ASTM D97: Standard Test Method for Pour Point of Petroleum Products
1. Purpose and Scope:
This test method is designed to determine the pour point of a petroleum product. The pour point is defined as the lowest temperature at which the oil shows movement when the test jar is tilted under prescribed conditions. It is a critical property for assessing the low-temperature flow characteristics of lubricating oils, crude oils, and other petroleum products, indicating the temperature below which the product may not flow readily.
2. Basic Principle:
The test involves heating the sample to remove any previous thermal history and then cooling it at a specified rate. At pre-defined temperature intervals (typically 3°C or 5°F), the test jar is removed from the cooling bath and tilted to check for surface movement. The pour point is recorded as the temperature at which the sample shows no movement when the jar is held horizontally for 5 seconds.
3. Key Apparatus:
Test Jar: A clear glass jar of specific dimensions.
Thermometer: ASTM Low-Cloud and Pour Point Thermometer (-38°C to +50°C or -36°F to +120°F).
Jar Cork: with a hole for the thermometer.
Jacket: A cylindrical metal jacket that provides an air insulation layer around the test jar.
Cooling Baths: A series of baths maintained at specified low temperatures (e.g., using mechanical refrigeration or mixtures of ice and alcohol/dry ice).
4. Procedure Summary:
Preparation: The sample is heated to 45°C (± 2°C) to ensure it is completely liquid and homogenous. It is then poured into the test jar to a specified level.
Assembly: The thermometer is inserted through the cork so its bulb is at the bottom of the jar. The jar is placed into the jacket, and the assembly is positioned in the first cooling bath, which is maintained at a temperature that is not more than 30°F (17°C) above the expected pour point.
Cooling and Inspection: The sample is cooled at a controlled rate. Every time the temperature reaches a multiple of 3°C (5°F), the jar is quickly removed, tilted slightly to check if the oil surface is still fluid, and immediately replaced.
Endpoint Determination:
The Upper Pour Point is the temperature at which the sample shows no movement when the jar is held horizontally for 5 seconds.
The test is then continued to determine the Lower Pour Point (or just the reported pour point). After the upper pour point is found, the jar is continued to be cooled. The jar is inspected at each 3°C (5°F) interval until the sample shows no movement when the jar is held horizontally for 5 seconds. The temperature 3°C (5°F) above this temperature is recorded as the pour point.
Example: If the sample shows no movement at -24°C, the pour point is reported as -21°C.
5. Reporting:
The result is reported as ASTM D97 Pour Point, in degrees Celsius or Fahrenheit, and must include any observed irregularities (e.g., wax crystals, gel formation).
