Standard Practice for Storage and Use of Liquefied Petroleum Gases (LPG) in Sample Cylinders for LPG Test Methods

SIGNIFICANCE AND USE
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.
Monitoring of ongoing precision and bias on QC materials using control chart techniques in accordance with Practice D 6299 can be used to establish the need for calibration or maintenance.
SCOPE
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 D 1265 and floating piston cylinders used in sampling method, Practice D 3700.
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 D 2163) or vapor pressure (Test Method D 6897) that use only a few mL per test, since relatively small portable Department of Transportation (DOT) cylinders (for example, 20 lb common barbecue cylinders) can be used. 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 D 1267) will require QC volumes in excess of 1000 L if stored in standard DOT cylinders or American Society of Mechanical Engineers (ASME) vessels.

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Publication Date
09-Dec-2002
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ASTM D6849-02 - Standard Practice for Storage and Use of Liquefied Petroleum Gases (LPG) in Sample Cylinders for LPG Test Methods
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Please
contact ASTM International (www.astm.org) for the latest information.
An American National Standard
Designation: D 6849 – 02
Standard Practice for
Storage and Use of Liquefied Petroleum Gases (LPG) in
Sample Cylinders for LPG Test Methods
This standard is issued under the fixed designation D 6849; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope leum Gases (LPG) (Expansion Method)
1.1 This practice covers information for the storage and use
3. Terminology
of LPG samples in standard cylinders of the type used in
3.1 Definitions of Terms Specific to This Standard:
sampling method, Practice D 1265 and floating piston cylin-
3.1.1 floating piston cylinder (FPC)—a high-pressure
ders used in sampling method, Practice D 3700.
sample container with a free floating internal piston(s) that
1.2 This practice is especially applicable when the LPG
effectively divides the container into two or more separate
sample is used as a quality control (QC) reference material for
compartments. The sample is contained on one side of the
LPG test methods, such as gas chromatography (GC) analysis
piston (the sample or product side). The chamber on the other
(Test Method D 2163) or vapor pressure (Test Method D 6897)
side of the piston (the charge or pre-charge side) is maintained
that use only a few mL per test, since relatively small portable
at a higher pressure than the vapor pressure of the sample with
Department of Transportation (DOT) cylinders (for example,
an inert gas. This allows collection of a sample with no loss of
20 lb common barbecue cylinders) can be used. This practice
volatile components and no formation of a gaseous phase that
can be applied to other test methods. However, test methods
may alter the composition of the sample. The cylinder is
that require a large amount of sample per test (for example,
equipped with a piston follower or indicating rod or other
manual vapor pressure Test Method D 1267) will require QC
indicating device to show the position of the floating piston.
volumes in excess of 1000 L if stored in standard DOT
3.1.2 standard 80 % fill cylinder—a pressure rated cylinder
cylinders or American Society of Mechanical Engineers
or vessel such as described in Practice D 1265, or conforming
(ASME) vessels.
to DOT or ASME cylinder standards. These cylinders are not
2. Referenced Documents equipped with a floating piston, and have both an equilibrium
liquid and vapor phase when used for LPG.
2.1 ASTM Standards:
D 1265 Practice for Sampling Liquefied Petroleum (LP)
4. Summary of Practice
Gases (Manual Method)
4.1 This practice provides information for the design and
D 1267 Test Method for Gage Vapor Pressure of Liquefied
2 operation of LPG sample storage cylinders taking into account
Petroleum (LP) Gases (LP-Gas Method)
properties of LPG and types of cylinders in common use for
D 2163 Test Method for Analysis of Liquefied Petroleum
storage of LPG.
(LP) Gases and Propane Concentrates by Gas Chromatog-
4.2 This practice provides additional guidelines to Practice
raphy
D 6299 to determine the minimum volume of LPG sample
D 3700 PracticeforContainingHydrocarbonFluidSamples
material required, when used as a QC reference material.
Using a Floating Piston Cylinder
D 6299 Practice for Applying Statistical Quality Assurance
5. Significance and Use
Techniques to Evaluate Analytical Measurement System
4 5.1 LPG samples can change composition during storage
Performance
and use from preferential vaporization of lighter (lower mo-
D 6897 Test Method for Vapor Pressure of Liquefied Petro-
lecular weight) hydrocarbon components, dissolved inert gases
(N , Ar, He, and so forth) and other dissolved gases/liquids
(NH ,CO ,H S, H O, etc.). Careful selection of cylinder type,
3 2 2 2
cylinder volume, and use of inert gas for pressurizing cylinders
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum
is required to ensure that composition changes are small
Products and Lubricants and is the direct responsibility of Subcommittee D02.08 on
enough to maintain the integrity of LPG when used as a QC
Volatility.
reference material for various LPG test methods.
Current edition approved Dec. 10, 2002. Published March 2003.
Annual Book of ASTM Standards, Vol 05.01.
Annual Book of ASTM Standards, Vol 05.02.
4 5
Annual Book of ASTM Standards, Vol 05.03. Annual Book of ASTM Standards, Vol 05.04.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Please
contact ASTM International (www.astm.org) for the latest information.
D6849–02
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
mustbecontrolledtoensurethatintheshortterm,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-
FIG. 1 Typical Floating Piston Cylinder (FPC) matelylinearatlowvaportoliquid(V/L)ratios.Thesechanges
accelerate and become more significant as the remaining
volume of liquid decreases and the cylinder approaches empty.
5.2 Monitoring of ongoing precision and bias on QC mate-
However, if the initial volume is sufficiently large, and the final
rials using control chart techniques in accordance with Practice
V/L ratio is limited, the change will occur very slowly over
D 6299 can be used to establish the need for calibration or
time,andthematerialisstillsuitableasaQC.Intheshortterm,
maintenance.
the composition is essentially constant relative to the precision
of the method.
6. Reference Materials
8.2.2 In the long run, the control limits can be periodically
adjusted to compensate for any long-term trend, or the charted
6.1 The LPG QC reference material should have a vapor
response can be compensated for the long-term trend using
pressure and composition in the range of the samples regularly
historical data, or equation of state calculations based on
tested by the equipment. This is particularly important for
cylinder weight or volume. Consult a statistician for appropri-
LPG/natural gas liquid (NGL) mixtures near the critical
ate techniques to develop a prediction model for the long-term
temperature, as these liquids have large thermal and pressure
trend.
expansion coefficients.
8.2.3 Operation between the 80 % and 20 % fill levels is
6.2 LPG QC reference materials should be stored in an
recommended to satisfy safety requirements and to limit the
environment suitable for long term storage without significant
V/L ratio from 0.25 (1:4) at 80 % liquid filled up to 4 (4:1) at
sample degradation for the test(s) being performed.
20 %filled.Thecylindermustb
...

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