1、Designation: D 6849 02 (Reapproved 2007)An 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
2、the year oforiginal 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 storag
3、e and useof LPG samples 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 met
4、hods, such as gas 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
5、 to other test methods. 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 Doc
6、uments2.1 ASTM Standards:2D 1265 Practice for Sampling Liquefied Petroleum (LP)Gases, Manual MethodD 1267 Test Method for Gage Vapor Pressure of LiquefiedPetroleum (LP) Gases (LP-Gas Method)D 2163 Test Method for Determination of Hydrocarbons inLiquefied Petroleum (LP) Gases and Propane/PropeneMixtu
7、res by Gas ChromatographyD 3700 Practice for Obtaining LPG Samples Using a Float-ing Piston CylinderD 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformanceD 6897 Test Method for Vapor Pressure of Liquefied Petro-leum Gases (LPG) (Expa
8、nsion Method)3. Terminology3.1 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 o
9、f thepiston (the sample 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 g
10、aseous phase thatmay alter 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, o
11、r conformingto DOT or 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
12、into accountproperties 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 chan
13、ge composition during 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 i
14、nert gas for pressurizing cylinders1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibility of Subcommittee D02.08 onVolatility.Current edition approved Dec. 1, 2007. Published January 2008. Originallyapproved in 2002. Last p
15、revious edition approved in 2002 as D 684902.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM
16、International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.is 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.5.2 Monitoring of ongoing precision and
17、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 Materials6.1 The LPG QC reference material should have a vaporpressure and composition in the range of the samples regularlytested by th
18、e equipment. This is particularly important forLPG/natural gas liquid (NGL) mixtures near the criticaltemperature, 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 significan
19、tsample 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 the establishedstatistical control limits and average value determined for the test initially,may indicate that the composition
20、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 referencematerial is the cause for the out-of-control situation.7. Use of Floating Piston Cylinders for LPG Samples7.1 Minimum LPG sa
21、mple 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 conduct the appropri-ate test(s) and the number of analytical measurements that are expected tobe made over the intended period o
22、f 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 pressure should be avoided for longterm storage of vapor pressure QC or calibrant materials infloating piston cylinders. Leakage o
23、f 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 % Fill Cylinders for LPG QCMaterials8.1 Common 80 % filled storage tanks or cylinders can beused for LPG QC materials provided
24、 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 materials stored in standard 80 % fill cylindersmust be controlled to ensure that in the short term, compositionis constant relative
25、 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 in a small, but predictable, change incomposition and vapor pressure from preferential vaporizationof lighter components from t
26、he 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 more significant as the remainingvolume of liquid decreases and the cylinder approaches empty.However, if the initial volume
27、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 composition is essentially constant relative to the precisionof the method.8.2.2 In the long run, the control limits can be periodic
28、allyadjusted 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 based oncylinder weight or volume. Consult a statistician for appropri-ate techniques to develop a prediction model for the lo
29、ng-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 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 l
30、iquid can bewithdrawn (see 8.2). This guards against excessive changes inconcentration 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
31、 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 versus zero. Upon a non-significantoutcome, continue to perform this regression after every tenadditional results until either
32、 the slope fails the significance testFIG. 1 Typical Floating Piston Cylinder (FPC)D 6849 02 (2007)2or the control 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 resul
33、ts 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) equipped with a20 % liquid level dip tube have been found to be suitable forlaboratory GC or instrument vapor press
34、ure (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 Practice D 1265 (see Fig.2).8.4 Pressurizing a standard 80 % fill cylinder with an inertgas will result in the inert ga
35、s 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 re-settablepressure relief valves and not burst disks for laboratory use.)8.4.1 Common 80 % filled LPG storage cylin
36、ders may bepressurized to facilitate liquid transfer and repeatable liquidinjections for GC analysis (see Appendix 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 s
37、torage 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 generating sufficienttransfer/injection pressure are acceptable, such as magneticallycoupled or other sealed cavity pumps
38、.9. Keywords9.1 floating piston cylinder; liquefied petroleum gas (LPG);LPG sample storage cylinders; quality control (QC); standard80% fill cylinderAPPENDIX(Nonmandatory Information)X1. INERT GAS PRESSURIZATION WITH STANDARD 80 % FILL CYLINDERSX1.1 Pressurizing a standard 80 % fill cylinder with an
39、 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 working pressure of 240 psig will result in approxi-mately 2 mole % nitrogen in the liquid propane, and about50/50 molar
40、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 test cells can still result in formation of vapor.X1.3 Liquid sample (inject) valves (LSV) are generallyslightly above a
41、mbient temperature due to proximity to theinstrument, and this can cause localized vaporization in thevalve and erratic injection volumes. Flushing the valve severaltimes prior to injection provides some local cooling, and itprovides for more repeatable liquid injections. In general, theLSV should b
42、e 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 obtain repeatable liquid injections.X1.4 Use of higher inert gas pressures than required toobtain repeatable liquid
43、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 dissolved in the liquid. The increase in thetotal pressure due to inert gas does NOT cause the volatilehydrocarbons to conden
44、se 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 errors will be incurred fromexcessive vapor formation with or without addition of inert gasto the cylinder. The same
45、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 thermal conduc-tivity detector instruments, since it is used as the carrier gas inthe GC and will not be detected. Nit
46、rogen 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, but it may not give asrepeatable results as helium at high LSV temperatures due toFIG. 2 Typical Standard 80 % Fill
47、LPG CylinderD 6849 02 (2007)3higher dissolved nitrogen concentration at the same pressure(lower vapor/liquid relative volatility “K” ratio). Heavier inertgases are not recommended.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item m
48、entionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committ
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