ASTM D91-97

Designation: D 91 – 97 An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
1
Precipitation Number of Lubricating Oils
This standard is issued under the fixed designation D 91; 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.
This test method has been adopted for use by government agencies to replace Method 3101 of Federal Test Method Standard No. 791b.
1. Scope naphtha insoluble material in the oil. This quantity is reported
as the precipitation number.
1.1 This test method covers the determination of the
precipitation number of steam cylinder stocks and black oils,
5. Apparatus
and can be used for other lubricating oils.
5.1 Centrifuge Tube, cone-shaped, conforming to the
1.2 The values stated in acceptable SI units are to be
dimensions given in Fig. 1, and made of thoroughly annealed
regarded as the standard.
glass. The graduations, numbered as shown in Fig. 1, shall be
1.3 This standard does not purport to address all of the
clear and distinct, and the mouth shall be constructed in a shape
safety concerns, if any, associated with its use. It is the
suitable for closure with a cork. Scale-error tolerances and
responsibility of the user of this standard to establish
smallest graduations between various calibration marks are
appropriate safety and health practices and determine the
given in Table 1 and apply to calibrations made with air-free
applicability of regulatory limitations prior to use.
water at 20°C.
2. Referenced Documents 5.2 Centrifuge, meeting all the safety requirements for
normal use and capable of whirling two or more filled
2.1 ASTM Standards:
2 centrifuge tubes at a speed which can be controlled to give a
D 86 Test Method for Distillation of Petroleum Products
relative centrifugal force (rcf) between 600 and 700 at the tip
D 611 Test Methods for Aniline Point and Mixed Aniline
2 of the tubes. The revolving head, trunnion rings, and trunnion
Points of Petroleum Products and Hydrocarbon Solvents
cups, including the rubber cushion, shall be soundly
D 1298 Test Method for Density, Relative Density (Specific
constructed to withstand the maximum centrifugal force
Gravity), or API Gravity of Crude Petroleum and Liquid
2
capable of being delivered by the power source. The trunnion
Petroleum Products by Hydrometer Method
cups and cushions shall firmly support the tubes when the
D 4057 Practice for Manual Sampling of Petroleum and
3
centrifuge is in motion. The centrifuge shall be enclosed by a
Petroleum Products
metal shield or case strong enough to eliminate danger if any
D 4177 Practice for Automatic Sampling of Petroleum and
3
breakage occurs. Calculate the speed of the rotating head by
Petroleum Products
means of the following equation:
3. Terminology
rpm 5 1337 rcf/d
=
3.1 Definitions of Terms Specific to This Standard: (1)
3.1.1 ASTM precipitation number, n of lubricating oils—the
where:
number of millilitres of precipitate formed when 10 mL of
rcf 5 relative centrifugal force, and
lubricating oil are mixed with 90 mL of ASTM precipitation
d 5 diameter of swing, in mm, measured between tips of
naphtha, and centrifuged under the conditions of the test.
opposite tubes when in rotating position.
Table 2 shows the relationship between diameter swing, rcf,
4. Significance and Use
and revolutions per minute.
4.1 Fully refined petroleum oils normally contain no
naphtha insoluble material. Semirefined or black oils
6. Reagent
frequently contain some naphtha insoluble material (sometimes
6.1 ASTM Precipitation Naphtha (Warning—see Note 1)
referred to as asphaltenes). This test measures the amount of
shall conform to the following requirements:
ASTM
1
This test method is under the jurisdiction of ASTM Committee D-2 on
Test Requirement Designation
Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee
Density at 15°C 0.692 to 0.702 D 1298
D02.06on Analysis of Lubricants.
Aniline point 58 to 60°C D 611
Current edition approved Dec. 10, 1997. Published June 1998.
Initial boiling point not less than 50°C D 86
. Originally published as D 91 – 21 T. Last previous edition D 91 – 92.
50 % point 70 to 80°C D 86
2
Annual Book of ASTM Standards, Vol 05.01. End point not more than 130°C D 86
3
Annual Book of ASTM Standards, Vol 05.02.
1

---------------------- Page: 1 ----------------------
D91
to the 100-mL mark with the naphtha and close tightly with a
softened cork (not a rubber stopper). Then invert each tube at
least 20 times, allowing the liquid to drain thoroughly from the
tapered tip of the tube each time. Place the tubes in a water bath
at 32 to 35°C for 5 6 1 min. Momentarily
...