1、Designation: D 5305 97 (Reapproved 2007)An American National StandardStandard Test Method forDetermination of Ethyl Mercaptan in LP-Gas Vapor1This standard is issued under the fixed designation D 5305; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、 case of revision, the year 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 a rapid and simple procedureusing length of stain tubes for fi
3、eld 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 et
4、hyl mercaptan inLP-gas vapors.NOTE 1A 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.1.3 This standard does not purport to address all of thesafety concerns, i
5、f 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:2NFPA 58 Standard for the Storage and Handling o
6、f Lique-fied Petroleum Gases3. Summary of Test Method3.1 Using a manually-operated vacuum pump, a sample ofLP-gas is drawn through a detector tube made specifically fordetection of mercaptans. The length of stain (color change)produced in the detector tube when exposed to a measuredvolume of sample
7、is directly proportional to the amount ofethyl mercaptan present in the sample being tested. The lengthof stain produced in the detector tube is converted to concen-tration, in parts per million volume (ppmv), by comparisonwith a calibration scale provided by the manufacturer of thestain tubes.4. Si
8、gnificance 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 commercialuse is intentionally odorized so as to be readily detectable wellbelow flammable or suffocating concentra
9、tion levels of LP-gasin air. (See Appendix X1.) The most common odorant forLP-gas is ethyl mercaptan. The field use of this test method willrapidly determine the presence and concentration of ethylmercaptan in LP-gas vapor without the necessity for complexlaboratory equipment.5. Interferences5.1 Det
10、ector 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 ins
11、tructions 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 i
12、n refineryoperations often does contain propylene (propene). Detectortubes calibrated for t-butyl mercaptan eliminate this interfer-ence, and should be used if the presence of propylene (pro-pene) is suspected. Some tubes designed for measurement oft-butyl mercaptan are calibrated in milligrams per
13、cubic metre(mg/m3) and should be converted to ppmv ethyl mercaptan asshown in Annex A1.6. 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 glass withbreak-off t
14、ips sized to fit the orifice of the pump used (tubesand pumps from different manufacturers should not be inter-changed). The tube used must be appropriate for the determi-nation of ethyl mercaptan and must produce a distinct colorchange when exposed to a sample of LP-gas containing ethylmercaptan. A
15、ny substance known to interfere must be listed in1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.H0 on Liquefied Petroleum Gas.Current edition approved May 1, 2007. Published June 2007. Original
16、lyapproved in 1992. Last previous edition approved in 2002 as D 5305 97 (2002).2Available from National Fire Protection Association (NFPA), 1 BatterymarchPark, Quincy, MA 02169-7471, http:/www.nfpa.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-295
17、9, United States.instructions accompanying the tubes (see 5.2). A calibrationscale or other markings referenced to a scale must be etcheddirectly on the tube to allow direct interpretation of ethylmercaptan concentration.36.2.1 Detector tubes must be calibrated for a tube tempera-ture of approximate
18、ly 20C and normal atmospheric pressure.Shelf life of the detector tubes must be a minimum of two yearswhen stored according to the manufacturers recommenda-tions.6.2.2 Detector tubes and pumps form an integrally designedunit, that must be used as a unit. Each manufacturer calibratesdetector tubes to
19、 match the flow characteristics of its pump,and the use of one brand of tube with another brand of pumpwill give unreliable results.6.3 A suitable container can be devised from a half-litrepolyethylene bottle (see Fig. 1). A 6 mm outside diameterpolyethylene tubing sealed into the bottle and dischar
20、ging nearthe bottom of the bottle provides for flow into the samplingcontainer. A 12 mm hole cut into the cap of the bottle providesboth access for the detector tube and a vent for the excess gasflow.6.3.1 Gas Sampling ContainerAny container of a mate-rial that is not reactive with mercaptan and tha
21、t provides foraccess of the detector tube into a uniform flow of sample gasat atmospheric pressure and isolated from the surroundingatmosphere.6.4 Needle Valve and TubingAstainless steel needle valvethat can be adjusted to control the flow of gas into the samplecontainer. Although a stainless steel
22、needle valve is preferred,a pressure regulator can be used in lieu of a needle valve tocontrol the flow of gas into the sample container. Polyethyleneor TFE-fluorocarbon tubing can be used to connect the needlevalve or pressure regulator to the gas sampling container.7. Sampling7.1 Select a sampling
23、 point that provides access to arepresentative sample of LP-gas vapor from the container to besampled.7.1.1 Open the source valve (Valve A in Fig. 1) and blowdown vigorously to clear foreign material from the sourcevalve and connecting nipple. Close the source valve.7.1.2 Install the control valve (
24、Valve B in Fig. 1) or pressureregulator on the outlet of the source valve. Connect outlet ofthe control valve to the gas sampling container using theshortest length practicable of suitable tubing.7.1.3 Open the source valve and then the control valve toobtain a slight positive flow through the gas s
25、ample container,venting to atmosphere through the tube access and vent (VentCinFig. 1). Purged gas must be vented at a sufficient rate sothat pressure does not build up in the sampling container andincrease the flow rate through the detector tube.7.1.4 Purge the gas sample container for at least 3 m
26、in todisplace air.7.1.5 Maintain flow of LP-gas during the test procedure inSection 9.8. Preparation of Apparatus8.1 Before sampling, all sampling equipment should bethoroughly clean and dry.8.2 Immediately before each series of tests, test the pumpfor tightness in accordance with manufacturers inst
27、ructions. Aloss in vacuum on the pump within 60 s indicates a leak. If aleak occurs, follow the pump manufacturers instructions forre-sealing the pump and retest. If the pump vacuum cannot bemaintained, do not use the pump for testing.9. Procedure9.1 Select the tube range that includes the expected
28、concen-tration of ethyl mercaptan present in the sample. Readingaccuracy is improved when the stain extends at least one-halfof the tube length. Consider multiple strokes or a lower rangetube, or both, to achieve this length of stain.9.2 Break off both tips of the glass stain tube and insert theoutl
29、et of the tube (indicated by arrow in direction of flow)snugly into the pump head. Temperature of tube must bemaintained in the 0 to 40C range throughout the test.9.3 Insert the detector tube well into the gas samplingcontainer through the tube access and vent (Vent C).9.4 Operate the pump to draw a
30、 measured amount of samplethrough the detector tube. Within any limits set by themanufacturers instructions, use multiple strokes to achieve astain extending to approximately one-half the tube length.9.5 Remove the tube from the pump and follow the manu-facturers instructions if further handling of
31、the tube is neces-sary.3Detector tube No. 72, manufactured by Gastec Corporation, based on thepalladium sulfate detection principle, is calibrated for ethyl mercaptan; Gastecdetector tubes No. 75 and 75L, using mercuric chloride detection chemistry, arecalibrated for t-butyl mercaptan. Other manufac
32、turers tubes may be based on otherdetection chemistry.FIG. 1 Half Litre Polyethylene BottleD 5305 97 (2007)29.6 Immediately (within 30 s), read the concentration ofethyl mercaptan from graduations on the tube or from chartssupplied with the tubes. The scale reading nearest the end ofthe stain is the
33、 measured concentration of ethyl mercaptan.10. Interpretation of Results10.1 If the number of pump strokes used is different fromthe number specified by the manufacturer, a correction must bemade as follows:corrected ethyl mercaptan concentration 5 scale reading (1)3specified strokes/actual strokes!
34、10.2 Some detector tubes that can be used in this testmethod may be calibrated for other mercaptans in milligramsper cubic metre (mg/m3). The conversion from mg/m3oft-butyl mercaptan to ppmv of ethyl mercaptan shall be per-formed as documented in Annex A1.10.3 Correct the reading for barometric pres
35、sure, especiallyat high altitudes. For details of this correction, see Annex A1.10.4 Readings of concentrations below 5 ppmv may not bereliable, and may warrant further investigation. (See AppendixX2.)NOTE 2This test method is a direct measure of the concentration ofethyl mercaptan in the vapor phas
36、e of LP-gas. If the temperature of thesystem is known, results can be used to obtain an approximation of theconcentration of ethyl mercaptan in the liquid phase. (See Appendix X1.)11. Report11.1 Report the observed tube reading and corrected con-centration of ethyl mercaptan in parts per million by
37、volume(ppmv) to the nearest 0.5 ppm.12. Precision and Bias12.1 Precision:12.1.1 The precision of this test method as determined bystatistical analysis of interlaboratory test results is as follows:12.1.1.1 RepeatabilityThe difference between successivetest results, obtained by the same operator usin
38、g the sameapparatus under constant operating conditions on identical testmaterial, would, in the long run, in the normal and correctoperation of the test method, exceed the following values onlyin one case in twenty: from 5 to 20 ppmv, the larger of 1 ppmor 615 % of the mean of the two results; abov
39、e 20 ppmv,620 % of the mean of the two results.12.1.1.2 ReproducibilityThe difference between twosingle and independent results, obtained by different operatorsworking in different laboratories on identical test material,would, in the normal and correct operation of the test method,exceed the follow
40、ing value only in one case in twenty: thelarger of 1.5 ppmv or 620 % of the mean of the two results.NOTE 3The preceding repeatability and reproducibility were obtainedfrom statistical analysis of results submitted by twelve testers whocooperatively tested five samples of propane with ethyl mercaptan
41、concentrations ranging from 3.3 to 32 ppmv in the vapor phase.12.2 BiasWithin the precision limits defined in 12.1.1.1and 12.1.1.2, this test method has no bias.13. Keywords13.1 ethyl mercaptan; liquefied petroleum gases; odorant;stain tubeANNEX(Mandatory Information)A1. CONVERSION AND CORRECTION IN
42、FORMATIONA1.1 Conversion of mg/m3t-butyl mercaptan (TBM) tomg/m3ethyl mercaptan (EM):mg/m3EM 5 mg/m3TBM3mol weight EM/mol weight TBM! (A1.1)Therefore:1 mg/m3TBM 5 1362.14/90.19!50.689 mg/m3EM (A1.2)A1.2 Conversion of mg/m3EM to ppmv EM at approxi-mately 25C:ppmv 5mg/m3!324.45!/mol weight EM! (A1.3)T
43、herefore:1 mg/m3EM 51!324.45!/62.14!50.393 ppmv EM (A1.4)NOTE A1.11 g mol = 22.4 L at 0 = 24.45 L at 25C.A1.3 A convenient tabulation of conversions:mg/m3mg/m3ppmvTBM 3 0.689 = EM 3 0.393 = EM2.5 1.72 0.685.0 3.45 1.3610 6.89 2.7115 10.34 4.0620 13.78 5.4225 17.23 6.7730 20.67 8.12A1.4 Correction fo
44、r barometric pressure:ppmv corrected!5ppmv3760 mm Hg/barometric pressure, mm Hg! (A1.5)Atmospheric Pres-sure, kPa (mm Hg)Elevation inmetres (feet)ppmReadingppmCorrected101.325 (760) 0 (0) 10 10.097.709 (733) 305 (1000) 10 10.493.977 (705) 610 (2000) 10 10.890.644 (680) 915 (3000) 10 11.2D 5305 97 (2
45、007)3Atmospheric Pres-sure, kPa (mm Hg)Elevation inmetres (feet)ppmReadingppmCorrected87.312 (655) 1220 (4000) 10 11.684.246 (632) 1524 (5000) 10 12.0Atmospheric Pres-sure, kPa (mm Hg)Elevation inmetres (feet)ppmReadingppmCorrected81.313 (610) 1829 (6000) 10 12.5APPENDIXES(Nonmandatory Information)X
46、1. RELATIONSHIP OF VAPOR-LIQUID CONCENTRATIONSX1.1 Published data on vapor-liquid equilibria (k-ratios) ofthe ethyl mercaptan/propane system are as follows:Temperature, C 30 20 10 0 10 20 30Temperature, F 22 4 14 32 50 68 86K-ratiofvariant40.12 0.15 0.18 0.21 0.24 0.27 0.31NOTE X1.1The K-ratios give
47、n herein are for a pure propane/ethylmercaptan system and may vary for commercial propane/ethyl mercaptansystems.X1.2 Assuming system equilibrium and accurate data onthe temperature of the system, the liquid-phase concentrationof ethyl mercaptan can be approximated, based on the follow-ing relations
48、hip:liquid2phase concentration, ppmv5vapor2phase concentration, ppmvK2ratio at system temperature!(X1.1)X2. ODORIZATION REQUIREMENTSX2.1 NFPA 58 is the basis for most regulatory require-ments for odorization of LP-gas. This standard stipulates, inpart:“1-4.1.1 All LP-gases shall be odorized prior to
49、 the deliveryto a distributing plant by the addition of a warning agent ofsuch character that they are detectable, by a distinct odor, downto a concentration in air of not over15 the lower limit offlammability.“Exception: Odorization, however, is not required if harmfulin the use or further processing of LP-gas, or if such odoriza-tion will serve no useful purpose as a warning agent in suchfurther use or processing.“1-4.4.2 If odorization is required, the presence of suchodorants shall be determined by sniff testing or other meansand t
