ASTM D1657 Test Method for Density or Relative Density of Light Hydrocarbons by Pressure Hydrometer
11. Calculation and Report
11.1 Apply hydrometer corrections, if any, to the observed readings and report the corrected reading to the nearest 0.5 kg/m3 or 0.0005 relative density.
11.2 If the determinations were not carried out within 0.2°C of the reference temperature, correct the results by use of the appropriate Adjunct to D1250 Guide for Petroleum Measurement Tables (API MPMS Chapter 11.1) or API MPMS Chapter 11.2.4 (GPA TP-27).
11.2.1 When a density-scaled hydrometer was used, use Table 53E for densities up to 635 kg/m3 to obtain density at 15°C.
11.2.2 When a relative density hydrometer was used, use Table 23E for relative densities up to 0.655 to obtain relative density at 60°F.
11.3 Report the final result as density to the nearest 0.5 kg/m3 at 15°C or as relative density to the nearest 0.0005 and specify the reference temperature.
11.3.1 The test report shall contain at least the following information:
11.3.1.1 A reference to this standard.
11.3.1.2 The type and complete identification of the product tested.
11.3.1.3 The result of the test.
11.3.1.4 The date of the test.
11.3.1.5 Any deviations from the test method.
11.3.1.6 State whether a thermohydrometer was used.
11.4 The reporting values have no precision or bias determination. It is up to the user to determine whether this test method provides results of sufficient accuracy for the intended purpose.
11.5 Certified hydrometers from a recognized standardizing body, such as NIST, report the output density as "Density in Vacuo".
12. Precision and Bias
12.1 Precision - The precision of this test method as determined by statistical examination of interlaboratory test results is as follows:
12.1.1 Repeatability - The difference between two test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following value only one case in twenty.
Repeatability = 1 kg/m3
12.1.2 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following value only in one case in twenty.
Reproducibility = 3 kg/m3
NOTE 5 - The precision of this test method has only been determined in the units of density.
NOTE 6 - No precision data are available for thermohydrometers.
12.2 Bias - Bias for this test method has not been determined. However, to determine that the bias is within acceptable limits, verification of the hydrometer and thermometer using standards traceable to international standards shall occur before the thermohydrometer or hydrometer and thermometer are placed into service. Periodic re-verification may be required.
12.3 The repeatability and reproducibility values provided are not based on any interlaboratory round robin results. They should be considered historical numbers, the source of which cannot be verified by either ASTM or API and have been in this standard prior to the current slate of Light Hydrocarbons including liquefied petroleum gases (LPG). These values do not apply to the current calculation procedures, and it is up to the user to determine whether this test method provides results of sufficient accuracy for the intended purpose.
13. Keywords
13.1 density; hydrocarbons; hydrometer; petroleum products; pressure hydrometer; relative density
