Overview
ISO 23306:2020 - Specification of liquefied natural gas as a fuel for marine applications - defines quality requirements, test methods and reporting for Liquefied Natural Gas (LNG) used as a ship fuel. The standard covers LNG from any source (conventional gas, shale gas, coalbed methane, biomethane, synthetic methane) and applies to fuel delivered at the time and place of custody transfer (the delivery/bunkering point). It supports safe, consistent bunkering and engine performance by specifying measurable parameters, limit values and reference test methods.
Key topics and technical requirements
- Scope and reference conditions
- Applies to LNG from fossil or renewable sources; gaseous reference conditions: 288.15 K, 101.325 kPa.
- Mandatory measured parameters
- Net Calorific Value (NCV): minimum 33.6 MJ/m3 (calculation method: ISO 6976).
- Nitrogen content: maximum 1.0% (mol) (measurement: ISO 6974).
- Methane Number (MN) (knock resistance): method (e.g., Propane Knock Index - PKI - or EN 16726) and required minimum must be agreed between supplier and user; supplier shall calculate and report actual MN at delivery.
- Composition and reporting
- Density (liquid phase), methane, ethane, propane, butanes, pentane and other main components must be reported (test method: ISO 6974, ISO 6578).
- Sampling
- Sampling procedures follow ISO 8943 (continuous and intermittent methods). Liquid samples must be gasified instantly without partial vaporization to ensure representativity.
- Contaminants and safety
- LNG must be free from materials at concentrations harmful to personnel, ship safety or machinery. Common removed compounds (sulfur species, heavy hydrocarbons, H2S) are addressed; some species are listed as not requiring routine measurement but must be controlled via quality assurance.
- Supporting guidance (Annexes)
- Includes methods for MN calculation (Annex A), LNG composition examples (Annex B), MN vs Wobbe index guidance (Annex C), ageing along the bunkering chain (Annex D), particles (Annex E) and boiling/melting points of components (Annex F).
Practical applications and who uses it
- Shipowners and operators: to specify acceptable LNG fuel quality at bunkering and reduce engine/machinery risk.
- LNG suppliers and terminals: to define delivery specifications, sampling procedures and custody-transfer documentation.
- Engine and equipment OEMs: to reference fuel quality limits (MN, calorific value, contaminants) for engine tuning and warranty conditions.
- Bunker surveyors, port authorities and regulatory bodies: for quality verification, compliance and safety assessments.
- Naval architects and fuel-system designers: to design LNG fuel systems compatible with specified fuel properties (density, composition, contaminants).
Related standards (key references)
- ISO 6974 - Natural gas composition by gas chromatography
- ISO 6976 - Calculation of calorific values and Wobbe index
- ISO 8943 - Sampling of LNG (continuous and intermittent)
- EN 16726 - Gas quality (Group H) and alternative MN methods
- ISO 6578, ISO 19739, ISO 20729, ISO 13443 - referenced for measurement, density, sulfur and reference conditions
Keywords: ISO 23306:2020, LNG fuel quality, marine applications, methane number, Wobbe index, bunkering, LNG sampling, calorific value, custody transfer, biomethane.