1、Designation: D 6849 02An American National StandardStandard Practice forStorage and Use of Liquefied Petroleum Gases (LPG) inSample Cylinders for LPG Test Methods1This standard is issued under the fixed designation D 6849; the number immediately following the designation indicates the year oforigina
2、l adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers information for the storage and useof LPG sa
3、mples in standard cylinders of the type used insampling method, Practice D 1265 and floating piston cylin-ders used in sampling method, Practice D 3700.1.2 This practice is especially applicable when the LPGsample is used as a quality control (QC) reference material forLPG test methods, such as gas
4、chromatography (GC) analysis(Test Method D 2163) or vapor pressure (Test Method D 6897)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 met
5、hods. However, test methodsthat require a large amount of sample per test (for example,manual vapor pressure Test Method D 1267) 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 Sta
6、ndards:D 1265 Practice for Sampling Liquefied Petroleum (LP)Gases (Manual Method)2D 1267 Test Method for Gage Vapor Pressure of LiquefiedPetroleum (LP) Gases (LP-Gas Method)2D 2163 Test Method for Analysis of Liquefied Petroleum(LP) Gases and Propane Concentrates by Gas Chromatog-raphy2D 3700 Practi
7、ce for Containing Hydrocarbon Fluid SamplesUsing a Floating Piston Cylinder3D 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformance4D 6897 Test Method for Vapor Pressure of Liquefied Petro-leum Gases (LPG) (Expansion Method)53. Termin
8、ology3.1 Definitions of Terms Specific to This Standard:3.1.1 floating piston cylinder (FPC)a high-pressuresample container with a free floating internal piston(s) thateffectively divides the container into two or more separatecompartments. The sample is contained on one side of thepiston (the sampl
9、e or product side). The chamber on the otherside of the piston (the charge or pre-charge side) is maintainedat a higher pressure than the vapor pressure of the sample withan inert gas. This allows collection of a sample with no loss ofvolatile components and no formation of a gaseous phase thatmay a
10、lter the composition of the sample. The cylinder isequipped with a piston follower or indicating rod or otherindicating device to show the position of the floating piston.3.1.2 standard 80 % fill cylindera pressure rated cylinderor vessel such as described in Practice D 1265, or conformingto DOT or
11、ASME cylinder standards. These cylinders are notequipped with a floating piston, and have both an equilibriumliquid and vapor phase when used for LPG.4. Summary of Practice4.1 This practice provides information for the design andoperation of LPG sample storage cylinders taking into accountproperties
12、 of LPG and types of cylinders in common use forstorage of LPG.4.2 This practice provides additional guidelines to PracticeD 6299 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
13、storageand use from 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 pressuriz
14、ing cylindersis required to ensure that composition changes are smallenough to maintain the integrity of LPG when used as a QCreference material for various LPG test methods.1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsib
15、ility of Subcommittee D02.08 onVolatility.Current edition approved Dec. 10, 2002. Published March 2003.2Annual Book of ASTM Standards, Vol 05.01.3Annual Book of ASTM Standards, Vol 05.02.4Annual Book of ASTM Standards, Vol 05.03.5Annual Book of ASTM Standards, Vol 05.04.1Copyright ASTM International
16、, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 Monitoring of ongoing precision and bias on QC mate-rials using control chart techniques in accordance with PracticeD 6299 can be used to establish the need for calibration ormaintenance.6. Reference Materials6
17、.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 criticaltemperature, as these liquids have large thermal and pressureexpansion c
18、oefficients.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 bias in theLPG QC reference material results obtained relative to th
19、e 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 beconducted to determine if the long term stability of the QC referen
20、cematerial 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 D 6299.NOTE 2Estimating the minimum LPG sample volume needed in-cludes such things as the sample volume needed to con
21、duct 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 accurate determina-tion of light gases.7.3 Excessive inert gas pres
22、sure 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 concentration and vapor pressure of the QC samplematerial.8. Use of Standard 80
23、% 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.8.2 The total initial volume and the minimum unusedvolume of QC materi
24、als 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 remaining liquid must vaporize to replace thevolume. This results i
25、n 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 low vapor to liquid (V/L) ratios. These changesaccelerate and become
26、 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 the material is still suitable as a QC. In the short term,the compos
27、ition 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-term trend usinghistorical data, or equation of state calculations
28、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 requirements and to limit theV/L ratio from 0.25 (1:4) at 80 % liquid fille
29、d 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 inconcentration of the remaining QC liquid as would occur withthe exponentially increasing vapor/liquid
30、 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 linear regression of the first 20valid QC results against the observation number and by testingthe slope for significance
31、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 chart detects a trend. The total number of QCruns cumulated will then constitute the maximum useful runsfor the QC batch
32、volume.FIG. 1 Typical Floating Piston Cylinder (FPC)D6849022NOTE 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 DOT approved cylinders (usedfor home barbecues and mobile applications
33、) 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 by inverting the cylinder andventing liquid using the procedure in Pr
34、actice D 1265 (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 working temperature or pres-sure of the storage cylinder.) (WarningUse
35、 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 X1). Some GC testmethods require specific injection conditions, for
36、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, as this will affect the result.8.5 Other vapor tight means of gene
37、rating 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 control (QC); standard80% fill cylinderAPPENDIX(Nonmandatory Information)
38、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 results.X1.2 Pressurizing a common 20 lb DOT cylinder to themaximum work
39、ing 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 temperature or decrease in pressure in sample lines orinstrument tes
40、t 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 erratic injection volumes. Flushing the valve severaltimes prior to inj
41、ection 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 LPG samples at about 5 to 8C (10 to 15F) aboveambient temperature to
42、 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 equilibrates with both the liquid and vapor phases,becoming partially dissolve
43、d 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 compensate for excessive vaporiza-tion of the liquid sample. The same
44、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 pressurizea standard (non-floating piston) cylinder.X1.5 Helium is the preferred inert gas for t
45、hermal 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, and it may interfere withthe analysis. Nitrogen is not detected and may be used in flameionization detector (FID) methods,
46、 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 volatility “K” ratio). Heavier inertgases are not recommended.FIG. 2 Typical Standard 80 % Fill LPG CylinderD6849023ASTM Interna
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