A profitable plant is reliable, safe and a cost-effectively maintained plant.
The Seasoned Analyst
CBM Conference 2019 UK
I presented at my first Conference, and it was the first CBM Conference in the UK. It was well worth attending as I got to discuss various challenges in the condition monitoring and reliability sector, and the most common discussion point was buying from senior management and how to continually highlight the benefits of a condition monitoring program.
In addition there were vendors there demonstrating the latest advancements in condition motioning technology from vibration online and walk around, thermal imaging safety, ultrasound new high sampling rates time waveform analysis to motor electrical condition monitoring.
When all else fails, leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery.
The seasoned Analyst
Online vibration monitoring is a great tool that enables monitoring of a vast number of assets, it helps the analyst when they “can’t see the woods for trees”.
This post is to highlight that for a full assessment of an asset you don’t just sit in your air conditioned office looking at the data on the screen. You must use other technologies and inspection tools to assess the Reliability of the system, the best tool is experienceand your human senses.
The SPM online system alarmed on a fan bearing. This fan has a direct drive AC motor to a fan lay shaft with two SKF/Cooper split bearings.
The onsite vibration analyst called for an inspection of the bearing due to mechanical/component looseness and an outer race defect. I was asked to confirm the diagnosis and provide further details.
On review of the data, and the new on demand live data, from the SPM system I concluded that the analyst was correct in the diagnosis of mechanical/component looseness and an outer race defect on the split bearing.
Figure 1 is
the SPM online Velocity spectrum from the 1st September, with low
overall one order and no harmonics.
Figure 2 is the SPM online Velocity spectrum on the 3rd September, and shows many running speed harmonics indicating a component/mechanical looseness.
Before I issued my comments I decided to “Leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery”. Within seconds I spotted the issues and using my personal Motion Amplification tool, my finger! I felt and confirmed what my eyes were seeing.
Image 1 is of the drive end (Motor side) split bearing, all good.
Image 2 is of the fan NDE bearing (Fan side). The top cap retaining bolts were coming loose!
This was reported immediately to the on site maintenance team. Maintenance re-secured and torqued the bearing top cap bolts. It was found that both bolts were loose!
Post Vibration Analysis:
Figure 3 is the SPM online Velocity spectrum after the corrective actions, 3rd September. This shows a large reduction in the 1 order harmonics, confirming the loose bolts were the cause of the harmonics. It was also noticed that there were still some higher frequency data evident that was not there prior to the 3rd September.
analysis of the SPM HD Envelope spectrum displayed a clear defect signal for
the outer raceway. This is a split bearing so you would expect to see some
bearing signal but the fan end is a lot higher. This is not surprising giving
that the fan end bearing was in operation with a loose top bearing cap!
The data below compares the drive end (motor side) Figure 4 and non-drive end (fan side) Figure 5 SPM HD Envelope spectrum. This confirming that the fan end bearing signal is a lot higher.
This highlights that there is a place for an online monitoring system in some aplications.
In addition to preventing a catastrophic failure of the fan and this having a effect to the profitability of the site, this prevented what could have been a very dangerous safety incident with a fan coming loose at full speed.
For a full assessment of the system please leave
the air conditioning, and go examine the operating equipment. Go look, touch,
feel, smell and listen to the machinery. Don’t site and rely on one form of
data to make a decision that will affect the reliability and probability of the
A profitable plant is reliable, safe and a cost-effectively maintained plant.
A profitable plant is reliable, safe and a cost-effectively maintained plant.
I often am lucky enough to use different vibration technologies and this post is a great example of how a vibration analysis program can protect the business using the SPM HD Enveloping technique. This post is with thanks to assistance from Dean Whiteside.
As part of a routine vibration data collection program a change in condition was noted at the fan motor vibration levels. Vibration monitoring frequencies were increased to daily as the defect deteriorated. This enabled planning and a controlled change out of the motor.
On inspection of the vibration data, bearing outer raceway (BPFO) damage was diagnosed at the drive end motor bearing. This was clearly evident in the SPM HD Enveloping.
Figure 1 shows the Acceleration RMS trend from the motor drive end (DE) bearing location. This shows the steep increase in the impacting levels with an exponential increase in the final days of monitoring.
SPM HD Enveloping Data:
Figure 2 shows the SPM HD Envelope spectrum from the motor drive end bearing. This technique shows a clear impact at 3.09 Orders that matches the defect frequency for the bearing fitted. There are many harmonics indicating a very impactive signal.
Summary of vibration:
There is a clear distinct defect in bearing outer raceway, at these levels this would confirm a spalling to the raceway.
Due to the risk of failure, a new motor was sourced and placed on-site encase of instant catastrophic failure. The risks was discussed with production and was deemed too high to the process and a plan was put in place for a controlled stop. But prior to this date there was an unexpected line stop, and as the motor was all prepared on site, the motor was changed during this downtime.
Vibration data after controlled change-out:
Figure 3 are the SPM HD Enveloping spectra from before and after motor change out. The top plot showed the clear bearing damage and now with the replacement motor there are no bearing defect signals present.
Figure 4 is the Acceleration trend from the motor drive end bearing location. This trend shows the increasing and then the lowest record level with the new motor installed.
Bearing Inspection: After sectioning and cleaning
inspection, it was found as expected, a large visible defect in the loadzone of
the bearing outer raceway. Motor Drive End Bearing FAG 6316-C3
Image 1 is the drive end bearing sectioned.
Image 2 is the defect located in the loadzone of the outer raceway.
Notice the flat bottom of the spalled area and the “neat” cracks around it. These are cracks that have come to the surface and in time, more material will break away.
Image 3 is the defect located in the loadzone of the outer raceway.
Particle over roll as the bearing comes out of the load zone.
ISO 15243:2004: 5.1.2 Subsurface initiated fatigue. Primary causes of Subsurface initiated fatigue are repeated stress changes and material structural changes. This leads to microcracks under the surface, crack propagation and then spalling.
The bearing is damaged as soon as spalling occurs. Spalling gradually increases and gives rise to noise and vibration levels in the machine. This machine was stopped and repaired before the bearing collapsed. The period from initial spalling to failure depends on the type of machine and its operating conditions.
What is sub surface fatigue? In a rotating bearing, cyclic stress changes occur beneath the contact surfaces of the raceways and rolling elements. Consider the rotating inner ring of a radial bearing with a radial load acting on it. As the ring rotates, one particular point on the raceway enters the load zone and continues through an area to reach a maximum load (stress) before it exits the load zone.
During each revolution, as that one point on the raceway enters and exits the load zone, compressive and shear stresses occur. Depending on the load, temperature and the number of stress cycles over a period of time, there is a build-up of residual stresses that cause the material to change from a randomly oriented grain structure to fracture planes.
In these planes, so-called subsurface microcracks develop beneath the surface at the weakest location, around the zone of maximum shear stress, typically at a depth of 0,1 to 0,5 mm. The depth depends on the load, material, cleanliness, temperature and the microstructure of the steel. The crack finally propagates to the surface and spalling occurs.
This is another example of how vibration technology
and knowing system health and risk of failure enables data driven decisions to
benefit the business. The motor was replaced when the line was down due to an
unplanned shutdown, with no additional downtime occurred.
If this motor had failed without any planning this would have lost product and reduced profit. In addition these actions have protected the customers, supply chain and brand our reputation.
Apologies for the lack of posts, work and life has been busy but fun, now back to my hobby.
Whilst going though some of my files I found a spreadsheet I wrote first back in 2012/2013 (ish). I thought it would be a good spreadsheet to share.
The reason I created this spreadsheet was that in my job at the time I had to create Vibration Standards for database creation/standardisation across multiple business units and locations, and so I needed a quick way to decide upon the best data collection parameters that would resolve the defect of interest. There was also limited server space so I didn’t want to collect unnecessary data. Obviously, now with the advance in technology you can take one large data set with huge number of samples and a high sample rate.
The spreadsheet is self explanatory and has notes on each section to explain, please read the ‘Introduction’ tab first. Even though it was designed for the CSI Emerson MHM the ‘Vibration Calculator’ tab is universal (other than the Special time waveform option) whereas the ‘PeakVue Calculator’ tab is unique to CSI MHM.
This interactive calculator is good to help understand how the sample rate and number of samples affects the frequency and time domain resolution for what you want to resolve.
Apologies in advance on any terminology errors as I wrote this in the English/Aussie tongue, therefore there may be some miss interpretation from my English/Aussie to other cultures.
Click on the link below and have fun 🙂 and feel free to share.
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!
This share has two questions;
What the highest Acceleration levels you have recorded on a fan rotating at around 1498 RPM?
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?
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.
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.
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.
Figure 3 is the Acceleration Spectrum. This again shows that all this activity is being generated from the bearing outer raceway.
Vibration PeakVue Data:
Figure 4 is the PeakVue Acceleration Time waveform. This shows very high general impacting up to 34.9g’s Peak.
Figure 5 is
the Autocorrelation of the PeakVue Time Waveform. This shows that all this activity
is being generated from the bearing outer raceway.
Figure 6 is
the PeakVue Spectrum. This shows that all this activity is being generated from
the bearing outer raceway.
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.
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.
Images 9 to
12: These are further images of the grease condition.
Image 13: This shows the two tracks for the rolling elements on the outer raceway, and that it was highly loaded to one side.
and 15: These are close-ups of the defected area.
Summary and Questions:
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
I have been privileged and blessed to have experienced varied fields of Vibration Analysis, Condition Monitoring and Reliability, and had the opportunity to study under some of the great mentors and trainers in these discipline. I feel it is always good to share knowledge and learnings to help others who want to progress and to promote our discipline.
Often people discuss what makes a good vibration analyst? – electrical or mechanical background – degree or apprenticeship level, certification or experience……….. Then when we find an issue we always get asked “How long will it last?”, and our answer to this question, I feel, greatly depends on our experience and training.
In the discussions I have had with many other people, we have all spoken ‘Pearls of Wisdom’. The 14 statements below I feel are very important in the way we operate in our discipline.
1) The most important part of any program is the person performing the data collection and analysis.
2) The second most important part of any program is the training and mentoring given to the person selected.
3) 5 years of experience is not the same as 1 year of experience 5 times.
4) The most important question you can ever ask is “why”.
5) It is important to understand the values of the numbers you are using.
6) Physics of the machine is really important.
7) You can’t analyse what you don’t know or understand.
8) A person may not be stupid, they may just not understand what you are saying.
9) 1 times RPM is not always unbalance.
10) There are no universal vibration severity limits.
11) Absolute amplitude in the frequency domain is relatively useless. Don’t forget the time domain & phase.
12) There are no ghost frequencies or unknown frequencies but only frequencies not analysed enough.
13) Don’t ignore the potential benefits of chit chat in the crib/break room with the operators and maintenance teams. They know their machines!
14) When all else fails, leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery.
Please share and if you have anymore ‘Pearls of Wisdom’ let everyone know.
Slow speed bearing defect detected though vibration analysis (Case Study of a ≈ 20RPM Bearing Defect)
What is Condition Monitoring?
Condition Monitoring techniques use instrumentation to take regular or
continuous measurements of condition parameters, in order to determine the
physical state of an item or system without disturbing its normal operation.
Condition Monitoring is basically applicable to components whose condition deteriorates with time. The objective of the Condition Monitoring technique is therefore to provide information with respect to the actual condition of the system and any change in that condition.
This information is required to schedule
conditional maintenance tasks, on an as needed basis instead of relying on
predetermined times. The selection of the Condition Monitoring technique(s)
usually depend on the behaviour of the failures, type of equipment used and
finally on economic and safety consequences.
This case study shows that when you collect the correct data parameters, vibration analysis can be invaluable in early detected of slow rotating bearings to enable a controlled change out prior to disruption to production.
The main benefits of applying an effective condition based maintenance programme are that repairs can be scheduled during non-peak times, machine productivity and service life are enhanced, and repair costs due to a loss of production time are eliminated. Safety is improved – Maintenance costs managed – Reliability reduces Maintenance costs
Case History Background
asked if we could offer a solution to detect when a rolling element bearing was
failing prior to catastrophic failure. The clients concerns was not the cost of
the bearing but the cost of the disruption to the production schedule if the
bearing failed during a production run. The client was unsure what would detect
the bearing issues as the bearing only rotates at around 20 RPM and it is in a
This is a
slurry pot in a dusty foundry environment, the slurry pot is approximately 1.5meters
in diameter and 2 meters in height. The bearing installed is an INA U250433 four
point contact bearing. The outer raceway is stationary and the slurry pot is
connected to the inner raceway that rotates.
We set up
various sampling rates, various number of sample and utilised different filters.
Data was collected using a magnetically mounted 100mV/g accelerometer. Velocity,
Acceleration and PeakVue data was stored for analysis in the frequency and time
data that clearly indicated a defect was the PeakVue Time Waveform.
The PeakVue time waveforms above are from the initial trial, and this compares the suspect failed bearing and a bearing that is expected to be good.
The above PeakVue
spectrum is from the suspect bearing on the trial data. This data shows a mound
of activity at 24.50 orders, and this activity is sidebanded by 1 orders. The theoretical
overrolloing defect frequency for the rotating inner race way is 24.47. This indicates
that we have an inner raceway defect.
We selected the slurry pot with the damaged bearing and requested the bearing to be change out and removed for inspection.
PeakVue time waveform comparisons show the before (in red) and the after with
the new bearing fitted (in blue). This data confirms the new bearing has been
fitted correctly and has no early defects. This also confirms that the bearing
indeed had a defect.
the bearing cage elements had fatigued and failed, there is also a lot of
spalling to the inner and outer raceway most probably due to subsurface and
surface initiated fatigue.
ISO 15243: 5.4.2 Subsurface initiated fatigue
that this bearing had reached its end of life, the cyclic stress changes
occurring beneath the contact surfaces had initiated subsurface micro cracks
this would have been in part of the bearing at the maximum shear stress. We are
at the point where the crack has propagated to the surface and spalling has
started to occur.
ISO 15243: 5.1.3 Surface Initiated Fatigue
initiated fatigue basically comes from damage to the rolling contact surface
asperities. This is generally caused by inadequate lubrication.
Damage to Retainers
damage to retainers can be due to Poor lubrication, Excessive heat (plastic
retainer in particular) and Excessive moment load.
Once the bearing was split the outer races were
moved to allow the rolling elements and cage pockets to be inspected as a
whole. On inspection there are many areas of bearing cage failure.
Inner raceway, on the load side, has various stages
of spalling all the way around with one area of heavy spalling.
The outer raceway has less of spalling but again
there is one area of higher spalling.
The rolling elements display damage from over-roll
of the spalled inner and outer raceways
The inspection confirmed that by utilising the correct data collection parameters a slow speed bearing defect can be detected in this working environment. We were successful in determining a failed bearing prior to catastrophic failure