ASTM D5771 Standard Test Method for Cloud Point of Petroleum Products and Liquid Fuels (Optical Detection Stepped Cooling Method)
4. Summary of Test Method
4.1 After insertion of the prescribed test jar (6.3) containing the specimen into the apparatus, and the initiation of the program, the specimen is cooled incrementally according to the cooling profile listed in Table 1. The specimen is continuously monitored by a reflective optical system (6.1 and Fig. 1) for the formation ofa crystalline structure. When the crystallization of the wax in the specimen is detected by the optical system, the temperature is recorded to within 0.1 °C resolution. The specimen is then heated to facilitate the start of the next test.
5. Significance and Use
5.1 For petroleum products and biodiesel fuels, the cloud point is an index of the lowest temperature of their utility for certain applications. Wax crystals of sufficient quantity can plug filters used in some fuel systems.
5.2 Petroleum blending operations require precise measurement of the cloud point.
5.3 This test method can determine the temperature of the test specimen at which wax crystals have formed sufficiently to be observed as a cloud with a resolution of 0.1 °C.
5.4 This test method provides results that, when rounded to the next lower integer, are equivalent to Test Method D2500. Refer to 12.2.
5.5 This test method is more precise than Test Method D2500.
NOTE 1 - According to interlaboratory examination, the reproducibility of this test method has been found to be more precise than Test Method D2500.
