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D2472-15 – Standard Test Method Technical Guide
📐 Specifications and Scope
This specification, D2472−15 (Reapproved 2023), applies to sulfur hexafluoride (SF₆) for use as an electrical insulating gas. The standard is intended for gas as purchased, but the test methods may be useful for evaluating in-service gas. All values are stated in SI units, and the standard does not address all safety concerns; users must establish appropriate practices.
⚙️ Sample Collection Methods
Sampling is critical for accurate analysis. Samples may be withdrawn from the vapor space or liquid phase. For liquid phase samples, ensure the cylinder valve is attached to a dip tube or invert the cylinder if not equipped. Vapor phase samples are suitable for routine testing, but the liquid phase is more representative of the overall composition.
| 🟦 Sample Type | 📐 Procedure | ⚡ Recommendation |
|---|---|---|
| Vapor Space | Direct sampling from vapor | Use for routine or preliminary tests |
| Liquid Phase | Dip tube or invert cylinder | Preferred for comprehensive analysis |
💡 Tip: If vapor phase analysis indicates impurities out of specification, obtain a liquid phase sample for confirmation. The liquid phase analysis governs when discrepancies exist between vapor and liquid results.
📊 Analytical Test Methods
Sulfur hexafluoride must conform to requirements prescribed in Table 1 of the standard. The following test methods are employed for key parameters:
| 🟦 Parameter | 📐 Test Method | ⚡ Details |
|---|---|---|
| Water Content | D2029 | Measurement of dew point |
| Hydrolyzable Fluorides | D2284 | Acidity expressed as HF |
| Air (Noncondensable Gases) | D2685 | Gas chromatography, expressed as nitrogen |
| Carbon Tetrafluoride | D2685 | Gas chromatography |
| Assay | By difference | After impurity content determined |
⚠️ Important: Test Method D2284 for acidity should not be used to evaluate total SF₆ decomposition or identify contaminant species. Use gas chromatography for that purpose.
❓ Frequently Asked Questions
🔍 Why is sampling from the liquid phase recommended?
The liquid phase comprises most of the material in the container and is more representative of the overall SF₆ composition.
💡 How are hydrolyzable fluorides determined?
Hydrolyzable fluorides are measured as acidity expressed as HF using Test Method D2284.
⚡ What does assay by difference mean?
The assay is calculated by subtracting all identified impurity percentages from 100%.
📌 Which test method is used for air and carbon tetrafluoride?
Both are analyzed via gas chromatography in accordance with Test Method D2685.