Acoustic Emission
Not the audible range up to 20kHz but above that is what we are interested in here
The technique of Acoustic Emission (AE) is the one where I have the most experience applying it to rotating equipment in the automotive, food and utilities sectors with multiple examples of cost benefits and case studies.
AE technology is transferrable to any industry that uses rotational equipment, it is compliant to very low speed rotation and it can also be used to monitor pressure systems similar to Ultrasound.
Ultrasound and AE are close as twin sisters, but not identical
The AE instrument I use is the Holroyd MHC Memo Pro, it's a data-logger that can be used by engineers, maintainers and front line operators. UPTIME Consultant has a Holroyd MHC to demonstrate if required.
Previously I have trained Predictive Specialists, Reliability Engineers, Technicians, Maintainers and Operators how to use an AE data-logger, including, asset criticality, taking meaningful readings, forming inspection routes, trending software, signature triggers and Spectrum Analysis if required.
The UPTIME Consultant articles explain more about this little known Predictive technology.
You can contact me direct at: andy@uptimeconsultant.co.uk for more information about training or a proposal.
AE technology is transferrable to any industry that uses rotational equipment, it is compliant to very low speed rotation and it can also be used to monitor pressure systems similar to Ultrasound.
Ultrasound and AE are close as twin sisters, but not identical
The AE instrument I use is the Holroyd MHC Memo Pro, it's a data-logger that can be used by engineers, maintainers and front line operators. UPTIME Consultant has a Holroyd MHC to demonstrate if required.
Previously I have trained Predictive Specialists, Reliability Engineers, Technicians, Maintainers and Operators how to use an AE data-logger, including, asset criticality, taking meaningful readings, forming inspection routes, trending software, signature triggers and Spectrum Analysis if required.
The UPTIME Consultant articles explain more about this little known Predictive technology.
You can contact me direct at: andy@uptimeconsultant.co.uk for more information about training or a proposal.
Acoustic Emission saves a critical asset
The benefits of using a Predictive Technology as part of a holistic reliability strategy
It's always good to have an example from the front line that demonstrates the way joined up thinking and collaboration can return the maximum benefit. This one explains not just the mitigation of future failures but the wider benefits delivered.
The first line of defence in any industrial plant are our operators, they spend most of their time living with these assets whilst they are producing the products that pay our wages.
To anyone starting a predictive program, make sure you include this staff and identify individuals that notice things more often than others, as a Predictive practitioner make sure you talk with them regularly about how their process is running and anything unusual happening with the product, sometimes this information can reveal hidden issues that no technology can identify.
It was a daily chat with an operator that mentioned and unusual 'surge' sound coming from an extruder, that lead us to examine ingredient throughputs and ruled out process variables. Sometimes ingredient powder can 'bridge' causing issues with the mixture into the barrel of an extruder, I could still consider this, but put it to the back of the queue in my mind.
The asset was a twin screw extruder that cooked a snack food half product; this is a pellet that is cooked later to produce the final savoury snack. Criticality was high on this asset as it and the sister extruder were the only two that produced this product in Europe. Disruption to this equipment would reduce availability in the supply chain causing a chain reaction of ramifications, not only in the plant but across the entire customer base. Some customers readily reallocate shelf space in their supermarkets if a product was 'crossed off' due to disruption or shortage of supply, it's a nightmare to retrieve that space back.
The first line of defence in any industrial plant are our operators, they spend most of their time living with these assets whilst they are producing the products that pay our wages.
To anyone starting a predictive program, make sure you include this staff and identify individuals that notice things more often than others, as a Predictive practitioner make sure you talk with them regularly about how their process is running and anything unusual happening with the product, sometimes this information can reveal hidden issues that no technology can identify.
It was a daily chat with an operator that mentioned and unusual 'surge' sound coming from an extruder, that lead us to examine ingredient throughputs and ruled out process variables. Sometimes ingredient powder can 'bridge' causing issues with the mixture into the barrel of an extruder, I could still consider this, but put it to the back of the queue in my mind.
The asset was a twin screw extruder that cooked a snack food half product; this is a pellet that is cooked later to produce the final savoury snack. Criticality was high on this asset as it and the sister extruder were the only two that produced this product in Europe. Disruption to this equipment would reduce availability in the supply chain causing a chain reaction of ramifications, not only in the plant but across the entire customer base. Some customers readily reallocate shelf space in their supermarkets if a product was 'crossed off' due to disruption or shortage of supply, it's a nightmare to retrieve that space back.
The consumer would also be unhappy if they couldn't eat their favourite snack food!
These extruders were monitored every week during production cycles with Acoustic Emission (AE) using the Holroyd MHC Memo Pro, I also sampled the lubricant each month through a take off port, CAT Finning Fluid Lab analysed and tracked the condition of the 40 Litre volume of oil. Various points on the assets were identified with Nodes for repeatability as shown below.
I interrogated the history of the oil samples and trends of the AE outputs over the past few months. There had been no warnings previously and this review revealed no anomalies, some might leave it at that but I trusted what the operator heard and I knew the asset's history.
This is another key thing, 'Know Your Asset' the more you know the better, I knew this extruder was 18 months older than its sister and that it had been in service 11 years. I also knew it had never had a main or transfer gearbox failure or refurbishment, so here we were well into the asset life cycle and understood it had been well looked after.
I decided to take an ad hoc early Oil Sample and send it to the laboratory, I also moved to the next level with the AE inspection and took Spectra samples from the main gearbox and the transfer gearbox; the transfer was a 5:1 step down transmission that coupled the drive motor and twin screw main extruder gearbox.
CAT Finning Oil analysis pack shown below:
The oil sample would take 3-4 days in the post, but I rang the Lab and asked them to expedite the sample which they did and I had an on-line database result within 48 hours, this showed an elevated Fe (Iron) reading but nothing too alarming.
I scheduled to take more samples at weekly intervals.
The Spectra result was more interesting as it showed a peak indicating a possible anomaly at the inner race frequency.
The Holroyd also has the option of using headphones to 'listen' to specific points of interest, something I rarely used unless I was lubricating bearings in operation, you can get an excellent measure the right volume greasing using this method, similar to some Ultrasound equipment. This audio inspection indicated an intermittent 'click' at a sub rotational speeds.
Another aspect about Predictive is shout about it!
I now had evidence of this asset requiring remedial action in the near future, emails and conversations were held with the operations manager, product specialist, maintenance and engineering managers, maintenance planner and our refurbishment partners.
Everyone had a heads up so we could put a plan in place
I ran the Preventative and Lubrication program, but for me it always include planning the way forward, considering the whole operation and in case some re-engineering may be involved. Another key benefit of Predictive is driving improvement and engineering changes backed by evidence and not hearsay.
Having ready access to the asset manual in our library I knew the original specification, could identify the SKF Bearing type without having to guess the values to put into the Spectra software. I also advised the refurbisher to purchase two of these SKF Explorer bearings to replace both the input and output at the same time, they also visited the site to work out a plan to turn this transmission around in a 12 hour period, using the 48 hour planned sanitation and maintenance window.
I contacted SKF who were our bearing partner to work together on the RCA when I had the used parts in hand, our rebuilder photographed the parts as they were disassembled for more evidence.
A couple of weeks later the transmission was removed, shipped, repaired and re-installed with no issues.
The main gearbox was flushed (both units used the same lubricant) and I checked filter patches for any other debris.
The bearings were returned so that I could clean, dis-assemble and inspect, I photographed the spalling damage that had occurred on the inner race so when I discussed it further with SKF we had more information, see below.
Having ready access to the asset manual in our library I knew the original specification, could identify the SKF Bearing type without having to guess the values to put into the Spectra software. I also advised the refurbisher to purchase two of these SKF Explorer bearings to replace both the input and output at the same time, they also visited the site to work out a plan to turn this transmission around in a 12 hour period, using the 48 hour planned sanitation and maintenance window.
I contacted SKF who were our bearing partner to work together on the RCA when I had the used parts in hand, our rebuilder photographed the parts as they were disassembled for more evidence.
A couple of weeks later the transmission was removed, shipped, repaired and re-installed with no issues.
The main gearbox was flushed (both units used the same lubricant) and I checked filter patches for any other debris.
The bearings were returned so that I could clean, dis-assemble and inspect, I photographed the spalling damage that had occurred on the inner race so when I discussed it further with SKF we had more information, see below.
In this case the asset was 'saved' and we lost no availability, but what else did this Predictive intervention deliver?
The last point is most pertinent, as I said earlier this was the 'older sibling' of the twin extruder assets, the other was 18 months younger. My attention was now drawn to this and two years later I picked up a similar anomaly on the output bearing that lead to an intervention that avoided another unplanned event.
The conclusion working with SKF was that the bearings had come to the end of their life (>10yrs) due to an age related mode of failure. Considering the load, environment and stresses they were under I believe they did remarkably well.
I will conclude with these thoughts that I share when training others:
Always listen to your front line operators, use multiple technologies if available, known your assets, keep your manuals in good order, talk to your preferred rebuilder, make sure the planners for maintenance and operations are in the picture, think holistically about the impacts on internal and external customers, make sure operations understand that you deliver their availability, run a RCA even when there are no losses, consider if redesign is required, record and share everything, shout about the risks and the wins when they happen, the list goes on and the benefits are multiple.
My experience with this particular incident is that Operations and Engineering grew closer in their respect for each other working as a team with a common goal.
- Avoided unplanned disruption to the process
- Technician labour used as planned not reactive
- Planned work is safer than working reactively
- Collateral damage to the main gearbox avoided
- Resulted in zero product cross offs across the supply chain
- Involved the front line operators in the Predictive activity
- Demonstrated the value of the Predictive and Lubrication Program
- Involved Engineering and Operations working towards a shared goal
- Increased my knowledge of bearing life cycles working with SKF
- Instigated an RCA (even though we incurred no losses) that gave us more information
- Built confidence in the Engineering function from the Operations team
- Used a cross functional team to avoid a future catastrophic event
- Improved our knowledge of the asset for future reference
The last point is most pertinent, as I said earlier this was the 'older sibling' of the twin extruder assets, the other was 18 months younger. My attention was now drawn to this and two years later I picked up a similar anomaly on the output bearing that lead to an intervention that avoided another unplanned event.
The conclusion working with SKF was that the bearings had come to the end of their life (>10yrs) due to an age related mode of failure. Considering the load, environment and stresses they were under I believe they did remarkably well.
I will conclude with these thoughts that I share when training others:
Always listen to your front line operators, use multiple technologies if available, known your assets, keep your manuals in good order, talk to your preferred rebuilder, make sure the planners for maintenance and operations are in the picture, think holistically about the impacts on internal and external customers, make sure operations understand that you deliver their availability, run a RCA even when there are no losses, consider if redesign is required, record and share everything, shout about the risks and the wins when they happen, the list goes on and the benefits are multiple.
My experience with this particular incident is that Operations and Engineering grew closer in their respect for each other working as a team with a common goal.
If you are interested in booking a training course introducing Predictive, Lubrication, RCM or Reliability Strategies, either onsite or supported virtually on-line then please contact me directly at: andy@uptimeconsultant.co.uk
Acoustic Emission (AE) the earliest warning of Potential Failure in Prediction?
Acoustic Emission, is that the noise we can hear?
No, this is structural borne 'noise' from the earliest inception of component wear.
So why isn't it more widely used in Industry?
No, this is structural borne 'noise' from the earliest inception of component wear.
So why isn't it more widely used in Industry?
Acoustic Emission is a little known technology in the industrial predictive field, this article aims to explore the basics of 'how it works', and the pragmatic, practical side of its use in Industry without getting too technical.
The slides here are from UPTIME Consultant's "Introduction to Condition Monitoring" used to train front line operators, engineers, technicians and maintenance teams; a full day session that includes hands on with instruments and time in your production areas to identify solutions on the spot.
If you are reading this then you probably already know the importance of prediction and the positive impact it can have on availability, with reduced unplanned downtime and less reactive work.
Implemented correctly the predictive tools will serve you well, most have heard of Vibration and Ultrasound but less will know about AE. There is a reason for this that I will cover later.
So where does Predictive sit in the grand scheme of things?
See the slide below:
The slides here are from UPTIME Consultant's "Introduction to Condition Monitoring" used to train front line operators, engineers, technicians and maintenance teams; a full day session that includes hands on with instruments and time in your production areas to identify solutions on the spot.
If you are reading this then you probably already know the importance of prediction and the positive impact it can have on availability, with reduced unplanned downtime and less reactive work.
Implemented correctly the predictive tools will serve you well, most have heard of Vibration and Ultrasound but less will know about AE. There is a reason for this that I will cover later.
So where does Predictive sit in the grand scheme of things?
See the slide below:
Slide shows where the Predictive technologies (or tools) sit in the lifecycle of our assets, the trick is to identify evidence before the 'Potential' or within the P-F interval. The five disciplines listed are those I cover in UPTIME Consultant's training.
AE like all Predictive disciplines augments a human sense, in this case hearing
Human hearing has a range of 20Hz to 20kHz, the frequencies where thinks start to happen is 20kHz and above.
Condition Monitoring starts in the audible range as we move around or operate in a plant, our hearing picks up differences in how machines sound when we work with them every day.... if we take notice!
Our hearing is also a great way to start thinking about how we can deploy AE.
One thing to clear up is that AE is not Vibration (Vib) or Ultrasound, I can see where people get confused as Vib has waves and sound is transmitted by sound waves. In fact all the predictive technologies involve 'waves'.
AE refers more to structural borne 'sound' waves outside of our hearing range.
Ultrasound is a very close relation but has more to do with fluid and airborne equipment inspection, pneumatics, steam traps, pressure vessels, valves, arcing, discharge and tracking in electrical equipment.
Some Ultrasound equipment is now being marketed for bearing inspections, but it's not AE.
The other thing to set straight is that AE uses Transducers that are not the same as a Vibration Accelerometer.
It's been known for hundreds if not thousands of years that metals 'sing' or 'cry' when under stress as witnessed by tinsmiths and metal workers. In the late 1940s with the advent of high frequency sensors and amplifiers we were able to 'listen' to materials 'crying' under load.
Josef Kaiser was the researcher who published his thesis in 1950 reporting that materials under stress emit low amplitude 'clicks', this lead to a new NDT (Non Destructive Testing) branch called Acoustic Emission. It has uses not just in metallic engineered structures but also in large concrete vessels and civil engineering applications including bridges, dams, motorway flyovers, silos and pipelines where whole structures can be monitored. In fact this is where AE is more wide spread and known.
I'm interested in process equipment in production facilities, utilities and manufacturing.
The breakdown in rotating or sliding surfaces is triggered by a number of modes including lack of lubrication allowing surfaces to clash or rub, too much lubrication causing stick slip and other effects, excessive heat, ingress of water or other harmful chemicals, excessive loads, environmental issues with dirt and debris, poor quality parts or sub standard assembly.
Condition Monitoring starts in the audible range as we move around or operate in a plant, our hearing picks up differences in how machines sound when we work with them every day.... if we take notice!
Our hearing is also a great way to start thinking about how we can deploy AE.
One thing to clear up is that AE is not Vibration (Vib) or Ultrasound, I can see where people get confused as Vib has waves and sound is transmitted by sound waves. In fact all the predictive technologies involve 'waves'.
AE refers more to structural borne 'sound' waves outside of our hearing range.
Ultrasound is a very close relation but has more to do with fluid and airborne equipment inspection, pneumatics, steam traps, pressure vessels, valves, arcing, discharge and tracking in electrical equipment.
Some Ultrasound equipment is now being marketed for bearing inspections, but it's not AE.
The other thing to set straight is that AE uses Transducers that are not the same as a Vibration Accelerometer.
It's been known for hundreds if not thousands of years that metals 'sing' or 'cry' when under stress as witnessed by tinsmiths and metal workers. In the late 1940s with the advent of high frequency sensors and amplifiers we were able to 'listen' to materials 'crying' under load.
Josef Kaiser was the researcher who published his thesis in 1950 reporting that materials under stress emit low amplitude 'clicks', this lead to a new NDT (Non Destructive Testing) branch called Acoustic Emission. It has uses not just in metallic engineered structures but also in large concrete vessels and civil engineering applications including bridges, dams, motorway flyovers, silos and pipelines where whole structures can be monitored. In fact this is where AE is more wide spread and known.
I'm interested in process equipment in production facilities, utilities and manufacturing.
The breakdown in rotating or sliding surfaces is triggered by a number of modes including lack of lubrication allowing surfaces to clash or rub, too much lubrication causing stick slip and other effects, excessive heat, ingress of water or other harmful chemicals, excessive loads, environmental issues with dirt and debris, poor quality parts or sub standard assembly.
The transducer is connected via a co-axial cable to the hand held instrument and the readings are captured as close to the centre line and perpendicular to the component of interest.
If you had to go and download, use complicated software and have years of experience to interpret (sound familiar) this would be a long winded process for little gain so would probably have little or no benefit.
I'm all about proving a benefit before using any Predictive technology and this AE device gets around this issue by crunching the data in the collector, transposing it to an easy to read understandable figure that can be compared to the previous reading (if Known) for immediate action.
Multiple data points and routes can be inspected and downloaded into a history file that can trend points of interest and flag warnings if required.
It can also be set up to capture Spectra readings that can be transposed as FFT (Fast Fourier Transform) to analyse specific frequencies associated with outer/inner race, cage, element, journal or ball spin frequency.
This analysis can pinpoint early damage like spalling or fretting inside bearing assemblies (see above).
So how does it work?
If you can imagine a defect on a single roller in a bearing, every time that imperfection contacts the inner or outer race it sends out a high frequency low amplitude 'ping'; some refer to this as Shock Pulse or Spike Energy but hopefully you get the idea.
If we can track this anomaly over time and trend its journey then we will witness the degradation from a very early state before things get bad enough for vibration to be detected readily. We then have advanced warning to plan bearing or asset replacements or overhauls in a planned event; maybe in a product change or in planned maintenance.
It can also be used as a pure Condition Based Maintenance tool to target a Lubrication program.
I have removed fixed time Lubrication tasks that risked under or over lubrication,only lubricating from the AE outputs.
This reduces the PM labour time, and lubricant use whilst enhancing the lifespan of equipment and equipment efficiency.
I have just covered the basics of AE and hopefully it has given you an insight.
If you had to go and download, use complicated software and have years of experience to interpret (sound familiar) this would be a long winded process for little gain so would probably have little or no benefit.
I'm all about proving a benefit before using any Predictive technology and this AE device gets around this issue by crunching the data in the collector, transposing it to an easy to read understandable figure that can be compared to the previous reading (if Known) for immediate action.
Multiple data points and routes can be inspected and downloaded into a history file that can trend points of interest and flag warnings if required.
It can also be set up to capture Spectra readings that can be transposed as FFT (Fast Fourier Transform) to analyse specific frequencies associated with outer/inner race, cage, element, journal or ball spin frequency.
This analysis can pinpoint early damage like spalling or fretting inside bearing assemblies (see above).
So how does it work?
If you can imagine a defect on a single roller in a bearing, every time that imperfection contacts the inner or outer race it sends out a high frequency low amplitude 'ping'; some refer to this as Shock Pulse or Spike Energy but hopefully you get the idea.
If we can track this anomaly over time and trend its journey then we will witness the degradation from a very early state before things get bad enough for vibration to be detected readily. We then have advanced warning to plan bearing or asset replacements or overhauls in a planned event; maybe in a product change or in planned maintenance.
It can also be used as a pure Condition Based Maintenance tool to target a Lubrication program.
I have removed fixed time Lubrication tasks that risked under or over lubrication,only lubricating from the AE outputs.
This reduces the PM labour time, and lubricant use whilst enhancing the lifespan of equipment and equipment efficiency.
I have just covered the basics of AE and hopefully it has given you an insight.
But if it's so good and user friendly, why is it not as popular or ubiquitous as Vibration?
Firstly it's niche, not many manufacturers exist that produce analysers or the software.
Vibration has hundreds of options for equipment, loads of standards that support the technology.
The practitioners are also protective, some still like to guard it as a 'black art' that needs years of qualification and experience.
In some cases that unfortunately is true; you'll need a degree in Vibration to understand some data outputs, and it probably doesn't provide the return on investment and benefits that I would expect.
Vibration and AE co-exist as tools in the CM toolkit, along with Ultrasound or Thermography, each has its strengths or weakness depending on the mode of failure.
Strengths wise AE is largely unaffected by background noise, it is more sensitive to faults under normal running, applicable to all machines at almost all running speeds, presents faults at the asset and has good parameters to trend from.
On the other hand it needs special transducers and signal processing, it's sensitive to turbulence and crushing forces, so it doesn't like turbines, chains or some servos that emit ultrasonics.
It's not sensitive to minor imbalance, mis-alignment or bent shafts; aspects Vibration is very good at measuring.
Vibration has hundreds of options for equipment, loads of standards that support the technology.
The practitioners are also protective, some still like to guard it as a 'black art' that needs years of qualification and experience.
In some cases that unfortunately is true; you'll need a degree in Vibration to understand some data outputs, and it probably doesn't provide the return on investment and benefits that I would expect.
Vibration and AE co-exist as tools in the CM toolkit, along with Ultrasound or Thermography, each has its strengths or weakness depending on the mode of failure.
Strengths wise AE is largely unaffected by background noise, it is more sensitive to faults under normal running, applicable to all machines at almost all running speeds, presents faults at the asset and has good parameters to trend from.
On the other hand it needs special transducers and signal processing, it's sensitive to turbulence and crushing forces, so it doesn't like turbines, chains or some servos that emit ultrasonics.
It's not sensitive to minor imbalance, mis-alignment or bent shafts; aspects Vibration is very good at measuring.
How does Acoustic Emission work?
The Condition Monitoring technology of Acoustic Emission is an area where I have decades of experience applying it to equipment in the Food, Automotive and Utility sectors, with multiple examples of cost benefit case studies
The technology is transferrable to any industry that uses rotational equipment, it can also be used as a device to monitor pneumatic systems in a similar way to Ultrasound.
The Holroyd MHC Memo Pro, is simple to use instrument in the field, I've trained reliability engineers, technicians, maintenance engineers and operators how to use this data-logger including, equipment criticality, taking meaningful readings, how to approach inspection routes, database trending, signature triggers and Spectrum Analysis.
Holroyd Kittiwake have produced a few YouTube videos if you would like to take a closer look, the best one by far is in the one below as it gives a really good understanding of this technology and the instrument
If you would like more information please give me a call or email me at andy@uptimeconsultant.co.uk
I own a Holroyd MHC Memo Pro as demonstrated in the video, if you are interested in finding out more about the technology or have a critical asset you need inspecting please get in touch.
www.kittiwakeholroyd.com/images/looptb4/Onsite_instruments.pdf
The technology is transferrable to any industry that uses rotational equipment, it can also be used as a device to monitor pneumatic systems in a similar way to Ultrasound.
The Holroyd MHC Memo Pro, is simple to use instrument in the field, I've trained reliability engineers, technicians, maintenance engineers and operators how to use this data-logger including, equipment criticality, taking meaningful readings, how to approach inspection routes, database trending, signature triggers and Spectrum Analysis.
Holroyd Kittiwake have produced a few YouTube videos if you would like to take a closer look, the best one by far is in the one below as it gives a really good understanding of this technology and the instrument
If you would like more information please give me a call or email me at andy@uptimeconsultant.co.uk
I own a Holroyd MHC Memo Pro as demonstrated in the video, if you are interested in finding out more about the technology or have a critical asset you need inspecting please get in touch.
www.kittiwakeholroyd.com/images/looptb4/Onsite_instruments.pdf