[Report] "Minus 163 Degrees No Problem" Visiting the Heart of LNG Transport Innovation 'High Manganese Steel' Production

Birth of LNG Transport Innovation at POSCO Gwangyang Steelworks
Enhancing Competitiveness by Increasing High-Manganese Steel Ratio
Overcoming Challenging Processes with Proprietary Technology

POSCO Gwangyang Steelworks in Gwangyang-si, Jeollanam-do, considered the 'heart' of domestic steel production. When the curtains surrounding the auditorium were drawn open, a vast network of massive pipes, intricately yet orderly connected like spider webs, came into view at once. The vigorous steam emitted from about ten thick chimneys and the movement of dozens of cargo trucks and large trucks conveyed the unique vitality of the steelworks.

On the afternoon of the 26th of last month, we visited the site where the world’s first newly developed high-manganese steel by POSCO is produced, the heart of South Korea’s steel production. As it is a national security facility, personal photography was strictly prohibited; the press covered their phone cameras with stickers and kept laptops in bags before stepping into the steelworks.

At POSCO Gwangyang Steelworks' heavy plate mill, high manganese steel heavy plate products are stacked after undergoing the rolling process. The longest product visible in the photo is about the height of a 4 to 5-story apartment building. Photo by POSCO

Liquefied natural gas (LNG) is produced by removing impurities such as ammonia and hydrogen sulfide from natural gas and compressing and liquefying it to about 1/600th of its volume at minus 163 degrees Celsius, making it transportable by ship. This is why LNG requires highly advanced material properties such as cryogenic resistance, high strength, and wear resistance to enable large-scale transportation and storage.

Until now, LNG tanks have mainly been made from alloy materials such as nickel and aluminum, which are expensive raw materials. However, nickel is produced only in certain countries, leading to unstable supply and price volatility depending on supply and demand. POSCO anticipated a continuous increase in LNG demand following the strengthening of international environmental regulations in 2008 and recognized the need to develop new materials. Leveraging decades of accumulated control rolling and cooling technology in the steel sector, POSCO succeeded in producing a product with high strength while increasing the proportion of manganese, which is prone to brittleness. In particular, POSCO developed a new high-manganese (22.5?25.5%) alloy steel that compensates for the shortcomings of existing nickel alloy steel, securing competitiveness not only in LNG but also in the future energy market.

Senior Researcher Lee Soon-gi of POSCO explained, “When we first developed and launched the material, many customers were reluctant to use the product, but POSCO decided to create the code first on land and sea and prove the results by launching the world’s first LNG fuel-powered bulk carrier using high-manganese steel,” adding, “After more than ten years of effort, we have also completed code registration with the International Maritime Organization (IMO).”

The image shows high-manganese steel being rolled at the heavy plate mill. The process is carried out under precise calculations to meet the thickness requirements requested by the customer. The high-manganese steel slab is pressed and turned in the rolling mill here, then repeatedly cooled in cold water, eventually becoming a high-manganese steel heavy plate product. Photo by POSCO

After a 20-minute drive from headquarters, the interior of the thick plate factory did not require wearing outerwear. When the bright red, square high-manganese steel slabs appeared, the heat could be felt even from a distance of 10 to 20 meters. Jung Young-deok, leader of POSCO’s thick plate technology development section, explained, “When the high-manganese steel is heated to 1100?1300 degrees Celsius and ready for rolling, the slab arrives at this thick plate factory. High-manganese materials are highly reactive with oxygen, so heating requires considerable technical expertise.”

When waterfall-like water poured over the slab moving on the steel rollers, steam rose to the height of a 2- to 3-story apartment. White steam remained on the rollers where the slab had passed for several minutes, indicating how hot the slab was. Leader Jung added, “The slab heating time takes about 200 to 300 minutes, and the high-manganese steel slabs are managed with stricter time control than other materials. The entire process from start to finish takes 4 to 5 hours.”

Each time the slab passed through POSCO’s powerful rolling mill, its surface became smoother and cleaner. Leader Jung said, “High-manganese steel is much stronger than other materials, so it requires greater force to press it,” adding, “The rollers wear down with each pressing of the slab.” He continued, “It is important to precisely reduce the slab thickness, so the thickness is measured every time in a ‘radiation zone’ to manage the high-manganese steel,” noting, “Tolerance ranges vary by product but are generally about 0.8 to 1 mm.”

While high-manganese steel has advantages such as high strength and suitability for cryogenic conditions, its processing is very challenging. Leader Jung said, “Since we are producing a product that has never been attempted worldwide, we have continuously worked to resolve process peculiarities,” explaining, “Because it takes considerable time to raise the temperature during the melting process of manganese steel, POSCO has established an integrated process from steelmaking to rolling, including melting manganese at high temperatures.” Leader Jung added, “Thanks to these efforts, we were able to maximize the advantages and overcome the disadvantages, making it a next-generation energy steel.”

A thinly rolled high manganese steel plate is being moved by a vacuum crane at the heavy plate mill. High manganese steel is non-magnetic, so it cannot be moved using a magnetic crane as in the traditional method. Provided by POSCO

After walking about five more minutes, the thick high-manganese steel, which looked like a mattress, was spread out in a thin and flat form. Products that had recently undergone the rolling and cooling process sometimes showed a slight pink hue. Because high-manganese steel is non-magnetic, it cannot be moved with magnetic cranes like ordinary products; instead, vacuum cranes that suction like vacuum cleaners are used. Due to its thickness, it cannot be coiled and must be transported as individual sheets, which is cumbersome.

On this day, construction of the 7th LNG tank applying high-manganese steel was in full swing at the LNG terminal. POSCO International applied high-manganese steel starting from the 5th and 6th storage tanks at the LNG terminal. When all tanks are completed in 2026, POSCO will secure a total LNG storage capacity of 1.33 million cubic meters, enough to supply heating gas for the entire population for 40 days. Kim Myung-gyu, General Manager of POSCO International, introduced, “The company is focusing on expanding the global value chain from LNG production and transportation to storage, sales, and construction,” adding, “We have established an independent LNG terminal by applying our directly developed cryogenic high-manganese steel to LNG storage tanks.”

Inside Tank No. 7 of Gwangyang 2nd LNG Terminal. The parts in direct contact with LNG at minus 163 degrees Celsius were made of high manganese steel. POSCO has demonstrated safety by conducting various performance tests, including more than 1,000 LNG filling and emptying tests. Photo by POSCO

The International Maritime Organization (IMO) implemented regulations from 2020 to reduce sulfur oxide emissions from ships from 3.5% to 0.5%. In response, shipping companies are adopting LNG-powered vessels with almost no sulfur oxide emissions, and demand for POSCO’s LNG fuel tanks is expected to increase further.

Senior Researcher Lee Soon-gi said, “POSCO is continuing efforts to expand the transportation applications of high-manganese steel tanks not only for LNG but also for ammonia, hydrogen, and other uses,” and added, “We will continuously strengthen global competitiveness through the development of high value-added products, cost reduction, and the establishment of a low-carbon production system.”