ASTM D6811 Standard Test Method for Measurement of Thermal Stability of Aviation Turbine Fuels under Turbulent Flow Conditions (HiReTS Method)
8. Sampling and Sample Containers
8.1 Obtain samples for testing in accordance with Practices D4057 or D4177, with the following additional requirements:
8.1.1 Containers shall be fully epoxy lined or made of polytetrafluoroethylene (PTFE). See Note 2 and Practice D4306.

8.1.2 Prior to sampling, all containers and their closures shall be rinsed at least three times with the fuel being sampled.

8.1.3 Test samples as soon as possible after sampling.

NOTE 2 - Test methods for measuring thermal stability are known to be sensitive to trace contamination during the sampling operation and from sample containers. New containers are recommended, but when only used containers are available, a thorough rinse with trisolvent (see 7.2) followed by cleaning solvent (see 7.1 and 7.3), and drying with a stream of air is recommended.

8.2 Aeration of Test Sample - Aerate the test sample, with dry air, through the sparger at an air flow rate of 1 to 2 L/min for 10 min.

8.3 Sample Size - Standard operating conditions are: 3 L for 13 scans (65–min test) and 5 L for 25 scans (125-min test).

9. Preparation of Apparatus
9.1 Prepare the instrument for operation in accordance with the manufacturer's instructions. (Warning - Installing and removing the capillary tube may result in exposure to fuel or solvent. It is recommended that impermeable gloves and safety glasses are worn.)

9.2 Remove the sample filter and inlet tubing and clean by rinsing with heptane and then by back flushing with heptane, and then refit.

9.3 Set the instrument in accordance with Table 1 and check that the correct standard operating conditions are in accordance with Section 10.

9.4 Inspect 40 mm of the blackened section at both ends of the capillary tube and reject the tube if any scratches, pinholes or cracks are deep enough to expose the capillary tube's bright metal surface.

9.5 Commence the pre-test by installing a new capillary tube and carrying out the following in accordance with the manufacturer's instructions.

9.6 Immerse the input tube and sample filter in heptane.

9.7 Clean the tubeways with heptane and reset the bypass valve to TEST.

9.8 Visually check the system for leaks. If a leak is found, abort the pre-test and vent the system using the bypass valve. Tighten or replace any leaking fittings, if necessary, and repeat 9.6.

9.9 Check the alignment and focus of the pyrometer and the straightness of the capillary tube in accordance with the manufacturer's handbook.

10. Standard Operating Conditions
10.1 Fuel Test Temperature, preset at 290°C or as specified in applicable specifications or as agreed upon between the parties.

10.2 Fuel Flow Rate, preset at 35 mL/min or as specified in applicable specifications or as agreed upon between the parties.

10.3 Number ofCapillary Scans, preset as 13 (for a 65 min test) or 25 (for a 125 min test), or as specified in applicable specifications or as agreed upon between the parties.

NOTE 3 - Each capillary scan takes 5 min to complete.

NOTE 4 - Other test temperatures, besides 290°C, and flow rates, besides 35 mL/min, can be used but the precision may be affected.

11. Calibration and Standardization
11.1 Ensure that all of the manufacturer's instructions for calibrating, checking, cleaning, and operating the apparatus are followed.

11.2 Verify the performance of the temperature, flow, and pressure sensors at least every 6 months. The testing of fuels with poor thermal stability may necessitate more frequent equipment verification and cleaning.