Comparative Wet Drop Experiments of Mark III and KC-1 for Membrane Type LNG Carriers

The increasing demand for safe storage and transportation of LNG (Liquefied Natural Gas) in the global energy market initiated a trend for further development of the design technology for LNG tanks. An LNG tank in LNG carriers or FLNGs (LNG-FPSO, LNG-FSRU) of the membrane type is constituted with primary and secondary metal alloy membrane barriers incorporated in insulation panels. One of the key technical issues associated with LNG carriers or FLNGs is the ability of the cargo containment system to withstand sloshing loads induced by ship motion in harsh environment. To assess the safety of membrane LNG tanks with a newly proposed configuration of CCS (Cargo Containment System) against sloshing, usually a comparative approach is adopted through numerical simulations and/or testing. The aim of the comparative approach is to assess the relative sloshing load and structural capacity under the fundamental assumption that the current membrane systems are safe. Over the period 2004-08, a JDP (joint development project) for an LNG CCS was carried out by Korea Gas Corporation (KOGAS) in corporation with major Korean shipyards and Korean universities. The aim of the project was to develop “a new CCS for membrane Type LNG carriers” which could lead to the improved and updated CCS of the structural safety. In this paper, experimental research results for the evaluation of structural performance of GTT MARK III type and KC-1 (Korean Cargo Containment System) insulation system, which is currently under development by KOGAS in corporation with major Korean shipyards, under hydro impact loads are presented. Based on the results of wet drop tests, a comparative evaluation was carried out for the time history of the impact pressure on the primary barrier and damage characteristics and so on. It is expected that the state-of-the art of engineering research described in this work can be directly applicable for the design and the development of high-valued LNG carriers and FLNGs.