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Ultrasound Inspection On Rotating Assets

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GVS Reliability Products in conjunction with SDT Ultrasound Solutions is proud to present the below case study, Ultrasound Inspection On Rotating Assets, submitted by Mike Halls.

Mike is Technical Officer of Condition Monitoring at Rio Tinto’s Yarwun alumina refinery where he has held this position for over seven years. Mike has over 20 years working in the condition monitoring field, utilising popular technologies such as VA, Thermography and Oil Analysis. And now Ultrasound for the last 2 years!

Mike’s years of experience have given him a unique perspective on using ‘alternative’ condition monitoring tools such as the SDT 270 PROthe world’s flagship ultrasound inspection device. With the SDT 270 delivering reliable, repeatable and calibrated ultrasound data and, with the power of signal analysis using SDT’s UAS software, Mike has been able to clearly demonstrate that ultrasound inspection should be the technology of choice for certain applications.

When using Ultrasound inspection technology in a harmonious relationship with other condition monitoring inspection devices, plant coverage increases, as does the overall reliability and availability of monitored assets. This then translates into greater production capacity and therefore overall profitability of an enterprise/company.

A portion of this case history was first published in The Industrial Eye: The official journal of the Australian Institute for Non-Destructive Testing – Condition Monitoring Issue – March/April 2017. 
It has since been edited and rectified to give further information regarding the case.

Read on for Mike’s ultrasound inspection success story…

Case History: Mike Halls – Rio Tinto Yarwun – 16-10-2017

Bearing Life Extension using SDT 270 Contact Ultrasound measurement

vaccum pump

Equipment Details

Equipment: P2620Vacuum Pump

Bearings: Tapered Roller Bearings

Pump Speed: 222 RPM

Motor: 630Kw – 6 Poles

Number of Vacuum Pumps on Site: 21

Costs associated with bearing failure

Overhaul cost due to a bearing failure: $120K
Total Replacement cost: $300K
Costs due to lost production or downtime: Currently there is some redundancy (as long as there are not too many other problems…). This may change in the near as further production demands are made on the plant.

History

Previous vacuum pump equipment failure modes and RCA’s have revealed that there has been an increase in bearing internal clearances & cage wear resulting in premature bearing failure. Due to the nature of these machines, vibration spectral analysis only revealed bearing defects in the later stages of the failure mode. Vibration analysis identified advanced propagation of fatigue due to surface cracks and spalling of the bearing raceway surfaces which were already resulting in unsatisfactory equipment performance.

Contributing factors to consider when using a vibration analysis approach are

a) a relatively low operating speed and

b) fluctuating ‘flow related’ vibration

Both of the above plant characteristics have the tendency to mask the early stage, low level amplitude bearing defect fault frequencies which, had they been detectable, would have indicated sub-surface bearing raceway defects and/or lubrication related anomalies. See the vibration analysis plots below as reference.

Vibration Analysis Plots

Below is the vibration Acceleration & PkVue spectral data taken the day after the acoustic vibration route was collected and, prior to any maintenance or lubricant/greasing intervention. Vibration analysis of the spectral plots indicates that the dominant frequencies relate to the vacuum pump pressure pulse fundamental & related harmonics. Neither of the plots indicates incipient bearing anomalies or lubrication related issues.

vibration analysis_1
vibration analysis_2

Challenge

With traditional condition monitoring technologies being limited in their capacity for detection of the early stages of the bearing failure modes, trending of the degradation process was not possible. Without being able to detect and trend the early stages of the failure modes, this left the plant exposed when needing to determine a projected planned maintenance window. So, once the later stage defects were finally identified, the asset was already at a critical crossroad in

a) needing immediate attention or

b) risk plant failure with consequent potential safety hazards or production loses.

Solution: Acoustic Vibration Monitoring Trial

Acoustic Vibration Monitoring or contact Ultrasound, are terms used when an Ultrasound inspection instrument (in this case the SDT 270 PRO), utilises a sensor to contact (touch) a surface to detect attenuated ultrasound signals. Using a sophisticated instrument such as the SDT 270 PRO, the ultrasound signals can then be acquired as either dynamic (for analysis and playback) or static measurements (for trending) and logged in SDT’s proprietary database, Ultra Analysis Suite (UAS).

Just over twelve months ago, an Acoustic Vibration Monitoring strategy was implemented on a trial basis to complement the vibration analysis program on the vacuum pump routes. This was done mainly to assist with lubrication related concerns and incipient bearing defects that vibration analysis was unable to confidently detect. After employing the ultrasound inspection strategy (with the 270), and the data analysed in UAS, a number of lubrication concerns with the vacuum pump bearings were rapidly identified. See figure 1 and 2 below.

Figure 1. Static trend

graph

Figure 2. Dynamic Signal

dynamic-signal_2

Listen to .WAV sound file at this Dropbox link.

Initial Results and Findings

The above Acoustic Vibration Analysis examples indicate a significant upward trend due to elevated ultrasound generated by the bearings. The ultrasound signal and trend indicate metal to metal contact that is identified by an outer race bearing defect. The causes for this are either inadequate lubrication or incipient bearing defect.

As already mentioned above, at these locations vibration analysis showed only high frequency data with a raised noise floor. This could be attributed to the product ‘flow’ and hence masked the true vibration signal. On the contrary (and unlike vibration), the Ultrasound signal is not affected by the ‘flow’ caused by the pump and hence did not mask/conceal the bearing condition data. Due to the clarity of this anomaly, we can call this a ‘text book case’ because in this example, increased readings in ultrasound data related directly to an inadequate bearing lubrication condition.

Due to the findings via the use of the SDT 270 Ultrasound inspection device, the recommended corrective action was; ‘grease the non-drive end bearing and re-evaluate the ultrasound values’.

Upon the recommendations being carried out in a timely manner, further readings were taken with results shown in Figure 3 and 4 below:

Figure 3. Static trend after recommended intervention

Static-Trend_alt

Figure 4. Dynamic signal after recommended intervention

dynamic-signal_alt

Note: the vertical y axis between fig 2 and 4 is different by approx. a factor of 4

Listen to .WAV sound file at this Dropbox link. 

Secondary Results and Findings

The data collected with the SDT 270 post lubrication intervention shown in figure 3 &4 showed drastically reduced static and dynamic ultrasound signals. Hence, the follow up survey indicated that the values had significantly decreased to within the acceptable ultrasound range. Further inspections were then planned to monitor the health of the asset. Through the unique attributes only available through ultrasound inspection with the SDT 270, the plant was protected.

Conclusion

Cost analysis:

Thanks to Ultrasound inspection and the access to complimentary software, a conservative estimate is that the company avoided a $120K+ cost to overhaul the pump due to a bearing failure. A catastrophic failure ($300K +) and potential compromise to personnel safety and plant production, would have seen the cost to the company far in excess of this $120K estimate.

Technology Analysis:

Ultrasound inspection has unique qualities which were instrumental in allowing condition monitoring to gain a true understanding of the health of the asset. For this application, other condition monitoring technologies were only useful once the asset was in the late stage of this particular failure mode exposing the company to high risks.

Furthermore, with the SDT 270’s ability to collect both dynamic and static data for trending and analysis, and the ability to record and analyse this data in the UAS software, the defect was easily identified and corrective actions taken.

Site Analysis and further actions:

Continued use of Ultrasound inspection technology to identify bearing condition will be employed so as to extend the reliability, availability and life expectancy of these important assets.

When using Ultrasound inspection technology in a harmonious relationship with other condition monitoring inspection devices, plant coverage increases as does the overall reliability and availability of monitored assets.

Thank you for reading.
I hope this study proved to be of use to you confirming best practice in technology integration results in determining a higher accuracy in detecting equipment failure modes.

For PDF download please view here Ultrasound-inspection-for-Rotating-assets-case-study-by-Mike-Halls-1.pdf

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