1、Designation: D5503 94 (Reapproved 2008)Standard Practice forNatural Gas Sample-Handling and Conditioning Systems forPipeline Instrumentation1This standard is issued under the fixed designation D5503; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of revision, 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. Scope1.1 This practice covers sample-handling and conditioningsystems for typical pipeline monitor
3、ing instrumentation (gaschromatographs, moisture analyzers, and so forth). The selec-tion of the sample-handling and conditioning system dependsupon the operating conditions and stream composition.1.2 This practice is intended for single-phase mixtures thatvary in composition. A representative sampl
4、e cannot be ob-tained from a two-phase stream.1.3 The values stated in SI units are to regarded as standard.The values stated in English units are for information only.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of
5、 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:2D1142 Test Method for Water Vapor Content of GaseousFuels by Measurement of Dew-Point TemperatureD3764 P
6、ractice for Validation of the Performance of ProcessStream Analyzer Systems2.2 Other Standards:ANSI/API 2530 (AGA Report Number 3)3AGA Report Number 84NACE Standard MR-01-7553. Terminology3.1 Definitions:3.1.1 compressed natural gasnatural gas compressed toapproximately 3600 psi.3.1.2 densitymass pe
7、r unit volume of the substance beingconsidered.3.1.3 dew pointthe temperature and pressure at which thefirst droplet of liquid forms from a vapor.3.1.4 lag timetime required to transport the sample to theanalyzer.3.1.5 natural gasmixture of low molecular weight hydro-carbons obtained from petroleum-
8、bearing regions.3.1.6 sample probedevice to extract a representativesample from the pipeline.3.1.7 system turnaround timethe time required to trans-port the sample to the analyzer and to measure the desiredcomponents.4. Significance and Use4.1 A well-designed sample-handling and conditioning sys-tem
9、 is essential to the accuracy and reliability of pipelineinstruments. Approximately 70 % of the problems encounteredare associated with the sampling system.5. Selection of Sample-Handling and ConditioningSystem5.1 The sample-handling and conditioning system mustextract a representative sample from a
10、 flowing pipeline, trans-port the sample to the analyzer, condition the sample to becompatible with the analyzer, switch sample streams andcalibration gases, transport excess sample to recovery (ordisposal), and resist corrosion by the sample.5.2 The sample probe should be located in a flowingpipeli
11、ne where the flow is fully developed (little turbulence)and where the composition is representative. In areas of highturbulence, the contaminates that normally flow along thebottom or the wall of the pipeline will form aerosols.5.3 The purpose of the sample probe is to extract a repre-sentative samp
12、le by obtaining it near the center of the pipelinewhere changes in stream composition can be quickly detected.1This practice is under the jurisdiction of ASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.01 on Collection andMeasurement of Gaseous Samples.Current
13、 edition approved Dec. 1, 2008. Published July 2009. Originally approvedin 1994. Last previous edition approved in 2003 as D5503 94 (2003). DOI:10.1520/D5503-94R08.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Boo
14、k of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from American Gas Association, 1515 Wilson Blvd., Arlington
15、, VA22209.5Available from NACE International (NACE), 1440 South Creek Dr., Houston,TX 77084-4906, http:/www.nace.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesNOTICE: This standard has either been superseded and replaced by a new
16、 version or withdrawn.Contact ASTM International (www.astm.org) for the latest information15.3.1 The tip in the sample probe should be positioned in thecenter one third of the pipeline, away from the pipeline wallwhere large particles accumulate.5.3.2 The probe should be a minimum of five pipe diame
17、tersfrom any device that could produce aerosols or significantpressure drop.5.3.3 The sample probe should not be located within adefined meter tube region (see ANSI/API 2530 AGA ReportNumber 3 and AGA Report Number 8 for more information).5.3.4 The sample probe should be mounted vertically fromthe t
18、op on horizontal pipelines. The sample probe should not belocated on vertical pipelines.5.4 The sampling-handling system must transport thesample to the analyzer and dispose of excess sample. Since thesampling point and the analyzer may be separated by somedistance, the time required to transport th
19、e sample to theanalyzer can contribute significantly to the system turnaroundtime.5.4.1 The analyzer should be located as close to the sam-pling point as is practical to minimize the sample lag time.5.4.2 The sample-handling system should be equipped witha full open ball valve and a particular filte
20、r.5.5 The sizing of the sample transport line will be influ-enced by a number of factors:5.5.1 The sample point pressure and the location of thepressure reduction regulator.5.5.2 The acceptable lag time between the sample point andthe analyzer.5.5.3 The requirements of the analyzer, such as flow rat
21、e,pressure, and temperature for the analysis. For multistreamsystems, the sample line and associated manifold tubing shouldbe flushed with sufficient sample to assure a representativesample of the selected stream.5.5.4 The presence of sample-conditioning elements willcontribute to the lag time and m
22、ust be considered in thecalculation of the minimum sample flow rate.5.5.4.1 Each element could be considered as an equivalentlength of sample line and added to the length of line from thesample point to the analyzer.5.5.4.2 The purge time of each element is calculated as thetime necessary for five v
23、olumes of sample to flow through theelement.5.5.5 A vapor sample must be kept at least 10C above thehydrocarbon dew point temperature to prevent condensation ofthe sample. The sample line should be heat traced and insulatedwhen appropriate.5.5.5.1 For compressed natural gas (CNG), the pressuremust b
24、e reduced in two stages to avoid condensation of liquidscaused by the Joule-Thompson effect. In a heated zone atapproximately 50C, the pressure should be dropped to ap-proximately 10 MPa (1500 psig) and then to a suitable pressurefor the analyzer. Any conditioning of the sample must becompleted in t
25、he heated zone.5.5.5.2 The sample line from the heated zone to the analyzermust be heat traced to avoid partial condensation of the sample.6. Apparatus6.1 The following are common components of a sample-handling and conditioning system (see Refs (1) and (2)6formore information).6.1.1 Ball valves, ne
26、edle valves, and solenoid valves aretypically used for stream switching, sample shutoff, calibrationgas introduction, or sample vent and bypass systems.6.1.2 Most pipeline samples require some filtering. Since allfilter elements eventually plug, they should be replaced on aregular maintenance schedu
27、le. There are several types of filterdesigns.6.1.2.1 In-Line FilterAll of the sample passes through anin-line filter. The active filter elements are available in Teflonpolypropylene, copolymer, or stainless steel. (See Fig. 1.)6.1.2.2 Bypass FilterOnly a small portion of the samplepasses through a b
28、ypass filter, while a majority of the samplepasses across its surface keeping it clean. The active filterelement is either a disposable cartridge or a reusable sinteredmetal element. (See Fig. 2.)6.1.2.3 Cyclone FilterThe cyclone filter is a centrifugalcleanup device. The sample enters at high veloc
29、ity tangentiallyto the wall of a cylindrical-shaped vessel with a conical-shapedbottom. The centrifugal force developed by the spinning actionof the gas as it follows the shape of the vessel forces particlesand droplets to the wall where they are removed through thevent flow. (See Fig. 3.)6.1.2.4 Co
30、alescing FilterCoalescers, also known as mem-brane separators, are used to force finely divided liquiddroplets to combine into larger droplets so they can beseparated by gravity. The design of the coalescer body forcesthe heavier phase out the bottom and the lighter phase out thetop. The flow rates
31、out the top and the bottom are critical forproper operation. (See Fig. 4.)(1) Since this process removes part of the sample, theimpact on sample composition must be considered.6The boldface numbers in parentheses refer to the list of references at the end ofthis practice.FIG. 1 Cross Section of Comm
32、on In-Line FiltersD5503 94 (2008)2(2) The coalescer should be located immediately upstreamfrom the analyzer.6.1.3 The combination condenser/separator is used to re-move condensable liquids from a vapor sample. The sampleenters the separator and cools as it passes through the device.The condensed liq
33、uid phase is separated by gravity andremoved from the bottom of the separator. (See Fig. 5.)6.1.3.1 Since this process removes part of the sample, theimpact on sample composition must be considered.6.1.3.2 The condenser/separator should be located immedi-ately upstream from the analyzer.6.1.4 Pressu
34、re regulators are required to reduce and regulatepressure between the sampling point and the analyzer. Theregulator must be constructed of the proper materials to allowfor the corrosive nature of the sample.6.1.4.1 A combination sample probe and regulator withthermal fins around the probe could be u
35、sed to minimize theJoule-Thompson effect.6.1.5 Pressure gages should be installed downstream of thepressure regulator. Since the sensing element of these devices(Bourdon tube) consists of unswept volume, the pressure gageshould be installed either in a bypass line or after the analyzer.6.1.6 Rotamet
36、ers are used to indicate the flow rate of thesample. A typical rotameter consists of a ball or float mountedin a tapered tube. The reading is proportional to fluid densityand viscosity which may vary with the composition of thefluid.6.1.6.1 The rotameter should be located downstream of theanalyzer a
37、nd used as an indicator of flow and system cleanli-ness. A clean tube and a freely moving ball is an indicator of aclean system.6.1.7 Typical natural gas sample system. (See Fig. 6.)6.1.8 Compressed natural gas sample system. (See Fig. 7.)7. Materials7.1 Many of the common sample system components a
38、reconstructed of trademarked metals such as 316 stainless steel,FIG. 2 Cross Section of Common Bypass FiltersFIG. 3 Cyclone Filter/Centrifugal FilterFIG. 4 Coalescing FilterFIG. 5 Combination Condensor/SeparatorD5503 94 (2008)3Hastelloy, and Monel and compatible trademarked plasticssuch as Kel-F, Te
39、flon, and Kynar.7.1.1 The sample-handling and conditioning system shouldbe constructed of material capable of resisting corrosion fromthe sample and the environment.7.1.1.1 Sample system components should be chosen care-fully to avoid corrosion or adsorption by the sample.7.1.1.2 If sour gas (gas th
40、at contains hydrogen sulfide orcarbon dioxide, or both) is suspected, NACE Standard MR-01-75 should be followed.7.2 The sample-handling and conditioning system shouldcontain the sample under the most severe conditions ofpressure, temperature, and vibration that the pipeline willexperience during nor
41、mal and upset conditions.8. Calculation8.1 Sample transport time, or lag time, tlag, is a function ofthe sample line length and diameter, the absolute pressure inthe line, and the sample flow rate. Lag time is calculated asfollows:tlag5VLP1Patm!FaPatm(1)where:tlag= sample transport time, min;V = vol
42、ume of sample per unit length, cm3/m;L = equivalent length of sample length, m;P = sample pressure, N/m2;Patm= atmospheric pressure, N/m2; andFa= actual average flow rate of the sample, cm3/min.8.1.1 ExampleConsider a sample point located 100 ftaway from an analyzer requiring 200 cm3/min of sample.U
43、sing standard conditions and 0.19-in. inside diameter tubing,a lag time of 75 min can be calculated. By increasing thesample flow to 2200 cm3/min and splitting the excess sampleto a high-speed loop, the lag time decreases to 7.5 min. Thesample pressure should be reduced at the analyzer.8.1.2 Reducin
44、g the pressure at the sample point rather thanthe analyzer can also decrease the lag time. For a pressurereduction from 400 to 40 psig, the sample flow should be 2000cm3/min to compensate for the increase in sample volume.(See Fig. 8.)8.2 The equivalent length of sample line is calculated by thefoll
45、owing expression (see Ref (3) for more information):L 5 Ld1Leq(2)FIG. 6 Typical Natural Gas Sampling SystemFIG. 7 Pressure Reduction System for Compressed Natural Gas(CNG)FIG. 8 Example Calculations of Lag TimeD5503 94 (2008)4where:L = equivalent length of sample line, m;Ld= length of sample line, m
46、; andLeq= equivalent length of valves and fittings, m.8.3 Calculation of sample line size is a trial and errorprocess:8.3.1 Select a sample line size that meets the flow rate needsof the analyzer.8.3.2 Calculate the Reynolds number, the ratio of inertial-to-viscous forces by:Re5d(3)where:Re= Reynold
47、s number; = fluid density, Kg/m3; = fluid velocity, m/s;d = diameter of the pipe, m; and = viscosity of the fluid, Ns/m2.8.3.3 Calculate the pressure drop using Darcys equation(see (3) for more information):dp 5fLu22 dg(4)where:dp = pressure drop in the line, N/m2;f = frictional factor from Moodys t
48、ables; = fluid density, Kg/m3;L = equivalent length of sample line, m;u = velocity of the fluid, m/s;d = diameter of the line, m; andg = acceleration of gravity, 9.81 m/s2.8.3.4 The available pressure drop should be compared withthe calculated pressure drop. If the calculated pressure drop istoo gre
49、at, then select a larger sample line and repeat lag time,equivalent length, and pressure drop calculations.8.3.5 The majority of sample transport problems are solvedby application of prior experience and by use of tables relatingvelocity to pressure drop for different sample line diameters(see Refs (4) and (5) for more information).8.4 The dew point calculation relies on the use of distribu-tion coefficients, Ki, which are defined as the ratio of the molefraction of the component in the vapor phase, Yi, to the molefraction in the
