Wet drop test for LNG cargo containment systems. Discussion

In recent years, the worldwide demand for LNG is increasing significantly and larger sized LNG carriers are being considered for economical transport for this trade.. As the size of LNG carriers is getting larger, sloshing loads become a very important concern because higher impact pressures will be applied on the cargo containment system, which may cause severe damage. It is therefore necessary to verify the strength and safety of these large vessels under sloshing loads. Based on this interest, this paper intends to introduce the results of wet drop tests for MARK III LNG containment system. The objectives of wet drop tests are to confirm the structural safety and to understand the characteristics of the LNG insulation system under impact loads. The test rig, which can drop the model into water with various impact speeds and water entry angles, has been developed by SHI. Three type models have been made: a rigid steel model and two MARK III system models with flat/corrugated membrane, respectively. The pressure time histories on the membrane side have been recorded by a data acquisition system with high sampling frequency. By comparing the pressures of each model, one can obtain the damping effect of insulation panel and cushioning effect by entrapped gas between corrugations of MARK III system.