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Introduction

China National Offshore Oil Corp. (CNOOC) is the largest LNG importer in China. Up to now, CNOOC has built 10 LNG receiving terminals and 30 large LNG storage tanks, which imported 13.39 million tonnes of LNG in 2015,  which accounted for 70% of total LNG imports in China. LNG tank storage is complex and construction costs are high. LNG tank technology is one of the cutting-edge technologies in the field of energy and CNOOC has the biggest demand for LNG tanks design and build. Early technology providers were all international contractors. Based on the design and construction experience of the relevant company, after several years of research, the LNG storage tank technology system “CGTankTM” was developed successfully in 2012, which marks China’s  full mastery of LNG storage technology. CGTankTM includes a number of technological breakthroughs, multiple patents, software copyrights, and specially developed algorithms. In a CGTankTM technical system, computing software is developed independently, all conditions and calculations for the tank are completed with a fluid-solid coupling FEM model. In consideration of multi-point contact; seismic action research and  inner examination research based on European standards and combined with a response spectrum analysis; the stress calculated by the theory of maximum shear failure is set as the standard of evaluation for the first time.

Engineering application of CGTankTM in Tianjin LNG Phase 1 Project

CGTankTM techniques have been applied to the construction of two full containment tanks of 3×104 m3 for the Tianjin LNG Phase 1 Project, during which several difficulties have been overcome. The first is low bearing pressure on the terrestrial foundation constituted by dredger fill in a short period. The second is the challenge of dealing with high earthquake accelerations (up to 7.875 m/s2 locally, which was the highest at that time in China). The accomplishment of the Tianjin LNG Phase 1 Project is a landmark of independently designing and constructing LNG tanks by CNOOC with the aid of other domestic companies for the first time.

Engineering application of CGTankTM in Guangxi LNG Project

CGTankTM techniques have been applied to the construction of two full containment tanks of 3×104 m3 for Guangxi LNG Project, which was also used in the Tianjin LNG Phase 1 Project. Compared with Tianjin LNG Phase 1 , Guangxi LNG has better geological conditions and thus, the earthquake threat is reduced, so the CGTankTM design has been optimized, such that the length and the number of piles were reduced.

Engineering application of CGTankTM in Fujian LNG Phase 2 Project

CGTankTM techniques have been applied to the construction of two full containment tanks of 16×104 m3 for Fujian LNG Phase 2 Project. This is the first time that the CGTankTM has been used in 16×104 m3 tank size construction.

The Fujian LNG Phase 2 Project faced many difficulties, such as the risk of significant earthquake threat, extremely complicated geological conditions, a large rock line angle, high rock strength and a few other minor considerations. For the CGTankTM, the difficulties are both a challenge and an opportunity. During the design phase, full consideration is given to the actual situation from both multi-angle and multi-level demonstrations.

Through a series of analyses it becomes possible to solve all of these practical problems. The CGTankTM  system has been constantly undergoing improvement with each new project. Anchorage zone and thermal corner protection unified analysis technology have been developed and refined in this manner. The technology of the roof beam frame nonlinear analysis, which considers  initial defects has also been used for the first time in this most recent project. Pile foundation project solutions have undergone expert review right from the initial phase of construction.

  

Engineering application of CGTankTM in Tianjin LNG Phase 2 Project

CGTankTM techniques have been applied to the construction of one of the  16×104 m3 containment tanks for the Tianjin LNG Phase 2 Project.

The biggest difficulties faced by the Tianjin project are low bearing pressure on the terrestrial foundation constituted by dredger fill in a short period and the challenge from high earthquake accelerations. In order to solve these problems, the length of the pile foundation has been designed for 56 m, and the total number of piles was adjusted to be 454.

Conclusion

The engineering application of CGTankTM technology has demonstrated the capability of custom design for full containment LNG tanks by CNOOC. From Tianjin LNG Phase 1, the R&D center of CNOOC Gas and Power Group has continued design review, preliminary design and technical support for several LNG receiving terminal projects. These projects are are being built to improve these customised techniques and provide detail design for many projects. CNOOC has got fully capable of participating in international projects of LNG terminal.

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