Overview
ISO 8943:2007 - "Refrigerated light hydrocarbon fluids - Sampling of liquefied natural gas - Continuous and intermittent methods" - specifies standardized procedures for collecting representative LNG samples while LNG is being transferred through an LNG transfer line. The second edition (2007) updates the technical requirements for both continuous and intermittent sampling to support accurate composition analysis used in density and calorific-content calculations for custody transfer and quality control.
Key topics and technical requirements
- Scope and purpose: Methods for continuous and intermittent sampling of LNG during transfer, ensuring representative samples for composition and calorific-value determination.
- Sampling system outline: All methods require gasifying the liquid sample in an LNG sample vaporizer before collection. Continuous and intermittent flows are described with flow diagrams for water-seal and waterless sample holders, and for CP/FP (constant pressure / floating piston) containers.
- Apparatus: Descriptions and requirements for key components - sample probe, LNG sample vaporizer, accumulator, pressure regulator, compressors (for transferring and for charging samples), gas sample holders (water-seal and waterless), gas sample containers, sample filters and piping arrangements.
- Sample probe placement: Probes must be located where LNG is sub-cooled; degree of sub-cooling is checked by temperature/pressure comparison (see Annex A).
- Sampling procedures: Guidance on sampling periods, consecutiveness, suspension of sampling, and specific steps for continuous vs intermittent sampling. Continuous sampling maintains a constant flow; intermittent sampling collects in CP/FP containers and can feed online gas chromatographs.
- Precautions & supervision: Safety measures for handling cryogenic LNG (frostbite, asphyxiation, fire), mitigation of partial evaporation effects, continuous monitoring of pressures, temperatures and flow rates, and inspection of insulation and leaks.
- Annexes: Annex A - example calculation of degree of sub-cooling; Annex B - technical specifications for CP/FP sample containers.
Practical applications
- Custody transfer of LNG where composition determines billing (calorific-content basis).
- Quality control and acceptance testing at LNG terminals, loading/unloading arms, vessels and pipeline transfer points.
- Sampling protocols for laboratory analysis, offline and online gas chromatography.
- Procedural basis for metrology, auditing and regulatory compliance in LNG operations.
- LNG terminal operators and transfer line engineers
- Laboratory analysts and gas chromatograph users
- Custody transfer and commercial teams requiring accurate calorific calculations
- HSE and operations personnel responsible for safe sampling and cryogenic handling
- Equipment suppliers (sample probes, vaporisers, CP/FP containers) and system integrators
Related standards
- ISO 10715:1997 (Natural gas - Sampling guidelines) - normative reference for sampling principles used with ISO 8943.
Keywords: ISO 8943, LNG sampling, continuous sampling, intermittent sampling, CP/FP sample container, LNG transfer line, sample probe, LNG vaporizer, custody transfer, gas chromatograph.
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