Class NK GDA for World First Vessel Tank Tech
Mitsubishi Shipbuilding Co., Ltd., part of Mitsubishi Heavy Industries (MHI) Group, and Nippon Steel Corporation have received the world’s first General Design Approval (GDA) from ClassNK for a breakthrough tank technology that enables the manufacture of large low-pressure liquefied CO₂ (LCO₂) cargo tanks without post-weld heat treatment (PWHT). The achievement marks a significant step toward scaling up CO₂ transport capacity to support global carbon capture, utilization and storage (CCUS) value chains.
At the core of the innovation is a newly developed high-strength steel—conforming to Nippon Kaiji Kyokai (NK) standard KF460—engineered by Nippon Steel to deliver high strength, exceptional low-temperature toughness and cost efficiency. Mitsubishi Shipbuilding applied this steel to large LCO₂ tank structures and performed an Engineering Critical Assessment (ECA) to validate structural integrity without PWHT, a process traditionally mandated by the IGC Code for carbon-manganese steel welds.
PWHT has long been a bottleneck in the scale-up of LCO₂ carrier designs. Few heat-treatment furnaces worldwide are capable of annealing tanks of the size required for next-generation CO₂ carriers, constraining shipyard productivity and limiting vessel capacity. By eliminating the need for PWHT through ECA-based justification, Mitsubishi Shipbuilding and Nippon Steel aim to streamline production, reduce manufacturing costs and support the rapid growth of the CO₂ shipping segment.
The GDA from ClassNK confirms that the PWHT-exempt tank design meets safety, strength and reliability requirements, making it the first approved solution of its kind globally. Mitsubishi Shipbuilding said the technology aligns with its broader cross-industry program to standardize large LCO₂ carriers, reduce transport costs and accelerate market adoption of CO₂ shipping as a key component of CCUS infrastructure.
Both companies plan to work with supply-chain partners to commercialize the steel and tank design, supporting shipyards and equipment manufacturers as LCO₂ carrier demand expands.
The project also reflects the MHI Group’s wider strategy to advance energy-transition technologies—from carbon transport to next-generation marine engineering—through technical collaboration and global partnerships. Mitsubishi Shipbuilding said the milestone underscores its commitment to delivering practical, scalable technologies that enable the maritime sector’s decarbonization pathways.
