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D6378-22 – Standard Test Method Technical Guide
📐 Scope and Application
This test method covers the determination of vapor pressure (VPX) using automated vapor pressure instruments for petroleum products, hydrocarbons, and hydrocarbon-oxygenate mixtures, including ethanol blends up to 85% volume fraction. It is applicable for samples with boiling points above 0°C (32°F) and vapor pressures between 7 kPa and 150 kPa (1.0 psi to 21 psi) at 37.8°C (100°F) with a vapor-to-liquid ratio of 4:1. The method also applies to aviation turbine fuels with vapor pressures from 0 kPa to 110 kPa at temperatures between 25°C and 100°C (77°F to 212°F) at a 4:1 ratio. The test method is valid for temperatures from 0°C to 100°C and vapor-to-liquid ratios from 4:1 to 1:1, with pressures up to 500 kPa (70 psi).
⚙️ Test Procedure and Parameters
The triple expansion method utilizes automated instruments that determine vapor pressure in a vacuum. The liquid sample volume required depends on the instrument’s measuring chamber capacity and the selected vapor-to-liquid ratio, which can range from 4:1 to 1:1. The test is conducted at specified temperatures, typically 37.8°C for standard petroleum products, but can be adjusted from 0°C to 100°C. The pressure is measured up to 500 kPa.
| 🟦 Parameter | 📏 Value/Range |
|---|---|
| Vapor Pressure (Petroleum Products) | 7 kPa – 150 kPa at 37.8°C and 4:1 V/L |
| Vapor Pressure (Aviation Turbine Fuels) | 0 kPa – 110 kPa at 25°C – 100°C and 4:1 V/L |
| Temperature Range | 0°C – 100°C (32°F – 212°F) |
| Vapor-to-Liquid Ratio (V/L) | 1:1 to 4:1 (X = 1 to 4) |
| Maximum Pressure | 500 kPa (70 psi) |
📊 Precision and Correlation
The precision of this test method is based on interlaboratory studies (ILS). For general petroleum products, precision data from a 2003 ILS using 1 L containers and a 2016 ILS using 250 mL containers are applicable. For aviation turbine fuels, a 2007 ILS using 100 mL containers provides precision data. The vapor pressure (VPX) at 37.8°C with a 4:1 vapor-to-liquid ratio for gasoline and gasoline-oxygenate blends correlates to the dry vapor pressure equivalent (DVPE) from Test Method D5191. This correlation does not apply to aviation turbine fuels.
| 🎯 Sample Type | 📅 ILS Year | 🔬 Container Size |
|---|---|---|
| Petroleum Products | 2003 | 1 L |
| Petroleum Products | 2016 | 250 mL |
| Aviation Turbine Fuels | 2007 | 100 mL |
💡 Tip: For accurate correlation to DVPE in Test Method D5191, ensure the vapor-to-liquid ratio is 4:1 and the temperature is 37.8°C.
⚠️ Warning: This test method is not intended for samples with boiling points at or below 0°C. Refer to sections 7.2–7.8 for specific safety warnings.
❓ Frequently Asked Questions
🔍 What is the vapor pressure range for this test method?
The vapor pressure range is 7 kPa to 150 kPa for petroleum products at 37.8°C, and 0 kPa to 110 kPa for aviation turbine fuels between 25°C and 100°C.
💡 How does the vapor-to-liquid ratio affect the test results?
The vapor-to-liquid ratio can be set from 4:1 to 1:1. The liquid sample volume required depends on this ratio and the instrument’s chamber capacity. The precision statement may not apply outside the 4:1 ratio for certain applications.
⚡ What safety precautions should be followed?
Users must establish appropriate safety practices per sections 7.2–7.8 of the standard. These include precautions for volatile liquid samples.
📌 How is this method correlated to Test Method D5191?
For gasoline and gasoline-oxygenate blends, the VPX at 4:1 vapor-to-liquid ratio at 37.8°C correlates to the DVPE value from Test Method D5191. This condition does not apply to aviation turbine fuels.