ASTM D2500-23

Standard Test Method for Cloud Point of Petroleum Products and Liquid Fuels

SIGNIFICANCE AND USE
5.1 For petroleum products and biodiesel fuels, cloud point of a petroleum product is an index of the lowest temperature of their utility for certain applications.
SCOPE
1.1 This test method covers only petroleum products and biodiesel fuels that are transparent in layers 40 mm in thickness, and with a cloud point below 49 °C.
Note 1: The interlaboratory program consisted of petroleum products of Test Method D1500 color of 3.5 and lower. The precisions stated in this test method may not apply to samples with ASTM color higher than 3.5.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 WARNING—Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use caution when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their location.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see Section 7.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 28-Feb-2023
• ICS: 75.080 - Petroleum products in general
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.07 - Flow Properties

Relations

• Refers: ASTM D6300-24 - Standard Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Mar-2024
• Refers: ASTM D1500-24 - Standard Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
• Effective Date: 01-Mar-2024
• Refers: ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 15-Dec-2023
• Refers: ASTM D6300-23a - Standard Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Dec-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023
• Refers: ASTM D6300-19a - Standard Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants
• Effective Date: 01-Dec-2019
• Refers: ASTM E644-11(2019) - Standard Test Methods for Testing Industrial Resistance Thermometers
• Effective Date: 01-Nov-2019
• Refers: ASTM E2877-12(2019) - Standard Guide for Digital Contact Thermometers
• Effective Date: 01-May-2019
• Refers: ASTM D6751-18 - Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels
• Effective Date: 01-Oct-2018
• Refers: ASTM D7962-16 - Standard Practice for Determination of Minimum Immersion Depth and Assessment of Temperature Sensor Measurement Drift
• Effective Date: 01-Dec-2016
• Refers: ASTM D6300-16 - Standard Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants
• Effective Date: 01-Apr-2016
• Refers: ASTM D6751-15c - Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels
• Effective Date: 01-Dec-2015
• Refers: ASTM D7962-15a - Standard Practice for Determination of Minimum Immersion Depth and Assessment of Temperature Sensor Measurement Drift
• Effective Date: 01-Dec-2015
• Refers: ASTM D6751-15b - Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels
• Effective Date: 01-Oct-2015
• Refers: ASTM D6300-15 - Standard Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants
• Effective Date: 01-Jun-2015

Overview

ASTM D2500-23: Standard Test Method for Cloud Point of Petroleum Products and Liquid Fuels specifies the procedure for determining the cloud point of petroleum products and biodiesel fuels. The cloud point is defined as the temperature at which wax crystals first become visible in a liquid fuel upon cooling under controlled laboratory conditions. This method is crucial for evaluating the low-temperature operability of fuels, as the presence of wax crystals can impact flow properties and filterability in cold environments.

ASTM D2500-23 applies to transparent petroleum products and biodiesel fuels with cloud points below 49 °C, using samples not exceeding ASTM D1500 color 3.5. Testing is conducted using either liquid-in-glass thermometers or calibrated digital contact thermometers, ensuring reliable and consistent results in laboratory and industrial settings.

Key Topics

• Significance of Cloud Point in Fuels:
  The cloud point serves as an index for the lowest practical temperature at which petroleum products and biodiesel fuels can be utilized safely without operational issues due to wax formation. This is especially critical for applications in cold climates and for compliance with fuel specifications.
• Scope and Applicability:
  • Suitable for petroleum and biodiesel fuels that are clear at 40 mm thickness
  • Not intended for samples with high color or opaque fuels
  • SI units are standard for all measurements
• Testing Apparatus and Method:
  • Requires a clear, cylindrical glass test jar, temperature measurement device (liquid-in-glass thermometer or digital contact thermometer), and a temperature-controlled cooling bath
  • The sample is cooled at a prescribed rate, with periodic inspection to record the temperature at which clouding is first observed
• Precision and Bias:
  • Repeatability: Generally within 2 °C for petroleum, 3 °C for biodiesel blends
  • Reproducibility: Generally within 4 °C for petroleum, 5 °C for biodiesel blends
  • Test results are relevant for fuels within the method's scope
• Safety Guidance:
  Users should follow appropriate safety, health, and environmental protocols and consult applicable regulations, as certain equipment or reagents (e.g., mercury thermometers, flammable solvents) may be hazardous or restricted by law.

Applications

• Fuel Quality Control:
  The ASTM D2500 cloud point test is routinely used by refineries, fuel terminals, and laboratories to ensure petroleum diesel, heating oils, lubricants, and biodiesel meet low-temperature performance standards.
• Product Specification and Compliance:
  Regulatory agencies and industry organizations may require cloud point testing to qualify fuels for use, sale, or export, particularly for regions subject to cold weather operation.
• Formulation and Additive Effectiveness:
  Fuel suppliers use the cloud point data to optimize blends and evaluate the effectiveness of cold flow improvers or additives intended to enhance fuel performance at low temperatures.

Related Standards

• ASTM D1500: Test Method for ASTM Color of Petroleum Products
• ASTM D4175: Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• ASTM D6751: Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels
• ASTM D7962: Practice for Determination of Minimum Immersion Depth and Assessment of Temperature Sensor Measurement Drift
• ASTM E1 / E2251: Specifications for ASTM Liquid-in-Glass Thermometers
• ASTM E2877: Guide for Digital Contact Thermometers
• Energy Institute IP Standards: Specifications for IP Standard Thermometers

Keywords: cloud point, ASTM D2500, petroleum products, biodiesel, liquid fuels, wax crystals, cold flow properties, fuel quality, low-temperature performance, laboratory test method

By following the procedures set forth in ASTM D2500-23, stakeholders in the petroleum and biodiesel industries can ensure accurate assessment of the cloud point, supporting product quality, safety, and regulatory compliance.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2500 − 23 British Standard 4458
Standard Test Method for
Cloud Point of Petroleum Products and Liquid Fuels
This standard is issued under the fixed designation D2500; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers only petroleum products and
D1500 Test Method for ASTM Color of Petroleum Products
biodiesel fuels that are transparent in layers 40 mm in
(ASTM Color Scale)
thickness, and with a cloud point below 49 °C.
D4175 Terminology Relating to Petroleum Products, Liquid
NOTE 1—The interlaboratory program consisted of petroleum products Fuels, and Lubricants
of Test Method D1500 color of 3.5 and lower. The precisions stated in this
D6300 Practice for Determination of Precision and Bias
test method may not apply to samples with ASTM color higher than 3.5.
Data for Use in Test Methods for Petroleum Products,
Liquid Fuels, and Lubricants
1.2 The values stated in SI units are to be regarded as
D6751 Specification for Biodiesel Fuel Blend Stock (B100)
standard. No other units of measurement are included in this
for Middle Distillate Fuels
standard.
D7962 Practice for Determination of Minimum Immersion
1.3 WARNING—Mercury has been designated by many
Depth and Assessment of Temperature Sensor Measure-
regulatory agencies as a hazardous substance that can cause ment Drift
serious medical issues. Mercury, or its vapor, has been dem- E1 Specification for ASTM Liquid-in-Glass Thermometers
E644 Test Methods for Testing Industrial Resistance Ther-
onstrated to be hazardous to health and corrosive to materials.
mometers
Use caution when handling mercury and mercury-containing
E2251 Specification for Liquid-in-Glass ASTM Thermom-
products. See the applicable product Safety Data Sheet (SDS)
eters with Low-Hazard Precision Liquids
for additional information. The potential exists that selling
E2877 Guide for Digital Contact Thermometers
mercury or mercury-containing products, or both, is prohibited
2.2 Energy Institute Standard:
by local or national law. Users must determine legality of sales
Specifications for IP Standard Thermometers
in their location.
1.4 This standard does not purport to address all of the 3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions:
responsibility of the user of this standard to establish appro-
3.1.1 For definitions of terms used in this test method, refer
priate safety, health, and environmental practices and deter-
to Terminology D4175.
mine the applicability of regulatory limitations prior to use.
3.1.2 biodiesel, n—a fuel comprised of mono-alkyl esters of
For specific hazard statements, see Section 7.
long chain fatty acids derived from vegetable oils or animal
fats, designated B100.
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard- 3.1.2.1 Discussion—Biodiesel is typically produced by a
reaction of vegetable oil or animal fat with an alcohol such as
ization established in the Decision on Principles for the
methanol or ethanol in the presence of a catalyst to yield
Development of International Standards, Guides and Recom-
mono-esters and glycerin. The fuel typically may contain up to
mendations issued by the World Trade Organization Technical
14 different types of fatty acids that are chemically transformed
Barriers to Trade (TBT) Committee.
into fatty acid methyl esters (FAME).
1 2
This test method is under the jurisdiction of ASTM Committee D02 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Subcommittee D02.07 on Flow Properties. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved March 1, 2023. Published March 2023. Originally the ASTM website.
approved in 1966. Last previous edition approved in 2017 as D2500 – 17a. DOI: Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR,
10.1520/D2500-23. U.K., http://www.energyinst.org.uk.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2500 − 23
3.1.3 biodiesel blend (BXX), n—a homogeneous mixture of
hydrocarbon oils and mono-alkyl esters of long chain fatty
acids.
3.1.3.1 Discussion—In the abbreviation BXX, the XX rep-
resents the volume percentage of biodiesel in the blend.
3.1.3.2 Discussion—The mono-alkyl esters of long chain
fatty acids (that is, biodiesel) used in the mixture shall meet the
requirements of Specification D6751.
3.1.3.3 Discussion—Diesel fuel, fuel oil, and non-aviation
gas turbine oil are examples of hydrocarbon oils.
3.1.4 digital contact thermometer (DCT), n—an electronic
device consisting of a digital display and associated tempera-
ture sensing probe.
3.1.4.1 Discussion—This device consists of a temperature
sensor connected to a measuring instrument; this instrument
measures the temperature-dependent quantity of the sensor,
computes the temperature from the measured quantity, and
provides a digital output. This digital output goes to a digital
display and/or recording device that may be internal or external
NOTE 1—All dimensions are in milllimetres.
to the device. These devices are referred to as “digital FIG. 1 Apparatus for Cloud Point Test
thermometers.”
3.1.4.2 Discussion—PET is an acronym for portable elec-
tronic thermometers, a subset of digital contact thermometers
The rate of crystal growth is slow, the opacity contrast is weak,
(DCT).
and the boundary of the cluster is more diffuse. As the
3.2 Definitions of Terms Specific to This Standard:
temperature of these specimens decrease below the cloud
3.2.1 cloud point, n—in petroleum products and biodiesel
point, the diffuse cluster will increase in size and can form a
fuels, the temperature of a liquid specimen when the smallest
general haze throughout. A slight haze throughout the entire
observable cluster of wax crystals first occurs upon cooling
sample, which slowly becomes more apparent as the tempera-
under prescribed conditions.
ture of the specimen decreases, can also be caused by traces of
3.2.1.1 Discussion—To many observers, the cluster of wax
water in the specimen instead of crystal formation (see Note 6).
crystals looks like a patch of whitish or milky cloud, hence the
With these difficult samples, drying the sample prior to testing
name of the test method. The cloud appears when the tempera-
can eliminate this type of interference.
ture of the specimen is low enough to cause wax crystals to
3.2.1.4 Discussion—The purpose of the cloud point method
form. For many specimens, the crystals first form at the lower
is to detect the presence of the wax crystals in the specimen;
circumferential wall of the test jar where the temperature is
however trace amounts of water and inorganic compounds may
lowest. The size and position of the cloud or cluster at the cloud
also be present. The intent of the cloud point method is to
point varies depending on the nature of the specimen. Some
capture the temperature at which the liquids in the specimen
samples will form large, easily observable, clusters, while
begin to change from a single liquid phase to a two-phase
others are barely perceptible.
system containing solid and liquid. It is not the intent of this
3.2.1.2 Discussion—Upon cooling to temperatures lower
test method to monitor the phase transition of the trace
than the cloud point, clusters of crystals will grow in multiple
components, such as water.
directions; for example, around the lower circumference of the
test jar, towards the center of the jar, or vertically upwards. The
4. Summary of Test Method
crystals can develop into a ring of cloud along the bottom
4.1 The specimen is cooled at a specified rate and examined
circumference, followed by extensive crystallization across the
periodically. The temperature at which a cloud is first observed
bottom of the test jar as temperature decreases. Nevertheless,
at the bottom of the test jar is recorded as the cloud point.
the cloud point is defined as the temperature at which the
crystals first appear, not when an entire ring or full layer of wax
5. Significance and Use
has been formed at the bottom of the test jar.
5.1 For petroleum products and biodiesel fuels, cloud point
3.2.1.3 Discussion—In general, it is easier to detect the
of a petroleum product is an index of the lowest temperature of
cloud point of samples with large clusters that form quickly,
their utility for certain applications.
such as paraffinic samples. The contrast between the opacity of
the cluster and the liquid is also sharper. In addition, small
6. Apparatus (see Fig. 1)
brightly-reflective spots can sometimes be observed inside the
cluster when the specimen is well illuminated. For other more 6.1 Test Jar, clear, cylindrical glass, flat bottom, 33.2 mm to
difficult samples, such as naphthenic, hydrocracked, and those 34.8 mm outside diameter and 115 mm to 125 mm in height.
samples whose cold flow behavior have been chemically The inside diameter of the jar may range from 30 mm to
altered, the appearance of the first cloud can be less distinct. 32.4 mm within the constraint that the wall thickness be no
D2500 − 23
TABLE 1 Cooling Mixtures and Bath Temperatures
Bath Temperature
Ice and water 0 °C ± 1.5 °C
Crushed ice and sodium chloride crystals, or –18 °C ± 1.5 °C
Acetone or petroleum naphtha or methanol or ethanol (see Section 7)
with solid carbon dioxide added to give the desired temperature
Acetone or petroleum naphtha or methanol or ethanol (see Section 7) –33 °C ± 1.5 °C
with solid carbon dioxide added to give the desired temperature
Acetone or petroleum naphtha or methanol or ethanol (see Section 7) –51 °C ± 1.5 °C
with solid carbon dioxide added to give the desired temperature
Acetone or petroleum naphtha or methanol or ethanol (see Section 7) –69 °C ± 1. 5 °C
with solid carbon dioxide added to give the desired temperature
greater than 1.6 mm. The jar should be marked with a line to 6.2.2 Digital Contact Thermometer Requirements:
indicate sample height 54 mm 6 3 mm above the inside
Parameter Requirement
DCT Guide E2877 Class F or better
bottom.
Nominal Tempera- High Cloud: –38 °C to +50 °C
A
6.2 Temperature Measuring Device—Either liquid-in-glass
ture range
Low Cloud: –80 °C to +20 °C
thermometers as described in 6.2.1 or digital contact thermom-
Display resolution 0.1 °C minimum
eter (DCT) meeting the requirements described in 6.2.2.
B
Accuracy ±500 mK (±0.5 °C)
6.2.1 Liquid-in-Glass Thermometers, having ranges shown Sensor type Platinum Resistance Thermometer (PRT), thermistor
C
Sensor sheath 4.2 mm O.D. maximum
below and conforming to the requirements as prescribed in
D
Sensor length Less than 10 mm
Specifications E1 or E2251, or Specifications for IP Standard
E
Immersion depth Less than 40 mm per Practice D7962
Thermometers. Sample immersion As shown in Fig. 1 or subsection 8.3
depth
Thermometer
E
Measurement Drift less than 500 mK (0.5 °C) per year
Number
F
Response time less than or equal to 4 s per Footnote F
Thermometer Temperature Range ASTM IP
Calibration error less than 500 mK (0.5 °C) over the range of intended use.
High cloud and pour −38 °C to +50 °C 5C, S5C 1C
Calibration range Consistent with temperature range of use
Low cloud and pour −80 °C to +20 °C 6C 2C
Calibration data Four data points evenly distributed over the calibration
range that is consistent with the range of use. The calibra-
tion data is to be included in calibration report.
Calibration report From a calibration laboratory with demonstrated compe-
tency in temperature calibration which is traceable to a
national calibration laboratory or metrology standards body
A
The nominal temperature range may be different from the values shown provided
the calibration and accuracy criteria are met.
B
Accuracy is the combined accuracy of the DCT unit which is the display and
sensor.
C
Sensor sheath is the tube that holds the sensing element. The value is the
outside diameter of the sheath segment containing the sensor element.
D
The physical length of the temperature sensing element.
E
As determined by Practice D7962 or an equivalent procedure.
F
Response Time—The time for a DCT to respond to a step change in temperature.
The response time is 63.2 % of the step change time as determined per Section 9
of Test Method E644. The step change evaluation begins at 20 °C ± 5 °C air to
77 °C ± 5 °C with water circulating at 0.9 m ⁄s ± 0.09 m ⁄s past the sensor.
NOTE 2—When
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D2500 − 17a D2500 − 23 British Standard 4458
Standard Test Method for
Cloud Point of Petroleum Products and Liquid Fuels
This standard is issued under the fixed designation D2500; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers only petroleum products and biodiesel fuels that are transparent in layers 40 mm in thickness, and with
a cloud point below 49 °C.
NOTE 1—The interlaboratory program consisted of petroleum products of Test Method D1500 color of 3.5 and lower. The precisions stated in this test
method may not apply to samples with ASTM color higher than 3.5.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 WARNING—Mercury has been designated by many regulatory agencies as a hazardous materialsubstance that can cause
central nervous system, kidney and liver damage. serious medical issues. Mercury, or its vapor, may has been demonstrated to be
hazardous to health and corrosive to materials. Caution should be taken Use caution when handling mercury and mercury
containing mercury-containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and EPA’s
website—http://www.epa.gov/mercury/faq.htm—for additional information. Users should be aware (SDS) for additional informa-
tion. The potential exists that selling mercury and/or mercury containing products into your state or country may be prohibited by
law.or mercury-containing products, or both, is prohibited by local or national law. Users must determine legality of sales in their
location.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. For specific hazard statements, see Section 7.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1500 Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.07 on Flow Properties.
Current edition approved Dec. 1, 2017March 1, 2023. Published January 2018March 2023. Originally approved in 1966. Last previous edition approved in 2017 as
D2500 – 17.D2500 – 17a. DOI: 10.1520/D2500-17A.10.1520/D2500-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2500 − 23
D6300 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products, Liquid Fuels, and
Lubricants
D6751 Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels
D7962 Practice for Determination of Minimum Immersion Depth and Assessment of Temperature Sensor Measurement Drift
E1 Specification for ASTM Liquid-in-Glass Thermometers
E644 Test Methods for Testing Industrial Resistance Thermometers
E2251 Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
E2877 Guide for Digital Contact Thermometers
2.2 Energy Institute Standard:
Specifications for IP Standard Thermometers
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
3.1.2 biodiesel, n—a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats,
designated B100.
3.1.2.1 Discussion—
Biodiesel is typically produced by a reaction of vegetable oil or animal fat with an alcohol such as methanol or ethanol in the
presence of a catalyst to yield mono-esters and glycerin. The fuel typically may contain up to 14 different types of fatty acids that
are chemically transformed into fatty acid methyl esters (FAME).
3.1.3 biodiesel blend (BXX), n—a homogeneous mixture of hydrocarbon oils and mono-alkyl esters of long chain fatty acids.
3.1.3.1 Discussion—
In the abbreviation BXX, the XX represents the volume percentage of biodiesel in the blend.
3.1.3.2 Discussion—
The mono-alkyl esters of long chain fatty acids (that is, biodiesel) used in the mixture shall meet the requirements of Specification
D6751.
3.1.3.3 Discussion—
Diesel fuel, fuel oil, and non-aviation gas turbine oil are examples of hydrocarbon oils.
3.1.4 digital contact thermometer (DCT), n—an electronic device consisting of a digital display and associated temperature
sensing probe.
3.1.4.1 Discussion—
This device consists of a temperature sensor connected to a measuring instrument; this instrument measures the temperature-
dependent quantity of the sensor, computes the temperature from the measured quantity, and provides a digital output. This digital
output goes to a digital display and/or recording device that may be internal or external to the device. These devices are referred
to as “digital thermometers.”
3.1.4.2 Discussion—
PET is an acronym for portable electronic thermometers, a subset of digital contact thermometers (DCT).
3.2 Definitions of Terms Specific to This Standard:
3.2.1 biodiesel, n—a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats,
designated B100.
3.2.1.1 Discussion—
Biodiesel is typically produced by a reaction of vegetable oil or animal fat with an alcohol such as methanol or ethanol in the
presence of a catalyst to yield mono-esters and glycerin. The fuel typically may contain up to 14 different types of fatty acids that
are chemically transformed into fatty acid methyl esters (FAME).
3.2.2 biodiesel blend, n—a blend of biodiesel fuel with petroleum-based diesel fuel designated BXX, where XX is the volume %
of biodiesel.
3.2.1 cloud point, n—in petroleum products and biodiesel fuels, the temperature of a liquid specimen when the smallest observable
cluster of wax crystals first occurs upon cooling under prescribed conditions.
Available from Energy Institute, 61 New Cavendish St., London, WIG 7AR, U.K., http://www.energyinst.org.uk.
D2500 − 23
3.2.1.1 Discussion—
To many observers, the cluster of wax crystals looks like a patch of whitish or milky cloud, hence the name of the test method.
The cloud appears when the temperature of the specimen is low enough to cause wax crystals to form. For many specimens, the
crystals first form at the lower circumferential wall of the test jar where the temperature is lowest. The size and position of the
cloud or cluster at the cloud point varies depending on the nature of the specimen. Some samples will form large, easily observable,
clusters, while others are barely perceptible.
3.2.1.2 Discussion—
Upon cooling to temperatures lower than the cloud point, clusters of crystals will grow in multiple directions; for example, around
the lower circumference of the test jar, towards the center of the jar, or vertically upwards. The crystals can develop into a ring
of cloud along the bottom circumference, followed by extensive crystallization across the bottom of the test jar as temperature
decreases. Nevertheless, the cloud point is defined as the temperature at which the crystals first appear, not when an entire ring
or full layer of wax has been formed at the bottom of the test jar.
3.2.1.3 Discussion—
In general, it is easier to detect the cloud point of samples with large clusters that form quickly, such as paraffinic samples. The
contrast between the opacity of the cluster and the liquid is also sharper. In addition, small brightly-reflective spots can sometimes
be observed inside the cluster when the specimen is well illuminated. For other more difficult samples, such as naphthenic,
hydrocracked, and those samples whose cold flow behavior have been chemically altered, the appearance of the first cloud can be
less distinct. The rate of crystal growth is slow, the opacity contrast is weak, and the boundary of the cluster is more diffuse. As
the temperature of these specimens decrease below the cloud point, the diffuse cluster will increase in size and can form a general
haze throughout. A slight haze throughout the entire sample, which slowly becomes more apparent as the temperature of the
specimen decreases, can also be caused by traces of water in the specimen instead of crystal formation (see Note 6). With these
difficult samples, drying the sample prior to testing can eliminate this type of interference.
3.2.1.4 Discussion—
The purpose of the cloud point method is to detect the presence of the wax crystals in the specimen; however trace amounts of
water and inorganic compounds may also be present. The intent of the cloud point method is to capture the temperature at which
the liquids in the specimen begin to change from a single liquid phase to a two-phase system containing solid and liquid. It is not
the intent of this test method to monitor the phase transition of the trace components, such as water.
4. Summary of Test Method
4.1 The specimen is cooled at a specified rate and examined periodically. The temperature at which a cloud is first observed at
the bottom of the test jar is recorded as the cloud point.
5. Significance and Use
5.1 For petroleum products and biodiesel fuels, cloud point of a petroleum product is an index of the lowest temperature of their
utility for certain applications.
6. Apparatus (see Fig. 1)
6.1 Test Jar, clear, cylindrical glass, flat bottom, 33.2 mm to 34.8 mm outside diameter and 115 mm to 125 mm in height. The
inside diameter of the jar may range from 30 mm to 32.4 mm within the constraint that the wall thickness be no greater than
1.6 mm. The jar should be marked with a line to indicate sample height 54 mm 6 3 mm above the inside bottom.
6.2 Temperature Measuring Device—Either liquid-in-glass thermometers as described in 6.2.1 or digital contact thermometer
(DCT) meeting the requirements described in 6.2.2.
D2500 − 23
NOTE 1—All dimensions are in milllimetres.
FIG. 1 Apparatus for Cloud Point Test
6.2.1 Liquid-in-Glass Thermometers, having ranges shown below and conforming to the requirements as prescribed in
Specifications E1 or E2251, or Specifications for IP Standard Thermometers.
Thermometer
Number
Thermometer Temperature Range ASTM IP
High cloud and pour −38 °C to +50 °C 5C, S5C 1C
Low cloud and pour −80 °C to +20 °C 6C 2C
D2500 − 23
6.2.2 Digital Contact Thermometer Requirements:
Parameter Requirement
DCT Guide E2877 Class F or better
A
Nominal Temperature range High Cloud: –38 °C to +50 °C
Low Cloud: –80 °C to +20 °C
Display resolution 0.1 °C minimum
B
Accuracy ±500 mK (±0.5 °C)
Sensor type Platinum Resistance Thermometer (PRT), thermistor
C
Sensor sheath 4.2 mm O.D. maximum
D
Sensor length Less than 10 mm
E
Immersion depth Less than 40 mm per Practice D7962
Sample immersion depth As shown in Fig. 1 or subsection 8.3
E
Measurement Drift less than 500 mK (0.5 °C) per year
F
Response time less than or equal to 4 s per Footnote F
Calibration error less than 500 mK (0.5 °C) over the range of intended use.
Calibration range Consistent with temperature range of use
Calibration data Four data points evenly distributed over the calibration range that is consistent with the range of use. The calibration data
is to be included in calibration report.
Calibration report From a calibration laboratory with demonstrated competency in temperature calibration which is traceable to a national
calibration laboratory or metrology standards body
A
The nominal temperature range may be different from the values shown provided the calibration and accuracy criteria are met.
B
Accuracy is the combined accuracy of the DCT unit which is the display and sensor.
C
Sensor sheath is the tube that holds the sensing element. The value is the outside diameter of the sheath segment containing the sensor element.
D
The physical length of the temperature sensing element.
E
As determined by Practice D7962 or an equivalent procedure.
F
Response Time—The time for a DCT to respond to a step change in temperature. The response time is 63.2 % of the step change time as determined per Section 9 of
Test Method E644. The step change evaluation begins at 20 °C ± 5 °C air to 77 °C ± 5 °C with water circulating at 0.9 m ⁄s ± 0.09 m ⁄s past the sensor.
NOTE 2—When making measurements below –40 °C with a PRT, it may be necessary to use a 1000 ohm sensor in order to obtain accurate measurements.
NOTE 3—When the DCT display is mounted on the end to the probe’s sheath, the test jar with the probe inserted will be unstable. To resolve this, it is
recommended that the probe be less than 30 cm in length but no less than 15 cm. A 5 cm long stopper that has a low t
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