Don’t forget the Velocity and Acceleration data.

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A profitable plant is reliable, safe and a cost-effectively maintained plant

The Seasoned Analyst

Introduction:

This short post is to remind analysts not to forget the Velocity and Acceleration data when classifying a defect, don’t just rely on the demodulation/PeakVue/Shock Pulse……..

Background:

This was a one off asset assessment to enable the plant owners to decide where to spend the maintenance budget in the pump house.

The analyst surveyed the pump sets and provided a list of maintenance actions to prolong useful life. Of these actions one motor was recommended to be removed due to an outer raceway bearing defect.

This was a critical pump to the process.

Pump Sets

Vibration Analysis:

Figure 1 is the PeakVue Spectrum from the drive end of the motor. On this plot, as the unit is on a VSD, the electrical 2X pulse frequency has been removed from the spectrum.

This shows an exponentially decaying signal at 3.143 Orders that matches the defect frequency for the outer raceway of the bearing fitted.

Fig 1:

PeakVue Spectrum

To confirm the severity of this we then analysed the Velocity and Acceleration data.

Figure 2 is the Velocity spectrum. The motor has low overall vibration but a clear signal at 3.104 Orders with harmonics is evident, BPFO.

Fig 2:

Velocity Spectrum

Figure 3 is the Acceleration spectrum and also has a clear signal with harmonics at 3.143 Orders, BPFO.

Fig 3:

Acceleration Spectrum

Inspection:

The bearings were removed and inspected.

Image 1 is of the bearing before cleaning, here you can see the blacked grease, due to the electrical discharge from the drive carbonising the grease.

Image 1:

Photo showing grease condition

Image 2 is a photo of the outer raceway. Here the defect is evident with the naked eye, as well as the frosted path due to the VSD operation.

Image 2:

Photo of the damaged bearing raceway

Image 3 is a microscope image of the bearing defect. This clearly shows that this was starting to spall and was very close to failure. The defect was located in the highest loaded section of the outer raceway.

Image 3:

Microscope image of the defect

Summary:

This highlights that you should always use as many technologies and/or techniques when evaluating a defect criticality.

In addition, to preventing any secondary damage to the motor this asset survey enabled a controlled change out of the motor as to not interrupt the process. It also has ensure that the maintenance budget is being spent in the areas that need it the most.

A profitable plant is reliable, safe and a cost-effectively maintained plant

The Seasoned Analyst
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