POSCO and Hanwha Ocean Take High-Manganese Steel Into the Last Fortress of Nickel: The LNG Cargo Tank

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, moving the material out of the comparatively modest LNG fuel-tank niche and into the containment system of the ship itself. The partners intend to build a demonstration vessel fitted with high-manganese cargo tanks and to evaluate safety, durability and operational efficiency under real trading conditions, with the explicit aim of accumulating a service record that shipowners and class societies will accept.

The commercial arithmetic is the reason this is more than another materials R&D MOU. According to POSCO, an LNG fuel-tank installation consumes roughly 1,000 t of steel per vessel; LNG carrier cargo containment can require more than 10,000 t. That is an order-of-magnitude step in steel intensity per hull, and it explains why a steelmaker would accept the long, expensive qualification path that cargo containment demands.

What the announcement actually commits to

The reported facts are limited and should be read precisely: an MOU, a demonstration vessel, a testing programme covering safety, durability and operational efficiency, and a stated sequence of follow-on applications — LNG bunkering vessels and FSRUs, then cryogenic transport of hydrogen, ethane and ammonia. No tonnage for the demonstration ship, no capacity in cubic metres, no delivery or trial date, no classification society, no containment-system licensor and no owner-operator are named in the available reporting. Neither company's own newsroom had published a detailed release at the time of writing.

That gap matters because the missing names are precisely the ones that determine whether this is a two-year demonstration or a decade-long qualification campaign.

The material is not the hard part

POSCO's high-manganese austenitic steel — typically in the 22–25% manganese range with aluminium and carbon additions — was developed as a lower-cost alternative to nickel-bearing cryogenic steels. It retains strength and impact toughness at LNG carriage temperatures of about −163 °C, and POSCO claims cost and supply advantages over the INVAR nickel-iron alloy used as the primary barrier in the dominant membrane containment systems.

The metallurgy, in other words, is largely settled: POSCO has already placed the grade in LNG fuel tanks, where it operates under the IMO IGF Code framework. The cargo tank is a different problem class. LNG cargo containment is not a steel specification but a qualified system — material, weld procedures, insulation, leak detection, secondary barrier and structural analysis approved as a package by a classification society, and in the membrane case licensed by the containment designer. The two dominant families, GTT's Mark III (stainless steel corrugated primary barrier) and NO96 (INVAR primary barrier), are approved as integrated systems.

Substituting a new primary-barrier material therefore requires the containment designer and the class society to re-qualify the system, not simply to accept a mill certificate. POSCO and Hanwha Ocean will have to decide whether to:

The announcement does not say which route the demonstration vessel follows. This is the single most consequential unknown, because the tonnage claim of ">10,000 t per vessel" only holds if the material penetrates primary containment at scale in membrane ships.

Sizing the prize, cautiously

Treat the following as an illustrative calculation rather than a forecast. At roughly 10,000 t of high-manganese plate per large LNG carrier and, say, ten such ships a year adopting the grade, incremental demand would be on the order of 100,000 t annually — meaningful for a specialised plate product, but a rounding error against POSCO's overall plate output. The value case rests less on volume than on margin: a qualified, proprietary, class-approved cryogenic grade commands a premium and displaces an imported nickel alloy whose cost and supply are exposed to nickel markets and a concentrated supplier base.

For Hanwha Ocean, the incentive is competitive differentiation. Korean yards are under sustained price pressure from Chinese competitors, and control over a domestically sourced containment material offers both a cost lever and a marketing story to shipowners facing decarbonisation-driven fleet renewal.

Why the sequence to FSRUs and ammonia is the real strategic signal

The follow-on list — bunkering vessels, FSRUs, then hydrogen, ethane and ammonia — is where the MOU's logic becomes clear. FSRUs and ammonia carriers share the same cryogenic or semi-refrigerated containment problem, and an approved high-manganese grade would travel across all of them. If the demonstration succeeds at the cargo-tank level, POSCO is not selling into one ship type but into a family of gas-carriage applications whose common denominator is a material qualification it would own.

That is also why the track record framing is correct and unusually candid. Shipowners and their insurers will not accept a novel primary barrier on the strength of laboratory toughness data; they will want years of in-service inspection. The demonstration vessel is a qualification instrument, and its value lies in the data it generates, not in the steel it contains.

What to watch

• Containment concept and licensor. Any GTT involvement, or a decision to pursue independent Type B/C tanks, reveals the ambition level.
• Class society approval. A general approval or approval-in-principle from KR, LR, DNV or ABS for high-manganese steel as cargo-containment material would be the decisive technical milestone; without one, the demonstration remains a science project.
• Demo vessel specification and funding. Capacity, newbuild versus conversion, trial date and any Korean government co-funding (MOTIE and related programmes have historically supported cryogenic material development) will indicate how serious the commitment is.
• An in-service reference for the fuel-tank application. The credibility of the cargo-tank case rests on the operating history of the earlier, simpler application.

Until those details emerge, the appropriate reading is that POSCO has opened a credible but long front against nickel-based containment — one whose outcome will be decided in class-society committee rooms rather than at the steelworks.