Significance of Results: Oxidation stability is
an important factor in the prediction of an oil's
performance. Without adequate oxidation sta-
bility, the service life of an oil may be extremely
limited. Unless the oil is constantly replaced,
there is a serious possibility of damage to lubri-
cated parts. Acids formed by oxidation may be
corrosive to metals with which the oil comes in
contact. Sludges may become deposited on
sliding surfaces, causing them to stick or wear,
or they may plug oil screens or oil passages.
an important factor in the prediction of an oil's
performance. Without adequate oxidation sta-
bility, the service life of an oil may be extremely
limited. Unless the oil is constantly replaced,
there is a serious possibility of damage to lubri-
cated parts. Acids formed by oxidation may be
corrosive to metals with which the oil comes in
contact. Sludges may become deposited on
sliding surfaces, causing them to stick or wear,
or they may plug oil screens or oil passages.
Oxidation stability is a prime requisite of oils
serving in closed lubrication systems, where the
oil is recirculated for extended periods. The
higher the operating temperature, the greater
the need for oxidation stability, especially if
water, catalytic metals, or dirt are present. Re-
sistance to oxidation is of special importance in
a steam-turbine oil because of the serious con-
sequences of turbine bearing failure. Gear oils,
electric transformer oils, hydraulic fluids, heat-
transfer oils, and many crankcase oils also
require a high degree of oxidation stability.
serving in closed lubrication systems, where the
oil is recirculated for extended periods. The
higher the operating temperature, the greater
the need for oxidation stability, especially if
water, catalytic metals, or dirt are present. Re-
sistance to oxidation is of special importance in
a steam-turbine oil because of the serious con-
sequences of turbine bearing failure. Gear oils,
electric transformer oils, hydraulic fluids, heat-
transfer oils, and many crankcase oils also
require a high degree of oxidation stability.
Obviously, the ability to predict oxidation life by
a test, and to do it with reasonable accuracy is
highly desirable. There are certain factors,
however, that make reliable test results difficult
a test, and to do it with reasonable accuracy is
highly desirable. There are certain factors,
however, that make reliable test results difficult
to obtain. In the first place, the tests themselves
are very time-consuming: a method such as
ASTM D 943 may require the better part of a
year to complete. Prolonged though the test
may be, moreover, its duration usually
represents but a small fraction of the service life
of the oil under investigation. A steam turbine
oil, for example, may well last for a decade or
more without serious deterioration. It is
impossible to reproduce service conditions of
this sort In the laboratory with a test even of
several hundred hours duration. And, in addition
to the time factor, there are many other
operational variables that cannot be duplicated
under test conditions. Results can be distorted
also by presence of certain additives in the oil.
are very time-consuming: a method such as
ASTM D 943 may require the better part of a
year to complete. Prolonged though the test
may be, moreover, its duration usually
represents but a small fraction of the service life
of the oil under investigation. A steam turbine
oil, for example, may well last for a decade or
more without serious deterioration. It is
impossible to reproduce service conditions of
this sort In the laboratory with a test even of
several hundred hours duration. And, in addition
to the time factor, there are many other
operational variables that cannot be duplicated
under test conditions. Results can be distorted
also by presence of certain additives in the oil.
For these reasons, the correlation between ox-
idation test results and field experience leaves
much to be desired. Test results are subject only
to broad Interpretations. It would be difficult to
show, for example, that an oil with a 3000-hour
ASTM test life gives better service than an oil
with a 2500-hour test life. In evaluating the
oxidation stability of an oil, primary
consideration should be given to the record that
it has established over the years in the type of
service for which it is to be used.
idation test results and field experience leaves
much to be desired. Test results are subject only
to broad Interpretations. It would be difficult to
show, for example, that an oil with a 3000-hour
ASTM test life gives better service than an oil
with a 2500-hour test life. In evaluating the
oxidation stability of an oil, primary
consideration should be given to the record that
it has established over the years in the type of
service for which it is to be used.
POUR POINT
ASTM D 97
It is often necessary to know how cold a partic-
ular petroleum oil can become before it loses its
fluid characteristics. This information may be of
considerable importance, for wide variations
exist in this respect between different oils, even
between oils of comparable viscosity.
ular petroleum oil can become before it loses its
fluid characteristics. This information may be of
considerable importance, for wide variations
exist in this respect between different oils, even
between oils of comparable viscosity.
If a lubricating oil is chilled sufficiently, it even-
tually reaches a temperature at which it will no
longer flow under the influence of gravity. This
condition may be brought about either by the
tually reaches a temperature at which it will no
longer flow under the influence of gravity. This
condition may be brought about either by the
thickening of the oil that always accompanies a
reduction in temperature, or by the crystalliza-
tion of waxy materials that are contained in the
oil and that restrain the flow of the fluid portions.
For many applications, an oil that does not flow
of its own accord at low temperatures will not
provide satisfactory lubrication. The extent to
which an oil can be safely chilled is indicated by
its pour point, the lowest temperature at which
the undisturbed oil can be poured form a con-
tainer.
reduction in temperature, or by the crystalliza-
tion of waxy materials that are contained in the
oil and that restrain the flow of the fluid portions.
For many applications, an oil that does not flow
of its own accord at low temperatures will not
provide satisfactory lubrication. The extent to
which an oil can be safely chilled is indicated by
its pour point, the lowest temperature at which
the undisturbed oil can be poured form a con-
tainer.
A-13 (FIST 2-4 11/90)