ASTM D6897 Standard Test Method for Vapor Pressure of Liquefied Petroleum Gases (LPG) (Expansion Method)
4. Summary of Test Method
4.1 Employing a measuring chamber with a built-in piston, the chamber is rinsed three times with a portion of sample, which is then discarded. A sample of defined volume is drawn from a pressurized sampling system into the temperature-controlled chamber at 5 °C by moving the piston to the filling position. After sealing the chamber, the volume is expanded by moving the piston until the final volume produces the desired vapor to liquid ratio of 0.5:1. The temperature of the measuring chamber is then regulated to the test temperature of interest, such as 37.8 °C.
4.2 The observed total pressure at equilibrium is corrected relative to 101.3 kPa and reported as the LPG vapor pressure at the selected test temperature.
5. Significance and Use
5.1 Information on the vapor pressures of liquefied petroleum gas is pertinent to selection of properly designed storage vessels, shipping containers, and customer utilization equipment to ensure safe handling of these products.
5.2 Determination of the vapor pressure of liquefied petroleum gas is important for safety reasons to ensure that the maximum operating design pressures of storage, handling, and fuel systems will not be exceeded under normal operating temperature conditions.
5.3 For liquefied petroleum gases, vapor pressure can be considered a semi-quantitative measure of the amount of the most volatile material present in the product.
5.4 This test method uses a small sample volume and excludes any manual handling of a measuring chamber under high pressure.
