11. Procedure
11.1 Sample Aging:
11.1.1 Adjust the storage oven for sample storage to a temperature of 43 ± 1°C (110 ± 2°F).
11.1.2 Place 400 mL of filtered fuel into each bottle. Use two bottles for each sampling period. (Commonly used sampling periods are 0, or any of the following: 4, 8, 12, and 24 weeks). Fill three extra bottles with fuel to be used in case of accidents, for further tests at other times of storage, or to extend the overall test duration.
11.1.3 Label each storage bottle with the time and date the test is started, sample identification, and the time and date when the bottle is to be removed from storage. Place the bottles in the oven in random order.
11.1.4 Perform zero-week analyses on the same day as the other samples are placed in storage. Zero-week data are necessary to provide base data and assure satisfactory technique.
11.2 Determination of Filterable Insolubles:
11.2.1 At the end of each prescribed period of time, remove two bottles from the storage oven and allow them to cool to 21 to 27°C (70 to 80°F) in a dark environment. This may take from 4 to 24 h.
11.2.2 After cooling, pour fuel from the sample container to the graduated cylinder, start the vacuum, and then transfer 100 mL of fuel to the filter funnel.
11.2.2.1 Continue transferring 100-mL increments of fuel to the filter funnel. When all the fuel from the sample container has been filtered, or if filtration slows so that 100 mL of sample requires greater than 10 min for complete filtration, then remove the filter support/filter funnel from the receiving flask, pour the filtered fuel into a clean graduated cylinder, and record the volume of fuel that was filtered in millilitres. Keep the fuel sample filtrate separate from the solvent washings filtrate. This allows the fuel to be used for additional analyses. If all the fuel has been filtered, thoroughly rinse the sample container and the graduated cylinder with one or more portions of filtered flushing fluid, pour the rinses into the funnel, and proceed to 11.2.2.2. If all the fuel has not been filtered, proceed to 11.2.2.2 and 11.2.2.3, and then repeat from 11.2.2.1.
11.2.2.2 Wash down the inside of the funnel and the outside of the joint between the funnel and filter base filtered with flushing fluid. With the vacuum applied, carefully separate the funnel from the filter base. Wash the periphery of the membrane filter by directing a gentle stream of filtered flushing fluid from the edge to the center, exercising care not to wash any of the particulate from the surface of the membrane filter. Maintain vacuum after the final washing for 10 to 15 s to remove excess filtered flushing fluid from the membrane filter.
11.2.2.3 Using clean forceps, carefully remove the test and control membrane filters from the filter base and place them side by side on clean glass support rods or watch glasses in a clean, covered petri dish. Dry and reweigh the membrane filters as described in 9.3, taking care not to disturb the particulate on the surface of the test membrane filter. Record the final control membrane filter mass and the final test membrane filter mass to the nearest 0.0001 g for each filtration.
NOTE 2 - Do not mix rinsings and filtrate if filtrate color changes are being measured.
NOTE 3 - If severe filter plugging is encountered so that filtration is not complete in 3 h, discontinue the test with the notation that filter plugging occurred.
11.2.3 Repeat the procedure in 11.2.2-11.2.2.3 for the second bottle.
11.3 Determination of Adherent Insolubles on Sample Bottle - After the final washing with the hydrocarbon solvent, dissolve any adherent gum on the sample container walls with two washings of 30 to 35 mL of the adherent insolubles solvent. Pour each washing into previously weighed 100-mL beakers. Evaporate the solvent at 160°C (320°F) by the air jet method in accordance with Test Method D381. After the solvent is completely evaporated, place the beakers in a desiccator without desiccant and allow to cool to room temperature. Weigh the beakers to the nearest 0.1 mg. Use a tare beaker (moisture blank) in accordance with Test Method D381.
12. Calculation
12.1 Calculate the total insolubles (Ti) in milligrams per 100 mL of fuel after aging, as follows:
where:
Ti = total insolubles, mg/100 mL,
Fi = mass of filterable insolubles, mg, as determined in 11.2, and
Ai = moisture corrected mass of adherent insolubles, mg, as determined in 11.3.