ISO 4257:2001 - Liquefied petroleum gases (LPG) - Method of sampling
Overview
- ISO 4257:2001 specifies the standardized procedure for obtaining representative liquid samples of unrefrigerated liquefied petroleum gases (LPG) for laboratory testing and compositional analysis.
- It is intended primarily for sampling from bulk containers and pipelines and supports compositional testing by ISO 7941. It is not intended for trace analysis of low‑boiling components (see ASTM D 3700 for variable‑volume receivers).
Key topics and technical requirements
- Scope and purpose: Sampling method for liquid‑phase LPG (propane, butanes and related hydrocarbons) to produce representative samples for laboratory analysis.
- Representative sampling: Take samples from the liquid phase only; avoid vessel bottoms; improve homogeneity by circulation and wait 30 minutes before sampling to allow settling and dissipation of static charge.
- Sample container design: Use metal, corrosion‑resistant two‑valve containers with an ullage tube sized so that the container is filled to 80% (V/V) liquid (20% ullage). Stainless steel is recommended; aluminium is not permitted. Single‑valve containers are not acceptable. Label cylinders with sampling metadata.
- Transfer line and fittings: Use metal transfer lines with a control valve, vent valve, and a pressure‑relief valve vented to a safe location. The section to the container valve should use armoured flexible tubing. Use metal sample connectors.
- Purging and filling procedure: Purge transfer line, purge the container (repeat at least three times) and then fill. Steps include controlled venting and rotation of the container to flush residual contamination.
- Ullage and leak checking: Immediately provide ullage by releasing excess liquid until vapour appears, leaving 80% liquid. Check for leaks (for example by immersion). Discard and re‑sample if leaks occur.
- Safety precautions: Ground/bond equipment, use PPE (gloves, goggles), avoid skin contact and inhalation, pressure‑test containers, cap valves for transport, and comply with local transport regulations. Cleaning with acetone then pentane and purging with gaseous propane is described for previously contaminated containers.
Applications and users
- Useful to: petroleum terminal operators, ship/shore transfer personnel, sampling technicians, quality control (QC) laboratories, regulators and inspection bodies involved in LPG trade, custody transfer and product quality verification.
- Typical applications: creating representative LPG samples for gas chromatography compositional analysis, product specification verification (ISO 9162), custody transfer disputes, and routine quality control.
Related standards
- ISO 7941 - Commercial propane and butane - Analysis by gas chromatography.
- ISO 9162 - Liquefied petroleum gases - Specifications.
- ASTM D 3700 - Practice for containing hydrocarbon fluid samples (variable‑volume receiver for trace low‑boiling analysis).
Keywords: ISO 4257:2001, LPG sampling, liquefied petroleum gases, sampling method, sample container, ullage, transfer line, safety precautions, compositional analysis.