ASTM_D_4888_-_06_2015.pdf

Designation:D488806(Reapproved 2015)Standard Test Method forWater Vapor in Natural Gas Using Length-of-Stain DetectorTubes1This standard is issued under the fixed designation D4888;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.1.Scope1.1 This test method covers a procedure for rapid andsimple field determination of water vapor in natural gaspipelines.Available detector tubes provide a total measuringrange of 0.1 to 40 mg/L,although the majority of applicationswill be on the lower end of this range(that is,under 0.5 mg/L).At least one manufacturer provides tubes that read directly inpounds of water per million cubic feet of gas.See Note 1.1.2 Detector tubes are usually subject to interferences fromgases and vapors other than the target substance.Such inter-ferences may vary among brands because of the use of differentdetection methods.Consult manufacturers instructions forspecific interference information.Alcohols and glycols willcause interferences on some water vapor tubes because of thepresence of the hydroxyl group on those molecules.1.3 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.Summary of Test Method2.1 The sample is passed through a detector tube filled witha specially prepared chemical.Any water vapor present in thesample reacts with the chemical to produce a color change orstain.The length of the stain produced in the detector tube,when exposed to a measured volume of sample,is directlyproportional to the amount of water vapor present in thesample.A hand-operated piston or bellows-type pump is usedto draw a measured volume of sample through the tube at acontrolled rate of flow.The length of stain produced isconverted to milligrams per litre of H2O by comparison to acalibration scale supplied by the manufacturer for each box ofdetection tubes.The system is direct reading,easily portable,and completely suited to making rapid spot checks for watervapor under field conditions.NOTE1Detector tubes are available with calibration scales printed inpounds of water per million cubic feet of gas(lb/MMCF).The conversionfactor is 1 mg/L=62.3 lb/MMCF(7 lb/MMCF=0.11 mg L).3.Significance and Use3.1 The measurement of water vapor in natural gas isimportant because of the gas quality specifications,the corro-sive nature of water vapor on pipeline materials,and the effectsof water vapor on utilization equipment.3.2 This test method provides inexpensive field screening ofwater vapor.The system design is such that it may be used bynontechnical personnel with a minimum of proper training.4.Apparatus4.1 Length-of-Stain Detector TubesA sealed glass tubewith the breakoff tips sized to fit the tube holder of the pump.The reagent layer inside the tube,typically a silica gel substratecoated with the active chemical,must be specific for watervapor and produce a distinct color change when exposed to asample of gas containing water vapor.Any substances knownto interfere must be listed in the instructions accompanying thetubes.A calibration scale should be marked directly on thetube;however,other markings that provide for ready interpre-tation of water vapor content from a separate calibration scalesupplied with the tubes shall be acceptable.The calibrationscale shall correlate water vapor concentration to the length ofthe color stain.Shelf life of the detector tubes must be aminimum of two years from date of manufacture when storedaccording to manufacturers recommendations.4.2 Detector Tube PumpA hand-operated pump of apiston or bellows type.It must be capable of drawing 100 mLper stroke of sample through the detector tube with a volumetolerance of 65 mL.2It must be specifically designed for usewith detector tubes.NOTE2A detector tube and pump together form a unit and must beused as such.Each manufacturer calibrates detector tubes to match theflow characteristics of its specific pump.Crossing brands of pumps andtubes is not permitted,as considerable loss of system accuracy is likely tooccur.21This test method is under the jurisdiction of CommitteeD03 on Gaseous Fuelsand is the direct responsibility of Subcommittee D03.07Analysis of ChemicalComposition of Gaseous Fuels.Current edition approved Nov.1,2015.Published December 2015.Originallyapproved in 1988.Last previous edition approved in 2011 as D4888 06(2011).DOI:10.1520/D4888-06R15.2Direct Reading Colorimetric Indicator Tubes Manual,First ed.,AmericanIndustrial Hygiene Association,Akron,OH 44311,1976.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United Stat