1、Designation: D5305 97 (Reapproved 2007)D5305 12Standard 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
2、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 Scope*1.1 This test method covers a rapid and simple procedure using length of stain tubes for field measurement
3、of ethyl mercaptanin the vapor phase of LP-gas systems. Although length-of-stain tubes are available to detect ethyl mercaptan concentrations in therange of 0.5 to 120 parts per million volume (ppmv), this test method is specifically applicable to systems containing 5 ppmv ormore of ethyl mercaptan
4、in LP-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 regarded as the standard. The values in parentheses are for information only.1.3 This standard does not purpor
5、t to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 NFPA Standard:2NFPA 58
6、Standard for the Storage and Handling of Liquefied Petroleum Gases3. Summary of Test Method3.1 Using a manually-operated vacuum pump, a sample of LP-gas from the vapor space of an LP-gas cylinder, storage tank orother closed containment system is drawn through a detector tube made specifically for d
7、etection of mercaptans.The length of stain(color change) produced in the detector tube when exposed to a measured volume of sample is directly proportional to the amountof ethyl mercaptan present in the sample being tested. The length of stain produced in the detector tube is converted toconcentrati
8、on, in parts per million volume (ppmv), by comparison with a calibration scale provided by the manufacturer of the staintubes.tube.4. Significance and Use4.1 LP-gas is colorless and odorless, and not detectable by normal human senses. To provide an olfactory warning in the eventof a leak, LP-gas int
9、ended for domestic or commercial fuel use is intentionally odorized so as to be readily detectable well belowflammable or suffocating concentration levels of LP-gas in air. (See Appendix X1.) The most common odorant for LP-gas is ethylmercaptan. The field use of this test method will rapidly determi
10、ne the presence and concentration of ethyl mercaptan in LP-gasvapor without the necessity for complex laboratory equipment.5. Interferences5.1 Detector tubes can be subject to interferences from materials other than the target substance. Methyl mercaptan will likelyinterfere with tubes designed to m
11、easure ethyl mercaptan. Because of different detection chemistry by different manufacturers,interferences can vary. Consult the manufacturers instructions for specific interference information and observe any instructionsgiven.5.2 Propylene (propene) will cause an interfering (gray) discoloration wi
12、th some tubes designed for ethyl mercaptan. LP-gasfrom natural gas sources usually does not contain propylene (propene). However, LP-gas produced in refinery operations oftendoes contain propylene (propene). Detector tubes calibrated for t-butyl mercaptan eliminate this interference, and should be u
13、sed1 This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products and Lubricants and is the direct responsibility of Subcommittee D02.H0 onLiquefied Petroleum Gas.Current edition approved May 1, 2007Nov. 1, 2012. Published June 2007February 2013. Originally approved in 1992
14、. Last previous edition approved in 20022007 asD5305 97D530597(2007). (2002). DOI: 10.1520/D5305-97R07.10.1520/D5305-12.2 Available from National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02169-7471, http:/www.nfpa.org.This document is not an ASTM standard and is intended o
15、nly to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current ver
16、sionof the standard as published by ASTM is to be considered the official document.*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 States1if the presence of propylene (propene)
17、 is suspected. Some tubes designed for measurement of t-butyl mercaptan are calibrated inmilligrams per cubic metre (mg/m3) and should be converted to ppmv ethyl mercaptan as shown in Annex A1.5.3 The validity of this test method depends on the ethyl mercaptan in the LP-gas vapor phase being in equi
18、librium with ethylmercaptan in the LP-gas liquid phase. If LP-gas vapor has recently been vented, or if a significant volume of vapor relative to thetotal volume of the vapor phase is vented during this test procedure, the concentration of ethyl mercaptan in the vapor phase samplecan be lower than t
19、he equilibrium concentration.6. Apparatus6.1 PumpAmanually-operated vacuum pump, capable of drawing 100 mLper stroke of sample through the detector tube withan accuracy of 62.0 mL.6.2 Detector TubesSealed tubes, made of glass with break-off tips sized to fit the orifice of the pump used (tubes and p
20、umpsfrom different manufacturers shouldshall not be interchanged). The tube used mustshall be appropriate for the determination ofethyl mercaptan and mustshall produce a distinct color change when exposed to a sample of LP-gas containing ethyl mercaptan.Any substance known to interfere mustshall be
21、listed in instructions accompanying the tubes (see 5.2).Acalibration scale or othermarkings referenced to a scale mustshall be etched directly on the tube to allow direct interpretation of ethyl mercaptanconcentration.36.2.1 Detector tubes mustshould be calibrated for a tube temperature of approxima
22、tely 20C and normal atmospheric pressure.Shelf life of the detector tubes mustshall be a minimum of two years when stored according to the manufacturersrecommendations.6.2.2 Detector tubes and pumps form an integrally designed unit, that must are to be used as a unit. Each manufacturer calibratesdet
23、ector tubes to match the flow characteristics of its pump, and the use of one brand of tube with another brand of pump will giveunreliable results.6.3 Gas Sampling ChamberA suitable container can be devised from a half-litre polyethylene bottle (seeAny container of amaterial that is not Fig. 1). A 6
24、 mm outside diameter polyethylene tubing sealed into the bottle and discharging near the bottomof the bottle provides for flow into the sampling container. A 12 mm hole cut into the cap of the bottle provides both access forthe detector tube and a vent for the excess gas flow.reactive with mercaptan
25、 and that provides for access of the detector tube intoa uniform flow of sample gas at atmospheric pressure and isolated from the surrounding atmosphere.6.3.1 Gas Sampling ContainerAny container of a material that is notA suitable container may be devised from a half-litrepolyethylene bottle (see Fi
26、g. 1reactive with mercaptan and that provides for access of the detector tube into a uniform flow of3 Detector tube No. 72, manufactured by Gastec Corporation, based on the palladium sulfate detection principle, is calibrated for ethyl mercaptan; Gastec detector tubesNo. 75 and 75L, using mercuric c
27、hloride detection chemistry, are calibrated for t-butyl mercaptan. Other manufacturers tubes may be based on other detection chemistry.FIG. 1 Half Litre Polyethylene or Other Inert BottleD5305 122sample gas at atmospheric pressure and isolated from the surrounding atmosphere. ).A6 mm outside diamete
28、r polyethylene tubingsealed into the bottle and discharging near the bottom of the bottle provides for flow into the sampling container. A 12 mm holecut into the cap of the bottle provides both access for the detector tube and a vent for the excess gas flow.6.3.2 Other possible inert materials for t
29、he gas sampling chamber and tubing are nylon, polytetrafluoroethylene (PTFE),chlorinated or fluorinated polyethylene and chlorosulfonated polyethylene.6.4 Needle Valve and TubingA stainless steel needle valve that can be adjusted to control the flow of gas into the samplecontainer. gas sampling cham
30、ber. Although a stainless steel needle valve is preferred, a pressure regulator canmay be used in lieuof a needle valve to control the flow of gas into the sample container. gas sampling chamber. Polyethylene or TFE-fluorocarbonPTFE-fluorocarbon tubing canmay be used to connect the needle valve or p
31、ressure regulator to the gas samplingcontainer.chamber.7. Sampling the LP-Gas Vapor Phase7.1 Select a sampling point that provides access to a representative sample of LP-gas vapor from the container to be sampled.(WarningWhen selecting a sample point, consider the safety aspects of the release of L
32、PG vapor.)7.1.1 Open the source valve (ValveAin Fig. 1) and briefly blow down vigorously to clear foreign material from the source valveand connecting nipple. Close the source valve.7.1.1.1 Excess venting can result in a lower concentration of ethyl mercaptan in the vapor phase.7.1.2 Install the con
33、trol valve (Valve B in Fig. 1) or pressure regulator on the outlet of the source valve. Connect outlet of thecontrol valve to the gas sampling containerchamber using the shortest length practicable of suitable tubing.7.1.3 Open the source valve and then the control valve to obtain a slight positive
34、flow through the gas sample container,samplingchamber, venting to atmosphere through the tube access and vent (Vent C in Fig. 1). Purged gas must be vented at a sufficient rateso that pressure does not build up in the sampling container and increase the flow rate through the detector tube.7.1.3.1 Pu
35、rged gas shall be vented at a suitable rate so that pressure does not build up in the sampling chamber and increasethe flow rate through the detector tube.7.1.3.2 Conversely, the positive flow of LP gas vapor shall be sufficient so that operation of the detector tube pump does notpull ambient air in
36、to the gas sampling chamber which would dilute the LP-gas vapor.7.1.4 Purge the gas sample containersampling chamber for at least 3 min to displace air.7.1.5 Maintain flow of LP-gas during the test procedure in Section 9.8. Preparation of Apparatus8.1 Before sampling, all sampling equipment should b
37、e thoroughly clean and dry.8.2 Immediately before each series of tests, test the pump for tightness leak-free operation in accordance with manufacturersinstructions. A loss in vacuum on the pump within 60 s indicates a leak. If a leak occurs, follow the pump manufacturersinstructions for re-sealingr
38、esealing the pump and retest. If the pump vacuum cannot be maintained, do not use the pump for testing.9. Procedure9.1 Select the tube range that includes the expected concentration of ethyl mercaptan present in the sample. Reading accuracyis improved when the stain extends at least one-half of the
39、tube length. Consider multiple strokes or a lower range tube, or both,to achieve this length of stain.9.2 Break off both tips of the glass stain tube and insert the outlet of the tube (indicated by arrow in direction of flow) snuglyinto the pump head. Temperature of tube mustshall be maintained in t
40、he 0 to 40C range throughout the test.9.3 Insert the detector tube well into the gas sampling containerchamber through the tube access and vent (Vent C).9.4 Operate the pump to draw a measured amount of sample through the detector tube. Within any limits set by themanufacturers instructions, use mul
41、tiple strokes to achieve a stain extending to approximately one-half the tube length.9.5 Remove the tube from the pump and follow the manufacturers instructions if further handling of the tube is necessary.9.6 Immediately (within Within 30 s),seconds, read the concentration of ethyl mercaptan from g
42、raduations on the tube or fromcharts supplied with the tubes.tube. The scale reading nearest the end of the stain is the measured concentration of ethylmercaptan.taken as the appropriate scale reading.10. Interpretation of Results10.1 If the number of pump strokes used is different from the number s
43、pecified by the manufacturer, apply a correction mustbe made as follows:corrected ethyl mercaptan concentration5scale reading (1)3specified strokes/actual strokes!D5305 12310.2 Some detector tubes that canmay be used in this test method may be calibrated for other mercaptans in milligrams per cubicm
44、etre (mg/m3). The Perform the conversion from mg/m3 of t-butyl mercaptan to ppmv of ethyl mercaptan shall be performed asdocumented in Annex A1.10.3 Correct the reading for barometric pressure, especially at high altitudes. For details of this correction, see Annex A1.10.4 Readings of concentrations
45、 below 5 ppmv may not be reliable, and may warrant further investigation. (See Appendix X2.)NOTE 2This test method is a direct measure of the concentration of ethyl mercaptan in the vapor phase of LP-gas. If the temperature of the systemis known, results can be used to obtain an approximation of the
46、 concentration of ethyl mercaptan in the liquid phase. (See Appendix X1.)11. Report11.1 Report the observed tube reading and corrected concentration of ethyl mercaptan in parts per million by volume (ppmv)to the nearest 0.5 ppm.ppmv.12. Precision and Bias12.1 Precision:12.1.1 The precision of this t
47、est method as determined by statistical analysis of interlaboratory test results is as follows:12.1.1.1 RepeatabilityThe difference between successive test results, obtained by the same operator using the same apparatusunder constant operating conditions on identical test material, would, in the lon
48、g run, in the normal and correct operation of thetest method, exceed the following values only in one case in twenty: from 5 to 20 ppmv, the larger of 1 ppm or 615 % of the meanof the two results; above 20 ppmv, 620 % of the mean of the two results.12.1.1.2 ReproducibilityThe difference between two
49、single and independent results, obtained by different operators workingin different laboratories on identical test material, would, in the normal and correct operation of the test method, exceed thefollowing value only in one case in twenty: the larger of 1.5 ppmv or 620 % of the mean of the two results.NOTE 3The preceding repeatability and reproducibility were obtained from statistical analysis of results submitted by twelve testers whocooperatively tested five samples of propane with ethyl mercaptan concentrations ranging from 3.3 to 32 ppmv in the vapor p
