ASTM D6468 Test Method for High Temperature Stability of Distillate Fuels
8. Sampling
8.1 When samples of a fuel batch are obtained to determine stability, obtain samples in accordance with Practice D4057. Use only epoxy-lined cans or borosilicate glass bottles. Shield clear glass bottles from sunlight to prevent photochemical reactions.
8.2 When samples are from a fuel or component rundown line, exercise care to ensure that the sampling line and valving are thoroughly flushed with current mainstream sample.
8.3 Because stability of some fuels, as determined in this test method, changes over time, the sampling date shall be recorded; record time and date if sample is from a fuel or component rundown line. Samples should be stored at temperatures below 5°C. If storage for more than a few days is expected, oxygen should be removed from the fuel by subsurface purging with a stream of nitrogen; for example, by bubbling nitrogen for 1 min/L of sample.
9. Preparation of Apparatus
9.1 Cleaning Aging Tubes - Clean new tubes using adherent insolubles solvent, then with a mildly alkaline or neutral laboratory detergent, followed by copious rinsing with deionized or distilled water to remove all traces of detergent. Then rinse with acetone and air dry. Rinse used tubes with adherent insolubles solvent, dry, then clean as above for new tubes. Visually inspect tubes before use, and reclean or reject if there is the slightest trace of contamination.
9.1.1 Because of the small sample size and the high surface to volume ratio in this test method, carefully avoid carry-over from past tests or from cleaning agents. There are especially strong effects from traces of copper, strong acids, and strong bases.
9.2 Cleaning Membrane Filter Holder - Rinse with adherent insolubles solvent, acetone, and air dry.
10. Calibration and Standardization
10.1 Turn on the reflection meter and allow at least 30 min for warm-up. The gain should be set in LO position for search unit Y with green filter.
10.2 Follow the manufacturer's instructions to carry out a two point calibration of the reflection meter, using the black standard and standard plaque supplied with the search unit.
NOTE 7 - The calibration procedure ensures that the instrument is working properly. It also indirectly sets a nominal 100 % reflectance setting that is subsequently reset in 10.3.
10.3 Place a new filter paper on top of a stack of at least ten unused Whatman No. 1 filters of the same size. Place the search unit on the center of the filter, and adjust the meter reading to 100 %, using the sensitivity control.
NOTE 8 - Such adjustment, which sets the test method 100 % reflectance point, alters the reflectance scale; as a result, the reflection meter will no longer read the recited reflectance of the standard plaque.
10.4 Place the search unit on the center of the black glass standard, and (if necessary) adjust the meter reading to 0 %, using the ZERO control. Recheck the 100 % adjustment against the new filter paper, and continue adjustment until the meter reads both 0 % with the black glass standard and 100 % with the new filter pad.
