ASTM D6468-99
(Test Method)Standard Test Method for High Temperature Stability of Distillate Fuels
Standard Test Method for High Temperature Stability of Distillate Fuels
SCOPE
1.1 This test method covers relative stability of middle distillate fuels under high temperature aging conditions with limited air exposure. This test method is suitable for all No. 1 and No. 2 grades in Specifications D 396, D 975, D 2880, and for grades DMS and DMA in Specification D 2069. It is also suitable for similar fuels meeting other specifications.
1.2 This test method is not suitable for fuels whose flash point, as determined by Test Methods D 56, D 93, or D 3828, is less than 38°C. This test method is not suitable for fuels containing residual oil.
1.3 The values stated in SI units are to be regarded as the standard.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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An American National Standard
Designation:D6468–99
Standard Test Method for
High Temperature Stability of Distillate Fuels
This standard is issued under the fixed designation D 6468; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 4057 Practice for Manual Sampling of Petroleum and
Petroleum Products
1.1 This test method covers relative stability of middle
D 4625 Test Method for Distillate Fuel Storage Stability at
distillate fuels under high temperature aging conditions with
43°C (110°F)
limited air exposure. This test method is suitable for all No. 1
D 5452 Test Method for Particulate Contamination inAvia-
and No. 2 grades in Specifications D 396, D 975, D 2880, and
tion Fuels by Laboratory Filtration
D 3699 and for grades DMX and DMA in Specification
D 2069. It is also suitable for similar fuels meeting other
3. Terminology
specifications.
3.1 Definitions of Terms Specific to This Standard:
1.2 This test method is not suitable for fuels whose flash
3.1.1 adherent insolubles—material that is produced in the
point, as determined by Test Methods D 56, D 93, or D 3828,
course of stressing distillate fuel and that adheres to the
is less than 38°C. This test method is not suitable for fuels
glassware after fuel has been flushed from the system.
containing residual oil.
3.1.2 filterable insolubles—material that is produced in the
1.3 The values stated in SI units are to be regarded as the
course of stressing distillate fuel and that is capable of being
standard.
removed from the fuel by filtration.
1.4 This standard does not purport to address all of the
3.1.3 inherent stability—the resistance to change when
safety concerns, if any, associated with its use. It is the
exposed to air, but in the absence of other environmental
responsibility of the user of this standard to establish appro-
factors such as water, reactive metal surfaces, and dirt.
priate safety and health practices and determine the applica-
3.1.4 storage stability—the resistance of fuel to formation
bility of regulatory limitations prior to use.
of degradation products when stored at ambient temperatures.
2. Referenced Documents 3.1.5 thermal stability—the resistance of fuel to formation
of degradation products when thermally stressed.
2.1 ASTM Standards:
D 56 Test Method for Flash Point byTag Closed CupTester
4. Summary of Test Method
D 93 Test Methods for Flash Point by Pensky-Martens
4.1 Two 50-mLvolumes of filtered middle distillate fuel are
Closed Cup Tester
aged for 90 or 180 min at 150°C in open tubes with air
D 396 Specification for Fuel Oils
exposure.After aging and cooling, the fuel samples are filtered
D 975 Specification for Diesel Fuel Oils
and the average amount of filterable insolubles is estimated by
D 1500 Test Method for ASTM Color of Petroleum Prod-
measuring the light reflectance of the filter pads. The 100 and
ucts (ASTM Color Scale)
3 0 % extremes of the reflectance rating range are defined by an
D 2069 Specification for Marine Fuels
unused filter pad and a commercial black standard, respec-
D 2274 Test Method for Oxidation Stability of Distillate
tively.
Fuel Oil (Accelerated Method)
D 2880 Specification for Gas Turbine Fuel Oils
5. Significance and Use
D 3699 Specification for Kerosine
5.1 This test method provides an indication of thermal
D 3828 TestMethodsforFlashPointbySmallScaleClosed
oxidative stability of distillate fuels when heated to high
Cup Tester
temperatures that simulate those that may occur in some types
of recirculating engine or burner fuel delivery systems. Results
This test method is under the jurisdiction of ASTM Committee D02 on
have not been substantially correlated to engine or burner
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
operation. The test method can be useful for investigation of
D02.14 on Stability and Cleanliness of Liquid Fuels.
operational problems related to fuel thermal stability.
Current edition approved Nov. 10, 1999. Published January 2000.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Henry, C. P., “The du Pont F21 149°C (300°F) Accelerated Stability Test,”
the ASTM website. Distillate Fuel Stability and Cleanliness, ASTM STP 751, L. L. Stavinoha and C. P.
Withdrawn. Henry, Eds., ASTM, 1981, pp. 22-33.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6468–99
NOTE 2—Use of reduced vacuum improves retention of particulate on
5.2 When the test method is used to monitor manufacture or
the relatively porous filter media.
storage of fuels, changes in filter rating values can indicate a
relative change in inherent stability. Storage stability predic-
6.6 Reflection meter, Photovolt Model 577 Digital Reflec-
tions are more reliable when correlated to longer-term storage
tion Meter, complete with search unit Y with a green filter and
tests, for example, Test Method D 4625, or other lower
polished black glass standard.
temperature, long-term tests. When fuel samples are freshly
NOTE 3—Other reflection meters or search units, or both, can be used,
produced, aging for 180 min, instead of the traditional 90-min
but they are likely to provide only similar (not identical) results. For
interval, tends to give a result correlating more satisfactorily
example, Photovolt Model 577 digital reflection meter equipped with
with the above methods (see Appendix X2).
search unit W usually gives somewhat lower percent reflectance values.
5.3 The test method uses a filter paper with a nominal
Correlation of these values is discussed in Appendix X1.
porosity of 11 µm, which will not capture all of the sediment
NOTE 4—Olderreflectionmeters,includingbutnotlimitedtoPhotovolt
formed during aging but allows differentiation over a broad Model 670 analog meter, are satisfactory.
range. Reflectance ratings are also affected by the color of
7. Reagents and Materials
filterableinsolubles,whichmaynotcorrelatetothemassofthe
material filtered from the aged fuel sample. Therefore, no
7.1 Purity of Reagents—Reagent grade chemicals shall be
quantitative relationship exists between the pad rating and the
used in all tests. Unless otherwise indicated, it is intended that
gravimetric mass of filterable insolubles.
all reagents conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society where
6. Apparatus
such specifications are available. Other grades may be used,
provided it is first ascertained that the reagent is of sufficiently
6.1 Aging Tubes,253 200 mm, heavy wall test tubes made
high purity to permit its use without lessening the accuracy of
of borosilicate glass.
the determination.
6.2 Heating Bath, with liquid heating medium, thermostati-
7.2 Acetone, reagent grade. (Warning—Extremely flam-
callycontrolledtomaintainthesampleintheagingtubewithin
mable.)
1.5°C of 150°C. It must be large enough to hold aging tubes
7.3 Adherent Insolubles Solvent (Trisolvent or TAM),a
immersed in the heating liquid to a depth above the level of
mixture of equal parts by volume of reagent grade toluene
samples in the tubes. The bath and its location shall be such to
(Warning—Flammable. Vapor harmful.), acetone
enable shielding of the samples from direct light during aging.
(Warning—see 7.2), and methanol (Warning—Flammable.
Thevolumeofbathanditsheatrecoveryrateshallbesuchthat
Vapor Harmful. May be fatal or cause blindness if swallowed
the temperature of the medium does not drop more than 5°C
or inhaled. Cannot be made nonpoisonous.).
when the maximum number of aging tubes are inserted, and
7.4 Hydrocarbon Solvent, 2,2,4-trimethylpentane (iso-
recovery to 150°C shall not require more than 15 min.
octane), 99.75 % purity minimum (Warning—see 7.2).
(Warning—The flash point of the liquid heating medium must
be at least 180°C. Bath vapors and oil sample vapors shall be
NOTE 5—Heptane is a satisfactory alternative hydrocarbon solvent.
properlyvented.Exposedhotsurfacesontheapparatusandhot
However, small differences may be seen due to slightly different solubility
heating medium can cause severe burns.)
characteristics. Iso-octane is specified to be in agreement with the
hydrocarbon solvent used in other middle distillate stability test methods
6.3 Thermometer, either glass or digital, whose accuracy in
such as Test Methods D 2274 and D 4625.
the 140 to 160°C range is certified or traceable to a certified
thermometer. Use to monitor the temperature of the heating
7.5 Filter Paper (Filter Pad), Whatman No. 1, 47-mm
bath in 6.2.
diameter, or equivalent.
6.4 Membrane Filter Holder,tofit47-mmmembranefilters,
NOTE 6—Filter papers of 42.5 or 55-mm diameter are technically
fitted to a heavy-walled 500-mL or 1-L vacuum flask.
satisfactory. Filters with a diameter of 47 mm permit a small unused
margin for identifying the sample and fit all filtration apparatuses.
NOTE 1—Several types of membrane filter holders are available. To
reduce electrostatic hazards, an all metal filter holder equipped with
grounding cables is recommended. Such an apparatus and correct 8. Sampling
grounding practices are described in Test Method D 5452. A fritted glass
8.1 When samples of a fuel batch are obtained to determine
filter holder is less preferred because of a tendency to become partially
stability, obtain samples in accordance with Practice D 4057.
cloggedduringusesothatfilterpadsthatdonothaveuniformdepositsare
Use only epoxy-lined cans or borosilicate glass bottles. Shield
obtained. Glass filter holders that use a 75-µm (200-mesh) screen to
clear glass bottles from sunlight to prevent photochemical
support the filter are available; however, since the screen can be an
unbonded electrostatic charge collector, these are not recommended for
reactions.
use with flammable liquids.
6.5 Vacuum Source, that limits the maximum vacuum to 27
kPa (200 mm Hg) below atmospheric pressure. The vacuum
Available from UMM Electronics Inc., Photovolt Instruments, 6911 Hillsdale
shouldriseto27kPawithin10to15safterthesampleisadded
Court, Indianapolis, IN 46250-2062.
to the filtration funnel.
Reagent Chemicals, American Chemical Society Specifications, 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
Asuitable filter holder is available from Millipore Corporation, 80Ashby Rd., and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
Bedford, MA 01730; Catalog No. XX20 047 20. MD.
D6468–99
8.2 When samples are from a fuel or component rundown the inline vacuum regulator so that the maximum vacuum is 27
line, exercise care to ensure that the sampling line and valving kPa(200mmHg).Measuretwo50 62-mLvolumesoffiltered
are thoroughly flushed with current mainstream sample. fuel and decant into each of two aging tubes (see Appendix
8.3 Because stability of some fuels, as determined in this X3).
test method, changes over time, the sampling date shall be
NOTE 9—Where practical, filter a fuel sample larger than 100 mL. This
recorded; record time and date if sample is from a fuel or
will reduce the possibility that the paper may absorb trace materials that
component rundown line. Samples should be stored at tem-
affect stability.
peratures below 5°C. If storage for more than a few days is
11.3 Placetheuncappedsampletubesintheheatingbathfor
expected, oxygen should be removed from the fuel by subsur-
90 6 3 min, or 180 6 5 min. Place the tubes in the bath in the
face purging with a stream of nitrogen; for example, by
sameorderinwhichtheyaretoberemoved.(Warning—Fuels
bubbling nitrogen for 1 min/L of sample.
will be heated above their flash points. There is a possibility
that certain light fuels such as kerosine will boil under
9. Preparation of Apparatus
conditionsofthetest.Bothsituationsraisetheriskoffirewhen
9.1 CleaningAging Tubes—Cleannewtubesusingadherent
an ignition source is present. Fuel samples that may contain
insolubles solvent, then with a mildly alkaline or neutral
gasoline or other volatile components should not be tested.)
laboratory detergent, followed by copious rinsing with deion-
ized or distilled water to remove all traces of detergent. Then NOTE 10—Theseverityofthetestisincreasedbyagingforlongertimes
at 150°C. The selection of the aging time depends on application and
rinse with acetone and air dry. Rinse used tubes with adherent
should be established by correlation with other tests or with application
insolubles solvent, dry, then clean as above for new tubes.
requirements.
Visually inspect tubes before use, and reclean or reject if there
is the slightest trace of contamination. 11.4 Removethesamplesfromtheheatingbathandallowto
cool gradually in air to 20 to 25°C over a period of 90 min to
9.1.1 Because of the small sample size and the high surface
to volume ratio in this test method, carefully avoid carry-over 4 h. Cool in the dark to prevent photochemical reactions. Do
not accelerate cooling by immersing in a cooling bath as this
from past tests or from cleaning agents. There are especially
strong effects from traces of copper, strong acids, and strong can result in small particle size and a lower pad rating. If
samples are allowed to stand more than 4 h before filtering,
bases.
insoluble gum may adhere to the aging tubes, resulting in
9.2 Cleaning Membrane Filter Holder—Rinse with adher-
erratic data. (Warning—The hot samples can cause severe
ent insolubles solvent, acetone, and air dry.
burns. Use protective equipment.)
10. Calibration and Standardization
11.5 Prepare a filtration assembly with a new filter paper,
and attach all grounding clips to ground. Filter one of the two
10.1 Turn on the reflection meter and allow at least 30 min
for warm-up. The gain should be set in LO position for search aged fuel samples.
11.6 While maintaining vacuum, wash the aging tube with
unit Y with green filter.
10.2 Follow the manufacturer’s instructions to carry out a three small portions, about 15 mLeach, of iso-octane and filter
through the filter paper. Wash the inside of the filter assembly
two point calibration of the reflection meter, using the black
standard and standard plaque supplied with the search unit. with iso-octane,andremovethefunnelportionoftheassembly.
While s
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