Technical Development of a Liquefied CO2 Tank for Low Pressure Application in Marine Transportation

Abstract Carbon Dioxide Capture and Storage (CCS) is expected to be a key technology to achieve a carbon-neutral society. In the CCS value chain, efficient transportation connecting capture sources and storage sites is essential, and a liquefied CO2 (LCO2) carrier is seen as a feasible option for long-distance transportation compared to pipelines. Ensuring economic performance for CO2 transportation is vital in putting CCS into practice. In general, the most effective way to enhance the economic performance is to increase the amount of transported cargo per voyage. Therefore, it is desirable to increase the capacity of the cargo tank. From this perspective, low-pressure (LP) type LCO2 carriers have the lowest design pressure, which is advantageous for enlarging cargo tanks, and they are expected to be highly economical solution. The main technical challenge in realizing large LP-type cargo tanks is the development of suitable material. Through extensive evaluation, the carbon manganese steel of KF460, which complies with the Class NK rule, was selected as the optimal material for LP application. While the material development of KF460 contributes to significantly increasing the capacity of cargo tanks, implementation of post weld heat treatment (PWHT) is required when a carbon manganese steel is applied to a Type C tank. The implementation of PWHT will create a bottleneck in the tank fabrication process. In light of this challenge, this paper also describes the evaluation process for omitting PWHT through engineering critical assessment (ECA).