1、Designation: D5454 111Standard Test Method forWater Vapor Content of Gaseous Fuels Using ElectronicMoisture Analyzers1This standard is issued under the fixed designation D5454; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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.1NOTEFig. 1 was editorially updated in July 2011.1. Scope1.1 This test method covers the determination of the watervapor con
3、tent of gaseous fuels by the use of electronic moistureanalyzers. Such analyzers commonly use sensing cells basedon phosphorus pentoxide, P2O5, aluminum oxide, Al2O3,orsilicon sensors piezoelectric-type cells and laser based tech-nologies.1.2 This standard does not purport to address all of thesafet
4、y concerns, if any, associated with its use. It is theresponsibility 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:2D1142 Test Method for Water Vapor
5、 Content of GaseousFuels by Measurement of Dew-Point TemperatureD1145 Test Method For Sampling Natural Gas3D4178 Practice for Calibrating Moisture Analyzers3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 capacitance-type cellthis cell uses aluminum coatedwith Al2O3as part of a
6、 capacitor. The dielectric Al2O3filmchanges the capacity of the capacitor in relation to the watervapor present. Silicone cells also operate on this principal byreporting a capacitance change when adsorbing or desorbingwater vapor.3.1.2 electrolytic-type cellthis cell is composed of twonoble metal e
7、lectrode wires coated with P2O5. A bias voltage isapplied to the electrodes, and water vapor chemically reacts,generating a current between the electrodes proportional to thewater vapor present.3.1.3 piezoelectric-type cell sensor consists of a pair ofelectrodes which support a quartz crystal (QCM)
8、transducer.When voltage is applied to the sensor a very stable oscillationoccurs. The faces of the sensor are coated with a hygroscopicpolymer.As the amount of moisture absorbed onto the polymervaries, a proportional change in the oscillation frequency isproduced.3.1.4 laser-type cell consists of a
9、sample cell with anoptical head mounted on one end and a mirror mounted on theother; however, some models will not need a mirror to reflectthe light wavelength emitted from the laser. The optical headcontains a NIR laser, which emits light at a wavelength knownto be absorbed by the water molecule. M
10、ounted, the laser is adetector sensitive to NIR wavelength light. Light from the laserpasses through the far end and returns to the detector in theoptical head. A portion of the emitted light, proportional to thewater molecules present, is absorbed as the light transits thesample cell and returns to
11、 the detector.3.1.5 water contentwater content is customarily ex-pressed in terms of dewpoint, F or C, at atmosphericpressure, or the nonmetric term of pounds per million standardcubic feet, lb/MMSCF. The latter term will be used in this testmethod because it is the usual readout unit for electronic
12、analyzers. One lb/MMSCF = 21.1 ppm by volume or 16.1mgm/m3of water vapor. Analyzers must cover the range 0.1 to50 lb/MMSCF.3.1.6 water dewpointthe temperature (at a specified pres-sure) at which liquid water will start to condense from thewater vapor present. Charts of dewpoints versus pressure andw
13、ater content are found in Test Method D1142.4. Significance and Use4.1 Water content in fuel gas is the major factor influencinginternal corrosion. Hydrates, a semisolid combination of hy-drocarbons and water, will form under the proper conditions1This test method is under the jurisdiction ofASTM Co
14、mmittee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.05 on Determination ofSpecial Constituents of Gaseous Fuels.Current edition approved June 1, 2011. Published July 2011. Originally approvedin 1993. Last previous edition approved in 2004 as D545404. DOI: 10.1520/D5454-1
15、1E01.2For 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.3Withdrawn. The last approved version of this historical
16、 standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.causing serious operating problems. Fuel heating value isreduced by water concentration. Water concentration levels aretherefore frequently measur
17、ed in natural gas systems. A com-mon pipeline specification is 4 to 7 lb/MMSCF. This testmethod describes measurement of water vapor content withdirect readout electronic instrumentation.5. Apparatus5.1 The moisture analyzer and sampling system will havethe following general specifications:5.1.1 Sam
18、pling SystemMost errors involved with mois-ture analysis can be eliminated with a proper sampling system.5.1.1.1 A pipeline sample should be obtained with a probeper Method D1145. The sample temperature must be main-tained 2C (3F) above the dewpoint of the gas to preventcondensation in the sample li
19、ne or analyzer. Use of insulationor heat tracing is recommended at cold ambient temperatures.5.1.1.2 Analyzer sensors are very sensitive to contamina-tion. Any contaminants injurious to the sensor must be re-moved from the sample stream before reaching the sensor. Thismust be done with minimum impac
20、t on accuracy or time ofresponse. If the contaminant is an aerosol of oil, glycol, and soforth, a coalescing filter or semipermeable membrane separatormust be used.5.1.2 ConstructionSampling may be done at high or lowpressure. All components subject to high pressure must berated accordingly. To mini
21、mize diffusion and absorption, allmaterials in contact with the sample before the sensor must bemade of stainless steel. Tubing of18-in. stainless steel isrecommended. (WarningUse appropriate safety precautionswhen sampling at high pressure.)5.1.2.1 Pressure gages with bourdon tubes should beavoided
22、 as a result of water accumulation in the stagnantvolume.5.1.2.2 Sample purging is important to satisfactory responsetime. There must be a method to purge the sample line andsample cleanup system.5.1.3 ElectronicsOutput from the sensor will be linear-ized for analog or digital display in desired uni
23、ts (usuallylb/MMSCF). There must be an adjustment for calibrationaccuracy available that can be used in the field if a suitablestandard is available. (This does not apply to instruments thatassume complete chemical reaction of water. Their accuracystill must be verified as in Section 6.)5.1.4 Power
24、SupplyAnalyzers for field use will haverechargeable or easily replaceable batteries. (WarningAnalyzers for use in hazardous locations because of combus-tible gas must be certified as meeting the appropriate require-ments.)6. Calibration6.1 A calibration technique is described in Practice D4178that s
25、hould be used to verify the accuracy of the analyzer. Thismethod uses the known vapor pressure of water at 0C andmixes wet gas and dry gas to make up the total pressure so thata standard gas of known water concentration is achieved.6.1.1 Instruments very sensitive to sample flow must becompensated f
26、or barometric pressure.6.2 Acommercially made water vapor calibrator is shown inFig. 1, which uses essentially the same technique. This methodis useful only between 5 to 50 lb/MMSCF.6.3 Low-range water vapor standards may be obtained bythe use of water permeation tubes. Permeation rates must beestab
27、lished by tube weight loss.6.4 Compressed gas water vapor standards may be used,provided they are checked by an independent method once amonth.6.5 Calibrate the analyzer using one of the standards in 6.3and 6.4 and respective procedures. Calibration must be at twopoints, one higher and one lower tha
28、n average expectedreadings. Some analyzers can have large nonlinear errors. Usethe calibration adjustment if applicable.7. Procedure7.1 PreparationThe analyzer operation and calibrationshould be checked according to the manufacturers recommen-dations prior to use. See Section 6. Verification of a dr
29、yinstrument using dry compressed nitrogen to get a readingbelow 1 lb/MMSCF is recommended before field use.7.2 Sample ProcedureSample as in 5.1.1.1. Use as short asample line as practical. Purge the sample for 2 min beforevalving to the sensor.7.3 ReadingThe time for a sensor to come to equilibriumi
30、s variable depending on its type and condition. The analyzermay require 20 min to stabilize. Some analyzers have anexternal recorder output, and these can be used with a chartrecorder to become familiar with the true equilibrium responsetime.8. Precision and Bias8.1 Precision data is being prepared
31、for this test method byan interlaboratory study.D5454 1112FIG. 1 Moisture CalibratorASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the
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