Overview
EN ISO 18453:2005 (ISO 18453:2004) defines a validated, composition‑dependent mathematical correlation between water content and water dew point in natural gas. Developed by GERG and adopted by CEN, the standard gives a reliable calculation method applicable in either direction (water content → dew point or dew point → water content). It provides the correlation uncertainty but does not quantify measurement uncertainties.
Key topics
- Correlation method: Based on GERG research and the Peng‑Robinson equation of state; thermodynamic principles and α‑function treatment for vapour pressure over ice and liquid are described (see Annex A).
- Validation: Experimental database gathered using the saturation method for seven representative natural gases and methane/water across the dew‑point range of interest.
- Working range:
- Absolute pressure: 0.5 MPa to 10 MPa
- Water dew‑point temperature: −15 °C to +5 °C
- Composition limits: accepts water plus typical natural‑gas components (methane, N2, CO2, C2–C6+ hydrocarbons) within ranges given in the standard (Table 1).
- Extended range (extrapolated, uncertainties unknown): pressures 0.1–30 MPa and dew points −50 °C to +40 °C.
- Uncertainty of correlation:
- Water dew point calculated from water content: ±2 °C
- Water content calculated from dew point: piecewise composition‑dependent expressions with an uncertainty band (refer to Annex B/C for formulas and examples).
- Traceability and examples: Annex B covers traceability; Annex C provides worked calculation examples.
Applications
EN ISO 18453 is practical for:
- Pipeline operators and gas transmission companies assessing condensation risk, corrosion, hydrate and ice formation.
- Custody transfer and gas metering where contractual water specifications must be converted between dew point and water content.
- Dehydration system design to size and specify molecular sieves or glycol units based on required water removal.
- Laboratories and instrument manufacturers validating moisture analysers that report water content or dew point.
- Gas quality engineers and researchers modelling moisture behaviour under changing pressure/temperature conditions.
Who should use it
Natural gas quality managers, metering engineers, pipeline integrity teams, lab analysts, instrument vendors and standards committees working with moisture measurement, custody transfer, dehydration design and thermodynamic modelling.
Related standards
- ISO 14532 (normal reference conditions, traceability)
- ISO 13443 (conversion between reference conditions)
- ISO 3534‑1 (terminology for correlation/statistics)
EN ISO 18453 provides a standardized, GERG‑based correlation that helps convert reliably between water content and water dew point in natural gas-essential for operational safety, contract compliance, and equipment design.
