ASTM D8446-22
(Test Method)Standard Test Method for Water Vapor Content in Compressed Air Using Electronic Moisture Analyzers
Standard Test Method for Water Vapor Content in Compressed Air Using Electronic Moisture Analyzers
SIGNIFICANCE AND USE
5.1 Water vapor is ubiquitous and a basic contaminant in compressed air. It cannot be eliminated but shall be controlled. Knowledge of the vapor content of compressed air is important for industrial processes to ensure that compressors that generate compressed air are functioning properly and equipment and systems that use the compressed air will function properly and maintain high reliability. This test method describes the measurement of water vapor using direct readout electronic instrumentation. Measurements are provided as dew point/frost point and calculations of related unitless quantities (ppm) are provided. Sampling techniques and warnings are provided to reduce false readings caused by contamination from the sampling method. Dry compressed air typically has a frost point between –80 °C and –40 °C (0.5 PPMV to 127 PPMV) at atmospheric pressure.
5.2 Measurement of moisture in compressed air can be done after regulating the pressure down to ATM or measured at elevated pressure up to the full system pressure. When measurements are made of the actual dew point (for example, condensation) or the related property of vapor pressure, the value of the dew point (and vapor pressure) is directly affected by the sample pressure since the vapor pressure is a component of the total pressure. The relationship between vapor pressure and moisture content (and dew point) is well defined below 5 MPa, but at greater pressures, additional study needs to be done to define this relationship.
5.3 Electronic moisture analyzers are also used for measuring moisture levels in other gases, including gaseous fuels. See Test Method D5454. In addition, tunable diode laser spectroscopy (TDLAS) is another technology that may be applicable to detecting moisture in compressed air. This technology is already being used in gases. See Test Method D7904.
SCOPE
1.1 This test method covers the determination of the water vapor content in compressed air using portable or in-situ electronic moisture analyzers. Such analyzers commonly use sensing cells based on phosphorus pentoxide, P2O5, aluminum oxide, Al2O3, or silicon piezoelectric-type cells or laser-based technologies.
1.2 This test method is applicable for the range of condensation temperatures from –80 °C to 60 °C.
1.3 Testing is often performed at reduced pressure from the full pressure of the system or source of compressed air depending on the capability of the specific analyzer. Testing above 2000 kPa may introduce additional uncertainty because of changes in the relationship between water vapor pressure and actual moisture content at elevated pressures.
1.4 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.
1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 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.
General Information
Relations
Standards Content (Sample)
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.
Designation: D8446 − 22
Standard Test Method for
Water Vapor Content in Compressed Air Using Electronic
1
Moisture Analyzers
This standard is issued under the fixed designation D8446; 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 D1356 Terminology Relating to Sampling and Analysis of
Atmospheres
1.1 This test method covers the determination of the water
D4178 Practice for Calibrating Moisture Analyzers
vapor content in compressed air using portable or in-situ
D4230 Test Method for Measuring Humidity with Cooled-
electronic moisture analyzers. Such analyzers commonly use
Surface Condensation (Dew-Point) Hygrometer
sensing cells based on phosphorus pentoxide, P O , aluminum
2 5
D5454 Test Method for Water Vapor Content of Gaseous
oxide, Al O , or silicon piezoelectric-type cells or laser-based
2 3
Fuels Using Electronic Moisture Analyzers
technologies.
D7904 Test Method for Determination of Water Vapor
1.2 This test method is applicable for the range of conden-
(Moisture Concentration) in Natural Gas by Tunable
sation temperatures from –80 °C to 60 °C.
Diode Laser Spectroscopy (TDLAS)
1.3 Testing is often performed at reduced pressure from the
full pressure of the system or source of compressed air 3. Terminology
depending on the capability of the specific analyzer. Testing
3.1 Definitions—For definitions of other terms used in this
above 2000 kPa may introduce additional uncertainty because
test method, refer to Terminology D1356.
of changes in the relationship between water vapor pressure
3.2 Definitions of Terms Specific to This Standard:
and actual moisture content at elevated pressures.
3.2.1 capacitance-type cell, n—this cell typically uses alu-
1.4 Units—The values stated in SI units are to be regarded
minum coated with aluminum oxide, Al O , as part of a
2 3
as the standard. No other units of measurement are included in
capacitor.
this standard.
3.2.1.1 Discussion—The dielectric Al O film changes the
2 3
1.5 This standard does not purport to address all of the
capacity of the capacitor in relation to the water vapor present.
safety concerns, if any, associated with its use. It is the
Silicone cells also operate on this principal by reporting a
responsibility of the user of this standard to establish appro-
capacitance change when adsorbing or desorbing water vapor.
priate safety, health, and environmental practices and deter-
3.2.2 dew point, n—temperature (at a specified pressure) at
mine the applicability of regulatory limitations prior to use.
which liquid water will start to condense from the water vapor
1.6 This international standard was developed in accor-
present as measured over water.
dance with internationally recognized principles on standard-
3.2.2.1 Discussion—The term “dew point” is often used to
ization established in the Decision on Principles for the
include “frost point” (see 3.2.4) when generally referring to the
Development of International Standards, Guides and Recom-
water content based upon this principle, but there are unique
mendations issued by the World Trade Organization Technical
values for each for temperatures below 0 °C.
Barriers to Trade (TBT) Committee.
3.2.3 electrolytic-type cell, n—this cell is composed of two
noble metal electrode wires coated with phosphorus pentoxide,
2. Referenced Documents
P O .
2
2 5
2.1 ASTM Standards:
3.2.3.1 Discussion—A bias voltage is applied to the elec-
trodes and water vapor chemically reacts generating a current
between the electrodes proportional to the reaction with the
1
This test method is under the jurisdiction of ASTM Committee D22 on Air
water vapor present.
Quality and is the direct responsibility of Subcommittee D22.13 on CompressedAir
Quality.
3.2.4 frost point, n—temperature (at a specified pressure) at
Current edition approved June 1, 2022. Published August 2022. DOI: 10.1520/
which liquid water will start to condense from the water vapor
D8446-22.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
present as measured over ice.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.2.5 laser-type cell, n—consists of a sample cell with an
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. optical head mounted on one end and a mirror mounted on the
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.