Development of Design Procedure for LNG Carriers With IMO Type-B Independent Tank

There is a growing interest in applying the technology to small and medium-sized Liquefied Natural Gas (LNG) carriers to meet the recent increase in demand for LNG as an ecofriendly fuel and for expanding LNG bunkering infrastructure. The purpose of this study is to apply the IMO Type B tank to small and medium-sized LNG carriers and verify the safety and suitability of the design. One of the key technical issues of Type B LNG tank is heat transfer analysis and selection of hull steel grade. In this study, a heat transfer analysis was performed for hull temperature calculation and steel grade selection. Also, the stress levels and the thermal movements of the tank were checked through thermal stress analysis applying thermal and mechanical loads. Another key technical issue of a Type B tank is to determine the size of a partial secondary barrier based on fracture mechanics. For the accurate analysis, a procedure was developed and verified based on direct analysis and international regulations. Finally, the related safety and suitability of the IMO Type B for LNG cargo tanks required by International Gas Carrier (IGC) code were verified. Two key technical issues with applied examples are thoroughly analyzed in this study, could be applied in the design of independent Type B LNG carrier.