ASTM D7157-23

Standard Test Method for Determination of Intrinsic Stability of Asphaltene-Containing Residues, Heavy Fuel Oils, and Crude Oils (<emph type="ital">n</emph >-Heptane Phase Separation; Optical Detection)

SIGNIFICANCE AND USE
5.1 This test method describes a sensitive method for estimating the intrinsic stability of an oil. The intrinsic stability is expressed as S-value. An oil with a low S-value is likely to undergo flocculation of asphaltenes when stressed (for example, extended heated storage) or blended with a range of other oils. Two oils each with a high S-value are likely to maintain asphaltenes in a peptized state and not lead to asphaltene flocculation when blended together.  
5.2 This test method can be used by petroleum refiners to control and optimize the refinery processes and by blenders and marketers to assess the intrinsic stability of blended asphaltene-containing heavy fuel oils.
SCOPE
1.1 This test method covers procedures for quantifying the intrinsic stability of the asphaltenes in an oil by automatic instruments using optical detection.  
1.2 This test method is applicable to residual products from thermal and hydrocracking processes, to products typical of Specifications D396 Grades No. 5L, 5H, and 6, and D2880 Grades No. 3-GT and 4-GT, and to crude oils, providing these products contain 0.5 % by mass or greater concentration of asphaltenes (see Test Method D6560).  
1.3 This test method quantifies asphaltene stability in terms of state of peptization of the asphaltenes (S-value), intrinsic stability of the oily medium (So) and the solvency requirements of the peptized asphaltenes (Sa).  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 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.  
1.6 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: 75.040 - Crude petroleum
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.14 - Stability, Cleanliness and Compatibility of Liquid Fuels

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 D6708-24 - Standard Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport to Measure the Same Property of a Material
• 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 D6792-23c - Standard Practice for Quality Management Systems in Petroleum Products, Liquid Fuels, and Lubricants Testing Laboratories
• Effective Date: 01-Nov-2023
• Refers: ASTM D6792-23b - Standard Practice for Quality Management Systems in Petroleum Products, Liquid Fuels, and Lubricants Testing Laboratories
• Effective Date: 01-Oct-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023
• Refers: ASTM D396-19a - Standard Specification for Fuel Oils
• Effective Date: 15-Dec-2019
• 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 D6708-19 - Standard Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport to Measure the Same Property of a Material
• Effective Date: 01-May-2019
• Refers: ASTM D396-19 - Standard Specification for Fuel Oils
• Effective Date: 01-May-2019
• Refers: ASTM D396-18a - Standard Specification for Fuel Oils
• Effective Date: 01-Oct-2018
• Refers: ASTM D2880-18a - Standard Specification for Gas Turbine Fuel Oils
• Effective Date: 01-Oct-2018
• Refers: ASTM D2880-18 - Standard Specification for Gas Turbine Fuel Oils
• Effective Date: 01-May-2018
• Refers: ASTM D396-18 - Standard Specification for Fuel Oils
• Effective Date: 01-May-2018

Overview

ASTM D7157-23 is the Standard Test Method for Determination of Intrinsic Stability of Asphaltene-Containing Residues, Heavy Fuel Oils, and Crude Oils (n-Heptane Phase Separation; Optical Detection). Developed by ASTM International, this test method provides a standardized procedure for estimating and quantifying the intrinsic stability of oils containing asphaltenes, including residual products, heavy fuel oils, and crude oils. The method utilizes automatic instrumentation with optical detection to monitor asphaltene precipitation, evaluating oil stability using parameters such as the S-value, which indicates the tendency of asphaltenes to flocculate under stress or blending conditions.

Key Topics

• Intrinsic Stability Measurement: The method expresses oil stability as the S-value, quantifying the solvency power of an oil concerning asphaltene precipitation.
• Optical Detection Technology: Asphaltene precipitation is detected optically, providing sensitive and consistent measurement during n-heptane titration.
• Automatic and Manual Procedures: Two procedures are included-manual dilution (Procedure A) and automatic dilution (Procedure B)-both using automated analytical systems.
• Applicability: The test is suitable for residual products from refining processes (including thermal and hydrocracking), and for oils with asphaltene concentrations of at least 0.5% by mass.
• Parameters Reported: S-value (intrinsic stability), So (aromatic equivalent or peptizing power of the oil), and Sa (peptizability or ability of asphaltenes to remain in dispersion).
• SI Units Only: All results are expressed in SI units, ensuring universal application and consistency across international laboratories.

Applications

• Refinery Process Control: Petroleum refiners use ASTM D7157-23 to monitor and optimize processes involving heavy oils and residues, mitigating the risk of asphaltene precipitation, which can cause operational disruptions and fouling.
• Blending and Compatibility Testing: Oil blenders and marketers rely on this standard to evaluate the intrinsic stability and compatibility of oil blends, reducing the risk of asphaltene flocculation during storage or transport.
• Quality Assurance in Heavy Fuel Oils: The method helps determine if heavy fuel oils or crude oils will remain stable or if they are likely to deposit sediments during long-term storage or under changing processing conditions.
• Product Selection: Crude assay laboratories and quality control departments use ASTM D7157-23 results to select suitable feedstocks and ensure product integrity according to customer and regulatory requirements.

Related Standards

• ASTM D396: Specification for Fuel Oils, referenced for defining heavy fuel oil grades relevant to the test.
• ASTM D2880: Specification for Gas Turbine Fuel Oils, providing context for applicable product types.
• ASTM D4057 & D4177: Practices for manual and automatic sampling of petroleum products, ensuring representative sample collection for testing.
• ASTM D6560: Test Method for Determination of Asphaltenes (Heptane Insolubles) in Crude Petroleum, often used to assess sample suitability for ASTM D7157-23.
• ASTM D4870: Method for removing insoluble inorganic matter that may interfere with optical detection.
• ASTM D6708 & D6300: Practices for statistical analysis and quality management in petroleum testing laboratories.

Practical Value

Implementing ASTM D7157-23 enables refiners, blenders, and oil marketers to effectively assess and manage the stability of asphaltene-containing oils, reducing operational risks such as clogging, sedimentation, and loss of compatibility in storage or transport. The standard provides precision and repeatability in test results, helping stakeholders make informed decisions in product blending, quality control, and compliance with regulatory or commercial specifications.

Keywords: asphaltenes, oil stability, S-value, heavy fuel oil, crude oil compatibility, n-heptane phase separation, optical detection, ASTM D7157-23, refinery process optimization, fuel oil blending, petroleum testing.

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: D7157 − 23
Standard Test Method for
Determination of Intrinsic Stability of Asphaltene-Containing
Residues, Heavy Fuel Oils, and Crude Oils (n-Heptane
Phase Separation; Optical Detection)
This standard is issued under the fixed designation D7157; 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.
1. Scope* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers procedures for quantifying the
D396 Specification for Fuel Oils
intrinsic stability of the asphaltenes in an oil by automatic
D2880 Specification for Gas Turbine Fuel Oils
instruments using optical detection.
D4057 Practice for Manual Sampling of Petroleum and
1.2 This test method is applicable to residual products from
Petroleum Products
thermal and hydrocracking processes, to products typical of
D4175 Terminology Relating to Petroleum Products, Liquid
Specifications D396 Grades No. 5L, 5H, and 6, and D2880
Fuels, and Lubricants
Grades No. 3-GT and 4-GT, and to crude oils, providing these
D4177 Practice for Automatic Sampling of Petroleum and
products contain 0.5 % by mass or greater concentration of
Petroleum Products
asphaltenes (see Test Method D6560).
D4870 Test Method for Determination of Total Sediment in
Residual Fuels
1.3 This test method quantifies asphaltene stability in terms
D6300 Practice for Determination of Precision and Bias
of state of peptization of the asphaltenes (S-value), intrinsic
Data for Use in Test Methods for Petroleum Products,
stability of the oily medium (So) and the solvency requirements
Liquid Fuels, and Lubricants
of the peptized asphaltenes (Sa).
D6560 Test Method for Determination of Asphaltenes (Hep-
1.4 The values stated in SI units are to be regarded as
tane Insolubles) in Crude Petroleum and Petroleum Prod-
standard. No other units of measurement are included in this
ucts
standard.
D6708 Practice for Statistical Assessment and Improvement
of Expected Agreement Between Two Test Methods that
1.5 This standard does not purport to address all of the
Purport to Measure the Same Property of a Material
safety concerns, if any, associated with its use. It is the
D6792 Practice for Quality Management Systems in Petro-
responsibility of the user of this standard to establish appro-
leum Products, Liquid Fuels, and Lubricants Testing
priate safety, health, and environmental practices and deter-
Laboratories
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
3. Terminology
dance with internationally recognized principles on standard-
3.1 Definitions:
ization established in the Decision on Principles for the
3.1.1 For definitions of some terms used in this test method,
Development of International Standards, Guides and Recom-
refer to Terminology D4175.
mendations issued by the World Trade Organization Technical
3.1.2 asphaltenes, n—(rarely used in the singular), in petro-
Barriers to Trade (TBT) Committee.
leum technology, represent an oil fraction that is soluble in a
specified aromatic solvent but separates upon addition of an
excess of a specified paraffinic solvent.
This test method is under the jurisdiction of Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
mittee D02.14 on Stability, Cleanliness and Compatibility of Liquid Fuels. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 1, 2023. Published March 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ε1
approved in 2005. Last previous edition approved in 2022 as D7157 – 22 . DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D7157-23. 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
D7157 − 23
3.1.2.1 Discussion—In this test method, the aromatic sol- the ratio of So to S. Sa is linked to the length and number of
vent is toluene and the paraffinic solvent is n-heptane. aromatic chains within the asphaltenes.
3.1.3 compatibility, n—of crude oils or of heavy fuel oils, 3.2.4 So, n—the S-value of an oil.
the ability of two or more crude oils or fuel oils to blend 3.2.4.1 Discussion—So can also be described as the aro-
together within certain concentration ranges without evidence matic equivalent of the oil expressed as the ratio of the
of separation, such as the formation of multiple phases. aromatic solvent to the aromatic plus paraffinic solvent mixture
having the same peptizing power as the oil.
3.1.3.1 Discussion—Incompatible heavy fuel oils or crude
oils, when mixed or blended, result in the flocculation or
3.2.5 solvent aromaticity, n—of a binary mixture of a
precipitation of asphaltenes. Some oils may be compatible
paraffınic and an aromatic solvent, the solvency power of the
within certain concentration ranges in specific mixtures, but
binary mixture.
incompatible outside those ranges.
3.2.5.1 Discussion—For the purpose of this test method,
3.1.4 flocculation, n—of asphaltenes from crude oils or solvent aromaticity is defined as a ratio by volume of the
aromatic solvent (toluene) to the paraffinic solvent (n-heptane).
heavy fuel oils, the aggregation of colloidally dispersed as-
phaltenes into visible larger masses which may or may not
3.3 Symbols:
settle.
3.3.1 FR—flocculation ratio
3.1.5 peptization, n—of asphaltenes in crude oils or heavy
3.3.2 FR —maximum flocculation ratio
max
oils, the dispersion of asphaltenes to produce a colloidal
3.3.3 S—the intrinsic stability of an oil
dispersion.
3.3.4 Sa—the peptizability of an asphaltene
3.1.6 stability reserve, n—in petroleum technology, the
3.3.5 So—the peptizing power of an oil
property of an oil to maintain asphaltenes in a peptized state
and prevent flocculation of asphaltenes.
3.3.6 X —paraffinic solvent consumption of undiluted oil,
min
3.1.6.1 Discussion—An oil with a low stability reserve is
in mL/g of oil
likely to undergo flocculation of asphaltenes when stressed (for
example, extended heated storage) or blended with a range of
4. Summary of Test Method
other oils. Two oils each with a high stability reserve are likely
4.1 This test method uses an integrated automated analytical
to maintain asphaltenes in a peptized state and not lead to
measurement system with an optical probe or cell for the
flocculation when blended together.
detection of asphaltene precipitation from a toluene solution of
3.2 Definitions of Terms Specific to This Standard:
the sample.
3.2.1 intrinsic stability (S-value), n—of refinery residual
4.2 Three test specimens are dissolved in three different
streams, residual fuel oils and crude oils, an indication of the
quantities of toluene. The three specimen/toluene solutions are
stability or available solvency power of an oil with respect to
automatically and simultaneously titrated with n-heptane to
precipitation of asphaltenes.
cause precipitation of the asphaltenes. The optical probe or cell
3.2.1.1 Discussion—Since the equation defining S-value is
monitors the formation of flocculated asphaltenes during the
S = (1 + X ), where X is the minimum volume (in mL) of
min min
titration. Flocculated asphaltenes will alter the detected light
paraffinic solvent, n-heptane, to be added to 1 g of oil to result
intensity. Start of flocculation is interpreted when the optical
in flocculation of asphaltenes; the smallest S-value is 1, which
probe or cell detects a significant and sustained decrease in
means the oil is unstable and can precipitate asphaltenes
rate-of-change of the light intensity.
without addition of any paraffinic solvent. A higher S-value
indicates that an oil is more stable with respect to flocculation 4.3 A computer routine calculates stability parameters and
of asphaltenes. S-value by this test method relates specifically subsequently the intrinsic stability of the oil from the added
to toluene and n-heptane as the aromatic and paraffinic n-heptane at the inversion point, the mass of specimen, and the
solvents, respectively. volume of toluene, for the three specimen/toluene solutions.
3.2.2 inversion point, n—point in the n-heptane titration
5. Significance and Use
curve, where the onset of asphaltene flocculation leads to
inversion of the light intensity.
5.1 This test method describes a sensitive method for
3.2.2.1 Discussion—At the first stage of the addition of estimating the intrinsic stability of an oil. The intrinsic stability
n-heptane to a dilution of specimen and toluene, light intensity is expressed as S-value. An oil with a low S-value is likely to
increases through dilution. When asphaltenes start to undergo flocculation of asphaltenes when stressed (for
flocculate, there will be a point where the increase in light example, extended heated storage) or blended with a range of
intensity through dilution matches the light intensity decrease
other oils. Two oils each with a high S-value are likely to
(inversion) as a result of coagulated asphaltenes obstructing the maintain asphaltenes in a peptized state and not lead to
light beam. asphaltene flocculation when blended together.
3.2.3 Sa, n—the S-value of an asphaltene, which is the
5.2 This test method can be used by petroleum refiners to
peptizability or ability of an asphaltene to remain in a colloidal
control and optimize the refinery processes and by blenders and
dispersion.
marketers to assess the intrinsic stability of blended asphaltene-
3.2.3.1 Discussion—Sa can also be described as one minus containing heavy fuel oils.
D7157 − 23
6. Interferences 9.1.1 General—(See Fig. X1.1) This procedure uses an
4,5
integrated automated analytical measurement system com-
6.1 High content of insoluble inorganic matter (sediment)
prised of a PC-based computer and three titration stations.
has some interference in this test method. In this case, the
9.1.2 Computer—PC-based computer with associated
insoluble matter shall be removed by filtration according to
software, capable of controlling up to three independent
Test Method D4870.
titration stations, controlling test sequencing, and acquisition of
6.2 Free water present in the oil can cause difficulties with
optical probe signal data. The associated software also pro-
the optical detector and should be removed by any suitable
vides for processing calculations and automatically produces a
means (for example, centrifugation) prior to testing.
report of important test parameters.
9.1.3 Titration Stations:
7. Reagents and Materials
9.1.3.1 Titration Unit, automatic computer controlled, ad-
justable motor-driven ceramic piston pump, capable of deliv-
7.1 Purity of Reagents—Reagent grade chemicals shall be
ering solvent at a rate of 0.01 mL ⁄s to 0.5 mL ⁄s, with a volume
used in all tests. Unless otherwise indicated, it is intended that
dispensing accuracy of 60.01 mL.
all reagents conform to the specifications of the Committee on
9.1.3.2 Magnetic Stirrer, adjustable from 200 r ⁄min to
Analytical Reagents of the American Chemical Society where
400 r ⁄min.
such specifications are available. Other grades may be used,
9.1.3.3 Optical Probe, consisting of a system of three areas
provided it is first ascertained that the reagent is of sufficiently
of light emitters (880 nm) and three areas of light receivers.
high purity to permit its use without lessening the accuracy of
The analytical measurement system will automatically select
the determination.
the optimum area, based on the level of translucency of the
7.1.1 Toluene. (Warning—Flammable. Health hazard. Va-
sample.
por may cause flash fire.) (See Annex A1.)
9.1.3.4 Titration Cell, of borosilicate glass, flat bottom,
7.1.2 n-Heptane. (Warning—Flammable. Vapor harmful.
outside diameter 30 mm 6 2 mm, volume 95 mL 6 15 mL,
Vapor may cause flash fire.) (See Annex A1.)
fitted with a tapered ground glass joint (female).
7.2 Quality Control Sample—A stable and homogeneous
9.1.4 Balance, capable of reading to 0.1 mg or better.
residual fuel oil having physical and chemical properties
9.1.5 Dispenser, capable of delivering up to 10 mL of
similar to those of typical sample fuels routinely tested.
toluene with an accuracy of 60.1 mL.
9.1.6 Condenser, double surface with a tapered ground-glass
8. Apparatus and Procedure
joint (male) at the bottom to fit the top of the titration cell.
8.1 Two procedures exist and are mainly differentiated by 9.1.7 Magnetic Stirrer/Hotplate, stirrer speed adjustable
the method of dilution of the sample with toluene: Procedure from 100 r ⁄min to 1000 r ⁄min.
A—Manual Dilution (Rofa apparatus) and Procedure 9.1.8 Stirring Bar, magnetic, PFTE-coated, 20 mm in
B—Automatic Dilution (AD Systems apparatus).
length.
8.2 Both procedures use the same dilution table (see Table 9.2 Sampling and Test Specimens:
9.2.1 Sampling:
1).
TABLE 1 Specimen and Toluene Dilutions 9.2.1.1 Obtain representative samples in accordance with
Product Type Dilution 1 Dilution 2 Dilution 3 recognized sampling procedures such as Practices D4057 or
1: Liquid at Mass sample, g 9 5.5 3 D4177.
<30 °C Volume toluene, mL 2 5.5 8
9.2.1.2 Samples of very viscous materials may be warmed
until they are reasonably fluid before they are sampled.
2: Liquid between Mass sample, g 7 5.5 3
30 °C – 100 °C Volume toluene, mL 4 5.5 8 9.2.1.3 Store samples prior to taking test specimens at
ambient temperatures.
3: Liquid at Mass sample, g 4 3 2
9.2.2 Test Specimen Preparation:
>100 °C Volume toluene, mL 7 8 9
9.2.2.1 Sample Temperature—If necessary, warm viscous
Very stable Mass sample, g 3 2 1
samples until they can be mixed readily before opening the
products Volume toluene, mL 1 2 3
storage container. For fuels with a high wax content (high pour
8.3 These dilutions are the dilutions usually used, but it is
point) the temperature must be at least 15 °C above the pour
possible to use other dilutions in certain circumstances.
point.
9.2.2.2 Manually shake the sample thoroughly. If the sample
9. Procedure A (Manual Dilution)
contains high content of insoluble inorganic matter, filter the
9.1 Apparatus:
The sole source of supply of the Procedure A apparatus (Automated Stability
Analyzer) known to the committee at this time is Rofa France, 6 Rue Raymond
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Poincare, F-25300, Les Allies, France. If you are aware of alternative suppliers,
Standard-Grade Reference Materials, American Chemical Society, Washington, please provide this information to ASTM International Headquarters. Your com-
DC. For suggestions on the testing of reagents not listed by the American Chemical ments will receive careful consideration at a meeting of the responsible technical
Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, committee, which you may attend.
U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharma- The Rofa stability analyzer is covered by a patent owned by Total Raffinage
copeial Convention, Inc. (USPC), Rockville, MD. France; INPI, date 18/05/04, registration number 04.05406.
D7157 − 23
sample through a 47 mm diameter glass fiber filter medium 9.4.6 n-heptane is added in steps of 0.05 mL at a rate of
(such as Whatman Grade GF/A), using the Test Method D4870 0.05 mL ⁄s. Addition of n-heptane is discontinued for 2 s
filtration apparatus. Specimen should be representative of the between each step.
whole sample. 9.4.7 For dilutions of very stable samples (see Table 1), it is
needed to pre-add an accurately known quantity of 7 mL of
9.2.3 Preparation of Specimen Dilutions—Prepare three
n-heptane by the automatic titration unit to ensure that the
dilutions of specimen in toluene in different ratios (see Table 1)
probe is fully immersed.
as follows:
9.2.3.1 Place a magnetic stirrer bar into a clean titration cell.
NOTE 2—The addition of 7 mL of n-heptane is automatically performed
by the apparatus when “pre-dilution” mode is selected by the operator.
9.2.3.2 Add the required amount of specimen to the titration
cell and obtain the mass of the specimen to the nearest 0.001 g
9.4.8 The test is completed when either an inversion point is
(M ).
encountered (V ) or when the total liquid content of the
oil
para
9.2.3.3 Add the appropriate volume of toluene to the nearest titration cell reaches a maximum of 50 mL. A report is
0.1 mL to the titration cell. displayed automatically at that time or earlier if requested by
the operator.
9.2.3.4 Stir dilutions of sample Type 1, without heating, for
at least two minutes. Obtain the mass of the specimen plus
NOTE 3—The apparatus will stop automatically when the maximum
toluene to the nearest 0.001 g (M ). Proceed with 9.4.
limit of 50 mL liquid has been reached.
9.2.3.5 For specimen dilutions of Type 2 and 3, place a
9.4.9 Draw a straight line through the three points (see Fig.
condenser on the titration cell, place on the hot plate, and boil
1) using the least squares fit equation. For a valid result the
under reflux, while stirring, for a minimum of 10 min for
measure of goodness of fit (R-squared) should be = >0.98. If
specimens of Type 2 and for a minimum of 15 min for
R-squared <0.98, discard the result and repeat the test with
specimens of Type 3.
fresh dilutions from 9.2.3 onwards.
9.2.3.6 Discontinue heating and while stirring, allow the
NOTE 4—See Appendix X1 for detailed automatic test program and
dilutions to cool to ambient temperature. Disconnect the
examples of the titration curve and regression report.
condenser and obtain the mass of specimen plus toluene to the
9.4.10 When, for any of the three dilutions, n-heptane has
nearest 0.001 g (M ). Proceed with 9.4.
been added up to a total of 50 mL liquids in the titration cell
NOTE 1—In this context, “liquid” means the minimum temperature at without encountering an inversion, the sample is considered to
which the product has sufficient fluidity to be handled as a liquid.
be very stable. In such a case, the test shall be repeated from
9.2.3 onwards, using fresh dilutions as given in Table 1 under
9.3 Preparation of Apparatus:
“Very stable products.”
9.3.1 Prepare and set up the instrument for operation ac-
cording to the manufacturer’s manual. (Refer to Fig. X1.1.)
10. Procedure B (Automatic Dilution)
9.3.2 Plug the optical probes into their connectors and place
10.1 Apparatus :
them in their standby position.
10.1.1 General—(See Fig. X2.1). This procedure uses an
9.3.3 Ensure that the reagent vessel contains sufficient
integrated automated analytical measurement system compris-
n-heptane to run the tests (minimum 200 mL).
ing a user interface and three fully automated titration stations.
9.3.4 Cleaning Instructions—Perform the following clean-
10.1.2 User Interface, capable of controlling up to three
ing procedure after the test procedure (see 9.4.8).
independent titration stations, controlling test sequencing, and
9.3.4.1 Carefully remove the dosing tube and the optical
acquisition of optical signal data. This also provides data for
probe from the titration cell. Clean the optical probe with an
processing calculations and automatically produces a test
appropriate solvent (toluene) (see 7.1.1).
report and important test parameters.
9.3.4.2 Remove the stirrer bar. Empty the titration cell. 10.1.3 Titration Stations:
Clean the reactor cell and stirrer bar with an appropriate
10.1.3.1 Dilution Unit, automatically controlled, adjustable
solvent (toluene) (see 7.1.1). motor-driven piston pump, capable of delivering solvent
(toluene), with a volume dispensing accuracy of 60.01 mL.
9.4 Test Procedure:
10.1.3.2 Titration Unit, automatically controlled, adjustable
9.4.1 Place the titration cells containing the specimen solu-
motor-driven ceramic piston pump, capable of delivering
tions (9.2.3.4 and 9.2.3.6) into their slot positions in the
solvent at a rate of 0.01 mL ⁄s to 0.3 mL ⁄s, with a volume
measurement system.
dispensing accuracy of 60.01 mL.
9.4.2 Position the optical probes in the titration cells.
10.1.3.3 Magnetic Stirrer, adjustable from 0 r ⁄min to
9.4.3 Place the dosing tubes of the titration apparatus into
600 r ⁄min.
the titration cell. The position of the tube is such that droplets
fall directly into the sample vortex so that mixing is optimal.
The sole source o
...

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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.
´1
Designation: D7157 − 22 D7157 − 23
Standard Test Method for
Determination of Intrinsic Stability of Asphaltene-Containing
Residues, Heavy Fuel Oils, and Crude Oils (n-Heptane
Phase Separation; Optical Detection)
This standard is issued under the fixed designation D7157; 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.
ε NOTE—Editorial corrections made throughout in September 2022.
1. Scope*
1.1 This test method covers a procedure procedures for quantifying the intrinsic stability of the asphaltenes in an oil by an
automatic instrumentinstruments using an optical device.detection.
1.2 This test method is applicable to residual products from thermal and hydrocracking processes, to products typical of
Specifications D396 Grades No. 5L, 5H, and 6, and D2880 Grades No. 3-GT and 4-GT, and to crude oils, providing these products
contain 0.5 % by mass or greater concentration of asphaltenes (see Test Method D6560).
1.3 This test method quantifies asphaltene stability in terms of state of peptization of the asphaltenes (S-value), intrinsic stability
of the oily medium (So) and the solvency requirements of the peptized asphaltenes (Sa).
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
1.6 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:
D396 Specification for Fuel Oils
D2880 Specification for Gas Turbine Fuel Oils
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
This test method is under the jurisdiction of Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee D02.14
on Stability, Cleanliness and Compatibility of Liquid Fuels.
Current edition approved July 1, 2022March 1, 2023. Published August 2022March 2023. Originally approved in 2005. Last previous edition approved in 20182022 as
ε1
D7157 – 18.D7157 – 22 . DOI: 10.1520/D7157-22E01.10.1520/D7157-23.
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
D7157 − 23
D4870 Test Method for Determination of Total Sediment in Residual Fuels
D6300 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products, Liquid Fuels, and
Lubricants
D6560 Test Method for Determination of Asphaltenes (Heptane Insolubles) in Crude Petroleum and Petroleum Products
D6708 Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport
to Measure the Same Property of a Material
D6792 Practice for Quality Management Systems in Petroleum Products, Liquid Fuels, and Lubricants Testing Laboratories
3. Terminology
3.1 Definitions:
3.1.1 For definitions of some terms used in this test method, refer to Terminology D4175.
3.1.2 asphaltenes, n—(rarely used in the singular), in petroleum technology, represent an oil fraction that is soluble in a specified
aromatic solvent but separates upon addition of an excess of a specified paraffinic solvent.
3.1.2.1 Discussion—
In this test method, the aromatic solvent is toluene and the paraffinic solvent is n-heptane.
3.1.3 compatibility, n—of crude oils or of heavy fuel oils, the ability of two or more crude oils or fuel oils to blend together within
certain concentration ranges without evidence of separation, such as the formation of multiple phases.
3.1.3.1 Discussion—
Incompatible heavy fuel oils or crude oils, when mixed or blended, result in the flocculation or precipitation of asphaltenes. Some
oils may be compatible within certain concentration ranges in specific mixtures, but incompatible outside those ranges.
3.1.4 flocculation, n—of asphaltenes from crude oils or heavy fuel oils, the aggregation of colloidally dispersed asphaltenes into
visible larger masses which may or may not settle.
3.1.5 peptization, n—of asphaltenes in crude oils or heavy oils, the dispersion of asphaltenes to produce a colloidal dispersion.
3.1.6 stability reserve, n—in petroleum technology, the property of an oil to maintain asphaltenes in a peptized state and prevent
flocculation of asphaltenes.
3.1.6.1 Discussion—
An oil with a low stability reserve is likely to undergo flocculation of asphaltenes when stressed (for example, extended heated
storage) or blended with a range of other oils. Two oils each with a high stability reserve are likely to maintain asphaltenes in a
peptized state and not lead to flocculation when blended together.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 intrinsic stability (S-value), n—of refinery residual streams, residual fuel oils and crude oils, an indication of the stability
or available solvency power of an oil with respect to precipitation of asphaltenes.
3.2.1.1 Discussion—
Since the equation defining S-value is
S = (1 + X ), where X is the minimum volume (in mL) of paraffinic solvent, n-heptane, to be added to 1 g 1 g of oil to result
min min
in flocculation of asphaltenes,asphaltenes; the smallest S-value is 1, which means the oil is unstable and can precipitate asphaltenes
without addition of any paraffinic solvent. A higher S-value indicates that an oil is more stable with respect to flocculation of
asphaltenes. S-value by this test method relates specifically to toluene and n-heptane as the aromatic and paraffinic solvents,
respectively.
3.2.2 inversion point, n—point in the n-heptane titration curve, where the onset of asphaltene flocculation leads to inversion of the
light intensity.
3.2.2.1 Discussion—
At the first stage of the addition of n-heptane to a dilution of specimen and toluene, light intensity increases through dilution. When
asphaltenes start to flocculate, there will be a point where the increase in light intensity through dilution matches the light intensity
decrease (inversion) as a result of coagulated asphaltenes obstructing the light beam.
3.2.3 Sa, n—the S-value of an asphaltene, which is the peptizability or ability of an asphaltene to remain in a colloidal dispersion.
D7157 − 23
3.2.3.1 Discussion—
Sa can also be described as one minus the ratio of So to S.Sa is linked to the length and number of aromatic chains within the
asphaltenes.
3.2.4 So, n—the S-value of an oil.
3.2.4.1 Discussion—
So can also be described as the aromatic equivalent of the oil expressed as the ratio of the aromatic solvent to the aromatic plus
paraffinic solvent mixture having the same peptizing power as the oil.
3.2.5 solvent aromaticity, n—of a binary mixture of a paraffınic and an aromatic solvent, the solvency power of the binary mixture.
3.2.5.1 Discussion—
For the purpose of this test method, solvent aromaticity is defined as a ratio by volume of the aromatic solvent (toluene) to the
paraffinic solvent (n-heptane).
3.3 Symbols:
3.3.1 FR—flocculation ratio
3.3.2 FR —maximum flocculation ratio
max
3.3.3 S—the intrinsic stability of an oil
3.3.4 Sa—the peptizability of an asphaltene
3.3.5 So—the peptizing power of an oil
3.3.6 X —paraffinic solvent consumption of undiluted oil, in mL/g of oil
min
4. Summary of Test Method
4.1 This test method uses an integrated automated analytical measurement system with an optical probe or cell for the detection
of asphaltene precipitation from a toluene solution of the sample.
4.2 Three test specimens are dissolved in three different quantities of toluene. The three specimen/toluene solutions are
automatically and simultaneously titrated with n-heptane to cause precipitation of the asphaltenes. The optical probe or cell
monitors the formation of flocculated asphaltenes during the titration. Flocculated asphaltenes will alter the detected light intensity.
Start of flocculation is interpreted when the optical probe or cell detects a significant and sustained decrease in rate-of-change of
the light intensity.
4.3 A computer routine calculates stability parameters and subsequently the intrinsic stability of the oil from the added n-heptane
at the inversion point, the mass of specimen, and the volume of toluene, for the three specimen/toluene solutions.
5. Significance and Use
5.1 This test method describes a sensitive method for estimating the intrinsic stability of an oil. The intrinsic stability is expressed
as S-value. An oil with a low S-value is likely to undergo flocculation of asphaltenes when stressed (for example, extended heated
storage) or blended with a range of other oils. Two oils each with a high S-value are likely to maintain asphaltenes in a peptized
state and not lead to asphaltene flocculation when blended together.
5.2 This test method can be used by petroleum refiners to control and optimize the refinery processes and by blenders and
marketers to assess the intrinsic stability of blended asphaltene-containing heavy fuel oils.
6. Interferences
6.1 High content of insoluble inorganic matter (sediment) has some interference in this test method. In this case, the insoluble
matter shall be removed by filtration according to Test Method D4870.
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6.2 Free water present in the oil can cause difficulties with the optical detector and should be removed by any suitable means (for
example, centrifugation) prior to testing.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such
specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity
to permit its use without lessening the accuracy of the determination.
7.1.1 Toluene. (Warning—Flammable. Health hazard. Vapor may cause flash fire.) (See Annex A1.)
7.1.2 n-Heptane. (Warning—Flammable. Vapor harmful. Vapor may cause flash fire.) (See Annex A1.)
7.2 Quality Control Sample—A stable and homogeneous residual fuel oil having physical and chemical properties similar to those
of typical sample fuels routinely tested.
8. Apparatus and Procedure
8.1 Two procedures exist and are mainly differentiated by the method of dilution of the sample with toluene: Procedure
A—Manual Dilution (Rofa apparatus) and Procedure B—Automatic Dilution (AD Systems apparatus).
8.2 Both procedures use the same dilution table (see Table 1).
TABLE 1 Specimen and Toluene Dilutions
Product Type Dilution 1 Dilution 2 Dilution 3
1: Liquid at Mass sample, g 9 5.5 3
<30 °C Volume toluene, mL 2 5.5 8
2: Liquid between Mass sample, g 7 5.5 3
30 °C – 100 °C Volume toluene, mL 4 5.5 8
3: Liquid at Mass sample, g 4 3 2
>100 °C Volume toluene, mL 7 8 9
Very stable Mass sample, g 3 2 1
products Volume toluene, mL 1 2 3
8.3 These dilutions are the dilutions usually used, but it is possible to use other dilutions in certain circumstances.
9. Procedure A (Manual Dilution)
9.1 Apparatus:
4,5
9.1.1 General—(See Fig. X1.1) This procedure uses an integrated automated analytical measurement system comprised of a
PC-based computer and three titration stations.
9.1.2 Computer, Computer—PC-based computer with associated software, capable of controlling up to three independent titration
stations, controlling test sequencing, and acquisition of optical probe signal data. The associated software also provides for
processing calculations and automatically produces a report of important test parameters.
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
The sole source of supply of the Procedure A apparatus (Automated Stability Analyzer) known to the committee at this time is Rofa France, 6 Rue Raymond Poincare,
F-25300, Les Allies, France. If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful
consideration at a meeting of the responsible technical committee, which you may attend.
The Rofa stability analyzer is covered by a patent owned by Total Raffinage France; INPI, date 18/05/04, registration number 04.05406.
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9.1.3 Titration Stations:
9.1.3.1 Titration Unit, automatic computer controlled, adjustable motor-driven ceramic piston pump, capable of delivering solvent
at a rate of 0.01 mL ⁄s to 0.5 mL ⁄s, with a volume dispensing accuracy of 60.01 mL.
9.1.3.2 Magnetic Stirrer, adjustable from 200 r ⁄min to 400 r ⁄min.
9.1.3.3 Optical Probe, consisting of a system of three areas of light emitters (880 nm) and three areas of light receivers. The
analytical measurement system will automatically select the optimum area, based on the level of translucency of the sample.
9.1.3.4 Titration Cell, of borosilicate glass, flat bottom, outside diameter 30 mm 6 2 mm, volume 95 mL 6 15 mL, fitted with a
tapered ground glass joint (female).
9.1.4 Balance, capable of reading to 0.1 mg or better.
9.1.5 Dispenser, capable of delivering up to 10 mL of toluene with an accuracy of 60.1 mL.
9.1.6 Condenser, double surface with a tapered ground-glass joint (male) at the bottom to fit the top of the titration cell.
9.1.7 Magnetic Stirrer/Hotplate, stirrer speed adjustable from 100 r ⁄min to 1000 r ⁄min.
9.1.8 Stirring Bar, magnetic, PFTE-coated, 20 mm in length.
9.2 Sampling and Test Specimens:
9.2.1 Sampling:
9.2.1.1 Obtain representative samples in accordance with recognized sampling procedures such as Practices D4057 or D4177.
9.2.1.2 Samples of very viscous materials may be warmed until they are reasonably fluid before they are sampled.
9.2.1.3 Store samples prior to taking test specimens at ambient temperatures.
9.2.2 Test Specimen Preparation:
9.2.2.1 Sample Temperature—If necessary, warm viscous samples until they can be mixed readily before opening the storage
container. For fuels with a high wax content (high pour point) the temperature must be at least 15 °C above the pour point.
9.2.2.2 Manually shake the sample thoroughly. If the sample contains high content of insoluble inorganic matter, filter the sample
through a 47 mm diameter glass fiber filter medium (such as Whatman Grade GF/A), using the Test Method D4870 filtration
apparatus. Specimen should be representative of the whole sample.
9.2.3 Preparation of Specimen Dilutions—Prepare three dilutions of specimen in toluene in different ratios (see Table 1) as
follows:
9.2.3.1 Place a magnetic stirrer bar into a clean titration cell.
9.2.3.2 Add the required amount of specimen to the titration cell and obtain the mass of the specimen to the nearest 0.001 g (M ).
oil
9.2.3.3 Add the appropriate volume of toluene to the nearest 0.1 mL to the titration cell.
9.2.3.4 Stir dilutions of sample Type 1, without heating, for at least two minutes. Obtain the mass of the specimen plus toluene
to the nearest 0.001 g (M ). Proceed with Section 9.4.
9.2.3.5 For specimen dilutions of Type 2 and 3, place a condenser on the titration cell, place on the hot plate, and boil under reflux,
while stirring, for a minimum of 10 min for specimens of Type 2 and for a minimum of 15 min for specimens of Type 3.
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9.2.3.6 Discontinue heating and while stirring, allow the dilutions to cool to ambient temperature. Disconnect the condenser and
obtain the mass of specimen plus toluene to the nearest 0.001 g (M ). Proceed with Section 9.4.
NOTE 1—In this context, “liquid” means the minimum temperature at which the product has sufficient fluidity to be handled as a liquid.
9.3 Preparation of Apparatus:
9.3.1 Prepare and set up the instrument for operation according to the manufacturer’s manual. (Refer to Fig. X1.1.)
9.3.2 Plug the optical probes into their connectors and place them in their stand by standby position.
9.3.3 Ensure that the reagent vessel contains sufficient n-heptane to run the tests (minimum 200 mL).
9.3.4 Cleaning Instructions—Perform the following cleaning procedure after the test procedure (see 9.4.8).
9.3.4.1 Carefully remove the dosing tube and the optical probe from the titration cell. Clean the optical probe with an appropriate
solvent (toluene) (see 7.1.1).
9.3.4.2 Remove the stirrer bar. Empty the titration cell. Clean the reactor cell and stirrer bar with an appropriate solvent (toluene)
(see 7.1.1).
9.4 Test Procedure:
9.4.1 Place the titration cells containing the specimen solutions (9.2.3.4 and 9.2.3.6) into their slot positions in the measurement
system.
9.4.2 Position the optical probes in the titration cells.
9.4.3 Place the dosing tubes of the titration apparatus into the titration cell. The position of the tube is such that droplets fall
directly into the sample vortex so that mixing is optimal.
9.4.4 Switch on the magnetic stirrer and adjust the speed so that agitation is just visible on the surface of the sample.
9.4.5 Initiate the automatic test procedure according to the manufacturer’s instruction manual. For further details, refer to
Appendix X1.
9.4.6 n-heptane is added in steps of 0.05 mL at a rate of 0.05 mL ⁄s. Addition of n-heptane is discontinued for 2 s between each
step.
9.4.7 For dilutions of very stable samples (see Table 1), it is needed to pre-add an accurately known quantity of 7 mL of n-heptane
by the automatic titration unit to ensure that the probe is fully immersed.
NOTE 2—The addition of 7 mL of n-heptane is automatically performed by the apparatus when “pre-dilution” mode is selected by the operator.
9.4.8 The test is completed when either an inversion point is encountered (V ) or when the total liquid content of the titration
para
cell reaches a maximum of 50 mL. A report is displayed automatically at that time or earlier if requested by the operator.
NOTE 3—The apparatus will stop automatically when the maximum limit of 50 mL liquid has been reached.
9.4.9 Draw a straight line through the three points (see Fig. 1) using the least squares fit equation. For a valid result the measure
of goodness of fit (R-squared) should be = >0.98. If R-squared <0.98, discard the result and repeat the test with fresh dilutions from
9.2.3 onwards.
NOTE 4—See Appendix X1 for detailed automatic test program and examples of the titration curve and regression report.
D7157 − 23
9.4.10 When, for any of the three dilutions, n-heptane has been added up to a total of 50 mL liquids in the titration cell without
encountering an inversion, the sample is considered to be very stable. In such a case, the test shall be repeated from 9.2.3 onwards,
using fresh dilutions as given in Table 1 under “Very stable products.”
10. Procedure B (Automatic Dilution)
10.1 Apparatus :
10.1.1 General—(See Fig. X2.1). This procedure uses an integrated automated analytical measurement system comprising a user
interface and three fully automated titration stations.
10.1.2 User Interface, capable of controlling up to three independent titration stations, controlling test sequencing, and acquisition
of optical signal data. This also provides data for processing calculations and automatically produces a test report and important
test parameters.
10.1.3 Titration Stations:
10.1.3.1 Dilution Unit, automatically controlled, adjustable motor-driven piston pump, capable of delivering solvent (toluene),
with a volume dispensing accuracy of 60.01 mL.
10.1.3.2 Titration Unit, automatically controlled, adjustable motor-driven ceramic piston pump, capable of delivering solvent at
a rate of 0.01 mL ⁄s to 0.3 mL ⁄s, with a volume dispensing accuracy of 60.01 mL.
10.1.3.3 Magnetic Stirrer, adjustable from 0 r ⁄min to 600 r ⁄min.
10.1.3.4 Optical Cell, consisting of an infrared light emitter and receiver system. This infrared light beam crosses the sample, and
the analytical measurement system will automatically select the optimum settings, based on the level of translucency of the sample.
10.1.3.5 Titration Cell, made of borosilicate glass, flat bottom, volume 95 mL 6 15 mL.
10.1.3.6 Heating Crucible,
...