ASTM_D_1142_-_95_2012.pdf

Designation:D114295(Reapproved 2012)Standard Test Method forWater Vapor Content of Gaseous Fuels byMeasurement of Dew-Point Temperature1This standard is issued under the fixed designation D1142;the number immediately following the designation indicates the year oforiginal adoption or,in the case 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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This test method covers the determination of the watervapor content of gaseous fuels by measurement of the dew-point temperature and the calculation therefrom of the watervapor content.NOTE1Some gaseous fuels contain vapors of hydrocarbons or othercomponents that easily condense into liquid and sometimes interfere withor mask the water dew point.When this occurs,it is sometimes veryhelpful to supplement the apparatus in Fig.1 with an optical attachmentthat uniformly illuminates the dewpoint mirror and also magnifies thecondensate on the mirror.With this attachment it is possible,in somecases,to observe separate condensation points of water vapor,hydrocarbons,and glycolamines as well as ice points.However,if the dewpoint of the condensable hydrocarbons is higher than the water vapor dewpoint,when such hydrocarbons are present in large amounts,they mayflood the mirror and obscure or wash off the water dew point.Best resultsin distinguishing multiple component dew points are obtained when theyare not too closely spaced.NOTE2Condensation of water vapor on the dew-point mirror mayappear as liquid water at temperatures as low as 0 to 10F(18to 23C).At lower temperatures an ice point rather than a water dewpoint likely will be observed.The minimum dew point of any vapor thatcan be observed is limited by the mechanical parts of the equipment.Mirror temperatures as low as 150F(100C)have been measured,using liquid nitrogen as the coolant with a thermocouple attached to themirror,instead of a thermometer well.1.2 This standard does not purport to address all of thesafety 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.Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 saturated water vapor or equilibrium watervaporcontentthe water vapor concentration in a gas mixture that isin equilibrium with a liquid phase of pure water that issaturated with the gas mixture.When a gas containing watervapor is at the water dew-point temperature,it is said to besaturated at the existing pressure.2.1.2 specific volumeof a gaseous fuel,the volume of thegas in cubic feet per pound.2.1.3 water dew-point temperature of a gaseous fuel,thetemperature at which the gas is saturated with water vapor atthe existing pressure.3.Significance and Use3.1 Generally,contracts governing the pipeline transmissionof natural gas contain specifications limiting the maximumconcentration of water vapor allowed.Excess water vapor cancause corrosive conditions,degrading pipelines and equipment.It can also condense and freeze or form methane hydratescausing blockages.Watervapor content also affects the heat-ing value of natural gas,thus influencing the quality of the gas.This test method permits the determination of water content ofnatural gas.4.Apparatus4.1 Any properly constructed dew-point apparatus may beused that satisfies the basic requirements that means must beprovided:4.1.1 To permit a controlled flow of gas to enter and leavethe apparatus while the apparatus is at a temperature at least3F above the dew point of the gas.4.1.2 To cool and control the cooling rate of a portion(preferably a small portion)of the apparatus,with which theflowing gas comes in contact,to a temperature low enough tocause vapor to condense from the gas.4.1.3 To observe the deposition of dew on the cold portionof the apparatus.4.1.4 To measure the temperature of the cold portion on theapparatus on which the dew is deposited,and4.1.5 To measure the pressure of the gas within the appara-tus or the deviation from the known existing barometricpressure.4.1.6 The apparatus should be constructed so that the“coldspot,”that is,the cold portion of the apparatus on which dew1This test method is under 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 Nov.1,2012.Published December 2012.Originallyapproved in 1950.Last previous edition approved in 2006 as D1142 95(2006).DOI:10.1520/D1142-95R12.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 is deposited,is protected from all gases other than the gasunder test.The apparatus may or may not