1、Designation: D 3700 07An American National StandardStandard Practice forObtaining LPG Samples Using a Floating Piston Cylinder1This standard is issued under the fixed designation D 3700; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, 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. Scope*1.1 This practice covers the equipment and procedures forobtaining a representative sample of specificat
3、ion liquefiedpetroleum gas (LPG), such as specified in SpecificationD 1835, GPA 2140, and comparable international standards. Itmay also be used for other natural gas liquid (NGL) productsthat are normally single phase (NGL mix, field butane, and soforth), defined in other industry specifications or
4、 contractualagreements.1.2 This practice is not intended for non-specification prod-ucts that contain significant quantities of undissolved gases(N2,CO2), free water or other separated phases, such as raw orunprocessed gas/liquids mixtures and related materials. Thesame equipment can be used for the
5、se purposes, but additionalprecautions are generally needed to obtain representativesamples of multi-phase products (see Appendix X1).1.3 This practice includes recommendations for the locationof a sample point in a line or vessel. It is the responsibility ofthe user to ensure that the sampling poin
6、t is located so as toobtain a representative sample.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsi
7、bility of the user of this standard to establish appro-priate safety and health practices, and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1265 Practice for Sampling Liquefied Petroleum (LP)Gases, Manual MethodD 1835 Specification
8、for Liquefied Petroleum (LP) Gases2.2 GPA Standards:3GPA 2174 Obtaining Liquid Hydrocarbon Samples forAnalysis by Gas ChromatographyGPA 2140 Liquefied Petroleum Gas Specifications and TestMethods3. Terminology3.1 Definitions:3.1.1 floating piston cylinder (FPC)a high pressuresample container, with a
9、 free floating internal piston thateffectively divides the container into two separate compart-ments.3.1.2 maximum fill density (reduced fill density)the vol-ume of a container occupied by the sample, usually expressedas a percentage of the total capacity.4. Summary of Practice4.1 A liquid LPG sampl
10、e is transferred under pressure froma sample point to a floating piston cylinder. The floating pistoncylinder (FPC) is designed to collect liquid samples with novaporization by displacing a piston against a pressurizing fluid(usually an inert gas). The piston serves as a physical barrierbetween the
11、sample and the pressurizing fluid, at the samplingpressure. The position of the piston at the end of samplingindicates the percent fill of the sample cylinder.4.2 It is the responsibility of the user of this practice tolocate the sample point at a suitable location where the productbeing sampled is
12、a representative, single phase, homogeneousliquid.5. Significance and Use5.1 This practice allows the collection of a representativesample of LPG that may contain trace volatile componentssuch as methane, nitrogen, and ethane. Sampling by PracticeD 1265 may result in a small, but predictable loss of
13、 theselighter components. Practice D 1265 is suitable for collectingsamples for routine specification testing, as the small loss oflight components is not significant under Specification D 1835specification requirements. Practice D 3700 is recommendedwhenever highly accurate determination of light c
14、omponents is1This practice is under the jurisdiction of ASTM Committee D02 on PetroleumProducts and Lubricants and is the direct responsibility of Subcommittee D02.H0 onLiquefied Petroleum Gas.Current edition approved Feb. 15, 2007. Published March 2007. Originallyapproved in 1978. Last previous edi
15、tion approved in 2001 as D 370001.2For 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.3Available from Gas Process
16、ors Association (GPA), 6526 E. 60th St., Tulsa, OK74145.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.required. For example, composition determined on samplescollect
17、ed according to Practice D 3700 may be used to estab-lish product value of NGL mixtures (see Appendix X1).6. Interferences6.1 An interference in a sampling procedure is anythingwhich compromises the integrity of the sample.6.2 Sample point location can give a non-representativesample due to solid or
18、 liquid contaminants, two phases, storagetank stratification, and so forth.6.3 Reactivity of steel surfaces can remove or chemicallyalter trace reactive components such as H2S, COS, andmercaptan.6.4 A lubricant that is soluble in LPG can contaminate thesample.6.5 Pre-charge gas can leak into the sam
19、ple due to worn ordamaged seals or poor surface finish (see 8.1).6.5.1 Consult manufacturers guidelines for suitable proce-dure to verify a leak-free cylinder, such as pressure testing eachside of the cylinder. It is also possible to analyze the sample forinert gas, or the inert gas for hydrocarbon,
20、 to detect leakage ineither direction.6.6 Failure to flush sample lines and dead volumes canresult in contaminants in samples.6.7 Sampling from stratified tanks, dead zones in flowingsystems, or inappropriate time periods in composite samplingsystems will result in non-representative samples.7. Appa
21、ratus7.1 Floating Piston Cylinder (FPC):7.1.1 Construction, typically fabricated from corrosion re-sistant 316 stainless steel, in accordance with the pressurevessel certification requirements in the jurisdictions in which itis to be used, and through which it will be transported.Protective internal
22、 coatings or surface treatments are accept-able provided that they do not adversely affect the freemovement of the piston, or effectiveness of the seals (see Fig.1).NOTE 1At present, there is no international approval process forpressure cylinders. Cylinders require appropriate approval in each juri
23、s-diction in which they are used or transported.7.1.2 Volume of Sample, as required by the tests to beperformed, typically 400 mL (that is, 80 % of 500 mL samplecylinder at 15C).NOTE 2For safe handling of these cylinders under extremes ofproduct or ambient temperatures, or both, the user must consid
24、er theeffects of thermal expansion on the volume of product in the cylinder. Forexample, if a very cold product is sampled, 40C (40F) for example,the cylinder should be expected to warm considerably before analysis isperformed during transport and in the laboratory. During summer months,the temperat
25、ure of the cylinder and product could reasonably be expectedto rise to as high as 46C (115F) in hot environments. A cylinder initiallyfilled to 80 % of its capacity will be over-pressured and the relief device(s)will activate under these conditions. Releases of this type are unexpectedand dangerous.
26、 In such an extreme, but not uncommon case, the cylindershould not be filled more than approximately 60 % during the initial fill.Users should reviewASTM/GPAvolume correction factor calculations, ordata, or both, to determine the maximum fill for the product beingsampled, but should always leave at
27、least 10 % vapor space after allowingfor the worst likely case of thermal expansion.NOTE 3It is recommended that users work with the manufacturer ofthese sample cylinders and sample collection systems any time ambient orproduct temperatures, or both, exceed the range of 29C (20F) to 60C(140F). The c
28、onsideration of extreme temperatures shall consider effectson metal, O-rings, valve seats, seals, gauges, relief devices, sample pumpcomponents and other devices and components in the system.7.1.3 Piston Position IndicatorThe FPC shall beequipped with a piston position indicator such as a magneticfo
29、llower, piston rod, or equivalent which can be used toindicate the sample volume to comply with the maximumpercent fill (maximum fill density) allowed for storage andtransportation.7.1.3.1 Floating piston cylinders that are not equipped witha piston position indicator shall not be used without a pro
30、ce-dure to allow the operator to verify fill density immediatelyafter sampling prior to transport. Consult the authority havingjurisdiction for acceptable procedures.7.1.4 The cylinder shall include a mechanism to mix thesample in the sample chamber in case of stratified mixtures orwater haze that m
31、ay settle after sampling. This mechanism maybe a mechanical mixer/vortex plate on a movable rod, a freelymoving rolling ball or slider, magnetically coupled stirrer, orsimilar device. It is the responsibility of the user to providesufficient mixing with the mechanism used to allow a repre-sentative
32、sample to be withdrawn.7.2 Lubricants used to lubricate or seal the floating piston, Oring seals, and other components shall be inert to LPG.NOTE 4DuPont Krytox AC or AD4have been found to be suitable.7.3 A safety relief device is required to prevent over-pressure in the event that a cylinder become
33、s fully liquid filled(hydraulically locked) from either overfilling or liquid thermalexpansion from excessive temperature increase.7.3.1 A rupture disk or a self-resetting pressure relief valveshall be fitted to the cylinder to prevent overpressure fromhydraulic filling due to temperature increase.N
34、OTE 5DuPont KEL-F,4or similar materials have been found to besuitable. Polytetrafluoroethylene (PTFE) or other materials that are proneto creep under pressure, and metal-to-metal valve seals are not recom-mended.7.3.2 Users may not alter valves or safety relief devices thatare part of a cylinder per
35、mit or exemption. (The USA has anexemption system and Canada has a permitting procedure fornon-ASME or DOT cylinders.)7.4 Sampling SystemIt is not possible to provide a singleprocedure that will be applicable for all sampling situations.Different procedures and sampling equipment may be requiredfor
36、sampling pipes, storage tanks, rail cars, trucks, and smallerstorage vessels in order to obtain a representative sample (see4.2).7.4.1 Sample equipment and procedures shall be designedand used to obtain representative samples of a product, and tomaintain sample integrity for the tests being performe
37、d. Atypical sampling system for LPG flowing in a pipe is shown inFig. 2.4Registered trademarks of E. I. du Pont de Nemours and Company, Wilmington,DE.D3700072NOTE 6While not required by this practice, the use of a sample probein a flowing line is recommended. The sample probe should be located onthe
38、 top or side of a line, extending into the center third of the flowingstream. Sample points should not be installed on the bottom of a line,unless provisions are made to flush any accumulated debris from thesample point immediately prior to sampling.7.4.2 Transfer lines, valves, pressure gages and s
39、o forth inthe transfer system shall be corrosion resistant and designedconsistent with maximum anticipated pressure (typically stain-less steel). Experience has shown that the transfer lines shouldhave a minimum internal diameter of 3 mm nominal (18 in.)and be as short as practical to minimize line
40、blockage orsample vaporization, or both. The use of filters, dryers, needlevalves and so forth are not recommended, unless provisions aremade to prevent excessive flow restriction and pressure drop.AT junction with a purge valve at the sample connection point isrecommended to allow purging of the de
41、ad volume at thesampler connection. Flexible hose or tubing with adequatepressure rating may be used.FIG. 1 Typical Floating Piston CylindersD3700073NOTE 7While not required by this practice, the use of non-reactiveand non-absorptive materials is recommended, especially when samplingto determine tra
42、ce levels of reactive or polar materials such as H2S andwater.7.4.3 Other piping arrangements may be acceptable, butmay require different flushing procedures prior to samplecollection. Typical sample loops are shown in Figs. 3 and 4.7.4.4 Closed loop side stream samplers designed to mini-mize volati
43、le light end losses during sampling may be used.The sample system shall be connected to on-line analysers orcomposite samplers in a manner that ensures sample integrityis maintained for the tests being performed.7.4.5 Sample loops should preferably be installed aroundpumps, valves, or other sources
44、of pressure drop to minimizeatmospheric emissions from purging of sample lines.7.4.6 Sampling pumps or other means of controlling pres-sures higher than the vapor pressure of the sample may beacceptable, and may be used to flush both the lines and/or thecylinder dead volume, if any, prior to sample
45、collection. Thecylinder may be partially filled and then emptied prior tocollection of the sample as an alternative to venting hydrocar-bon to flush lines.7.5 Composite Sampler:7.5.1 A composite sampler (also called a proportional sam-pler) is a device that is used to obtain a representative samplef
46、rom a flowing product stream by accumulating small portionsof product over a period of time. The sampling system consistsof a sample probe, a means of collecting repetitive smallportions, and a floating piston cylinder to accumulate the totalsample. Figs. 5 and 6 show typical sample systems using ap
47、robe-mounted sample pump (Fig. 5), or a flow-throughsample injection valve (Fig. 6).7.5.2 Thorough purging of sample lines, pumps, and con-nections to the sample cylinder is necessary to avoid contami-nation of the sample. A suitable purging arrangement at thepoint of sampling shall be provided. Thi
48、s purging arrangementmay take the form of a T connection and purging valve, or anoperating procedure that allows slight loosening of the connec-tion to vent the dead volume at the sample connection (ifallowed by the local jurisdiction). Composite sampler systemsshall be designed to minimize dead end
49、 lines that could resultin the sample not being representative of the LPG source.7.5.3 Take precautions to avoid vaporization in sample looplines when operating near the equilibrium vapor pressure of theLPG. In some instances, it may be necessary either to cool orinsulate the sample line and sample container, or to control thepressure or temperature of sample containers.7.5.4 Ensure that the pressure at the sample point is abovethe vapor pressure of the sample to avoid vaporization in thepipe or sampling lines when using a device such as an orificeplate or va
