Standard Test Method for Determination of Ethyl Mercaptan in LP-Gas Vapor

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.
1.3 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.

General Information

Status
Historical
Publication Date
09-Nov-1997
Current Stage
Ref Project

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ASTM D5305-97(2002) - Standard Test Method for Determination of Ethyl Mercaptan in LP-Gas Vapor
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Designation: D 5305 – 97 (Reapproved 2002)
Standard Test Method for
Determination of Ethyl Mercaptan in LP-Gas Vapor
This standard is issued under the fixed designation D 5305; 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 (e) 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-gas is ethyl mercaptan. The field use of this test method will
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.
NFPA 58 Standard for the Storage and Handling of Lique-
LP-gas from natural gas sources usually does not contain
fied 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 interfer-
3.1 Using a manually-operated vacuum pump, a sample of
ence, and should be used if the presence of propylene (pro-
LP-gas is drawn through a detector tube made specifically for
pene) is suspected. Some tubes designed for measurement of
detection of mercaptans. The length of stain (color change)
t-butyl mercaptan are calibrated in milligrams per cubic metre
produced in the detector tube when exposed to a measured
(mg/m ) and should be converted to ppmv ethyl mercaptan as
volume of sample is directly proportional to the amount of
shown in Annex A1.
ethyl mercaptan present in the sample being tested. The length
of stain produced in the detector tube is converted to concen-
6. Apparatus
tration, in parts per million volume (ppmv), by comparison
6.1 Pump—A manually-operated vacuum pump, capable of
with a calibration scale provided by the manufacturer of the
drawing 100 mL per stroke of sample through the detector tube
stain tubes.
with an accuracy of 62.0 mL.
6.2 Detector Tubes—Sealed tubes, made of glass with
break-off tips sized to fit the orifice of the pump used (tubes
This test method is under the jurisdiction of ASTM Committee D02 on
and pumps from different manufacturers should not be inter-
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
changed). The tube used must be appropriate for the determi-
D02.H on Liquified Petroleum Gas.
Current edition approved Nov. 10, 1997. Published June 1998. Originally
nation of ethyl mercaptan and must produce a distinct color
published as D 5305 - 92. Last previous edition D 5305 - 92.
change when exposed to a sample of LP-gas containing ethyl
Available from National Fire Protection Association, 1 Batterymarch Park,
mercaptan. Any substance known to interfere must be listed in
Quincy, MA 02269.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5305
instructions accompanying the tubes (see 5.2). A calibration container. Although a stainless steel needle valve is preferred,
scale or other markings referenced to a scale must be etched a pressure regulator can be used in lieu of a needle valve to
directly on the tube to allow direct interpretation of ethyl control the flow of gas into the sample container. Polyethylene
mercaptan concentration. or TFE-fluorocarbon tubing can be used to connect the needle
6.2.1 Detector tubes must be calibrated for a tube tempera- valve or pressure regulator to the gas sampling container.
ture of approximately 20°C and normal atmospheric pressure.
7. Sampling
Shelf life of the detector tubes must be a minimum of two years
when stored according to the manufacturer’s recommenda- 7.1 Select a sampling point that provides access to a
representative sample of LP-gas vapor from the container to be
tions.
6.2.2 Detector tubes and pumps form an integrally designed sampled.
7.1.1 Open the source valve (Valve A in Fig. 1) and blow
unit, that must be used as a unit. Each manufacturer calibrates
detector tubes to match the flow characteristics of its pump, down vigorously to clear foreign material from the source
valve and connecting nipple. Close the source valve.
and the use of one brand of tube with another brand of pump
will give unreliable results. 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
6.3 A suitable container can be devised from a half-litre
polyethylene bottle (see Fig. 1). A 6 mm outside diameter the control valve to the gas sampling container using the
shortest length practicable of suitable tubing.
polyethylene tubing sealed into the bottle and discharging near
the bottom of the bottle provides for flow into the sampling 7.1.3 Open the source valve and then the control valve to
obtain a slight positive flow through the gas sample container,
container. A 12 mm hole cut into the cap of the bottle provides
venting to atmosphere through the tube access and vent (Vent
both access for the detector tube and a vent for the excess gas
flow. C in Fig. 1). Purged gas must be vented at a sufficient rate so
that pressure does not build up in the sampling container and
6.3.1 Gas Sampling Container—Any container of a mate-
rial that is not reactive with mercaptan and that provides for increase the flow rate through the detector tube.
7.1.4 Purge the gas sample container for at least 3 min to
access of the detector tube into a uniform flow of sample gas
at atmospheric pressure and isolated from the surrounding displace air.
7.1.5 Maintain flow of LP-gas during the test procedure in
atmosphere.
6.4 Needle Valve and Tubing—A stainless steel needle valve Section 9.
that can be adjusted to control the flow of gas into the sample
8. Preparation of Apparatus
8.1 Before sampling, all sampling equipment should be
Detector tube No. 72, manufactured by Gastec Corporation, based on the
thoroughly clean and dry.
palladium sulfate detection principle, is calibrated for ethyl mercaptan; Gastec
8.2 Immediately before each series of tests, test the pump
detector tubes No. 75 and 75L, using mercuric chloride detection chemistry, are
calibrated for t-butyl mercaptan. Other manufacturer’s tubes may be based on other for tightness in accordance with manufacturer’s instructions. A
detection chemistry.
loss in vacuum on the pump within 60 s indicates a leak. If a
leak occurs, follow the pump manufacturer’s instructions for
re-sealing the pump and retest. If the pump vacuum cannot be
maintained, do not use the pump for testing.
9. Procedure
9.1 Select the tube range that includes the expected concen-
tration of ethyl mercaptan present in the sample. Reading
accuracy is improved when the stain extends at least one-half
of the 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 ins
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