1、Designation: D91 02 (Reapproved 2012)1Standard Test Method forPrecipitation Number of Lubricating Oils1,2This standard is issued under the fixed designation D91; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () 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.1NOTESubsection 5.2 was corrected editorially in July
3、 2016.1. Scope1.1 This test method covers the determination of the pre-cipitation number of steam cylinder stocks and black oils, andcan be used for other lubricating oils.1.2 The values stated in acceptable SI units are to beregarded as the standard.1.3 This standard does not purport to address all
4、 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 ASTM Standards:3D4057 Practice for Ma
5、nual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum Products3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 ASTM precipitation number, of lubricating oils, nthenumber of millilitres of precipitate formed when 10 mL of
6、lubricating oil are mixed with 90 mL of ASTM precipitationnaphtha, and centrifuged under the conditions of the test.4. Significance and Use4.1 Fully refined petroleum oils normally contain no naph-tha insoluble material. Semirefined or black oils frequentlycontain some naphtha insoluble material (so
7、metimes referredto as asphaltenes ). This test measures the amount of naphthainsoluble material in the oil. This quantity is reported as theprecipitation number.5. Apparatus5.1 Centrifuge Tube, cone-shaped, conforming to the di-mensions given in Fig. 1, and made of thoroughly annealedglass. The grad
8、uations, numbered as shown in Fig. 1, shall beclear and distinct, and the mouth shall be constructed in a shapesuitable for closure with a cork. Scale-error tolerances andsmallest graduations between various calibration marks aregiven in Table 1 and apply to calibrations made with air-freewater at 2
9、0 C.5.2 Centrifuge, meeting all the safety requirements fornormal use and capable of whirling two or more filledcentrifuge tubes at a speed which can be controlled to give arelative centrifugal force (rcf) between 600 and 700 at the tipsof the tubes. The revolving head, trunnion rings, and trunnionc
10、ups, including the rubber cushion, shall be soundly con-structed to withstand the maximum centrifugal force capable ofbeing delivered by the power source. The trunnion cups andcushions shall firmly support the tubes when the centrifuge isin motion. The centrifuge shall be enclosed by a metal shield
11、orcase strong enough to eliminate danger if any breakage occurs.Calculate the speed of the rotating head by means of thefollowing equation:speed, r/min 5 1337 =rcf/d (1)where:rcf = relative centrifugal force, andd = diameter of swing, in mm, measured between tips ofopposite tubes when in rotating po
12、sition.Table 2 shows the relationship between diameter swing, rcf,and revolutions per minute.6. Reagent6.1 Hexanes, Reagent Grade. (WarningExtremelyflammable, harmful if inhaled.)1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and
13、is the direct responsibility ofSubcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.Current edition approved Nov. 1, 2012. Published November 2012. Originallyapproved in 1921. Last previous edition approved in 2007 as D91 02 (2007). DOI:10.1520/D0091-02R12E01.2This test method has been ado
14、pted for use by government agencies to replaceMethod 3101 of Federal Test Method Standard No. 791b.3For 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 standards Doc
15、ument Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17. Sampling7.1 For sampling techniques, see Practices D4057 or Prac-tice D4177.8. Procedure8.1 Add 10 mL 6 1 mL of the oil to be tested in each of t
16、woclean, dry centrifuge tubes at room temperature. Fill each tubeto the 100 mL mark with hexanes and close tightly with asoftened cork (not a rubber stopper). Then invert each tube atleast 20 times, allowing the liquid to drain thoroughly from thetapered tip of the tube each time. Place the tubes in
17、 a water bathat 32 C to 35 C for 5 min 6 1 min. Momentarily remove thecorks to relieve any pressure, and invert each tube again at least20 times exactly as before. The success of this method dependsto a large degree upon having a thoroughly homogeneousmixture which will drain quickly and completely
18、from thetapered tip when the tube is inverted.8.2 Balance the two centrifuge tubes or pairs of tubes withtheir respective trunnion cups and place them on opposite sidesof the centrifuge head. Then whirl them for 10 min at a ratesufficient to produce a relative centrifugal force (rcf) between600 and
19、700 at the tips of the whirling tubes (see 5.2). Repeatthis operation until the volume of sediment in each tuberemains constant for three consecutive readings. In general, notmore than four whirlings will be required for oils having a lowprecipitation number.9. Calculation and Report9.1 Read the vol
20、ume of the solid sediment at the bottom ofeach centrifuge tube, estimating to 0.1 mL or closer if possible.If the two readings differ by not more than 0.1 mL, report themean of the two as the ASTM Precipitation Number. If the tworeadings differ by more than 0.1 mL, make two more determi-nations and
21、report the average of the four determinations.10. Precision and Bias10.1 The precision of this test method as determined bystatistical examination of interlaboratory results is as follows:10.2 RepeatabilityThe difference between two test results,obtained by the same operator with the same apparatus
22、underconstant operating conditions on identical test material, wouldin the long run, in the normal and correct operation of the testmethod, exceed the following values only in one case intwenty:Precipitation Number Repeatability0.00 to 1.20 10 % of Mean10.3 ReproducibilityThe difference between two
23、singleand independent results obtained by different operators work-ing in different laboratories on identical test material would, inthe long run, in the normal and correct operation of the testmethod, exceed the following values only in one case intwenty:Precipitation Number Reproducibility0.00 to
24、1.20 30 % of Mean10.4 BiasThis procedure is empirical, precipitation num-ber is defined solely by this procedure, therefore, no statementof bias can be made.11. Keywords11.1 asphaltenes; lubricating oils; precipitation numberNOTE 1For volumetric tolerances see Table 1.FIG. 1 ASTM Cone-Shaped Centrif
25、uge TubeTABLE 1 Calibration Tolerances for 200 mm Centrifuge TubeRange, mL Subdivision, mL Volume Tolerance, mL0 to 0.1 0.05 0.02Above 0.1 to 0.3 0.05 0.03Above 0.3 to 0.5 0.05 0.05Above 0.5 to 1.0 0.10 0.05Above 1.0 to 2.0 0.10 0.10Above 2.0 to 3.0 0.20 0.10Above 3.0 to 5.0 0.5 0.20Above 5.0 to 10
26、1.0 0.50Above 10 to 25 5.0 1.00Above 25 to 100 25 1.00TABLE 2 Rotation Speeds for Centrifuges of Various DiametersDiameter of Swing, mmAr/min at 600 rcf r/min at 700 rcf483 1490 1610508 1450 1570533 1420 1530559 1390 1500AMeasured in millimetres between tips of opposite tubes when in rotating positi
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