Page 593 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Preventive and Predictive Maintenance Best Practices Best Practice 1 1.1
One final word. Do not be afraid to admit to management Preventive maintenance
that you do not know certain aspects of a problem. But be sure Preventive maintenance is performed at predetermined
to state that you will find out. After all, management must
intervals. It is time based. A very common preventive mainte-
understand that this is a learning process and does require time. nance step is an automotive oil change. The objective of this
To aid in the understanding of component function defini-
tion, we have included an example for an anti-friction bearing in action is to remove the oil from the engine before oil contami-
nation and deterioration cause excessive wear to the engine
Figure 11.1.5.
components. Figure 11.1.7 presents the components of a typical
site preventive maintenance program.

An anti-friction bearing continuously supports all static and dynamic
forces of a rotor by providing sufficient bearing area and requires oil
flow to remove the generated frictional heat.
This statement then defines the items that must be monitored to
determine the bearing's condition:
Static and dynamic forces
Bearing area
Oil flow
Frictional heat

Fig 11.1.5 Component function example
Naturally, we cannot measure directly all of the items noted
in Figure 11.1.5. However, based on the instruments and
measuring devices available on site, what can be measured to
Fig 11.1.7 A typical preventive maintenance program (Courtesy of
ensure the component (bearing) is performing correctly? M.E. Crane, Consultant)

Component condition monitoring e ‘What is In our experience, a well-planned preventive maintenance
program can truly be effective. However, the question must be
it doing?’
asked, ‘Is the maintenance performed always necessary?’ Refer
to Figure 11.1.8.
In reference to the anti-friction bearing example, the component
condition monitoring parameters are presented in Figure 11.1.6.

Preventive maintenance prevents but ... takes time.
Is it always necessary?
Bearing housing vibration
Bearing housing temperature
Lube oil condition Fig 11.1.8 Preventive maintenance
Viscosity
Water content
Oil particle content What is the basis for replacing components? Unnecessary
component replacement exposes the machinery unit to a failure
Fig 11.1.6 Component condition monitoring parameters (for anti- classification (improper assembly of components, improper
friction bearing) installation, component malfunction, improper component
storage procedures, etc.).
A similar exercise can be conducted for all of the major In addition, preventive maintenance can cause a mindset that
components and systems in any piece of equipment. automatically determines maintenance at every turnaround
What are the major components and systems of any piece of regardless of component condition. This can be a costly practice.
rotating equipment? How many are there? And are the same A case history also demonstrates where preventive mainte-
components contained in any type of rotating equipment? The nance can lead if not properly monitored. A centrifugal com-
answers to these questions will be discussed in a later chapter of pressor in a large refinery was scheduled for maintenance during
this book and form the principle of component condition the upcoming turnaround. Maintenance planning had scheduled
monitoring. bearing inspection and change if necessary. During the turn-
around when bearings were inspected, excessive clearances and
signs of deterioration were found. Naturally the bearings were
Preventive (PM) and predictive replaced. However, because the bearings were replaced, it was
maintenance (PDM) decided that the seals, which are more difficult to remove and
inspect, should be observed. Upon seal removal the seals were
At this point, the distinctions between preventive maintenance also in a distressed condition and needed to be replaced. Now
(PM), predictive maintenance (PDM) and troubleshooting must the tough decisions had to be made. It was decided that the
be discussed. compressor would be disassembled, to inspect the interior

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