Maintworld 1/2020
ROTATING EQUIPMENT SERVICES: A COMPREHENSIVE, WORRY-FREE PACKAGE // SELF-INFLICTED RELIABILITY PROBLEMS OF ROTATING MACHINERY // VIEWING MAINTENANCE AS A SYSTEM TO OPTIMIZE PERFORMANCE
ROTATING EQUIPMENT SERVICES: A COMPREHENSIVE, WORRY-FREE PACKAGE // SELF-INFLICTED RELIABILITY PROBLEMS OF ROTATING MACHINERY // VIEWING MAINTENANCE AS A SYSTEM TO OPTIMIZE PERFORMANCE
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ASSET MANAGEMENT<br />
root causes exist? If you are not sure,<br />
then they almost certainly do.<br />
We will now take a quick look at just<br />
a few of those areas so that you can see<br />
why seemingly minor issues cause such<br />
serious problems.<br />
Shaft alignment<br />
When two shafts are “collinear” (no<br />
angle or offset between their centerlines),<br />
it reduces the stress on the bearings,<br />
couplings, shafts, and the rest of<br />
the machine components. Research was<br />
performed that revealed that just 5/60 th<br />
of a degree of angular misalignment can<br />
halve the life of your bearings.<br />
If you use laser alignment with<br />
appropriate tolerances, and you remove<br />
soft foot in all its forms (base issues, pipestrain,<br />
etc.), then you will have eliminated<br />
a common root cause of failure.<br />
Balancing<br />
When you balance to ISO 21940-11 grade<br />
G 1.0, the cyclical forces on the bearings,<br />
shaft, and structure are minimized, and<br />
thus you gain greater reliability. If you<br />
do not have a balancing standard, then<br />
unbalance will be a root cause of failure.<br />
And if you wait until the unbalance<br />
generates “high” vibration, “forcing”<br />
you to perform corrective maintenance,<br />
then you will have reduced the life of the<br />
equipment and supporting structure.<br />
Why is that? The life of a bearing is<br />
inversely proportional to the cube of the<br />
load. That sounds very complicated, but<br />
an easier way to say it is that if you double<br />
the load, the life will be reduced to<br />
one-eighth (23).<br />
Therefore, while the rotor is out-ofbalance,<br />
the bearings are being stressed,<br />
and their life expectancy will be reduced.<br />
Misalignment also generates these forces,<br />
and that is why it must be minimized.<br />
The unbalance is also generating<br />
forces that stress the structure, potentially<br />
resulting in fatigue failure of the<br />
structure itself or its foundations.<br />
The unbalance forces are also amplified<br />
by resonance. The structure will<br />
“naturally” vibrate back-and-forth, or<br />
side-to-side, or in other ways at certain<br />
frequencies. If the vibration generated<br />
by unbalance (or misalignment, or<br />
pump-vane vibration, or other avoidable<br />
“forcing frequencies”) is close to one of<br />
these natural resonant frequencies, the<br />
motion will be amplified. That is not<br />
good for the machine or structure.<br />
Lubrication<br />
When you correctly lubricate bearings<br />
and gears, whether you use grease or<br />
oil, and that lubricant is free of contaminants,<br />
you will achieve maximum<br />
life. But if bearings are not adequately<br />
greased, their life will be reduced. If the<br />
oil is contaminated, or the viscosity is<br />
incorrect, or the additives are depleted,<br />
then the life of gears and bearings will be<br />
greatly reduced.<br />
Research was performed to determine<br />
which particles caused the greatest<br />
damage. It was not the 40 µm particles,<br />
or the 10 µm particles - it was the tiny<br />
“3-5 µm” particles.<br />
And you may think that if you can’t<br />
see the water in oil, then the oil must<br />
be fine. Sadly, that is not correct. By the<br />
time you can see the water, the life of the<br />
bearing has been reduced by 70 percent.<br />
We could continue the discussion,<br />
but suffice to say that there is a great deal<br />
we can do to avoid problems that arise<br />
due to imperfect maintenance and operating<br />
practices.<br />
The number two cause of<br />
reliability problems<br />
It is one thing to understand all of the<br />
root causes we have just discussed – and<br />
there are many others – but it is another<br />
thing to be able to get approval to establish<br />
standards and purchase all of the<br />
tools, such as laser alignment systems,<br />
that enable the technicians and operators<br />
to do the job correctly. But owning<br />
the tools and having standard operating<br />
procedures will not solve the problem.<br />
The problem will only be solved when<br />
the maintenance technicians and operators<br />
want to use them properly, and they<br />
are given the time and encouragement to<br />
use them.<br />
So we will need to address the desire,<br />
i.e., the culture. Culture is the key to<br />
success.<br />
The number one cause of<br />
reliability problems<br />
A strong case could be made that the root<br />
cause of all failures ultimately derives<br />
from the lack of senior management support<br />
for a culture that values reliability.<br />
Without their support, it will be impossible<br />
to change the culture and thus<br />
change behaviour.<br />
Just think of the initiative to improve<br />
safety at your plant. If senior management<br />
did not support it, do you think<br />
your plant would have made the gains<br />
14 maintworld 1/<strong>2020</strong>