Avoiding free water in a lubrication system0 pages

/ APPLICATION NOTE
Avoiding free water in a lubrication system
Free water in lubrication oil can
cause major failures to large
machinery, especially in applications
where water is constantly present
as in ship propulsion systems and
hydro power turbines.
Free water prevents oil from forming
a uniform lubricating layer on
metal surfaces deteriorating both
the lubrication performance and
the ability of the oil to protect the
machine. Equipment is damaged
by corrosion, cavitation, micro
pitting, and spot heating. Free
water also ruins polar additives
of oil. In offshore applications,
free water tends to be even more
destructive due to the presence of
salt water creating a more corrosive
environment for the metals it is in
contact with.
In cases of sudden leaks, a free water
layer can form quickly, and if only
periodic oil sampling is performed,
water is most likely detected too
late resulting in damage. On-line
monitoring enables the machinery
operator to make corrective actions
before any failure occurs.
Formation of free water
based on oil's water
solubility
Just like air, every fluid (e.g.
lubricating oils, hydraulic fluids)
has the ability to hold water in the
dissolved state below the saturation
point. Once the saturation point of
that fluid has been reached, any
additional water that enters the fluid
will separate out into “free water”
which can be seen as a distinct layer
– usually below the oil.
Oils typically have very limited
water solubility. The saturation
point of oil is affected not only by
the base oil type, additives and
anti-oxidants, but also by the fluid’s
age, temperature and the chemical
reactions that take place over the life
of the fluid. It is also very typical that
different commercial oils used for the
same application, vary significantly
with respect to their ability to hold
dissolved water (Figure 1). A safe
moisture level indicated in parts
per million (ppm) for one oil may be
above saturation in another.
Figure 1 Water solubility of different commercial lubrication oils (2001).
Tests run at 31 °C.