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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.

More information can be found here on the conferences https://thecbmconference.com/ and this web site is great for condition monitoring information https://www.cbmconnect.com/

My Presentation was on a case study solving a reliability issue at a pumping station by designing and using a Dynamic Vibration Absorber. You can download the presentation below.

And these are the videos in the presentation.

Slide 23: Side by Side Comparison
Slide 24: Bed Plate
Slide 25: Upside down base plate
Slide 32: Live Speed
Slide 33: Slow Motion

If you do get the opportunity to attend a CBM or Reliability conference I fully encourage it.

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

The Seasoned Analyst

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

Introduction:

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 experience and your human senses.

Background:

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.

Pre-Vibration Analysis:

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 1 – Before the online alarming

Figure 2 is the SPM online Velocity spectrum on the 3rd September, and shows many running speed harmonics indicating a component/mechanical looseness.

Figure 2 – After the online alarming

Inspection :

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 1 – Fan DE bearing (Motor Side)

Image 2 is of the fan NDE bearing (Fan side). The top cap retaining bolts were coming loose!

Image 2 – Fan NDE Bearing (Fan Side)

Corrective Actions:

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.

Figure 3 – After the bolts were tightened

Further 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.

Figure 4 – Drive end bearing (Motor Side)
Figure 5 – Non-drive end bearing (Fan Side)

Summary:

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 system.

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

The Seasoned Analyst

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

Introduction:

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.

Background:

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.

Air Fan

Vibration Analysis:

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.

Acceleration Data:

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.

Fig1:

Acceleration RMS Trend

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.

Fig 2:

SPM HD Enveloping

Summary of vibration:

There is a clear distinct defect in bearing outer raceway, at these levels this would confirm a spalling to the raceway.

Corrective Actions:

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.

Fig 3:

Original Motor
New Motor

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.

Fig 4:

Acceleration RMS Trend

Bearing Inspection: After sectioning and cleaning

On visual 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 1:

Drive End Bearing

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 2:

Microscopic Image Outer Raceway

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.

Image 3:

Microscopic Image Outer Raceway

Failure Mode:

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.

This bearing was close to catastrophic failure

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.

Summary:

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.

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

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.

Calculator – Vibration Acquisition Criteria – Version1.1.3

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

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

Background:

During an asset assessment survey of a Pump Set we detected an anomaly in the vibration data.

This is a ‘Brook Crompton Parkinson’ motor D112 Frame, 2865 RPM, 50Hz 3 Phase, 415V 4.9A with and integral ‘APE-Lee Howl Limited’ pump end.

Image 1 is of the pump set, this is a circulation pump for a water system.

Image 1:

Pump Set

Analysis:

Using experience, the human sense and the vibration data the conclusion was that there is a flow related issue.

 

Vibration Data:

Figure 1 is the Autocorrelation of the pump end PeakVue data in a circular plot.

Fig 1:

Figure 1.

This data shows the abnormal ‘wobble’ operation of the pump and that for each revolution there are three restrictions in the motion.

 

Inspection:

On visual inspection of the pump system it was found that the pump supply valve was closed. This was opened and water was then allowed thought the pump.

 

Follow up Vibration:

Figure 2 is the same PeakVue data as before but now with the pump system in its correct operational state.

Figure 2.

This data now shows the smooth circular motion of the pump.

 

Summary:

This case study brings a few things to mind

  1. The most important part of any program is the person performing the data collection and analysis
  2. When all else fails, leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery

 

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

Slow speed bearing defect detected though vibration analysis
(Case Study of a ≈ 20RPM Bearing Defect)

What is Condition Monitoring?

In general, 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.

Benefits of Reliability

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

We were 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 harsh environment.

Application:

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.

The image above is the four-point contact ball bearing, these are radial single row angular contact ball bearings with raceways that are designed to support axial loads in both directions.

Trial:

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 domain.

Trial Summary:

The vibration data that clearly indicated a defect was the PeakVue Time Waveform.

Trial data – Defective bearing PeakVue TWF
Trial data – Good bearing PeakVue TWF

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.

Trial data – Plot of an inner raceway defect

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.

Comparisons of the original and new bearing

The above 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.

Bearing Inspection:

On inspection 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

This shows 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

Surface initiated fatigue basically comes from damage to the rolling contact surface asperities. This is generally caused by inadequate lubrication.

Damage to Retainers

Causes of damage to retainers can be due to Poor lubrication, Excessive heat (plastic retainer in particular) and Excessive moment load.

Bearing Images:

Image 1: Bearing as received collected from site prior to Sectioning
Image 2: Bearing as received collected from site prior to Sectioning

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.

Image 3: Bearing cage pocket failure
Image 4: Bearing cage pocket failure
Image 5: Cracked cage pocket
Image 6: Cage pockets in various stages of failure
Image 7: Inner raceway

Inner raceway, on the load side, has various stages of spalling all the way around with one area of heavy spalling.

Image 8: Inner raceway ‘Cracking and spalling’
Image 9: Inner raceway Spalling
Image 10: Inner raceway overrolling
Image 11: Outer raceway

The outer raceway has less of spalling but again there is one area of higher spalling.

Image 12: Outer raceway Spalling
Image 13: Outer raceway Splaing
Image 14: Outer raceway Cracking and spalling
Image 15: Rolling element damage

The rolling elements display damage from over-roll of the spalled inner and outer raceways

Summary:

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

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant


Failure mode ISO 15243: 5.4.2 Subsurface initiated fatigue

Is this normal Fatigue Failure, how many of you get to see a bearing actually fail from normal fatigue? Usually we come across bearing failures/damage due to secondary factors such as misalignment, over or under lubrication, imbalance, resonance and poor installation……

This is also a great example of how important knowing the asset you are monitoring is as to know when to remove the asset from service, ensuring that the client has got the maximum life out of the asset for the associated risks.

# You can’t analyse what you don’t know or understand #

 

This Case Study Application:

This is a DC motor that is direct coupled driving a gearbox.

 

 

Summary:

We have been monitoring this motor since 2006 and in May 2017 a subtle change in the PeakVue level was noticed, closer monitoring was initiated and a bearing inner raceway frequency was found. Next in June 2018 there was a further step change that prompted the decision to remove from service as we felt the risk of failure was too high.The motor was overhauled at the next opportunity, this was in July 2018.

 

 

Vibration Data:

Figure 1 is the Velocity spectrum, there are no indications of any defect in this data.

Fig 1:

 

Figure 2 is the Peak Acceleration 10 KHz FMax trend from October 2017 until change out in July 2018, this displays an increasing trend.

Fig 2:

 

Figure 3 is the PeakVue Max Peak Acceleration trend from October 2017 until change out, this also shows the increasing trend.

Fig 3:

 

Figure 4 is the PeakVue spectrum. This shows the running speed activity and a beautiful text book bearing ball pass inner raceway defect frequency with harmonics and sidebands at 1 Order.

Fig 4:

 

Figure 5 is the PeakVue time waveform, this shows a distinct periodic impactive activity.

Fig 5:

 

Figure 6 is the Auto correlation of the PeakVue time waveform. Auto correlation is great tool for distinguishing periodic activity within a time signal. This data shows us that there is a defect that is modulating by 1 Order. Therefore a component on the motor shaft, rotating with the motor shaft has a defect.

Fig 6:

 

Figure 7 is a zoom in on the Auto correlation of the PeakVue time waveform. From this we can see that the 1 Order activity is side banded by the inner raceway defect frequency.

Fig 7:

 

 

Images of the bearing defect

Image 1 is of the bearing inner raceway. This shows the track of the rolling element in the race way, due to the DC drive, also within the arrows there is the defect.

Image 1:

 

Image 2 is a microscopic image of the defect. Has anyone else pulled a bearing with this type of defect?

Image 2:

 

 

Failure Mode:

Suspected failure mode is ISO 15243: 5.4.2 Subsurface initiated fatigue,

The images show that this bearing had reached its end of life, the cyclic stress changes occurring beneath the contact surfaces had initiated subsurface micro cracks, and 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.

 

 

Final Note:

A special thanks to James Pearce for the data and working with me on the analysis.

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

What’s the highest Acceleration levels on Gears you have recorded?

Apologies for the lack of posts over the month, it’s been a very busy time with the family.

This post is a short one just inquiring what levels of Acceleration impacting you have seen in the field from a gear set. This is one I came across a couple of months ago.

 

Summary:

  • Vibration data was collected with FMax of 10 KHz and Sample rate of 32,768.
  • The shaft rotates at 2990 RPM.
  • The gears are small and both have 65 teeth, their function is to transfer drive to an oil pump in a gearbox.
  • We recorded a Peak to Peak of 51.67 G’s compared to another identical asset running at 9.176 G’s.
  • Two weeks later the gears had a functional failure and stopped doing what they’re were designed to do.

 

 

Vibration Data:

This is the 1.3 Second Acceleration Time waveform comparing the suspect unit and an identical unit.

 

 

Images of Gears after Functional Failure:

Images of the gears on inspection.

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

Electrical defect found with Velocity data – Case Study

Has anyone found many electrical defects though vibration analysis? We know that VA will show the indications of electrical activity but not necessary the severity. This case study shows that the Velocity vibration data can indicate what the cause of the vibration problem is, this will enable the engineer to target the investigation.

Thanks to James Pearce for the data. linkedin.com/in/james-pearcevibrationanalysis

 

Background:

A routine client called after the operators noticed an increase in noise and vibration from a main plant drive motor. This is a DC motor and usually operates around 400-500 RPM. This is a rather old motor and drive system.

 

 

Initial Vibration Survey:

On attending site vibration data was collected, analysed and before leaving site recommendations were given.

Figure 1 is the Velocity Spectrum collected from the motor. This showed a 1 Order amplitude of 0.07mm/s RMS, with a dominant peak at 49.95Hz with an amplitude of 3.2 mm/s RMS with many harmonics. The motor was operating at 384 RPM during data collection.

Fig 1:

 

 

Figure 2 is the PeakVue Spectrum. This displayed a dominant peak at 149.86Hz, 3xLf. This was also sidebanded by running speed.

Fig 2:

 

The recommendations was to check all supply cable connections and inspect the variable speed drive components for condition.

 

 

Maintenance Inspection:

The site electrical engineer was dispatched to inspect the drive for this variable speed motor. Upon inspection 2 Thyristors were replaced and all electrical connections checked for security.

The operator then reported that the vibration magically disappeared.

 

 

Post Maintenance Vibration Survey:

Vibration data was then collected after maintenance. The motor was running at a higher speed of 456 RPM on the follow up survey.

Figure 3 is the Velocity overall trend from the initial survey and post maintenance survey. This trend shows the reduction on motion from 4.301 mm/s RMS to 1.162 mm/s RMS.

Fig 3:

 

 

Figure 4 compares the before and after maintenance Velocity Spectra’s. From this you can see the dominant 49.55Hz and harmonics have disappeared. The only activity left is a peak at 299.74Hz again sidebanded by 1 Order.

Fig 4:

 

 

 

Summary:

This again shows the benefits of sending a certified, experienced and correctly mentored Vibration Engineer and not a data dog to investigate vibration issues. James quickly pinpointed the cause of the excess vibration that enabled the client to efficiently target the area of concern and quickly rectify the issue saving time and money.

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

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