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This blog is to remind everyone that ‘this is the way we have allays done it’ doesn’t wash and also how important using the correct lubrication and lubricant cleanliness is!

Introduction:

This share has two questions;

  1. What the highest Acceleration levels you have recorded on a fan rotating at around 1498 RPM?
  2. Which bearing do you put as the fixed bearing on a fan shaft?

I appreciate the Accelerometer was only technically good for 50g’s but we had a reading of 116.28g’s Peak to Peak. Can you beat that?

Background:

We were requested to inspect a fan due to repeat failures of the fan bearings.

This fan process cold air, it is direct driven at 1498RPM and has two 22222 straight bore double row spherical roller bearings.

The fan NDE (Non-drive end / fan end) bearing was set as the fixed located bearing. The DE bearing at the coupling was set as the float bearing.

This fan had been in operation for 17 days.

Data was collected with a 100mV/g Accelerometer with a flat rare earth magnet.

Analysis:

The vibration data indicated that the motor to fan shaft alignment was good and there were no issues with the Velocity imbalance levels.

There was however extremely high Acceleration levels indicating excessive damage to the outer raceway together with an indication of poor lubricant condition.

Vibration Acceleration Data:

Figure 1 is the Acceleration Time Waveform from the Fan NDE (Fan end bearing). This shows the very high impacting levels with a -52.59g’s peak to +63.69g’s peak.

Fig 1: Acceleration Time Waveform

Figure 2 is the Autocorrelation of the Acceleration Time Waveform. This shows that all this activity is being generated mostly from the bearing outer raceway.


Fig 2: Autocorrelation of PeakVue Data

Figure 3 is the Acceleration Spectrum. This again shows that all this activity is being generated from the bearing outer raceway.

Fig 3: Acceleration Spectrum

Vibration PeakVue Data:

Figure 4 is the PeakVue Acceleration Time waveform. This shows very high general impacting up to 34.9g’s Peak.

Fig 4: PeakVue Time Waveform

Figure 5 is the Autocorrelation of the PeakVue Time Waveform. This shows that all this activity is being generated from the bearing outer raceway.


Fig 5: Autocorrelation of the PeakVue Time Waveform

Figure 6 is the PeakVue Spectrum. This shows that all this activity is being generated from the bearing outer raceway.

Fig 6: PeakVue Spectrum

Vibration Velocity Data:

Figure 7 is the Velocity Spectrum. This confirms that this is a late stage defect and that this energy is from the bearing outer raceway.

Fig 7: Velocity Spectrum

Inspection:

On visual inspection it was found as expected the grease looked oxidised in a poor state and there was a high area of damage to the bearing outer raceway – noticeably on one side of the rollers. Damage to this side of the raceway would have been caused by axial thrust from the fan shaft and motor.

Image 8: This is on removal of the bearing caps. This shows the oxidised poor condition lubricant.

Image 8

Images 9 to 12: These are further images of the grease condition.

Image 9: Grease extracted from the bearing housing
Image 10: Microscope image
Image 11 : Microscope image
Image 12 : Microscope image

Image 13: This shows the two tracks for the rolling elements on the outer raceway, and that it was highly loaded to one side.

Image 13

Images 14 and 15: These are close-ups of the defected area.

Image 14: Microscope image
Image 15 : Microscope image

Summary and Questions:

Researching the lubricant used we know this is not suitable for this application and that it will displace/separate and then oxidise.

But the question is what caused the high thrusting to the one side of the raceway, is it related to what is the fixed and free bearing? Is it true to say that due to the NDE (fan end) being the fixed bearing that expansion from the motor/ fan shaft would load up one side of the raceway?

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

Introduction:

Fluid film bearings are mainly monitored with proximity probes. It is often stated that “you can’t detect early defects in fluid film bearings with normal vibration techniques (Velocity, Acceleration or a bearing condition unit)”. But in fact you can detect the effects of a fluid film bearing deteriorating with a normal accelerometer.

Under abnormal circumstances metal to metal contact might occur, leading to occasional high-frequency noise that can be detected with normal vibration equipment. The following case study is a great example of this and also using lubrication analysis as part of a maintenance program.

This case history covers a Production facility Extraction Fan which has been monitored as part of a site wide Condition Based Monitoring program. The drive of this program is to integrate condition monitoring techniques and to drive the maintenance program.

This fan unit had a motor that is a direct drive to a fan shaft, the fan shaft has a white metal fluid film bearing. The fan is a standard overhung centrifugal of about 2.5 meters diameter.

This data was collected over an extended period by myself and Ian Graham.

 

Vibration Analysis:

Ian Graham flagged this reliability risk very early in the program for having a considerable 1 Order impact present in the PeakVue™ data (see Figure 1).

Figure 1 shows the initial Vibration data collected on the fan bearing with the 1 Order event present.

 

 

Vibration Trend Analysis:

Figure 2 is the PeakVue™ Trend of the bearing as it was nursed through until maintenance could be conducted.

This showed the initial level, reduction in levels after an oil flush, then a period of monitoring until another oil change and a bearing inspection.

 

 

Lubricant Analysis:

As the initial fan data had a dominant 1 order event and was being monitored on a monthly basis, we needed to determine whether the event was consistent or deteriorating, and what possible causes were.

Oil samples were then taken (see image 1), on visual inspection the oil was in a very poor contaminated condition. The lab report (see image 2) stated a serious concern with particulate matter contamination and high levels of Sodium, Iron, and Tin.

The indications of Tin suggested probable sleeve (Babbitt) wear of the bearing.

Image 1 is the Fan DE bearing oil sample:

Image 2 shows the initial oil sample report and diagnosis with emphasis on the high Tin levels:

 

Maintenance Actions:

This fan was a critical component of the facilities production process, however with a plant upgrade planned for the very near future, the decision was made to closely monitor the deterioration of the assembly rather than to rectify this potentially expensive piece of equipment.

The temporary measure of an oil flush and change was conducted immediately, with a visual inspection planned for the next shutdown.

 

Maintenance Inspection:

During the shutdown the bearing housing was split and the bearing shells separated. The damage to the bearing was very extensive with ‘scalloping’ of the Babbitt material evident in the direction of rotation forming a build-up at the end of the lower shell. The cause of this is most likely the failure of the lubricants ability to sustain an adequate oil wedge between the shaft and the bearing.

Image 3 shows the Fan DE white metal bearing upon inspection:

Image 4 shows the Lower half shell of the white metal bearing with a piece of ‘free floating’ Babbitt that was found in the sump:

 

Conclusion:

In conclusion, with the company’s utilisation of all the available Condition Monitoring technologies and tools, they were able to monitor and be consistently and accurately informed of the state of deterioration of the bearing. This allowed them to implement a rolling program of temporary measures to stave off what was essentially an unserviceable critical machine until the Factory upgrade was conducted.

.

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

 

 

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7th August 2018: Additional data as requested by JUAN CARLOS URQUIOLA

Below is the Velocity data from September 2017 and June 2018, there is a difference in the number of an amplitude of the 1 order as associated harmonics.

 

Below is the Acceleration high frequency spectrum, this shows two mounds of activity that has side bands of 1 order and 2 orders.

 

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