ASTM D8446-22 PDF
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
- Статус документа:
- Действующий
- Формат:
- Электронный (PDF)
- Количество страниц:
- 7
- Дата публикации:
- 1 июня 2022 г.
- Издание:
- D8446
- ICS:
- 71.100.20
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.
Abstract
Overview
ASTM D8446-22, "Standard Test Method for Water Vapor Content in Compressed Air Using Electronic Moisture Analyzers," provides a rigorous method to determine water vapor content in compressed air systems. Published by ASTM International, this standard focuses on using both portable and in-situ electronic moisture analyzers, ensuring reliable and accurate moisture measurements vital for industrial and commercial compressed air applications. The method is applicable to a wide range of condensation temperatures, from –80 °C to 60 °C, and is designed for sample pressures up to 2000 kPa, beyond which additional precautions and uncertainties may arise.
Water vapor is a ubiquitous contaminant in compressed air, impacting the operation, longevity, and reliability of compressors and downstream equipment. By identifying and controlling water vapor levels using this standard, facilities can help ensure optimal equipment function, minimize downtime due to moisture-related issues, and maintain high product and process quality.
Key Topics
- Types of Electronic Moisture Analyzer Technologies: Includes phosphorus pentoxide, aluminum oxide, silicon piezoelectric, and tunable diode laser (TDLAS) cells.
- Measurement Ranges and Units: Moisture quantified in dew point/frost point (°C) as well as in parts per million by volume (PPMV) and weight (PPMW).
- Sampling Techniques: Emphasizes the importance of correct sampling procedures and equipment material selection to minimize false readings due to contamination or moisture retention.
- Pressure Considerations: Outlines the effect of sample pressure on moisture readings and highlights uncertainties above 2000 kPa (20 bara).
- Calibration and Validation: Stresses regular calibration and periodic validation of analyzers to ensure data integrity.
- Safety and Environmental Precautions: Addresses handling compressed air safely and mitigating hazards during sampling and testing.
Applications
- Compressed Air Quality Monitoring: Ensures that air supplied to industrial processes meets required dryness criteria, preventing equipment corrosion, malfunctions, or product contamination.
- System Performance Verification: Confirms the efficiency and health of compressors and air dryers.
- Preventive Maintenance: Early detection of rising moisture levels allows for proactive maintenance, reducing downtime and repair costs.
- Broad Gas Analysis Use: Electronic moisture analyzers described in ASTM D8446-22 can also be adapted for moisture measurement in other gases, including gaseous fuels, by referencing related ASTM methods.
Testing is carried out using commercial or portable hygrometers and sample test rigs that are constructed from materials with low moisture absorption properties, such as 300-series stainless steel or PTFE-coated hoses. The methodology includes detailed sampling, measurement, calibration, and reporting procedures suitable for both direct line and portable test scenarios.
Related Standards
Understanding ASTM D8446-22’s context is enhanced by familiarity with related ASTM standards, which address complementary aspects of moisture measurement:
- ASTM D1356 – Terminology Relating to Sampling and Analysis of Atmospheres
- ASTM D4178 – Practice for Calibrating Moisture Analyzers
- ASTM D4230 – Test Method for Measuring Humidity with Cooled-Surface (Dew-Point) Hygrometer
- ASTM D5454 – Test Method for Water Vapor Content of Gaseous Fuels Using Electronic Moisture Analyzers
- ASTM D7904 – Test Method for Determination of Water Vapor (Moisture Concentration) in Natural Gas by Tunable Diode Laser Spectroscopy (TDLAS)
These standards collectively support best practices for quantifying and controlling water vapor in various gaseous environments, enhancing reliability and compliance across industries.
Keywords: ASTM D8446-22, water vapor, compressed air, electronic moisture analyzers, dew point, frost point, moisture content, calibration, compressed air quality, industrial air systems, TDLAS, air sampling method, ppmv, moisture measurement.
Технические детали
- Технический комитет
- D22 - Air Quality
- SKU
- ASTM D8446-22
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