ASTM D381 standard test method for gum content in fuels by jet evaporation
13. Report
13.1 For aviation fuels with existent gum contents not less than 1 mg/100 mL, express the results to the nearest 1 mg/100 mL as existent gum content by Test Method D381. Round figures in accordance with Practice E 29 or Appendix E of IP Standard Methods for Analysis and Testing of Petroleum and Related Products. For results <1 mg/100 mL, report as "<1 mg/100 mL".
13.2 For non-aviation fuels with either solvent washed or unwashed gum content values not less than 0.5 mg/100 mL, express the results to the nearest 0.5 mg/100 mL as either solvent washed gum or unwashed gum content, or both, by Test Method D381. Round figures in accordance with Practice E 29 or Appendix E of IP Standard Methods for Analysis and Testing of Petroleum and Related Products. For results <0.5 mg/100 mL, report as "<0.5 mg/100 mL". If the unwashed gum content is <0.5 mg/100 mL, the washed gum may also be reported as "<0.5 mg/100 mL" (see 11.8).
13.3 For all fuels, if the filtration step (see 11.4) has been carried out before evaporation, the expression filtered shall follow the numerical value.
14. Precision and Bias
14.1 The precision, as obtained by statistical examination of interlaboratory test results, is given in 14.1.1 and 14.1.2, and illustrated graphically in Fig. 2. Analysis details are in the research report.
14.1.1 Repeatability - The difference between successive 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 values below only in one case in twenty.
where: x is the average of the results being compared.
14.1.2 Reproducibility - The difference between two test results independently obtained by different operators operating in different laboratories on nominally identical test material would, in the long run, in the normal and correct operation of the test method, exceed the values below only in one case in twenty:
R = 2.09 + 0.126x for existent gum (aviation gasoline),
R = 2.941 + 0.2794x for existent gum (aviation turbine fuel),
R = 1.928xˆ 0.4 for unwashed gum content
R = 2.494xˆ 0.3 for solvent washed gum content
where: x is the average of the results being compared.
NOTE 6 - The precision values given above for solvent washed and unwashed gum content were obtained on finished motor gasolines, including those containing alcohol and ether type oxygenates as well as deposit control additives as determined in a 1997 interlaboratory study. The precision values for the solvent washed and unwashed gum content are based on samples containing between 0 to 15 mg/100 mL and 0 to 50 mg/100mL gum content, respectively.
14.2 Bias - Since there is no accepted reference material suitable for determining the bias for the procedure in Test Method D 381 for measuring existent gum (solvent washed or unwashed gum), bias has not been determined.
15. Keywords
15.1 aviation fuels; existent gum; motor gasoline; solvent washed gum; unwashed gum