1、Designation: D 5454 04Standard Test Method forWater Vapor Content of Gaseous Fuels Using ElectronicMoisture Analyzers1This standard is issued under the fixed designation D 5454; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear 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 test method covers the determination of the watervapor content of gaseous fuels by the use of electronic
3、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 thesafety concerns, if any, associated with its use. It
4、 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:D 1142 Test Method for Water Vapor Content of GaseousFuels by Measurement of Dew-
5、Point TemperatureD 1145 Test Method for Sampling Natural GasD 4178 Practice for Calibrating Moisture Analyzers2D 4888 Test Method for Water Vapor In Natural Gas UsingLength-of-Stain Detector Tubes3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 capacitance-type cellthis cell us
6、es aluminum coatedwith Al2O3as part of a capacitor. The dielectric Al2O3filmchanges the capacity of the capacitor in relation to the watervapor present. Unlike P2O5cells, this type is nonlinear in itsresponse. If silicon is used instead of aluminum, the silicon cellgives improved stability and very
7、rapid response.3.1.2 electrolytic-type cellthis cell is composed of twonoble metal electrode 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-ty
8、pe cell sensor consists of a pair ofelectrodes which support a quartz crystal (QCM) 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
9、 change in the oscillation frequency isproduced.3.1.4 laser-type cell consists of a sample cell with anoptical head mounted on one end and a mirror mounted on theother. The optical head contains a NIR laser, which emits lightat a wavelength known to be absorbed by the water molecule.Mounted along si
10、de the laser is a detector sensitive to NIRwavelength light. Light from the laser passes through the thefar end and returns to the detector in the optical head.Aportionof the emitted light, proportional to the water moleculespresent, is absorbed as the light transits the sample cell andreturns to th
11、e 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 electronicana
12、lyzers. 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 andwate
13、r content are found in Test Method D 1142.4. 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 conditionscausing serious operating problems. Fuel heating value
14、isreduced by water concentration. Water concentration levels aretherefore frequently measured 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.1This test method is u
15、nder the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.05 on Determination ofSpecial Constituents of Gaseous Fuels.Current edition approved Dec. 1, 2004. Published January 2005. Originallyapproved in 1993. Last previous edition approved in 199
16、9 as D545493(1999).2Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Apparatus5.1 The moisture analyzer and sampling system will havethe following general specifications:5.1.1 Sampling SystemMost errors involved with mois
17、-ture analysis can be eliminated with a proper sampling system.5.1.1.1 A pipeline sample should be obtained with a probeper Method D 1145. The sample temperature must be main-tained 2C (3F) above the dewpoint of the gas to preventcondensation in the sample line or analyzer. Use of insulationor heat
18、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 impact on accuracy or time ofresponse. If the
19、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 minimize diffusion and absorption, allmateria
20、ls 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 as a result of water accumulation in the
21、 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 units (usuallylb/MMSCF). There must be an ad
22、justment 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 SupplyAnalyzers for field use will havere
23、chargeable 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 D 4178that should be used to verify the accuracy of
24、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 for barometric pressure.6.2 Acommercially
25、 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 beestablished by tube weight loss.6.4 Compresse
26、d 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 than average expectedreadings. Some analyze
27、rs 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 dryinstrument using dry compressed nitroge
28、n 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 equilibriumis variable depending on its type and con
29、dition. 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 for this test method byan interlaborator
30、y study.D5454042FIG. 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 validity of any such patent rights, and t
31、he riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision
32、of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shoul
33、dmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D5454043
