ASTM D4888-20

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Designation: D4888 − 06 (Reapproved 2015) D4888 − 20
Standard Test Method for
Water Vapor in Natural Gas Using Length-of-Stain Detector
Tubes
This standard is issued under the fixed designation D4888; 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
1.1 This test method covers a procedure for rapid and simple field determination of water vapor in natural gas pipelines. Available
detector tubes provide a total measuring range of 0.1 to 40 mg/L, although the majority of applications will be on the lower end
of this range (that is, under 0.5 mg/L). At least one manufacturer provides tubes that read directly in pounds of water per million
cubic feet of gas. See Note 1.
1.2 Detector tubes are usually subject to interferences from gases and vapors other than the target substance. Such interferences
may vary among brands because of the use of different detection methods. Consult manufacturer’s instructions for specific
interference information. Alcohols and glycols will cause interferences on some water vapor tubes because of the presence of the
hydroxyl group on those molecules.
1.3 Units—The values stated in SI units are to be regarded as the standard.
1.4 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D4150 Terminology Relating to Gaseous Fuels
3. Terminology
3.1 Definitions—For definitions of general terms used in D03 Gaseous Fuels standards, refer to Terminology D4150.
4. Summary of Test Method
4.1 The sample is passed through a detector tube filled with a specially prepared chemical. Any water vapor present in the sample
This test method is under the jurisdiction of ASTM Committee D03 on Gaseous Fuels and is the direct responsibility of Subcommittee D03.07 on Analysis of Chemical
Composition of Gaseous Fuels.
Current edition approved Nov. 1, 2015Dec. 15, 2020. Published December 2015January 2021. Originally approved in 1988. Last previous edition approved in 20112015
as D4888 – 06 (2011).(2015). DOI: 10.1520/D4888-06R15.10.1520/D4888-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
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D4888 − 20
reacts with the chemical to produce a color change or stain. The length of the stain produced in the detector tube, when exposed
to a measured volume of sample, is directly proportional to the amount of water vapor present in the sample. A hand-operated
piston or bellows-type pump is used to draw a measured volume of sample through the tube at a controlled rate of flow. The length
of stain produced is converted to milligrams per litreliter of H O by comparison to a calibration scale supplied by the manufacturer
for each box of detection tubes. The system is direct reading, easily portable, and completely suited to making rapid spot checks
for water vapor under field conditions.
NOTE 1—Detector tubes are available with calibration scales printed in pounds of water per million cubic feet of gas (lb/MMCF). The conversion factor
is 1 mg/L = 62.3 lb/MMCF (7 lb/MMCF = 0.11 mg ⁄L).
5. Significance and Use
5.1 The measurement of water vapor in natural gas is important because of the gas quality specifications, the corrosive nature of
water vapor on pipeline materials, and the effects of water vapor on utilization equipment.
5.2 This test method provides inexpensive field screening of water vapor. The system design is such that it may be used by
nontechnical personnel with a minimum of proper training.
6. Apparatus
6.1 Length-of-Stain Detector Tubes—A sealed glass tube with the breakoff tips sized to fit the tube holder of the pump. The reagent
layer inside the tube, typically a silica gel substrate coated with the active chemical, must be specific for water vapor and produce
a distinct color change when exposed to a sample of gas containing water vapor. Any substances known to interfere must be listed
in the instructions accompanying the tubes. A calibration scale should be marked directly on the tube; however, other markings
that provide for ready interpretation of water vapor content from a separate calibration scale supplied with the tubes shall be
acceptable. The calibration scale shall correlate water vapor concentration to the length of the color stain. Shelf life of the detector
tubes must be a minimum of two years from date of manufacture when stored according to manufacturers’ recommendations.
6.2 Detector Tube Pump—A hand-operated pump of a piston or bellows type. It must be capable of drawing 100 mL per stroke
of sample through the detector tube with a volume tolerance of 65 mL. It must be specifically designed for use with detector
tubes.
NOTE 2—A detector tube and pump together form a unit and must be used as such. Each manufacturer calibrates detector tubes to match the flow
characteristics of its specific pump. Crossing brands of pumps and tubes is not permitted, as considerable loss of system accuracy is likely to occur.
6.3 Gas Sampling Chamber—Any container that provides for access of the detector tube into a uniform flow of sample gas at
atmospheric pressure and isolates the sample from the surrounding atmosphere. A stainless steel needle valve (or pressure
regulator) is placed between the source valve and the sampling chamber for the purpose of throttling the sample flow. Flow rate
should approximate one to two volume changes per minute or, at minimum, provide exit gas flow throughout the detector tube
sampling period.
NOTE 3—A suitable chamber may be devised from a polyethylene wash bottle of nominal 500-mL (16-oz) or 1-L (32-oz)500 mL (16 oz) or 1 L (32 oz)
size. The wash bottle’s internal delivery tube provides for delivery of sample gas to the bottom of the bottle. A ⁄2-in. in. hole cut in the bottle’s cap
provides access for the detector tube and vent for the purge gas (Fig. 1).
7. Procedure
7.1 Select a sampling point that will provide access to a representative sample of the gas to be tested (source valve on the main
line). The sample point should be on top of the pipeline and equipped with a stainless steel sample probe ext
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