October - Library - Central Queensland University

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CONDITION MONITORING TECHNIQUES
Items can take years, months, weeks, days, etc to fail once the onset of failure starts. It is during this period of decay that physical
conditions within the equipment will change and this change will become detectable during the P-F interval. Condition based
(predictive) maintenance is the process by which we seek to identify this change in condition/s so as to enable action to be taken
to prevent the failure and/or avoid the consequences. Examples of change in equipment condition include:
• Vibrations indicating imminent bearing failure.
• Wear particles in oil indicating imminent bearing, gear, engine, etc failure.
• Hot spots within an electrical connection indicating poor connection.
• Metal / wear surfaces becoming thin indicating wear, corrosion, etc.
• Cracks in welded connections indicating imminent failure due to fatigue.
• The list goes on.
The benefits of predictive maintenance is that it is normally perf o rmed on-line - i.e. whilst the equipment is either running or stopped
but left in situ. The key here is that predictive maintenance is usually very efficient, from a timing perspective, but more importantly
is non-intrusive hence minimising the reliability issues associated with infant mortality.
The four main categories of condition monitoring include; human senses (look, listen, feel and smell), condition monitoring techniques
(oil analysis, vibration analysis, etc), variations in equipment running conditions (speed, flow rate, pre s s u re, temperature, power,
current, etc) and variations in product quality.
It is not the intent to go into any great depth and discuss the hundreds of diff e rent condition monitoring techniques associated within
each of the main categories. The objective here is to raise an overall awareness of their existence and the fact that each present
their own advantages and disadvantages, which should be taken into consideration when selecting.
WORK FLOW SYSTEM
Once the foundation has been laid in terms of establishing the asset maintenance plans, referring to Figure 3, the next layer within
the pyramid of key maintenance management processes is ready for construction.
At a glance it seems difficult to ascertain which of the key processes to establish next or whether they should all be progressed in
parallel. Although there will be many a good debate proclaiming the importance of progressing all of the key processes (within the
second layer) at the same time, it is strongly recommended that the initial focus be on establishing a work flow system, and support i n g
planning and re s o u rce stru c t u re, as this is key to the success of the journ e y. The importance of the work flow system will (hopefully)
become obvious throughout this section and the remaining key processes will be discussed in order of priority.
As stated earlier, the successful implementation of the maintenance plans will realise a reduction in the reactive work. The only
way that this will happen however is if the maintenance plans are completed on time - i.e. schedule compliance in excess of 90%,
and completed properly. In what seems like a vicious circle, if the maintenance plans are completed, which in itself will be a huge
addition in terms of workload, this will create further work identified through formal time based inspections, condition monitoring
p rograms, etc. To make matters worse, initially there will be a huge bow wave of additional work given that the equipment will have
deteriorated, due to the past reactiveness of the organisation, and will need to be brought back up to a standard.
All of the upfront eff o rt (and hence money) in establishing the maintenance plans will count for little, hence realising minimal
i m p rovements in terms of re l i a b i l i t y, if the sum total of the additional workload is not managed and actioned in a disciplined and
pragmatic approach and in line with budget constraints.
For example, a preventive / time based monthly inspection requests a tradesperson inspect a gearbox for oil leaks. He completes
his inspection route and diligently raises a request for work to replace an identified leaking oil seal (at a later date). If there is no
work flow system in place to accommodate this additional work then the request will most likely sit un-actioned until the next time
that this inspection is due. How many times will the same tradesperson diligently complete further monthly inspections and raise
further requests for work if he sees no action time and again? As a result, not only will the tradespeople (and others) place very
little value in the maintenance plans, the worst case scenario is that the gearbox will ultimately fail due to no oil, ingress of dirt, etc
and the very thing that was set out to be achieved - i.e. increased reliability, reduction in reactive work, etc, will not be realised.
JOB
ORIGINATION
JOB
PLANNING
JOB
SCHEDULING
JOB
ALLOCATION
Figure 6 Work flow process (Kelly 1999b, p. 1 to 6)
JOB
EXECUTION &
CONTROL
REPORTING