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ASTM D6849-13(R2021) pdf free download

ASTM D6849-13(R2021) pdf free download.Standard Practice for Storage and Use of Liquefied Petroleum Gases (LPG) in Sample Cylinders for LPG Test Methods
3. Terminology
3.1 Definitions: 3.1.1 floating piston cylinder (FPC), n—high-pressure sample container with a free-floating internal piston that effectively divides the container into two separate compart- ments. Discussion—A floating piston cylinder is used to collect a sample of liquid under pressure without the formation of a gaseous phase which can result in changes in the composition of the liquid sample. 3.1.2 high-pressure sample cylinder, n—a container used for storage and transportation of a sample obtained at pressures above atmospheric pressure. Discussion—This type of sample cylinder, some- times called a ‘standard 80 % fill cylinder’, when used for LPG typically contains both liquid and vapor phase material. 3.1.3 liquefied petroleum gas, (LP Gas, LPG), n—a narrow boiling range mixture of hydrocarbons consisting of propane, propylene, butanes and butylenes, individually or in specified combinations, with limited amounts of other hydrocarbons and naturally occurring non-hydrocarbons. Discussion—LPG is typically maintained in a liquid state by containing it within a closed container or storage tank that can withstand the vapor pressure of the LPG at ambient temperature, or at a low temperature in refrigerated storage. 3.1.4 maximum fill volume (reduced fill volume), n—the volume ofa container that may be safely occupied by the liquid sample, usually expressed as a percentage of the total capacity. Discussion—Some regulatory agencies use the ex- pressions ‘maximum fill density’ and ‘reduced fill density.’
6. Reference Materials
6.1 The LPG QC reference material should have a vapor pressure and composition in the range of the samples regularly tested by the equipment. This is particularly important for LPG/natural gas liquid (NGL) mixtures near the critical temperature, as these liquids have large thermal and pressure expansion coefficients. 6.2 LPG QC reference materials should be stored in an environment suitable for long term storage without significant sample degradation for the test(s) being performed. N OTE 1—As an example, evidence of a long term shift or bias in the LPG QC reference material results obtained relative to the established statistical control limits and average value determined for the test initially, may indicate that the composition of the LPG QC reference material has significantly degraded or changed over time. An investigation should be conducted to determine if the long term stability of the QC reference material is the cause for the out-of-control situation.
7. Use of Floating Piston Cylinders for LPG Samples
7.1 Minimum LPG sample volume can be determined in accordance with Practice D6299. N OTE 2—Estimating the minimum LPG sample volume needed in- cludes such things as the sample volume needed to conduct the appropri- ate test(s) and the number of analytical measurements that are expected to be made over the intended period of use. 7.2 Floating piston cylinders (see Fig. 1) are preferred for LPG sample materials for tests involving accurate determina- tion of light gases. 7.3 Excessive inert gas pressure should be avoided for long term storage of vapor pressure QC or calibrant materials in floating piston cylinders. Leakage of inert gas past worn or damaged floating piston seals can cause an increase in dis- solved gas concentration and vapor pressure of the QC sample material.
8. Use of Standard 80 % Fill Cylinders for LPG QC Materials
8.1 Common 80 % filled storage tanks or cylinders can be used for LPG QC materials provided that the QC material batch volume is sufficiently large to avoid adverse short term vaporization effects. 8.2 The total initial volume and the minimum unused volume of QC materials stored in standard 80 % fill cylinders must be controlled to ensure that in the short term, composition is constant relative to the precision of the test method. 8.2.1 As liquid is withdrawn from LPG cylinders, a small amount of the remaining liquid must vaporize to replace the volume. This results in a small, but predictable, change in composition and vapor pressure from preferential vaporization of lighter components from the remaining liquid. The compo- sition and vapor pressure changes are known to be approxi- mately linear at low vapor to liquid (V/L) ratios. These changes accelerate and become more significant as the remaining volume of liquid decreases and the cylinder approaches empty. However, ifthe initial volume is sufficiently large, and the final V/L ratio is limited, the change will occur very slowly over time, and the material is still suitable as a QC. In the short term, the composition is essentially constant relative to the precision of the method.

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