ASTM D7153 Test Method for Freezing Point of Aviation Fuels (Automatic Laser Method)
11. Report
11.1 Report the temperature recorded in 10.8 as the freezing point, determined by Test Method D7153.
12. Precision and Bias
12.1 Precision - The precision of this test method as determined by the statistical examination of the 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 this test method, exceed 0.6 °C only in one case in twenty.
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 this test method, exceed 0.9 °C only in one case in twenty.
12.2 Bias - Because there are no liquid hydrocarbon mixtures of known freezing point, which simulate aviation fuels, bias cannot be established.
12.3 Relative Bias - The results for all the samples from the interlaboratory program were examined for biases relative to Test Method D2386 and IP 16. A systemic bias was observed and is quantified with the following equation:
D2386 and IP 16 = X - 0.347
where:
D2386 and IP 16 = mean of the result tested by D2386 and IP 16.
X = mean of the result tested by this test method (D7153).
12.3.1 As example: For a D2386 and IP 16 result of -60 °C, the result from this test method is -59.65 °C , or 0.347 °C warmer than the D2386 and IP 16 result.
12.3.2 However, the relative bias is within the reproducibility of both test methods.
12.3.3 The cross method reproducibility (Rxy), identified in the research report, between this test method and Test Method D2386 is 1.9. (See research report for further information on relative bias and the methods used to derive them.)
12.4 The precision statements were derived from a 2003 interlaboratory cooperative test program. Participants analyzed 13 samples sets comprised of various aviation fuels over the temperature range of -42 °C to -60 °C. Thirteen laboratories participated with the automatic laser method and fifteen with the manual D2386 or IP 16 test methods. The precision statistics were compiled and calculated based on the 0.1 °C resolution offered by the automatic laser method. Information on the types of samples and their respective average freezing point is contained in the research report available at ASTM Headquarters.
13. Keywords
13.1 aviation turbine fuels; freezing point; wax crystals
