An Actual Case

A problem was developing on the outboard bearing of a digester surge pump in a large paper mill. The machinery health transmitter detected the degradation and sent an alert message to the process automation system, indicating the bearing problem had reached a point where the pump health was so low that immediate action was needed.

Since the data on the condition that caused the device to generate the alert message had been saved, the mill's vibration analyst was able to walk out to the device, connect his portable machinery health analyzer and retrieve the key information along with the historical trend data.

An examination of the velocity spectrum in the machinery health management software (shown in Figure 1) indicates the presence of a fundamental outer race bearing frequency at 5.4 orders of the shaft frequency.

Figure 1

The spectrum in the top half of Figure 2 indicates the presence of these fault frequencies.

Figure 2

The peak time waveform in the lower half of Figure 3 shows extremely high peak levels that are greater than 34 g's of peak acceleration.

Figure 3

The defective bearing was replaced during a schedule maintenance opportunity, and subsequent vibration data from the same bearing location shows that the high frequency vibration is no longer present (as seen in Figure 3). The harmonics of turning speed in the data indicate there is still some possible looseness in the machine, but the amplitudes do not warrant immediate action.

Continued monitoring of this digester pump by the machinery health transmitter will keep both operations and maintenance personnel alerted to new problems as they develop. The device will continue to support the needs of the vibration analyst by allowing him to retrieve stored data needed for detailed analysis, thus enabling the analyst to truly extend his reach onto the plant floor - even while remaining in his office.

Todd Reeves and Stewart Bowers are with the Machinery Health Management Business of Emerson Process Management, 835 Innovation Drive, Knoxville, TN 37932, 865-675-2400, Fax: 865-218-1401, www.emersonprocess.com.

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