Overview
EN ISO 6570:2004 - Natural gas: Determination of potential hydrocarbon liquid content - Gravimetric methods (ISO 6570:2001) specifies two gravimetric procedures to measure the potential hydrocarbon liquid content (PHLC) or condensate that can form from natural gas at a given pressure and temperature. The standard is intended for representative gas samples and defines both a manual weighing reference method (Method A) and an indirect automatic weighing method (Method B). Unless otherwise stated, gas volumes are expressed in cubic metres at 273.15 K and 101.325 kPa.
Key topics and technical requirements
- Two defined methods
- Method A (manual weighing): direct collection and gravimetric determination of condensate; used as the reference method.
- Method B (indirect automatic weighing): semi-continuous method that infers condensate mass from the pressure difference caused by liquid accumulation in a vertical tube; calibrated against Method A.
- Principle: pressurize a representative sample, heat before pressure reduction to avoid premature condensation, then cool isobarically to the measurement temperature and collect formed liquid.
- Apparatus and installation: requirements for sample lines (stainless steel tubing), cyclone separators, measuring tubes, differential pressure gauges and safe instrumentation for hazardous areas.
- Sampling and sample handling: conditions for direct and indirect sampling and guidance to ensure representative samples (normative reference to ISO 10715 sampling guidelines).
- Procedure and results: step-by-step measurement, expression of results, and reporting requirements.
- Quality and metrology: uncertainty of measurement, calibration examples (Annex C), checks for correct installation, and factors affecting precision (leakage, bath liquid, wet gas).
- Informative annexes: selection of measurement temperature/pressure (Annex A), apparatus line-up examples (Annex B), calibration and example measurements (Annixes C and D).
Applications and users
This standard is practical for professionals involved in:
- Gas producers and processing plants - design and verification of condensate recovery and treatment systems.
- Transmission and distribution network operators - assessing condensate formation risk and sizing of separators and pigging/drainage systems.
- Metering and custody-transfer laboratories - calibrating or validating continuous dew-point/condensate monitors.
- Instrument manufacturers and calibration labs - developing or validating semi-continuous condensate measurement equipment (Method B).
- Regulatory and compliance teams - documenting test reports and measurement uncertainty for operational or contractual requirements.
Related standards
- ISO 10715 (Natural gas - Sampling guidelines) is normative for sampling practice referenced in EN ISO 6570:2004.
- Other gas-property calculation standards (e.g., ISO 6976, ISO 12213 series) are relevant when reporting volumes, compression factors and derived properties.
This standard is essential for accurate determination of condensable hydrocarbon liquids in natural gas and for calibrating instruments that estimate dew point or potential liquid content.
