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D3429-93 – Standard Test Method Technical Guide
The ASTM D3429-93 (Reapproved 2012) standard test method defines a precise procedure for measuring the solubility of nonreactive fixed gases, such as helium and nitrogen, in low-boiling liquids. This method is essential for engineering applications involving cryogenic fluids and hydraulic systems operating under demanding temperature and pressure conditions.
📐 Scope and Applicability
This standard strictly governs the determination of gas solubilities in solvents that boil below 273 K. The applicable testing environment spans temperatures from 77 K to 300 K and pressures from subambient levels up to 6.5 MPa (65 atm). While the written procedure specifically details the solubility determination for helium and nitrogen, it can be adapted for other nonreactive gases, including argon, hydrogen, and oxygen, with appropriate modifications to the gas chromatographic analysis.
⚙️ Test Method Summary and Key Parameters
The method involves saturating a sample of the test liquid with the target test gas at a specified temperature and pressure. A portion of this saturated solution is then withdrawn and allowed to vaporize in an evacuated container at room temperature. The concentration of the gas in the vaporized sample is determined using gas chromatography (per ASTM E260 for packed columns).
A critical requirement for success is that the molar concentration of gas in the sample container must remain identical to that in the original liquid phase. This is achieved by strictly avoiding fractionation during sample withdrawal, preventing any decomposition or polymerization of the liquid upon vaporization, and ensuring the vapor phase does not react with the container walls. The test method assumes ideal gas behavior for both the test gas and the liquid vapor at 101 kPa (1 atm). If these stringent conditions are met, the method estimates solubility with an accuracy of ± 2%.
| 🟦 Parameter | 📐 Specified Value / Notes |
|---|---|
| Temperature Range | 77 K to 300 K |
| Pressure Range | Subambient to 6.5 MPa (65 atm) |
| Test Liquid Boiling Point | Below 273 K |
| Target Gases (Written) | Helium and Nitrogen |
| Analysis Conditions | 101 kPa (1 atm), GC analysis |
| Stated Accuracy | ± 2 % |
📊 Significance and Key Measured Properties
The solubility of fixed gases in low-boiling liquids is a fundamental engineering parameter, particularly for the design of hydraulic and cryogenic systems. It provides a measure of the amount of gas that can come out of solution when a system experiences changes in temperature and pressure. This standard provides an accurate chromatographic method for separating and quantifying these dissolved gases, restricted specifically to low-boiling liquid samples.
⚠️ Critical Requirement: Avoiding Fractionation
To achieve the stated ±2 % accuracy, fractionation of the sample must be strictly avoided during the withdrawal from the liquid phase. Any change in the composition of the sample due to pressure changes invalidates the results.
💡 Extending the Method
While the primary procedure targets helium and nitrogen, the solubility of other nonreactive gases such as argon, hydrogen, and oxygen can be determined by making suitable modifications to the gas chromatographic analytical measurements. Always refer to Sections 6.1.2, 7.1, and Annex A1 for specific safety and hazard statements.
❓ Frequently Asked Questions
🔍 What types of gases can be tested using this method?
The method is written for nonreactive fixed gases, specifically helium and nitrogen. However, with modifications to the gas chromatography analysis, it can also be used for argon, hydrogen, and oxygen.
💡 What is the required boiling point of the test liquid?
The standard specifies that the procedure is restricted to use with low-boiling liquid samples, specifically those that boil below 273 K (0 °C).
⚡ What is the accuracy of this test method?
The standard test method provides estimates of solubility with an accuracy of ±2%, provided that strict procedures are followed to avoid sample fractionation, decomposition, or chemical reactions.
📌 What temperature and pressure limits apply?
The test method is applicable at temperatures from 77 K to 300 K. The pressure range is from subambient pressure up to 6.5 MPa (65 atm).