Safety of LNG Transportation in Arctic Conditions When Using Systems of Various Types

Abstract

Possible expansion of the LNG sea transportation region to the Russian Arctic makes topical the issue on feasibility of using various types of cargo containment systems for large ice LNG carriers of higher ice class notations. When analyzing safety of LNG transportation in the Arctic conditions in case of using cargo containment systems of various types, both fatigue issues adjusted for ice effects (this is especially topically for membrane containment systems) and consequences of emergency situations shall be studied. To evaluate fatigue of membrane cargo containment systems, a special finite element analysis was performed; at that ice effects on the hull were considered together with vibration caused by screws and engines for the purpose of determining maximum possible excitations occurring during the ice navigation. Static, dynamic and life tests, that permitted to estimate experimentally the fatigue margin of membrane containment system elements’ attachment to the vessel hull, were conducted as well.. The study results permit to conclude that the fatigue of CCS NO96 membrane cargo containment system is quite sufficient for resisting vibration loads, which occur during 40-year service life of large Arctic LNG carriers in severe ice conditions. Another important aspect of LNG transportation safety in Arctic conditions consists in accidental load problems. The following types of emergency situations were considered: • accident collision of vessels (LNG carrier ramming by another vessel); • landing on rock (bottom collision with rock in sea conditions); • hull side impact against an iceberg fragment during turning. Consequences of vessels’ collision and impacts against an iceberg were evaluated with the use of software LS-DYNA. It was ascertained based on the performed analysis that the feasibility of LNG carriers with membrane containment systems is minimal; the feasibility of LNG carriers with SPB containment systems is slightly higher, and the feasibility of LNG carriers with MOSS containment systems is essentially higher than that of LNG carriers with membrane containment systems. It could be explained physically by the fact that MOSS cargo containers approach the outer shell plating near the centerline plane (for the bottom) and in the compartment middle (for the side and bottom) only; when moving off from the centerline plane and the compartment middle the distance between cargo containers and the outer shell plating essentially grows. Nevertheless, development of large Arctic LNG carriers having sufficient accidental load levels is possible on application of any containment system type.