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The Chemistry and Technology of Petroleum
To determine the cloud point and the pour point (ASTM D97, ASTM D5327, ASTM D5853,
ASTM D5949, ASTM D5950, ASTM D5985, IP 15, IP 219, IP 441) the oil is contained in a glass
test tube fitted with a thermometer and immersed in one of three baths containing coolants. The
sample is dehydrated and filtered at a temperature 25°C (45°F) higher than the above the anticipated
cloud point. It is then placed in a test tube and cooled progressively in coolants held at −1°C to +2°C
(30°F to 35°F), −18°C to −20°C (−4°F to 0°F) and −32°C to −35°C (−26°F to −31°F), respectively.
The sample is inspected for cloudiness at temperature intervals of 1°C (2°F). If conditions or oil
properties are such that reduced temperatures are required to determine the pour point, alternate
tests are available that accommodate the various types of samples.
Related to the cloud point, the wax appearance temperature or wax appearance point is also
determined (ASTM D3117, IP 389).
The pour point of petroleum or a petroleum product is determined using this same technique
(ASTM D97, IP 15) and it is the lowest temperature at which the oil pours or flows. It is actually
2°C (3°F) above the temperature at which the oil ceases to flow under these definitely prescribed
conditions when it is chilled without disturbance at a standard rate. To determine the pour point, the
sample is first heated to 46°C (115°F) and cooled in air to 32°C (90°F) before the tube is immersed
in the same series of coolants as used for the determination of the cloud point. The sample is
inspected at temperature intervals of 2°C (3°F) by withdrawal and holding horizontal for 5 s until
no flow is observed during this time interval.
Cloud and pour points are useful for predicting the temperature at which the observed viscosity
of oil deviates from the true (Newtonian) viscosity in the low-temperature range. They are also useful for identification of oils or when planning the storage of oil supplies, as low temperatures may
cause handling difficulties with some oils.
The pour point of a crude oil was originally applied to crude oil that had a high wax content.
More recently, the pour point, like the viscosity, is determined principally for use in pumping arid
pipeline design calculations. Difficulty occurs in these determinations with waxy crude oils that
begin to exhibit irregular flow behavior when wax begins to separate. These crude oils possess viscosity relationships that are difficult to predict in pipeline operation. In addition, some waxy crude
oils are sensitive to heat treatment that can also affect their viscosity characteristics. This complex
behavior limits the value of viscosity and pour point tests on waxy crude oils. At the present time,
long crude oil pipelines and the increasing production of waxy crude oils make an assessment of the
pumpability of a wax-containing crude oil through a given system—a matter of some difficulty that
can often only be resolved after field trials.
Consequently, considerable work is in progress to develop a suitable laboratory pumpability test
(such as described in IP 230) that gives an estimate of minimum handling temperature and minimum line or storage temperature.
10.4.3 CArBon resIdue
Petroleum products are mixtures of many compounds that differ widely in their physical and chemical properties. Some of them may be vaporized in the absence of air at atmospheric pressure without
leaving an appreciable residue. Other nonvolatile compounds leave a carbonaceous residue when
destructively distilled under such conditions. This residue is known as carbon residue when determined in accordance with prescribed procedure.
The carbon residue is a property that can be correlated with several other properties of petroleum
(Speight, 2000); hence it also presents indications of the volatility of the crude oil and the cokeforming (or gasoline-producing) propensity. However, tests for carbon residue are sometimes used
to evaluate the carbonaceous depositing characteristics of fuels used in certain types of oil-burning
equipment and internal combustion engines.
The Chemistry and Technology of Petroleum
To determine the cloud point and the pour point (ASTM D97, ASTM D5327, ASTM D5853,
ASTM D5949, ASTM D5950, ASTM D5985, IP 15, IP 219, IP 441) the oil is contained in a glass
test tube fitted with a thermometer and immersed in one of three baths containing coolants. The
sample is dehydrated and filtered at a temperature 25°C (45°F) higher than the above the anticipated
cloud point. It is then placed in a test tube and cooled progressively in coolants held at −1°C to +2°C
(30°F to 35°F), −18°C to −20°C (−4°F to 0°F) and −32°C to −35°C (−26°F to −31°F), respectively.
The sample is inspected for cloudiness at temperature intervals of 1°C (2°F). If conditions or oil
properties are such that reduced temperatures are required to determine the pour point, alternate
tests are available that accommodate the various types of samples.
Related to the cloud point, the wax appearance temperature or wax appearance point is also
determined (ASTM D3117, IP 389).
The pour point of petroleum or a petroleum product is determined using this same technique
(ASTM D97, IP 15) and it is the lowest temperature at which the oil pours or flows. It is actually
2°C (3°F) above the temperature at which the oil ceases to flow under these definitely prescribed
conditions when it is chilled without disturbance at a standard rate. To determine the pour point, the
sample is first heated to 46°C (115°F) and cooled in air to 32°C (90°F) before the tube is immersed
in the same series of coolants as used for the determination of the cloud point. The sample is
inspected at temperature intervals of 2°C (3°F) by withdrawal and holding horizontal for 5 s until
no flow is observed during this time interval.
Cloud and pour points are useful for predicting the temperature at which the observed viscosity
of oil deviates from the true (Newtonian) viscosity in the low-temperature range. They are also useful for identification of oils or when planning the storage of oil supplies, as low temperatures may
cause handling difficulties with some oils.
The pour point of a crude oil was originally applied to crude oil that had a high wax content.
More recently, the pour point, like the viscosity, is determined principally for use in pumping arid
pipeline design calculations. Difficulty occurs in these determinations with waxy crude oils that
begin to exhibit irregular flow behavior when wax begins to separate. These crude oils possess viscosity relationships that are difficult to predict in pipeline operation. In addition, some waxy crude
oils are sensitive to heat treatment that can also affect their viscosity characteristics. This complex
behavior limits the value of viscosity and pour point tests on waxy crude oils. At the present time,
long crude oil pipelines and the increasing production of waxy crude oils make an assessment of the
pumpability of a wax-containing crude oil through a given system—a matter of some difficulty that
can often only be resolved after field trials.
Consequently, considerable work is in progress to develop a suitable laboratory pumpability test
(such as described in IP 230) that gives an estimate of minimum handling temperature and minimum line or storage temperature.
10.4.3 CArBon resIdue
Petroleum products are mixtures of many compounds that differ widely in their physical and chemical properties. Some of them may be vaporized in the absence of air at atmospheric pressure without
leaving an appreciable residue. Other nonvolatile compounds leave a carbonaceous residue when
destructively distilled under such conditions. This residue is known as carbon residue when determined in accordance with prescribed procedure.
The carbon residue is a property that can be correlated with several other properties of petroleum
(Speight, 2000); hence it also presents indications of the volatility of the crude oil and the cokeforming (or gasoline-producing) propensity. However, tests for carbon residue are sometimes used
to evaluate the carbonaceous depositing characteristics of fuels used in certain types of oil-burning
equipment and internal combustion engines.