POSCO and Hanwha Ocean have signed a memorandum of understanding to develop and test high-manganese steel in the cargo tanks of large LNG carriers, extending a material already used in LNG fuel tanks into the far more demanding role of primary cargo containment. The agreement, reported on 21 October 2026, is a research and demonstration compact rather than a construction contract: the stated deliverable is a demonstration vessel whose tanks would be built from the new steel and evaluated for safety, durability and operational efficiency under real operating conditions.
That distinction matters commercially. There is no ship order, no nominated shipowner, no classification society approval for cargo containment in the public record, and no steel tonnage booked. Anyone reading the announcement as the start of a procurement cycle is ahead of the evidence.
Why this is an order-of-magnitude question, not a material substitution
The strategic logic is steel volume per ship. According to figures cited in the announcement, an LNG fuel tank consumes roughly 1,000 tonnes of steel, while an LNG carrier's cargo tanks can require more than 10,000 tonnes. For POSCO, qualifying a cargo-tank steel converts a niche market sized in hundreds of tonnes per hull into one sized in thousands.
| Application | Indicative steel content per vessel | Status of high-Mn steel |
|---|---|---|
| LNG fuel tank | ~1,000 t | In use (material qualified and deployed) |
| LNG carrier cargo tank | >10,000 t | Demonstration stage; no cargo-containment service history |
These are company-supplied rules of thumb, not audited take-offs for any specific design, and should be read as orders of magnitude only. They nonetheless explain why the partners are pursuing this.
POSCO's material is claimed to retain high strength and impact toughness at cryogenic temperatures of −163 °C and below — just under LNG's atmospheric boiling point of about −162 °C — and is positioned against nickel-alloy steel, specifically the 36% nickel INVAR used in the incumbent GTT NO96 membrane system, on cost and security-of-supply grounds.
The gap the demonstration has to close
A demonstration vessel is still needed, in the partners' framing, to build an operational track record. That implies the material's metallurgy is mature enough for scrutiny while its service credentials in cargo containment are not yet established — a reasonable inference from the announcement, not a confirmed statement about which approvals exist. Classification society acceptance of high-Mn steel specifically for LNG cargo containment, and containment-system design acceptance by a licensor, are the gating items, and neither is named.
Technically the step up is bigger than the tonnage suggests. Cargo tanks form the ship's primary and secondary barrier, so qualification goes beyond low-temperature toughness to fatigue and crack-arrest behaviour, weldability at the very high plate thicknesses a 10,000-tonne tank implies, thermal expansion compatibility and acceptance of the containment design by class societies and by the charterers and oil-and-gas majors who vet LNG tonnage. That is a fabrication-industrialisation challenge for the yard as much as a metallurgical one for POSCO.
The competitive detail the announcement omits
The explicit benchmark is INVAR-based NO96. The more direct comparator is arguably GTT Mark III, whose corrugated stainless steel membranes sidestep both INVAR cost and nickel supply risk — and which already carries service experience. How high-Mn plate compares with stainless membrane systems on total installed cost, weld productivity and repair strategy is the question that will decide adoption, and it is not addressed in the public material.
Hanwha Ocean's role
Hanwha Ocean, the Geoje-based shipyard formerly known as DSME and part of Hanwha Group, is an experienced membrane-type LNG carrier builder with recent deliveries including 15 Arc7 ice-class LNG carriers for Yamal LNG. It has the containment credentials to qualify a new tank material, but its own English-language newsroom did not carry the high-manganese announcement at the time of writing, which may indicate the release was issued by POSCO or published only in Korean.
Status: what is and is not settled
The instrument is an MOU, so the programme sits at feasibility stage. Beyond Hanwha Ocean, no tank fabricator, shipowner, charterer, class society or containment licensor has been identified.
- Settled: the partnership, the material's cryogenic rating, the intended demonstration, and the extended ambitions towards LNG bunkering vessels, FSRUs and cryogenic hydrogen, ethane and ammonia transport. Those extensions are stated intent, not committed scope.
- Open: demonstration vessel timing, size, steel tonnage and owner; cargo-containment class approval; and when shipowners might adopt the material for commercial LNG carriers.
For steel suppliers and fabricators, the practical read is a multi-year qualification path, not an open package. No plate procurement has been announced. Any future tonnage would depend on classification approval and a shipowner stepping forward — neither of which is evidenced today.