G,day all, here is another interesting job I got called to
Background:
This pump and motor had a history of reliability failures from bearings, shaft shearing and pipework flanges leaking. This was a pair of pumps on separate base frames but secured to the same concrete floor with a pipework common outlet.
I performed vibration analysis with phase analysis and diagnosed a foundation and structural problems as the root cause.
Vibration Data:
Pump Vibration Data:
Figure 1 shows the overall Velocity vibration trend from our first visit and second visit. This is gathered at the motor DE.
From this trend you can see a marked increase in the velocity vibration levels from 6.304 mm/s RMS and 8.388 mm/s RMS.
Fig 1:
Fig 2 compares the acceleration time waveforms from the motor drive end bearings
From this comparison you can see the lower levels of pump A (Blue Plot) and the very high impacting from pump B (Green Plot)
Fig 2:
Fig 3 is the vibration data from the motor drive end bearing
There is high impacting form the motor bearing and damage to the inner and outer raceway
Fig 3:
Pump B – Motor Bearing Inspection
Failure Mode:
From inspection the failure mode as per ISO 15243:2004 is 5.3.3.3 False Brinelling.
False Brinelling occurs in the contact area due to micromovements and/or resilience of the elastic contact under cyclic vibrations. Depending on the intensity of the vibrations, lubrication conditions and load, a combination of corrosion and wear can occur, forming shallow depressions in the raceway. In the case of a stationary bearing, the depressions appear at rolling element pitch.
In many cases, it is possible to discern rust at the bottom of the depressions. This is caused by oxidation of the detached particles, which have a large area in relation to their volume, as a result of their exposure to air.
Key Points are:
- rolling element / raceway contact areas
- micromovements / elastic deformation
- vibrations
- corrosion/wear & shiny or reddish depressions
- when stationary: at rolling element pitch
- when rotating: parallel “flutes”
Findings:
- Depressions appearing at rolling element pitch indicating damage while the pump was in standby stationary bearing (Image 1)
- Indications of oxidation of the detached particles, which have a large area in relation to their volume, as a result of their exposure to air.
Bearing Inspection: Motor Drive End Bearing – FAG X-lite NU319E.TVP2
Image 1 is the outer raceway, and displays depressions appearing at rolling element pitch which indicates damage to the bearing when the motor was stationary
Image 1:
Image 2 is a close up of the depression at rolling element pitch on the outer raceway, this is from the load side of the bearings and also shows the roll over.
Image 2:
Image 3 is a microscopic image of a depression on the outer raceway.
Image 3:
Image 4 is an image from the inner raceway, this also displays the depressions at the pitch of the rolling elements.
Image 4:
Image 5 is a microscopic image of a rolling element.
Image 5:
Motion Amplification
Even with this vibration data the client was not convinced so I had to use another technology to show the client how the structural and base was causing them their reliability headache.
This first video shows how the pipe work was moving, this was the cause of the stress and strain to the flange joints that led to the leaks
This second video is of the base plate, this showed the true motion of the pump and how these failures were being induced.