1、Designation: D6849 13Standard Practice forStorage and Use of Liquefied Petroleum Gases (LPG) inSample Cylinders for LPG Test Methods1This standard is issued under the fixed designation D6849; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers information for the storage and useof LPG samples in standard cylinders of
3、the type used insampling method, Practice D1265 and floating piston cylindersused in sampling method, Practice D3700.1.2 This practice is especially applicable when the LPGsample is used as a quality control (QC) reference material forLPG test methods, such as gas chromatography (GC) analysis(Test M
4、ethod D2163) or vapor pressure (Test Method D6897)that use only a few mL per test, since relatively small portableDepartment of Transportation (DOT) cylinders (for example,20 lb common barbecue cylinders) can be used. This practicecan be applied to other test methods. However, test methodsthat requi
5、re a large amount of sample per test (for example,manual vapor pressure Test Method D1267) will require QCvolumes in excess of 1000 L if stored in standard DOTcylinders or American Society of Mechanical Engineers(ASME) vessels.2. Referenced Documents2.1 ASTM Standards:2D1265 Practice for Sampling Li
6、quefied Petroleum (LP)Gases, Manual MethodD1267 Test Method for Gage Vapor Pressure of LiquefiedPetroleum (LP) Gases (LP-Gas Method)D2163 Test Method for Analysis of Liquefied Petroleum(LP) Gases and Propene Concentrates by Gas Chromatog-raphyD3700 Practice for Obtaining LPG Samples Using a Float-in
7、g Piston CylinderD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System PerformanceD6897 Test Method for Vapor Pressure of Liquefied Petro-leum Gases (LPG) (Expansion Method)3. Terminology3.1 Definitions:3.1.1 floating piston
8、 cylinder (FPC), nhigh-pressuresample container with a free-floating internal piston thateffectively divides the container into two separate compart-ments.3.1.1.1 DiscussionA floating piston cylinder is used tocollect a sample of liquid under pressure without the formationof a gaseous phase which ca
9、n result in changes in thecomposition of the liquid sample.3.1.2 high-pressure sample cylinder, na container used forstorage and transportation of a sample obtained at pressuresabove atmospheric pressure.3.1.2.1 DiscussionThis type of sample cylinder, some-times called a standard 80 % fill cylinder,
10、 when used for LPGtypically contains both liquid and vapor phase material.3.1.3 liquefied petroleum gas, (LP Gas, LPG), na narrowboiling range mixture of hydrocarbons consisting of propane,propylene, butanes and butylenes, individually or in specifiedcombinations, with limited amounts of other hydro
11、carbons andnaturally occurring non-hydrocarbons.3.1.3.1 DiscussionLPG is typically maintained in a liquidstate by containing it within a closed container or storage tankthat can withstand the vapor pressure of the LPG at ambienttemperature, or at a low temperature in refrigerated storage.3.1.4 maxim
12、um fill volume (reduced fill volume), nthevolume of a container that may be safely occupied by the liquidsample, usually expressed as a percentage of the total capacity.3.1.4.1 DiscussionSome regulatory agencies use the ex-pressions maximum fill density and reduced fill density.4. Summary of Practic
13、e4.1 This practice provides information for the design andoperation of LPG sample storage cylinders taking into accountproperties of LPG and types of cylinders in common use forstorage of LPG.1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is th
14、e direct responsibility of Subcommittee D02.08 onVolatility.Current edition approved June 15, 2013. Published July 2013. Originallyapproved in 2002. Last previous edition approved in 2012 as D684902 (2012).DOI: 10.1520/D6849-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, or
15、contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, We
16、st Conshohocken, PA 19428-2959. United States14.2 This practice provides additional guidelines to PracticeD6299 to determine the minimum volume of LPG samplematerial required, when used as a QC reference material.5. Significance and Use5.1 LPG samples can change composition during storageand use fro
17、m preferential vaporization of lighter (lower mo-lecular 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 cylindersis re
18、quired to ensure that composition changes are smallenough to maintain the integrity of LPG when used as a QCreference material for various LPG test methods.5.2 Monitoring of ongoing precision and bias on QC mate-rials using control chart techniques in accordance with PracticeD6299 can be used to est
19、ablish the need for calibration ormaintenance.6. Reference Materials6.1 The LPG QC reference material should have a vaporpressure and composition in the range of the samples regularlytested by the equipment. This is particularly important forLPG/natural gas liquid (NGL) mixtures near the criticaltem
20、perature, as these liquids have large thermal and pressureexpansion coefficients.6.2 LPG QC reference materials should be stored in anenvironment suitable for long term storage without significantsample degradation for the test(s) being performed.NOTE 1As an example, evidence of a long term shift or
21、 bias in theLPG QC reference material results obtained relative to the establishedstatistical control limits and average value determined for the test initially,may indicate that the composition of the LPG QC reference material hassignificantly degraded or changed over time. An investigation should
22、beconducted to determine if the long term stability of the QC referencematerial is the cause for the out-of-control situation.7. Use of Floating Piston Cylinders for LPG Samples7.1 Minimum LPG sample volume can be determined inaccordance with Practice D6299.NOTE 2Estimating the minimum LPG sample vo
23、lume 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 tobe made over the intended period of use.7.2 Floating piston cylinders (see Fig. 1) are preferred forLPG sample materials for tests involving
24、 accurate determina-tion of light gases.7.3 Excessive inert gas pressure should be avoided for longterm storage of vapor pressure QC or calibrant materials infloating piston cylinders. Leakage of inert gas past worn ordamaged floating piston seals can cause an increase in dis-solved gas concentratio
25、n and vapor pressure of the QC samplematerial.8. Use of Standard 80 % Fill Cylinders for LPG QCMaterials8.1 Common 80 % filled storage tanks or cylinders can beused for LPG QC materials provided that the QC materialbatch volume is sufficiently large to avoid adverse short termvaporization effects.8.
26、2 The total initial volume and the minimum unusedvolume of QC materials stored in standard 80 % fill cylindersmust be controlled to ensure that in the short term, compositionis constant relative to the precision of the test method.8.2.1 As liquid is withdrawn from LPG cylinders, a smallamount of the
27、 remaining liquid must vaporize to replace thevolume. This results in a small, but predictable, change incomposition and vapor pressure from preferential vaporizationof lighter components from the remaining liquid. The compo-sition and vapor pressure changes are known to be approxi-mately linear at
28、low vapor to liquid (V/L) ratios. These changesaccelerate and become more significant as the remainingvolume of liquid decreases and the cylinder approaches empty.However, if the initial volume is sufficiently large, and the finalV/L ratio is limited, the change will occur very slowly overtime, and
29、the material is still suitable as a QC. In the short term,the composition is essentially constant relative to the precisionof the method.8.2.2 In the long run, the control limits can be periodicallyadjusted to compensate for any long-term trend, or the chartedresponse can be compensated for the long
30、-term trend usinghistorical data, or equation of state calculations based oncylinder weight or volume. Consult a statistician for appropri-ate techniques to develop a prediction model for the long-termtrend.8.2.3 Operation between the 80 % and 20 % fill levels isrecommended to satisfy safety require
31、ments and to limit theV/L ratio from 0.25 (1:4) at 80 % liquid filled up to 4 (4:1) at20 % filled. The cylinder must be re-filled when the liquid leveldrops below the 20 % level and no further liquid can bewithdrawn (see 8.2). This guards against excessive changes inFIG. 1 Typical Floating Piston Cy
32、linder (FPC)D6849 132concentration of the remaining QC liquid as would occur withthe exponentially increasing vapor/liquid ratio as the liquidvolume approaches zero.8.2.4 The minimum initial QC volume and the maximumnumber of usable QC runs for the batch volume can beassessed by performing a simple
33、linear regression of the first 20valid QC results against the observation number and by testingthe slope for significance versus zero. Upon a non-significantoutcome, continue to perform this regression after every tenadditional results until either the slope fails the significance testor the control
34、 chart detects a trend. The total number of QCruns cumulated will then constitute the maximum useful runsfor the QC batch volume.NOTE 3This methodology requires the time between QC results to belong enough such that the long term variation of the test method isobservable.8.3 Common 20 lb or larger D
35、OT approved cylinders (usedfor home barbecues and mobile applications) equipped with a20 % liquid level dip tube have been found to be suitable forlaboratory GC or instrument vapor pressure (VP) applicationsthat use less than 15 mL per test. The dip tube can be used toestablish the 80 % liquid fill
36、by inverting the cylinder andventing liquid using the procedure in Practice D1265 (see Fig.2).8.4 Pressurizing a standard 80 % fill cylinder with an inertgas will result in the inert gas becoming partially soluble in theLPG QC material, which can affect some test results.(WarningDo not exceed the wo
37、rking temperature or pres-sure of the storage cylinder.) (WarningUse re-settablepressure relief valves and not burst disks for laboratory use.)8.4.1 Common 80 % filled LPG storage cylinders may bepressurized to facilitate liquid transfer and repeatable liquidinjections for GC analysis (see Appendix
38、X1). Some GC testmethods require specific injection conditions, for exampleminimum 200 psi above sample vapor pressure, to ensurerepeatable liquid injections.8.4.2 Common 80 % fill QC storage cylinders must not bepressurized with inert gas to facilitate liquid transfer for vaporpressure measurements
39、, as this will affect the result.8.5 Other vapor tight means of generating sufficienttransfer/injection pressure are acceptable, such as magneticallycoupled or other sealed cavity pumps.9. Keywords9.1 floating piston cylinder; liquefied petroleum gas (LPG);LPG sample storage cylinders; quality contr
40、ol (QC); standard80% fill cylinderAPPENDIX(Nonmandatory Information)X1. INERT GAS PRESSURIZATION WITH STANDARD 80 % FILL CYLINDERSX1.1 Pressurizing a standard 80 % fill cylinder with an inertgas will result in the inert gas becoming partially soluble in theLPG sample, which can affect some test resu
41、lts.X1.2 Pressurizing a common 20 lb DOT cylinder to themaximum working pressure of 240 psig will result in approxi-mately 2 mole % nitrogen in the liquid propane, and about50/50 molar ratio of nitrogen and propane in the equilibriumvapor. The mixture is still at its bubble point, so any increasein
42、temperature or decrease in pressure in sample lines orinstrument test cells can still result in formation of vapor.X1.3 Liquid sample (inject) valves (LSV) are generallyslightly above ambient temperature due to proximity to theinstrument, and this can cause localized vaporization in thevalve and err
43、atic injection volumes. Flushing the valve severaltimes prior to injection provides some local cooling, and itprovides for more repeatable liquid injections. In general, theLSV should be kept as close to ambient temperature aspractical. This allows the use of lower inert gas pressures orstoring the
44、LPG samples at about 5 to 8C (10 to 15F) aboveambient temperature to obtain repeatable liquid injections.X1.4 Use of higher inert gas pressures than required toobtain repeatable liquid injections does not limit or controlvapor losses in a standard cylinder. Inert gas in a standardcylinder equilibrat
45、es with both the liquid and vapor phases,becoming partially dissolved in the liquid. The increase in thetotal pressure due to inert gas does NOT cause the volatilehydrocarbons to condense or otherwise knock down thehydrocarbon vapor (this is a common misconception). Highinert gas pressures cannot co
46、mpensate for excessive vaporiza-tion of the liquid sample. The same errors will be incurred fromexcessive vapor formation with or without addition of inert gasto the cylinder. The same precautions must be taken to limitvapor losses with or without the use of inert gas to pressurizeFIG. 2 Typical Sta
47、ndard 80 % Fill LPG CylinderD6849 133a standard (non-floating piston) cylinder.X1.5 Helium is the preferred inert gas for thermal conduc-tivity detector instruments, since it is used as the carrier gas inthe GC and will not be detected. Nitrogen will be detected ina thermoconductivity (TC) detector,
48、 and it may interfere withthe analysis. Nitrogen is not detected and may be used in flameionization detector (FID) methods, but it may not give asrepeatable results as helium at high LSV temperatures due tohigher dissolved nitrogen concentration at the same pressure(lower vapor/liquid relative volat
49、ility “K” ratio). Heavier inertgases are not recommended.SUMMARY OF CHANGESSubcommittee D02.08 has identified the location of selected changes to this standard since the last issue(D6849 02 (2012) that may impact the use of this standard.(1) Section 3, Terminology, has been totally revised.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infri
