Large Scale LNG Carrier

Working with Shanghai Merchant Ship Design and Research Institute (SDARI), LNT Marine has scaled up its LNT A-BOX containment system to an Atlantic max size of 175,000m3 LNGC, with American Bureau of Shipping (ABS) granting the design an approval in principle in May this year. Increasing the capacity by 300% from the 45,000m3 design first installed on the pioneering ABS-classed LNGC Saga Dawn, the new design includes learnings from the construction as well as ongoing successful operation of Saga Dawn, now renamed LNG Jia Xing.

The SDARI designed 175,000m³ large-scale LNG carrier has 4 tanks (3 x 45,000m3 and 1 x 40,000m3) efficiently adopted to the carrier’s hull form. The overall hull lines give the carrier low resistance and fuel consumption. The tank structure is robust and reliable, with internal structure mitigating any sloshing and thus allowing no filling level restrictions. The primary barrier (the tank itself) is uninsulated while the insulation and secondary barrier is attached to the hull and separated from the cargo tank with a 600mm inter-barrier space. This space enables access for visual inspection of both tank and secondary barrier as well as the tank support system, which is unique for containment systems. The thickness of the insulation is about 400mm and the BOR is only 0.075% per day, which is lower than the industry standard for LNG carriers of similar size. Each tank has two pumps for loading/unloading capacity, and with partial re-liquefaction, the carrier meets the operational requirements of large LNG carriers.

The key drawings and calculations have been completed and the structural assessment has been carried out in accordance with the requirements of ABS’s LGC Guide. Yielding, buckling and fatigue strength of the main structures generally meets ABS’s acceptance criteria, subject to further optimization during the detail design stage.

Having previously focused mainly on the hull characteristics, ABS undertook a detailed analysis of the tank structure and its interaction with the ship’s hull. ABS Global Engineering teams and ABS Technology have assessed the design, furthering the original vessel’s AIP to include additional tank details and integration into the hull. A Finite Element Analysis (FEA) of the tanks was undertaken including the material change from steel to aluminum, and detailed fatigue assessments of critical areas using ABS’s total strength assessment methodology was utilised in the evaluation. 

LNT Marine is also in partnership with China First Heavy Industries (CFHI) Dalian Nuclear Power and Petrochemical Company, a large manufacturer of nuclear reactors as well as pressure vessels for the petrochemical industry. At their factory in Dalian, China, they have skilled welders and advanced welding facilities able to mass-produce large scale tanks. In collaboration with ABS, SDARI and LNT Marine, the technical team at CFHI Dalian has conducted thorough tests on aluminum alloy welding. CFHI Dalian has built a 3D corner mock-up of an aluminum tank with representative details including shell plate corners, web/girder crossing and brackets – for a mid-ship tank of 45,000m3. The completed mock-up demonstrates design principles and constructability, making CFHI ready to supply tanks for LNT A-BOX type carriers for all types of liquid gases including LNG, LEG and Ammonia.

A 6-months technical assessment program of the 175,000m3 design involving all parties mentioned above and led by a third-party engineering firm, was completed in September this year. It concluded that the new design is technically sound and constructable and meets all requirements expected of a large-scale LNG carrier.