ASTM D2878 Test Method for Estimating Apparent Vapor Pressures and Molecular Weights of Lubricating Oils
1. Scope
1.1 This test method provides a calculation procedure for converting data obtained by Test Method D972 to apparent vapor pressures and molecular weights. It has been demonstrated to be applicable to petroleum-based and synthetic ester lubricating oils, at temperatures of 395 to 535K (250 to 500°F). However, its applicability to lubricating greases has not been established.
NOTE 1 - Most lubricants boil over a fairly wide temperature range, a fact recognized in discussion of their vapor pressures. For example, the apparent vapor pressure over the range 0 to 0.1 % evaporated may be as much as 100 times that over the range 4.9 to 5.0 % evaporated.
1.2 The values stated in SI units are to be regarded as the standard. In cases in which materials, products, or equipment are available in inch-pound units only, SI units are omitted.
1.3 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 or regulatory limitations prior to use. For specific hazard statements, see Note 3, Note 4, and Note 6.
2. Referenced Documents
2.1 ASTM Standards:
A 240 Specification for Heat-Resisting Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels
D92 Test Method for Flash and Fire Points by Cleveland Open Cup
D972 Test Method for Evaporation Loss of Lubricating Greases and Oils
D2503 Test Method for Molecular Weight (Relative Molecular Mass) of Hydrocarbons by Thermoelectric Measurement of Vapor Pressure
D2595 Test Method for Evaporation Loss of Lubricating Greases over Wide Temperature Range
D2883 Test Method for Reaction Threshold Temperature of Liquid and Solid Materials
E 1 Specification for ASTM Thermometers
E 659 Test Method for Autoignition Temperature of Liquid Chemicals
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 apparent vapor pressure (p), n - the time-averaged value of the vapor pressure from the start to the end of the evaporation test.
3.1.1.1 Discussion - While this may include some effects of differences in nonideality of the vapor, heat of vaporization, surface tension, and viscosity between the m-terphenyl and the lubricating oil, these factors have been demonstrated to be negligible. Unless stated, this average shall cover the range 0 to 5 +/- 1 %.
3.1.2 cell constant (k), n - the ratio of the amount of m-terphenyl or lubricating oil carried off per unit volume of gas to that predicted by Dalton's law.
k = 22.41 PW /VpM
where:
k = call constant
P = ambient atmospheric pressure, torr
W = mass of lubricant evaporated, g
V = volume of gas passed through all litres at 273K and 101.3 kPa (760 torr)
p = apparent vapor pressure, torr
M = mole average molecular weight of lubricant vapor, g/mole
T = test temperature, K
It has been empirically determined that for m-terphenyl in air
k = 0.1266 - 12.60/(T - 273)
and that the cell constant is independent of the composition of the lubricant.
Test Method D972 is normally run with air, which may cause changes in easily oxidized fluids. In such cases, use of common reactive gas nitrogen and recalibration to obtain a slightly different cell constant (k') is mandatory.
