The behavior of an oil at low temperature de-
pends upon the type of crude from which it is
refined, the method of refining, and the pres-
ence of additives. Paraffinic base stocks contain
waxy components that remain completely in
solution at ordinary temperatures. When the
temperature drops, however, these waxy
components start to crystallize, and they
become fully crystallized at a temperature
slightly below the pour point At this temperature,
the undisturbed oil will not generally flow under
the Influence of gravity.
pends upon the type of crude from which it is
refined, the method of refining, and the pres-
ence of additives. Paraffinic base stocks contain
waxy components that remain completely in
solution at ordinary temperatures. When the
temperature drops, however, these waxy
components start to crystallize, and they
become fully crystallized at a temperature
slightly below the pour point At this temperature,
the undisturbed oil will not generally flow under
the Influence of gravity.
Crystallization of the waxy components does not
mean that the oil is actually solidified; flow is
prevented by the crystalline structure. If this
structure is ruptured by agitation, the oil will
proceed to flow, even though its temperature
remains somewhat below the pour point.
mean that the oil is actually solidified; flow is
prevented by the crystalline structure. If this
structure is ruptured by agitation, the oil will
proceed to flow, even though its temperature
remains somewhat below the pour point.
An oil that is predominantly naphthenic, on the
other hand, reacts in a somewhat different man-
ner. In addition to having a comparatively low
wax content, a naphthenic oil thickens more
than a paraffinic oil of comparable viscosity
does when it is cooled. For these reasons, its
pour point may be determined by the actual
congealing of the entire body of oil instead of by
the formation of waxy crystals. In such a case,
agitation has little effect upon fluidity, unless it
raises the temperature.
other hand, reacts in a somewhat different man-
ner. In addition to having a comparatively low
wax content, a naphthenic oil thickens more
than a paraffinic oil of comparable viscosity
does when it is cooled. For these reasons, its
pour point may be determined by the actual
congealing of the entire body of oil instead of by
the formation of waxy crystals. In such a case,
agitation has little effect upon fluidity, unless it
raises the temperature.
The pour point of a paraffinic oil may be lowered
substantially by a refining process that removes
the waxy components. For many lubricating oils,
however, these components impart advantages
in viscosity index and oxidation stability. Good
performance generally establishes a limit
beyond which the removal of these waxy com-
ponents is inadvisable. It is possible,
nevertheless, to lower the pour point of a
paraffinic oil by the introduction of a pour
depressant. Such an additive appears to stunt
the growth of the individual crystals so that they
offer less restriction to the fluid portions of the
oil. It is hardly necessary to point out, however,
substantially by a refining process that removes
the waxy components. For many lubricating oils,
however, these components impart advantages
in viscosity index and oxidation stability. Good
performance generally establishes a limit
beyond which the removal of these waxy com-
ponents is inadvisable. It is possible,
nevertheless, to lower the pour point of a
paraffinic oil by the introduction of a pour
depressant. Such an additive appears to stunt
the growth of the individual crystals so that they
offer less restriction to the fluid portions of the
oil. It is hardly necessary to point out, however,
that a pour depressant, as such, can have little,
if any, effect upon a naphthenic oil.
if any, effect upon a naphthenic oil.
Cloud point is the temperature, somewhat above
the pour point, at which wax crystal formation
gives the oil a cloudy appearance. Not all oils
exhibit a cloud point and, although this property
is related to pour point, it has little significance
for lubricating oils. It is significant, however, for
distillate fuels, and it is measured by ASTM D
2500.
the pour point, at which wax crystal formation
gives the oil a cloudy appearance. Not all oils
exhibit a cloud point and, although this property
is related to pour point, it has little significance
for lubricating oils. It is significant, however, for
distillate fuels, and it is measured by ASTM D
2500.
Apparatus: The oil sample is contained in a
jacketed glass test jar. The mouth of the jar is
sealed with a cork through which a thermometer
is introduced to Indicate the temperature of the
sample. This temperature is controlled by hot
and cold baths in which the jacketed glass test
jar may be partially Immersed.
jacketed glass test jar. The mouth of the jar is
sealed with a cork through which a thermometer
is introduced to Indicate the temperature of the
sample. This temperature is controlled by hot
and cold baths in which the jacketed glass test
jar may be partially Immersed.
Procedure: The pour point of an oil may be
distorted by its previous temperature history as
well as by agitation. To assure reproducible
results, elaborate sample pretreatment is re-
quired and specified heating and cooling
procedures must be followed. Pretreatment
consists of heating and cooling to prescribed
temperatures, which are dependent on the ex-
pected pour point and type of oil being tested.
distorted by its previous temperature history as
well as by agitation. To assure reproducible
results, elaborate sample pretreatment is re-
quired and specified heating and cooling
procedures must be followed. Pretreatment
consists of heating and cooling to prescribed
temperatures, which are dependent on the ex-
pected pour point and type of oil being tested.
The heated oil is cooled in increments of 5° F.
At each step, the test jar is removed from the
bath and tilted for not over 3 seconds. This
procedure is repeated until the sample ceases to
show movement when tilted.
At each step, the test jar is removed from the
bath and tilted for not over 3 seconds. This
procedure is repeated until the sample ceases to
show movement when tilted.
Reporting the results: The pour point is re-
ported as the temperature 5° F above that at
which the oil remained in position when the test
jar was tilted. (For example: If the oil being
tested shows movement at 10° F, but not at
5° F, the pour point is reported as 10° F.)
ported as the temperature 5° F above that at
which the oil remained in position when the test
jar was tilted. (For example: If the oil being
tested shows movement at 10° F, but not at
5° F, the pour point is reported as 10° F.)
Significance: The pour point of an oil is related
to its ability to start lubricating when a cold
machine is put in operation. Agitation by the
to its ability to start lubricating when a cold
machine is put in operation. Agitation by the
(FIST 2-4 11/90)
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