Presented at IMC-2003 the 18th International
Machinery Reliability with Oil Mist Technology
Douglas C. Branham – Lubrications System Company
Marketing Development and Planning Manager
Lubrication Systems Company
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presentation will take a snapshot view of the
history of oil mist, what oil mist
is, how it is generated, how it works, its benefits
justification, oil mist’s
environmental performance, and some case histories.
The sum and substance of oil mist is that it is
effective in improving machinery reliability by
typically reducing bearing failures by as much as 90%.
mist is and old solution for old lubrication problems.
Its invention takes us
back to Europe in the late 1930’s when the fibers
had a problem. The
high speed spindle bearings were failing at an
rate. The engineers
deduced that the problem was not the bearings as much
as it was the lubrication
technology. Grease would not work in high speed
and oil led to excessively high temperatures.
Subsequently, oil mist lubrication was invented
and the bearing problems were solved.
the 1960’s, oil mist came to the North America when
it was introduced to the
petroleum refineries and petrochemical plants.
Companies such as Exxon and
Chevron began apply oil mist to their pump bearings.
In the 1970’s oil mist
began to be applied to electric motors, which brings,
contrary to some conventional thought, noticeable
date, Lubrication Systems Company has sold over 2,000
major oil mist
systems around the world: from the extreme cold of the
Canadian far north to the searing heat of the Middle
East. Oil mist has become know and respected
worldwide as an essential and major component of any
process to improve machinery reliability. Some renown
reliability experts have gone so far as to say
that it is the most important part of a machinery
Description of Oil Mist
what is oil mist, anyway? One expert has summed
it up this way. “Today’s oil mist is a
lubrication system that continuously and
efficiently atomizes oil into small particles and
then conveys and delivers the correct
amount of the pressurized oil mist lubricant
to bearings and metal surfaces, resulting in
improved lubrication, fewer failures/repairs,
lower life cycle costs and extended
machinery life.” Whew!
know that you must be impressed by now with this
definition but, what does all of this cleverly
assembled verbiage mean? Well, here goes. Oil mist is
generated by introduction of liquid oil and air into
the sonic velocities of a vortex
throat. There, the oil experiences the mechanical
phenomena of shear forces
and unstable vibrations of the high angular velocities
of the air. Working
together, these combined actions ultimately form
oil particles or droplets 1 to 3 microns with air.
oil suspension in dry, instrument air, is a mixture
if 1 part oil and 200,000
parts of air. It is a lean, fairly stable mixture and
can be conveyed horizontally up to 600 feet in 2 inch
galvanized, screwed piping under a pressure of 20
water column. It appears as a thin, cigarette smoke
plume. Incidentally, ambient
temperatures do not affect oil mist during the 7
maximum it takes for the oil mist to arrive at the
Why Oil Mist Works
of the primary failure mechanisms of rolling
element bearings is fatigue.
Much of the fatigue is caused by dirt and wear
that approximately the
thickness of the oil wedge, hence the clearance of the
Obviously, particles thicker than this will not enter
into the clearances to cause
fatigue. On the other side of things, particles
the oil wedge are not likely to cause fatigue.
You will recall that the oil mist droplets are 1-3
microns in size. Because of their
small size, the dirt or wear particles that can cause
fatigue will not remain in
suspension with the oil mist and will therefore drop
in the oil mist generator.
As some have accurately commented, oil mist is the
ultimate oil filter.
is another important factor as to why oil mist works
as well as it does. In
graduate research done by Texas A&M University, they
discovered that, in some
cases, pure oil mist deposits a wear resistant,
dry film on the wear surfaces of rolling element
bearings. They did not find this layer to be on
bearings in conventional splash lubrication service.
OK, so oil mist deposits this layer. So what? One of
the concerns of those not
familiar with oil mist fear it because of what they
happen if the oil mist
ceases to flow while their machinery is in operation.
They think that the bearings
will fail immediately. On the contrary, research
and field experience have shown
that, because of this carbonaceous layer, machinery
can safely operate 8 hours
without oil mist. Some users have operated safely for
much longer than that. Certainly, nobody would
recommend purposely shutting down oil mist but
there need not be the life or death sense of urgency
one would need with conventional lubrication methods.
Forms of Oil Mist
mist can be applied in two formats: pure mist (dry
sump oil mist) or purge mist
(wet sump oil mist). With purge mist applications,
the oil mist is applied to the
vapor space above the liquid oil in primarily gear
oil reservoirs, and
journal (plain) bearings. This is done to exclude
With pure mist applications, the mist replaces the
liquid oil in rolling element
bearing housings; there is no other lubricant going
to the bearings.
users mistakenly believe that purge mist is
better because it combines the
benefits of both forms; it is a belts and suspenders
insurance policy. In fact, pure
mist has substantial benefits over purge mist as
below. Most of the potential benefits are missed with
Benefits of Oil Mist Lubrication
are numerous direct benefits of oil mist, not the
least of which is that it reduces bearing failures by
90% with pure mist. One user in West Texas even boasts
a 98% reduction. A bearing manufacturer says that the
bearing L10 life is extended by a factor of
6 by oil mist. It takes little imagination to see that
drastic reliability improvement will impact the
bottom line both in the reduction in expenses and Lost
Profit Opportunity. When you consider accounting’s
Formula, Revenue = Income + Liabilities, you can
see that oil mist impacts
both sides of the equation, namely revenue (increase
on-spec product) and liabilities (repair expenses).
purge mist on cooling tower, angle gear boxes,
users typically experience a 75% reduction in gear box
failures. This improvement is directly attributable to
the slight positive pressure of the oil mist. As
cooling tower cells are shut down
and as gear boxes go through the inhalation/exhalation
cause by thermal cycles,
water vapor is inhaled and subsequently condenses.
This water causes
devastating corrosion which will lead to premature
mist reduces lubricant consumption by as much
as 40% for once through systems.
If a closed loop system is used, the oil consumption
is reduced by considerably more. Conservation happens
because the oil is precisely metered
to each bearing: the right amount at the right time.
This reduction in oil
consumption becomes critical when the lubricant is
switched from mineral oils
(about $3 per gallon) to synthetic oils (about $18
Because there is no liquid oil level and liquid
friction, operating temperatures are about 20° F
cooler. One user reported a 90û F cooler on
a crude unit charge pump. According to bearing
manufacturers, there is an inverse relation between
bearing life and temperatures: the higher the
the shorter the life.
Another collateral benefit is up to a 3% reduction
in energy consumption. In
virtually all hot oil pumps equipped with bearing
cooling jackets, the cooling water
can be deleted. This is beneficial because cooling
water can actually decrease bearing life. Cooling
water shrinks the outer race while the heat conducted
the shaft expands the inner race, making the bearing
run hotter because of reduced clearances.
Oil mist requires 47% fewer man hours to operate than
do the conventional
systems. The extra 53% free man hours can be used to
on the reason
operators are there, to maximize profitable
and frees up maintenance
personnel to focus on reliability improvement.
Environmental, Health, and Safety
Environmental laws, such as California’s Rule #1173,
titled Fugitive Emissions of Volatile Organic
Compounds (VOC), specifically exempt oil mist as a
Organic Compound (VOC). This means that oil mist is
not a smog producing
mixture. Remember that oil mist is not a vapor but a
mixture of very fine oil
droplets and air. In time, the oil droplets will drop
of the air.
According to NIOSH publication 81-123-b-0472.pdf says
that the “Permissible
Exposure Limit (PEL)… is 5 milligrams of mineral oil
mist per cubic meter of air (mg/m3)
averaged over an eight-hour work shift.” Incidentally,
Occupational Safety Administration sets oil mist
Exposure Limits at 5 mg/m3
for an 8 hour Occupational Exposure Limit (OEL) and
10 mg/m3 for a 15 minute OEL. Field
measurements and testing never found measurements to
be anywhere near close to the imposed limits.
Since oil mist is so lean, 1 part oil to 200,000 parts
air, explosions are impossible.
For the mixture to burn, the concentration would
have to more than 1 to 250. Therefore, oil mist is
Because of oil mist’s many benefits, there is a
high payout and fast return on invested capital.
Typically, the payouts are one to two years with one
company reporting 7 months.
An aluminum refinery in the Gulf Coast has a bank of 34
large fans equipped with pillow block bearings. The
failure rate was such that bearings lasted only six
months. The bearings were switched to pure oil mist in
1998. To date, there have been no reports of bearing
2. One of the largest oil companies in the world says
that they have two
similar olefin plants; both have about 200 pumps.
They are both operated under the same operating
philosophy. One plant has oil mist and the
other doesn’t. The one without oil mist has an average
of 50 pump
failures per year. The plant with oil mist has an
of 4 pump failures per year.
3. A Gulf Coast refinery operating unit spent on average
$35,000 per year on pump repairs. They installed oil
mist in 1989. Since that time, their pump repairs have
averaged < $5,000 per year.
4. Another refinery had annual pump cost before and
after oil mist on selected unit as follows: coker -
$60,000 to $25,000, cat cracker - $85,000 to $28,000,
and the crude unit - $82,000 to $23,000.
5. In a Philippine refinery, the Mean Time Between
Failure of their pumps
before oil mist was 3 years. After the installation
of oil mist, their MTBF after 6 years of service was > 9
6. There are many more success stories but I will end
with a comparison of two similar refineries in Thailand.
Both are owned by the same company
and, like Case Sty # 2, they have the same operating
philosophy and the same reliability improvement
programs. The difference between the two is
that one does not have oil mist and the other one does.
There are the
differences between the performance parameters
in year 2001:
a. Annual oil consumption in liters/bearing/year – 14
b. Bearing failures as a % of installed bearings – 4.4
c. Seal life (MTBF) in years – 4 versus 9
Oil mist is a proven technology that demonstrates every
day around the world
that it significantly reduces bearing failures,
reduces maintenance costs,
improves machinery availability, reduces energy
reduces the need
for warehoused repair parts, reduces life cycle costs,
and reduces the stress of
operating a plant. It not only improves machinery
but frees up
operators and maintenance personnel to perform their
functions, to put
on spec product out the door and to help make the
a profitable business. Oil mist is discretionary but
there is probably not another thing that a
plant may do that can achieve these level reliability
improvements than as can oil mist lubrication.
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