ISO 20257-1:2020

Overview - ISO 20257-1:2020 (Floating LNG design general requirements)

ISO 20257-1:2020 sets out the general requirements and guidance for the design and operation of floating liquefied natural gas (LNG) installations. It covers floating liquefaction units (FLNG), floating storage and regasification units (FSRU), and floating storage units (FSU) in offshore, near‑shore or docked conditions. The standard addresses liquefaction, storage, vaporisation, transfer and handling of LNG with the objective of safe and environmentally acceptable design and operation. It applies to both newbuild and converted floating LNG vessels and includes mooring considerations for docked installations. Exclusions include onshore LNG plants (except docked FSRU/FLNG), non‑floating offshore structures (e.g., GBS), support onshore facilities and LNG bunkering.

Key topics and technical requirements

ISO 20257-1 provides comprehensive, high‑level design guidance across major technical disciplines:

• Basis of design: site and metocean studies, seismic and location considerations, design criteria for topsides, hull, transfer systems, LNG storage and piping.
• Health, safety and environment (HSE): safety philosophies, barrier identification, environmental impact considerations, emergency response and occupational hygiene.
• Mooring & stationkeeping: permanent and temporary mooring concepts, disconnectable moorings, jetty interface and mooring requirements for open‑water and docked operations.
• Hull design: structural design philosophies, limit states, fatigue, slamming, green water and watertight integrity.
• Transfer systems & LNG handling: requirements for safe transfer, containment loads, vaporisation and cargo handling procedures.
• Human factors: ergonomics, crew accommodations, lighting, noise and support for onboard operators.

These topics are structured to support risk‑based design reviews, qualitative risk assessments (QRA) and safety certification processes.

Practical applications and users

ISO 20257-1 is intended for professionals involved in the lifecycle of floating LNG projects:

• Offshore engineers and naval architects designing FLNG, FSRU or FSU hulls and topsides
• Process and safety engineers developing liquefaction, storage, vaporisation and transfer systems
• Project managers and classification societies conducting design reviews and certification
• Owners/operators assessing conversion projects and docking/mooring arrangements
• Regulators and HSE specialists evaluating environmental and emergency response requirements

Use cases include concept and FEED stages, detailed design, conversion scope definition and safety/environmental compliance checks.

Related guidance and standards

For a complete compliance and technical basis, ISO 20257-1 should be used alongside:

• other parts of the ISO 20257 series and applicable maritime/LNG industry codes
• classification society rules and project‑specific regulatory requirements

Keywords: ISO 20257-1, floating LNG, FLNG, FSRU, FSU, floating storage, LNG transfer, mooring, hull design, LNG safety, environmental design.