RMS are pleased to offer The Reliability Team’s latest book, ‘Have a listen to Ultrasound’, by Thomas J Murphy. The paperback contains 212 pages, is available in English, and has the following ISBN: 9798412080727. To show our support for this important book, ‘Have a listen to Ultrasound’ will be included for RMS students attending a public CAT-I Ultrasound course during 2022.
Every little helps!
Have a listen to Ultrasound
Introduction – Tom Murphy
‘I graduated from the University of Salford in 1979 with a bachelor’s degree in the little-known subject of Electroacoustics. My interest in Acoustics, however, goes back a long way – from music through sound reproduction. There is considerable information carried in sound. Using sound as a diagnostic tool is not new – lots of people still use screwdrivers or stethoscopes to listen and make decisions about condition. It has been my great pleasure to be part of that worldwide group of listeners and this book is intended to help you to become an active and successful member of that global family of sound users.
My condition monitoring started with vibration measurement. Long before my entry into condition monitoring, I was using accelerometers to measure vibration and shock in all sorts of applications in the greater field of test and measurement. Having moved into condition monitoring, it was not long before I was drawn to thermography. What a fantastic tool! So tragically under-used in non-electrical applications.
After a while I began to realise that there needed to be more to this “con mon” game than just those two technologies. So, around 1997, I started digging and came across Ultrasound.
Ultrasound is an eye-opener. It pushed me towards a much wider awareness of Reliability. Up to that time, only things that rotated and electrical installations had been of interest. I began to wonder how many thousands of air leaks, valves and steam traps I had walked past in my life.
I saw the world of assets and failure modes. I had never dreamed that people would be interested in finding these failures because I had never heard anyone talk about them.
Every day that I introduce somebody to Ultrasound, I feel that thrill again and see in the faces of others the dawning realisation of just how powerful this technology really is.
Which brings me to this book. After 20 years of using Ultrasound and teaching people how to use Ultrasound around most of this beautiful World, the time is right to pass that experience on in an informal but still understandable format.
One of my hopes in writing this book is that it will make it on to the approved reading lists for some of the certification courses. So, whether you are preparing for your ISO Ultrasound certification course and exam or just need to know something more about an application, happy reading.’
A look inside, ‘Have a listen to Ultrasound’
Table of Contents
Failure to prepare …3
Is your FMEA Fit? …4
Important Sound fundamentals …8
What is Sound? …9
What is Ultrasound? …10
Reflection and transmission at a boundary … 13
The Decibel … 16
The Inverse Distance Law … 24
Condition Indicators … 26
Measurements and sensors … 30
Getting the Acoustics right … 31
Contact sensors … 32
Airborne sensors … 35
Instruments … 38
Analysis and diagnostics using Time … 42
Practical tips to find meaning in the time signal … 54
Healthy bearing … 55
Poor lubrication … 56
Early stage bearing defect … 57
Clear defect … 58
VFD noise … 59
A clipped recording … 60
Analysis methods … 61
Using Statistics to understand your data … 67
Building and implementing a successful programme … 71
The budget …77
The eight pillars of Ultrasound … 79
Pressurised gas and vacuum leaks … 81
Vacuum leaks … 88
Pneumatic leaks … 90
Test methods and considerations … 91
Steam leaks and steam traps … 95
Test methods and considerations … 101
Valves … 105
Test methods and considerations … 109
Hydraulics … 112
Test methods and considerations … 115
Electrical … 116
Corona … 120
Tracking … 123
Arcing … 125
Test methods and considerations … 126
Lubrication … 128
Test methods and considerations … 136
Rotating machinery … 146
Bearing defects as events … 149
Bearing deterioration considerations … 151
Variable speed applications … 153
Revisiting clipping … 155
Slow-speed bearings …156
High vibration applications … 160
Couplings … 161
Chains … 164
Gearboxes … 166
Belts … 168
Reciprocating machinery … 169
Test methods and considerations … 174
Tightness testing … 180
Test methods and considerations … 184
Unusual applications … 186
Tanker delivery … 186
Wine transportation … 187
Window seals on high rise buildings … 188
Strange noises on a conveyor … 189
A selection of time signals … 9
Tracking … 191
Corona … 192
Vibrating washer on a transformer foot … 193
Arcing and tracking together … 194
Slow speed bearing … 10
Bearing needs grease … 11
Bearing already overgreased … 12
Chain … 198
Bearing defect … 199
Valve cavitation … 200
Pump bearing lubrication … 201
VFD – good bearing … 202
VFD – failing bearing … 203
FAILURE TO PREPARE
My first Sales Manager was a former Royal Navy man who loved his sayings. One of those sayings which he injected so deeply into my brain that I use it either consciously or subconsciously almost every day was “to fail to prepare is to prepare to fail”.
It is simple and yet so obviously true.
The relevance here is that I have seen so many plant failures, breakdowns, stoppages and programme failures over the years which have been fundamentally caused by failed preparation.
Condition monitoring needs to be prepared for and that preparation is called Failure Mode and Effect Analysis, or FMEA. This task is hugely important in the preparation and yet, sadly, it is frequently either not performed or performed poorly.
In a nutshell, part of FMEA is the formal structured application of Murphy’s Law. Look at a system and identify all of its failure modes. Then, give each failure mode a ranking to develop a hit list based upon severity, detectability and occurence. Now you have something to get stuck in to. Which failures can be designed out, or eliminated by changing an operating procedure, or mitigated so that the failure is less severe or, and this is the big one for us, which can be identified at an early stage by measurement or inspection?
IS YOUR FMEA FIT?
There should be little doubt left in the world of Predictive Maintenance (PdM) that Ultrasound is an important element of a complete programme. Unfortunately, there is. Why?
Somewhere around 2010, I wrote an article entitled “not all problems rotate” and this thought has become an essential part of my life ever since. Time and again I have visited businesses where Condition Monitoring has been synonymous with vibration measurement on rotating machines. Nothing, to me, highlights the “fail to prepare” state more than this mentality. I would say that there is probably another book to be written on why 21st century maintenance education fails to teach more about failure, FMEA and what can be measured.
This attitude runs deep. I remember visiting a plant where the sign over the department door had been changed. The shadows of the letters VIBR remained behind their replacements, CONDI. But it takes a lot more than changing a few letters to turn the mentality of the Vibration Monitoring department into the Condition Monitoring department.
Can an air leak be a Reliability issue?
Yes. Consider a pneumatic cylinder that is leaking or a pneumatically controlled valve. A failure of the pneumatic system in either of these cases will be an operational failure. So, yes, even the lowly air leak has a role to play in improving plant Reliability.
There is a growing recognition of the power of Ultrasound, but the ability to find problems quickly, easily and without recourse to a computer seems to be a little hard for some to accept.
Also difficult to accept can be the reality that some defects are not trendable – there is nothing to trend in the measurements of a binary failure. What was a leak, before it was a leak? Nothing! So there is no trend. Some defects simply appear or begin and our job is to have a surveillance plan in place which offers sufficient frequency of inspection that the new defect can be caught at an early stage. Monthly vs. quarterly vs. annual inspection.
Ultrasound is the undisputed champion for finding compressed air leaks, steam leaks, vacuum leaks and electrical defects such as corona, tracking and arcing. None of these problems rotate and so are not within the sphere of influence of the vibration engineer. They are though, potentially, hugely important problems which should be within the sphere of influence of a broadly-based predictive maintenance program.
The problem tends to be more associated with contact or structure borne ultrasound than with airborne. It seems that when the world of PdM talks about structure or contact ultrasound it is almost always in the limited context of bearings.
There is more to life than bearings. There is a whole lot more to PdM than bearings too. How often do you read that?
The typical maintenance engineer is interested in far more than just bearings. Valves, steam traps, hydraulic systems, cylinders, sealing, tightness testing, actuators and many more such items are just as important as motors, gearboxes, pumps and bearings. This is why I felt that this thought process could be summarised by “not all problems rotate”. There are also some rotating applications which are so low-tech, so low speed or so low power or even so low cost that they are ignored or removed from the vibration department.
Think about conveyors in a mine or small right-angled gearboxes driving small conveyors in a food plant, or packaging machinery.
Economical or even technically feasible to be monitored by vibration analysis? Probably not.
Ultrasound is great for detecting three properties:
Some time ago, I came up with this simple question “is your FMEA FIT?”.
People ask me about applications all the time. Can I use Ultrasound to find……? Where can I use Ultrasound in a ……Plant? My answer remains the same: “If you have a defect which is identifiable by the presence, or absence, of Friction, Impacting or Turbulence, then Ultrasound is probably going to be the most useful tool in the toolbox”.
That thought lead to the creation of the eight pillars of Ultrasound – the 8 major application areas which involve the detection of Friction, Impacts and Turbulence:
- Pressurised gas and vacuum leaks
- Steam leaks and steam traps
- Rotating machinery
- Tightness testing
At this stage, some strong supporters of another technology will say something in support of IR or Vibration along the lines of “I can do this with….”. That supporting stance may or may not be justifiable, but, the fact that one technology can be used for all of these applications must surely make that technology interesting. As the American saying goes, more bang for Buck. Furthermore, saying that I can use Ultrasound to detect something is not meant to be detrimental to any other technology. Having multiple technologies capable of detecting a defect is highly beneficial because it makes it easier to ensure that the defect is going to be detected by someone, somehow using something.
The business reality is perhaps even more interesting and yet so infrequently grasped. Middle-managers have been pounded into believing that increasing headcount is bad. The reality, however, is that any one of these Pillars can easily become gainful, profitable, employment for one or a group of people within a business with those problems. Each of the applications pillars can therefore become a profit centre.
A SELECTION OF TIME SIGNALS
To round off this journey, I have pulled together a selection of some of my favourite and, yes I’m biased, most interesting sounds and signals.
Each of these examples has a QR code next to it. Assuming that everything works out correctly, if you point your phone camera to one of these QR codes, you should be able to follow a web link and play a recording of the sound file you are looking at.’
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If you haven’t already, do also connect with Tom Murphy on LinkedIn:
THOMAS J MURPHY: Have a listen to Ultrasound | RMS Ltd
RMS are pleased to offer The Reliability Team's latest book, 'Have a listen to Ultrasound', by Thomas J Murphy. The paperback contains 212 pages, is available in English, and has the following ISBN: 9798412080727. To show our support for this important book, 'Have a listen to Ultrasound' will be included for RMS students attending a public CAT-I Ultrasound course during 2022.
Author: Thomas J Murphy