ASTM D5771 Standard Test Method for Cloud Point of Petroleum Products and Liquid Fuels (Optical Detection Stepped Cooling Method)
8. Sampling
8.1 Obtain a sample in accordance with Practice D4057 or D4177.
8.2 Samples of very viscous materials may be warmed until they are reasonably fluid before they are sampled. However, no sample should be heated more than is absolutely necessary.
8.3 The sample shall not be heated above 70 °C. If the sample is heated above 70 °C, allow the sample to cool below 70 °C before filtering or inserting into the apparatus.
8.4 When moisture is present in the sample, remove the moisture by a method such as filtration through dry, lint-free filter paper, until the oil is perfectly clear, but make such filtration at a temperature at least 14 °C above the expected cloud point.
NOTE 2 - A wax cloud or haze is always noted at the bottom of the test jar where the temperature is lowest. A slight haze throughout the entire specimen, which slowly becomes more apparent as the temperature is lowered, is usually due to water in the specimen. Generally this water haze will not interfere with the determination of the wax cloud point. In most cases of interference, filtration through dry lint-free filter papers such as described in 11.2 is sufficient.
8.5 For diesel fuels, ifthe haze is very dense, a fresh portion of sample must be dried by shaking 100 mL with 5 g of anhydrous sodium sulfate for at least 5 min and then filtering through dry lint-free filter paper. Given sufficient contact time, this procedure will remove or sufficiently reduce the water haze so that the wax cloud can be readily discerned. Drying and filtering should always be done at a temperature at least 14 °C above the approximate cloud point, but otherwise not in excess of 49 °C.
9. Preparation of Apparatus
9.1 Prepare the instrument for operation in accordance with the manufacturer's instructions.
9.2 Clean and dry the test head and test jar using suitable solvents as prescribed by the manufacturer.
9.3 Adjust the set point of the cooling system, when necessary, to the appropriate temperature to cool the jacket to the required temperature (see Table 1).
10. Calibration and Standardization
10.1 Ensure that all of the manufacturer's instructions for calibrating, checking, and operating the apparatus are followed.
10.1.1 A test head simulator with a known resistance is used to calibrate the equipment. Follow the manufacturer's calibration instructions.
NOTE 3 - A test head simulator may be obtained from the apparatus supplier which can assist in verification of temperature measurement.
10.2 A sample with a mutually agreed upon cloud point such as a sample from a interlaboratory test program can be used to verify performance of the apparatus.
