ASTM D5305-97(2007)
(Test Method)Standard Test Method for Determination of Ethyl Mercaptan in LP-Gas Vapor
Standard Test Method for Determination of Ethyl Mercaptan in LP-Gas Vapor
SIGNIFICANCE AND USE
LP-gas is colorless and odorless, and not detectable by normal human senses. To provide an olfactory warning in the event of a leak, LP-gas intended for domestic or commercial use is intentionally odorized so as to be readily detectable well below flammable or suffocating concentration levels of LP-gas in air. (See Appendix X1.) The most common odorant for LP-gas is ethyl mercaptan. The field use of this test method will rapidly determine the presence and concentration of ethyl mercaptan in LP-gas vapor without the necessity for complex laboratory equipment.
SCOPE
1.1 This test method covers a rapid and simple procedure using length of stain tubes for field measurement of ethyl mercaptan in the vapor phase of LP-gas systems. Although length-of-stain tubes are available to detect ethyl mercaptan concentrations in the range of 0.5 to 120 parts per million volume (ppmv), this test method is specifically applicable to systems containing 5 ppmv or more of ethyl mercaptan in LP-gas vapors.
Note 1 - A 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.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D5305 − 97(Reapproved 2007)
Standard Test Method for
Determination of Ethyl Mercaptan in LP-Gas Vapor
This standard is issued under the fixed designation D5305; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
1.1 This test method covers a rapid and simple procedure 4.1 LP-gas is colorless and odorless, and not detectable by
using length of stain tubes for field measurement of ethyl normal human senses. To provide an olfactory warning in the
mercaptan in the vapor phase of LP-gas systems. Although event of a leak, LP-gas intended for domestic or commercial
length-of-stain tubes are available to detect ethyl mercaptan use is intentionally odorized so as to be readily detectable well
concentrations in the range of 0.5 to 120 parts per million below flammable or suffocating concentration levels of LP-gas
volume (ppmv), this test method is specifically applicable to in air. (See Appendix X1.) The most common odorant for
systems containing 5 ppmv or more of ethyl mercaptan in LP-gasisethylmercaptan.Thefielduseofthistestmethodwill
LP-gas vapors. rapidly determine the presence and concentration of ethyl
mercaptan in LP-gas vapor without the necessity for complex
NOTE 1—A chromatographic technique can be used for more precise,
laboratory equipment.
quantitative determination of ethyl mercaptan in LP-gas.
1.2 The values stated in SI (metric) units are to be regarded
5. Interferences
as the standard.
5.1 Detector tubes can be subject to interferences from
1.3 This standard does not purport to address all of the
materials other than the target substance. Methyl mercaptan
safety concerns, if any, associated with its use. It is the
will likely interfere with tubes designed to measure ethyl
responsibility of the user of this standard to establish appro-
mercaptan. Because of different detection chemistry by differ-
priate safety and health practices and determine the applica-
ent manufacturers, interferences can vary. Consult the manu-
bility of regulatory limitations prior to use.
facturer’s instructions for specific interference information and
observe any instructions given.
2. Referenced Documents
5.2 Propylene (propene) will cause an interfering (gray)
2.1 NFPA Standard:
discoloration with some tubes designed for ethyl mercaptan.
NFPA58 StandardfortheStorageandHandlingofLiquefied
LP-gas from natural gas sources usually does not contain
Petroleum Gases
propylene (propene). However, LP-gas produced in refinery
operations often does contain propylene (propene). Detector
3. Summary of Test Method
tubes calibrated for t-butyl mercaptan eliminate this
3.1 Using a manually-operated vacuum pump, a sample of
interference, and should be used if the presence of propylene
LP-gas is drawn through a detector tube made specifically for
(propene) is suspected. Some tubes designed for measurement
detection of mercaptans. The length of stain (color change)
of t-butyl mercaptan are calibrated in milligrams per cubic
produced in the detector tube when exposed to a measured
metre (mg/m ) and should be converted to ppmv ethyl mer-
volume of sample is directly proportional to the amount of
captan as shown in Annex A1.
ethyl mercaptan present in the sample being tested. The length
of stain produced in the detector tube is converted to
6. Apparatus
concentration, in parts per million volume (ppmv), by com-
6.1 Pump—A manually-operated vacuum pump, capable of
parison with a calibration scale provided by the manufacturer
drawing 100 mLper stroke of sample through the detector tube
of the stain tubes.
with an accuracy of 62.0 mL.
6.2 Detector Tubes—Sealed tubes, made of glass with
This test method is under the jurisdiction of ASTM Committee D02 on
break-off tips sized to fit the orifice of the pump used (tubes
Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee
and pumps from different manufacturers should not be inter-
D02.H0 on Liquefied Petroleum Gas.
Current edition approved May 1, 2007. Published June 2007. Originally
changed). The tube used must be appropriate for the determi-
approved in 1992. Last previous edition approved in 2002 as D5305 – 97 (2002).
nation of ethyl mercaptan and must produce a distinct color
DOI: 10.1520/D5305-97R07.
change when exposed to a sample of LP-gas containing ethyl
Available from National Fire Protection Association (NFPA), 1 Batterymarch
Park, Quincy, MA 02169-7471, http://www.nfpa.org. mercaptan.Any substance known to interfere must be listed in
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5305 − 97 (2007)
6.4 NeedleValveandTubing—Astainless steel needle valve
that can be adjusted to control the flow of gas into the sample
container. Although a stainless steel needle valve is preferred,
a pressure regulator can be used in lieu of a needle valve to
control the flow of gas into the sample container. Polyethylene
or TFE-fluorocarbon tubing can be used to connect the needle
valve or pressure regulator to the gas sampling container.
7. Sampling
7.1 Select a sampling point that provides access to a
representative sample of LP-gas vapor from the container to be
sampled.
7.1.1 Open the source valve (Valve A in Fig. 1) and blow
down vigorously to clear foreign material from the source
valve and connecting nipple. Close the source valve.
7.1.2 Install the control valve (Valve B in Fig. 1) or pressure
regulator on the outlet of the source valve. Connect outlet of
the control valve to the gas sampling container 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 flow through the gas sample container,
venting to atmosphere through the tube access and vent (Vent
Cin Fig. 1). Purged gas must be vented at a sufficient rate so
FIG. 1 Half Litre Polyethylene Bottle
that pressure does not build up in the sampling container and
increase the flow rate through the detector tube.
7.1.4 Purge the gas sample container for at least 3 min to
instructions accompanying the tubes (see 5.2). A calibration
displace air.
scale or other markings referenced to a scale must be etched
7.1.5 Maintain flow of LP-gas during the test procedure in
directly on the tube to allow direct interpretation of ethyl
Section 9.
mercaptan concentration.
6.2.1 Detector tubes must be calibrated for a tube tempera-
8. Preparation of Apparatus
ture of approximately 20°C and normal atmospheric pressure.
8.1 Before sampling, all sampling equipment should be
Shelflifeofthedetectortubesmustbeaminimumoftwoyears
thoroughly clean and dry.
when stored according to the manufacturer’s recommenda-
8.2 Immediately before each series of tests, test the pump
tions.
for tightness in accordance with manufacturer’s instructions.A
6.2.2 Detector tubes and pumps form an integrally designed
loss in vacuum on the pump within 60 s indicates a leak. If a
unit, that must be used as a unit. Each manufacturer calibrates
leak occurs, follow the pump manufacturer’s instructions for
detector tubes to match the flow characteristics of its pump,
re-sealing the pump and retest. If the pump vacuum cannot be
and the use of one brand of tube with another brand of pump
maintained, do not use the pump for testing.
will give unreliable results.
6.3 A suitable container can be devised from a half-litre
9. Procedure
polyethylene bottle (see Fig. 1). A 6 mm outside diameter
polyethylene tubing sealed into the bottle and discharging near 9.1 Select the tube range that includes the expected concen-
the bottom of the bottle provides for flow into the sampling tration of ethyl mercaptan present in the sample. Reading
container.A12 mm hole cut into the cap of the bottle provides accuracy is improved when the stain extends at least one-half
both access for the detector tube and a vent for the excess gas of the tube length. Consider multiple strokes or a lower range
tube, or both, to achieve this length of stain.
flow.
6.3.1 GasSamplingContainer—Anycontainerofamaterial
9.2 Break off both tips of the glass stain tube and insert the
that is not reactive with mercaptan and that provides for access
outlet of the tube (indicated by arrow in direction of flow)
of the detector tube into a uniform flow of sample gas at
snugly into the pump head. Temperature of tube must be
atmospheric pressure and isolated from the surrounding atmo-
maintained in the 0 to 40°C range throughout the test.
sphere.
9.3 Insert the detector tub
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