Overview
EN ISO 6327:2008 is a key European and international standard developed by CEN and ISO that specifies methods for the determination of the water dew point in natural gas using cooled surface condensation hygrometers. This standard is crucial for gas analysis, focusing on accurately measuring the water vapor content by detecting condensation on a cooled mirror surface. The method provides absolute measurements without requiring calibration, operating effectively at pressures equal to or greater than atmospheric pressure.
This standard, originally issued as ISO 6327:1981 and adopted unchanged by CEN as EN ISO 6327:2008, provides comprehensive guidance on the design, operation, and limitations of condensation hygrometers used in natural gas water dew point determination. It addresses essential technical details including apparatus characteristics, measurement principles, and common sources of error, ensuring precise moisture content analysis of natural gas.
Key Topics
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Principle of Measurement
Water dew point is determined by cooling a reflective surface (mirror) exposed to natural gas until water vapor condenses. The temperature at which condensation first appears is considered the dew point temperature, corresponding to the water vapor pressure in the gas.
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Apparatus Description
The hygrometer consists of a metallic mirror surface cooled via different methods such as indirect contact cooling, thermo-electric (Peltier) cooling, or gas expansion cooling. It includes a temperature measurement system for precise mirror temperature monitoring and often incorporates optical systems or photoelectric cells for detecting condensation.
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Operational Guidelines
Key operational aspects emphasize minimizing sample line length to reduce pressure drops, maintaining the temperature of all parts other than the mirror above the dew point to avoid unwanted condensation, and the importance of mirror cleanliness for accurate readings.
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Sources of Error and Interferences
Attention is placed on identifying and mitigating factors affecting accuracy such as presence of condensable hydrocarbons, solid impurities, or vapor contaminants other than water vapor. The cold wall error-condensation occurring on surfaces other than the mirror-is discussed, with recommendations to keep the apparatus temperature controlled above condensation thresholds.
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Applications with Methanol and Hydrocarbon Condensates
The standard notes that methanol presence affects measurements since it also condenses on the mirror; specific correction factors are suggested. Hydrocarbon condensation does not directly alter water dew point but complicates condensation detection and interpretation.
Applications
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Natural Gas Transmission and Distribution
Ensuring optimal dryness levels in pipelines to prevent equipment corrosion and hydrate formation by regular dew point measurement.
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Gas Quality Control
Monitoring water vapor content during gas processing to meet industry specifications and regulatory standards.
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Industrial Gas Analysis
Used in industries where natural gas moisture content is critical, such as petrochemical plants, power generation, and LNG facilities.
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Research and Development
Instrument calibration, design verification, and new sensor development for precise water content analysis in gaseous fuels.
Related Standards
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ISO/TC 193 “Natural Gas” Standards
This technical committee develops related standards dealing with natural gas analysis and quality, including moisture measurement and gas composition.
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ISO 14956 - Natural gas - Determination of water content by chilled mirror hygrometer
Complements EN ISO 6327 by providing more detailed procedures and instrumentation for water vapor measurement.
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EN 14181 - Quality assurance for automated measuring systems
Relevant for ensuring reliable and traceable moisture measurement systems in gas analysis.
Practical Value
Adopting EN ISO 6327:2008 enables industry professionals to:
- Perform accurate and reproducible water dew point measurements critical for safe and efficient natural gas handling.
- Utilize standardized procedures and equipment specifications, reducing variability across measurements and operators.
- Identify and mitigate measurement interferences and environmental factors, ensuring data integrity.
- Facilitate compliance with regulatory and contractual moisture content requirements in natural gas markets.
This standard is indispensable for engineers, laboratory technicians, and quality assurance specialists involved in natural gas humidity measurement and control.