This revision incorporates the ‘Revised Interim Recommendations for Carriage of Liquefied Hydrogen in Bulk,’* adopted by the IMO in 2026, and updates the existing safety requirements, including guidance on the selection of materials and welding practices for hydrogen equipment. Through this revision, shipyards, designers, shipowners, and other maritime stakeholders can gain a clear understanding of the safety requirements for liquefied hydrogen carriers and can proceed with their design studies and safety assessments more smoothly.
Hydrogen is expected to play a key role as an energy carrier in realizing a decarbonized society, and the development of liquefied hydrogen carriers as a means of large-scale transportation is advancing worldwide. In recent years, the design of such vessels has become increasingly diverse, including the development of liquefied hydrogen carriers fitted with membrane-type cargo containment systems.
In response to recent developments in liquefied hydrogen carrier design, the Revised Interim Recommendations for Carriage of Liquefied Hydrogen in Bulk were adopted at the 111th session of the IMO Maritime Safety Committee (MSC 111), introducing additional safety requirements for cargo containment systems based on new design concepts.
The revised ClassNK Guidelines incorporate the provisions of these IMO Interim Recommendations while also reflecting the latest knowledge and experience gained through the construction and operation of demonstration vessels, as well as various research and development projects.
Main Revisions:
Requirements for Membrane-Type Cargo Containment Systems:
Following the adoption of the IMO Interim Recommendations at MSC 111, requirements have been developed for liquefied hydrogen carriers fitted with membrane tanks using vacuum insulation. In addition to incorporating the content of the IMO Interim Recommendations, the design requirements relating to vacuum insulation systems, monitoring devices, pressure control equipment, and emergency response have been clarified. This enables developers of newly designed liquefied hydrogen carriers fitted with membrane-type cargo containment systems to refer to internationally recognized safety requirements and to proceed smoothly with studies toward Flag Administration approval and safety demonstration.
Improved guidance on materials and welding for hydrogen equipment:
Based on ClassNK’s experience in design reviews and technical assessments in actual projects, the verification procedures for the selection of metallic materials, testing, and quality control have been updated. The revised guidance clarifies how to address material degradation that requires particular attention in the design of liquefied hydrogen carriers, such as low-temperature embrittlement, hydrogen embrittlement, and hydrogen attack, and is expected to reduce the risk of design changes and additional verification.
As a third-party certification body, ClassNK will continue to support the efforts of stakeholders to address environmental challenges through the development of standards, certification, and provision of technical information.
* IMO Resolution MSC.597(111) ‘Revised Interim Recommendations for Carriage of Liquefied Hydrogen in Bulk’
The guidelines are available to download via ‘Guidelines’ of My Page on ClassNK’s website after registration.
