In its 100th session last week, International Maritime Organisation's (IMO) Maritime Safety Committee approved interim guidelines on applying high manganese austenitic steel in cryogenic LNG storage and fuel tanks.
Known to resist corrosion, austenitic steels are non-magnetic stainless steels that contain high levels of chromium and nickel and low levels of carbon.
Liquefied natural gas (LNG) is cooled to very low temperatures for carriage, and IMO's interim guidelines set forth requirements for designing and manufacturing high manganese austenitic steel LNG cargo and fuel tanks and to ensure compliance with international gas carriage and fuel use maritime safety codes.
South Korea's POSCO steel manufacturing company stands to benefit from the new guidelines, which open the way for sales of the material to IMO's 170-plus member states.
Following more than a decade of research, POSCO developed the high-manganese austenitic steel with the storage and transport of LNG specifically in mind. Of proven strength and cryogenic toughness, the steel can withstand temperatures as low as -196℃. Among the steelmaker’s claims for the product is its ease of weldability and a cost 20-30% below the nickel alloy steel, stainless steel and aluminum alloy alternatives.
POSCO developed the high manganese steel for LNG tanks in 2013 and estimated it could sell nearly US$100M of the product by 2021, according to South Korea's state-funded Yonhap news agency.
Thus far, IMO has allowed nickel steel, aluminum alloy and stainless steel for LNG tanks. Currently, high manganese austenitic steel costs about six times less than nickel steel and is more than twice as cheap as aluminum alloys, Yonhap reported.
High-manganese steel has also shown superiority over existing cryogenic materials in terms of ultimate tensile strength and elongation. In addition, the relatively small thermal expansion coefficient of the steel means that the displacement caused by the temperature changes inherent in cryogenic applications is minimal.
POSCO’s high-manganese steel was registered as a standard technology with the American Society for Testing and Materials (ASTM) in May 2017. The ASTM stamp of approval means that the steel is recognised as a material that can be safely used worldwide.
In May 2016, following a proposal from South Korea, IMO began to consider the suitability of high-manganese austenitic steels as a suitable material for cargo tanks, fuel tanks and piping on LNG carriers and LNG-fuelled ships. The initiative was launched with a view to amending the IGF Code and the International Gas Carrier Code (IGC Code) to include this steel.
IMO members agreed a draft of the interim guidelines in a meeting of the Sub-Committee on Carriage of Cargoes and Containers (CCC) on 10-14 September 2018
The MSC group also agreed to look at the procedure for considering and approving alternative metallic material for cryogenic service in the IGC and IGF Codes; and gather and evaluate information and data on any practical experience gained with design and production when using high manganese austenitic steel for cryogenic service. The group will report back to CCC 6.