1、Designation:D198806(Reapproved 2015)Standard Test Method forMercaptans in Natural Gas Using Length-of-Stain DetectorTubes1This standard is issued under the fixed designation D1988;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()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a rapid and simple field deter-mination of mercaptans in natural gas pipelines.Availabledete
3、ctor tubes provide a total measuring range of 0.5 to 160ppm by volume of mercaptans,although the majority ofapplications will be on the lower end of this range(that is,under 20 ppm).Besides total mercaptans,detector tubes arealso available for methyl mercaptan(0.5 to 100 ppm),ethylmercaptan(0.5 to 1
4、20 ppm),and butyl mercaptan(0.5 to 30mg/M3or 0.1 to 8 ppm).NOTE1Certain detector tubes are calibrated in terms of milligramsper cubic metre(mg/M3)instead of parts per million by volume.Theconversion is as follows for 25C(77F)and 760 mm Hg.mg/M35ppm3molecular weight24.45(1)1.2 Detector tubes are usua
5、lly subject to interferences fromgases and vapors other than the target substance.Such inter-ferences may vary among brands because of the use of differentdetection principles.Many detector tubes will have a pre-cleanse layer designed to remove interferences up to somemaximum level.Consult manufactu
6、rers instructions for spe-cific interference information.Hydrogen sulfide and othermercaptans are usually interferences on mercaptan detectortubes.See Section 5 for interferences of various methods ofdetection.1.3 This standard does not purport to address all of thesafety concerns,if any,associated
7、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.For specific hazardstatements,see 7.3.2.Referenced Documents2.1 Gas Processors Association Standard:GPA Stan
8、dard 2188 Tentative Method for the Determinationof Ethyl Mercaptan in LP Gas Using Length-of-StainDetector Tubes,Appendix B,Test for Ethyl MercaptanOdourant in Propane,Field Method,198823.Summary of Test Method3.1 The sample is passed through a detector tube filled witha specially prepared chemical.
9、Any mercaptan 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 mercaptan present in the sample.A hand-operated piston or bellows-t
10、ype pump is used to drawa measured volume of sample through the tube at a controlledrate of flow.The length of stain produced is converted to partsper million(ppm)by volume mercaptan by comparison to acalibration scale supplied by the manufacturer for each box ofdetection tubes.The system is direct
11、reading,easily portable,and completely suited to making rapid spot checks for mer-captans under field conditions(see Note 1).4.Significance and Use4.1 The measurement of mercaptans in natural gas isimportant,because mercaptans are often added as odorants tonatural gas to provide a warning property.T
12、he odor providedby the mercaptan serves to warn consumers(for example,residential use)of natural gas leaks at levels that are well belowthe flammable or suffocating concentration levels of natural gasin air.Field determinations of mercaptans in natural gas areimportant because of the tendency of the
13、 mercaptan concen-tration to fade over time.4.2 This test method provides inexpensive field screening ofmercaptans.The system design is such that it may be used bynontechnical personnel,with a minimum of proper training.5.Interferences5.1 Interference from hydrogen sulfide gas(H2S)is acommon problem
14、 with mercaptan detector tubes and its extentshould be understood to make use of tube readings.There areat least three detection principles used in mercaptan detectortubes and each is summarized below.1This test method is under the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct
15、responsibility of Subcommittee D03.07 on Analysis ofChemical Composition of Gaseous Fuels.Current edition approved Nov.1,2015.Published December 2015.Originallyapproved in 1991.Last previous edition approved in 2011 as D1988 06(2011).DOI:10.1520/D1988-06R15.2Available from Gas ProcessorsAssociation,
16、6526 E.60th St.,Tulsa,OK 74145.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.1.1 Palladium sulfate is used by at least one manufacturer.It has a positive interference from H2S,but H2S may beremoved in a preconditioning layer at the front of the tube.Ifthis is the case,the manufacturer will state some finite level ofH2S at which interference initiates(for example,greater than500-ppm H2S causes a positive error).Consult manufacturer