Efficient Plant July/August 2020 - 19

feature | lubrication solutions
Left. Asset life is significantly shortened when
lubricants are contaminated with water. This
is particularly true in high-humidity environments.

ture, a conventional anti-wear hydraulic fluid
may be able to hold as much as 200 ppm
(0.02% v/v) of water in solution. As the oil
cools, the solubility of water in oil decreases.
At 40 F, the oil may only hold 50 ppm of
water in solution. The maximum amount of
water an oil can hold in solution at a given
temperature is referred to as the saturation
point.
When water comes out of solution, it will
co-exist with the oil in one of two phases-
free or emulsified. Free water has completely
separated from the oil and settled to the bottom of the tank or oil sump. Emulsified oil
refers to a suspension of small water droplets
(the dispersed phase) in the oil (the continuous phase). Whether oil and water exist in
the free or emulsified phase depends on a

property of the oil known as demulsibility.
Like solubility, demulsibility is dependent
on the type of oil, the degree to which the
oil has degraded, and the presence of certain
contaminants. Oils with small amounts of
additives will separate (demulsify) fairly
quickly-usually in less than 5 to 10 min.
Separation takes much longer when larger
amounts of additives are present and/or the
oil is severely degraded. Some oils, particularly those that contain detergents, are
severely degraded. Those that have contaminants, such as soaps or other process fluids,
may lose the ability to shed water completely,
forming a stable emulsion.
When it comes to the ability of a lubricant
to do its job, the presence of free or emulsified water is of great concern. This is particularly true for wet-sump applications such
as small process pumps or splash-lubricated
gearboxes, since the lubricated components
operate directly in the oil sump. Free and

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emulsified water in wet-sump applications
not only causes rust and corrosion to occur
but can significantly affect film strength,
while accelerating oil degradation, leading to
the formation of sludge and varnish.
Figure 1 (p. 20) shows the impact that
water can have on equipment life. In this
seminal study, researchers were able to
derive an empirical relationship between the
amount of water in an oil (in this case an
R&O ISO VG 68 fluid) and the life expectancy of a rolling-element bearing. This would
mirror exactly what might happen in a small
centrifugal pump. As the graph illustrates,
bearings that operate with water above the
saturation point (approximately 100 ppm in
this case) will have a significantly reduced
life expectancy, often as low as 50% of the
anticipated bearing life.
Water can enter an oil in a number of
different ways, but one of the most common
is when equipment is operated in a high-

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JUL/AUG 2020

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Efficient Plant July/August 2020

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