(68c) Safety Assessment and Code Development for Application of Kogas Membrane Type LNG Storage Tank

The objective of this project was to support the commercialized construction of KOGAS membrane LNG storage tank developed through about 6 years R&D activities.First of all, feasibility study for the dike function of outer pre-stressed concrete tank was performed by investigation of overseas code and standards and case study.And then, a comparative Risk Assessment between membrane tank and full containment tank was done using FTA for verification of safety on KOGAS membrane LNG storage tank.A traditional full containment tank, an initial KOGAS membrane tank and 4 modified KOGAS membrane tank with combined safety equipment(absorber structure, thermal protection system, pump catcher) were compared in ?outer LNG leak(top event)' in failure frequency.A frequency has been assessed for the three types of release: 1) external LNG liquid leak to the environment, 2) internal liquid leak(retained within the concrete vessel) and 3) vapour leak to the atmosphere. The external LNG leak is the critical safety concern. The internal liquid and vapour leaks to the atmosphere are largely operational issues.The predicted frequencies of an external LNG leak for the full containment and 4 modified KOGAS membrane tanks except an initial KOGAS membrane tank are very similar. According to the result of this comparative risk assessment, dike function of outer concrete tank of membrane LNG storage tank has approved from related government office on the assumption that absorber structure and thermal protection system shall be installed.In addition, for support to commercialized construction for KOGAS membrane LNG storage tank, Korean code for above-ground membrane LNG storage tank was developed in 2006. It was made a performance based code suitable domestic circumstances and in harmony with internationally recognized standards. It was written by referring to national related codes and standards and overseas standards such as EN 14620 series and JGA RPIS(Recommended Practice for LNG In-ground Storage).Based on Safety Verification and Code development of above-ground membrane LNG tank, the commercialized construction of it will be free in a view-point of safety and have a good prospect.

Conclusions: Verification of safety on above-ground membrane LNG Storage tank was performed after improving safety of Kogas membrane LNG storage tank, and the predicted risk level of membrane tank was predicted to pose essentially the same level of risk comparing with a traditional full-containment LNG storage tank. Based on the safety assessment, Korean code for membrane LNG storage tank was developed as a performance based inspection.