ASTM D6749 for pour point of petroleum products (Automatic air pressure method)
4. Summary of Test Method
4.1 After inserting the test jar containing the specimen into the automatic pour point apparatus and initiating the test program, the specimen is automatically heated to the designated temperature and then cooled at a controlled rate. At temperature intervals of 1 or 3°C, depending on the selection made by the user prior to the test, a slightly positive air pressure is gently applied onto the surface of the specimen which is contained in an air-tight test jar equipped with a communicating tube. Since one end of the communicating tube is inserted into the specimen while the other end is maintained at atmospheric pressure, a small amount of downward movement or deformation of the specimen surface, as a result of the application of air pressure, is observed by means of upward movement of the specimen in the communicating tube. This upward movement of the specimen is detected by a pressure sensor which is installed at the atmospheric end of the communicating tube. The lowest temperature at which deformation of the specimen is observed upon application of air pressure is recorded as the pour point, Test Method D6749.
5. Significance and Use
5.1 The pour point of a petroleum product is an index of the lowest temperature of its utility for certain applications. Flow characteristics, like pour point, can be critical for the correct operation of lubricating systems, fuel systems, and pipeline operations.
5.2 Petroleum blending operations require precise measurement of the pour point.
5.3 Test results from this test method can be determined at either 1 or 3°C intervals.
5.4 This test method yields a pour point in a format similar to Test Method D97/IP15 when the 3°C interval results are reported. However, when specification requires Test Method D97/IP15, do not substitute this test method.
NOTE 2 - Since some users may wish to report their results in a format similar to Test Method D97/IP15 (in 3°C intervals), the precision data were derived for the 3°C intervals. For statements on bias relative to Test Method D97/IP15, see 13.3.1.
5.5 This test method has better repeatability and reproducibility relative to Test Method D97/IP15 as measured in the 1998 interlaboratory test program.
