ASTM_D_5305_-_12.pdf

Designation:D530512Standard Test Method forDetermination of Ethyl Mercaptan in LP-Gas Vapor1This standard is issued under the fixed designation D5305;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.Scope*1.1 This test method covers a rapid and simple procedureusing length of stain tubes for field measurement of ethylmercaptan in the vapor phase of LP-gas systems.Althoughlength-of-stain tubes are available to detect ethyl mercaptanconcentrations in the range of 0.5 to 120 parts per millionvolume(ppmv),this test method is specifically applicable tosystems containing 5 ppmv or more of ethyl mercaptan inLP-gas vapors.NOTE1A chromatographic technique can be used for more precise,quantitative determination of ethyl mercaptan in LP-gas.1.2 The values stated in SI(metric)units are to be regardedas the standard.The values in parentheses are for informationonly.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.Referenced Documents2.1 NFPA Standard:2NFPA58 Standard for the Storage and Handling of LiquefiedPetroleum Gases3.Summary of Test Method3.1 Using a manually-operated vacuum pump,a sample ofLP-gas from the vapor space of an LP-gas cylinder,storagetank or other closed containment system is drawn through adetector tube made specifically for detection of mercaptans.The length of stain(color change)produced in the detector tubewhen exposed to a measured volume of sample is directlyproportional to the amount of ethyl mercaptan present in thesample being tested.The length of stain produced in thedetector tube is converted to concentration,in parts per millionvolume(ppmv),by comparison with a calibration scale pro-vided by the manufacturer of the stain tube.4.Significance and Use4.1 LP-gas is colorless and odorless,and not detectable bynormal human senses.To provide an olfactory warning in theevent of a leak,LP-gas intended for domestic or commercialfuel use is intentionally odorized so as to be readily detectablewell below flammable or suffocating concentration levels ofLP-gas in air.(See Appendix X1.)The most common odorantfor LP-gas is ethyl mercaptan.The field use of this test methodwill rapidly determine the presence and concentration of ethylmercaptan in LP-gas vapor without the necessity for complexlaboratory equipment.5.Interferences5.1 Detector tubes can be subject to interferences frommaterials other than the target substance.Methyl mercaptanwill likely interfere with tubes designed to measure ethylmercaptan.Because of different detection chemistry by differ-ent manufacturers,interferences can vary.Consult the manu-facturers instructions for specific interference information andobserve any instructions given.5.2 Propylene(propene)will cause an interfering(gray)discoloration with some tubes designed for ethyl mercaptan.LP-gas from natural gas sources usually does not containpropylene(propene).However,LP-gas produced in refineryoperations often does contain propylene(propene).Detectortubes calibrated for t-butyl mercaptan eliminate thisinterference,and should be used if the presence of propylene(propene)is suspected.Some tubes designed for measurementof t-butyl mercaptan are calibrated in milligrams per cubicmetre(mg/m3)and should be converted to ppmv ethyl mer-captan as shown in Annex A1.5.3 The validity of this test method depends on the ethylmercaptan in the LP-gas vapor phase being in equilibrium withethyl mercaptan in the LP-gas liquid phase.If LP-gas vapor hasrecently been vented,or if a significant volume of vaporrelative to the total volume of the vapor phase is vented duringthis test procedure,the concentration of ethyl mercaptan in thevapor phase sample can be lower than the equilibrium concen-tration.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,Liquid Fuels,and Lubricants and is the direct responsibility ofSubcommittee D02.H0 on Liquefied Petroleum Gas.Current edition approved Nov.1,2012.Published February 2013.Originallyapproved in 1992.Last previous edition approved in 2007 as D530597(2007).DOI:10.1520/D5305-12.2Available from National Fire Protection Association(NFPA),1 BatterymarchPark,Quincy,MA 02169-7471,http:/www.nfpa.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.Apparatus6.1 PumpA manually-operated vacuum pump,capable ofdrawing 100 mL per stroke of sample through the detector tubewith an accuracy of 62.0 mL.6.2 Detector TubesSealed tubes,made of gl