Overview
ISO 6570:2001 - Natural gas: Determination of potential hydrocarbon liquid content - Gravimetric methods describes two gravimetric procedures for measuring the quantity of hydrocarbon condensate that a natural gas (or similar gas) can form at a specified pressure and temperature. The standard defines a manual weighing reference method (Method A) and an indirect automatic method (Method B) based on differential pressure caused by liquid accumulation. It is used to quantify potential hydrocarbon liquid content (PHLC) for design, control and instrument calibration. Note: gas volumes are by default referenced to 273.15 K and 101.325 kPa.
Key topics and technical requirements
- Measurement principle: bring a representative gas sample to set pressure, cool isobarically to the measurement temperature, collect condensed liquid and determine mass (gravimetric basis).
- Two methods:
- Method A - Manual weighing of collected condensate or cyclone separator (reference method).
- Method B - Indirect automatic weighing using pressure difference in a vertical tube (suitable for semi-continuous control).
- Sampling and sample handling: heated, temperature-controlled sample lines; options for direct or indirect sampling; optional drying tube to prevent hydrate formation (use agents that do not absorb hydrocarbons).
- Apparatus requirements: stainless-steel tubing, dust filters (e.g., 5 µm), heat exchangers, pressure regulators/controllers (pressure stability requirement noted), gas/liquid cyclone separator and thermostatically controlled baths.
- Instrumentation: gas flow meters (mass or volumetric; meter error ≤ 1% recommended), temperature and pressure monitoring (gas and ambient), and for indirect sampling a heated cabinet for sample cylinders.
- Quality and uncertainty: procedures for checking installation, calibration of differential pressure gauges, addressing leakage, bath liquid stability, wet-gas effects and reporting uncertainty of measurement.
- Supporting material: annexes for selecting measurement temperature/pressure, example line-ups, calibration examples and sample measurements.
Applications and who uses it
- Gas producers and processing plants - quantify condensate formation for process design and removal systems.
- Transmission and distribution operators - assess condensate risks in pipelines and networks and design mitigation.
- Calibration and testing laboratories - reference method (Method A) for calibrating dew-point or condensate-measuring instruments.
- Instrument manufacturers and OEMs - validate semi-continuous condensate monitors (Method B).
- Regulators and auditors - provide standardized test reports and compliance evidence.
Related standards
- ISO 6976 (calorific values and density)
- ISO 10715 (natural gas sampling guidelines)
- ISO 12213 parts 1–3 (compression factor calculations)
Keywords: ISO 6570:2001, natural gas, potential hydrocarbon liquid content, PHLC, gravimetric methods, condensate measurement, Method A, Method B, gas sampling, dew point, gas/liquid cyclone separator.
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