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D3902-90 – Standard Test Method Technical Guide
📐 Scope and Significance
Under the jurisdiction of ASTM Committee D11, this test method covers the determination of the volume of liquefied petroleum gas (LPG) diffusing through the wall of a rubber hose during a specified period. The test quantitatively measures the inherent characteristic of rubber hose to permit gas diffusion, providing a standard metric for evaluating hose permeability.
The values stated in SI units are regarded as standard. Users must establish appropriate safety, health, and environmental practices prior to use, as a specific precautionary statement is given in Section 5 of the standard.
⚠️ Regulatory Compliance: This international standard was developed in accordance with internationally recognized principles on standardization established by the WTO Technical Barriers to Trade (TBT) Committee.
⚙️ Apparatus and Test Specimen
Specialized apparatus is required to ensure accurate volumetric measurement of diffused gas. The water bath must accommodate the assembly, and the gas supply must include a suitable pressure gage and an emergency excess flow shutoff valve in case of hose failure. The test setup also requires a barometer and two thermometers to record water and air temperature at the gas-collection point.
| 🟦 Apparatus Component | 📏 Specification Requirement |
|---|---|
| Gas-Collecting Tube | Glass tube, at least 10% longer and 10% larger ID than test hose |
| Funnel | Conical, 25 mm in diameter |
| Measuring Cylinder | 500 cm³ capacity, graduated at 5.0 cm³ intervals |
| Test Gas (LP-Gas) | Minimum 99 mol% propane, sulfur content less than 0.005 mass% |
| Valve Requirements | Excess flow shutoff valve and safety relief valve |
The test hose must have a 0.50-m free length between couplings and shall be coupled with band-it-type couplings. If the test hose is rubber covered, the cover must be thoroughly perforated with a pricker roll to allow diffused gas to escape freely and not restrict the measurement.
💡 Specimen Alignment: Position the test hose in the exact center of the glass tube. Mount the assembly in the water bath at an incline angle of approximately 20°.
📊 Test Procedure and Critical Conditions
The procedure involves flushing the hose with LP-gas to remove air, then sealing one end and connecting the other to the gas supply. The test is conducted with the LP-gas in the liquid phase. The pressure is regulated by adjusting the water bath temperature to approximately 28°C.
| 🎯 Test Parameter | ⚡ Specified Value |
|---|---|
| Test Pressure (Liquid Phase) | 1000 ± 20 kPa (145 ± 3 psi) |
| Water Bath Temperature | Approx. 28°C |
| Safety Relief Valve Set Point | 1200 ± 35 kPa (175 ± 5 psi) |
| Hose Orientation | ~20° incline in water bath |
🚨 Explosion Hazard Warning: Take special precautions to ensure the water bath temperature cannot rise accidentally, as this will significantly increase gas pressure. The system must be equipped with a safety relief valve set at 1200 ± 35 kPa. Perform all testing in a well-ventilated area.
Once the system is stabilized at the target pressure and temperature, the diffused gas is collected in the graduated cylinder over the specified period. Barometric pressure must be recorded throughout the test to ensure accurate volumetric calculations.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D3902-90? This test method quantitatively measures the volume of liquefied petroleum gas that diffuses through the wall of a rubber hose during a specified period of time.
💡 What are the specific purity requirements for the test gas? The standard requires LP-gas with a minimum purity of 99 mol% propane and a sulfur content of less than 0.005 mass%.
⚡ At what pressure and temperature is the test conducted? Unless otherwise specified, the hose is tested at a gage pressure of 1000 ± 20 kPa (145 ± 3 psi) in the liquid phase, achieved by maintaining the water bath at approximately 28°C.
📌 Why must the hose cover be perforated if it is rubber covered? The rubber cover is thoroughly perforated with a pricker roll to ensure it does not act as a barrier that restricts gas diffusion, allowing the test to accurately measure the diffusion characteristics of the hose wall itself.