Engineering Critical Assessment for Alternative Materials to IGC Code for LCO2 Carriers Type-C Tanks

Abstract With the developing market of Carbon Capture, Utilisation and Storage (CCUS), large volumes of CO2 need to be transported over large distances. To this end, a cost-effective solution is to consider the maritime transportation of liquefied CO2 (LCO2). Within the LCO2 carriers, the LCO2 can be contained in large diameter type-C tanks under high pressure / low temperature conditions, typically 19bara at −30°C but with now considering alternates with lower pressures (10bara @−50°C). The consideration of such pressures together with the intended tank diameter leads to the use of high strength steel grades, which are not covered by the International Maritime Organization regulations (IGC Code) governing the design of type-C tanks in liquefied gas carriers. Furthermore, the high strength steel grades intended for this application are known to exhibit a ductile to brittle transition at moderately low temperature, contrary to the materials usually used for transport of liquefied gases which can exhibit a ductile behaviour at very low temperatures. Therefore, in order to quantify the toughness requirements of these high strength steel grades for application on type-C tanks on LCO2 carriers, engineering critical assessment (ECA) have been carried out taking into account various design parameters such as the design pressure, the plate thickness or the stress relief method. In order to allow a continuity with the IGC Code requirements and maintain its inherent safety level, the IGC Code building assumptions were kept whenever possible and complemented otherwise with guidance from BS7910 standard. The analyses allowed defining minimum required CTOD toughness levels and provide useful guidance for steel manufacturers and construction yards for the material selection, the welding procedures and associated NonDestructive Testing procedures.