1、Designation: D6468 08 (Reapproved 2013)Standard Test Method forHigh Temperature Stability of Middle Distillate Fuels1This standard is issued under the fixed designation D6468; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers relative stability of middledistillate fuels under high temperature aging conditions with
3、limited air exposure. This test method is suitable for all No. 1and No. 2 grades in Specifications D396, D975, D2880, andD3699. It is also suitable for similar fuels meeting otherspecifications.1.2 This test method is not suitable for fuels whose flashpoint, as determined by Test Methods D56, D93,or
4、D3828,isless than 38C. This test method is not suitable for fuelscontaining residual oil.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3.1 ExceptionThe maximum vacuum includes inch-pound units in 6.5 and 11.2.1.4 This st
5、andard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1
6、 ASTM Standards:2D56 Test Method for Flash Point by Tag Closed Cup TesterD93 Test Methods for Flash Point by Pensky-MartensClosed Cup TesterD396 Specification for Fuel OilsD975 Specification for Diesel Fuel OilsD1500 Test Method for ASTM Color of Petroleum Products(ASTM Color Scale)D2274 Test Method
7、 for Oxidation Stability of Distillate FuelOil (Accelerated Method)D2880 Specification for Gas Turbine Fuel OilsD3699 Specification for KerosineD3828 Test Methods for Flash Point by Small Scale ClosedCup TesterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4625 Test Method for
8、 Middle Distillate Fuel StorageStability at 43C (110F)D5452 Test Method for Particulate Contamination in Avia-tion Fuels by Laboratory Filtration3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 adherent insolublesmaterial that is produced in thecourse of stressing distillate fu
9、el and that adheres to theglassware after fuel has been flushed from the system.3.1.2 filterable insolublesmaterial that is produced in thecourse of stressing distillate fuel and that is capable of beingremoved from the fuel by filtration.3.1.3 inherent stabilitythe resistance to change when ex-pose
10、d to air, but in the absence of other environmental factorssuch as water, reactive metal surfaces, and dirt.3.1.4 storage stabilitythe resistance of fuel to formationof degradation products when stored at ambient temperatures.3.1.5 thermal stabilitythe resistance of fuel to formationof degradation p
11、roducts when thermally stressed.4. Summary of Test Method4.1 Two 50-mL volumes of filtered middle distillate fuel areaged for 90 or 180 min at 150C in open tubes with airexposure.After aging and cooling, the fuel samples are filteredand the average amount of filterable insolubles is estimated bymeas
12、uring the light reflectance of the filter pads. The 100 and0 % extremes of the reflectance rating range are defined by anunused filter pad and a commercial black standard, respec-tively.5. Significance and Use35.1 This test method provides an indication of thermaloxidative stability of distillate fu
13、els when heated to high1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.14 on Stability and Cleanliness of Liquid Fuels.Current edition approved Oct. 1, 2013. Published October 201
14、3. Originallyapproved in 1999. Last previous edition approved in 2008 as D6468 08. DOI:10.1520/D6468-08R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the stand
15、ards Document Summary page onthe ASTM website.3Henry, C. P., “The du Pont F21 149C (300F) Accelerated Stability Test,”Distillate Fuel Stability and Cleanliness, ASTM STP 751, Stavinoha, L. L. andHenry, C. P., Eds., ASTM International, 1981, pp. 2233.Copyright ASTM International, 100 Barr Harbor Driv
16、e, PO Box C700, West Conshohocken, PA 19428-2959. United States1temperatures that simulate those that may occur in some typesof recirculating engine or burner fuel delivery systems. Resultshave not been substantially correlated to engine or burneroperation. The test method can be useful for investig
17、ation ofoperational problems related to fuel thermal stability.5.2 When the test method is used to monitor manufacture orstorage of fuels, changes in filter rating values can indicate arelative change in inherent stability. Storage stability predic-tions are more reliable when correlated to longer-t
18、erm storagetests, for example, Test Method D4625, or other lowertemperature, long-term tests. When fuel samples are freshlyproduced, aging for 180 min, instead of the traditional 90-mininterval, tends to give a result correlating more satisfactorilywith the above methods (see Appendix X2).5.3 The te
19、st method uses a filter paper with a nominalporosity of 11 m, which will not capture all of the sedimentformed during aging but allows differentiation over a broadrange. Reflectance ratings are also affected by the color offilterable insolubles, which may not correlate to the mass of thematerial fil
20、tered from the aged fuel sample. Therefore, noquantitative relationship exists between the pad rating and thegravimetric mass of filterable insolubles.6. Apparatus6.1 Aging Tubes, 25 200 mm, heavy wall test tubes madeof borosilicate glass.6.2 Heating Bath, with liquid heating medium, thermostati-cal
21、ly controlled to maintain the sample in the aging tube within1.5C of 150C. It must be large enough to hold aging tubesimmersed in the heating liquid to a depth above the level ofsamples in the tubes. The bath and its location shall be such toenable shielding of the samples from direct light during a
22、ging.The volume of bath and its heat recovery rate shall be such thatthe temperature of the medium does not drop more than 5Cwhen the maximum number of aging tubes are inserted, andrecovery to 150C shall not require more than 15 min.(WarningThe flash point of the liquid heating medium mustbe at leas
23、t 180C. Bath vapors and oil sample vapors shall beproperly vented. Exposed hot surfaces on the apparatus and hotheating medium can cause severe burns.)6.3 Bath Thermometer, either glass or digital measuringtemperature measuring device, whose accuracy in the 140 to160C range is certified or traceable
24、 to a certified thermometer.6.4 Membrane Filter Holder, to fit 47-mm membrane filters,fitted to a heavy-walled 500-mL or 1-L vacuum flask.NOTE 1Several types of membrane filter holders are available. Toreduce electrostatic hazards, an all metal filter holder equipped withgrounding cables is recommen
25、ded.4Such an apparatus and correctgrounding practices are described in Test Method D5452. A fritted glassfilter holder is less preferred because of a tendency to become partiallyclogged during use so that filter pads that do not have uniform deposits areobtained. Glass filter holders that use a 75-m
26、 (200-mesh) screen tosupport the filter are available; however, since the screen can be anunbonded electrostatic charge collector, these are not recommended foruse with flammable liquids.6.5 Vacuum Source, that limits the maximum vacuum to 27kPa (200 mm Hg) below atmospheric pressure. The vacuumshou
27、ld rise to 27 kPa within 10 to 15 s after the sample is addedto the filtration funnel.NOTE 2Use of reduced vacuum improves retention of particulate onthe relatively porous filter media.6.6 Reflection meter, Photovolt Model 577 Digital Reflec-tion Meter, complete with search unit Y with a green filte
28、r andpolished black glass standard.5NOTE 3Other reflection meters or search units, or both, can be used,but they are likely to provide only similar (not identical) results. Forexample, Photovolt Model 577 digital reflection meter equipped withsearch unit W usually gives somewhat lower percent reflec
29、tance values.Correlation of these values is discussed in Appendix X1.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of t
30、he American Chemical Society wheresuch specifications are available.6Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.7.2 Acetone, (WarningExtremely flammable.)7.3 Adherent In
31、solubles Solvent (Trisolvent or TAM), amixture of equal parts by volume of reagent grade toluene(WarningFlammable. Vapor harmful), acetone (Warningsee 7.2), and methanol (WarningFlammable. Vapor harm-ful. May be fatal or cause blindness if swallowed or inhaled.Cannot be made nonpoisonous).7.4 Hydroc
32、arbon Solvent, 2,2,4-trimethylpentane (iso-octane), 99.75 % purity minimum (Warningsee 7.2).NOTE 4Heptane is a satisfactory alternative hydrocarbon solvent.However, small differences may be seen due to slightly different solubilitycharacteristics. Iso-octane is specified to be in agreement with theh
33、ydrocarbon solvent used in other middle distillate stability test methodssuch as Test Methods D2274 and D4625.7.5 Filter Paper (Filter Pad), Whatman No. 1, 47-mmdiameter, or equivalent.NOTE 5Filter papers of 42.5 or 55-mm diameter are technicallysatisfactory. Filters with a diameter of 47 mm permit
34、a small unused4The sole source of supply of the apparatus known to the committee at this timeis a suitable filter holder available from Millipore Corporation, 80 Ashby Rd.,Bedford, MA 01730; Catalog No. XX20 047 20. If you are aware of alternativesuppliers, please provide this information to ASTM In
35、ternational Headquarters.Your comments will receive careful consideration at a meeting of the responsibletechnical committee,1which you may attend.5The sole source of supply of the apparatus known to the committee at this timeis available from UMM Electronics Inc., Photovolt Instruments, 6911 Hillsd
36、aleCourt, Indianapolis, IN 46250-2062. If you are aware of alternative suppliers, pleaseprovide this information to ASTM International Headquarters. Your comments willreceive careful consideration at a meeting of the responsible technical committee,1which you may attend.6Reagent Chemicals, American
37、Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.
38、S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D6468 08 (2013)2margin for identifying the sample and fit all filtration apparatuses.8. Sampling8.1 When samples of a fuel batch are obtained to determinestability, obtain samples in accordance with Practice D4057.Use only epoxy-lined cans or bo
39、rosilicate glass bottles. Shieldclear glass bottles from sunlight to prevent photochemicalreactions.8.2 When samples are from a fuel or component rundownline, exercise care to ensure that the sampling line and valvingare thoroughly flushed with current mainstream sample.8.3 Because stability of some
40、 fuels, as determined in thistest method, changes over time, the sampling date shall berecorded; record time and date if sample is from a fuel orcomponent rundown line. Samples should be stored at tem-peratures below 5C. If storage for more than a few days isexpected, oxygen should be removed from t
41、he fuel by subsur-face purging with a stream of nitrogen; for example, bybubbling nitrogen for 1 min/L of sample.8.3.1 If samples are taken out of cold storage, warm them toambient temperature and thoroughly mix prior to aliquotsampling.NOTE 6If multiple analyses are to be performed on a sample, it
42、is nota good practice to warm the whole sample repeatedly for this purpose.One way of doing this would be to pour an aliquot of the cold sample intoa graduated cylinder, cap, allow to warm, and then dispense into the agingtube for analysis. If the cloud point of the fuel is above 5C, warm to atemper
43、ature 5C higher than the cloud point before dispensing.9. Preparation of Apparatus9.1 Cleaning Aging TubesClean new tubes using adherentinsolubles solvent, then with a mildly alkaline or neutrallaboratory detergent, followed by copious rinsing with deion-ized or distilled water to remove all traces
44、of detergent. Thenrinse with acetone and air dry. Rinse used tubes with trisolvent,dry, then clean as above for new tubes. Visually inspect tubesbefore use, and reclean or reject if there is the slightest trace ofcontamination.9.1.1 Because of the small sample size and the high surfaceto volume rati
45、o in this test method, carefully avoid carryoverfrom past tests or from cleaning agents. There are especiallystrong effects from traces of copper, strong acids, and strongbases.NOTE 7Clean test tubes carefully to avoid carryover from past tests orfrom cleaning agents. As a result of the small sample
46、 size evaluated andthe high surface to volume ratio inherent to the test method, the resultsobtained can be greatly influenced by the presence of trace contaminantssuch as copper, strong acids, or strong bases.9.2 Cleaning Membrane Filter Holder Rinse withtrisolvent, then with acetone, and air dry.1
47、0. Calibration and Standardization10.1 Turn on the reflection meter and allow at least 30 minfor warm-up. Set the gain to LO position for search unit Y withgreen filter.10.2 Follow the manufacturers instructions to carry out atwo point calibration of the reflection meter, using the blackstandard and
48、 standard plaque supplied with the search unit.NOTE 8The calibration procedure ensures that the instrument isworking properly. It also indirectly sets a nominal 100 % reflectancesetting that is subsequently reset in 10.3.10.3 Place a new filter paper on top of a stack of at least tenunused Whatman N
49、o. 1 filters of the same size. Place thesearch unit on the center of the filter, and adjust the meterreading to 100 %, using the sensitivity control.NOTE 9Such adjustment, which sets the test method 100 % reflec-tance point, alters the reflectance scale; as a result, the reflection meter willno longer read the recited reflectance of the standard plaque.10.4 Place the search unit on the center of the black glassstandard, and adjust the meter reading to 0 %, using the ZEROcontrol. Recheck the 100 % adjustment against the new filterpaper, and
