【国外标准】 Standard Practice for Storage and Use of Liquefied Petroleum Gases (LPG) in Sample Cylinders for LPG Test Methods

5.1 LPG samples can change composition during storage and use from preferential vaporization of lighter (lower molecular weight) hydrocarbon components, dissolved inert gases (N2, Ar, He, and so forth) and other dissolved gases/liquids (NH3, CO2, H2S, H2O, etc.). Careful selection of cylinder type, cylinder volume, and use of inert gas for pressurizing cylinders is required to ensure that composition changes are small enough to maintain the integrity of LPG when used as a QC reference material for various LPG test methods.5.2 Monitoring of ongoing precision and bias on QC materials using control chart techniques in accordance with Practice D6299 can be used to establish the need for calibration or maintenance.1.1 This practice covers information for the storage and use of LPG samples in standard cylinders of the type used in sampling method, Practice D1265 and floating piston cylinders used in sampling method, Practice D3700.1.2 This practice is especially applicable when the LPG sample is used as a quality control (QC) reference material for LPG test methods, such as gas chromatography (GC) analysis (Test Method D2163) or vapor pressure (Test Method D6897) that use only a few mL per test, since relatively small portable Department of Transportation (DOT) cylinders (for example, 20 lb common barbecue cylinders, or common Mower/Forklift cylinders) can be used.1.2.1 Modification of the pressure relief (QCC1) valve on single access port cylinders may prohibit the collection or transport of cylinders outside of permitted facilities such as refineries, gas plants or pipeline stations. No modification is generally required for multi-port mower/forklift cylinders that have a separate access port for pressure relief and additional access ports for filling, liquid/vapor withdrawal or liquid level indication. Consult the Authority having Jurisdiction for detailed regional regulatory requirements for transport of LPG in pressurized cylinders.1.3 This practice can be applied to other test methods. However, test methods that require a large amount of sample per test (for example, manual vapor pressure Test Method D1267) will require QC volumes in excess of 1000 L if stored in standard DOT cylinders or American Society of Mechanical Engineers (ASME) vessels.1.3.1 Test methods for trace materials that may be sensitive to vessel surfaces (for example H2O, H2S/sulfur, or trace residues) could preferably use aluminum, stainless steel or internally coated vessels to minimize surface absorption/reaction or larger vessels to minimize surface/volume ratio.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.